Peralta Skies Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Peralta Skies Observatory clear sky chart from 2005-11-06 to 2024-01-17.

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
75%
24024
37%
74384
33%
23976
80%
23976
52%
35503

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
68%
759
33%
2457
32%
756
75%
756
44%
1230
January11th to 20thNight
67%
748
38%
2430
34%
748
75%
748
48%
1152
January21st to endNight
62%
792
36%
2574
33%
792
72%
792
40%
1343
February1st to 10thNight
68%
720
36%
2290
33%
720
77%
720
51%
1065
February11th to 20thNight
62%
700
34%
2099
30%
700
70%
700
44%
1112
February21st to endNight
62%
592
37%
1732
33%
592
70%
592
45%
921
March1st to 10thNight
64%
720
38%
1980
29%
720
72%
720
53%
1011
March11th to 20thNight
70%
720
38%
1980
31%
720
76%
720
55%
1008
March21st to endNight
69%
792
38%
2178
28%
792
77%
792
56%
1083
April1st to 10thNight
74%
720
36%
1980
26%
720
81%
720
60%
951
April11th to 20thNight
69%
587
40%
1831
33%
587
78%
587
62%
779
April21st to endNight
77%
540
47%
1692
40%
540
85%
540
69%
674
May1st to 10thNight
78%
540
43%
1620
37%
540
84%
540
69%
674
May11th to 20thNight
81%
531
42%
1594
36%
531
84%
531
68%
672
May21st to endNight
83%
582
42%
1746
35%
582
86%
582
77%
682
June1st to 10thNight
86%
540
37%
1620
32%
540
87%
540
68%
683
June11th to 20thNight
92%
540
41%
1620
35%
540
93%
540
82%
614
June21st to endNight
88%
540
33%
1620
30%
540
88%
540
64%
712
July1st to 10thNight
83%
525
27%
1575
23%
525
83%
525
49%
801
July11th to 20thNight
86%
522
26%
1566
22%
522
86%
522
46%
812
July21st to endNight
79%
591
24%
1674
21%
558
80%
558
35%
978
August1st to 10thNight
88%
537
29%
1602
26%
534
88%
534
50%
801
August11th to 20thNight
80%
534
34%
1602
32%
534
80%
534
43%
862
August21st to endNight
84%
656
32%
1991
31%
656
84%
656
45%
1038
September1st to 10thNight
80%
720
35%
1980
32%
720
81%
720
50%
1049
September11th to 20thNight
84%
720
42%
1980
35%
720
86%
720
62%
948
September21st to endNight
81%
720
40%
1980
31%
720
86%
720
60%
961
October1st to 10thNight
78%
720
41%
2035
32%
720
83%
720
61%
956
October11th to 20thNight
83%
720
45%
2160
41%
720
87%
720
72%
883
October21st to endNight
80%
792
46%
2376
39%
792
87%
792
71%
977
November1st to 10thNight
79%
740
44%
2220
38%
740
85%
740
62%
982
November11th to 20thNight
77%
760
42%
2384
38%
760
84%
760
59%
1047
November21st to endNight
67%
760
39%
2470
36%
760
75%
760
50%
1159
December1st to 10thNight
68%
760
39%
2470
38%
760
74%
760
46%
1190
December11th to 20thNight
65%
759
34%
2942
35%
758
72%
758
32%
1620
December21st to endNight
65%
825
23%
4334
34%
817
71%
817
26%
2073

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
4213323346%68%
74989
Night
5%213323446%66%
74876
TransparencyDay
19%2312%25%39%
74716
Night
20%2312%24%39%
74671
SeeingDay
5%415%32%31%14%
13811
Night
5%212%42%34%4
24043

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
7%324323346%63%
1708
11th to 20thDay
8%213223335%67%
1674
21st to endDay
8%41332235%5%63%
1782
February1st to 10thDay
5%323323446%67%
1665
11th to 20thDay
10%323424345%60%
1750
21st to endDay
8%422423346%62%
1523
March1st to 10thDay
7%31432346%7%60%
1980
11th to 20thDay
5%41332345%7%64%
1980
21st to endDay
5%21332334469%
2178
April1st to 10thDay
2212223338%71%
1980
11th to 20thDay
221131223477%
2077
21st to endDay
221112335%79%
2263
May1st to 10thDay
1212212335%79%
2340
11th to 20thDay
1111213235%78%
2301
21st to endDay
21111122287%
2530
June1st to 10thDay
1211112336%79%
2340
11th to 20thDay
11111112288%
2340
21st to endDay
1112222236%77%
2340
July1st to 10thDay
22234235%6%8%64%
2340
11th to 20thDay
3224436%7%7%11%51%
2340
21st to endDay
6%325%5%46%6%8%12%44%
2545
August1st to 10thDay
3223435%5%6%9%58%
2328
11th to 20thDay
3314435%6%7%10%55%
2299
21st to endDay
231343446%9%59%
2358
September1st to 10thDay
431323445%7%64%
1980
11th to 20thDay
311212345%78%
1980
21st to endDay
3112223335%76%
1980
October1st to 10thDay
3212313445%72%
1923
11th to 20thDay
21111123483%
1800
21st to endDay
211222223479%
1980
November1st to 10thDay
3211212347%74%
1859
11th to 20thDay
2213223345%73%
1791
21st to endDay
6%314423435%65%
1710
December1st to 10thDay
8%313424346%62%
1710
11th to 20thDay
8%5%25%5%3346%8%52%
2169
21st to endDay
12%5%14423446%54%
3146
January1st to 10thNight
7%31442445%6%60%
2457
11th to 20thNight
8%31332433466%
2430
21st to endNight
10%414323445%60%
2574
February1st to 10thNight
6%313322346%67%
2290
11th to 20thNight
9%5%13423345%60%
2098
21st to endNight
9%324323336%61%
1732
March1st to 10thNight
6%32331346%6%64%
1980
11th to 20thNight
8%312323245%68%
1980
21st to endNight
5%323322347%66%
2178
April1st to 10thNight
3212224346%70%
1980
11th to 20thNight
311222333476%
1831
21st to endNight
3111112235%80%
1692
May1st to 10thNight
2212212346%76%
1620
11th to 20thNight
213212235%78%
1594
21st to endNight
21111122386%
1746
June1st to 10thNight
2112212236%77%
1620
11th to 20thNight
1111222486%
1620
21st to endNight
2112223335%75%
1620
July1st to 10thNight
31245%245%5%9%59%
1620
11th to 20thNight
1214446%7%9%13%50%
1620
21st to endNight
4325%6%47%8%9%14%39%
1773
August1st to 10thNight
2214435%6%7%10%56%
1611
11th to 20thNight
3425%5%445%8%8%52%
1602
21st to endNight
33245%25%6%7%9%55%
1991
September1st to 10thNight
43144245%6%7%59%
1980
11th to 20thNight
321331334474%
1980
21st to endNight
2213323345%72%
1980
October1st to 10thNight
411231335%5%71%
2035
11th to 20thNight
221111223482%
2160
21st to endNight
221121223481%
2376
November1st to 10thNight
4212213345%73%
2220
11th to 20thNight
221332323475%
2384
21st to endNight
7%223322346%66%
2470
December1st to 10thNight
8%21332345%6%63%
2470
11th to 20thNight
10%5%26%42345%6%52%
3041
21st to endNight
12%423334445%57%
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
25%1416%29%24%
1709
11th to 20thDay
23%1312%29%32%
1674
21st to endDay
24%2215%27%29%
1782
February1st to 10thDay
21%2315%23%37%
1665
11th to 20thDay
29%2212%25%29%
1760
21st to endDay
26%2114%27%30%
1523
March1st to 10thDay
24%2110%29%33%
1980
11th to 20thDay
22%2211%26%38%
1980
21st to endDay
21%119%35%32%
2178
April1st to 10thDay
15%218%36%39%
1980
11th to 20thDay
13%217%28%50%
2080
21st to endDay
11%119%26%52%
2263
May1st to 10thDay
12%217%25%53%
2340
11th to 20thDay
12%118%25%53%
2304
21st to endDay
8%15%22%64%
2530
June1st to 10thDay
10%1421%63%
2340
11th to 20thDay
7%1111%80%
2340
21st to endDay
12%216%18%62%
2340
July1st to 10thDay
20%3411%21%42%
2276
11th to 20thDay
26%411%25%22%12%
2271
21st to endDay
30%416%23%18%10%
2404
August1st to 10thDay
23%39%18%18%29%
2313
11th to 20thDay
24%49%22%22%20%
2299
21st to endDay
22%37%18%28%22%
2358
September1st to 10thDay
21%25%16%25%31%
1980
11th to 20thDay
11%229%31%45%
1980
21st to endDay
14%228%24%50%
1980
October1st to 10thDay
16%2313%24%43%
1923
11th to 20thDay
8%127%26%56%
1800
21st to endDay
12%1210%26%49%
1980
November1st to 10thDay
12%212%36%38%
1859
11th to 20thDay
16%2111%26%44%
1791
21st to endDay
24%1212%24%36%
1710
December1st to 10thDay
26%2215%25%31%
1710
11th to 20thDay
31%15%18%25%20%
2168
21st to endDay
33%2318%27%17%
3146
January1st to 10thNight
26%2313%32%25%
2457
11th to 20thNight
23%1211%30%32%
2430
21st to endNight
29%2212%27%28%
2574
February1st to 10thNight
21%1312%24%39%
2290
11th to 20thNight
28%2215%24%30%
2099
21st to endNight
27%2110%27%33%
1732
March1st to 10thNight
21%2212%26%37%
1980
11th to 20thNight
21%2110%25%41%
1980
21st to endNight
20%1210%35%32%
2178
April1st to 10thNight
17%218%31%42%
1980
11th to 20thNight
14%26%27%50%
1831
21st to endNight
11%116%25%56%
1692
May1st to 10thNight
11%118%26%52%
1620
11th to 20thNight
12%128%22%56%
1595
21st to endNight
8%15%19%67%
1746
June1st to 10thNight
12%1319%65%
1620
11th to 20thNight
6%1312%78%
1620
21st to endNight
14%225%12%65%
1620
July1st to 10thNight
24%25%12%16%41%
1575
11th to 20thNight
23%5%12%23%24%14%
1566
21st to endNight
33%414%22%17%10%
1674
August1st to 10thNight
21%49%21%15%30%
1602
11th to 20thNight
27%310%19%19%21%
1602
21st to endNight
24%47%17%24%23%
1991
September1st to 10thNight
23%36%20%20%28%
1980
11th to 20thNight
16%229%25%46%
1980
21st to endNight
16%318%24%48%
1980
October1st to 10thNight
16%2214%23%44%
2035
11th to 20thNight
10%118%23%58%
2160
21st to endNight
10%2110%24%54%
2376
November1st to 10thNight
15%119%30%43%
2220
11th to 20thNight
16%1111%25%45%
2384
21st to endNight
22%1211%29%36%
2470
December1st to 10thNight
23%2217%24%32%
2470
11th to 20thNight
34%2314%25%22%
3041
21st to endNight
32%1218%26%20%
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
12%416%40%24%5%
270
11th to 20thDay
14%314%36%26%7%
258
21st to endDay
5%5%19%42%21%7%
264
February1st to 10thDay
6%422%34%26%7%
285
11th to 20thDay
11%6%25%36%20%1
415
21st to endDay
10%7%27%39%16%1
346
March1st to 10thDay
6%9%26%39%17%3
420
11th to 20thDay
8%6%23%30%27%5%
420
21st to endDay
6%9%26%39%17%3
462
April1st to 10thDay
5%5%24%36%22%8%
420
11th to 20thDay
38%27%35%20%6%
412
21st to endDay
28%25%33%21%10%
420
May1st to 10thDay
27%23%33%26%10%
423
11th to 20thDay
2319%40%25%10%
448
21st to endDay
16%19%38%29%7%
485
June1st to 10thDay
3214%33%35%13%
450
11th to 20thDay
2215%34%34%14%
450
21st to endDay
127%36%42%12%
450
July1st to 10thDay
2431%39%23%
446
11th to 20thDay
5%1320%40%32%
444
21st to endDay
41117%42%34%
487
August1st to 10thDay
41221%41%32%
447
11th to 20thDay
32120%43%32%
437
21st to endDay
11217%44%35%
495
September1st to 10thDay
5%16%24%42%22%
450
11th to 20thDay
418%24%45%18%
450
21st to endDay
3311%33%32%17%
450
October1st to 10thDay
4216%32%34%12%
393
11th to 20thDay
414%29%39%13%
270
21st to endDay
3114%36%34%13%
297
November1st to 10thDay
5%313%37%33%9%
270
11th to 20thDay
4312%39%34%8%
270
21st to endDay
7%121%37%27%7%
270
December1st to 10thDay
10%312%40%28%7%
270
11th to 20thDay
5%317%46%24%4
270
21st to endDay
16%5%22%31%22%4
297
January1st to 10thNight
8%215%49%23%3
760
11th to 20thNight
9%217%44%25%3
748
21st to endNight
11%417%46%19%3
792
February1st to 10thNight
8%316%45%26%2
720
11th to 20thNight
10%219%48%20%1
704
21st to endNight
10%318%48%19%2
592
March1st to 10thNight
7%222%50%18%2
720
11th to 20thNight
8%314%40%29%7%
720
21st to endNight
5%317%44%29%2
792
April1st to 10thNight
3215%53%24%3
720
11th to 20thNight
3221%49%23%2
587
21st to endNight
4215%52%24%4
540
May1st to 10thNight
3314%49%29%3
540
11th to 20thNight
2211%52%29%4
531
21st to endNight
3111%50%31%4
584
June1st to 10thNight
216%47%41%2
540
11th to 20thNight
16%52%39%2
540
21st to endNight
21437%51%4
540
July1st to 10thNight
22432%54%6%
525
11th to 20thNight
31219%66%9%
522
21st to endNight
41314%65%13%
591
August1st to 10thNight
2118%67%11%
537
11th to 20thNight
31320%64%9%
534
21st to endNight
31221%63%10%
656
September1st to 10thNight
5%1428%52%9%
720
11th to 20thNight
217%38%46%6%
720
21st to endNight
228%41%40%7%
720
October1st to 10thNight
4111%47%34%3
720
11th to 20thNight
329%48%35%4
720
21st to endNight
2213%42%34%7%
792
November1st to 10thNight
4111%48%31%5%
740
11th to 20thNight
3113%49%31%4
760
21st to endNight
6%217%44%27%4
760
December1st to 10thNight
8%314%45%28%2
760
11th to 20thNight
12%313%46%24%2
760
21st to endNight
10%215%48%22%4
836
Page generated at 2024-01-14 07:55:00. Version ac07

Copyright 2024 Attilla Danko


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