White House Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the White House Observatory clear sky chart from 2005-11-06 to 2024-01-12.

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
47%
23393
22%
74015
16%
23339
54%
23339
27%
45803

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
23%
760
21%
2459
9%
757
37%
757
21%
1570
January11th to 20thNight
24%
727
20%
2290
9%
727
34%
727
17%
1587
January21st to endNight
24%
792
28%
2376
12%
792
40%
792
24%
1557
February1st to 10thNight
26%
720
21%
2160
10%
720
36%
720
23%
1441
February11th to 20thNight
23%
703
18%
2098
8%
699
32%
699
20%
1420
February21st to endNight
21%
592
21%
1776
8%
592
31%
592
18%
1256
March1st to 10thNight
30%
720
21%
2160
11%
720
38%
720
26%
1355
March11th to 20thNight
30%
720
17%
2087
9%
720
37%
720
24%
1407
March21st to endNight
34%
656
22%
2042
13%
656
43%
656
26%
1299
April1st to 10thNight
37%
540
26%
1800
17%
540
50%
540
29%
1046
April11th to 20thNight
41%
533
27%
1775
18%
533
55%
533
30%
1010
April21st to endNight
42%
540
25%
1800
18%
540
53%
540
31%
1017
May1st to 10thNight
51%
540
22%
1658
14%
540
59%
540
34%
971
May11th to 20thNight
55%
531
19%
1592
14%
531
60%
531
29%
991
May21st to endNight
65%
582
21%
1744
18%
582
67%
582
32%
1062
June1st to 10thNight
65%
540
19%
1620
16%
540
67%
540
30%
1000
June11th to 20thNight
77%
540
23%
1556
18%
540
80%
540
43%
850
June21st to endNight
72%
540
21%
1440
15%
540
75%
540
39%
873
July1st to 10thNight
71%
525
14%
1400
11%
525
72%
525
30%
930
July11th to 20thNight
75%
522
16%
1536
15%
522
76%
522
33%
957
July21st to endNight
73%
591
16%
1715
16%
558
74%
558
27%
1111
August1st to 10thNight
82%
537
17%
1778
19%
534
82%
534
33%
1033
August11th to 20thNight
73%
534
15%
1776
18%
534
74%
534
26%
1113
August21st to endNight
68%
594
20%
1980
24%
594
68%
594
25%
1246
September1st to 10thNight
70%
540
23%
1800
26%
540
71%
540
32%
1032
September11th to 20thNight
62%
716
22%
1976
18%
716
64%
716
33%
1239
September21st to endNight
65%
720
30%
1980
21%
720
70%
720
39%
1158
October1st to 10thNight
61%
720
33%
1980
25%
720
66%
720
43%
1110
October11th to 20thNight
49%
720
30%
2015
21%
720
57%
720
34%
1218
October21st to endNight
48%
792
29%
2502
25%
792
55%
792
32%
1453
November1st to 10thNight
52%
740
28%
2406
25%
740
59%
740
33%
1335
November11th to 20thNight
40%
760
29%
2470
20%
760
54%
760
32%
1420
November21st to endNight
38%
760
25%
2470
18%
760
49%
760
26%
1490
December1st to 10thNight
30%
760
23%
2470
13%
760
42%
760
20%
1624
December11th to 20thNight
32%
759
25%
2903
14%
758
43%
758
20%
1746
December21st to endNight
25%
827
13%
4425
11%
817
36%
817
11%
2876

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
11%6%36%6%35%5%6%8%41%
75244
Night
12%6%35%5%345%5%7%45%
74466
TransparencyDay
39%8%12%20%17%4
74964
Night
37%7%11%20%19%5%
74266
SeeingDay
15%10%22%24%19%10%
13776
Night
15%8%24%29%20%4
23405

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
17%8%37%5%33346%41%
1706
11th to 20thDay
18%10%46%5%24445%37%
1697
21st to endDay
15%6%35%5%2445%6%46%
1980
February1st to 10thDay
16%9%46%6%3445%6%39%
1800
11th to 20thDay
18%8%5%7%5%34445%37%
1748
21st to endDay
18%10%45%5%345%45%38%
1480
March1st to 10thDay
13%8%36%5%445%5%5%42%
1800
11th to 20thDay
15%8%37%6%446%6%6%36%
1872
21st to endDay
13%7%36%7%35%5%6%8%37%
2328
April1st to 10thDay
11%5%35%5%335%6%7%48%
2160
11th to 20thDay
12%6%25%5%3445%7%46%
2134
21st to endDay
9%5%35%5%35%5%6%8%46%
2160
May1st to 10thDay
13%6%35%425%45%8%46%
2299
11th to 20thDay
11%5%26%6%36%5%6%9%40%
2301
21st to endDay
9%5%36%5%45%6%7%10%41%
2531
June1st to 10thDay
9%5%36%7%46%7%6%9%38%
2340
11th to 20thDay
43245%46%7%8%11%45%
2395
21st to endDay
6%435%6%5%6%6%7%9%43%
2520
July1st to 10thDay
9%5%37%8%48%8%8%11%29%
2520
11th to 20thDay
8%425%6%5%9%7%9%11%34%
2368
21st to endDay
6%436%8%48%9%9%12%32%
2497
August1st to 10thDay
5%5%26%7%49%7%8%13%34%
2148
11th to 20thDay
8%5%35%7%5%8%7%9%9%35%
2125
21st to endDay
11%5%37%7%5%6%6%7%9%35%
2376
September1st to 10thDay
11%5%25%5%46%6%7%8%42%
2144
11th to 20thDay
11%5%36%5%46%5%5%8%42%
1980
21st to endDay
10%5%245%24447%53%
1980
October1st to 10thDay
10%425%42445%5%54%
1980
11th to 20thDay
10%5%2443445%7%54%
1942
21st to endDay
13%5%25%433445%51%
1854
November1st to 10thDay
11%424424445%56%
1672
11th to 20thDay
11%5%35%434345%52%
1710
21st to endDay
14%6%35%6%245%5%6%44%
1710
December1st to 10thDay
18%8%37%6%346%6%436%
1710
11th to 20thDay
14%8%46%5%35%446%41%
2153
21st to endDay
13%10%46%6%345%6%7%35%
3124
January1st to 10thNight
16%7%26%5%35%445%44%
2459
11th to 20thNight
17%9%46%6%35%35%6%36%
2290
21st to endNight
14%8%35%6%35%34444%
2376
February1st to 10thNight
17%9%36%5%24446%41%
2160
11th to 20thNight
19%8%35%5%2445%5%41%
2098
21st to endNight
20%7%45%6%35%45%5%37%
1776
March1st to 10thNight
15%6%3443445%7%45%
2160
11th to 20thNight
14%8%35%5%345%6%7%40%
2087
21st to endNight
13%6%25%5%345%5%6%44%
2042
April1st to 10thNight
10%425%5%345%6%9%47%
1800
11th to 20thNight
13%4245%2445%8%50%
1775
21st to endNight
11%4244345%5%7%51%
1800
May1st to 10thNight
8%5%244345%5%8%52%
1658
11th to 20thNight
9%435%5%45%6%6%9%45%
1592
21st to endNight
6%425%6%36%5%6%11%46%
1744
June1st to 10thNight
5%436%7%35%5%7%10%45%
1620
11th to 20thNight
33134346%7%12%53%
1556
21st to endNight
4335%425%6%7%10%50%
1440
July1st to 10thNight
9%436%5%37%6%7%9%41%
1440
11th to 20thNight
5%5%34446%6%9%12%42%
1588
21st to endNight
4425%6%5%6%7%8%13%39%
1816
August1st to 10thNight
42146%46%8%8%12%45%
1790
11th to 20thNight
6%425%6%35%8%8%11%41%
1776
21st to endNight
10%5%25%5%46%6%6%8%43%
1980
September1st to 10thNight
8%4244345%7%9%49%
1800
11th to 20thNight
9%6%26%5%3446%8%46%
1976
21st to endNight
9%42443445%7%55%
1980
October1st to 10thNight
10%413333336%61%
1980
11th to 20thNight
12%5%25%423446%52%
2015
21st to endNight
14%6%24423345%53%
2502
November1st to 10thNight
12%42432345%5%56%
2406
11th to 20thNight
11%6%24433446%53%
2470
21st to endNight
16%5%245%3435%5%48%
2470
December1st to 10thNight
17%8%35%5%345%5%6%39%
2470
11th to 20thNight
14%7%25%42445%5%47%
3042
21st to endNight
14%9%47%7%46%6%6%6%32%
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
44%48%19%19%5%
1707
11th to 20thDay
50%47%18%17%3
1697
21st to endDay
40%5%7%23%22%4
1980
February1st to 10thDay
48%47%19%19%3
1800
11th to 20thDay
51%5%6%19%16%4
1758
21st to endDay
48%5%9%13%19%6%
1480
March1st to 10thDay
43%6%8%15%19%9%
1800
11th to 20thDay
47%8%11%14%17%4
1872
21st to endDay
45%6%11%21%15%1
2328
April1st to 10thDay
34%7%11%24%17%6%
2160
11th to 20thDay
37%6%9%20%22%6%
2134
21st to endDay
34%7%10%27%19%2
2160
May1st to 10thDay
36%8%10%24%17%4
2299
11th to 20thDay
40%10%12%23%14%1
2305
21st to endDay
35%11%15%23%15%2
2531
June1st to 10thDay
40%10%13%18%17%1
2340
11th to 20thDay
28%12%17%25%16%2
2395
21st to endDay
35%11%16%20%14%4
2520
July1st to 10thDay
42%13%18%17%9%2
2451
11th to 20thDay
38%13%20%18%8%2
2297
21st to endDay
38%15%18%20%9%1
2357
August1st to 10thDay
37%13%18%22%9%1
2136
11th to 20thDay
39%12%16%19%12%1
2125
21st to endDay
43%12%12%20%10%3
2376
September1st to 10thDay
36%10%15%18%16%4
2144
11th to 20thDay
38%9%12%16%21%4
1980
21st to endDay
32%6%12%23%21%7%
1980
October1st to 10thDay
31%6%8%23%26%6%
1980
11th to 20thDay
30%6%10%20%26%8%
1942
21st to endDay
35%5%5%18%28%8%
1854
November1st to 10thDay
31%48%19%28%9%
1672
11th to 20thDay
35%47%20%26%8%
1710
21st to endDay
41%5%6%19%23%6%
1710
December1st to 10thDay
49%6%8%15%18%4
1710
11th to 20thDay
45%5%7%20%19%4
2150
21st to endDay
45%8%11%19%13%3
3124
January1st to 10thNight
44%49%20%20%4
2459
11th to 20thNight
50%6%8%18%16%4
2290
21st to endNight
43%45%21%21%5%
2376
February1st to 10thNight
46%49%18%19%4
2160
11th to 20thNight
46%5%7%17%18%6%
2099
21st to endNight
50%5%6%15%17%6%
1776
March1st to 10thNight
39%5%10%17%19%10%
2160
11th to 20thNight
43%7%11%18%17%5%
2087
21st to endNight
39%7%10%22%18%3
2042
April1st to 10thNight
34%6%12%25%19%4
1800
11th to 20thNight
33%6%9%20%22%11%
1775
21st to endNight
32%7%12%26%21%4
1800
May1st to 10thNight
31%7%12%22%24%4
1658
11th to 20thNight
34%10%18%20%17%2
1593
21st to endNight
30%11%14%26%15%4
1745
June1st to 10thNight
33%10%15%21%19%2
1620
11th to 20thNight
22%9%18%29%19%3
1556
21st to endNight
27%10%16%26%18%4
1440
July1st to 10thNight
36%11%22%20%10%3
1400
11th to 20thNight
29%12%23%22%11%2
1536
21st to endNight
32%15%21%21%11%1
1715
August1st to 10thNight
25%14%22%27%12%1
1778
11th to 20thNight
32%14%20%19%12%3
1776
21st to endNight
36%10%16%21%11%5%
1980
September1st to 10thNight
29%10%18%21%18%4
1800
11th to 20thNight
34%8%15%16%23%4
1976
21st to endNight
29%6%9%23%24%9%
1980
October1st to 10thNight
27%48%23%28%10%
1980
11th to 20thNight
34%5%8%20%22%11%
2015
21st to endNight
34%46%18%28%9%
2502
November1st to 10thNight
31%5%8%20%24%12%
2406
11th to 20thNight
33%47%16%28%11%
2470
21st to endNight
38%5%7%20%24%6%
2470
December1st to 10thNight
45%6%8%18%19%3
2470
11th to 20thNight
39%5%7%19%25%5%
3044
21st to endNight
47%9%10%18%14%3
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
23%27%34%12%4
270
11th to 20thDay
26%23%34%10%5%2
243
21st to endDay
20%27%38%11%31
264
February1st to 10thDay
22%28%32%17%1
240
11th to 20thDay
35%20%34%10%1
240
21st to endDay
33%22%35%9%2
198
March1st to 10thDay
26%20%33%18%31
240
11th to 20thDay
23%19%35%16%6%1
312
21st to endDay
20%19%34%18%8%
462
April1st to 10thDay
17%16%33%22%10%2
420
11th to 20thDay
18%17%29%23%12%1
412
21st to endDay
16%12%29%29%12%2
420
May1st to 10thDay
18%7%29%27%12%7%
423
11th to 20thDay
11%6%24%28%21%10%
447
21st to endDay
11%5%18%29%22%15%
485
June1st to 10thDay
12%414%30%23%16%
450
11th to 20thDay
5%315%29%27%21%
505
21st to endDay
8%317%29%29%14%
630
July1st to 10thDay
10%29%30%29%19%
621
11th to 20thDay
7%29%22%30%30%
470
21st to endDay
5%110%23%36%25%
488
August1st to 10thDay
7%311%24%32%24%
446
11th to 20thDay
9%18%30%36%16%
439
21st to endDay
15%29%21%34%20%
495
September1st to 10thDay
10%310%25%37%15%
450
11th to 20thDay
10%215%22%32%19%
450
21st to endDay
13%314%28%33%9%
450
October1st to 10thDay
11%420%30%26%10%
450
11th to 20thDay
11%11%27%35%14%2
412
21st to endDay
21%14%24%27%12%2
297
November1st to 10thDay
21%9%29%25%15%1
270
11th to 20thDay
15%17%37%25%6%1
270
21st to endDay
16%19%32%24%7%2
270
December1st to 10thDay
27%20%28%19%5%
270
11th to 20thDay
17%25%33%15%10%
270
21st to endDay
24%20%39%12%5%
297
January1st to 10thNight
21%18%37%20%5%
760
11th to 20thNight
21%18%33%22%7%
727
21st to endNight
19%16%38%24%2
792
February1st to 10thNight
22%13%36%25%5%
720
11th to 20thNight
26%16%33%23%3
703
21st to endNight
26%16%33%23%2
592
March1st to 10thNight
19%15%33%27%6%
720
11th to 20thNight
18%13%36%24%8%1
720
21st to endNight
16%12%34%26%12%
656
April1st to 10thNight
13%11%36%27%13%
540
11th to 20thNight
14%9%33%31%12%1
533
21st to endNight
13%8%32%29%17%1
540
May1st to 10thNight
9%7%28%33%20%3
540
11th to 20thNight
11%5%21%35%25%4
531
21st to endNight
8%216%35%33%6%
584
June1st to 10thNight
6%215%35%34%7%
540
11th to 20thNight
5%111%34%38%11%
540
21st to endNight
5%212%33%40%9%
540
July1st to 10thNight
8%27%28%42%13%
525
11th to 20thNight
7%18%27%42%16%
522
21st to endNight
6%110%30%41%13%
591
August1st to 10thNight
5%1327%52%12%
537
11th to 20thNight
7%16%32%43%10%
534
21st to endNight
11%18%27%43%9%
594
September1st to 10thNight
9%110%29%43%7%
540
11th to 20thNight
11%214%30%37%6%
716
21st to endNight
10%116%33%36%3
720
October1st to 10thNight
11%319%30%29%7%
720
11th to 20thNight
15%6%24%34%19%2
720
21st to endNight
17%8%23%31%19%2
792
November1st to 10thNight
14%8%21%34%19%3
740
11th to 20thNight
14%10%32%31%12%1
760
21st to endNight
18%12%28%29%11%1
760
December1st to 10thNight
22%14%29%27%7%
760
11th to 20thNight
20%12%32%26%9%
760
21st to endNight
23%14%33%25%5%
836
Page generated at 2024-01-09 06:14:45. Version ac07

Copyright 2024 Attilla Danko


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