Grasslands Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grasslands Observatory clear sky chart from 2005-11-06 to 2024-02-20.

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
66%
24055
34%
79313
27%
23968
75%
23968
46%
37693

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
63%
753
40%
3974
28%
736
71%
736
36%
1472
January11th to 20thNight
64%
751
47%
3881
31%
740
76%
740
46%
1198
January21st to endNight
54%
828
23%
4308
28%
814
68%
814
23%
2278
February1st to 10thNight
59%
760
36%
2437
30%
760
72%
760
47%
1143
February11th to 20thNight
51%
738
33%
2212
24%
738
65%
738
44%
1118
February21st to endNight
50%
592
40%
1651
27%
592
64%
592
47%
855
March1st to 10thNight
50%
720
37%
1980
22%
720
65%
720
47%
1020
March11th to 20thNight
60%
720
37%
1980
23%
720
71%
720
54%
976
March21st to endNight
57%
792
37%
2178
21%
792
70%
792
50%
1101
April1st to 10thNight
60%
720
38%
1980
23%
720
72%
720
60%
928
April11th to 20thNight
54%
559
41%
1803
27%
559
72%
559
56%
756
April21st to endNight
59%
540
45%
1800
33%
540
77%
540
64%
681
May1st to 10thNight
61%
540
40%
1659
27%
540
75%
540
63%
683
May11th to 20thNight
66%
531
40%
1594
30%
531
74%
531
65%
659
May21st to endNight
67%
582
44%
1746
31%
582
78%
582
76%
673
June1st to 10thNight
76%
540
36%
1620
31%
540
79%
540
63%
703
June11th to 20thNight
76%
540
37%
1620
30%
540
79%
540
70%
662
June21st to endNight
77%
540
27%
1620
23%
540
78%
540
51%
792
July1st to 10thNight
80%
525
19%
1575
16%
525
80%
525
39%
861
July11th to 20thNight
76%
522
12%
1566
11%
522
76%
522
24%
1043
July21st to endNight
75%
591
11%
1674
10%
558
75%
558
22%
1165
August1st to 10thNight
82%
537
17%
1602
16%
534
82%
534
33%
949
August11th to 20thNight
78%
534
22%
1638
22%
534
78%
534
33%
967
August21st to endNight
78%
603
24%
1989
25%
603
79%
603
31%
1160
September1st to 10thNight
73%
720
24%
1980
22%
720
74%
720
37%
1210
September11th to 20thNight
82%
720
39%
1980
32%
720
84%
720
56%
1002
September21st to endNight
78%
720
36%
1980
25%
720
84%
720
60%
962
October1st to 10thNight
76%
720
38%
2071
29%
720
82%
720
62%
957
October11th to 20thNight
74%
720
41%
2160
31%
720
82%
720
65%
932
October21st to endNight
76%
792
44%
2376
35%
792
84%
792
69%
977
November1st to 10thNight
72%
740
44%
2220
34%
740
81%
740
64%
941
November11th to 20thNight
73%
760
42%
2280
33%
760
81%
760
57%
1036
November21st to endNight
58%
760
37%
2432
30%
760
68%
760
43%
1191
December1st to 10thNight
64%
760
36%
2470
33%
760
71%
760
45%
1194
December11th to 20thNight
58%
759
31%
2944
29%
759
68%
759
32%
1571
December21st to endNight
57%
826
23%
4333
29%
817
68%
817
29%
1877

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
332443445%7%62%
78884
Night
331342445%7%64%
80369
TransparencyDay
22%5%7%12%27%27%
78611
Night
19%5%7%13%28%27%
80164
SeeingDay
7%12%26%31%19%5%
13869
Night
46%18%37%30%5%
24096

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
2324433445%65%
2858
11th to 20thDay
241342345%6%65%
2860
21st to endDay
35%35%5%345%6%8%54%
3146
February1st to 10thDay
4413423446%65%
1738
11th to 20thDay
45%34323445%63%
1841
21st to endDay
3423413346%67%
1602
March1st to 10thDay
33244235%5%7%60%
1980
11th to 20thDay
3314423346%67%
1980
21st to endDay
221332445%6%70%
2178
April1st to 10thDay
1112334446%71%
1980
11th to 20thDay
221221223479%
2103
21st to endDay
1112212236%80%
2160
May1st to 10thDay
121322232477%
2296
11th to 20thDay
1113222345%76%
2301
21st to endDay
111121212385%
2530
June1st to 10thDay
2212324336%72%
2340
11th to 20thDay
111121333479%
2340
21st to endDay
32135%3446%7%60%
2340
July1st to 10thDay
4425%6%5%7%7%8%9%43%
2340
11th to 20thDay
45%38%9%5%8%10%9%10%29%
2340
21st to endDay
8%7%38%8%6%9%8%8%10%24%
2545
August1st to 10thDay
6%5%37%7%47%9%8%9%34%
2328
11th to 20thDay
45%36%6%49%8%8%10%37%
2263
21st to endDay
5%417%7%5%8%7%6%10%40%
2361
September1st to 10thDay
6%435%7%46%6%6%7%44%
1980
11th to 20thDay
42134346%6%7%60%
1980
21st to endDay
321343445%6%65%
1980
October1st to 10thDay
221332346%6%69%
1886
11th to 20thDay
2211322346%76%
1800
21st to endDay
2112223446%75%
1980
November1st to 10thDay
111232335%7%73%
1859
11th to 20thDay
2213323335%72%
1900
21st to endDay
3424325%446%63%
1744
December1st to 10thDay
5%3135%3345%7%61%
1710
11th to 20thDay
46%35%5%3446%8%52%
2169
21st to endDay
34145%3445%7%61%
3146
January1st to 10thNight
232342445%6%66%
4097
11th to 20thNight
121221335%6%75%
4110
21st to endNight
6%5%25%5%35%5%6%8%49%
4521
February1st to 10thNight
231243345%6%66%
2437
11th to 20thNight
3324434346%64%
2211
21st to endNight
242433345%5%65%
1651
March1st to 10thNight
23235%2346%7%63%
1980
11th to 20thNight
2313333346%69%
1980
21st to endNight
2313324446%67%
2178
April1st to 10thNight
1212313336%73%
1980
11th to 20thNight
131222333477%
1803
21st to endNight
1212211235%80%
1800
May1st to 10thNight
1112212445%78%
1659
11th to 20thNight
1112212346%76%
1594
21st to endNight
1111222287%
1746
June1st to 10thNight
3112222336%75%
1620
11th to 20thNight
2212111235%79%
1620
21st to endNight
221343446%7%64%
1620
July1st to 10thNight
33236%45%7%7%11%49%
1620
11th to 20thNight
2437%6%6%8%9%10%13%32%
1620
21st to endNight
5%5%36%7%5%9%7%12%15%28%
1773
August1st to 10thNight
3325%5%46%6%8%11%46%
1611
11th to 20thNight
35%25%5%36%6%7%12%44%
1638
21st to endNight
5%3246%45%7%8%10%46%
1989
September1st to 10thNight
6%4345%35%6%6%10%48%
1980
11th to 20thNight
3313323447%68%
1980
21st to endNight
2212323448%70%
1980
October1st to 10thNight
111322435%5%73%
2071
11th to 20thNight
2212312335%77%
2160
21st to endNight
1112212235%81%
2376
November1st to 10thNight
112222347%75%
2220
11th to 20thNight
2313323346%72%
2280
21st to endNight
3423424347%64%
2432
December1st to 10thNight
33143245%5%7%63%
2470
11th to 20thNight
35%25%5%35%5%5%6%55%
3041
21st to endNight
3325%5%345%5%5%59%
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
20%45%10%33%27%
2859
11th to 20thDay
20%46%12%38%20%
2860
21st to endDay
26%6%6%16%31%15%
3146
February1st to 10thDay
22%3411%26%34%
1738
11th to 20thDay
24%4413%26%29%
1851
21st to endDay
21%2310%27%37%
1602
March1st to 10thDay
23%448%32%29%
1980
11th to 20thDay
20%348%32%33%
1980
21st to endDay
17%3311%39%27%
2178
April1st to 10thDay
15%338%38%32%
1980
11th to 20thDay
12%227%30%47%
2106
21st to endDay
10%149%34%43%
2160
May1st to 10thDay
13%238%26%49%
2296
11th to 20thDay
12%349%28%44%
2304
21st to endDay
8%125%30%53%
2530
June1st to 10thDay
14%338%28%44%
2340
11th to 20thDay
9%246%21%58%
2340
21st to endDay
22%6%7%11%22%33%
2340
July1st to 10thDay
32%11%11%15%16%16%
2276
11th to 20thDay
41%16%18%17%6%2
2271
21st to endDay
47%17%18%10%7%1
2404
August1st to 10thDay
40%13%14%15%13%5%
2313
11th to 20thDay
38%11%16%16%14%5%
2263
21st to endDay
36%11%13%17%15%8%
2361
September1st to 10thDay
36%8%11%14%17%13%
1980
11th to 20thDay
21%6%9%14%28%22%
1980
21st to endDay
19%5%8%16%31%21%
1980
October1st to 10thDay
14%5%8%15%28%30%
1886
11th to 20thDay
11%35%10%33%38%
1800
21st to endDay
12%3411%29%41%
1980
November1st to 10thDay
11%4413%37%30%
1859
11th to 20thDay
17%3411%34%31%
1900
21st to endDay
22%45%14%25%30%
1744
December1st to 10thDay
23%46%15%29%24%
1710
11th to 20thDay
30%37%14%28%18%
2168
21st to endDay
22%46%12%39%18%
3146
January1st to 10thNight
18%5%6%11%36%25%
4097
11th to 20thNight
12%3419%41%21%
4110
21st to endNight
30%8%7%15%27%13%
4521
February1st to 10thNight
19%45%14%22%37%
2437
11th to 20thNight
23%36%13%27%28%
2212
21st to endNight
21%4411%26%34%
1651
March1st to 10thNight
21%35%12%29%30%
1980
11th to 20thNight
17%36%11%27%36%
1980
21st to endNight
19%35%11%37%24%
2178
April1st to 10thNight
14%2311%39%30%
1980
11th to 20thNight
13%338%31%42%
1803
21st to endNight
10%2310%35%41%
1800
May1st to 10thNight
11%248%30%45%
1659
11th to 20thNight
9%36%10%28%43%
1595
21st to endNight
6%127%34%49%
1746
June1st to 10thNight
13%336%30%46%
1620
11th to 20thNight
10%235%23%58%
1620
21st to endNight
17%7%7%11%20%38%
1620
July1st to 10thNight
24%9%18%16%15%19%
1575
11th to 20thNight
35%16%21%18%7%3
1566
21st to endNight
37%16%26%14%5%2
1674
August1st to 10thNight
26%13%16%21%17%7%
1602
11th to 20thNight
30%10%20%17%18%6%
1638
21st to endNight
29%11%17%18%18%7%
1989
September1st to 10thNight
29%8%14%18%18%12%
1980
11th to 20thNight
17%5%8%16%31%23%
1980
21st to endNight
14%5%9%17%34%21%
1980
October1st to 10thNight
12%5%8%18%28%29%
2071
11th to 20thNight
11%36%14%28%38%
2160
21st to endNight
9%2413%32%39%
2376
November1st to 10thNight
11%2416%35%31%
2220
11th to 20thNight
15%3316%31%31%
2280
21st to endNight
22%35%13%30%26%
2432
December1st to 10thNight
20%5%7%15%28%24%
2470
11th to 20thNight
28%6%6%13%27%20%
3041
21st to endNight
22%6%7%12%28%24%
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
13%16%22%36%13%
270
11th to 20thDay
9%10%31%34%15%1
270
21st to endDay
6%16%32%34%10%2
297
February1st to 10thDay
11%15%28%28%14%3
298
11th to 20thDay
13%26%30%23%7%
452
21st to endDay
15%30%30%19%5%1
346
March1st to 10thDay
11%26%35%18%8%1
420
11th to 20thDay
12%22%27%21%13%5%
420
21st to endDay
11%30%34%16%8%2
462
April1st to 10thDay
419%39%24%10%4
420
11th to 20thDay
7%28%34%17%11%2
412
21st to endDay
6%20%35%25%11%4
420
May1st to 10thDay
8%18%35%23%13%4
423
11th to 20thDay
5%13%35%30%13%3
448
21st to endDay
413%40%28%12%3
485
June1st to 10thDay
48%35%34%15%4
450
11th to 20thDay
25%35%35%19%4
450
21st to endDay
4227%41%21%4
450
July1st to 10thDay
4114%46%29%7%
446
11th to 20thDay
6%19%43%30%11%
444
21st to endDay
10%17%34%36%12%
487
August1st to 10thDay
8%17%31%35%18%
447
11th to 20thDay
6%210%35%35%13%
437
21st to endDay
5%18%32%38%16%
495
September1st to 10thDay
8%318%38%26%8%
450
11th to 20thDay
4219%40%26%8%
450
21st to endDay
5%8%23%34%22%7%
450
October1st to 10thDay
310%26%31%22%8%
356
11th to 20thDay
36%27%35%20%9%
270
21st to endDay
46%27%33%24%6%
297
November1st to 10thDay
6%14%25%34%19%3
270
11th to 20thDay
5%7%30%34%22%1
270
21st to endDay
9%21%25%33%11%1
270
December1st to 10thDay
11%12%26%33%17%1
270
11th to 20thDay
8%13%36%29%14%
270
21st to endDay
10%19%28%31%10%2
297
January1st to 10thNight
5%5%21%41%23%4
760
11th to 20thNight
5%5%20%42%24%3
760
21st to endNight
8%8%24%39%19%2
836
February1st to 10thNight
5%8%25%35%24%4
760
11th to 20thNight
6%11%27%37%17%2
742
21st to endNight
6%12%28%38%14%2
592
March1st to 10thNight
5%13%29%36%16%1
720
11th to 20thNight
5%11%22%32%27%4
720
21st to endNight
49%25%38%21%3
792
April1st to 10thNight
28%26%41%20%3
720
11th to 20thNight
312%29%37%18%1
559
21st to endNight
29%27%42%17%3
540
May1st to 10thNight
37%26%40%21%2
540
11th to 20thNight
15%24%43%24%3
531
21st to endNight
15%26%41%27%
584
June1st to 10thNight
4314%49%30%2
540
11th to 20thNight
2316%49%30%1
540
21st to endNight
3113%38%41%5%
540
July1st to 10thNight
317%32%50%7%
525
11th to 20thNight
36%25%56%10%
522
21st to endNight
5%25%24%51%14%
591
August1st to 10thNight
41420%56%17%
537
11th to 20thNight
415%21%54%15%
534
21st to endNight
7%419%53%16%
603
September1st to 10thNight
6%39%24%47%12%
720
11th to 20thNight
318%36%44%8%
720
21st to endNight
2114%37%38%8%
720
October1st to 10thNight
2315%39%36%5%
720
11th to 20thNight
3317%40%32%5%
720
21st to endNight
2415%37%33%8%
792
November1st to 10thNight
45%16%38%31%7%
740
11th to 20thNight
45%15%40%32%4
760
21st to endNight
6%10%20%39%20%5%
760
December1st to 10thNight
5%6%20%43%21%5%
760
11th to 20thNight
6%9%21%41%20%3
760
21st to endNight
6%7%23%39%20%5%
836
Page generated at 2024-02-17 04:28:40. Version ac07

Copyright 2024 Attilla Danko


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