White Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the White Mountain clear sky chart from 2005-11-06 to 2024-03-06.

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
54%
24821
20%
80426
17%
24741
59%
24741
31%
47657

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
48%
885
13%
4297
11%
877
52%
877
16%
2758
January11th to 20thNight
45%
757
16%
4077
14%
740
53%
740
14%
2543
January21st to endNight
47%
825
10%
4509
14%
814
53%
814
12%
3319
February1st to 10thNight
42%
760
15%
2470
12%
760
49%
760
24%
1563
February11th to 20thNight
47%
741
16%
2403
14%
740
52%
740
27%
1467
February21st to endNight
45%
628
17%
1937
12%
628
52%
628
26%
1241
March1st to 10thNight
49%
742
16%
2040
12%
742
52%
742
28%
1350
March11th to 20thNight
53%
720
20%
1980
13%
720
59%
720
35%
1204
March21st to endNight
44%
792
16%
2178
10%
792
49%
792
29%
1418
April1st to 10thNight
43%
586
18%
1846
11%
586
51%
586
27%
1116
April11th to 20thNight
42%
533
18%
1777
14%
533
47%
533
25%
1102
April21st to endNight
47%
540
21%
1620
15%
540
54%
540
28%
986
May1st to 10thNight
47%
540
19%
1620
14%
540
51%
540
30%
967
May11th to 20thNight
54%
531
20%
1525
17%
531
56%
531
36%
910
May21st to endNight
55%
584
20%
1552
17%
582
58%
582
34%
949
June1st to 10thNight
59%
540
22%
1440
15%
540
65%
540
46%
799
June11th to 20thNight
55%
540
25%
1440
18%
540
61%
540
48%
771
June21st to endNight
70%
540
29%
1440
26%
540
73%
540
61%
704
July1st to 10thNight
73%
525
20%
1400
18%
525
76%
525
46%
775
July11th to 20thNight
71%
522
24%
1490
22%
522
73%
522
50%
762
July21st to endNight
76%
591
26%
1674
25%
558
77%
558
49%
840
August1st to 10thNight
74%
537
27%
1602
24%
534
75%
534
45%
831
August11th to 20thNight
76%
534
34%
1602
28%
534
79%
534
52%
774
August21st to endNight
75%
594
34%
1898
33%
594
78%
594
50%
897
September1st to 10thNight
72%
540
36%
1800
33%
540
79%
540
54%
776
September11th to 20thNight
70%
654
33%
1914
27%
654
75%
654
53%
952
September21st to endNight
68%
720
34%
1997
25%
720
74%
720
55%
1003
October1st to 10thNight
57%
720
26%
2160
18%
720
63%
720
41%
1170
October11th to 20thNight
58%
720
32%
2160
21%
720
67%
720
44%
1109
October21st to endNight
56%
792
29%
2376
20%
792
63%
792
41%
1271
November1st to 10thNight
56%
759
27%
2307
20%
759
63%
759
37%
1304
November11th to 20thNight
50%
950
22%
2660
15%
950
54%
950
37%
1564
November21st to endNight
53%
950
21%
2660
16%
950
57%
950
35%
1579
December1st to 10thNight
45%
950
14%
2660
10%
950
48%
950
27%
1754
December11th to 20thNight
44%
948
16%
3155
11%
948
47%
948
22%
2066
December21st to endNight
37%
1031
7%
4760
7%
1026
41%
1026
13%
3063

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
46%36%6%45%5%6%8%47%
78650
Night
36%36%6%35%5%6%8%48%
80940
TransparencyDay
31%9%14%21%17%8%
78366
Night
30%9%16%23%16%6%
80746
SeeingDay
7%10%25%30%21%8%
14556
Night
6%7%25%42%19%1
24870

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
25%411%11%6%8%8%7%9%30%
2643
11th to 20thDay
27%412%11%5%6%5%6%8%35%
2860
21st to endDay
28%6%17%12%7%5%35%6%28%
3146
February1st to 10thDay
38%47%7%46%6%6%9%41%
1710
11th to 20thDay
37%48%7%47%5%6%9%40%
1665
21st to endDay
27%48%7%45%7%7%7%42%
1514
March1st to 10thDay
38%47%6%35%6%7%10%41%
2036
11th to 20thDay
27%37%7%46%7%7%10%40%
1980
21st to endDay
411%47%6%36%5%7%8%38%
2178
April1st to 10thDay
5%10%36%5%35%5%6%9%42%
2114
11th to 20thDay
5%9%37%5%45%6%6%7%41%
2131
21st to endDay
5%8%26%6%445%6%9%44%
2336
May1st to 10thDay
7%8%25%7%45%5%7%9%41%
2340
11th to 20thDay
6%6%35%5%46%5%7%10%43%
2371
21st to endDay
8%6%26%6%46%6%7%9%40%
2724
June1st to 10thDay
6%3145%35%5%7%8%52%
2520
11th to 20thDay
5%32443445%7%58%
2520
21st to endDay
23133345%6%6%64%
2520
July1st to 10thDay
42245%35%6%6%8%56%
2520
11th to 20thDay
4324435%5%6%7%57%
2417
21st to endDay
4323435%6%7%9%54%
2545
August1st to 10thDay
5%324445%6%7%8%52%
2328
11th to 20thDay
43134345%6%8%59%
2299
21st to endDay
3324425%46%8%60%
2458
September1st to 10thDay
3323424446%65%
2160
11th to 20thDay
3215%5%2345%8%61%
2044
21st to endDay
5%423323335%67%
1962
October1st to 10thDay
6%5%2442445%6%57%
1800
11th to 20thDay
5%5%2432446%7%59%
1800
21st to endDay
36%345%3445%8%56%
1980
November1st to 10thDay
35%25%5%35%5%7%9%51%
1749
11th to 20thDay
46%35%43446%9%50%
1520
21st to endDay
25%37%5%47%5%6%9%48%
1520
December1st to 10thDay
37%49%8%45%5%7%8%40%
1520
11th to 20thDay
38%47%7%47%7%7%10%37%
1926
21st to endDay
28%49%10%5%8%8%7%8%31%
2794
January1st to 10thNight
27%49%8%5%6%6%7%9%36%
4342
11th to 20thNight
17%5%10%9%45%5%6%9%39%
4110
21st to endNight
29%6%14%13%5%6%45%6%31%
4521
February1st to 10thNight
26%37%7%47%7%6%10%42%
2470
11th to 20thNight
27%37%5%46%6%6%9%44%
2402
21st to endNight
26%5%7%6%45%6%7%9%42%
1937
March1st to 10thNight
47%37%8%47%6%7%8%40%
2040
11th to 20thNight
37%35%5%35%5%6%10%48%
1980
21st to endNight
5%9%47%7%345%5%9%43%
2178
April1st to 10thNight
5%9%45%436%6%5%7%47%
1846
11th to 20thNight
6%9%36%6%35%6%5%7%43%
1777
21st to endNight
5%7%35%5%36%6%6%8%46%
1620
May1st to 10thNight
5%7%35%6%35%5%5%8%47%
1620
11th to 20thNight
7%6%26%5%245%7%9%47%
1524
21st to endNight
6%435%5%45%5%8%9%47%
1552
June1st to 10thNight
4423425%7%6%9%55%
1440
11th to 20thNight
5%32342445%7%62%
1440
21st to endNight
321232445%7%67%
1440
July1st to 10thNight
33245%37%47%9%54%
1440
11th to 20thNight
33145%345%6%9%57%
1539
21st to endNight
33244345%7%10%57%
1773
August1st to 10thNight
23145%345%7%8%57%
1611
11th to 20thNight
221333346%7%65%
1602
21st to endNight
32134245%5%7%64%
1898
September1st to 10thNight
5%21221345%6%69%
1800
11th to 20thNight
422342345%7%65%
1914
21st to endNight
4313323346%67%
1997
October1st to 10thNight
5%5%2433446%6%58%
2160
11th to 20thNight
45%24414347%62%
2160
21st to endNight
45%2442345%8%58%
2376
November1st to 10thNight
35%25%335%46%9%55%
2307
11th to 20thNight
46%26%4345%6%9%51%
2660
21st to endNight
27%35%6%3445%9%51%
2660
December1st to 10thNight
28%47%8%45%5%6%9%42%
2660
11th to 20thNight
48%47%6%46%7%7%10%38%
3271
21st to endNight
28%49%8%5%8%6%7%8%35%
4873

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
39%19%17%16%7%1
2644
11th to 20thDay
40%16%19%18%6%1
2860
21st to endDay
52%14%17%12%5%1
3146
February1st to 10thDay
39%11%18%21%10%1
1710
11th to 20thDay
38%10%18%24%9%1
1674
21st to endDay
34%10%20%21%13%1
1514
March1st to 10thDay
35%10%20%25%8%1
2036
11th to 20thDay
34%10%22%21%12%1
1980
21st to endDay
42%8%17%22%9%1
2178
April1st to 10thDay
37%8%18%20%14%3
2114
11th to 20thDay
38%9%15%22%14%1
2134
21st to endDay
35%8%12%25%18%1
2336
May1st to 10thDay
35%10%13%22%17%2
2340
11th to 20thDay
33%9%14%26%14%4
2375
21st to endDay
35%10%15%23%14%2
2724
June1st to 10thDay
26%7%14%23%22%7%
2520
11th to 20thDay
23%7%10%19%25%15%
2520
21st to endDay
18%5%8%18%27%24%
2520
July1st to 10thDay
25%7%9%17%23%19%
2451
11th to 20thDay
24%6%8%16%23%24%
2343
21st to endDay
25%7%10%16%22%21%
2404
August1st to 10thDay
26%8%12%19%20%16%
2313
11th to 20thDay
21%7%9%17%27%19%
2299
21st to endDay
22%6%10%16%30%17%
2458
September1st to 10thDay
21%48%15%28%25%
2160
11th to 20thDay
21%6%9%20%27%17%
2044
21st to endDay
21%47%24%33%12%
1962
October1st to 10thDay
26%6%13%25%25%5%
1800
11th to 20thDay
23%6%14%31%20%6%
1800
21st to endDay
26%6%18%29%19%2
1980
November1st to 10thDay
28%8%17%27%18%2
1749
11th to 20thDay
29%8%22%26%14%1
1520
21st to endDay
31%9%17%25%16%1
1520
December1st to 10thDay
38%11%21%18%11%2
1520
11th to 20thDay
37%12%21%22%8%
1924
21st to endDay
43%13%16%16%9%4
2794
January1st to 10thNight
38%15%20%20%7%1
4342
11th to 20thNight
38%15%20%18%8%1
4110
21st to endNight
48%16%17%12%5%1
4521
February1st to 10thNight
35%13%21%22%8%1
2470
11th to 20thNight
33%10%17%26%12%2
2403
21st to endNight
35%11%21%19%13%1
1937
March1st to 10thNight
37%10%19%25%9%
2040
11th to 20thNight
29%9%19%28%14%1
1980
21st to endNight
37%9%19%25%9%1
2178
April1st to 10thNight
34%8%18%21%15%4
1846
11th to 20thNight
38%7%16%24%14%
1777
21st to endNight
32%10%15%29%13%1
1620
May1st to 10thNight
32%8%15%25%18%2
1620
11th to 20thNight
30%8%15%30%13%4
1525
21st to endNight
29%9%17%28%15%1
1552
June1st to 10thNight
22%7%18%25%21%7%
1440
11th to 20thNight
21%5%11%20%26%17%
1440
21st to endNight
14%5%8%17%31%26%
1440
July1st to 10thNight
23%7%10%18%24%19%
1400
11th to 20thNight
20%6%11%19%20%25%
1490
21st to endNight
18%7%12%20%23%20%
1674
August1st to 10thNight
21%7%12%23%19%17%
1602
11th to 20thNight
17%5%8%21%26%22%
1602
21st to endNight
17%6%10%18%29%19%
1898
September1st to 10thNight
15%410%19%28%25%
1800
11th to 20thNight
18%5%12%21%28%16%
1914
21st to endNight
18%49%26%34%9%
1997
October1st to 10thNight
25%6%11%28%23%7%
2160
11th to 20thNight
23%410%34%23%5%
2160
21st to endNight
24%7%18%31%18%3
2376
November1st to 10thNight
25%9%14%28%20%3
2307
11th to 20thNight
28%7%19%31%11%2
2660
21st to endNight
31%6%16%28%17%2
2660
December1st to 10thNight
36%11%21%20%11%2
2660
11th to 20thNight
37%12%18%24%9%
3272
21st to endNight
41%13%16%16%13%2
4873

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
8%11%13%38%22%7%
270
11th to 20thDay
6%11%23%36%20%4
270
21st to endDay
5%7%26%36%21%7%
297
February1st to 10thDay
7%17%29%36%8%3
270
11th to 20thDay
5%12%29%31%19%4
270
21st to endDay
7%11%27%40%13%3
275
March1st to 10thDay
8%11%33%32%12%4
441
11th to 20thDay
6%12%26%32%21%3
420
21st to endDay
12%13%27%33%13%2
462
April1st to 10thDay
13%12%26%27%18%4
420
11th to 20thDay
13%20%31%23%11%2
412
21st to endDay
12%20%29%17%17%6%
420
May1st to 10thDay
10%19%27%22%17%5%
423
11th to 20thDay
10%13%25%27%19%6%
518
21st to endDay
10%11%23%25%21%10%
679
June1st to 10thDay
7%9%21%27%26%11%
630
11th to 20thDay
7%12%27%32%20%3
630
21st to endDay
37%25%32%28%6%
630
July1st to 10thDay
4319%33%33%8%
621
11th to 20thDay
36%25%29%28%9%
516
21st to endDay
5%220%30%28%15%
487
August1st to 10thDay
6%5%22%29%26%13%
447
11th to 20thDay
35%23%30%26%12%
437
21st to endDay
35%24%30%20%18%
495
September1st to 10thDay
5%6%26%26%23%14%
450
11th to 20thDay
5%8%29%24%18%15%
450
21st to endDay
8%10%24%23%22%13%
432
October1st to 10thDay
8%8%20%23%24%17%
270
11th to 20thDay
9%13%22%24%23%9%
270
21st to endDay
7%17%26%30%16%4
297
November1st to 10thDay
9%14%24%32%13%8%
270
11th to 20thDay
8%10%22%37%19%5%
270
21st to endDay
6%9%24%34%20%7%
270
December1st to 10thDay
6%8%24%40%18%5%
270
11th to 20thDay
6%9%19%47%16%3
270
21st to endDay
8%9%30%31%13%8%
297
January1st to 10thNight
5%9%26%40%19%1
901
11th to 20thNight
5%10%28%39%16%2
760
21st to endNight
46%29%44%14%2
836
February1st to 10thNight
410%36%39%11%1
760
11th to 20thNight
49%32%43%11%2
744
21st to endNight
5%8%33%44%10%
628
March1st to 10thNight
6%7%28%45%13%1
742
11th to 20thNight
5%5%27%47%16%1
720
21st to endNight
8%6%33%41%12%
792
April1st to 10thNight
9%10%30%40%11%
586
11th to 20thNight
11%10%30%39%9%1
533
21st to endNight
7%12%29%36%15%1
540
May1st to 10thNight
8%9%29%37%15%1
540
11th to 20thNight
10%6%22%39%19%3
531
21st to endNight
7%8%23%39%22%2
584
June1st to 10thNight
6%5%24%40%24%2
540
11th to 20thNight
5%8%27%43%17%
540
21st to endNight
3221%48%26%1
540
July1st to 10thNight
3214%45%35%1
525
11th to 20thNight
3216%45%32%1
522
21st to endNight
3110%48%37%2
591
August1st to 10thNight
3112%47%36%1
537
11th to 20thNight
2213%46%36%1
534
21st to endNight
3213%41%37%4
594
September1st to 10thNight
5%416%41%31%3
540
11th to 20thNight
4318%44%27%5%
654
21st to endNight
45%18%37%32%4
720
October1st to 10thNight
8%5%25%35%24%3
720
11th to 20thNight
7%7%22%39%23%1
720
21st to endNight
6%6%25%42%18%2
792
November1st to 10thNight
6%7%26%42%19%1
759
11th to 20thNight
6%9%28%42%13%1
950
21st to endNight
5%10%25%43%16%1
950
December1st to 10thNight
6%10%29%43%12%1
950
11th to 20thNight
9%7%27%45%12%
950
21st to endNight
6%12%30%39%12%2
1045
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