Chula Vista Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chula Vista 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
69%
25009
28%
74544
26%
24958
71%
24958
39%
42350

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
65%
757
29%
2457
29%
756
70%
756
38%
1318
January11th to 20thNight
70%
728
34%
2244
34%
728
74%
728
40%
1217
January21st to endNight
65%
792
35%
2376
31%
792
71%
792
40%
1317
February1st to 10thNight
70%
720
33%
2160
34%
720
74%
720
43%
1155
February11th to 20thNight
62%
700
29%
2098
29%
700
65%
700
34%
1225
February21st to endNight
62%
592
28%
1776
29%
592
66%
592
35%
1050
March1st to 10thNight
60%
720
22%
2160
24%
720
63%
720
32%
1303
March11th to 20thNight
65%
720
24%
2072
25%
720
67%
720
36%
1230
March21st to endNight
65%
792
24%
2065
20%
792
67%
792
38%
1270
April1st to 10thNight
64%
720
26%
1800
19%
720
65%
720
39%
1133
April11th to 20thNight
60%
711
27%
1779
18%
711
61%
711
39%
1126
April21st to endNight
61%
720
24%
1800
16%
720
62%
720
38%
1157
May1st to 10thNight
61%
623
22%
1703
15%
623
62%
623
33%
1097
May11th to 20thNight
58%
531
18%
1595
13%
531
59%
531
28%
1059
May21st to endNight
57%
582
21%
1746
17%
582
57%
582
30%
1134
June1st to 10thNight
60%
540
19%
1620
16%
540
61%
540
31%
1044
June11th to 20thNight
70%
540
23%
1620
19%
540
70%
540
40%
945
June21st to endNight
73%
540
24%
1620
21%
540
73%
540
42%
923
July1st to 10thNight
76%
525
22%
1575
18%
525
76%
525
45%
862
July11th to 20thNight
79%
522
25%
1566
21%
522
79%
522
44%
855
July21st to endNight
74%
721
23%
1797
16%
681
74%
681
42%
1077
August1st to 10thNight
80%
716
28%
1780
18%
712
80%
712
55%
972
August11th to 20thNight
76%
712
30%
1780
19%
712
76%
712
50%
1015
August21st to endNight
80%
792
34%
1980
25%
792
80%
792
54%
1093
September1st to 10thNight
76%
720
32%
1819
27%
720
76%
720
48%
1055
September11th to 20thNight
80%
720
34%
1980
34%
720
80%
720
54%
1009
September21st to endNight
77%
720
38%
1980
37%
720
79%
720
54%
1013
October1st to 10thNight
75%
720
31%
1980
29%
720
76%
720
46%
1092
October11th to 20thNight
73%
720
36%
1980
34%
720
75%
720
48%
1070
October21st to endNight
73%
792
36%
2433
38%
792
76%
792
46%
1211
November1st to 10thNight
74%
740
31%
2405
36%
740
75%
740
46%
1175
November11th to 20thNight
76%
760
36%
2470
40%
760
80%
760
48%
1180
November21st to endNight
69%
760
31%
2470
33%
760
73%
760
39%
1300
December1st to 10thNight
68%
760
30%
2470
31%
760
70%
760
36%
1342
December11th to 20thNight
63%
759
28%
2956
31%
758
66%
758
26%
1743
December21st to endNight
63%
822
19%
4432
31%
817
68%
817
20%
2583

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%42442445%7%60%
74827
Night
7%8%35%43445%7%52%
74932
TransparencyDay
23%47%18%26%23%
74562
Night
30%47%16%21%22%
74719
SeeingDay
7%6%22%38%21%5%
14600
Night
9%39%34%36%10%
25033

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
9%4143235%5%9%54%
1708
11th to 20thDay
7%5%2443445%6%57%
1750
21st to endDay
9%5%24423336%58%
1980
February1st to 10thDay
7%415%424445%60%
1800
11th to 20thDay
8%5%244235%6%8%52%
1750
21st to endDay
10%425%446%6%46%49%
1480
March1st to 10thDay
8%5%35%5%2446%10%49%
1800
11th to 20thDay
8%4145%35%46%8%53%
1886
21st to endDay
5%425%43445%7%58%
2287
April1st to 10thDay
6%435%5%335%5%7%54%
2160
11th to 20thDay
442342445%7%62%
2129
21st to endDay
6%5%23323349%62%
2160
May1st to 10thDay
7%6%2433345%8%55%
2254
11th to 20thDay
47%24424346%60%
2301
21st to endDay
5%6%24423447%58%
2530
June1st to 10thDay
47%25%42345%7%58%
2340
11th to 20thDay
3423323346%67%
2340
21st to endDay
25%24323346%65%
2340
July1st to 10thDay
26%24335%447%60%
2340
11th to 20thDay
142433446%9%60%
2340
21st to endDay
24233245%7%9%58%
2412
August1st to 10thDay
1413323447%68%
2149
11th to 20thDay
2313323346%71%
2122
21st to endDay
231332345%7%67%
2376
September1st to 10thDay
331332445%7%65%
2139
11th to 20thDay
3222223236%71%
1980
21st to endDay
2312223346%72%
1980
October1st to 10thDay
332443435%7%62%
1980
11th to 20thDay
5%423332346%65%
1980
21st to endDay
3313213335%72%
1915
November1st to 10thDay
432343335%7%63%
1674
11th to 20thDay
431332435%6%65%
1710
21st to endDay
6%41342445%8%59%
1710
December1st to 10thDay
7%32444446%8%55%
1710
11th to 20thDay
11%6%25%5%35%5%6%8%45%
2169
21st to endDay
10%6%25%6%46%6%6%8%41%
3146
January1st to 10thNight
10%5%14424447%55%
2457
11th to 20thNight
7%5%2432445%7%56%
2244
21st to endNight
11%5%24323346%57%
2376
February1st to 10thNight
7%5%25%43335%6%58%
2160
11th to 20thNight
10%7%35%4245%35%52%
2098
21st to endNight
10%5%35%5%345%5%6%50%
1776
March1st to 10thNight
10%8%35%5%3445%7%47%
2160
11th to 20thNight
10%8%244335%7%8%46%
2072
21st to endNight
7%7%35%435%5%5%7%48%
2065
April1st to 10thNight
10%8%35%42345%9%47%
1800
11th to 20thNight
9%10%36%423336%51%
1779
21st to endNight
9%10%37%5%3435%7%47%
1800
May1st to 10thNight
8%12%36%4445%48%41%
1703
11th to 20thNight
7%15%5%7%5%35%35%7%37%
1594
21st to endNight
11%14%35%5%33446%41%
1746
June1st to 10thNight
6%17%5%7%5%3446%8%35%
1620
11th to 20thNight
413%45%435%4410%45%
1620
21st to endNight
311%46%435%5%5%7%47%
1620
July1st to 10thNight
312%36%4345%6%9%45%
1620
11th to 20thNight
19%35%5%36%5%6%9%48%
1620
21st to endNight
310%46%5%345%5%10%45%
1903
August1st to 10thNight
28%343345%5%9%54%
1790
11th to 20thNight
38%45%435%45%9%51%
1780
21st to endNight
37%3432445%8%59%
1980
September1st to 10thNight
48%245%335%47%56%
1819
11th to 20thNight
47%22324346%63%
1980
21st to endNight
37%23224346%63%
1980
October1st to 10thNight
5%6%23424347%58%
1980
11th to 20thNight
6%6%23334346%60%
1980
21st to endNight
5%6%23323345%63%
2433
November1st to 10thNight
5%5%34323346%62%
2405
11th to 20thNight
45%23323345%65%
2470
21st to endNight
6%5%35%435%46%7%54%
2470
December1st to 10thNight
9%6%2433445%6%54%
2470
11th to 20thNight
11%8%35%5%245%5%8%45%
3041
21st to endNight
9%7%37%7%46%5%6%7%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
27%47%17%23%21%
1709
11th to 20thDay
27%5%6%14%22%26%
1750
21st to endDay
30%37%16%16%28%
1980
February1st to 10thDay
27%26%13%22%29%
1800
11th to 20thDay
29%47%14%24%22%
1760
21st to endDay
34%6%7%13%22%19%
1480
March1st to 10thDay
31%6%8%19%17%20%
1800
11th to 20thDay
28%5%8%18%25%16%
1886
21st to endDay
25%6%8%26%21%14%
2287
April1st to 10thDay
28%410%22%25%10%
2160
11th to 20thDay
22%410%19%27%19%
2132
21st to endDay
22%38%27%28%13%
2160
May1st to 10thDay
27%49%20%26%14%
2254
11th to 20thDay
24%37%24%29%12%
2304
21st to endDay
26%48%23%33%7%
2530
June1st to 10thDay
24%38%22%28%15%
2340
11th to 20thDay
17%25%13%33%30%
2340
21st to endDay
19%339%29%38%
2340
July1st to 10thDay
20%35%11%30%31%
2276
11th to 20thDay
17%410%25%26%17%
2271
21st to endDay
20%6%13%27%26%9%
2278
August1st to 10thDay
16%35%19%31%27%
2135
11th to 20thDay
14%36%20%34%24%
2122
21st to endDay
16%3417%32%28%
2376
September1st to 10thDay
17%46%12%32%30%
2139
11th to 20thDay
13%3412%34%35%
1980
21st to endDay
14%3415%33%31%
1980
October1st to 10thDay
21%37%17%24%29%
1980
11th to 20thDay
21%3412%28%32%
1980
21st to endDay
16%3414%24%40%
1915
November1st to 10thDay
20%36%18%19%33%
1674
11th to 20thDay
20%36%15%20%37%
1710
21st to endDay
23%48%14%19%31%
1710
December1st to 10thDay
26%49%16%19%26%
1710
11th to 20thDay
35%5%11%14%17%18%
2168
21st to endDay
37%7%9%21%14%12%
3146
January1st to 10thNight
29%46%15%22%24%
2457
11th to 20thNight
28%5%6%13%21%28%
2244
21st to endNight
30%39%14%13%31%
2376
February1st to 10thNight
27%37%14%21%29%
2160
11th to 20thNight
33%46%13%20%23%
2099
21st to endNight
34%46%13%24%19%
1776
March1st to 10thNight
36%48%17%15%19%
2160
11th to 20thNight
33%5%8%17%21%16%
2072
21st to endNight
32%5%10%21%19%13%
2065
April1st to 10thNight
34%49%23%20%11%
1800
11th to 20thNight
34%47%17%21%17%
1779
21st to endNight
36%47%20%20%13%
1800
May1st to 10thNight
38%5%8%18%17%14%
1703
11th to 20thNight
43%5%8%20%12%13%
1595
21st to endNight
42%48%21%18%8%
1746
June1st to 10thNight
41%29%18%18%11%
1620
11th to 20thNight
32%3412%28%21%
1620
21st to endNight
31%2312%23%29%
1620
July1st to 10thNight
28%26%12%26%25%
1575
11th to 20thNight
26%410%22%26%13%
1566
21st to endNight
30%412%25%21%7%
1797
August1st to 10thNight
21%37%19%30%19%
1780
11th to 20thNight
25%36%22%27%18%
1780
21st to endNight
23%36%14%29%26%
1980
September1st to 10thNight
26%5%5%13%24%28%
1819
11th to 20thNight
21%349%30%32%
1980
21st to endNight
20%3313%35%25%
1980
October1st to 10thNight
26%46%16%20%27%
1980
11th to 20thNight
25%36%16%21%31%
1980
21st to endNight
23%3311%22%37%
2433
November1st to 10thNight
23%36%16%17%34%
2405
11th to 20thNight
21%36%14%17%39%
2470
21st to endNight
28%47%16%16%29%
2470
December1st to 10thNight
30%5%7%15%16%26%
2470
11th to 20thNight
37%5%8%13%20%17%
3041
21st to endNight
36%9%11%19%11%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
18%419%38%20%2
270
11th to 20thDay
13%5%24%37%18%3
362
21st to endDay
9%10%30%35%13%3
462
February1st to 10thDay
10%6%28%36%15%5%
420
11th to 20thDay
9%12%34%30%13%1
415
21st to endDay
12%12%35%32%8%1
346
March1st to 10thDay
12%11%37%27%11%2
420
11th to 20thDay
12%10%31%33%13%2
420
21st to endDay
7%16%37%29%9%2
462
April1st to 10thDay
10%9%38%26%13%5%
420
11th to 20thDay
6%11%36%35%9%3
412
21st to endDay
6%11%31%32%15%5%
420
May1st to 10thDay
11%10%28%35%13%4
423
11th to 20thDay
10%9%27%37%15%3
448
21st to endDay
10%10%27%36%14%3
485
June1st to 10thDay
4421%43%24%3
450
11th to 20thDay
4220%43%25%6%
450
21st to endDay
6%213%48%25%7%
450
July1st to 10thDay
417%43%36%9%
446
11th to 20thDay
35%41%37%14%
444
21st to endDay
31442%38%11%
487
August1st to 10thDay
210%44%32%11%
447
11th to 20thDay
316%47%32%11%
437
21st to endDay
417%44%35%9%
495
September1st to 10thDay
6%112%51%23%7%
450
11th to 20thDay
4222%46%21%5%
450
21st to endDay
4421%42%22%7%
450
October1st to 10thDay
47%24%41%20%4
450
11th to 20thDay
7%428%38%19%4
450
21st to endDay
5%324%35%25%8%
412
November1st to 10thDay
6%7%17%40%26%5%
270
11th to 20thDay
5%319%39%29%4
270
21st to endDay
10%5%22%36%20%6%
270
December1st to 10thDay
9%321%41%21%4
270
11th to 20thDay
5%322%39%25%5%
270
21st to endDay
16%8%25%31%16%4
297
January1st to 10thNight
11%413%39%24%10%
760
11th to 20thNight
10%210%40%30%7%
728
21st to endNight
13%313%41%26%5%
792
February1st to 10thNight
10%210%39%31%9%
720
11th to 20thNight
11%414%40%24%6%
704
21st to endNight
12%315%43%24%3
592
March1st to 10thNight
13%414%41%24%3
720
11th to 20thNight
13%49%38%28%7%
720
21st to endNight
10%313%41%29%4
792
April1st to 10thNight
12%39%42%28%5%
720
11th to 20thNight
10%6%12%39%27%6%
711
21st to endNight
12%410%36%31%7%
720
May1st to 10thNight
11%312%36%32%7%
623
11th to 20thNight
12%411%35%32%7%
531
21st to endNight
14%411%36%30%5%
584
June1st to 10thNight
11%39%39%32%5%
540
11th to 20thNight
8%28%32%45%5%
540
21st to endNight
6%16%29%51%7%
540
July1st to 10thNight
7%1223%54%13%
525
11th to 20thNight
4117%63%14%
522
21st to endNight
6%1116%55%20%
721
August1st to 10thNight
5%1219%52%21%
716
11th to 20thNight
6%1211%56%25%
712
21st to endNight
6%1113%55%25%
792
September1st to 10thNight
7%1220%54%15%
720
11th to 20thNight
6%2424%52%12%
720
21st to endNight
6%16%31%42%14%
720
October1st to 10thNight
8%25%36%42%7%
720
11th to 20thNight
10%27%36%35%10%
720
21st to endNight
8%28%33%33%15%
792
November1st to 10thNight
7%26%38%35%11%
740
11th to 20thNight
5%17%40%34%12%
760
21st to endNight
7%212%39%31%9%
760
December1st to 10thNight
11%311%42%26%8%
760
11th to 20thNight
14%410%42%23%7%
760
21st to endNight
10%415%39%25%8%
836
Page generated at 2024-01-09 13:24:21. Version ac07

Copyright 2024 Attilla Danko


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