University of Oklahoma Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the University of Oklahoma Observatory clear sky chart from 2005-11-05 to 2017-12-20.

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
46%
16111
29%
48067
18%
16067
57%
16067
39%
26274

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
36%
899
32%
2327
13%
895
49%
895
41%
1315
January16th to endNight
37%
960
34%
2496
14%
960
49%
960
42%
1418
February1st to 15thNight
31%
778
25%
2187
9%
775
42%
775
35%
1287
February16th to endNight
29%
632
31%
1894
11%
632
44%
632
33%
1054
March1st to 15thNight
35%
564
26%
2004
16%
564
47%
564
27%
1131
March16th to endNight
28%
576
21%
2112
12%
576
42%
576
27%
1188
April1st to 15thNight
28%
539
23%
1974
11%
539
46%
539
29%
1026
April16th to endNight
33%
540
27%
1630
15%
540
50%
540
33%
944
May1st to 15thNight
34%
539
25%
1620
15%
539
50%
539
32%
966
May16th to endNight
49%
562
27%
1684
21%
561
61%
561
40%
927
June1st to 15thNight
60%
540
23%
1620
18%
540
69%
540
46%
831
June16th to endNight
65%
540
27%
1620
23%
540
71%
540
49%
814
July1st to 15thNight
73%
510
20%
1530
21%
510
76%
510
42%
837
July16th to endNight
87%
564
31%
1594
35%
531
89%
531
57%
756
August1st to 15thNight
81%
539
30%
1610
35%
536
83%
536
49%
815
August16th to endNight
78%
573
30%
1835
34%
573
80%
573
45%
918
September1st to 15thNight
63%
540
25%
1980
28%
540
67%
540
32%
1066
September16th to endNight
63%
537
34%
1980
31%
537
73%
537
38%
979
October1st to 15thNight
49%
610
31%
2050
23%
610
58%
610
37%
1071
October16th to endNight
48%
768
38%
2304
19%
768
61%
768
49%
1139
November1st to 15thNight
43%
867
29%
2387
13%
867
53%
867
44%
1293
November16th to endNight
37%
975
34%
2535
15%
975
48%
975
42%
1459
December1st to 15thNight
38%
975
31%
2535
13%
975
49%
975
39%
1473
December16th to endNight
34%
984
30%
2559
13%
984
46%
984
35%
1567

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
9%424424446%52%
48770
Night
8%313323347%57%
48263
Cloud CoverDay
9%42432445%6%52%
48768
Night
8%313323346%58%
48263
TransparencyDay
31%5%10%24%22%6%
48468
Night
27%49%24%25%8%
48068
SeeingDay
10%6%25%30%22%5%
5997
Night
10%8%31%33%14%1
16115

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 15thDay
9%423313445%56%
1611
16th to endDay
9%5%25%313236%57%
1728
February1st to 15thDay
10%6%34313336%52%
1684
16th to endDay
11%5%24413245%53%
1580
March1st to 15thDay
12%7%34423346%48%
1956
16th to endDay
14%8%24413336%47%
2112
April1st to 15thDay
10%424424445%53%
1974
16th to endDay
13%5%245%24335%48%
2328
May1st to 15thDay
13%6%35%42335%5%47%
2331
16th to endDay
10%5%245%346%6%7%43%
2430
June1st to 15thDay
7%42342445%9%52%
2340
16th to endDay
6%213425%5%6%8%55%
2340
July1st to 15thDay
7%3245%36%6%7%9%44%
2340
16th to endDay
41124245%7%10%54%
2466
August1st to 15thDay
4214446%5%6%8%51%
2340
16th to endDay
5%314435%6%6%9%49%
2363
September1st to 15thDay
11%41432445%7%49%
1980
16th to endDay
8%314412437%57%
1980
October1st to 15thDay
12%43212235%60%
1896
16th to endDay
6%31332233366%
1920
November1st to 15thDay
8%313213347%60%
1797
16th to endDay
9%31222222463%
1755
December1st to 15thDay
11%5%24313446%52%
1755
16th to endDay
14%6%24324235%50%
1764
January1st to 15thNight
8%31331233462%
2327
16th to endNight
8%323313335%61%
2496
February1st to 15thNight
11%5%2332323456%
2177
16th to endNight
10%423312347%55%
1894
March1st to 15thNight
9%5%24423436%52%
2004
16th to endNight
13%5%23323337%50%
2112
April1st to 15thNight
10%313223446%55%
1974
16th to endNight
12%323323345%54%
1630
May1st to 15thNight
9%433423445%53%
1619
16th to endNight
7%21342336%9%55%
1683
June1st to 15thNight
42133133410%60%
1620
16th to endNight
422221335%8%62%
1620
July1st to 15thNight
42144245%6%10%52%
1620
16th to endNight
21222336%11%62%
1702
August1st to 15thNight
3134245%6%11%56%
1620
16th to endNight
21134245%7%9%57%
1835
September1st to 15thNight
10%414423345%55%
1980
16th to endNight
6%314323348%56%
1980
October1st to 15thNight
9%313223346%58%
2050
16th to endNight
6%212212335%68%
2304
November1st to 15thNight
6%414323236%62%
2387
16th to endNight
9%313313235%61%
2535
December1st to 15thNight
10%31332335%6%56%
2535
16th to endNight
13%5%24313235%54%
2559

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
9%423323445%56%
1611
16th to endDay
9%5%24222235%57%
1728
February1st to 15thDay
10%5%34323336%52%
1684
16th to endDay
11%5%24313245%53%
1580
March1st to 15thDay
12%6%34423346%48%
1956
16th to endDay
14%8%24413335%48%
2110
April1st to 15thDay
10%424424345%54%
1974
16th to endDay
13%5%24433345%48%
2328
May1st to 15thDay
13%6%3442335%6%46%
2331
16th to endDay
10%5%245%346%6%7%43%
2430
June1st to 15thDay
7%42432445%8%52%
2340
16th to endDay
6%2134245%5%8%55%
2340
July1st to 15thDay
7%2145%36%5%7%10%43%
2340
16th to endDay
4212425%5%6%10%54%
2466
August1st to 15thDay
4214445%5%6%8%51%
2340
16th to endDay
5%314435%6%7%8%50%
2363
September1st to 15thDay
12%41442445%7%49%
1980
16th to endDay
8%32432245%6%57%
1980
October1st to 15thDay
12%31321223460%
1896
16th to endDay
6%31332233366%
1920
November1st to 15thDay
7%313213347%60%
1797
16th to endDay
9%412212335%63%
1755
December1st to 15thDay
10%5%24313346%52%
1755
16th to endDay
13%6%24324335%50%
1764
January1st to 15thNight
8%413313335%62%
2327
16th to endNight
8%32321334461%
2496
February1st to 15thNight
11%5%2332333456%
2177
16th to endNight
10%423313346%55%
1894
March1st to 15thNight
10%5%24324335%52%
2004
16th to endNight
12%5%23323347%50%
2112
April1st to 15thNight
10%313314446%55%
1974
16th to endNight
11%413323445%54%
1630
May1st to 15thNight
9%433324445%53%
1619
16th to endNight
7%21332346%8%55%
1683
June1st to 15thNight
5%31331335%9%60%
1620
16th to endNight
421222345%8%63%
1620
July1st to 15thNight
4213425%5%6%9%53%
1620
16th to endNight
21222346%11%63%
1702
August1st to 15thNight
3234235%6%11%56%
1620
16th to endNight
311332446%10%57%
1835
September1st to 15thNight
9%414423346%55%
1980
16th to endNight
7%324323448%56%
1980
October1st to 15thNight
10%313223346%59%
2050
16th to endNight
6%212211335%68%
2304
November1st to 15thNight
6%314322335%62%
2387
16th to endNight
9%32431223461%
2535
December1st to 15thNight
10%41332235%6%56%
2535
16th to endNight
13%5%24313235%54%
2559

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
30%38%25%26%5%
1612
16th to endDay
30%25%26%27%7%
1728
February1st to 15thDay
32%37%27%23%5%
1685
16th to endDay
34%26%24%24%7%
1580
March1st to 15thDay
37%47%23%18%8%
1956
16th to endDay
39%410%22%18%4
2112
April1st to 15thDay
32%5%10%24%19%7%
1974
16th to endDay
38%48%21%21%5%
2328
May1st to 15thDay
39%5%9%19%21%4
2331
16th to endDay
37%7%14%23%15%1
2434
June1st to 15thDay
30%5%16%25%20%2
2340
16th to endDay
26%7%13%24%22%5%
2340
July1st to 15thDay
32%8%15%26%15%1
2201
16th to endDay
21%7%14%30%23%2
2311
August1st to 15thDay
27%7%14%24%18%8%
2326
16th to endDay
28%8%12%28%17%5%
2363
September1st to 15thDay
33%6%10%23%19%8%
1980
16th to endDay
27%48%27%25%6%
1980
October1st to 15thDay
28%39%24%24%9%
1896
16th to endDay
23%37%22%30%12%
1920
November1st to 15thDay
24%39%25%27%9%
1797
16th to endDay
26%16%23%30%10%
1755
December1st to 15thDay
32%410%25%22%4
1755
16th to endDay
37%28%20%25%5%
1764
January1st to 15thNight
26%37%23%32%7%
2327
16th to endNight
26%37%22%31%9%
2496
February1st to 15thNight
32%36%24%24%7%
2187
16th to endNight
30%37%25%24%9%
1894
March1st to 15thNight
33%5%7%21%21%10%
2004
16th to endNight
34%411%23%19%5%
2112
April1st to 15thNight
29%411%22%20%10%
1974
16th to endNight
31%410%23%20%9%
1630
May1st to 15thNight
33%5%10%19%22%8%
1620
16th to endNight
25%6%15%29%18%3
1685
June1st to 15thNight
21%5%16%30%21%4
1620
16th to endNight
19%5%12%28%26%7%
1620
July1st to 15thNight
24%6%14%29%22%2
1530
16th to endNight
14%5%13%32%29%4
1594
August1st to 15thNight
19%6%14%25%25%7%
1610
16th to endNight
21%6%13%28%23%7%
1835
September1st to 15thNight
31%48%22%21%11%
1980
16th to endNight
25%48%25%26%9%
1980
October1st to 15thNight
27%411%20%22%13%
2050
16th to endNight
20%26%21%34%14%
2304
November1st to 15thNight
24%39%22%28%11%
2387
16th to endNight
27%26%22%29%11%
2535
December1st to 15thNight
28%39%25%25%8%
2535
16th to endNight
33%38%20%25%8%
2559

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
16%11%43%24%4
90
16th to endDay
11%14%48%18%5%1
96
February1st to 15thDay
10%12%52%21%4
90
16th to endDay
9%14%55%17%2
81
March1st to 15thDay
18%17%43%15%31
90
16th to endDay
11%19%34%22%9%2
96
April1st to 15thDay
8%12%35%39%3
93
16th to endDay
19%11%37%24%5%1
438
May1st to 15thDay
13%13%35%27%8%1
468
16th to endDay
14%8%34%22%16%3
517
June1st to 15thDay
7%226%34%22%5%
495
16th to endDay
6%218%37%25%8%
495
July1st to 15thDay
8%113%38%30%8%
475
16th to endDay
4429%48%12%
515
August1st to 15thDay
6%8%35%41%7%
493
16th to endDay
8%11%39%30%10%
403
September1st to 15thDay
28%31%39%17%
135
16th to endDay
12%13%39%20%14%
135
October1st to 15thDay
8%7%28%27%20%7%
135
16th to endDay
7%10%31%30%18%2
144
November1st to 15thDay
22%5%32%19%16%4
135
16th to endDay
17%15%37%20%8%
135
December1st to 15thDay
7%9%45%28%5%2
135
16th to endDay
22%12%39%19%5%
108
January1st to 15thNight
11%13%35%32%5%
900
16th to endNight
9%10%39%32%7%
960
February1st to 15thNight
14%12%40%27%5%
779
16th to endNight
13%14%40%26%4
632
March1st to 15thNight
14%12%34%34%4
564
16th to endNight
16%11%40%24%6%
576
April1st to 15thNight
13%14%41%23%5%
539
16th to endNight
14%11%39%27%7%
540
May1st to 15thNight
10%8%42%25%11%1
540
16th to endNight
9%333%31%18%2
563
June1st to 15thNight
6%325%42%20%2
540
16th to endNight
4223%45%22%2
540
July1st to 15thNight
5%13%51%26%1
510
16th to endNight
2444%43%3
564
August1st to 15thNight
38%46%38%3
539
16th to endNight
312%39%39%4
573
September1st to 15thNight
12%115%34%32%2
540
16th to endNight
8%120%40%21%6%
537
October1st to 15thNight
11%431%30%19%2
610
16th to endNight
8%8%32%34%15%
768
November1st to 15thNight
8%9%34%32%12%1
867
16th to endNight
12%10%38%28%9%
975
December1st to 15thNight
13%12%32%32%7%
975
16th to endNight
17%10%35%29%7%
984
Page generated at 2017-12-21 06:04:48. Version ac04

Copyright 2017 A. Danko


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