This page made possible by the sponsorship of: Buffalo Astronomical Association.

Beaver Meadow Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Beaver Meadow Observatory clear sky chart from 2005-11-06 to 2024-01-31.

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
24%
23010
11%
75073
7%
22958
29%
22958
13%
56524

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
7%
758
6%
2649
2%
757
12%
757
4%
2278
January11th to 20thNight
10%
760
4%
2534
2%
760
12%
760
4%
2230
January21st to endNight
9%
835
5%
2711
2%
835
13%
835
4%
2367
February1st to 10thNight
4%
720
4%
2340
1%
720
9%
720
4%
2039
February11th to 20thNight
6%
703
7%
2275
1%
700
13%
700
5%
1888
February21st to endNight
8%
592
9%
1844
2%
592
16%
592
7%
1510
March1st to 10thNight
13%
720
12%
1991
5%
720
20%
720
10%
1577
March11th to 20thNight
16%
720
14%
1980
5%
720
24%
720
13%
1513
March21st to endNight
18%
792
15%
2174
6%
792
25%
792
14%
1666
April1st to 10thNight
17%
720
13%
1800
3%
720
23%
720
16%
1376
April11th to 20thNight
22%
711
14%
1775
5%
711
28%
711
20%
1316
April21st to endNight
29%
581
15%
1661
6%
581
34%
581
19%
1181
May1st to 10thNight
32%
528
12%
1608
9%
528
36%
528
16%
1157
May11th to 20thNight
31%
354
17%
1416
14%
354
40%
354
17%
918
May21st to endNight
41%
388
16%
1551
14%
388
50%
388
21%
913
June1st to 10thNight
37%
360
14%
1440
12%
360
47%
360
19%
894
June11th to 20thNight
39%
360
14%
1440
14%
360
48%
360
20%
860
June21st to endNight
39%
360
13%
1440
10%
360
49%
360
20%
881
July1st to 10thNight
49%
350
15%
1400
18%
350
55%
350
24%
791
July11th to 20thNight
45%
348
18%
1392
18%
348
55%
348
25%
790
July21st to endNight
47%
538
16%
1622
11%
508
51%
508
27%
1016
August1st to 10thNight
52%
537
17%
1600
11%
534
56%
534
31%
1005
August11th to 20thNight
50%
534
18%
1598
12%
534
53%
534
26%
1042
August21st to endNight
49%
738
18%
1926
10%
738
52%
738
30%
1273
September1st to 10thNight
44%
720
18%
1800
8%
720
48%
720
30%
1216
September11th to 20thNight
49%
720
25%
1835
16%
720
53%
720
34%
1187
September21st to endNight
40%
720
19%
2058
14%
720
43%
720
22%
1427
October1st to 10thNight
32%
720
14%
2160
11%
720
38%
720
19%
1524
October11th to 20thNight
21%
720
11%
2160
6%
720
28%
720
14%
1582
October21st to endNight
14%
792
12%
2376
5%
792
22%
792
11%
1861
November1st to 10thNight
22%
740
16%
2401
12%
740
30%
740
16%
1708
November11th to 20thNight
16%
760
11%
2660
7%
760
23%
760
10%
2005
November21st to endNight
14%
760
8%
2660
4%
760
19%
760
7%
2135
December1st to 10thNight
8%
760
4%
2660
2%
760
11%
760
4%
2316
December11th to 20thNight
8%
760
4%
3272
1%
759
11%
759
3%
2795
December21st to endNight
6%
831
3%
4864
1%
817
10%
817
2%
4287

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%13%5%9%6%35%45%6%27%
74832
Night
16%14%6%9%7%3445%6%27%
75289
TransparencyDay
57%6%11%17%9%1
74546
Night
58%6%11%16%8%1
75109
SeeingDay
25%19%29%17%8%2
13494
Night
24%19%28%20%8%1
23018

By Month

Percentage Cloud Cover NE (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
11%21%10%17%11%45%43410%
1517
11th to 20thDay
14%22%10%16%8%6%433411%
1643
21st to endDay
11%17%12%19%13%46%4348%
1872
February1st to 10thDay
15%22%9%14%12%5%442311%
1620
11th to 20thDay
12%17%10%17%11%3443414%
1573
21st to endDay
18%16%6%14%9%43345%17%
1412
March1st to 10thDay
15%13%9%15%8%44335%22%
1963
11th to 20thDay
13%19%8%8%7%34435%26%
1980
21st to endDay
19%17%6%8%6%345%5%5%24%
2182
April1st to 10thDay
16%17%7%7%5%34445%28%
2160
11th to 20thDay
19%14%26%5%24446%33%
2134
21st to endDay
21%14%47%5%34345%30%
2312
May1st to 10thDay
20%12%46%5%35%447%30%
2349
11th to 20thDay
20%8%36%6%35%5%5%7%33%
2478
21st to endDay
14%7%26%6%35%5%5%7%40%
2725
June1st to 10thDay
19%8%35%5%3446%6%36%
2520
11th to 20thDay
18%5%26%6%35%5%6%9%34%
2520
21st to endDay
17%7%25%5%35%5%5%8%37%
2520
July1st to 10thDay
12%6%36%5%35%5%6%9%40%
2520
11th to 20thDay
15%7%26%6%35%7%6%9%34%
2520
21st to endDay
14%6%36%7%47%6%7%9%31%
2596
August1st to 10thDay
13%6%26%6%35%5%7%9%37%
2327
11th to 20thDay
14%8%35%7%45%7%8%9%29%
2303
21st to endDay
16%6%26%5%45%5%6%8%36%
2412
September1st to 10thDay
18%7%36%5%346%5%8%35%
2160
11th to 20thDay
17%6%35%6%3446%8%39%
2122
21st to endDay
19%7%36%6%36%46%7%32%
1900
October1st to 10thDay
24%8%36%5%35%5%5%6%31%
1800
11th to 20thDay
23%14%47%6%24445%26%
1800
21st to endDay
27%18%37%5%3433421%
1980
November1st to 10thDay
14%18%5%8%5%35%445%29%
1674
11th to 20thDay
15%24%6%8%5%2345%6%21%
1520
21st to endDay
17%23%7%9%6%34345%17%
1520
December1st to 10thDay
16%26%11%14%6%3343411%
1520
11th to 20thDay
17%19%9%17%7%3443413%
1906
21st to endDay
22%27%9%13%7%3322210%
2772
January1st to 10thNight
13%21%10%15%10%5%6%43311%
2649
11th to 20thNight
14%20%11%15%11%5%433411%
2534
21st to endNight
11%18%11%15%12%5%6%43311%
2711
February1st to 10thNight
15%19%9%15%12%45%43311%
2340
11th to 20thNight
12%15%8%17%10%46%5%4415%
2273
21st to endNight
16%16%6%16%9%3435%5%17%
1844
March1st to 10thNight
13%14%7%13%8%5%4346%23%
1981
11th to 20thNight
16%16%7%8%6%3434429%
1979
21st to endNight
15%15%5%10%6%34445%29%
2174
April1st to 10thNight
18%13%5%8%6%34446%29%
1800
11th to 20thNight
18%13%36%5%3435%6%34%
1775
21st to endNight
17%12%46%5%35%45%6%32%
1661
May1st to 10thNight
19%9%37%6%35%5%5%7%30%
1608
11th to 20thNight
13%6%37%6%45%5%6%7%36%
1415
21st to endNight
12%7%25%5%25%45%8%45%
1550
June1st to 10thNight
15%6%36%6%46%5%7%7%35%
1440
11th to 20thNight
14%7%26%435%5%5%9%40%
1440
21st to endNight
14%6%35%5%35%6%5%6%42%
1440
July1st to 10thNight
9%6%26%6%3446%9%46%
1440
11th to 20thNight
11%6%35%435%47%8%45%
1440
21st to endNight
12%5%26%435%6%6%8%44%
1718
August1st to 10thNight
10%5%25%5%345%6%9%44%
1611
11th to 20thNight
12%6%27%6%35%5%6%8%40%
1598
21st to endNight
12%7%35%5%35%5%6%7%43%
1926
September1st to 10thNight
16%8%25%4245%5%6%44%
1800
11th to 20thNight
14%6%25%42445%6%48%
1835
21st to endNight
18%8%25%5%35%6%6%7%36%
2058
October1st to 10thNight
20%8%36%5%35%46%6%35%
2160
11th to 20thNight
21%13%46%5%3445%6%28%
2160
21st to endNight
27%15%36%5%34446%23%
2376
November1st to 10thNight
15%16%48%5%34445%33%
2401
11th to 20thNight
16%18%5%9%6%35%45%7%22%
2660
21st to endNight
15%20%8%12%6%34445%18%
2660
December1st to 10thNight
18%23%12%12%7%3433311%
2660
11th to 20thNight
17%22%10%16%7%3433313%
3288
21st to endNight
20%25%10%10%7%344448%
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
76%6%8%8%3
1518
11th to 20thDay
78%38%6%4
1643
21st to endDay
80%48%6%3
1872
February1st to 10thDay
79%49%6%2
1620
11th to 20thDay
74%37%11%5%
1582
21st to endDay
69%311%11%41
1412
March1st to 10thDay
65%411%15%5%1
1966
11th to 20thDay
61%410%15%9%2
1980
21st to endDay
62%5%6%16%9%2
2182
April1st to 10thDay
58%5%10%17%10%1
2160
11th to 20thDay
52%5%9%20%12%2
2134
21st to endDay
56%5%9%17%12%1
2312
May1st to 10thDay
55%5%9%20%10%2
2349
11th to 20thDay
51%6%10%19%13%1
2482
21st to endDay
43%7%15%21%12%2
2725
June1st to 10thDay
47%7%12%21%13%1
2520
11th to 20thDay
46%8%13%21%11%1
2520
21st to endDay
44%7%12%22%13%1
2520
July1st to 10thDay
41%9%10%26%12%2
2450
11th to 20thDay
43%10%14%22%12%
2445
21st to endDay
46%9%13%19%12%1
2451
August1st to 10thDay
40%9%14%25%11%1
2314
11th to 20thDay
47%10%13%22%8%1
2303
21st to endDay
44%8%12%24%10%1
2412
September1st to 10thDay
45%8%11%24%11%1
2160
11th to 20thDay
43%5%12%25%14%1
2122
21st to endDay
50%7%10%21%11%1
1900
October1st to 10thDay
53%6%11%17%11%2
1800
11th to 20thDay
59%7%12%15%7%1
1800
21st to endDay
67%49%12%7%1
1980
November1st to 10thDay
56%7%10%17%9%2
1674
11th to 20thDay
63%5%11%13%6%1
1520
21st to endDay
69%412%11%41
1520
December1st to 10thDay
78%38%8%3
1520
11th to 20thDay
75%6%10%7%11
1906
21st to endDay
82%46%7%1
2772
January1st to 10thNight
75%5%8%8%4
2649
11th to 20thNight
78%5%8%6%3
2534
21st to endNight
78%47%7%31
2711
February1st to 10thNight
76%5%8%7%4
2340
11th to 20thNight
71%5%9%10%5%1
2275
21st to endNight
68%5%8%12%6%
1844
March1st to 10thNight
63%410%16%6%1
1991
11th to 20thNight
58%5%10%17%9%2
1980
21st to endNight
59%5%7%15%12%2
2174
April1st to 10thNight
56%5%10%18%10%1
1800
11th to 20thNight
52%5%10%18%13%1
1775
21st to endNight
51%5%11%19%13%2
1661
May1st to 10thNight
51%7%9%20%12%1
1608
11th to 20thNight
46%7%11%23%12%1
1416
21st to endNight
37%8%15%22%16%2
1551
June1st to 10thNight
43%7%14%22%14%1
1440
11th to 20thNight
40%7%15%22%16%2
1440
21st to endNight
40%8%14%24%12%2
1440
July1st to 10thNight
35%8%14%24%17%2
1400
11th to 20thNight
36%6%14%28%15%1
1392
21st to endNight
37%8%15%24%14%1
1622
August1st to 10thNight
35%8%16%29%11%1
1600
11th to 20thNight
39%9%16%27%9%
1598
21st to endNight
37%9%14%27%12%2
1926
September1st to 10thNight
39%7%14%26%12%2
1800
11th to 20thNight
36%6%12%28%16%2
1835
21st to endNight
45%7%13%22%12%1
2058
October1st to 10thNight
48%7%11%18%14%1
2160
11th to 20thNight
54%6%14%16%9%1
2160
21st to endNight
62%6%11%13%7%1
2376
November1st to 10thNight
52%6%10%20%10%3
2401
11th to 20thNight
60%5%13%14%5%3
2660
21st to endNight
66%6%12%12%4
2660
December1st to 10thNight
78%48%8%2
2660
11th to 20thNight
75%5%9%8%2
3288
21st to endNight
78%6%8%7%1
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
34%23%29%10%21
180
11th to 20thDay
32%36%24%6%2
238
21st to endDay
28%32%28%10%2
294
February1st to 10thDay
37%34%25%4
240
11th to 20thDay
33%35%29%31
240
21st to endDay
41%26%26%7%
278
March1st to 10thDay
32%27%26%11%3
420
11th to 20thDay
30%25%33%9%3
420
21st to endDay
35%23%27%11%5%
462
April1st to 10thDay
34%20%30%10%5%1
420
11th to 20thDay
33%23%25%11%6%2
412
21st to endDay
30%20%30%15%31
420
May1st to 10thDay
32%18%28%13%6%2
423
11th to 20thDay
24%16%30%22%7%2
447
21st to endDay
17%16%31%21%12%3
485
June1st to 10thDay
22%16%34%19%7%2
450
11th to 20thDay
21%12%31%22%13%1
450
21st to endDay
18%15%38%19%6%2
450
July1st to 10thDay
14%9%27%30%14%5%
445
11th to 20thDay
14%9%30%28%15%4
444
21st to endDay
14%11%38%23%11%3
488
August1st to 10thDay
13%11%26%28%15%7%
446
11th to 20thDay
16%8%28%27%15%6%
439
21st to endDay
15%11%30%26%12%6%
495
September1st to 10thDay
20%12%28%22%14%5%
450
11th to 20thDay
14%10%26%22%20%7%
450
21st to endDay
19%18%24%21%12%5%
450
October1st to 10thDay
27%13%28%16%12%4
450
11th to 20thDay
30%21%27%16%5%1
450
21st to endDay
36%23%24%15%2
495
November1st to 10thDay
28%22%28%15%6%1
345
11th to 20thDay
31%30%27%10%21
180
21st to endDay
31%29%31%9%1
180
December1st to 10thDay
40%22%27%9%2
180
11th to 20thDay
35%32%22%9%2
180
21st to endDay
40%25%29%5%2
198
January1st to 10thNight
28%31%28%11%2
760
11th to 20thNight
29%30%26%12%2
760
21st to endNight
22%32%30%13%3
835
February1st to 10thNight
31%30%31%8%
720
11th to 20thNight
28%32%30%8%2
703
21st to endNight
31%30%27%10%1
592
March1st to 10thNight
24%28%30%14%3
720
11th to 20thNight
30%24%27%15%4
720
21st to endNight
23%23%33%15%6%1
792
April1st to 10thNight
27%21%31%19%2
720
11th to 20thNight
29%16%29%19%5%1
711
21st to endNight
23%15%28%27%7%
581
May1st to 10thNight
23%11%26%29%10%2
528
11th to 20thNight
14%10%37%32%7%
354
21st to endNight
14%10%31%30%14%1
389
June1st to 10thNight
15%9%34%30%11%1
360
11th to 20thNight
19%9%29%33%10%
360
21st to endNight
13%8%37%34%8%
360
July1st to 10thNight
7%7%26%40%19%1
350
11th to 20thNight
11%5%34%33%15%2
348
21st to endNight
12%6%30%34%18%1
538
August1st to 10thNight
11%5%27%33%21%3
537
11th to 20thNight
13%7%22%30%25%3
534
21st to endNight
13%9%25%31%20%2
738
September1st to 10thNight
19%9%22%31%17%2
720
11th to 20thNight
16%8%23%28%22%3
720
21st to endNight
20%13%22%27%15%3
720
October1st to 10thNight
24%12%26%21%15%1
720
11th to 20thNight
29%18%27%21%5%1
720
21st to endNight
37%16%30%16%2
792
November1st to 10thNight
25%18%29%20%7%
740
11th to 20thNight
27%24%28%13%6%1
760
21st to endNight
27%28%27%14%4
760
December1st to 10thNight
33%29%26%9%3
760
11th to 20thNight
31%27%29%12%1
760
21st to endNight
30%30%29%10%1
836
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