Sierra Stars Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sierra Stars Observatory clear sky chart from 2005-11-06 to 2024-02-05.

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
53%
23496
19%
79885
14%
23410
60%
23410
19%
51792

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
43%
750
18%
4323
9%
736
51%
736
10%
2368
January11th to 20thNight
48%
754
17%
4274
12%
740
56%
740
11%
2607
January21st to endNight
46%
833
11%
4350
11%
814
54%
814
10%
2868
February1st to 10thNight
47%
738
17%
2375
13%
738
55%
738
19%
1619
February11th to 20thNight
44%
700
17%
2099
11%
700
53%
700
17%
1461
February21st to endNight
43%
592
18%
1776
12%
592
51%
592
17%
1228
March1st to 10thNight
38%
720
14%
2160
7%
720
46%
720
15%
1537
March11th to 20thNight
44%
720
17%
2018
12%
720
50%
720
16%
1425
March21st to endNight
37%
792
14%
2031
5%
792
45%
792
17%
1453
April1st to 10thNight
42%
720
17%
1800
6%
720
49%
720
19%
1310
April11th to 20thNight
42%
711
17%
1779
6%
711
47%
711
20%
1261
April21st to endNight
47%
720
18%
1800
6%
720
53%
720
24%
1246
May1st to 10thNight
48%
617
20%
1697
10%
617
54%
617
22%
1133
May11th to 20thNight
55%
423
24%
1485
20%
423
61%
423
22%
915
May21st to endNight
58%
388
19%
1552
16%
388
65%
388
16%
993
June1st to 10thNight
59%
360
19%
1440
17%
360
68%
360
17%
923
June11th to 20thNight
61%
360
26%
1440
22%
360
75%
360
21%
822
June21st to endNight
67%
360
25%
1440
26%
360
76%
360
24%
806
July1st to 10thNight
72%
350
25%
1400
25%
350
81%
350
28%
740
July11th to 20thNight
66%
348
26%
1392
23%
348
77%
348
24%
791
July21st to endNight
73%
457
25%
1548
23%
432
77%
432
23%
958
August1st to 10thNight
71%
580
23%
1645
14%
577
75%
577
31%
1039
August11th to 20thNight
69%
712
25%
1780
12%
712
74%
712
34%
1160
August21st to endNight
68%
792
27%
1980
13%
792
72%
792
37%
1251
September1st to 10thNight
71%
720
29%
1800
15%
720
77%
720
37%
1134
September11th to 20thNight
66%
720
31%
1836
20%
720
72%
720
33%
1183
September21st to endNight
64%
720
27%
1980
20%
720
71%
720
30%
1240
October1st to 10thNight
61%
720
20%
2111
15%
720
68%
720
24%
1401
October11th to 20thNight
67%
720
27%
2160
25%
720
73%
720
27%
1350
October21st to endNight
62%
792
25%
2420
24%
792
69%
792
26%
1500
November1st to 10thNight
59%
740
15%
2405
12%
740
64%
740
16%
1667
November11th to 20thNight
52%
760
21%
2470
15%
760
62%
760
18%
1646
November21st to endNight
52%
760
21%
2496
16%
760
60%
760
20%
1616
December1st to 10thNight
45%
760
15%
2660
10%
760
52%
760
16%
1799
December11th to 20thNight
43%
760
14%
3201
11%
759
50%
759
10%
2313
December21st to endNight
37%
827
8%
4762
7%
817
45%
817
6%
3029

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
23234245%5%8%63%
78319
Night
132332445%8%64%
80571
TransparencyDay
13%37%8%13%16%12%
78027
Night
13%37%10%16%16%9%
80384
SeeingDay
9%22%31%23%12%3
14011
Night
5%14%25%32%20%5%
23529

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
1324335%6%8%12%54%
2539
11th to 20thDay
1425%5%36%7%8%10%49%
2615
21st to endDay
37%36%6%46%7%7%10%42%
3146
February1st to 10thDay
14234245%6%11%58%
1679
11th to 20thDay
1435%4346%6%12%53%
1750
21st to endDay
1325%4246%6%9%57%
1480
March1st to 10thDay
1435%445%7%9%11%47%
1800
11th to 20thDay
5%345%35%6%8%11%51%
1939
21st to endDay
13245%35%6%8%10%54%
2324
April1st to 10thDay
2324435%5%6%9%55%
2160
11th to 20thDay
24234346%6%8%60%
2129
21st to endDay
341332346%8%63%
2160
May1st to 10thDay
4424434448%60%
2261
11th to 20thDay
3424425%45%6%61%
2405
21st to endDay
5%5%35%435%5%6%7%53%
2723
June1st to 10thDay
32133345%5%7%64%
2520
11th to 20thDay
2112212336%77%
2520
21st to endDay
321332333473%
2520
July1st to 10thDay
111222333478%
2520
11th to 20thDay
2212313335%74%
2520
21st to endDay
2223423445%69%
2673
August1st to 10thDay
2213323335%72%
2285
11th to 20thDay
1112323435%75%
2122
21st to endDay
111121222383%
2376
September1st to 10thDay
1111222345%79%
2160
11th to 20thDay
2212323345%74%
2124
21st to endDay
221331324476%
1980
October1st to 10thDay
3413323445%68%
1846
11th to 20thDay
2213212345%75%
1800
21st to endDay
121222245%7%73%
1936
November1st to 10thDay
131343447%8%62%
1674
11th to 20thDay
131222346%9%67%
1710
21st to endDay
12133245%6%10%63%
1681
December1st to 10thDay
15%133235%7%10%59%
1520
11th to 20thDay
25%37%6%46%7%8%9%44%
1928
21st to endDay
1435%6%36%5%7%13%47%
2794
January1st to 10thNight
1425%435%46%11%54%
4406
11th to 20thNight
426%6%35%6%8%10%49%
4344
21st to endNight
27%35%5%46%6%7%10%45%
4521
February1st to 10thNight
1325%325%5%6%8%59%
2375
11th to 20thNight
14243236%7%11%55%
2098
21st to endNight
142342446%10%59%
1776
March1st to 10thNight
5%344246%8%11%53%
2160
11th to 20thNight
1323425%7%8%11%56%
2018
21st to endNight
142342446%9%61%
2031
April1st to 10thNight
23234245%7%11%58%
1800
11th to 20thNight
132332446%9%64%
1779
21st to endNight
331321335%8%69%
1800
May1st to 10thNight
3313324348%65%
1697
11th to 20thNight
142331335%8%66%
1485
21st to endNight
4413424348%63%
1552
June1st to 10thNight
4312224445%70%
1440
11th to 20thNight
11212235%82%
1440
21st to endNight
221211322481%
1440
July1st to 10thNight
1121222485%
1440
11th to 20thNight
121221333478%
1440
21st to endNight
321231334473%
1639
August1st to 10thNight
2213323335%74%
1654
11th to 20thNight
211221223479%
1780
21st to endNight
121111122385%
1980
September1st to 10thNight
1111123486%
1800
11th to 20thNight
122212235%80%
1836
21st to endNight
211321233477%
1980
October1st to 10thNight
331332233472%
2111
11th to 20thNight
2212212335%78%
2160
21st to endNight
1211212348%76%
2420
November1st to 10thNight
131222346%9%66%
2405
11th to 20thNight
21222345%10%67%
2470
21st to endNight
232322345%9%66%
2496
December1st to 10thNight
23243335%6%10%60%
2660
11th to 20thNight
2426%435%5%7%12%49%
3276
21st to endNight
15%37%5%45%6%9%11%44%
4862

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
14%32%17%23%13%1
2539
11th to 20thDay
20%31%13%20%12%3
2615
21st to endDay
28%29%13%16%11%2
3146
February1st to 10thDay
15%36%11%16%17%6%
1679
11th to 20thDay
16%40%9%18%13%4
1760
21st to endDay
14%41%13%16%13%3
1480
March1st to 10thDay
17%41%13%16%13%1
1800
11th to 20thDay
18%42%13%13%12%2
1939
21st to endDay
15%41%15%18%10%1
2324
April1st to 10thDay
16%39%12%16%13%5%
2160
11th to 20thDay
14%39%11%16%14%5%
2132
21st to endDay
13%37%12%18%17%3
2160
May1st to 10thDay
12%37%6%19%21%5%
2261
11th to 20thDay
13%38%7%16%20%6%
2408
21st to endDay
17%39%9%16%16%3
2724
June1st to 10thDay
15%39%9%14%19%5%
2520
11th to 20thDay
8%36%5%11%25%15%
2520
21st to endDay
10%36%48%22%19%
2520
July1st to 10thDay
5%36%35%13%39%
2451
11th to 20thDay
8%36%35%14%34%
2445
21st to endDay
10%37%46%12%30%
2524
August1st to 10thDay
8%36%37%14%32%
2269
11th to 20thDay
8%34%46%15%33%
2122
21st to endDay
5%34%2419%35%
2376
September1st to 10thDay
6%36%37%19%29%
2160
11th to 20thDay
9%36%411%23%17%
2124
21st to endDay
7%35%5%11%24%18%
1980
October1st to 10thDay
13%38%7%11%18%14%
1846
11th to 20thDay
8%36%5%18%21%13%
1800
21st to endDay
8%38%7%16%22%9%
1936
November1st to 10thDay
13%43%10%14%13%7%
1674
11th to 20thDay
9%40%13%14%20%3
1710
21st to endDay
10%41%7%15%20%7%
1681
December1st to 10thDay
12%41%10%17%15%5%
1520
11th to 20thDay
28%38%9%12%8%4
1928
21st to endDay
20%32%16%17%13%2
2794
January1st to 10thNight
18%29%17%24%12%1
4406
11th to 20thNight
21%31%15%19%11%3
4344
21st to endNight
26%30%14%19%8%2
4521
February1st to 10thNight
16%38%8%17%15%6%
2375
11th to 20thNight
15%39%10%20%12%3
2099
21st to endNight
15%39%14%17%12%3
1776
March1st to 10thNight
16%41%12%17%13%1
2160
11th to 20thNight
13%41%15%18%9%3
2018
21st to endNight
13%41%16%18%10%2
2031
April1st to 10thNight
15%40%13%18%11%5%
1800
11th to 20thNight
13%39%14%17%13%5%
1779
21st to endNight
13%37%11%22%16%2
1800
May1st to 10thNight
11%38%7%16%24%5%
1697
11th to 20thNight
9%37%9%18%22%5%
1485
21st to endNight
15%37%11%20%16%1
1552
June1st to 10thNight
13%39%8%18%18%5%
1440
11th to 20thNight
6%36%5%14%24%14%
1440
21st to endNight
7%35%412%25%18%
1440
July1st to 10thNight
235%25%20%36%
1400
11th to 20thNight
7%36%4419%30%
1392
21st to endNight
9%38%35%15%29%
1548
August1st to 10thNight
7%36%310%15%29%
1645
11th to 20thNight
8%34%46%19%28%
1780
21st to endNight
5%34%3422%32%
1980
September1st to 10thNight
435%37%23%29%
1800
11th to 20thNight
5%37%5%13%22%19%
1836
21st to endNight
6%36%412%26%17%
1980
October1st to 10thNight
12%37%7%13%20%11%
2111
11th to 20thNight
8%36%5%18%23%10%
2160
21st to endNight
7%37%7%18%22%10%
2420
November1st to 10thNight
10%45%10%15%12%7%
2405
11th to 20thNight
9%43%10%18%17%3
2470
21st to endNight
8%41%8%19%18%7%
2496
December1st to 10thNight
12%43%11%13%16%5%
2660
11th to 20thNight
22%40%12%13%10%3
3276
21st to endNight
23%33%14%16%11%2
4862

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
19%30%24%17%9%1
180
11th to 20thDay
16%25%24%20%11%3
229
21st to endDay
8%26%29%23%10%3
407
February1st to 10thDay
16%28%26%19%8%3
363
11th to 20thDay
12%28%31%23%6%
415
21st to endDay
14%27%33%20%5%1
346
March1st to 10thDay
15%33%30%16%41
420
11th to 20thDay
15%32%26%16%10%1
420
21st to endDay
13%34%29%18%5%
462
April1st to 10thDay
13%31%32%16%7%1
420
11th to 20thDay
19%29%30%15%5%2
412
21st to endDay
13%26%31%18%9%3
420
May1st to 10thDay
13%29%30%19%7%2
423
11th to 20thDay
13%26%30%20%7%3
448
21st to endDay
14%19%28%21%13%5%
485
June1st to 10thDay
10%23%31%24%9%4
450
11th to 20thDay
9%24%35%20%8%4
450
21st to endDay
415%37%28%12%5%
450
July1st to 10thDay
215%39%27%15%3
446
11th to 20thDay
212%36%30%15%4
444
21st to endDay
210%38%27%18%5%
487
August1st to 10thDay
415%32%30%15%5%
447
11th to 20thDay
213%36%24%17%7%
437
21st to endDay
213%38%29%15%4
495
September1st to 10thDay
310%38%29%17%4
450
11th to 20thDay
5%19%32%29%12%2
450
21st to endDay
5%17%33%34%9%2
450
October1st to 10thDay
5%22%26%27%17%2
450
11th to 20thDay
6%17%27%31%15%4
450
21st to endDay
7%18%28%25%17%4
451
November1st to 10thDay
12%19%22%18%24%6%
270
11th to 20thDay
6%20%24%28%15%7%
270
21st to endDay
423%27%27%15%4
256
December1st to 10thDay
13%24%23%19%14%6%
180
11th to 20thDay
8%29%29%16%12%6%
180
21st to endDay
19%17%29%21%11%3
198
January1st to 10thNight
7%19%27%24%16%8%
760
11th to 20thNight
418%26%32%13%6%
760
21st to endNight
5%13%31%29%16%6%
836
February1st to 10thNight
6%15%28%31%17%3
738
11th to 20thNight
5%19%28%26%16%6%
704
21st to endNight
6%24%24%31%12%3
592
March1st to 10thNight
6%26%28%25%12%3
720
11th to 20thNight
6%21%28%23%19%4
720
21st to endNight
5%26%29%27%12%2
792
April1st to 10thNight
7%18%30%29%15%1
720
11th to 20thNight
8%19%28%26%15%4
711
21st to endNight
6%16%28%29%17%4
720
May1st to 10thNight
6%17%26%30%18%3
617
11th to 20thNight
413%25%37%19%2
423
21st to endNight
7%7%24%33%28%2
389
June1st to 10thNight
5%10%22%37%24%2
360
11th to 20thNight
211%25%34%27%1
360
21st to endNight
26%23%43%23%3
360
July1st to 10thNight
1322%45%28%1
350
11th to 20thNight
1425%44%26%
348
21st to endNight
3316%39%34%5%
457
August1st to 10thNight
3319%40%32%3
580
11th to 20thNight
2422%41%27%5%
712
21st to endNight
2423%42%25%3
792
September1st to 10thNight
15%22%38%31%5%
720
11th to 20thNight
38%21%32%30%6%
720
21st to endNight
29%22%30%28%7%
720
October1st to 10thNight
5%9%21%36%22%7%
720
11th to 20thNight
6%9%17%38%25%6%
720
21st to endNight
313%20%28%24%12%
792
November1st to 10thNight
5%15%20%29%24%8%
740
11th to 20thNight
415%27%32%15%6%
760
21st to endNight
6%16%24%29%19%6%
760
December1st to 10thNight
6%17%28%29%15%5%
760
11th to 20thNight
6%19%26%31%11%6%
760
21st to endNight
8%18%32%28%11%2
836
Page generated at 2024-02-02 02:20:29. Version ac07

Copyright 2024 Attilla Danko


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