document_title: Climate of California

question_text: where does it snow a lot in california

question_tokens: where does it snow a lot in california

text: Climate of California

text: Temperature range[edit]

text: The cool California Current offshore, enhanced by upwelling of cold sub-surface waters, often creates summer fog near the coast, creating a warm-summer Mediterranean climate (Köppen climate classification Csb). Further inland, the climate becomes more continental, with some areas turning semi-arid (Köppen BSk), with colder winters and markedly hotter summers. Low-lying inland valleys, especially the Central Valley, have a hot-summer Mediterranean climate (Köppen Csa), with subtropical temperatures but a well-defined summer dry season and a foggy, rainy season in winter.

text: The temperature gradient between immediate coast and low-lying inland valleys in the south is about 7 °F (4 °C) in winter, the coast being warmer, and in summer roughly 25 °F (14 °C), the interior being warmer. For example, the average daily high in San Francisco in July and August is between 62 and 68 °F (17 and 20 °C),[1][2] and in Walnut Creek, some 20 miles (32 km) inland, the average daily high in July and August is 90 °F (32 °C): a temperature gain of more than one degree (Fahrenheit) per mile.[3] In the south,[where?] the figures are approximately 4 °F and 23 °F (2 °C and 13 °C), respectively. At the coast in Santa Monica, the average high in August is 75 °F (24 °C), while in Burbank, approximately 10 miles (16 km) inland, the average high in August is 95 °F (35 °C): a temperature gain of about two degrees Fahrenheit per mile.[4]

text: During the cooler winter months (October–March), the Coachella Valley regularly has the warmest winter temperatures out of any place west of the Rocky Mountains. East Los Angeles,[clarification needed] the Gateway Cities, and parts of the San Gabriel Valley average the warmest winter high temps (72 °F, 22 °C) in all of the western U.S., and Santa Monica averages the warmest winter lows (52 °F, 11 °C) in all of the western U.S. Palm Springs, a city in the Coachella Valley, averages high/low/mean temperatures of 75 °F/50 °F/63 °F, (24 °C/10 °C/17 °C) respectively during the period of cooler weather from November to April.[5]

text: The extreme southwest, around San Diego, has a subtropical semi-arid or steppe climate (Koppen BSh) as winters are drier there.

text: The southeastern regions have a hot arid climate (Koppen BWh), similar to that of the Sahara Desert. In the northern portion of the Mojave Desert on the east side of the state is Death Valley, which has recorded temperatures among the highest in the world. It is common in the summer for temperatures in the valley to reach 120 °F (49 °C). The highest reliably recorded temperature in the world,[6][7] 134 °F (56.7 °C), was recorded in Death Valley on July 10, 1913. Temperatures of 130 °F (54 °C) or higher have been recorded as recently as 2005. The 24-hour average July temperature in Death Valley is 101.8 °F (38.8 °C) (1981–2010 NCDC Normals).

text:
Alturas

Bakersfield

Bishop

Bodie

Death Valley

Eureka

Fresno

Los Angeles

Needles

Redding

Riverside

Sacramento

San Diego

San Francisco

San Jose

Santa Rosa

South Lake Tahoe

Map of locations in the table below

text:
Average daily high and low temperatures in °F (°C)
for locations in California,
colored and sortable by average monthly temperature

Place
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec

Alturas[8]
44 / 18
(7 / −8)
48 / 21
(9 / −6)
54 / 25
(12 / −4)
60 / 28
(16 / −2)
70 / 34
(21 / 1)
79 / 40
(26 / 4)
90 / 44
(32 / 7)
89 / 42
(32 / 6)
80 / 36
(27 / 2)
68 / 28
(20 / −2)
52 / 23
(11 / −5)
42 / 18
(6 / −8)

Bakersfield[9]
56 / 39
(13 / 4)
63 / 42
(17 / 6)
69 / 47
(21 / 8)
75 / 50
(24 / 10)
84 / 58
(29 / 14)
91 / 64
(33 / 18)
97 / 71
(36 / 22)
96 / 69
(36 / 21)
90 / 64
(32 / 18)
80 / 55
(27 / 13)
66 / 45
(19 / 7)
57 / 39
(14 / 4)

Bishop[10]
54 / 23
(12 / −5)
58 / 27
(14 / −3)
66 / 31
(19 / −1)
73 / 36
(23 / 2)
82 / 44
(28 / 7)
92 / 51
(33 / 11)
98 / 56
(37 / 13)
96 / 54
(36 / 12)
88 / 47
(31 / 8)
76 / 37
(24 / 3)
63 / 28
(17 / −2)
53 / 22
(12 / −6)

Bodie[11]
40 / 5
(4 / −15)
41 / 7
(5 / −14)
45 / 11
(7 / −12)
50 / 17
(10 / −8)
61 / 24
(16 / −4)
70 / 30
(21 / −1)
78 / 34
(26 / 1)
77 / 32
(25 / 0)
71 / 26
(22 / −3)
60 / 18
(16 / −8)
49 / 11
(9 / −12)
41 / 6
(5 / −14)

Death Valley[12]
67 / 40
(19 / 4)
73 / 46
(23 / 8)
82 / 55
(28 / 13)
91 / 62
(33 / 17)
101 / 73
(38 / 23)
110 / 81
(43 / 27)
117 / 88
(47 / 31)
115 / 86
(46 / 30)
107 / 76
(42 / 24)
93 / 62
(34 / 17)
77 / 48
(25 / 9)
65 / 38
(18 / 3)

Eureka[13]
56 / 41
(13 / 5)
56 / 42
(13 / 6)
57 / 43
(14 / 6)
58 / 44
(14 / 7)
60 / 48
(16 / 9)
62 / 50
(17 / 10)
63 / 52
(17 / 11)
64 / 53
(18 / 12)
64 / 50
(18 / 10)
62 / 47
(17 / 8)
58 / 44
(14 / 7)
55 / 41
(13 / 5)

Fresno[14]
55 / 38
(13 / 3)
62 / 42
(17 / 6)
68 / 46
(20 / 8)
75 / 49
(24 / 9)
84 / 56
(29 / 13)
92 / 62
(33 / 17)
98 / 68
(37 / 20)
97 / 66
(36 / 19)
91 / 62
(33 / 17)
80 / 53
(27 / 12)
65 / 43
(18 / 6)
55 / 38
(13 / 3)

Los Angeles[15]
68 / 48
(20 / 9)
69 / 49
(21 / 9)
70 / 51
(21 / 11)
73 / 54
(23 / 12)
75 / 57
(24 / 14)
78 / 60
(26 / 16)
83 / 64
(28 / 18)
84 / 64
(29 / 18)
83 / 63
(28 / 17)
79 / 59
(26 / 15)
73 / 52
(23 / 11)
68 / 48
(20 / 9)

Needles[16]
65 / 44
(18 / 7)
70 / 47
(21 / 8)
77 / 52
(25 / 11)
85 / 59
(29 / 15)
95 / 68
(35 / 20)
104 / 77
(40 / 25)
109 / 84
(43 / 29)
107 / 83
(42 / 28)
100 / 75
(38 / 24)
88 / 62
(31 / 17)
73 / 50
(23 / 10)
63 / 43
(17 / 6)

Redding[17]
55 / 37
(13 / 3)
60 / 39
(16 / 4)
65 / 43
(18 / 6)
71 / 46
(22 / 8)
81 / 54
(27 / 12)
90 / 61
(32 / 16)
98 / 66
(37 / 19)
97 / 63
(36 / 17)
90 / 58
(32 / 14)
78 / 50
(26 / 10)
63 / 41
(17 / 5)
55 / 36
(13 / 2)

Riverside[18]
69 / 43
(21 / 6)
70 / 45
(21 / 7)
73 / 46
(23 / 8)
78 / 50
(26 / 10)
83 / 55
(28 / 13)
89 / 60
(32 / 16)
95 / 64
(35 / 18)
96 / 65
(36 / 18)
92 / 61
(33 / 16)
83 / 55
(28 / 13)
75 / 47
(24 / 8)
68 / 42
(20 / 6)

Sacramento[19]
54 / 39
(12 / 4)
60 / 41
(16 / 5)
65 / 44
(18 / 7)
71 / 46
(22 / 8)
80 / 51
(27 / 11)
87 / 56
(31 / 13)
92 / 58
(33 / 14)
91 / 58
(33 / 14)
87 / 56
(31 / 13)
78 / 50
(26 / 10)
64 / 43
(18 / 6)
54 / 38
(12 / 3)

San Diego[20]
65 / 49
(18 / 9)
65 / 51
(18 / 11)
67 / 53
(19 / 12)
68 / 56
(20 / 13)
69 / 59
(21 / 15)
71 / 62
(22 / 17)
75 / 65
(24 / 18)
76 / 67
(24 / 19)
76 / 65
(24 / 18)
73 / 61
(23 / 16)
69 / 54
(21 / 12)
65 / 48
(18 / 9)

San
Francisco[1]
57 / 46
(14 / 8)
60 / 48
(16 / 9)
62 / 49
(17 / 9)
63 / 49
(17 / 9)
64 / 51
(18 / 11)
66 / 53
(19 / 12)
66 / 54
(19 / 12)
68 / 55
(20 / 13)
70 / 55
(21 / 13)
69 / 54
(21 / 12)
63 / 50
(17 / 10)
57 / 46
(14 / 8)

San Jose[21]
58 / 42
(14 / 6)
62 / 45
(17 / 7)
66 / 47
(19 / 8)
69 / 49
(21 / 9)
74 / 52
(23 / 11)
79 / 56
(26 / 13)
82 / 58
(28 / 14)
82 / 58
(28 / 14)
80 / 57
(27 / 14)
74 / 53
(23 / 12)
64 / 46
(18 / 8)
58 / 42
(14 / 6)

Santa Rosa[22]
59 / 39
(15 / 4)
63 / 41
(17 / 5)
67 / 43
(19 / 6)
70 / 45
(21 / 7)
75 / 48
(24 / 9)
80 / 52
(27 / 11)
82 / 52
(28 / 11)
83 / 53
(28 / 12)
83 / 52
(28 / 11)
78 / 48
(26 / 9)
67 / 43
(19 / 6)
59 / 39
(15 / 4)

South Lake
Tahoe[23]
43 / 16
(6 / −9)
44 / 18
(7 / −8)
49 / 23
(9 / −5)
54 / 27
(12 / −3)
64 / 32
(18 / 0)
72 / 37
(22 / 3)
81 / 41
(27 / 5)
80 / 40
(27 / 4)
74 / 35
(23 / 2)
63 / 28
(17 / −2)
51 / 22
(11 / −6)
43 / 17
(6 / −8)

text: Full statistics for selected cities[edit]

text:
[show]Climate data for Fresno, California (Fresno Airport), 1981–2010 normals, extremes 1881–present[a]

Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Year

Record high °F (°C)
78
(26)
84
(29)
90
(32)
101
(38)
110
(43)
112
(44)
115
(46)
113
(45)
111
(44)
102
(39)
90
(32)
77
(25)
115
(46)

Average high °F (°C)
54.8
(12.7)
61.6
(16.4)
67.6
(19.8)
74.6
(23.7)
84.1
(28.9)
92.0
(33.3)
98.4
(36.9)
97.1
(36.2)
90.9
(32.7)
79.5
(26.4)
65.1
(18.4)
54.9
(12.7)
76.7
(24.8)

Average low °F (°C)
38.3
(3.5)
41.5
(5.3)
45.6
(7.6)
49.4
(9.7)
56.2
(13.4)
62.4
(16.9)
67.6
(19.8)
66.2
(19)
61.5
(16.4)
53.0
(11.7)
43.4
(6.3)
38.0
(3.3)
51.9
(11.1)

Record low °F (°C)
17
(−8)
24
(−4)
26
(−3)
32
(0)
36
(2)
42
(6)
50
(10)
49
(9)
37
(3)
27
(−3)
26
(−3)
18
(−8)
17
(−8)

Average precipitation inches (mm)
2.19
(55.6)
2.03
(51.6)
2.03
(51.6)
0.95
(24.1)
0.43
(10.9)
0.21
(5.3)
0.01
(0.3)
0.01
(0.3)
0.17
(4.3)
0.63
(16)
1.07
(27.2)
1.77
(45)
11.50
(292.1)

Average precipitation days (≥ 0.01 in)
7.6
8.6
7.5
4.5
2.2
0.7
0.2
0.3
1.0
2.5
5.5
7.5
48.1

Average relative humidity (%)
83.3
77.2
68.9
57.4
47.3
41.9
39.2
44.7
50.0
58.5
74.1
84.2
60.6

Mean monthly sunshine hours
141.5
196.9
286.2
335.5
398.9
412.2
428.2
399.6
345.9
302.3
189.9
127.1
3,564.2

Percent possible sunshine
46
65
77
85
91
94
96
95
93
87
62
42
80

Source: NOAA (relative humidity and sun 1961–1990)[24][25][26], Weather.com[27]

text:
[hide]Climate data for Los Angeles (USC, Downtown), 1981–2010 normals, extremes 1877–present

Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Year

Record high °F (°C)
95
(35)
95
(35)
99
(37)
106
(41)
103
(39)
112
(44)
109
(43)
106
(41)
113
(45)
108
(42)
100
(38)
92
(33)
113
(45)

Mean maximum °F (°C)
83.3
(28.5)
84.3
(29.1)
85.8
(29.9)
91.2
(32.9)
89.7
(32.1)
90.2
(32.3)
94.1
(34.5)
95.3
(35.2)
98.9
(37.2)
95.5
(35.3)
88.0
(31.1)
81.4
(27.4)
102.7
(39.3)

Average high °F (°C)
68.2
(20.1)
68.6
(20.3)
70.2
(21.2)
72.7
(22.6)
74.5
(23.6)
78.1
(25.6)
83.1
(28.4)
84.4
(29.1)
83.1
(28.4)
78.5
(25.8)
72.8
(22.7)
67.7
(19.8)
75.2
(24)

Daily mean °F (°C)
58.0
(14.4)
58.9
(14.9)
60.6
(15.9)
63.1
(17.3)
65.8
(18.8)
69.2
(20.7)
73.3
(22.9)
74.3
(23.5)
73.1
(22.8)
68.6
(20.3)
62.4
(16.9)
57.6
(14.2)
65.4
(18.6)

Average low °F (°C)
47.8
(8.8)
49.3
(9.6)
51.0
(10.6)
53.5
(11.9)
57.1
(13.9)
60.3
(15.7)
63.6
(17.6)
64.1
(17.8)
63.1
(17.3)
58.7
(14.8)
52.0
(11.1)
47.5
(8.6)
55.7
(13.2)

Mean minimum °F (°C)
41.3
(5.2)
42.9
(6.1)
44.9
(7.2)
48.4
(9.1)
53.6
(12)
57.2
(14)
61.2
(16.2)
61.8
(16.6)
59.2
(15.1)
54.1
(12.3)
45.0
(7.2)
40.8
(4.9)
39.1
(3.9)

Record low °F (°C)
28
(−2)
28
(−2)
31
(−1)
36
(2)
40
(4)
46
(8)
49
(9)
49
(9)
44
(7)
40
(4)
34
(1)
30
(−1)
28
(−2)

Average rainfall inches (mm)
3.12
(79.2)
3.80
(96.5)
2.43
(61.7)
0.91
(23.1)
0.26
(6.6)
0.09
(2.3)
0.01
(0.3)
0.04
(1)
0.24
(6.1)
0.66
(16.8)
1.04
(26.4)
2.33
(59.2)
14.93
(379.2)

Average rainy days (≥ 0.01 in)
6.1
6.4
5.5
3.2
1.3
0.6
0.3
0.3
1.0
2.5
3.3
5.2
35.7

Mean monthly sunshine hours
225.3
222.5
267.0
303.5
276.2
275.8
364.1
349.5
278.5
255.1
217.3
219.4
3,254.2

Percent possible sunshine
71
72
72
78
64
64
83
84
75
73
70
71
73

Source: NOAA (sun 1961–1977)[28][29][30]

text:
[show]Climate data for Los Angeles (LAX), 1981–2010 normals, extremes 1944–present

Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Year

Record high °F (°C)
91
(33)
92
(33)
95
(35)
95
(35)
91
(33)
103
(39)
93
(34)
98
(37)
106
(41)
101
(38)
101
(38)
94
(34)
106
(41)

Mean maximum °F (°C)
81.2
(27.3)
81.0
(27.2)
79.6
(26.4)
83.4
(28.6)
79.9
(26.6)
80.0
(26.7)
83.6
(28.7)
85.7
(29.8)
90.1
(32.3)
89.9
(32.2)
85.5
(29.7)
78.9
(26.1)
94.7
(34.8)

Average high °F (°C)
64.6
(18.1)
64.3
(17.9)
64.4
(18)
66.4
(19.1)
68.1
(20.1)
70.6
(21.4)
73.8
(23.2)
74.9
(23.8)
74.6
(23.7)
72.5
(22.5)
68.9
(20.5)
64.6
(18.1)
69.0
(20.6)

Daily mean °F (°C)
56.7
(13.7)
57.1
(13.9)
58.0
(14.4)
60.1
(15.6)
62.7
(17.1)
65.5
(18.6)
68.8
(20.4)
69.6
(20.9)
68.9
(20.5)
65.9
(18.8)
61.1
(16.2)
56.6
(13.7)
62.6
(17)

Average low °F (°C)
48.8
(9.3)
50.0
(10)
51.7
(10.9)
53.8
(12.1)
57.3
(14.1)
60.5
(15.8)
63.7
(17.6)
64.3
(17.9)
63.2
(17.3)
59.3
(15.2)
53.2
(11.8)
48.7
(9.3)
56.2
(13.4)

Mean minimum °F (°C)
41.1
(5.1)
42.5
(5.8)
44.6
(7)
47.5
(8.6)
52.5
(11.4)
56.2
(13.4)
59.8
(15.4)
60.6
(15.9)
58.4
(14.7)
52.7
(11.5)
45.3
(7.4)
40.9
(4.9)
38.8
(3.8)

Record low °F (°C)
27
(−3)
34
(1)
35
(2)
42
(6)
45
(7)
48
(9)
52
(11)
51
(11)
47
(8)
43
(6)
38
(3)
32
(0)
27
(−3)

Average rainfall inches (mm)
2.71
(68.8)
3.25
(82.6)
1.85
(47)
0.70
(17.8)
0.22
(5.6)
0.08
(2)
0.03
(0.8)
0.05
(1.3)
0.21
(5.3)
0.56
(14.2)
1.11
(28.2)
2.05
(52.1)
12.82
(325.6)

Average rainy days (≥ 0.01 in)
6.0
6.6
5.8
2.8
1.2
0.6
0.5
0.3
1.0
2.3
3.4
5.2
35.7

Average relative humidity (%)
63.4
67.9
70.5
71.0
74.0
75.9
76.6
76.6
74.2
70.5
65.5
62.9
70.8

Source: NOAA (relative humidity 1961–1990)[28][31][32]

text:
[show]Climate data for Sacramento, California (Sacramento Executive Airport), 1981–2010 normals,[b] extremes 1941–present[c]

Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Year

Record high °F (°C)
76
(24)
76
(24)
88
(31)
95
(35)
105
(41)
115
(46)
114
(46)
110
(43)
108
(42)
104
(40)
87
(31)
73
(23)
115
(46)

Mean maximum °F (°C)
64.0
(17.8)
70.5
(21.4)
76.8
(24.9)
87.2
(30.7)
95.8
(35.4)
102.3
(39.1)
105.0
(40.6)
103.7
(39.8)
100.1
(37.8)
91.6
(33.1)
76.1
(24.5)
64.6
(18.1)
106.8
(41.6)

Average high °F (°C)
53.8
(12.1)
60.3
(15.7)
65.1
(18.4)
71.1
(21.7)
79.9
(26.6)
87.1
(30.6)
92.1
(33.4)
91.2
(32.9)
87.2
(30.7)
77.6
(25.3)
63.8
(17.7)
53.9
(12.2)
73.6
(23.1)

Average low °F (°C)
38.8
(3.8)
41.4
(5.2)
44.1
(6.7)
46.2
(7.9)
51.1
(10.6)
55.8
(13.2)
58.4
(14.7)
58.0
(14.4)
55.7
(13.2)
50.2
(10.1)
42.8
(6)
38.4
(3.6)
48.4
(9.1)

Mean minimum °F (°C)
29.1
(−1.6)
31.5
(−0.3)
35.1
(1.7)
38.0
(3.3)
42.9
(6.1)
48.7
(9.3)
53.1
(11.7)
53.0
(11.7)
49.2
(9.6)
41.7
(5.4)
32.5
(0.3)
28.5
(−1.9)
26.6
(−3)

Record low °F (°C)
20
(−7)
23
(−5)
26
(−3)
31
(−1)
34
(1)
41
(5)
48
(9)
48
(9)
42
(6)
35
(2)
26
(−3)
18
(−8)
18
(−8)

Average precipitation inches (mm)
3.64
(92.5)
3.47
(88.1)
2.75
(69.9)
1.15
(29.2)
0.68
(17.3)
0.21
(5.3)
trace
0.05
(1.3)
0.29
(7.4)
0.97
(24.6)
2.11
(53.6)
3.25
(82.6)
18.75
(476.3)

Average precipitation days (≥ 0.01 in)
10.3
9.4
9.1
4.9
3.2
1.2
0.0
0.3
1.3
3.6
6.9
9.9
60.0

Average relative humidity (%)
83.3
76.8
71.6
64.5
58.9
55.0
53.2
55.7
57.0
63.1
75.6
82.9
66.5

Mean monthly sunshine hours
145.5
201.3
278.0
329.6
406.3
419.5
440.2
406.9
347.8
296.7
194.9
141.1
3,607.8

Percent possible sunshine
48
67
75
83
92
94
98
96
93
86
64
48
81

Source: NOAA (relative humidity and sun 1961–1990)[34][35]

text:
[show]Climate data for Sacramento 5 ESE, California (1981–2010 normals,[b] extremes 1877–present)

Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Year

Record high °F (°C)
79
(26)
80
(27)
90
(32)
98
(37)
107
(42)
112
(44)
114
(46)
111
(44)
109
(43)
102
(39)
86
(30)
72
(22)
114
(46)

Mean maximum °F (°C)
65.7
(18.7)
72.8
(22.7)
80.0
(26.7)
90.2
(32.3)
97.9
(36.6)
104.1
(40.1)
106.6
(41.4)
105.4
(40.8)
101.7
(38.7)
93.1
(33.9)
77.0
(25)
65.6
(18.7)
108.3
(42.4)

Average high °F (°C)
54.4
(12.4)
61.2
(16.2)
66.8
(19.3)
72.7
(22.6)
80.9
(27.2)
87.9
(31.1)
93.3
(34.1)
92.2
(33.4)
87.9
(31.1)
77.9
(25.5)
63.7
(17.6)
54.3
(12.4)
74.4
(23.6)

Average low °F (°C)
40.7
(4.8)
43.7
(6.5)
46.5
(8.1)
49.0
(9.4)
53.9
(12.2)
58.4
(14.7)
60.9
(16.1)
60.5
(15.8)
58.4
(14.7)
52.8
(11.6)
45.5
(7.5)
40.4
(4.7)
50.9
(10.5)

Mean minimum °F (°C)
32.8
(0.4)
35.0
(1.7)
38.7
(3.7)
41.9
(5.5)
46.7
(8.2)
51.6
(10.9)
55.0
(12.8)
55.3
(12.9)
52.1
(11.2)
45.1
(7.3)
35.7
(2.1)
31.5
(−0.3)
30.1
(−1.1)

Record low °F (°C)
19
(−7)
21
(−6)
29
(−2)
34
(1)
37
(3)
43
(6)
47
(8)
48
(9)
44
(7)
34
(1)
27
(−3)
17
(−8)
17
(−8)

Average precipitation inches (mm)
3.63
(92.2)
3.90
(99.1)
2.86
(72.6)
1.36
(34.5)
0.75
(19)
0.21
(5.3)
0.02
(0.5)
0.04
(1)
0.35
(8.9)
1.06
(26.9)
2.46
(62.5)
3.43
(87.1)
20.06
(509.5)

Average precipitation days (≥ 0.01 in)
11.2
9.8
9.2
5.2
3.2
1.2
0.1
0.4
1.4
3.6
7.4
10.5
63.5

Source: NOAA[34], Western Regional Climate Center[36]

text:
[show]Climate data for San Francisco (downtown),[d] 1981–2010 normals,[e] extremes 1849–present

Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Year

Record high °F (°C)
79
(26)
81
(27)
87
(31)
94
(34)
97
(36)
103
(39)
98
(37)
98
(37)
106
(41)
102
(39)
86
(30)
76
(24)
106
(41)

Mean maximum °F (°C)
67.3
(19.6)
72.5
(22.5)
75.7
(24.3)
82.3
(27.9)
82.7
(28.2)
86.0
(30)
83.1
(28.4)
85.5
(29.7)
89.6
(32)
88.1
(31.2)
76.1
(24.5)
66.4
(19.1)
94.3
(34.6)

Average high °F (°C)
56.9
(13.8)
60.2
(15.7)
61.8
(16.6)
63.1
(17.3)
64.3
(17.9)
66.4
(19.1)
66.5
(19.2)
68.1
(20.1)
70.2
(21.2)
69.2
(20.7)
63.1
(17.3)
57.1
(13.9)
63.9
(17.7)

Daily mean °F (°C)
51.3
(10.7)
53.9
(12.2)
55.1
(12.8)
56.2
(13.4)
57.6
(14.2)
59.6
(15.3)
60.3
(15.7)
61.6
(16.4)
62.7
(17.1)
61.5
(16.4)
56.6
(13.7)
51.6
(10.9)
57.3
(14.1)

Average low °F (°C)
45.7
(7.6)
47.5
(8.6)
48.5
(9.2)
49.2
(9.6)
51.0
(10.6)
52.8
(11.6)
54.1
(12.3)
55.1
(12.8)
55.1
(12.8)
53.7
(12.1)
50.1
(10.1)
46.1
(7.8)
50.7
(10.4)

Mean minimum °F (°C)
40.3
(4.6)
41.8
(5.4)
43.6
(6.4)
45.1
(7.3)
47.7
(8.7)
50.2
(10.1)
51.5
(10.8)
52.6
(11.4)
52.0
(11.1)
49.6
(9.8)
44.2
(6.8)
40.1
(4.5)
38.2
(3.4)

Record low °F (°C)
29
(−2)
31
(−1)
33
(1)
40
(4)
42
(6)
46
(8)
47
(8)
46
(8)
47
(8)
43
(6)
38
(3)
27
(−3)
27
(−3)

Average rainfall inches (mm)
4.50
(114.3)
4.46
(113.3)
3.26
(82.8)
1.46
(37.1)
0.70
(17.8)
0.16
(4.1)
0.00
(0)
0.06
(1.5)
0.21
(5.3)
1.12
(28.4)
3.16
(80.3)
4.56
(115.8)
23.65
(600.7)

Average rainy days (≥ 0.01 in)
11.7
11.1
11.0
6.5
3.8
1.5
0.3
1.0
1.7
3.9
8.9
11.6
73.0

Average relative humidity (%)
80
77
75
72
72
71
75
75
73
71
75
78
74.5

Mean monthly sunshine hours
185.9
207.7
269.1
309.3
325.1
311.4
313.3
287.4
271.4
247.1
173.4
160.6
3,061.7

Percent possible sunshine
61
69
73
78
74
70
70
68
73
71
57
54
69

Source #1: NOAA (sun 1961–1974)[37][38][39]

Source #2: Met Office for humidity[40]

text:
[show]Climate data for San Diego Int'l Airport (1981–2010 normals,[f] extremes 1874–present)[g]

Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Year

Record high °F (°C)
88
(31)
90
(32)
99
(37)
98
(37)
98
(37)
101
(38)
100
(38)
98
(37)
111
(44)
107
(42)
100
(38)
88
(31)
111
(44)

Mean maximum °F (°C)
78.4
(25.8)
79.2
(26.2)
79.8
(26.6)
82.8
(28.2)
79.0
(26.1)
81.2
(27.3)
83.2
(28.4)
85.4
(29.7)
89.5
(31.9)
86.8
(30.4)
82.9
(28.3)
76.6
(24.8)
94.1
(34.5)

Average high °F (°C)
65.1
(18.4)
65.0
(18.3)
65.6
(18.7)
67.5
(19.7)
68.5
(20.3)
70.8
(21.6)
74.6
(23.7)
76.4
(24.7)
75.9
(24.4)
72.8
(22.7)
69.0
(20.6)
64.7
(18.2)
69.7
(20.9)

Average low °F (°C)
49.0
(9.4)
50.7
(10.4)
53.2
(11.8)
55.9
(13.3)
59.4
(15.2)
62.0
(16.7)
65.4
(18.6)
66.7
(19.3)
65.2
(18.4)
60.6
(15.9)
53.6
(12)
48.4
(9.1)
57.5
(14.2)

Mean minimum °F (°C)
41.9
(5.5)
44.6
(7)
47.1
(8.4)
50.7
(10.4)
55.0
(12.8)
59.1
(15.1)
62.5
(16.9)
63.3
(17.4)
60.4
(15.8)
54.4
(12.4)
45.8
(7.7)
41.4
(5.2)
40.3
(4.6)

Record low °F (°C)
25
(−4)
34
(1)
36
(2)
39
(4)
45
(7)
50
(10)
54
(12)
54
(12)
50
(10)
43
(6)
36
(2)
32
(0)
25
(−4)

Average rainfall inches (mm)
1.98
(50.3)
2.27
(57.7)
1.81
(46)
0.78
(19.8)
0.12
(3)
0.07
(1.8)
0.03
(0.8)
0.02
(0.5)
0.15
(3.8)
0.57
(14.5)
1.01
(25.7)
1.53
(38.9)
10.34
(262.6)

Average rainy days (≥ 0.01 in)
6.7
7.1
6.5
4.0
1.4
0.8
0.7
0.4
1.2
2.8
4.1
5.8
41.5

Average relative humidity (%)
63.1
65.7
67.3
67.0
70.6
74.0
74.6
74.1
72.7
69.4
66.3
63.7
69.0

Mean monthly sunshine hours
239.3
227.4
261.0
276.2
250.5
242.4
304.7
295.0
253.3
243.4
230.1
231.3
3,054.6

Percent possible sunshine
75
74
70
71
58
57
70
71
68
69
73
74
69

Source: NOAA (sun and relative humidity 1961–1990)[42][43][44]

text: Precipitation[edit]

text: This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (October 2014) (Learn how and when to remove this template message)

text: The large Westerly winds from the oceans also bring moisture, and the northern parts of the state generally receive higher annual rainfall amounts than the south. California's mountain ranges influence the climate as well: moisture-laden air from the west cools as it ascends the mountains, dropping moisture; some of the rainiest parts of the state are west-facing mountain slopes. Northwestern California has a temperate climate with rainfall of 15 inches (380 mm) to 50 inches (1,300 mm) per year. Some areas of Coast Redwood forest receive over 100 inches (2,500 mm) of precipitation per year.

text: The Central Valley has a wide range of precipitation. The northern parts of the Central Valley receive substantially greater precipitation from winter storms which sweep down from the Pacific Northwest, while the southernmost regions of the Central Valley are near desert-like because of a lack of precipitation. Parts of the Valley are occasionally filled with thick fog (known locally as "tule fog").

text: The high mountains, including the Sierra Nevada, the Cascade Range, and the Klamath Mountains, have a mountain climate with snow in winter and mild to moderate heat in summer. Ski resorts at Lake Tahoe, Mammoth Lakes, and Mount Shasta routinely receive over 10 feet (3.0 m) of snow in a season, and some years, substantially more – leading, for example, to annual ski races on the Fourth of July.

text: On the east side of the mountains is a drier rain shadow. California's desert climate regions lie east of the high Sierra Nevada and southern California's Transverse Ranges and Peninsular Ranges. The low deserts east of the southern California mountains, including the Imperial and Coachella valleys and the lower Colorado River, are part of the Sonoran Desert, with minimal frost in the winter; the higher elevation deserts of eastern California, including the Mojave Desert, Owens Valley, and the Modoc Plateau, are part of the Great Basin region, which has a more continental climate. During the summer months, especially from July through early September, the region is affected by the Mexican Monsoon (also called the "southwest monsoon"), which drives moisture from the tropical Pacific, Gulf of California, and/or Gulf of Mexico into the deserts, setting off brief, but often torrential thunderstorms, particularly over mountainous terrain.

text: Despite its long coastline, California is not vulnerable to tropical cyclones. Because of the cold California Current from the North Pacific Ocean and the fact that the storms tend to "steer" west, California has only been hit with two tropical storms in recorded history, a storm which came ashore in 1939 and dumped heavy rainfall on the Los Angeles Area and interior deserts and Tropical Storm Nora. The remnants of tropical systems will affect California more commonly, every several years.

text: The ENSO cycle has a huge effect on rainfall and snowfall patterns in California, especially during the winter and spring seasons. During the El Niño phase, the jet stream is located south through California, allowing for warmer temperatures and more heavy rains to occur, particularly in the southern portions of the state. During the La Niña phase, the jet stream is much further north, and therefore the far northern portions of California are wetter, while the southern half stays cool and dry.

text:
Snow in the mountains of Southern California

Summer in the Sierra Nevada at Lake Tahoe

High precipitation in 2005 caused an ephemeral lake in the Badwater Basin of Death Valley.

text: Wildfires[edit]

text:
External video

 Wildfires in California 2015.

text: Summers in inland California can see temperatures well over 100 °F (38 °C) during the day and less than 0.3 in (7.6 mm) of monthly rainfall, particularly in the southern areas. This makes them prone to wildfires. These can be life-threatening and cause evacuation. Wildfires are less common along the coast because of the cooler, more humid summers, but can occur in autumn when the marine layer is less common, making temperatures warmer and humidity drop significantly.

text: Glossary[edit]

text: The following are terms used to describe local or regional weather events.

text:
Santa Ana winds: Santa Anas are hot, high winds that blow from the eastern mountains and deserts towards coastal southern California, usually in the spring and fall. They are the result of air pressure buildup between the Sierra Nevada and the Rocky Mountains. This air mass spills out, is pulled by gravity, and circulates clockwise around the high pressure area, bringing winds from the east and northeast; as the air descends in elevation, it heats up and the humidity plummets to less than 15 percent. It is often said that the air is heated and dried as it passes through the nearby deserts, but according to meteorologists this is a popular misconception (it is actually due to adiabatic compression as the air flows from the higher elevations down to sea level); during Santa Ana conditions, it is typically hotter along the coast than in the deserts. As the Santa Ana winds are channeled through the mountain passes they can approach hurricane force. The combination of speed, heat, and dryness turns the chaparral into explosive fuel for wildfires.
Pineapple Express: A complex combination of events, bringing high levels of torrential precipitation to California. The Pineapple Express occurs when the jet stream dips across California, and warm, humid air from the mid-Pacific (from the vicinity of Hawaii–hence, the name) is drawn towards California. The resulting combination can cause extraordinarily heavy rains. A January 2005 Pineapple Express dropped nearly 25 inches (63.5 cm) of rain in Santa Barbara County.
Tule fog: A thick ground fog that settles in the San Joaquin Valley and Sacramento Valley areas of the California Central Valley. Tule fog forms during the mid fall, winter to early spring after the first significant rainfall. This phenomenon is named after the tule grass wetlands of the Central Valley. Tule fog can extend from Bakersfield to Chico. Accidents caused by the tule fog are the leading cause of weather-related deaths in California; visibility is usually less than an eighth of a mile (about 600 feet or 183–200 m), but can be less than 10 feet (3 m).
May Gray/June Gloom: A characteristic weather pattern of late spring (May and June) in which a combination of inland heat, off-shore cool water, and prevailing wind patterns bring foggy and overcast weather to coastal regions. From Point Conception northwards the gloom continues until early autumn. (See also: Catalina eddy)
Marine layer: The cool, moist layer of air coming in from the ocean which typically includes fog. A standard weather phenomenon along the northern and central California coast from late spring to early fall.
"Earthquake weather:" Any unseasonal, uncomfortable weather, typically hot and more humid than usual, and often associated with high and mid-level clouds, is spoken of (usually jokingly) as "earthquake weather."[citation needed]

text: Gallery[edit]

text:
Visitors at Redwood National Park

Mediterranean climate at Santa Barbara

Storms over California

Play media

Storms over California


document_title: Eye

question_text: at which part of eyes there is no sense of vision

root

text: Eye

text: Overview

text: Complex eyes can distinguish shapes and colours. The visual fields of many organisms, especially predators, involve large areas of binocular vision to improve depth perception. In other organisms, eyes are located so as to maximise the field of view, such as in rabbits and horses, which have monocular vision.

tag: p

text: The first proto-eyes evolved among animals 600 million years ago about the time of the Cambrian explosion.[4] The last common ancestor of animals possessed the biochemical toolkit necessary for vision, and more advanced eyes have evolved in 96% of animal species in six of the ~35[a] main phyla.[1] In most vertebrates and some molluscs, the eye works by allowing light to enter and project onto a light-sensitive panel of cells, known as the retina, at the rear of the eye. The cone cells (for colour) and the rod cells (for low-light contrasts) in the retina detect and convert light into neural signals for vision. The visual signals are then transmitted to the brain via the optic nerve. Such eyes are typically roughly spherical, filled with a transparent gel-like substance called the vitreous humour, with a focusing lens and often an iris; the relaxing or tightening of the muscles around the iris change the size of the pupil, thereby regulating the amount of light that enters the eye,[5] and reducing aberrations when there is enough light.[6] The eyes of most cephalopods, fish, amphibians and snakes have fixed lens shapes, and focusing vision is achieved by telescoping the lens—similar to how a camera focuses.[7]

text: Compound eyes are found among the arthropods and are composed of many simple facets which, depending on the details of anatomy, may give either a single pixelated image or multiple images, per eye. Each sensor has its own lens and photosensitive cell(s). Some eyes have up to 28,000 such sensors, which are arranged hexagonally, and which can give a full 360° field of vision. Compound eyes are very sensitive to motion. Some arthropods, including many Strepsiptera, have compound eyes of only a few facets, each with a retina capable of creating an image, creating vision. With each eye viewing a different thing, a fused image from all the eyes is produced in the brain, providing very different, high-resolution images.

text: Possessing detailed hyperspectral colour vision, the Mantis shrimp has been reported to have the world's most complex colour vision system.[8] Trilobites, which are now extinct, had unique compound eyes. They used clear calcite crystals to form the lenses of their eyes. In this, they differ from most other arthropods, which have soft eyes. The number of lenses in such an eye varied, however: some trilobites had only one, and some had thousands of lenses in one eye.

text: In contrast to compound eyes, simple eyes are those that have a single lens. For example, jumping spiders have a large pair of simple eyes with a narrow field of view, supported by an array of other, smaller eyes for peripheral vision. Some insect larvae, like caterpillars, have a different type of simple eye (stemmata) which usually provides only a rough image, but (as in sawfly larvae) can possess resolving powers of 4 degrees of arc, be polarization sensitive and capable of increasing its absolute sensitivity at night by a factor of 1,000 or more [9] . Some of the simplest eyes, called ocelli, can be found in animals like some of the snails, which cannot actually "see" in the normal sense. They do have photosensitive cells, but no lens and no other means of projecting an image onto these cells. They can distinguish between light and dark, but no more. This enables snails to keep out of direct sunlight. In organisms dwelling near deep-sea vents, compound eyes have been secondarily simplified and adapted to spot the infra-red light produced by the hot vents–in this way the bearers can spot hot springs and avoid being boiled alive.[10]

text: Types

text: There are ten different eye layouts—indeed every technological method of capturing an optical image commonly used by human beings, with the exceptions of zoom and Fresnel lenses, occur in nature.[1] Eye types can be categorised into "simple eyes", with one concave photoreceptive surface, and "compound eyes", which comprise a number of individual lenses laid out on a convex surface.[1] Note that "simple" does not imply a reduced level of complexity or acuity. Indeed, any eye type can be adapted for almost any behaviour or environment. The only limitations specific to eye types are that of resolution—the physics of compound eyes prevents them from achieving a resolution better than 1°. Also, superposition eyes can achieve greater sensitivity than apposition eyes, so are better suited to dark-dwelling creatures.[1] Eyes also fall into two groups on the basis of their photoreceptor's cellular construction, with the photoreceptor cells either being cilliated (as in the vertebrates) or rhabdomeric. These two groups are not monophyletic; the cnidaria also possess cilliated cells, [11] and some gastropods [12], as well as some annelids possess both.[13]

text: Non-compound eyes

text: Simple eyes are rather ubiquitous, and lens-bearing eyes have evolved at least seven times in vertebrates, cephalopods, annelids, crustaceans and cubozoa.[14][not in citation given]

text: Pit eyes

text: Pit eyes, also known as stemma, are eye-spots which may be set into a pit to reduce the angles of light that enters and affects the eyespot, to allow the organism to deduce the angle of incoming light.[1] Found in about 85% of phyla, these basic forms were probably the precursors to more advanced types of "simple eye". They are small, comprising up to about 100 cells covering about 100 µm.[1] The directionality can be improved by reducing the size of the aperture, by incorporating a reflective layer behind the receptor cells, or by filling the pit with a refractile material.[1]

text: Pit vipers have developed pits that function as eyes by sensing thermal infra-red radiation, in addition to their optical wavelength eyes like those of other vertebrates.

text: Spherical lensed eye

text: The resolution of pit eyes can be greatly improved by incorporating a material with a higher refractive index to form a lens, which may greatly reduce the blur radius encountered—hence increasing the resolution obtainable.[1] The most basic form, seen in some gastropods and annelids, consists of a lens of one refractive index. A far sharper image can be obtained using materials with a high refractive index, decreasing to the edges; this decreases the focal length and thus allows a sharp image to form on the retina.[1] This also allows a larger aperture for a given sharpness of image, allowing more light to enter the lens; and a flatter lens, reducing spherical aberration.[1] Such an inhomogeneous lens is necessary in order for the focal length to drop from about 4 times the lens radius, to 2.5 radii.[1]

text: Heterogeneous eyes have evolved at least nine times: four or more times in gastropods, once in the copepods, once in the annelids, once in the cephalopods,[1] and once in the chitons, which have aragonite lenses.[15] No extant aquatic organisms possess homogeneous lenses; presumably the evolutionary pressure for a heterogeneous lens is great enough for this stage to be quickly "outgrown".[1]

text: This eye creates an image that is sharp enough that motion of the eye can cause significant blurring. To minimise the effect of eye motion while the animal moves, most such eyes have stabilising eye muscles.[1]

text: The ocelli of insects bear a simple lens, but their focal point always lies behind the retina; consequently they can never form a sharp image. Ocelli (pit-type eyes of arthropods) blur the image across the whole retina, and are consequently excellent at responding to rapid changes in light intensity across the whole visual field; this fast response is further accelerated by the large nerve bundles which rush the information to the brain.[16] Focusing the image would also cause the sun's image to be focused on a few receptors, with the possibility of damage under the intense light; shielding the receptors would block out some light and thus reduce their sensitivity.[16] This fast response has led to suggestions that the ocelli of insects are used mainly in flight, because they can be used to detect sudden changes in which way is up (because light, especially UV light which is absorbed by vegetation, usually comes from above).[16]

text: Multiple lenses

text: Some marine organisms bear more than one lens; for instance the copepod Pontella has three. The outer has a parabolic surface, countering the effects of spherical aberration while allowing a sharp image to be formed. Another copepod, Copilia, has two lenses in each eye, arranged like those in a telescope.[1] Such arrangements are rare and poorly understood, but represent an alternative construction. Multiple lenses are seen in some hunters such as eagles and jumping spiders, which have a refractive cornea (discussed next): these have a negative lens, enlarging the observed image by up to 50% over the receptor cells, thus increasing their optical resolution.[1]

text: Refractive cornea

text: In the eyes of most mammals, birds, reptiles, and most other terrestrial vertebrates (along with spiders and some insect larvae) the vitreous fluid has a higher refractive index than the air.[1] In general, the lens is not spherical. Spherical lenses produce spherical aberration. In refractive corneas, the lens tissue is corrected with inhomogeneous lens material (see Luneburg lens), or with an aspheric shape.[1] Flattening the lens has a disadvantage; the quality of vision is diminished away from the main line of focus. Thus, animals that have evolved with a wide field-of-view often have eyes that make use of an inhomogeneous lens.[1]

text: As mentioned above, a refractive cornea is only useful out of water; in water, there is little difference in refractive index between the vitreous fluid and the surrounding water. Hence creatures that have returned to the water – penguins and seals, for example – lose their highly curved cornea and return to lens-based vision. An alternative solution, borne by some divers, is to have a very strongly focusing cornea.[1]

text: Reflector eyes

text: An alternative to a lens is to line the inside of the eye with "mirrors", and reflect the image to focus at a central point.[1] The nature of these eyes means that if one were to peer into the pupil of an eye, one would see the same image that the organism would see, reflected back out.[1]

text: Many small organisms such as rotifers, copepods and flatworms use such organs, but these are too small to produce usable images.[1] Some larger organisms, such as scallops, also use reflector eyes. The scallop Pecten has up to 100 millimetre-scale reflector eyes fringing the edge of its shell. It detects moving objects as they pass successive lenses.[1]

text: There is at least one vertebrate, the spookfish, whose eyes include reflective optics for focusing of light. Each of the two eyes of a spookfish collects light from both above and below; the light coming from above is focused by a lens, while that coming from below, by a curved mirror composed of many layers of small reflective plates made of guanine crystals.[17]

text: Compound eyes

text: A compound eye may consist of thousands of individual photoreceptor units or ommatidia (ommatidium, singular). The image perceived is a combination of inputs from the numerous ommatidia (individual "eye units"), which are located on a convex surface, thus pointing in slightly different directions. Compared with simple eyes, compound eyes possess a very large view angle, and can detect fast movement and, in some cases, the polarisation of light.[18] Because the individual lenses are so small, the effects of diffraction impose a limit on the possible resolution that can be obtained (assuming that they do not function as phased arrays). This can only be countered by increasing lens size and number. To see with a resolution comparable to our simple eyes, humans would require very large compound eyes, around 11 metres (36 ft) in radius.[19]

text: Compound eyes fall into two groups: apposition eyes, which form multiple inverted images, and superposition eyes, which form a single erect image.[20] Compound eyes are common in arthropods, and are also present in annelids and some bivalved molluscs.[21] Compound eyes, in arthropods at least, grow at their margins by the addition of new ommatidia.[22]

text: Apposition eyes

text: Apposition eyes are the most common form of eyes, and are presumably the ancestral form of compound eyes. They are found in all arthropod groups, although they may have evolved more than once within this phylum.[1] Some annelids and bivalves also have apposition eyes. They are also possessed by Limulus, the horseshoe crab, and there are suggestions that other chelicerates developed their simple eyes by reduction from a compound starting point.[1] (Some caterpillars appear to have evolved compound eyes from simple eyes in the opposite fashion.)

text: Apposition eyes work by gathering a number of images, one from each eye, and combining them in the brain, with each eye typically contributing a single point of information. The typical apposition eye has a lens focusing light from one direction on the rhabdom, while light from other directions is absorbed by the dark wall of the ommatidium.

text: Superposition eyes

text: The second type is named the superposition eye. The superposition eye is divided into three types; the refracting, the reflecting and the parabolic superposition eye. The refracting superposition eye has a gap between the lens and the rhabdom, and no side wall. Each lens takes light at an angle to its axis and reflects it to the same angle on the other side. The result is an image at half the radius of the eye, which is where the tips of the rhabdoms are. This type of compound eye, for which a minimal size exists below which effective superposition cannot occur [23], is normally found in nocturnal insects, because it can create images up to 1000 times brighter than equivalent apposition eyes, though at the cost of reduced resolution.[24] In the parabolic superposition compound eye type, seen in arthropods such as mayflies, the parabolic surfaces of the inside of each facet focus light from a reflector to a sensor array. Long-bodied decapod crustaceans such as shrimp, prawns, crayfish and lobsters are alone in having reflecting superposition eyes, which also have a transparent gap but use corner mirrors instead of lenses.

text: Parabolic superposition

text: This eye type functions by refracting light, then using a parabolic mirror to focus the image; it combines features of superposition and apposition eyes.[10]

text: Other

text: Another kind of compound eye, found in males of Order Strepsiptera, employs a series of simple eyes—eyes having one opening that provides light for an entire image-forming retina. Several of these eyelets together form the strepsipteran compound eye, which is similar to the 'schizochroal' compound eyes of some trilobites.[25] Because each eyelet is a simple eye, it produces an inverted image; those images are combined in the brain to form one unified image. Because the aperture of an eyelet is larger than the facets of a compound eye, this arrangement allows vision under low light levels.[1]

text: Good fliers such as flies or honey bees, or prey-catching insects such as praying mantis or dragonflies, have specialised zones of ommatidia organised into a fovea area which gives acute vision. In the acute zone, the eyes are flattened and the facets larger. The flattening allows more ommatidia to receive light from a spot and therefore higher resolution. The black spot that can be seen on the compound eyes of such insects, which always seems to look directly at the observer, is called a pseudopupil. This occurs because the ommatidia which one observes "head-on" (along their optical axes) absorb the incident light, while those to one side reflect it.[26]

text: There are some exceptions from the types mentioned above. Some insects have a so-called single lens compound eye, a transitional type which is something between a superposition type of the multi-lens compound eye and the single lens eye found in animals with simple eyes. Then there is the mysid shrimp Dioptromysis paucispinosa. The shrimp has an eye of the refracting superposition type, in the rear behind this in each eye there is a single large facet that is three times in diameter the others in the eye and behind this is an enlarged crystalline cone. This projects an upright image on a specialised retina. The resulting eye is a mixture of a simple eye within a compound eye.

text: Another version is a compound eye often referred to as "pseudofaceted", as seen in Scutigera[27]. This type of eye consists of a cluster of numerous ommatidia on each side of the head, organised in a way that resembles a true compound eye.

text: The body of Ophiocoma wendtii, a type of brittle star, is covered with ommatidia, turning its whole skin into a compound eye. The same is true of many chitons. The tube feet of sea urchins contain photoreceptor proteins, which together act as a compound eye; they lack screening pigments, but can detect the directionality of light by the shadow cast by its opaque body.[28]

text: Nutrients

text: The ciliary body is triangular in horizontal section and is coated by a double layer, the ciliary epithelium. The inner layer is transparent and covers the vitreous body, and is continuous from the neural tissue of the retina. The outer layer is highly pigmented, continuous with the retinal pigment epithelium, and constitutes the cells of the dilator muscle.

text: The vitreous is the transparent, colourless, gelatinous mass that fills the space between the lens of the eye and the retina lining the back of the eye.[29] It is produced by certain retinal cells. It is of rather similar composition to the cornea, but contains very few cells (mostly phagocytes which remove unwanted cellular debris in the visual field, as well as the hyalocytes of Balazs of the surface of the vitreous, which reprocess the hyaluronic acid), no blood vessels, and 98–99% of its volume is water (as opposed to 75% in the cornea) with salts, sugars, vitrosin (a type of collagen), a network of collagen type II fibres with the mucopolysaccharide hyaluronic acid, and also a wide array of proteins in micro amounts. Amazingly, with so little solid matter, it tautly holds the eye.

text: Evolution

text: Photoreception is phylogenetically very old, with various theories of phylogenesis.[30] The common origin (monophyly) of all animal eyes is now widely accepted as fact. This is based upon the shared genetic features of all eyes; that is, all modern eyes, varied as they are, have their origins in a proto-eye believed to have evolved some 540 million years ago,[31][32][33] and the PAX6 gene is considered a key factor in this. The majority of the advancements in early eyes are believed to have taken only a few million years to develop, since the first predator to gain true imaging would have touched off an "arms race" [34] among all species that did not flee the photopic environment. Prey animals and competing predators alike would be at a distinct disadvantage without such capabilities and would be less likely to survive and reproduce. Hence multiple eye types and subtypes developed in parallel (except those of groups, such as the vertebrates, that were only forced into the photopic environment at a late stage).

text: Eyes in various animals show adaptation to their requirements. For example, the eye of a bird of prey has much greater visual acuity than a human eye, and in some cases can detect ultraviolet radiation. The different forms of eye in, for example, vertebrates and molluscs are examples of parallel evolution, despite their distant common ancestry. Phenotypic convergence of the geometry of cephalopod and most vertebrate eyes creates the impression that the vertebrate eye evolved from an imaging cephalopod eye, but this is not the case, as the reversed roles of their respective ciliary and rhabdomeric opsin classes[35] and different lens crystallins show.[36]

text: The very earliest "eyes", called eyespots, were simple patches of photoreceptor protein in unicellular animals. In multicellular beings, multicellular eyespots evolved, physically similar to the receptor patches for taste and smell. These eyespots could only sense ambient brightness: they could distinguish light and dark, but not the direction of the light source.[1]

text: Through gradual change, the eyespots of species living in well-lit environments depressed into a shallow "cup" shape, the ability to slightly discriminate directional brightness was achieved by using the angle at which the light hit certain cells to identify the source. The pit deepened over time, the opening diminished in size, and the number of photoreceptor cells increased, forming an effective pinhole camera that was capable of dimly distinguishing shapes.[37] However, the ancestors of modern hagfish, thought to be the protovertebrate[35] were evidently pushed to very deep, dark waters, where they were less vulnerable to sighted predators, and where it is advantageous to have a convex eye-spot, which gathers more light than a flat or concave one. This would have led to a somewhat different evolutionary trajectory for the vertebrate eye than for other animal eyes.

text: The thin overgrowth of transparent cells over the eye's aperture, originally formed to prevent damage to the eyespot, allowed the segregated contents of the eye chamber to specialise into a transparent humour that optimised colour filtering, blocked harmful radiation, improved the eye's refractive index, and allowed functionality outside of water. The transparent protective cells eventually split into two layers, with circulatory fluid in between that allowed wider viewing angles and greater imaging resolution, and the thickness of the transparent layer gradually increased, in most species with the transparent crystallin protein.[38]

text: The gap between tissue layers naturally formed a bioconvex shape, an optimally ideal structure for a normal refractive index. Independently, a transparent layer and a nontransparent layer split forward from the lens: the cornea and iris. Separation of the forward layer again formed a humour, the aqueous humour. This increased refractive power and again eased circulatory problems. Formation of a nontransparent ring allowed more blood vessels, more circulation, and larger eye sizes.[38]

text: Relationship to life requirements

text: Eyes are generally adapted to the environment and life requirements of the organism which bears them. For instance, the distribution of photoreceptors tends to match the area in which the highest acuity is required, with horizon-scanning organisms, such as those that live on the African plains, having a horizontal line of high-density ganglia, while tree-dwelling creatures which require good all-round vision tend to have a symmetrical distribution of ganglia, with acuity decreasing outwards from the centre.

text: Of course, for most eye types, it is impossible to diverge from a spherical form, so only the density of optical receptors can be altered. In organisms with compound eyes, it is the number of ommatidia rather than ganglia that reflects the region of highest data acquisition.[1]:23–4 Optical superposition eyes are constrained to a spherical shape, but other forms of compound eyes may deform to a shape where more ommatidia are aligned to, say, the horizon, without altering the size or density of individual ommatidia.[39] Eyes of horizon-scanning organisms have stalks so they can be easily aligned to the horizon when this is inclined, for example if the animal is on a slope.[26]

text: An extension of this concept is that the eyes of predators typically have a zone of very acute vision at their centre, to assist in the identification of prey.[39] In deep water organisms, it may not be the centre of the eye that is enlarged. The hyperiid amphipods are deep water animals that feed on organisms above them. Their eyes are almost divided into two, with the upper region thought to be involved in detecting the silhouettes of potential prey—or predators—against the faint light of the sky above. Accordingly, deeper water hyperiids, where the light against which the silhouettes must be compared is dimmer, have larger "upper-eyes", and may lose the lower portion of their eyes altogether.[39] In the giant Antarctic isopod Glyptonotus a small ventral compound eye is physically completely separated from the much larger dorsal compound eye [40] Depth perception can be enhanced by having eyes which are enlarged in one direction; distorting the eye slightly allows the distance to the object to be estimated with a high degree of accuracy.[10]

text: Acuity is higher among male organisms that mate in mid-air, as they need to be able to spot and assess potential mates against a very large backdrop.[39] On the other hand, the eyes of organisms which operate in low light levels, such as around dawn and dusk or in deep water, tend to be larger to increase the amount of light that can be captured.[39]

text: It is not only the shape of the eye that may be affected by lifestyle. Eyes can be the most visible parts of organisms, and this can act as a pressure on organisms to have more transparent eyes at the cost of function.[39]

text: Eyes may be mounted on stalks to provide better all-round vision, by lifting them above an organism's carapace; this also allows them to track predators or prey without moving the head.[10]

text: Physiology

text: Visual acuity

text: Visual acuity, or resolving power, is "the ability to distinguish fine detail" and is the property of cone cells.[41] It is often measured in cycles per degree (CPD), which measures an angular resolution, or how much an eye can differentiate one object from another in terms of visual angles. Resolution in CPD can be measured by bar charts of different numbers of white/black stripe cycles. For example, if each pattern is 1.75 cm wide and is placed at 1 m distance from the eye, it will subtend an angle of 1 degree, so the number of white/black bar pairs on the pattern will be a measure of the cycles per degree of that pattern. The highest such number that the eye can resolve as stripes, or distinguish from a grey block, is then the measurement of visual acuity of the eye.

text: For a human eye with excellent acuity, the maximum theoretical resolution is 50 CPD[42] (1.2 arcminute per line pair, or a 0.35 mm line pair, at 1 m). A rat can resolve only about 1 to 2 CPD.[43] A horse has higher acuity through most of the visual field of its eyes than a human has, but does not match the high acuity of the human eye's central fovea region.[44]

text: Spherical aberration limits the resolution of a 7 mm pupil to about 3 arcminutes per line pair. At a pupil diameter of 3 mm, the spherical aberration is greatly reduced, resulting in an improved resolution of approximately 1.7 arcminutes per line pair.[45] A resolution of 2 arcminutes per line pair, equivalent to a 1 arcminute gap in an optotype, corresponds to 20/20 (normal vision) in humans.

text: However, in the compound eye, the resolution is related to the size of individual ommatidia and the distance between neighbouring ommatidia. Physically these cannot be reduced in size to achieve the acuity seen with single lensed eyes as in mammals. Compound eyes have a much lower acuity than vertebrate eyes.[46]

text: Colour perception

text: "Colour vision is the faculty of the organism to distinguish lights of different spectral qualities."[47] All organisms are restricted to a small range of electromagnetic spectrum; this varies from creature to creature, but is mainly between wavelengths of 400 and 700 nm.[48] This is a rather small section of the electromagnetic spectrum, probably reflecting the submarine evolution of the organ: water blocks out all but two small windows of the EM spectrum, and there has been no evolutionary pressure among land animals to broaden this range.[49]

text: The most sensitive pigment, rhodopsin, has a peak response at 500 nm.[50] Small changes to the genes coding for this protein can tweak the peak response by a few nm;[2] pigments in the lens can also filter incoming light, changing the peak response.[2] Many organisms are unable to discriminate between colours, seeing instead in shades of grey; colour vision necessitates a range of pigment cells which are primarily sensitive to smaller ranges of the spectrum. In primates, geckos, and other organisms, these take the form of cone cells, from which the more sensitive rod cells evolved.[50] Even if organisms are physically capable of discriminating different colours, this does not necessarily mean that they can perceive the different colours; only with behavioural tests can this be deduced.[2]

text: Most organisms with colour vision are able to detect ultraviolet light. This high energy light can be damaging to receptor cells. With a few exceptions (snakes, placental mammals), most organisms avoid these effects by having absorbent oil droplets around their cone cells. The alternative, developed by organisms that had lost these oil droplets in the course of evolution, is to make the lens impervious to UV light — this precludes the possibility of any UV light being detected, as it does not even reach the retina.[50]

text: Rods and cones

text: The retina contains two major types of light-sensitive photoreceptor cells used for vision: the rods and the cones.

text: Rods cannot distinguish colours, but are responsible for low-light (scotopic) monochrome (black-and-white) vision; they work well in dim light as they contain a pigment, rhodopsin (visual purple), which is sensitive at low light intensity, but saturates at higher (photopic) intensities. Rods are distributed throughout the retina but there are none at the fovea and none at the blind spot. Rod density is greater in the peripheral retina than in the central retina.

text: Cones are responsible for colour vision. They require brighter light to function than rods require. In humans, there are three types of cones, maximally sensitive to long-wavelength, medium-wavelength, and short-wavelength light (often referred to as red, green, and blue, respectively, though the sensitivity peaks are not actually at these colours). The colour seen is the combined effect of stimuli to, and responses from, these three types of cone cells. Cones are mostly concentrated in and near the fovea. Only a few are present at the sides of the retina. Objects are seen most sharply in focus when their images fall on the fovea, as when one looks at an object directly. Cone cells and rods are connected through intermediate cells in the retina to nerve fibres of the optic nerve. When rods and cones are stimulated by light, they connect through adjoining cells within the retina to send an electrical signal to the optic nerve fibres. The optic nerves send off impulses through these fibres to the brain.[50]

text: Pigmentation

text: The pigment molecules used in the eye are various, but can be used to define the evolutionary distance between different groups, and can also be an aid in determining which are closely related – although problems of convergence do exist.[50]

text: Opsins are the pigments involved in photoreception. Other pigments, such as melanin, are used to shield the photoreceptor cells from light leaking in from the sides. The opsin protein group evolved long before the last common ancestor of animals, and has continued to diversify since.[2]

text: There are two types of opsin involved in vision; c-opsins, which are associated with ciliary-type photoreceptor cells, and r-opsins, associated with rhabdomeric photoreceptor cells.[51] The eyes of vertebrates usually contain cilliary cells with c-opsins, and (bilaterian) invertebrates have rhabdomeric cells in the eye with r-opsins. However, some ganglion cells of vertebrates express r-opsins, suggesting that their ancestors used this pigment in vision, and that remnants survive in the eyes.[51] Likewise, c-opsins have been found to be expressed in the brain of some invertebrates. They may have been expressed in ciliary cells of larval eyes, which were subsequently resorbed into the brain on metamorphosis to the adult form.[51] C-opsins are also found in some derived bilaterian-invertebrate eyes, such as the pallial eyes of the bivalve molluscs; however, the lateral eyes (which were presumably the ancestral type for this group, if eyes evolved once there) always use r-opsins.[51] Cnidaria, which are an outgroup to the taxa mentioned above, express c-opsins – but r-opsins are yet to be found in this group.[51] Incidentally, the melanin produced in the cnidaria is produced in the same fashion as that in vertebrates, suggesting the common descent of this pigment.[51]

text: Additional images

text:
The structures of the eye labelled

Another view of the eye and the structures of the eye labelled

tag: ul


document_title: Filibuster in the United States Senate

question_text: when did senate rules change to 60 votes

text: Filibuster in the United States Senate

text: History[edit]

text: Constitutional design: simple majority voting[edit]

text: Although not explicitly mandated, the Constitution and its framers clearly envisioned that simple majority voting would be used to conduct business. The Constitution provides, for example, that a majority of each House constitutes a quorum to do business.[3] Meanwhile, a small number of super-majority requirements were explicitly included in the original document, including conviction on impeachment charges (2/3 of Senate)[4], expelling a member of Congress (2/3 of the chamber in question)[5], overriding presidential vetoes (2/3 of both Houses)[6], ratifying treaties (2/3 of Senate)[7], and proposing constitutional amendments (2/3 of both Houses).[8] Through negative textual implication, the Constitution also gives a simple majority the power to set procedural rules: "Each House may determine the Rules of its Proceedings, punish its Members for disorderly Behaviour, and, with the Concurrence of two thirds, expel a Member."[9]

text: Commentaries in The Federalist Papers confirm this understanding. In Federalist No. 58, the Constitution's primary drafter James Madison defended the document against routine super-majority requirements, either for a quorum or a "decision":

text: In Federalist No. 22, Alexander Hamilton described super-majority requirements as being one of the main problems with the previous Articles of Confederation, and identified several evils which would result from such a requirement:

text: Accidental creation and early use of the filibuster[edit]

text: In 1789, the first U.S. Senate adopted rules allowing senators to move the previous question (by simple majority vote), which meant ending debate and proceeding to a vote. But in 1806, the Senate's presiding officer, Vice President Aaron Burr argued that the previous-question motion was redundant, had only been exercised once in the preceding four years, and should be eliminated.[12] The Senate agreed and modified its rules.[12] Because it created no alternative mechanism for terminating debate, filibusters became theoretically possible.

text: Nevertheless, in the early 19th century the principle of simple-majority voting in the Senate was well established, and particularly valued by Southern slave-holding states. New states were admitted to the Union in pairs to preserve the sectional balance in the Senate, most notably in the Missouri Compromise of 1820.

text: Until the late 1830s, however, the filibuster remained a solely theoretical option, never actually exercised. The first Senate filibuster occurred in 1837.[13] In 1841, a defining moment came during debate on a bill to charter the Second Bank of the United States. Senator Henry Clay tried to end the debate via majority vote, and Senator William R. King threatened a filibuster, saying that Clay "may make his arrangements at his boarding house for the winter." Other senators sided with King, and Clay backed down.[12]

text: At the time, both the Senate and the House of Representatives allowed filibusters as a way to prevent a vote from taking place. Subsequent revisions to House rules limited filibuster privileges in that chamber, but the Senate continued to allow the tactic.[14]

text: In practice, narrow majorities could enact legislation by changing the Senate rules, but only on the first day of the session in January or March.[15]

text: The emergence of cloture (1917-1969)[edit]

text: In 1917, during World War I, a rule allowing cloture of a debate was adopted by the Senate on a 76-3 roll call vote[16] at the urging of President Woodrow Wilson,[17] after a group of 12 anti-war senators managed to kill a bill that would have allowed Wilson to arm merchant vessels in the face of unrestricted German submarine warfare.[18]

text: From 1917 to 1949, the requirement for cloture was two-thirds of senators voting.[19] Despite that formal requirement, however, political scientist David Mayhew has argued that in practice, it was unclear whether a filibuster could be sustained against majority opposition.[20] During the 1930s, Senator Huey Long of Louisiana used the filibuster to promote his populist policies. He recited Shakespeare and read out recipes for "pot-likkers" during his filibusters, which occupied 15 hours of debate.[17] In 1946, five Southern Democrats — senators John H. Overton (La.), Richard B. Russell (Ga.), Senator Millard E. Tydings (Md.), Clyde R. Hoey (N.C.), and Kenneth McKellar (Tenn.) — blocked a vote on a bill (S. 101)[21] proposed by Democrat Dennis Chávez of New Mexico that would have created a permanent Fair Employment Practice Committee (FEPC) to prevent discrimination in the workplace. The filibuster lasted weeks, and Senator Chávez was forced to remove the bill from consideration after a failed cloture vote, even though he had enough votes to pass the bill.

text: In 1949, the Senate made invoking cloture more difficult by requiring two-thirds of the entire Senate membership to vote in favor of a cloture motion.[22] Moreover, future proposals to change the Senate rules were themselves specifically exempted from being subject to cloture.[23]:191 In 1953, Senator Wayne Morse of Oregon set a record by filibustering for 22 hours and 26 minutes while protesting the Tidelands Oil legislation. Senator Strom Thurmond of South Carolina broke this record in 1957 by filibustering the Civil Rights Act of 1957 for 24 hours and 18 minutes,[24] although the bill ultimately passed.

text: In 1959, anticipating more civil rights legislation, the Senate under the leadership of Majority Leader Lyndon Johnson restored the cloture threshold to two-thirds of those voting.[22] Although the 1949 rule had eliminated cloture on rules changes themselves, Johnson acted at the very beginning of the new Congress on January 5, 1959, and the resolution was adopted by a 72-22 vote with the support of three top Democrats and three of the four top Republicans. The presiding officer, Vice President Richard Nixon, supported the move and stated his opinion that the Senate "has a constitutional right at the beginning of each new Congress to determine rules it desires to follow."[25] The 1959 change also eliminated the 1949 exemption for rules changes, allowing cloture to once again be invoked on future changes.[23]:193

text: One of the most notable filibusters of the 1960s occurred when Southern Democrats attempted to block the passage of the Civil Rights Act of 1964 by filibustering for 75 hours, including a 14 hour and 13 minute address by Senator Robert Byrd of West Virginia. The filibuster failed when the Senate invoked cloture for only the second time since 1927.[26]

text: The two-track system, 60-vote rule, and rise of the routine filibuster (1970 onward)[edit]

text: After a series of filibusters in the 1960s over civil rights legislation, the Senate put a "two-track system" into place in 1970 under the leadership of Majority Leader Mike Mansfield and Majority Whip Robert Byrd. Before this system was introduced, a filibuster would stop the Senate from moving on to any other legislative activity. Tracking allows the majority leader—with unanimous consent or the agreement of the minority leader—to have more than one bill pending on the floor as unfinished business. Under the two-track system, the Senate can have two or more pieces of legislation pending on the floor simultaneously by designating specific periods during the day when each one will be considered.[27][28]

text: The notable side effect of this change was that by no longer bringing Senate business to a complete halt, filibusters on particular legislation became politically easier for the minority to sustain.[30][31][32][33] As a result, the number of filibusters began increasing rapidly, eventually leading to the modern era in which an effective supermajority requirement exists to pass legislation, with no practical requirement that the minority party actually hold the floor or extend debate.

text: In 1975, the Senate revised its cloture rule so that three-fifths of sworn senators (60 votes out of 100) could limit debate, except for changing Senate rules which still requires a two-thirds majority of those present and voting to invoke cloture.[34][35] However, by returning to an absolute number of all Senators (60) rather than a proportion of those present and voting, the change also made any filibusters easier to sustain on the floor by a small number of senators from the minority party without requiring the presence of their minority colleagues. This further reduced the majority's leverage to force an issue through extended debate.

text: The Senate also experimented with a rule that removed the need to speak on the floor in order to filibuster (a "talking filibuster"), thus allowing for "virtual filibusters".[36] Another tactic, the post-cloture filibuster—which used points of order to delay legislation because they were not counted as part of the limited time allowed for debate—was rendered ineffective by a rule change in 1979.[37][38][39]

text: As the filibuster has evolved from a rare practice that required holding the floor for extended periods into a routine 60-vote supermajority requirement, Senate leaders have increasingly used cloture motions as a regular tool to manage the flow of business, often even in the absence of a threatened filibuster. Thus, the presence or absence of cloture attempts is not necessarily a reliable indicator of the presence or absence of a threatened filibuster. Because filibustering does not depend on the use of any specific rules, whether a filibuster is present is always a matter of judgment.[40]

text: Recent efforts to limit filibusters[edit]

text: In 2005, a group of Republican senators led by Majority Leader Bill Frist proposed having the presiding officer, Vice President Dick Cheney, rule that a filibuster on judicial nominees was unconstitutional, as it was inconsistent with the President's power to name judges with the advice and consent of a simple majority of senators.[41][42] This was a response to the Democrats' threat to filibuster some judicial nominees of President George W. Bush. Senator Trent Lott, the junior senator from Mississippi, used the word "nuclear" to describe the plan, and so it became known as the "nuclear option".[43]

text: With Republicans effectively controlling the Senate 55-45, a group of 14 senators—seven Democrats and seven Republicans, collectively dubbed the "Gang of 14"—reached an agreement to defuse the conflict. The seven Democrats promised not to filibuster Bush's nominees except under "extraordinary circumstances", while the seven Republicans promised to oppose the "nuclear option" unless they thought a nominee was being filibustered under non-extraordinary circumstances. Thus, there would be 62 votes to invoke cloture in most cases, and 52 votes to oppose the nuclear option.[44][45][46] This agreement was successful in the short term, but it expired in January 2007, at the end of the second session of the 109th United States Congress.[47]

text: From April to June 2010, under Democratic control, the Senate Committee on Rules and Administration held a series of monthly public hearings on the history and use of the filibuster in the Senate.[48] In response to the use of the filibuster in the 111th Congress, all Democratic senators returning to the 112th Congress signed a petition to Majority Leader Harry Reid (D-Nevada) requesting that the filibuster be reformed, including abolishing secret holds and reducing the amount of time allotted for post-cloture debate.

text: Minor 2013 changes[edit]

text: During the 113th Congress, two packages of amendments were adopted on January 25, 2013.[49] Changes to standing orders affecting just the 2013–14 Congress (Senate Resolution 15) were passed by a vote of 78 to 16, allowing Reid, the majority leader, to prohibit a filibuster on a motion to begin consideration of a bill.[49] Changes to the permanent Senate rules (Senate Resolution 16) were passed by a vote of 86 to 9.[49][50]

text: The changes removed the 60-vote requirement to begin debate on legislation, and allowed the minority two amendments to measures that reached the Senate floor. This change was implemented as a standing order that expired at the end of the term in which it was passed.[51][52] The new rules also reduced the amount of time allowed for debate after a motion to proceed from 30 hours to four hours. Additionally, they stated that a filibuster on a motion to proceed could be blocked with a petition signed by eight members of the minority, including the minority leader.[52] For district court nominations, the new rules reduced the maximum time between cloture and a confirmation vote from 30 hours to two hours.[52] Finally, if senators wished to block a bill or nominee after the motion to proceed, they had to be present in the Senate and debate.[53][51]

text: Despite these changes, 60 votes were still required to overcome a filibuster, and the "silent filibuster"—in which a senator can delay a bill even if they leave the floor—remained in place.[53][51]

text: Abolition for nominations, 2013 & 2017[edit]

text: On November 21, 2013, the Senate used the so-called "nuclear option," voting 52–48 — with all Republicans and three Democrats opposed — to eliminate the use of the filibuster on executive branch nominees and judicial nominees, except to the Supreme Court. At the time of the vote, there were 59 executive branch nominees and 17 judicial nominees awaiting confirmation.[54]

text: The Democrats' stated motivation was what they saw as an expansion of filibustering by Republicans during the Obama administration, especially with respect to nominations for the United States Court of Appeals for the District of Columbia Circuit.[55][56] Republicans had asserted that the D.C. Circuit was underworked[54] and cited a need to cut costs by reducing the number of judges.[57] Democrats responded that Republicans had not raised these concerns earlier, when President Bush had made nominations to the court, and argued that the size of the court needed to be maintained because of the complexity of the cases it hears.[58][59] Senate Democrats who supported the "nuclear option" also did so out of frustration with filibusters of executive branch nominees for agencies such as the Federal Housing Finance Agency.[55]

text: In 2015, Republicans took control of the Senate and kept the 2013 rules in place.[60] Finally, on April 6, 2017, the Senate eliminated the sole remaining exception to the 2013 change by invoking the "nuclear option" for Supreme Court nominees. This was done in order to allow a simple majority to confirm Neil Gorsuch to the Supreme Court. The vote to change the rules was 52 to 48 along party lines.[61]

text: Exceptions[edit]

text: The only bills that are not currently subject to effective 60-vote requirements are those considered under provisions of law that limit time for debating them.[62] These limits on debate allow the Senate to hold a simple-majority vote on final passage without obtaining the 60 votes normally needed to close debate. As a result, many major legislative actions in recent decades have been adopted through one of these methods.

text: Reconciliation is a procedure created in 1974 as part of the congressional budget process. In brief, the annual budget process begins with adoption of a budget resolution (passed by simple majority in each house, not signed by President, does not carry force of law) that sets overall funding levels for the government. The Senate may then consider a budget reconciliation bill, not subject to filibuster, that reconciles funding amounts in any annual appropriations bills with the amounts specified in the budget resolution. However, under the Byrd rule no non-budgetary "extraneous matter" may be considered in a reconciliation bill. The presiding officer, relying always (as of 2017) on the opinion of the Senate parliamentarian, determines whether an item is extraneous, and a 60-vote majority is required to include such material in a reconciliation bill.

text: The Congressional Review Act, adopted in 1995, allows Congress to review and repeal administrative regulations adopted by the Executive Branch within 60 legislative days. This procedure will most typically be used successfully shortly after a party change in the presidency. It was used once in 2001 to repeal an ergonomics rule promulgated under Bill Clinton), was not used in 2009, and was used 14 times in 2017 to repeal various regulations adopted in the final year of the Barack Obama presidency.

text: Policy and political effects[edit]

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tag: table

text: The modern-era filibuster — and the effective 60-vote supermajority requirement it has led to — have had very major policy and political effects, both institutionally and on specific major policy initiatives from Presidents of both parties.

text: Institutional effects[edit]

text: Congress. The supermajority rule has made it very difficult, often impossible, for Congress to pass any but the most non-controversial legislation in recent decades. During times of unified party control, majorities have attempted (with varying levels of success) to enact their major policy priorities through the budget reconciliation process, resulting in legislation constrained by budget rules. Meanwhile, public approval for Congress as an institution has fallen to its lowest levels ever, with large segments of the public seeing the institution as ineffective.[citation needed] Shifting majorities of both parties — and their supporters — have often been frustrated as major policy priorities articulated in political campaigns are unable to obtain passage following an election.

text: The Presidency. Presidents of both parties have increasingly filled the policymaking vacuum with expanded use of executive power, including executive orders in areas that had traditionally been handled through legislation. For example, Barack Obama effected major changes in immigration policy by issuing work permits to some undocumented workers,[citation needed] while Donald Trump has issued several significant executive orders since taking office in 2017 along with undoing many of Obama's initiatives.[citation needed] As a result, policy in these areas is increasingly determined by executive preference, and is more easily changed after elections, rather than through more permanent legislative policy.

text: Judiciary. The Supreme Court's caseload has declined significantly, with various commenters suggesting that the decline in major legislation has been a major cause.[63] Meanwhile, more policy issues are resolved judicially without action by Congress — despite the existence of potential simple majority support in the Senate — on topics such as the legalization of same-sex marriage.[citation needed]

text: Major presidential policy initiatives[edit]

text: The implied threat of a filibuster — and the resulting 60-vote requirement in the modern era — have had major impacts on the ability of recent Presidents to enact their top legislative priorities into law. The effects of the 60-vote requirement are most apparent in periods where the President and both Houses of Congress are controlled by the same political party, typically early in a presidential term.

text: Bill Clinton[edit]

text: In 1993-94, President Bill Clinton enjoyed Democratic majorities in both chambers of the 103rd Congress, including a 57-43 advantage in the Senate. Yet the Clinton health care plan of 1993, formulated by a task force led by First Lady Hillary Clinton, was unable to pass in part due to the filibuster. As early as April 1993, a memo to the task force noted that "While the substance is obviously controversial, there is apparently great disquiet in the Capitol over whether we understand the interactivity between reconciliation and health, procedurally, and in terms of timing and counting votes for both measures...."[64]

text: George W. Bush[edit]

text: In 2001, President George W. Bush was unable to obtain any Democratic support for his tax cut proposals. As a result, the Bush tax cuts of 2001 and 2003 were each passed using reconciliation, which required that the tax cuts expire within the 10-year budget window to avoid violating the Byrd rule in the Senate. The status of the tax cuts would remain unresolved until the late 2012 " fiscal cliff," with a significant portion of the cuts being made permanent by the American Taxpayer Relief Act of 2012, passed by a Republican Congress and signed by President Barack Obama.

text: Barack Obama[edit]

text: In 2009-10, President Barack Obama briefly enjoyed an effective 60-vote Democratic majority (including independents) in the Senate during the 111th Congress. During that time period, the Senate passed the Patient Protection and Affordable Care Act, commonly known as the ACA or "Obamacare," on Dec. 24, 2009 by a vote of 60-39 (after invoking cloture by the same 60-39 margin). However, Obama's proposal to create a public health insurance option was removed from the health care legislation because it could not command 60-vote support.

text: House Democrats did not approve of all aspects of the Senate bill, but after 60-vote Senate control was permanently lost in February 2010 due to the election of Scott Brown to fill the seat of the late Ted Kennedy, House Democrats decided to pass the Senate bill intact and it became law. Several House-desired modifications to the Senate bill — those sufficient to pass scrutiny under the Byrd rule — were then made under reconciliation via the Health Care and Education Reconciliation Act of 2010, which was enacted days later following a 56-43 vote in the Senate.

text: The near-60-vote Senate majority that Democrats held throughout the 111th Congress was also critical to passage of other major Obama initiatives, including the American Reinvestment and Recovery Act of 2009 (passed 60-38, two Republicans voting yes)[citation needed] and the Dodd-Frank Wall Street Reform and Consumer Protection Act (passed 60-39, three Republicans voting yes, one Democrat voting no).[citation needed] However, the House-passed American Clean Energy and Security Act, which would have created a cap-and-trade system and established a national renewable electricity standard to combat climate change, never received a Senate floor vote with Majority Leader Harry Reid saying "it's easy to count to 60."[65]

text: Donald Trump[edit]

text: In 2017, President Donald Trump and the 115th Congress have envisioned a strategy to use an FY17 reconciliation bill to repeal Obamacare, followed by an FY18 reconciliation bill to pass tax reform. A reconciliation strategy is being pursued since nearly all Democrats are expected to oppose these policies, making a filibuster threat insurmountable due to the 60-vote requirement.

text: An FY17 budget resolution that included reconciliation instructions for health care reform was passed by the Senate by a 51-48 vote on January 12, 2017,[66] and by the House on a 227-198 vote the following day.[67] The House later passed the American Health Care Act of 2017 as the FY17 budget reconciliation bill by a vote of 217-213 on May 4, 2017. In July, the Senate Parliamentarian ruled that certain provisions of the House bill must be stricken (as "extraneous" non-budgetary matter) under the Byrd rule before proceeding under reconciliation.[68] The Parliamentarian later ruled that an FY17 reconciliation bill must be adopted by end of FY17, establishing a September 30th deadline.[69] Senate Republicans were unable to obtain 51 votes for any health care reconciliation bill before the deadline, and the FY17 budget resolution expired.

text: An FY18 budget resolution that includes reconciliation instructions for tax reform was passed by the Senate by a 51-49 vote on October 19, 2017,[70] and by the House on a 216-212 vote on October 26, 2017.[71] The FY18 budget resolution enables passage of a reconciliation bill (by a simple majority) that would raise the deficit by $1.5 trillion over ten years, effectively setting the net cost of any eventual tax reform bill. The budget resolution also permits the reconciliation bill to open drilling in the Arctic National Wildlife Refuge, likely to help secure the vote of Alaska Sen. Lisa Murkowski who voted against FY17 health care reconciliation legislation.

text: Process for limiting or eliminating the filibuster[edit]

text: According to the Supreme Court's ruling in United States v. Ballin (1892), Senate rules can be changed by a simple majority vote. Nevertheless, under current Senate rules, a rule change could itself be filibustered, requiring two-thirds of senators who are present and voting to end debate. (This differs from the usual requirement for three-fifths of sworn senators.)[1]

text: However, despite this two-thirds requirement being written into the Senate rules, any Senator may attempt to nullify a Senate rule by making a point of order that the rule is unconstitutional or just that the meaning of the rule should not be followed. The presiding officer is generally expected to rule in favor of the rules of the Senate, but any ruling from the chair may be appealed and overturned by a simple majority of Senators. This happened in 2013, when Harry Reid of the Democratic Party made a point of order that "the vote on cloture under rule XXII for all nominations other than for the Supreme Court of the United States is by majority vote." Although there is no simple majority vote provision in the text of rule XXII,[72] Reid's point of order was sustained by a 52-48 vote, and that ruling established a Senate precedent that cloture on nominations other than those for the Supreme Court requires only a simple majority.[1] On April 6, 2017, that precedent was further changed by Mitch McConnell and the Republican majority to include Supreme Court nominations.[73][74]

text: Other forms of filibuster[edit]

text: While talking out a measure is the most common form of filibuster in the Senate, other means of delaying and killing legislation are available. Because the Senate routinely conducts business by unanimous consent, one member can create at least some delay by objecting to the request. In some cases, such as considering a bill or resolution on the day it is introduced or brought from the House, the delay can be as long as a day.[75] However, because this is a legislative day, not a calendar day, the majority can mitigate it by briefly adjourning.[76]

text: In many cases, an objection to a request for unanimous consent will compel a vote. While forcing a single vote may not be an effective delaying tool, the cumulative effect of several votes, which take at least 15 minutes apiece, can be substantial. In addition to objecting to routine requests, senators can force votes through motions to adjourn and through quorum calls. Quorum calls are meant to establish the presence or absence of a constitutional quorum, but senators routinely use them to waste time while waiting for the next speaker to come to the floor or for leaders to negotiate off the floor. In those cases, a senator asks for unanimous consent to dispense with the quorum call. If another senator objects, the clerk must continue to call the roll of senators, just as they would with a vote. If a call shows no quorum, the minority can force another vote by moving to request or compel the attendance of absent senators. Finally, senators can force votes by moving to adjourn, or by raising specious points of order and appealing the ruling of the chair.

text: The most effective methods of delay are those that force the majority to invoke cloture multiple times on the same measure. The most common example is to filibuster the motion to proceed to a bill, then filibuster the bill itself. This forces the majority to go through the entire cloture process twice in a row. If, as is common, the majority seeks to pass a substitute amendment to the bill, a further cloture procedure is needed for the amendment.

text: The Senate is particularly vulnerable to serial cloture votes when it and the House have passed different versions of the same bill and want to go to conference (i.e., appoint a special committee of both chambers to merge the bills). Normally, the majority asks for unanimous consent to:

text:
Insist on its amendment(s), or disagree with the House's amendments
Request, or agree to, a conference
Authorize the presiding officer to appoint members of the special committee

text: If the minority objects, those motions are debatable (and therefore subject to a filibuster) and divisible (meaning the minority can force them to be debated, and filibustered, separately).[75] Additionally, after the first two motions pass, but before the third does, senators can offer an unlimited number of motions to give the special committee members non-binding instructions, which are themselves debatable, amendable, and divisible.[77] As a result, a determined minority can cause a great deal of delay before a conference.

text: Longest filibusters[edit]

text: Below is a table of the ten longest filibusters to take place in the United States Senate since 1900.

text:
Longest filibusters in the U.S. Senate since 1900[78][79]

Senator
Date (began)
Measure
Hours & minutes

011
ThurmondStrom Thurmond (D-SC)
August 28, 1957
Civil Rights Act of 1957
24:18

022
DAmatoAlfonse D'Amato (R-NY)
October 17, 1986
Defense Authorization Act (1987), amendment
23:30

033
MorseWayne Morse (I-OR)
April 24, 1953
Submerged Lands Act (1953)
22:26

044
CruzTed Cruz (R-TX)
September 24, 2013
Continuing Appropriations Act (2014)
21:18

055
LaFolletteRobert M. La Follette, Sr. (R-WI)
May 29, 1908
Aldrich–Vreeland Act (1908)
18:23

066
ProxmireWilliam Proxmire (D-WI)
September 28, 1981
Debt ceiling increase (1981)
16:12

077
LongHuey Long (D-LA)
June 12, 1935
National Industrial Recovery Act (1933), amendment
15:30

8
MerkleyJeff Merkley (D-OR)
April 4, 2017
Neil Gorsuch Supreme Court confirmation
15:28

9
DAmatoAlfonse D'Amato (R-NY)
October 5, 1992
Revenue Act (1992), amendment
15:14

1010
MurphyChris Murphy (D-CT)
June 15, 2016
Nominally H.R. 2578; supporting gun control measures
14:50