Santa Monica Mountains Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Santa Monica Mountains Observatory clear sky chart from 2005-11-06 to 2024-01-12.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
72%
24356
32%
74442
29%
24301
77%
24301
48%
37330

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 10thNight
64%
756
28%
2646
28%
756
70%
756
38%
1332
January11th to 20thNight
65%
726
35%
2368
31%
726
75%
726
46%
1147
January21st to endNight
58%
792
39%
2404
31%
792
70%
792
44%
1242
February1st to 10thNight
67%
720
36%
2160
33%
720
74%
720
46%
1098
February11th to 20thNight
65%
700
33%
2098
30%
700
73%
700
45%
1079
February21st to endNight
59%
592
29%
1776
27%
592
66%
592
39%
966
March1st to 10thNight
60%
720
26%
2160
24%
720
68%
720
39%
1187
March11th to 20thNight
65%
720
25%
2094
22%
720
70%
720
41%
1143
March21st to endNight
64%
792
30%
1980
20%
792
70%
792
47%
1133
April1st to 10thNight
66%
720
30%
1800
20%
720
69%
720
47%
1042
April11th to 20thNight
66%
711
33%
1779
17%
711
72%
711
55%
951
April21st to endNight
66%
720
30%
1800
15%
720
71%
720
53%
982
May1st to 10thNight
68%
692
25%
1772
16%
692
70%
692
47%
1016
May11th to 20thNight
71%
531
27%
1595
21%
531
72%
531
45%
852
May21st to endNight
73%
582
30%
1746
23%
582
76%
582
54%
859
June1st to 10thNight
75%
473
26%
1553
24%
473
76%
473
47%
765
June11th to 20thNight
81%
360
34%
1440
40%
360
82%
360
53%
552
June21st to endNight
82%
360
33%
1440
40%
360
82%
360
50%
567
July1st to 10thNight
86%
350
36%
1400
44%
350
86%
350
58%
512
July11th to 20thNight
87%
354
34%
1398
41%
354
87%
354
55%
539
July21st to endNight
84%
768
29%
1842
21%
726
85%
726
61%
944
August1st to 10thNight
86%
716
32%
1780
20%
712
86%
712
65%
896
August11th to 20thNight
85%
712
36%
1780
23%
712
85%
712
67%
881
August21st to endNight
87%
792
40%
1980
28%
792
87%
792
71%
953
September1st to 10thNight
85%
720
39%
1800
31%
720
85%
720
64%
914
September11th to 20thNight
87%
720
42%
1912
38%
720
87%
720
70%
874
September21st to endNight
85%
720
41%
1980
40%
720
87%
720
69%
888
October1st to 10thNight
80%
720
37%
1980
35%
720
83%
720
58%
972
October11th to 20thNight
76%
720
38%
2124
39%
720
79%
720
55%
1010
October21st to endNight
76%
792
41%
2386
41%
792
80%
792
58%
1080
November1st to 10thNight
77%
740
35%
2405
37%
740
82%
740
55%
1063
November11th to 20thNight
76%
760
37%
2470
37%
760
83%
760
54%
1095
November21st to endNight
70%
760
35%
2470
35%
760
75%
760
45%
1202
December1st to 10thNight
63%
760
33%
2470
30%
760
71%
760
41%
1253
December11th to 20thNight
60%
760
29%
2971
30%
759
68%
759
27%
1775
December21st to endNight
60%
825
20%
4683
29%
817
69%
817
21%
2566

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
5%313323346%67%
74919
Night
6%423323347%63%
74807
TransparencyDay
19%48%18%27%25%
74645
Night
21%48%18%23%25%
74603
SeeingDay
6%6%21%35%25%7%
14457
Night
6%311%34%37%9%
24377

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
8%424423446%58%
1519
11th to 20thDay
7%5%24314346%62%
1615
21st to endDay
9%5%24313346%61%
1947
February1st to 10thDay
8%423323246%64%
1800
11th to 20thDay
8%21332335%6%64%
1750
21st to endDay
7%42332335%6%61%
1480
March1st to 10thDay
7%425%4345%5%7%55%
1800
11th to 20thDay
7%42332445%9%57%
1861
21st to endDay
6%32242445%7%62%
2376
April1st to 10thDay
5%423323448%62%
2160
11th to 20thDay
4313223346%68%
2129
21st to endDay
3313312437%70%
2160
May1st to 10thDay
4422323349%63%
2186
11th to 20thDay
45%23312336%66%
2301
21st to endDay
4423213347%67%
2530
June1st to 10thDay
5%6%23212237%65%
2401
11th to 20thDay
4412212236%72%
2520
21st to endDay
2422212235%74%
2520
July1st to 10thDay
3313222336%72%
2520
11th to 20thDay
2313222235%75%
2509
21st to endDay
2212313347%72%
2368
August1st to 10thDay
2212212225%77%
2149
11th to 20thDay
2212112225%80%
2122
21st to endDay
1212212246%77%
2376
September1st to 10thDay
3212212235%78%
2160
11th to 20thDay
2312212225%80%
2047
21st to endDay
2212212235%77%
1980
October1st to 10thDay
4312312345%73%
1980
11th to 20thDay
3312212335%75%
1832
21st to endDay
3212312345%73%
1967
November1st to 10thDay
3213222346%71%
1674
11th to 20thDay
5%21331235%5%69%
1710
21st to endDay
4413423448%63%
1710
December1st to 10thDay
7%33432345%6%60%
1710
11th to 20thDay
16%5%25%42435%8%46%
2169
21st to endDay
13%5%246%4446%7%45%
2881
January1st to 10thNight
9%413323447%58%
2646
11th to 20thNight
7%42332235%7%62%
2368
21st to endNight
10%423322335%63%
2404
February1st to 10thNight
7%424313237%64%
2160
11th to 20thNight
8%323323436%63%
2098
21st to endNight
10%324323435%61%
1776
March1st to 10thNight
8%5%245%2445%9%54%
2160
11th to 20thNight
7%5%234345%5%7%56%
2094
21st to endNight
7%5%1333435%7%60%
1980
April1st to 10thNight
7%6%33323337%60%
1800
11th to 20thNight
45%23323336%66%
1779
21st to endNight
442432345%7%63%
1800
May1st to 10thNight
5%6%2442335%8%59%
1772
11th to 20thNight
47%34422437%61%
1594
21st to endNight
46%13312346%67%
1746
June1st to 10thNight
27%4432435%8%59%
1553
11th to 20thNight
36%23312347%66%
1440
21st to endNight
17%33213348%65%
1440
July1st to 10thNight
15%14412249%67%
1440
11th to 20thNight
232431345%7%66%
1446
21st to endNight
3325%32345%8%63%
1950
August1st to 10thNight
3313323346%68%
1790
11th to 20thNight
35%22212248%68%
1780
21st to endNight
1324212347%71%
1980
September1st to 10thNight
4412212337%71%
1800
11th to 20thNight
2312211345%76%
1912
21st to endNight
1323212337%75%
1980
October1st to 10thNight
341332334470%
1980
11th to 20thNight
442321233471%
2124
21st to endNight
3412222245%73%
2386
November1st to 10thNight
3312323346%70%
2405
11th to 20thNight
3323323337%70%
2470
21st to endNight
432433445%7%62%
2470
December1st to 10thNight
7%425%423346%60%
2470
11th to 20thNight
17%6%34423347%48%
3041
21st to endNight
13%6%24435%5%5%7%47%
4773

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
27%48%17%23%22%
1519
11th to 20thDay
24%48%12%26%27%
1615
21st to endDay
26%47%17%17%28%
1947
February1st to 10thDay
23%36%14%24%29%
1800
11th to 20thDay
20%5%7%17%26%25%
1760
21st to endDay
24%5%10%18%24%20%
1480
March1st to 10thDay
28%6%8%20%17%21%
1800
11th to 20thDay
23%5%11%20%23%18%
1861
21st to endDay
22%6%12%23%21%16%
2376
April1st to 10thDay
22%6%14%24%21%13%
2160
11th to 20thDay
17%5%9%22%29%18%
2132
21st to endDay
16%5%10%26%30%14%
2160
May1st to 10thDay
18%7%12%22%27%14%
2186
11th to 20thDay
19%5%10%24%28%13%
2304
21st to endDay
19%6%11%28%28%7%
2530
June1st to 10thDay
20%5%12%20%30%14%
2401
11th to 20thDay
15%48%15%33%27%
2520
21st to endDay
14%26%11%34%33%
2520
July1st to 10thDay
14%36%13%25%40%
2451
11th to 20thDay
13%27%20%33%25%
2434
21st to endDay
13%49%24%33%18%
2237
August1st to 10thDay
12%3414%33%34%
2135
11th to 20thDay
8%25%14%37%33%
2122
21st to endDay
9%25%14%36%35%
2376
September1st to 10thDay
11%35%13%31%38%
2160
11th to 20thDay
10%25%15%32%36%
2047
21st to endDay
12%2418%34%29%
1980
October1st to 10thDay
15%37%20%23%32%
1980
11th to 20thDay
14%36%14%28%35%
1832
21st to endDay
14%45%14%21%42%
1967
November1st to 10thDay
16%36%17%24%34%
1674
11th to 20thDay
17%37%15%20%38%
1710
21st to endDay
20%48%12%24%32%
1710
December1st to 10thDay
25%5%7%16%21%26%
1710
11th to 20thDay
37%5%8%14%20%16%
2168
21st to endDay
35%7%9%22%15%12%
2881
January1st to 10thNight
26%47%16%24%22%
2646
11th to 20thNight
22%38%15%21%30%
2368
21st to endNight
25%37%16%18%30%
2404
February1st to 10thNight
23%37%14%23%29%
2160
11th to 20thNight
23%47%17%23%26%
2099
21st to endNight
28%48%15%23%22%
1776
March1st to 10thNight
28%5%10%18%21%19%
2160
11th to 20thNight
26%6%12%17%22%18%
2094
21st to endNight
24%5%11%22%23%16%
1980
April1st to 10thNight
25%5%13%23%19%15%
1800
11th to 20thNight
19%410%23%24%19%
1779
21st to endNight
19%5%14%23%27%13%
1800
May1st to 10thNight
22%8%12%22%22%14%
1772
11th to 20thNight
20%9%10%23%25%12%
1595
21st to endNight
18%5%11%32%25%9%
1746
June1st to 10thNight
19%6%15%22%24%13%
1553
11th to 20thNight
14%410%19%33%20%
1440
21st to endNight
17%38%14%29%30%
1440
July1st to 10thNight
14%15%17%24%38%
1400
11th to 20thNight
13%410%19%28%25%
1398
21st to endNight
16%411%26%27%16%
1842
August1st to 10thNight
15%26%16%31%30%
1780
11th to 20thNight
14%27%13%32%32%
1780
21st to endNight
12%16%17%32%32%
1980
September1st to 10thNight
15%36%11%28%37%
1800
11th to 20thNight
11%36%15%29%37%
1912
21st to endNight
11%26%16%32%32%
1980
October1st to 10thNight
17%37%18%21%34%
1980
11th to 20thNight
18%36%16%22%35%
2124
21st to endNight
15%35%12%21%44%
2386
November1st to 10thNight
16%48%17%21%35%
2405
11th to 20thNight
17%37%14%20%39%
2470
21st to endNight
21%5%6%17%19%32%
2470
December1st to 10thNight
25%47%15%19%30%
2470
11th to 20thNight
38%47%13%21%17%
3041
21st to endNight
34%8%10%19%16%12%
4773

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
16%6%26%33%17%2
180
11th to 20thDay
11%9%30%32%17%2
329
21st to endDay
10%11%33%30%14%2
448
February1st to 10thDay
9%9%30%31%16%4
420
11th to 20thDay
10%14%33%31%10%2
415
21st to endDay
8%15%34%32%11%
346
March1st to 10thDay
11%16%33%26%12%2
420
11th to 20thDay
10%12%31%31%13%2
420
21st to endDay
9%15%34%30%11%2
462
April1st to 10thDay
7%10%30%31%17%5%
420
11th to 20thDay
414%37%32%10%4
412
21st to endDay
312%31%31%16%7%
420
May1st to 10thDay
6%11%28%35%15%4
423
11th to 20thDay
7%6%25%36%22%4
448
21st to endDay
6%5%29%37%18%5%
485
June1st to 10thDay
7%318%38%28%7%
450
11th to 20thDay
5%314%39%30%10%
450
21st to endDay
4212%39%32%12%
450
July1st to 10thDay
31437%42%13%
446
11th to 20thDay
2229%49%19%
444
21st to endDay
2333%46%17%
487
August1st to 10thDay
217%37%39%13%
447
11th to 20thDay
3433%45%14%
437
21st to endDay
116%39%39%14%
495
September1st to 10thDay
4111%43%29%12%
450
11th to 20thDay
3215%43%29%8%
450
21st to endDay
2320%39%28%9%
450
October1st to 10thDay
35%20%42%26%5%
450
11th to 20thDay
3424%42%22%5%
450
21st to endDay
46%24%33%26%6%
482
November1st to 10thDay
36%18%36%30%8%
270
11th to 20thDay
45%21%41%23%6%
270
21st to endDay
5%6%23%31%29%6%
270
December1st to 10thDay
9%6%23%34%26%3
270
11th to 20thDay
7%7%18%37%26%4
270
21st to endDay
14%13%23%36%13%2
221
January1st to 10thNight
11%413%43%22%6%
760
11th to 20thNight
7%318%41%25%5%
726
21st to endNight
11%419%39%24%3
792
February1st to 10thNight
8%314%39%28%7%
720
11th to 20thNight
9%416%40%24%7%
704
21st to endNight
11%5%18%40%22%4
592
March1st to 10thNight
10%5%17%44%22%3
720
11th to 20thNight
9%414%38%29%6%
720
21st to endNight
8%5%16%43%24%4
792
April1st to 10thNight
9%413%43%29%4
720
11th to 20thNight
6%416%41%30%4
711
21st to endNight
5%6%15%38%29%7%
720
May1st to 10thNight
7%214%39%33%5%
692
11th to 20thNight
4215%38%37%4
531
21st to endNight
4116%39%35%4
584
June1st to 10thNight
3111%37%43%5%
473
11th to 20thNight
31331%55%7%
360
21st to endNight
5%326%59%7%
360
July1st to 10thNight
2212%72%11%
350
11th to 20thNight
19%72%17%
354
21st to endNight
31115%61%19%
768
August1st to 10thNight
4121%58%15%
716
11th to 20thNight
4114%63%19%
712
21st to endNight
21117%60%19%
792
September1st to 10thNight
6%1321%52%17%
720
11th to 20thNight
31328%53%13%
720
21st to endNight
116%29%52%12%
720
October1st to 10thNight
417%40%41%7%
720
11th to 20thNight
5%29%34%40%10%
720
21st to endNight
4212%33%35%13%
792
November1st to 10thNight
3411%38%34%11%
740
11th to 20thNight
6%29%39%34%10%
760
21st to endNight
6%214%41%29%7%
760
December1st to 10thNight
8%416%40%26%6%
760
11th to 20thNight
12%6%14%40%24%4
760
21st to endNight
11%6%18%42%19%5%
836
Page generated at 2024-01-09 04:14:42. Version ac07

Copyright 2024 Attilla Danko


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