OKAstronomy Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the OKAstronomy Observatory clear sky chart from 2005-11-06 to 2024-02-10.

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
38%
24365
25%
79567
15%
24255
49%
24255
29%
45999

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
25%
943
24%
4017
8%
926
38%
926
19%
2417
January11th to 20thNight
21%
950
24%
3999
7%
930
33%
930
22%
2011
January21st to endNight
25%
1037
20%
4482
10%
1023
38%
1023
18%
2773
February1st to 10thNight
19%
948
21%
2464
5%
948
30%
948
25%
1633
February11th to 20thNight
18%
825
20%
2220
5%
821
28%
821
25%
1415
February21st to endNight
18%
498
27%
1682
9%
498
36%
498
20%
1019
March1st to 10thNight
26%
540
24%
1980
12%
540
40%
540
22%
1159
March11th to 20thNight
24%
540
22%
1980
12%
540
38%
540
21%
1195
March21st to endNight
20%
594
20%
2178
8%
594
37%
594
21%
1315
April1st to 10thNight
24%
540
23%
1924
12%
540
42%
540
24%
1085
April11th to 20thNight
26%
533
25%
1775
13%
533
44%
533
28%
1027
April21st to endNight
24%
540
23%
1742
8%
540
43%
540
27%
1069
May1st to 10thNight
33%
540
21%
1620
15%
540
45%
540
29%
995
May11th to 20thNight
41%
531
21%
1594
16%
531
50%
531
31%
982
May21st to endNight
41%
584
19%
1746
12%
582
51%
582
30%
1085
June1st to 10thNight
63%
540
22%
1620
20%
540
68%
540
43%
855
June11th to 20thNight
55%
540
24%
1620
17%
540
64%
540
46%
837
June21st to endNight
67%
540
27%
1620
24%
540
72%
540
52%
786
July1st to 10thNight
69%
525
21%
1575
21%
525
72%
525
41%
868
July11th to 20thNight
74%
522
26%
1566
26%
522
78%
522
51%
767
July21st to endNight
76%
591
27%
1673
31%
558
79%
558
47%
859
August1st to 10thNight
71%
537
24%
1601
25%
534
75%
534
43%
863
August11th to 20thNight
69%
534
30%
1600
32%
534
73%
534
40%
887
August21st to endNight
73%
594
27%
1966
31%
594
75%
594
44%
989
September1st to 10thNight
66%
540
29%
1844
30%
540
70%
540
40%
935
September11th to 20thNight
63%
540
28%
1980
28%
540
71%
540
33%
1057
September21st to endNight
57%
540
33%
1980
30%
540
66%
540
37%
975
October1st to 10thNight
51%
686
31%
2126
20%
686
60%
686
43%
1096
October11th to 20thNight
37%
720
33%
2160
15%
720
50%
720
39%
1168
October21st to endNight
35%
792
28%
2376
16%
792
45%
792
30%
1410
November1st to 10thNight
33%
740
33%
2220
14%
740
50%
740
38%
1174
November11th to 20thNight
31%
850
29%
2370
12%
850
45%
850
35%
1356
November21st to endNight
28%
950
28%
2470
11%
950
40%
950
32%
1532
December1st to 10thNight
27%
950
27%
2470
9%
950
40%
950
29%
1578
December11th to 20thNight
25%
949
26%
2893
9%
948
36%
948
23%
1855
December21st to endNight
22%
1042
16%
4434
8%
1026
36%
1026
15%
2972

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
13%6%35%43445%7%46%
78752
Night
12%6%2442345%7%51%
80275
TransparencyDay
38%5%11%24%18%4
78476
Night
34%411%24%22%5%
80071
SeeingDay
16%12%28%26%14%3
14362
Night
16%12%30%29%12%1
24384

By Month

Percentage Cloud Cover SE (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
13%11%45%324445%47%
2847
11th to 20thDay
10%6%26%5%23346%54%
2850
21st to endDay
22%10%2432233444%
3135
February1st to 10thDay
17%10%36%5%2344441%
1701
11th to 20thDay
17%7%45%42345%6%44%
1642
21st to endDay
17%9%35%43435%5%41%
1574
March1st to 10thDay
17%7%25%42335%6%47%
1980
11th to 20thDay
20%8%34424345%42%
1980
21st to endDay
20%9%45%5%25%45%6%34%
2178
April1st to 10thDay
13%6%26%43446%6%45%
2034
11th to 20thDay
17%6%36%5%3445%6%42%
2134
21st to endDay
21%8%35%5%33445%40%
2214
May1st to 10thDay
17%7%35%5%3445%7%40%
2340
11th to 20thDay
14%6%36%5%45%5%6%6%40%
2302
21st to endDay
11%5%37%7%47%6%6%8%36%
2531
June1st to 10thDay
9%435%5%345%6%9%46%
2340
11th to 20thDay
8%5%24425%6%6%9%48%
2340
21st to endDay
5%32344446%7%57%
2340
July1st to 10thDay
9%415%5%37%7%9%11%39%
2340
11th to 20thDay
4314445%5%7%10%54%
2340
21st to endDay
7%5%26%5%35%5%8%11%43%
2546
August1st to 10thDay
6%4245%25%7%8%10%47%
2328
11th to 20thDay
9%5%245%346%7%9%45%
2301
21st to endDay
6%3245%35%5%5%9%53%
2390
September1st to 10thDay
11%42342345%8%54%
2112
11th to 20thDay
11%4245%345%6%7%47%
1980
21st to endDay
7%4245%3345%5%58%
1980
October1st to 10thDay
10%4235%34346%56%
1814
11th to 20thDay
13%5%14323235%59%
1800
21st to endDay
21%5%23323335%51%
1980
November1st to 10thDay
11%5%23323346%58%
1858
11th to 20thDay
12%6%24323346%55%
1805
21st to endDay
18%7%2331345%6%49%
1710
December1st to 10thDay
15%8%34433337%47%
1710
11th to 20thDay
14%9%36%5%24345%43%
2161
21st to endDay
17%15%6%6%42435%6%31%
3135
January1st to 10thNight
12%8%45%5%34445%46%
4108
11th to 20thNight
11%5%25%32345%6%53%
4120
21st to endNight
21%9%35%322235%45%
4532
February1st to 10thNight
15%10%35%323346%45%
2464
11th to 20thNight
15%7%35%423246%49%
2219
21st to endNight
16%9%34424445%46%
1682
March1st to 10thNight
14%6%35%42445%6%46%
1980
11th to 20thNight
17%6%35%32445%6%45%
1980
21st to endNight
16%6%35%5%34446%46%
2178
April1st to 10thNight
13%6%2333445%6%51%
1924
11th to 20thNight
13%6%24424447%50%
1775
21st to endNight
16%5%3442345%7%46%
1742
May1st to 10thNight
13%425%44445%8%47%
1620
11th to 20thNight
12%425%435%5%5%9%47%
1593
21st to endNight
10%5%245%35%5%7%10%43%
1745
June1st to 10thNight
5%4245%2346%10%56%
1620
11th to 20thNight
5%3233235%7%10%57%
1620
21st to endNight
411233345%8%65%
1620
July1st to 10thNight
6%3143346%7%12%51%
1620
11th to 20thNight
22133245%5%10%61%
1620
21st to endNight
32145%335%6%10%56%
1772
August1st to 10thNight
32145%35%6%7%10%54%
1611
11th to 20thNight
7%4234346%5%9%54%
1600
21st to endNight
341443346%9%59%
1966
September1st to 10thNight
9%31432345%6%60%
1844
11th to 20thNight
9%42442446%7%52%
1980
21st to endNight
7%42442345%6%59%
1980
October1st to 10thNight
8%323333446%61%
2126
11th to 20thNight
13%313323445%58%
2160
21st to endNight
17%6%23223435%54%
2376
November1st to 10thNight
11%5%23312235%63%
2220
11th to 20thNight
10%6%24323445%57%
2370
21st to endNight
17%6%23422345%53%
2470
December1st to 10thNight
14%7%25%5%24336%50%
2470
11th to 20thNight
14%8%35%434445%47%
3036
21st to endNight
17%11%6%6%423445%38%
4532

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
42%46%25%21%2
2848
11th to 20thDay
33%215%27%18%4
2850
21st to endDay
45%37%21%20%4
3135
February1st to 10thDay
47%49%22%15%3
1701
11th to 20thDay
43%39%25%17%3
1651
21st to endDay
46%37%20%17%7%
1574
March1st to 10thDay
40%28%22%19%9%
1980
11th to 20thDay
47%49%21%15%5%
1980
21st to endDay
51%49%22%12%2
2178
April1st to 10thDay
39%5%11%23%17%5%
2034
11th to 20thDay
44%412%21%15%4
2134
21st to endDay
47%49%22%15%2
2214
May1st to 10thDay
44%5%10%22%18%1
2340
11th to 20thDay
42%6%14%24%13%1
2306
21st to endDay
44%7%15%22%12%
2531
June1st to 10thDay
35%6%15%29%14%2
2340
11th to 20thDay
31%7%16%27%16%2
2340
21st to endDay
25%6%15%30%20%4
2340
July1st to 10thDay
35%9%17%26%13%1
2276
11th to 20thDay
23%7%16%32%19%3
2271
21st to endDay
31%8%17%30%13%1
2405
August1st to 10thDay
29%7%19%28%16%2
2314
11th to 20thDay
34%8%12%25%18%3
2301
21st to endDay
28%7%15%29%17%5%
2390
September1st to 10thDay
29%6%10%26%21%8%
2112
11th to 20thDay
34%6%10%22%22%6%
1980
21st to endDay
28%5%10%22%29%7%
1980
October1st to 10thDay
30%5%11%23%24%8%
1814
11th to 20thDay
29%36%24%29%9%
1800
21st to endDay
38%38%26%18%7%
1980
November1st to 10thDay
29%310%26%25%8%
1858
11th to 20thDay
32%38%26%23%8%
1805
21st to endDay
38%38%23%24%5%
1710
December1st to 10thDay
39%310%26%20%2
1710
11th to 20thDay
44%36%21%22%4
2159
21st to endDay
54%48%20%12%2
3135
January1st to 10thNight
43%28%23%21%3
4108
11th to 20thNight
32%317%21%24%2
4120
21st to endNight
44%39%19%21%4
4532
February1st to 10thNight
42%310%23%17%5%
2464
11th to 20thNight
40%38%26%20%4
2220
21st to endNight
42%27%19%23%8%
1682
March1st to 10thNight
38%5%8%18%21%10%
1980
11th to 20thNight
41%411%22%17%6%
1980
21st to endNight
41%49%27%15%4
2178
April1st to 10thNight
35%410%23%20%8%
1924
11th to 20thNight
35%5%11%23%19%8%
1775
21st to endNight
39%5%9%24%22%1
1742
May1st to 10thNight
36%6%13%22%20%3
1620
11th to 20thNight
35%6%14%24%18%2
1594
21st to endNight
35%8%17%25%14%1
1746
June1st to 10thNight
24%6%17%31%20%3
1620
11th to 20thNight
21%6%14%32%23%3
1620
21st to endNight
18%5%13%32%25%7%
1620
July1st to 10thNight
25%7%16%30%21%2
1575
11th to 20thNight
18%6%13%33%25%4
1566
21st to endNight
22%5%16%35%21%1
1673
August1st to 10thNight
23%7%16%33%19%2
1601
11th to 20thNight
27%6%12%25%26%4
1600
21st to endNight
22%6%14%30%22%6%
1966
September1st to 10thNight
26%49%27%25%9%
1844
11th to 20thNight
30%6%10%23%25%7%
1980
21st to endNight
26%5%7%25%30%7%
1980
October1st to 10thNight
24%412%24%26%10%
2126
11th to 20thNight
29%27%19%31%11%
2160
21st to endNight
36%37%21%24%10%
2376
November1st to 10thNight
27%29%25%27%10%
2220
11th to 20thNight
30%37%25%25%9%
2370
21st to endNight
36%38%21%27%6%
2470
December1st to 10thNight
38%310%23%21%5%
2470
11th to 20thNight
41%47%22%22%5%
3037
21st to endNight
49%49%19%16%4
4532

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
27%20%39%11%3
270
11th to 20thDay
29%24%37%8%2
270
21st to endDay
25%24%34%14%3
297
February1st to 10thDay
31%21%37%10%1
267
11th to 20thDay
30%32%27%11%1
240
21st to endDay
36%25%31%7%1
198
March1st to 10thDay
28%28%29%14%2
240
11th to 20thDay
35%20%33%12%
240
21st to endDay
33%24%34%7%2
264
April1st to 10thDay
21%25%34%14%5%1
294
11th to 20thDay
27%19%36%14%4
412
21st to endDay
27%21%33%14%5%
474
May1st to 10thDay
19%18%38%20%5%
603
11th to 20thDay
18%14%34%23%8%1
625
21st to endDay
15%10%36%21%13%4
679
June1st to 10thDay
10%7%24%34%22%3
630
11th to 20thDay
9%5%29%36%20%2
630
21st to endDay
6%433%36%18%4
630
July1st to 10thDay
8%417%35%28%7%
621
11th to 20thDay
4218%43%27%6%
618
21st to endDay
8%213%40%29%7%
684
August1st to 10thDay
8%216%45%25%4
626
11th to 20thDay
11%316%40%27%3
615
21st to endDay
8%114%39%32%7%
509
September1st to 10thDay
8%313%41%28%6%
402
11th to 20thDay
6%321%40%27%3
270
21st to endDay
11%5%23%36%22%3
270
October1st to 10thDay
10%11%36%26%14%3
270
11th to 20thDay
17%16%41%22%4
270
21st to endDay
31%17%31%15%5%
297
November1st to 10thDay
15%15%41%22%6%1
270
11th to 20thDay
17%20%37%19%6%1
270
21st to endDay
29%16%36%16%3
270
December1st to 10thDay
21%20%37%15%42
270
11th to 20thDay
24%21%39%10%41
270
21st to endDay
24%27%38%9%2
297
January1st to 10thNight
19%19%34%23%4
950
11th to 20thNight
23%20%35%19%3
950
21st to endNight
19%19%34%25%3
1045
February1st to 10thNight
24%19%35%19%3
948
11th to 20thNight
21%22%36%19%2
825
21st to endNight
24%20%35%19%2
498
March1st to 10thNight
20%18%34%25%3
540
11th to 20thNight
22%16%36%22%4
540
21st to endNight
20%18%40%17%4
594
April1st to 10thNight
19%20%34%22%5%
540
11th to 20thNight
17%16%39%22%7%
533
21st to endNight
19%14%42%17%8%1
540
May1st to 10thNight
14%12%38%29%7%
540
11th to 20thNight
14%9%33%31%13%
531
21st to endNight
11%7%37%24%19%2
584
June1st to 10thNight
6%420%43%26%1
540
11th to 20thNight
6%133%41%17%1
540
21st to endNight
4323%46%22%2
540
July1st to 10thNight
6%116%42%29%6%
525
11th to 20thNight
4117%44%30%4
522
21st to endNight
4110%47%35%3
591
August1st to 10thNight
3118%45%29%3
537
11th to 20thNight
8%216%47%24%3
534
21st to endNight
5%115%43%32%3
594
September1st to 10thNight
10%216%42%29%1
540
11th to 20thNight
11%217%43%23%4
540
21st to endNight
9%426%34%24%3
540
October1st to 10thNight
9%5%31%30%22%2
686
11th to 20thNight
15%9%36%30%9%
720
21st to endNight
21%13%29%26%10%1
792
November1st to 10thNight
14%12%38%26%9%
740
11th to 20thNight
16%15%36%26%7%
850
21st to endNight
24%15%32%23%7%
950
December1st to 10thNight
20%15%35%25%5%
950
11th to 20thNight
24%16%32%24%5%
950
21st to endNight
19%22%33%21%4
1045
Page generated at 2024-02-07 05:11:59. Version ac07

Copyright 2024 Attilla Danko


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