STAR School
Clear Sky Chart
History

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

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
62%
24102
34%
79532
25%
24012
72%
24012
50%
35986

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
57%
754
35%
4003
28%
736
71%
736
35%
1572
January11th to 20thNight
61%
755
40%
3923
30%
740
72%
740
43%
1263
January21st to endNight
54%
827
23%
4284
27%
814
68%
814
28%
2081
February1st to 10thNight
54%
760
35%
2470
25%
760
72%
760
53%
1099
February11th to 20thNight
48%
740
37%
2238
25%
740
64%
740
52%
1051
February21st to endNight
44%
628
38%
1855
24%
628
62%
628
53%
844
March1st to 10thNight
46%
742
36%
2040
21%
742
62%
742
52%
981
March11th to 20thNight
55%
720
36%
1980
22%
720
69%
720
57%
964
March21st to endNight
49%
792
35%
2178
15%
792
65%
792
55%
1057
April1st to 10thNight
44%
720
33%
1980
14%
720
59%
720
55%
942
April11th to 20thNight
40%
552
38%
1796
17%
552
62%
552
50%
757
April21st to endNight
47%
540
42%
1644
22%
540
67%
540
63%
678
May1st to 10thNight
52%
540
36%
1620
22%
540
65%
540
58%
724
May11th to 20thNight
58%
531
37%
1594
24%
531
69%
531
60%
701
May21st to endNight
51%
582
33%
1746
19%
582
62%
582
64%
725
June1st to 10thNight
62%
540
33%
1620
25%
540
68%
540
66%
683
June11th to 20thNight
62%
540
36%
1620
26%
540
70%
540
70%
654
June21st to endNight
73%
540
33%
1620
27%
540
78%
540
66%
688
July1st to 10thNight
79%
525
25%
1575
21%
525
81%
525
47%
798
July11th to 20thNight
79%
522
21%
1566
19%
522
80%
522
40%
862
July21st to endNight
73%
591
18%
1674
16%
558
73%
558
27%
1044
August1st to 10thNight
80%
537
26%
1602
23%
534
81%
534
42%
842
August11th to 20thNight
78%
534
30%
1602
25%
534
80%
534
42%
857
August21st to endNight
84%
595
33%
1904
32%
595
85%
595
47%
933
September1st to 10thNight
78%
720
30%
1980
26%
720
81%
720
51%
1054
September11th to 20thNight
79%
720
41%
1980
32%
720
84%
720
67%
902
September21st to endNight
74%
720
40%
1980
27%
720
82%
720
67%
900
October1st to 10thNight
64%
720
35%
2056
22%
720
74%
720
56%
996
October11th to 20thNight
71%
720
42%
2160
31%
720
80%
720
64%
934
October21st to endNight
69%
792
45%
2376
32%
792
80%
792
67%
995
November1st to 10thNight
67%
740
41%
2220
31%
740
77%
740
63%
970
November11th to 20thNight
71%
760
42%
2451
34%
760
82%
760
66%
972
November21st to endNight
62%
760
38%
2470
31%
760
73%
760
52%
1099
December1st to 10thNight
62%
760
36%
2470
30%
760
72%
760
53%
1094
December11th to 20thNight
58%
758
34%
2919
28%
758
70%
758
39%
1396
December21st to endNight
53%
825
22%
4336
25%
817
66%
817
29%
1874

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
231342445%7%63%
79033
Night
231332345%7%67%
80563
TransparencyDay
19%6%9%19%28%20%
78760
Night
16%5%9%20%30%21%
80358
SeeingDay
5%10%22%29%25%10%
13897
Night
36%25%37%25%4
24141

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
1325%42445%8%62%
2858
11th to 20thDay
1424325%5%5%6%63%
2860
21st to endDay
47%25%33345%7%57%
3146
February1st to 10thDay
1314423448%66%
1710
11th to 20thDay
24243235%6%7%63%
1829
21st to endDay
2213324447%68%
1598
March1st to 10thDay
232332336%9%65%
2036
11th to 20thDay
232331435%7%66%
1980
21st to endDay
242432345%7%65%
2178
April1st to 10thDay
1213324448%67%
1980
11th to 20thDay
1313322346%71%
2110
21st to endDay
2213223446%70%
2312
May1st to 10thDay
2213323446%70%
2340
11th to 20thDay
2313324447%67%
2301
21st to endDay
2213314345%72%
2530
June1st to 10thDay
22231335%5%74%
2340
11th to 20thDay
211221223480%
2340
21st to endDay
111233345%6%70%
2340
July1st to 10thDay
22235%48%6%8%8%52%
2340
11th to 20thDay
5%425%8%49%8%10%10%35%
2340
21st to endDay
45%37%8%6%10%10%10%11%28%
2545
August1st to 10thDay
4426%6%47%7%7%9%44%
2328
11th to 20thDay
3425%6%48%8%10%10%41%
2299
21st to endDay
33136%46%7%8%9%49%
2448
September1st to 10thDay
34145%46%6%6%8%53%
1980
11th to 20thDay
221232445%6%68%
1980
21st to endDay
2212322346%73%
1980
October1st to 10thDay
3312323345%70%
1903
11th to 20thDay
211221222381%
1800
21st to endDay
1212222345%76%
1980
November1st to 10thDay
1212212236%78%
1859
11th to 20thDay
1112313345%78%
1728
21st to endDay
3312413245%71%
1710
December1st to 10thDay
242342345%9%64%
1710
11th to 20thDay
25%25%5%3446%10%54%
2169
21st to endDay
45%26%43346%7%57%
3146
January1st to 10thNight
14244245%6%7%61%
4097
11th to 20thNight
221221235%8%72%
4110
21st to endNight
48%2442445%6%58%
4521
February1st to 10thNight
1313322446%71%
2470
11th to 20thNight
2313323446%69%
2237
21st to endNight
131222335%7%69%
1855
March1st to 10thNight
122332345%7%69%
2040
11th to 20thNight
231332246%6%69%
1980
21st to endNight
231232445%7%68%
2178
April1st to 10thNight
121322435%7%71%
1980
11th to 20thNight
1212223446%71%
1796
21st to endNight
1211223345%77%
1644
May1st to 10thNight
1212423346%72%
1620
11th to 20thNight
1213223335%75%
1594
21st to endNight
2212212236%76%
1746
June1st to 10thNight
2212313336%76%
1620
11th to 20thNight
221221222381%
1620
21st to endNight
1212211446%74%
1620
July1st to 10thNight
22135%35%6%7%9%57%
1620
11th to 20thNight
2315%5%36%6%8%10%50%
1620
21st to endNight
5%5%35%5%48%7%9%12%38%
1773
August1st to 10thNight
32145%45%47%8%57%
1611
11th to 20thNight
33135%45%7%8%10%51%
1602
21st to endNight
23124345%9%10%56%
1904
September1st to 10thNight
32134345%6%8%60%
1980
11th to 20thNight
2212212247%74%
1980
21st to endNight
2112222345%76%
1980
October1st to 10thNight
221322235%5%71%
2056
11th to 20thNight
321221222380%
2160
21st to endNight
2212212225%80%
2376
November1st to 10thNight
1112323346%75%
2220
11th to 20thNight
121221234478%
2451
21st to endNight
2212324337%71%
2470
December1st to 10thNight
331321345%7%68%
2470
11th to 20thNight
24134335%5%10%60%
3041
21st to endNight
442443445%6%61%
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
18%6%12%29%30%4
2859
11th to 20thDay
18%7%12%33%25%4
2860
21st to endDay
23%8%12%26%27%5%
3146
February1st to 10thDay
18%412%19%32%15%
1710
11th to 20thDay
18%5%9%24%27%18%
1839
21st to endDay
16%5%9%21%33%16%
1598
March1st to 10thDay
15%5%8%23%35%15%
2036
11th to 20thDay
16%47%24%34%14%
1980
21st to endDay
17%5%7%25%31%13%
2178
April1st to 10thDay
16%47%18%36%19%
1980
11th to 20thDay
13%37%16%35%25%
2113
21st to endDay
14%47%16%38%22%
2312
May1st to 10thDay
15%36%16%35%24%
2340
11th to 20thDay
17%47%16%33%23%
2304
21st to endDay
14%46%15%30%32%
2530
June1st to 10thDay
10%45%10%28%43%
2340
11th to 20thDay
9%246%21%58%
2340
21st to endDay
13%45%10%22%46%
2340
July1st to 10thDay
24%7%12%13%14%30%
2276
11th to 20thDay
33%13%15%16%11%11%
2271
21st to endDay
39%16%16%15%10%4
2404
August1st to 10thDay
30%10%15%13%13%19%
2313
11th to 20thDay
29%12%13%17%15%14%
2299
21st to endDay
26%10%12%17%23%12%
2448
September1st to 10thDay
26%7%12%13%16%26%
1980
11th to 20thDay
14%6%9%16%26%29%
1980
21st to endDay
14%36%16%33%29%
1980
October1st to 10thDay
17%47%17%28%27%
1903
11th to 20thDay
10%2411%35%37%
1800
21st to endDay
11%36%18%42%20%
1980
November1st to 10thDay
10%25%27%37%19%
1859
11th to 20thDay
11%36%23%41%16%
1728
21st to endDay
16%36%24%36%15%
1710
December1st to 10thDay
19%5%11%26%27%11%
1710
11th to 20thDay
24%7%14%26%23%5%
2168
21st to endDay
24%6%10%24%29%6%
3146
January1st to 10thNight
17%8%10%28%34%4
4097
11th to 20thNight
12%5%13%35%31%5%
4110
21st to endNight
26%6%10%24%29%5%
4521
February1st to 10thNight
15%48%23%32%17%
2470
11th to 20thNight
16%48%22%31%18%
2238
21st to endNight
13%48%21%34%19%
1855
March1st to 10thNight
14%48%22%36%15%
2040
11th to 20thNight
15%48%22%34%17%
1980
21st to endNight
14%5%10%23%33%15%
2178
April1st to 10thNight
14%47%18%36%22%
1980
11th to 20thNight
14%35%17%34%28%
1796
21st to endNight
11%27%17%38%25%
1644
May1st to 10thNight
14%38%16%31%28%
1620
11th to 20thNight
13%46%17%32%28%
1595
21st to endNight
10%28%14%31%36%
1746
June1st to 10thNight
10%45%8%24%49%
1620
11th to 20thNight
10%136%22%58%
1620
21st to endNight
11%249%20%53%
1620
July1st to 10thNight
19%7%11%13%16%34%
1575
11th to 20thNight
24%9%16%22%15%14%
1566
21st to endNight
34%11%18%17%12%7%
1674
August1st to 10thNight
23%7%12%18%17%23%
1602
11th to 20thNight
22%9%15%20%17%18%
1602
21st to endNight
19%7%12%23%26%14%
1904
September1st to 10thNight
19%7%12%17%21%25%
1980
11th to 20thNight
11%37%18%27%33%
1980
21st to endNight
11%36%12%31%36%
1980
October1st to 10thNight
14%5%7%18%23%31%
2056
11th to 20thNight
12%3312%31%40%
2160
21st to endNight
10%25%18%39%26%
2376
November1st to 10thNight
12%35%21%38%21%
2220
11th to 20thNight
10%36%19%41%21%
2451
21st to endNight
15%46%19%34%21%
2470
December1st to 10thNight
14%5%11%25%30%16%
2470
11th to 20thNight
19%8%10%26%30%7%
3041
21st to endNight
22%6%9%22%28%12%
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
6%10%26%38%19%3
270
11th to 20thDay
5%11%25%31%23%5%
270
21st to endDay
311%21%33%24%7%
297
February1st to 10thDay
314%25%31%18%8%
270
11th to 20thDay
7%16%28%35%12%1
434
21st to endDay
7%24%25%31%10%2
382
March1st to 10thDay
8%22%28%26%14%2
441
11th to 20thDay
6%19%26%27%18%4
420
21st to endDay
7%22%33%25%11%2
462
April1st to 10thDay
418%30%24%18%6%
420
11th to 20thDay
9%18%33%24%12%4
412
21st to endDay
5%21%28%24%18%4
420
May1st to 10thDay
417%30%29%16%4
423
11th to 20thDay
414%27%28%21%8%
448
21st to endDay
5%16%29%27%18%6%
485
June1st to 10thDay
27%28%30%26%9%
450
11th to 20thDay
312%24%30%21%10%
450
21st to endDay
25%21%29%34%9%
450
July1st to 10thDay
3113%32%35%17%
446
11th to 20thDay
6%110%26%33%24%
444
21st to endDay
427%21%36%30%
487
August1st to 10thDay
428%25%38%23%
447
11th to 20thDay
4212%24%38%20%
437
21st to endDay
319%27%37%23%
495
September1st to 10thDay
6%212%24%38%18%
450
11th to 20thDay
3319%34%30%11%
450
21st to endDay
49%16%29%32%10%
450
October1st to 10thDay
310%23%28%25%12%
373
11th to 20thDay
45%14%31%32%12%
270
21st to endDay
5%7%19%30%31%7%
297
November1st to 10thDay
6%10%17%29%31%7%
270
11th to 20thDay
26%19%33%31%9%
270
21st to endDay
313%23%28%26%9%
270
December1st to 10thDay
6%5%26%31%28%4
270
11th to 20thDay
39%26%34%23%5%
270
21st to endDay
7%13%25%40%13%3
297
January1st to 10thNight
46%28%34%23%5%
760
11th to 20thNight
46%24%39%23%4
760
21st to endNight
5%7%28%37%21%2
836
February1st to 10thNight
26%34%37%18%3
760
11th to 20thNight
38%39%33%15%2
744
21st to endNight
413%37%32%14%1
628
March1st to 10thNight
314%34%33%15%1
742
11th to 20thNight
38%30%35%19%5%
720
21st to endNight
310%35%36%13%2
792
April1st to 10thNight
214%36%32%14%2
720
11th to 20thNight
413%39%30%11%2
552
21st to endNight
38%40%35%11%4
540
May1st to 10thNight
26%36%43%12%1
540
11th to 20thNight
16%32%37%22%2
531
21st to endNight
46%35%36%17%2
584
June1st to 10thNight
1429%49%16%1
540
11th to 20thNight
2331%45%16%2
540
21st to endNight
2218%51%25%1
540
July1st to 10thNight
28%49%37%4
525
11th to 20thNight
31442%47%4
522
21st to endNight
6%15%31%49%7%
591
August1st to 10thNight
36%37%46%8%
537
11th to 20thNight
418%35%46%7%
534
21st to endNight
316%33%50%7%
595
September1st to 10thNight
419%35%46%6%
720
11th to 20thNight
2112%42%35%7%
720
21st to endNight
2416%36%34%8%
720
October1st to 10thNight
36%24%39%25%3
720
11th to 20thNight
4320%40%28%7%
720
21st to endNight
3422%36%28%8%
792
November1st to 10thNight
3424%37%27%5%
740
11th to 20thNight
2322%39%27%7%
760
21st to endNight
38%24%36%25%4
760
December1st to 10thNight
46%24%37%26%4
760
11th to 20thNight
47%26%37%25%2
760
21st to endNight
5%7%28%40%16%3
836
Page generated at 2024-03-03 04:28:54. Version ac07

Copyright © 2024 Attilla Danko.


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