OKAstronomy Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the OKAstronomy Observatory clear sky chart from 2005-11-05 to 2017-12-02.

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
39%
16039
26%
47802
15%
15992
50%
15992
33%
27504

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 15thNight
24%
899
28%
2327
8%
895
38%
895
32%
1400
January16th to endNight
27%
960
31%
2496
11%
960
39%
960
33%
1486
February1st to 15thNight
22%
880
22%
2288
6%
876
32%
876
29%
1434
February16th to endNight
19%
591
27%
1853
7%
591
36%
591
26%
1071
March1st to 15thNight
25%
540
23%
1980
11%
540
40%
540
21%
1192
March16th to endNight
25%
576
20%
2112
13%
576
36%
576
22%
1268
April1st to 15thNight
23%
539
22%
1879
10%
539
41%
539
25%
1076
April16th to endNight
27%
540
23%
1761
9%
540
46%
540
29%
1050
May1st to 15thNight
34%
540
22%
1619
14%
539
47%
539
29%
1010
May16th to endNight
43%
563
20%
1685
15%
561
52%
561
31%
1028
June1st to 15thNight
55%
540
21%
1620
16%
540
63%
540
44%
850
June16th to endNight
62%
540
25%
1620
18%
540
71%
540
47%
822
July1st to 15thNight
64%
510
19%
1530
18%
510
68%
510
42%
842
July16th to endNight
80%
564
29%
1594
32%
531
82%
531
50%
799
August1st to 15thNight
74%
539
27%
1610
30%
536
77%
536
45%
847
August16th to endNight
69%
573
27%
1842
30%
573
73%
573
39%
1002
September1st to 15thNight
62%
540
27%
1890
27%
540
68%
540
35%
1014
September16th to endNight
59%
537
33%
1980
29%
537
68%
537
35%
995
October1st to 15thNight
43%
698
29%
2138
18%
698
52%
698
38%
1172
October16th to endNight
39%
768
35%
2304
18%
768
53%
768
40%
1202
November1st to 15thNight
34%
760
31%
2280
13%
760
49%
760
36%
1231
November16th to endNight
29%
972
30%
2532
13%
972
41%
972
33%
1546
December1st to 15thNight
26%
910
24%
2366
8%
910
37%
910
28%
1514
December16th to endNight
24%
960
26%
2496
8%
960
36%
960
26%
1653

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
12%5%2442445%6%46%
48641
Night
10%424323346%52%
47998
TransparencyDay
36%5%11%25%17%3
48341
Night
31%411%25%21%5%
47803
SeeingDay
13%9%26%29%16%3
5989
Night
14%11%31%28%12%1
16040

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 15thDay
13%7%2331324352%
1611
16th to endDay
12%6%24313345%52%
1728
February1st to 15thDay
14%8%35%42234445%
1575
16th to endDay
14%7%3442335%5%45%
1629
March1st to 15thDay
17%6%2441435%6%43%
1980
16th to endDay
20%8%35%424345%37%
2110
April1st to 15thDay
15%6%24424445%45%
2067
16th to endDay
20%8%25%5%23345%39%
2196
May1st to 15thDay
17%6%345%3445%5%39%
2331
16th to endDay
11%5%26%6%36%5%6%8%38%
2430
June1st to 15thDay
9%5%244245%6%8%45%
2340
16th to endDay
7%3233245%6%9%49%
2340
July1st to 15thDay
9%5%15%436%6%8%9%38%
2340
16th to endDay
5%3144445%7%11%46%
2466
August1st to 15thDay
5%313425%7%8%10%45%
2340
16th to endDay
8%4245%345%6%9%46%
2360
September1st to 15thDay
13%4244235%5%7%47%
2067
16th to endDay
8%32442346%5%53%
1980
October1st to 15thDay
14%413423235%52%
1809
16th to endDay
12%41321323460%
1920
November1st to 15thDay
11%5%23312246%55%
1908
16th to endDay
16%6%1231234453%
1755
December1st to 15thDay
16%7%23413236%46%
1631
16th to endDay
16%8%24323235%45%
1728
January1st to 15thNight
14%423322235%55%
2327
16th to endNight
11%424312245%56%
2496
February1st to 15thNight
12%7%24322235%50%
2278
16th to endNight
11%5%24324346%51%
1853
March1st to 15thNight
14%6%3432445%6%44%
1980
16th to endNight
16%5%24424346%46%
2112
April1st to 15thNight
12%5%14423446%50%
1879
16th to endNight
13%5%2442335%6%48%
1761
May1st to 15thNight
12%425%434437%47%
1619
16th to endNight
10%424435%5%6%9%44%
1683
June1st to 15thNight
441441235%9%58%
1620
16th to endNight
41123235%6%8%59%
1620
July1st to 15thNight
6%3133235%6%12%51%
1620
16th to endNight
311342345%11%57%
1702
August1st to 15thNight
32123245%6%10%55%
1620
16th to endNight
43134345%7%9%52%
1842
September1st to 15thNight
11%42321345%6%54%
1890
16th to endNight
6%42432345%6%57%
1980
October1st to 15thNight
11%413323447%54%
2138
16th to endNight
10%31221243462%
2304
November1st to 15thNight
10%413312335%60%
2280
16th to endNight
13%5%2332223455%
2532
December1st to 15thNight
14%6%24423336%48%
2366
16th to endNight
14%8%35%323335%45%
2496

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 15thDay
37%37%26%20%3
1612
16th to endDay
34%29%30%19%3
1728
February1st to 15thDay
42%310%26%14%2
1576
16th to endDay
39%39%27%15%4
1629
March1st to 15thDay
41%310%22%16%5%
1980
16th to endDay
49%39%21%13%1
2112
April1st to 15thDay
40%412%22%16%3
2067
16th to endDay
48%49%19%16%2
2196
May1st to 15thDay
46%5%9%19%17%1
2331
16th to endDay
42%7%13%22%13%
2434
June1st to 15thDay
34%6%14%27%16%
2340
16th to endDay
29%6%16%26%17%2
2340
July1st to 15thDay
35%8%15%28%10%
2201
16th to endDay
28%6%17%32%14%1
2311
August1st to 15thDay
29%8%16%25%17%3
2326
16th to endDay
32%7%14%25%14%4
2360
September1st to 15thDay
35%6%10%22%16%8%
2067
16th to endDay
29%5%11%25%23%5%
1980
October1st to 15thDay
34%310%23%20%8%
1809
16th to endDay
27%28%27%25%8%
1920
November1st to 15thDay
30%210%27%21%7%
1908
16th to endDay
34%37%24%25%4
1755
December1st to 15thDay
41%211%25%16%2
1631
16th to endDay
41%38%25%16%4
1728
January1st to 15thNight
33%29%27%23%4
2327
16th to endNight
30%39%28%23%5%
2496
February1st to 15thNight
36%310%27%18%4
2288
16th to endNight
34%310%26%20%4
1853
March1st to 15thNight
39%5%10%18%19%6%
1980
16th to endNight
39%411%26%15%3
2112
April1st to 15thNight
34%5%11%21%20%7%
1879
16th to endNight
36%410%24%20%3
1761
May1st to 15thNight
37%5%12%19%21%3
1620
16th to endNight
33%7%17%25%15%1
1685
June1st to 15thNight
22%5%15%31%21%2
1620
16th to endNight
20%6%14%31%23%5%
1620
July1st to 15thNight
25%6%14%32%19%1
1530
16th to endNight
20%413%37%21%2
1594
August1st to 15thNight
21%6%15%28%23%3
1610
16th to endNight
26%6%13%29%19%5%
1842
September1st to 15thNight
30%39%25%19%11%
1890
16th to endNight
27%48%26%26%5%
1980
October1st to 15thNight
29%312%20%22%11%
2138
16th to endNight
25%27%23%30%11%
2304
November1st to 15thNight
28%29%26%23%9%
2280
16th to endNight
34%37%22%27%5%
2532
December1st to 15thNight
37%310%23%18%4
2366
16th to endNight
41%39%20%19%4
2496

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 15thDay
25%22%38%8%4
90
16th to endDay
12%38%30%14%31
96
February1st to 15thDay
21%26%38%13%
90
16th to endDay
22%29%30%14%2
81
March1st to 15thDay
27%24%42%41
90
16th to endDay
25%20%36%16%1
96
April1st to 15thDay
22%17%38%16%6%
186
16th to endDay
28%15%31%16%8%
306
May1st to 15thDay
19%16%35%20%6%1
468
16th to endDay
16%12%37%20%11%1
517
June1st to 15thDay
10%5%28%36%17%2
495
16th to endDay
8%327%38%18%4
495
July1st to 15thDay
10%222%40%20%3
475
16th to endDay
5%19%38%36%9%
515
August1st to 15thDay
7%113%41%30%4
493
16th to endDay
10%115%41%26%5%
400
September1st to 15thDay
4414%39%33%4
222
16th to endDay
5%224%43%20%3
135
October1st to 15thDay
13%11%36%31%6%1
135
16th to endDay
15%11%38%27%7%
144
November1st to 15thDay
18%10%34%25%9%
135
16th to endDay
29%24%28%14%2
135
December1st to 15thDay
21%27%32%11%33
94
16th to endDay
17%27%46%7%1
96
January1st to 15thNight
20%19%35%20%5%
900
16th to endNight
16%20%35%24%3
960
February1st to 15thNight
19%20%35%21%2
880
16th to endNight
16%19%40%20%2
591
March1st to 15thNight
21%16%33%25%2
540
16th to endNight
16%17%39%21%5%
576
April1st to 15thNight
17%18%39%19%5%
539
16th to endNight
16%12%43%17%9%
540
May1st to 15thNight
15%10%37%26%10%
540
16th to endNight
11%7%34%28%16%1
563
June1st to 15thNight
6%229%40%18%1
540
16th to endNight
5%225%41%23%2
540
July1st to 15thNight
7%120%42%23%3
510
16th to endNight
37%44%40%3
564
August1st to 15thNight
4114%43%31%5%
539
16th to endNight
6%117%42%27%3
573
September1st to 15thNight
12%215%40%26%2
540
16th to endNight
8%223%36%25%3
537
October1st to 15thNight
12%5%34%26%18%2
698
16th to endNight
12%13%32%28%12%1
768
November1st to 15thNight
13%15%34%26%10%
760
16th to endNight
20%14%34%22%7%
972
December1st to 15thNight
21%14%34%23%5%
910
16th to endNight
21%18%32%21%4
960
Page generated at 2017-12-03 10:16:45. Version ac04

Copyright 2017 A. Danko


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