Nicholas E. Wagman Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Nicholas E. Wagman Observatory clear sky chart from 2005-11-06 to 2024-03-28.

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
34%
23610
14%
80834
10%
23509
40%
23509
16%
58160

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
14%
755
9%
4137
5%
737
21%
737
5%
3295
January11th to 20thNight
14%
759
6%
4097
2%
740
19%
740
5%
3355
January21st to endNight
17%
829
5%
4515
4%
814
22%
814
5%
3813
February1st to 10thNight
21%
760
12%
2470
7%
760
27%
760
11%
1929
February11th to 20thNight
13%
742
10%
2405
4%
740
22%
740
11%
1829
February21st to endNight
17%
628
12%
1881
5%
628
23%
628
12%
1462
March1st to 10thNight
23%
760
16%
2090
8%
760
30%
760
17%
1534
March11th to 20thNight
25%
760
18%
2090
10%
760
33%
760
18%
1498
March21st to endNight
23%
821
16%
2256
7%
821
30%
821
19%
1640
April1st to 10thNight
26%
720
14%
1873
6%
720
31%
720
20%
1373
April11th to 20thNight
32%
707
17%
1771
7%
707
37%
707
24%
1253
April21st to endNight
30%
540
19%
1620
7%
540
37%
540
21%
1103
May1st to 10thNight
36%
540
14%
1620
9%
540
41%
540
19%
1148
May11th to 20thNight
41%
531
15%
1593
10%
531
45%
531
21%
1107
May21st to endNight
55%
409
17%
1572
15%
409
62%
409
26%
908
June1st to 10thNight
50%
360
16%
1440
18%
360
57%
360
23%
859
June11th to 20thNight
50%
360
16%
1440
19%
360
56%
360
20%
882
June21st to endNight
54%
360
18%
1440
19%
360
61%
360
24%
845
July1st to 10thNight
56%
384
14%
1434
16%
384
60%
384
23%
895
July11th to 20thNight
61%
522
18%
1566
16%
522
65%
522
34%
945
July21st to endNight
61%
591
16%
1672
14%
558
64%
558
26%
1085
August1st to 10thNight
65%
537
18%
1600
15%
534
66%
534
31%
995
August11th to 20thNight
60%
534
19%
1598
15%
534
63%
534
29%
1019
August21st to endNight
58%
702
20%
1890
14%
702
61%
702
32%
1217
September1st to 10thNight
56%
720
23%
1800
14%
720
60%
720
36%
1161
September11th to 20thNight
62%
720
26%
1952
20%
720
66%
720
38%
1184
September21st to endNight
44%
720
21%
1989
15%
720
49%
720
26%
1334
October1st to 10thNight
46%
720
18%
2160
16%
720
50%
720
25%
1400
October11th to 20thNight
33%
720
17%
2160
11%
720
41%
720
22%
1479
October21st to endNight
31%
792
19%
2376
12%
792
40%
792
19%
1680
November1st to 10thNight
39%
740
22%
2282
17%
740
46%
740
24%
1467
November11th to 20thNight
28%
760
17%
2617
12%
760
37%
760
16%
1825
November21st to endNight
24%
760
14%
2660
9%
760
32%
760
14%
1936
December1st to 10thNight
18%
760
8%
2660
5%
760
22%
760
8%
2139
December11th to 20thNight
20%
759
9%
3249
6%
759
26%
759
8%
2497
December21st to endNight
17%
828
6%
4859
6%
817
23%
817
4%
4069

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
17%10%47%6%35%5%5%7%30%
78824
Night
17%11%47%6%3445%6%32%
81159
TransparencyDay
53%7%12%18%9%1
78542
Night
52%7%11%18%10%1
80960
SeeingDay
22%14%27%21%12%4
13821
Night
21%11%27%27%12%1
23635

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
20%19%11%10%6%34335%17%
2781
11th to 20thDay
14%21%8%15%11%3232416%
2840
21st to endDay
25%21%7%12%7%3333411%
3124
February1st to 10thDay
20%17%6%10%8%44335%21%
1710
11th to 20thDay
16%13%8%12%6%4445%5%21%
1663
21st to endDay
21%13%5%10%7%3435%5%25%
1566
March1st to 10thDay
17%11%5%8%6%34445%31%
2090
11th to 20thDay
19%11%5%7%7%45%446%29%
2090
21st to endDay
20%11%48%6%35%45%6%27%
2255
April1st to 10thDay
16%10%5%7%6%45%5%5%6%32%
2085
11th to 20thDay
18%9%47%5%35%45%6%32%
2152
21st to endDay
23%8%36%5%35%446%33%
2340
May1st to 10thDay
19%9%37%6%45%5%6%7%29%
2340
11th to 20thDay
21%7%46%7%45%6%5%8%28%
2301
21st to endDay
13%5%25%6%45%6%8%10%37%
2699
June1st to 10thDay
14%6%36%6%46%6%6%9%34%
2520
11th to 20thDay
14%7%26%6%45%6%7%8%34%
2520
21st to endDay
14%6%25%6%45%46%10%37%
2520
July1st to 10thDay
11%6%36%6%45%5%5%8%40%
2480
11th to 20thDay
12%7%25%6%36%6%7%10%36%
2340
21st to endDay
12%6%36%7%36%7%6%9%34%
2547
August1st to 10thDay
11%5%36%7%5%6%7%7%10%34%
2327
11th to 20thDay
14%5%26%6%46%6%7%10%33%
2303
21st to endDay
13%5%25%5%45%6%7%10%37%
2446
September1st to 10thDay
16%6%25%5%335%5%6%42%
2160
11th to 20thDay
13%5%35%5%345%6%9%43%
2003
21st to endDay
18%7%36%5%445%47%37%
1969
October1st to 10thDay
17%6%26%435%6%6%8%38%
1800
11th to 20thDay
20%8%35%6%46%45%5%35%
1800
21st to endDay
23%10%37%5%34446%30%
1980
November1st to 10thDay
12%8%46%6%345%46%41%
1791
11th to 20thDay
18%13%5%6%5%35%346%32%
1560
21st to endDay
19%15%5%7%7%36%5%5%5%25%
1520
December1st to 10thDay
21%16%9%10%7%335%35%18%
1520
11th to 20thDay
21%16%9%9%5%24435%21%
1910
21st to endDay
25%23%7%9%6%23345%13%
2772
January1st to 10thNight
17%20%8%11%6%4444418%
4159
11th to 20thNight
17%18%7%13%9%45%44416%
4120
21st to endNight
28%16%8%8%9%3433316%
4532
February1st to 10thNight
21%12%6%10%7%44445%25%
2470
11th to 20thNight
19%12%5%11%7%35%45%425%
2403
21st to endNight
21%11%5%10%7%34445%25%
1881
March1st to 10thNight
19%10%5%6%6%35%45%6%33%
2090
11th to 20thNight
20%10%47%5%24347%35%
2090
21st to endNight
18%10%47%5%35%435%35%
2256
April1st to 10thNight
19%10%45%5%35%446%35%
1873
11th to 20thNight
16%7%37%5%35%5%48%37%
1771
21st to endNight
15%8%47%6%34449%36%
1620
May1st to 10thNight
18%7%37%5%35%5%5%5%34%
1620
11th to 20thNight
17%8%36%6%2445%8%36%
1592
21st to endNight
10%5%245%345%6%10%45%
1571
June1st to 10thNight
11%5%35%5%3446%8%44%
1440
11th to 20thNight
12%6%26%6%36%46%9%41%
1440
21st to endNight
11%5%245%45%5%7%10%43%
1440
July1st to 10thNight
8%5%36%6%36%46%9%43%
1476
11th to 20thNight
10%425%5%345%6%10%46%
1620
21st to endNight
10%5%27%6%35%7%7%10%38%
1771
August1st to 10thNight
7%5%26%5%36%5%7%9%45%
1611
11th to 20thNight
11%6%26%5%345%5%9%44%
1598
21st to endNight
10%6%35%435%6%6%9%44%
1890
September1st to 10thNight
13%5%145%345%5%7%48%
1800
11th to 20thNight
10%42442445%9%51%
1952
21st to endNight
15%7%36%6%345%5%5%43%
1989
October1st to 10thNight
15%6%26%4445%5%7%43%
2160
11th to 20thNight
19%7%25%6%34446%38%
2160
21st to endNight
24%8%35%434446%35%
2376
November1st to 10thNight
13%8%36%43445%7%43%
2282
11th to 20thNight
19%11%37%5%35%45%7%32%
2617
21st to endNight
20%13%5%6%5%25%446%29%
2660
December1st to 10thNight
23%15%8%9%5%34445%20%
2660
11th to 20thNight
19%16%6%9%6%34445%23%
3285
21st to endNight
24%19%6%9%7%45%445%14%
4884

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
69%6%9%11%4
2782
11th to 20thDay
73%48%11%31
2840
21st to endDay
78%5%7%8%2
3124
February1st to 10thDay
68%48%14%6%1
1710
11th to 20thDay
64%6%11%13%6%
1672
21st to endDay
62%5%11%14%7%1
1566
March1st to 10thDay
54%6%12%20%8%
2090
11th to 20thDay
57%6%9%18%9%1
2090
21st to endDay
56%6%10%17%10%1
2255
April1st to 10thDay
51%7%11%18%10%2
2085
11th to 20thDay
50%7%11%16%14%2
2152
21st to endDay
52%6%11%20%10%2
2340
May1st to 10thDay
51%8%14%17%9%1
2340
11th to 20thDay
53%8%12%15%11%2
2305
21st to endDay
39%11%18%22%8%2
2699
June1st to 10thDay
44%9%14%20%11%1
2520
11th to 20thDay
44%9%14%20%11%1
2520
21st to endDay
42%8%12%26%11%1
2520
July1st to 10thDay
42%10%12%20%13%3
2412
11th to 20thDay
40%9%14%23%13%1
2271
21st to endDay
44%9%13%20%14%1
2405
August1st to 10thDay
42%10%16%24%8%
2314
11th to 20thDay
42%9%16%22%9%1
2303
21st to endDay
40%8%14%23%12%3
2446
September1st to 10thDay
41%8%11%20%17%4
2160
11th to 20thDay
37%8%13%27%14%1
2003
21st to endDay
47%5%12%22%14%1
1969
October1st to 10thDay
42%7%14%21%15%1
1800
11th to 20thDay
49%7%11%23%10%
1800
21st to endDay
53%6%12%18%10%1
1980
November1st to 10thDay
43%6%12%21%16%2
1791
11th to 20thDay
54%5%12%18%10%2
1560
21st to endDay
60%5%12%17%5%1
1520
December1st to 10thDay
70%5%10%12%3
1520
11th to 20thDay
67%411%15%3
1906
21st to endDay
74%5%9%9%2
2772
January1st to 10thNight
68%6%9%13%3
4159
11th to 20thNight
71%5%11%10%2
4120
21st to endNight
74%5%6%12%3
4532
February1st to 10thNight
62%5%9%16%7%
2470
11th to 20thNight
61%411%17%7%
2405
21st to endNight
61%5%10%14%9%1
1881
March1st to 10thNight
52%6%10%20%11%1
2090
11th to 20thNight
50%5%12%21%9%2
2090
21st to endNight
52%5%9%18%13%3
2256
April1st to 10thNight
51%5%10%19%14%2
1873
11th to 20thNight
45%7%11%18%16%3
1771
21st to endNight
46%6%10%23%11%3
1620
May1st to 10thNight
49%7%10%19%12%3
1620
11th to 20thNight
47%7%11%17%15%3
1593
21st to endNight
33%9%17%27%13%2
1572
June1st to 10thNight
36%10%12%25%15%2
1440
11th to 20thNight
39%9%14%23%14%1
1440
21st to endNight
35%10%14%24%16%2
1440
July1st to 10thNight
37%10%11%21%16%4
1434
11th to 20thNight
32%8%15%24%19%2
1566
21st to endNight
37%10%15%21%13%3
1672
August1st to 10thNight
33%10%17%25%16%1
1600
11th to 20thNight
37%8%14%24%14%2
1598
21st to endNight
34%9%13%25%15%4
1890
September1st to 10thNight
34%7%13%23%19%5%
1800
11th to 20thNight
30%7%14%27%22%1
1952
21st to endNight
43%5%12%21%17%1
1989
October1st to 10thNight
40%8%13%24%14%2
2160
11th to 20thNight
46%6%10%24%13%1
2160
21st to endNight
50%5%11%21%12%1
2376
November1st to 10thNight
42%6%11%21%17%4
2282
11th to 20thNight
52%5%10%20%11%2
2617
21st to endNight
55%6%11%20%7%1
2660
December1st to 10thNight
67%6%11%12%4
2660
11th to 20thNight
64%5%11%16%3
3288
21st to endNight
71%8%9%10%2
4884

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
29%25%28%12%42
256
11th to 20thDay
32%28%28%9%31
270
21st to endDay
29%28%30%9%4
297
February1st to 10thDay
33%21%36%9%1
270
11th to 20thDay
34%28%28%10%1
270
21st to endDay
39%23%28%9%1
264
March1st to 10thDay
27%20%31%17%5%
460
11th to 20thDay
32%19%31%13%41
460
21st to endDay
31%19%29%16%41
490
April1st to 10thDay
27%22%25%17%7%2
420
11th to 20thDay
24%18%27%18%8%4
412
21st to endDay
30%18%27%17%5%2
420
May1st to 10thDay
30%16%26%18%8%3
423
11th to 20thDay
22%12%32%20%10%4
447
21st to endDay
14%9%25%28%18%6%
485
June1st to 10thDay
15%10%28%28%16%4
450
11th to 20thDay
18%13%22%28%14%5%
450
21st to endDay
14%10%30%28%15%3
450
July1st to 10thDay
13%7%18%27%23%11%
445
11th to 20thDay
13%6%25%30%18%9%
444
21st to endDay
15%5%24%30%19%7%
488
August1st to 10thDay
11%7%20%28%23%10%
446
11th to 20thDay
16%420%30%17%12%
439
21st to endDay
11%5%24%26%22%11%
495
September1st to 10thDay
19%6%21%26%20%9%
450
11th to 20thDay
13%420%30%22%11%
450
21st to endDay
23%10%24%22%14%6%
450
October1st to 10thDay
19%9%25%24%19%5%
450
11th to 20thDay
24%14%28%23%9%2
450
21st to endDay
32%13%28%19%7%1
495
November1st to 10thDay
20%16%30%20%11%3
389
11th to 20thDay
30%20%27%15%6%2
198
21st to endDay
21%21%46%10%31
180
December1st to 10thDay
31%24%28%12%41
180
11th to 20thDay
31%22%31%13%3
180
21st to endDay
32%20%30%14%4
198
January1st to 10thNight
28%19%34%16%3
760
11th to 20thNight
32%15%30%19%3
760
21st to endNight
27%17%31%20%3
836
February1st to 10thNight
28%16%29%25%3
760
11th to 20thNight
29%18%36%16%1
743
21st to endNight
28%15%35%20%3
628
March1st to 10thNight
25%16%32%24%4
760
11th to 20thNight
27%17%27%21%7%1
760
21st to endNight
24%14%33%22%5%1
821
April1st to 10thNight
25%16%29%23%6%1
720
11th to 20thNight
23%11%31%25%10%1
707
21st to endNight
19%10%35%30%7%
540
May1st to 10thNight
20%9%28%33%9%1
540
11th to 20thNight
21%8%25%34%12%
531
21st to endNight
10%226%34%25%3
411
June1st to 10thNight
11%426%39%19%1
360
11th to 20thNight
13%423%39%20%1
360
21st to endNight
11%228%36%21%1
360
July1st to 10thNight
9%321%40%23%5%
384
11th to 20thNight
9%417%36%29%4
522
21st to endNight
10%315%42%28%2
591
August1st to 10thNight
9%214%43%28%3
537
11th to 20thNight
11%5%14%35%31%4
534
21st to endNight
13%320%32%28%5%
702
September1st to 10thNight
15%318%32%27%4
720
11th to 20thNight
12%5%15%36%28%4
720
21st to endNight
17%8%24%25%21%4
720
October1st to 10thNight
17%8%22%30%22%1
720
11th to 20thNight
22%9%30%28%10%1
720
21st to endNight
27%12%26%28%7%1
792
November1st to 10thNight
18%10%27%31%13%
740
11th to 20thNight
25%14%28%24%7%1
760
21st to endNight
27%14%29%22%7%
760
December1st to 10thNight
32%17%27%19%5%
760
11th to 20thNight
27%18%29%23%4
760
21st to endNight
29%15%31%23%2
836
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