San Diego
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the San Diego clear sky chart from 2005-11-06 to 2024-03-28.

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
67%
25300
26%
79972
25%
25214
69%
25214
34%
46311

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
67%
750
35%
3994
30%
736
70%
736
29%
1647
January11th to 20thNight
70%
747
30%
3826
33%
740
73%
740
25%
1990
January21st to endNight
64%
828
22%
3989
30%
814
70%
814
22%
2328
February1st to 10thNight
66%
760
31%
2280
32%
760
69%
760
39%
1281
February11th to 20thNight
61%
740
27%
2218
28%
740
64%
740
33%
1314
February21st to endNight
61%
628
26%
1884
27%
628
65%
628
33%
1137
March1st to 10thNight
59%
760
21%
2280
23%
760
61%
760
30%
1390
March11th to 20thNight
62%
760
20%
2195
22%
760
64%
760
32%
1339
March21st to endNight
64%
820
23%
2123
19%
820
66%
820
36%
1342
April1st to 10thNight
61%
720
24%
1800
17%
720
62%
720
36%
1160
April11th to 20thNight
61%
711
25%
1779
17%
711
62%
711
38%
1138
April21st to endNight
61%
720
22%
1800
15%
720
62%
720
34%
1195
May1st to 10thNight
60%
630
20%
1710
14%
630
60%
630
29%
1159
May11th to 20thNight
54%
531
14%
1595
11%
531
55%
531
24%
1113
May21st to endNight
57%
582
19%
1746
14%
582
57%
582
26%
1187
June1st to 10thNight
56%
540
15%
1620
14%
540
56%
540
24%
1144
June11th to 20thNight
67%
540
19%
1620
15%
540
67%
540
34%
1006
June21st to endNight
68%
540
19%
1620
17%
540
68%
540
35%
1004
July1st to 10thNight
70%
525
18%
1575
15%
525
70%
525
37%
942
July11th to 20thNight
76%
522
22%
1566
19%
522
76%
522
39%
926
July21st to endNight
69%
732
20%
1808
14%
692
68%
692
33%
1184
August1st to 10thNight
74%
716
24%
1780
15%
712
74%
712
47%
1035
August11th to 20thNight
71%
712
25%
1780
17%
712
71%
712
42%
1094
August21st to endNight
77%
792
31%
1980
23%
792
77%
792
51%
1125
September1st to 10thNight
72%
720
29%
1812
24%
720
72%
720
44%
1092
September11th to 20thNight
78%
720
31%
1980
31%
720
79%
720
48%
1056
September21st to endNight
74%
720
34%
1980
34%
720
75%
720
47%
1077
October1st to 10thNight
74%
720
30%
1980
29%
720
75%
720
44%
1107
October11th to 20thNight
72%
720
33%
1980
32%
720
74%
720
45%
1089
October21st to endNight
74%
792
34%
2439
37%
792
75%
792
45%
1229
November1st to 10thNight
74%
740
29%
2405
34%
740
75%
740
45%
1182
November11th to 20thNight
76%
760
35%
2470
41%
760
77%
760
45%
1215
November21st to endNight
70%
760
30%
2470
33%
760
73%
760
37%
1342
December1st to 10thNight
67%
760
28%
2470
30%
760
69%
760
35%
1358
December11th to 20thNight
63%
759
27%
2958
31%
758
65%
758
25%
1748
December21st to endNight
64%
823
18%
4460
31%
817
68%
817
19%
2636

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
6%5%2442445%8%56%
79394
Night
8%8%35%43445%7%49%
80689
TransparencyDay
24%6%10%18%23%20%
79130
Night
31%6%10%15%19%19%
80476
SeeingDay
7%5%20%38%25%5%
14917
Night
10%310%31%36%11%
25351

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%313313347%62%
2858
11th to 20thDay
7%6%25%324448%56%
3084
21st to endDay
12%5%245%3435%8%49%
3498
February1st to 10thDay
9%425%424446%56%
1900
11th to 20thDay
7%5%343345%49%54%
1850
21st to endDay
9%5%26%5%35%5%5%7%48%
1570
March1st to 10thDay
7%5%25%4245%7%10%49%
1900
11th to 20thDay
7%434435%46%9%52%
1984
21st to endDay
5%424425%46%8%56%
2382
April1st to 10thDay
7%5%35%43446%8%53%
2160
11th to 20thDay
442342445%7%61%
2129
21st to endDay
5%5%34322349%59%
2160
May1st to 10thDay
6%6%345%3345%8%52%
2245
11th to 20thDay
6%7%25%324449%55%
2301
21st to endDay
6%7%2442435%8%55%
2530
June1st to 10thDay
6%9%3433345%9%51%
2340
11th to 20thDay
46%24323348%61%
2340
21st to endDay
47%34423348%58%
2340
July1st to 10thDay
47%35%4345%5%9%52%
2340
11th to 20thDay
25%3432446%11%56%
2340
21st to endDay
36%243245%6%9%56%
2401
August1st to 10thDay
2423323448%64%
2149
11th to 20thDay
25%23323448%65%
2122
21st to endDay
232433445%9%62%
2376
September1st to 10thDay
34134245%5%9%60%
2147
11th to 20thDay
3424323447%64%
1980
21st to endDay
3413323449%65%
1980
October1st to 10thDay
433433335%7%61%
1980
11th to 20thDay
5%4243245%48%61%
1980
21st to endDay
3424212436%69%
1909
November1st to 10thDay
4423423347%63%
1674
11th to 20thDay
5%424324347%63%
1710
21st to endDay
6%4233235%5%8%59%
1710
December1st to 10thDay
6%424435%5%6%8%53%
1710
11th to 20thDay
11%5%25%5%35%5%6%7%46%
2169
21st to endDay
10%6%25%5%46%5%6%8%41%
3146
January1st to 10thNight
7%423323346%62%
4097
11th to 20thNight
8%6%25%5%345%48%50%
3891
21st to endNight
14%6%25%42445%6%47%
4180
February1st to 10thNight
8%6%25%5%33346%55%
2280
11th to 20thNight
10%8%35%434445%52%
2218
21st to endNight
9%7%36%42446%6%48%
1884
March1st to 10thNight
10%7%36%5%35%45%8%45%
2280
11th to 20thNight
10%8%37%43445%7%44%
2195
21st to endNight
7%7%36%5%3446%7%48%
2123
April1st to 10thNight
11%9%35%5%24349%45%
1800
11th to 20thNight
11%10%25%424245%52%
1779
21st to endNight
9%12%46%433346%45%
1800
May1st to 10thNight
9%12%5%7%5%35%45%7%37%
1710
11th to 20thNight
10%16%5%8%5%24447%35%
1594
21st to endNight
12%14%5%6%5%33447%38%
1746
June1st to 10thNight
10%17%6%7%5%25%5%5%8%30%
1620
11th to 20thNight
5%14%46%6%4445%10%39%
1620
21st to endNight
5%14%5%8%43445%10%38%
1620
July1st to 10thNight
5%15%5%6%5%2446%10%38%
1620
11th to 20thNight
311%46%435%5%6%9%44%
1620
21st to endNight
5%11%5%6%6%3445%10%41%
1914
August1st to 10thNight
310%35%4345%5%9%49%
1790
11th to 20thNight
312%46%4245%48%47%
1780
21st to endNight
37%245%335%5%9%54%
1980
September1st to 10thNight
48%35%5%335%48%52%
1812
11th to 20thNight
5%7%243235%36%60%
1980
21st to endNight
5%8%34333446%58%
1980
October1st to 10thNight
46%25%5%24448%56%
1980
11th to 20thNight
6%7%243245%46%56%
1980
21st to endNight
5%6%24323336%62%
2439
November1st to 10thNight
5%6%24423347%60%
2405
11th to 20thNight
37%24323335%64%
2470
21st to endNight
6%5%35%435%5%5%7%54%
2470
December1st to 10thNight
9%6%25%4245%5%7%52%
2470
11th to 20thNight
11%7%35%5%245%5%7%45%
3041
21st to endNight
10%6%37%6%45%5%5%6%42%
4521

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
22%6%8%21%22%21%
2859
11th to 20thDay
25%8%14%24%15%15%
3084
21st to endDay
31%6%9%13%24%16%
3498
February1st to 10thDay
28%48%14%19%26%
1900
11th to 20thDay
28%6%9%15%24%19%
1860
21st to endDay
33%7%9%13%21%17%
1570
March1st to 10thDay
29%7%11%18%17%18%
1900
11th to 20thDay
26%7%11%19%22%13%
1984
21st to endDay
24%6%12%25%19%13%
2382
April1st to 10thDay
28%6%12%23%23%9%
2160
11th to 20thDay
21%7%10%19%26%18%
2132
21st to endDay
21%5%12%25%25%12%
2160
May1st to 10thDay
28%6%11%20%21%14%
2245
11th to 20thDay
26%5%10%23%24%11%
2304
21st to endDay
26%6%11%22%29%6%
2530
June1st to 10thDay
26%6%11%20%22%14%
2340
11th to 20thDay
19%410%14%26%26%
2340
21st to endDay
22%39%10%21%34%
2340
July1st to 10thDay
23%410%12%24%27%
2276
11th to 20thDay
20%6%15%21%24%15%
2271
21st to endDay
21%7%16%24%23%9%
2268
August1st to 10thDay
17%410%17%28%24%
2135
11th to 20thDay
16%411%17%29%23%
2122
21st to endDay
18%39%16%30%25%
2376
September1st to 10thDay
19%5%8%14%28%26%
2147
11th to 20thDay
17%38%11%31%30%
1980
21st to endDay
15%5%9%15%29%28%
1980
October1st to 10thDay
22%38%17%23%27%
1980
11th to 20thDay
22%48%13%24%30%
1980
21st to endDay
16%47%14%23%37%
1909
November1st to 10thDay
20%49%18%17%32%
1674
11th to 20thDay
20%48%15%18%35%
1710
21st to endDay
23%5%9%14%20%29%
1710
December1st to 10thDay
27%5%11%15%17%25%
1710
11th to 20thDay
34%8%11%13%18%15%
2168
21st to endDay
34%10%12%19%13%12%
3146
January1st to 10thNight
22%7%8%16%28%19%
4097
11th to 20thNight
29%9%12%21%13%15%
3891
21st to endNight
35%8%9%10%20%18%
4180
February1st to 10thNight
29%5%9%13%19%26%
2280
11th to 20thNight
34%5%7%13%20%21%
2219
21st to endNight
35%6%7%13%23%16%
1884
March1st to 10thNight
35%7%10%15%15%17%
2280
11th to 20thNight
34%7%11%16%18%15%
2195
21st to endNight
32%8%12%20%17%11%
2123
April1st to 10thNight
35%6%10%21%18%11%
1800
11th to 20thNight
33%6%9%16%21%16%
1779
21st to endNight
37%6%11%15%19%12%
1800
May1st to 10thNight
40%7%11%13%15%13%
1710
11th to 20thNight
44%8%11%14%11%12%
1595
21st to endNight
45%6%10%16%17%7%
1746
June1st to 10thNight
46%7%12%11%15%9%
1620
11th to 20thNight
37%411%12%19%18%
1620
21st to endNight
37%311%10%13%26%
1620
July1st to 10thNight
32%5%12%10%18%22%
1575
11th to 20thNight
30%6%13%19%21%11%
1566
21st to endNight
35%8%13%19%17%6%
1808
August1st to 10thNight
25%5%13%16%25%17%
1780
11th to 20thNight
31%411%18%21%16%
1780
21st to endNight
24%411%13%24%24%
1980
September1st to 10thNight
28%5%9%12%21%25%
1812
11th to 20thNight
23%47%8%30%27%
1980
21st to endNight
24%45%12%32%22%
1980
October1st to 10thNight
25%6%8%15%19%26%
1980
11th to 20thNight
25%5%9%13%19%29%
1980
21st to endNight
24%35%12%20%36%
2439
November1st to 10thNight
23%49%15%16%32%
2405
11th to 20thNight
23%46%13%17%37%
2470
21st to endNight
28%6%7%15%16%27%
2470
December1st to 10thNight
30%6%8%16%15%25%
2470
11th to 20thNight
36%7%9%14%19%15%
3041
21st to endNight
33%14%14%17%10%13%
4521

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
17%413%41%22%3
270
11th to 20thDay
11%5%21%38%20%4
403
21st to endDay
8%9%27%35%17%4
506
February1st to 10thDay
12%7%24%33%19%5%
460
11th to 20thDay
8%9%30%36%15%2
455
21st to endDay
9%13%36%30%12%1
382
March1st to 10thDay
11%8%37%31%12%2
460
11th to 20thDay
10%9%32%33%14%2
460
21st to endDay
6%12%34%35%10%2
491
April1st to 10thDay
11%5%30%33%16%4
420
11th to 20thDay
5%7%36%37%11%4
412
21st to endDay
6%7%30%36%17%4
420
May1st to 10thDay
10%7%29%35%16%4
423
11th to 20thDay
8%7%25%38%18%2
448
21st to endDay
10%7%29%36%16%2
485
June1st to 10thDay
6%321%40%27%2
450
11th to 20thDay
4116%46%27%5%
450
21st to endDay
6%113%44%30%6%
450
July1st to 10thDay
6%6%39%40%8%
446
11th to 20thDay
3436%47%11%
444
21st to endDay
4335%46%11%
487
August1st to 10thDay
37%42%38%10%
447
11th to 20thDay
315%39%41%11%
437
21st to endDay
45%41%41%8%
495
September1st to 10thDay
7%110%44%33%4
450
11th to 20thDay
4116%48%26%4
450
21st to endDay
4119%43%28%5%
450
October1st to 10thDay
5%5%21%43%23%3
450
11th to 20thDay
5%325%40%22%5%
450
21st to endDay
6%219%38%27%8%
419
November1st to 10thDay
46%15%39%27%8%
270
11th to 20thDay
5%315%40%32%5%
270
21st to endDay
8%5%21%35%23%8%
270
December1st to 10thDay
10%317%40%25%5%
270
11th to 20thDay
4418%41%27%6%
270
21st to endDay
15%9%19%36%16%5%
297
January1st to 10thNight
9%414%37%28%9%
760
11th to 20thNight
7%411%40%31%8%
760
21st to endNight
12%314%37%29%5%
836
February1st to 10thNight
10%312%34%32%9%
760
11th to 20thNight
11%415%37%26%6%
744
21st to endNight
11%414%43%24%3
628
March1st to 10thNight
11%415%40%26%4
760
11th to 20thNight
12%411%37%29%7%
760
21st to endNight
10%413%38%30%5%
820
April1st to 10thNight
13%311%37%30%6%
720
11th to 20thNight
12%414%35%28%7%
711
21st to endNight
14%411%31%32%8%
720
May1st to 10thNight
11%313%31%35%7%
630
11th to 20thNight
13%217%30%31%8%
531
21st to endNight
16%414%30%30%6%
584
June1st to 10thNight
14%212%33%32%7%
540
11th to 20thNight
11%18%27%46%7%
540
21st to endNight
10%17%25%48%9%
540
July1st to 10thNight
10%2318%49%18%
525
11th to 20thNight
5%313%55%24%
522
21st to endNight
8%1314%48%25%
732
August1st to 10thNight
7%316%48%25%
716
11th to 20thNight
9%2211%47%30%
712
21st to endNight
6%139%52%29%
792
September1st to 10thNight
8%1418%50%19%
720
11th to 20thNight
7%25%20%53%13%
720
21st to endNight
7%26%27%44%15%
720
October1st to 10thNight
7%27%33%44%7%
720
11th to 20thNight
10%28%33%37%10%
720
21st to endNight
8%28%32%34%16%
792
November1st to 10thNight
7%28%33%38%12%
740
11th to 20thNight
6%16%37%37%13%
760
21st to endNight
6%212%38%33%9%
760
December1st to 10thNight
11%211%39%29%7%
760
11th to 20thNight
13%312%40%26%7%
760
21st to endNight
10%414%37%28%8%
836
Page generated at 2024-03-24 20:37:03. Version ac07

Copyright © 2024 Attilla Danko.


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