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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 2005-11-05 to 2017-09-10.

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
25%
14867
11%
46818
7%
14829
30%
14829
14%
35063

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
7%
718
5%
2487
2%
716
11%
716
4%
2187
January16th to endNight
8%
768
5%
2496
2%
768
12%
768
4%
2196
February1st to 15thNight
6%
704
4%
2287
1%
701
10%
701
4%
1989
February16th to endNight
9%
631
9%
1997
2%
631
17%
631
7%
1631
March1st to 15thNight
15%
720
11%
1987
5%
720
21%
720
10%
1588
March16th to endNight
19%
768
15%
2109
6%
768
26%
768
14%
1591
April1st to 15thNight
18%
718
13%
1796
3%
718
24%
718
16%
1367
April16th to endNight
33%
627
17%
1707
7%
627
38%
627
24%
1170
May1st to 15thNight
36%
471
14%
1551
10%
471
42%
471
16%
1090
May16th to endNight
36%
374
16%
1497
13%
374
46%
374
21%
893
June1st to 15thNight
37%
360
12%
1440
10%
360
46%
360
19%
897
June16th to endNight
39%
360
11%
1440
10%
360
47%
360
20%
884
July1st to 15thNight
48%
340
14%
1360
17%
340
53%
340
24%
776
July16th to endNight
49%
471
15%
1505
11%
441
54%
441
27%
907
August1st to 15thNight
50%
539
15%
1609
9%
536
55%
536
30%
1004
August16th to endNight
54%
669
19%
1815
11%
669
58%
669
33%
1156
September1st to 15thNight
45%
700
20%
1750
10%
700
50%
700
31%
1188
September16th to endNight
45%
657
19%
1831
15%
657
49%
657
25%
1244
October1st to 15thNight
31%
660
14%
1980
11%
660
37%
660
19%
1417
October16th to endNight
13%
704
8%
2112
3%
704
20%
704
10%
1666
November1st to 15thNight
23%
700
16%
2334
13%
700
30%
700
16%
1653
November16th to endNight
17%
720
9%
2520
6%
720
22%
720
9%
1990
December1st to 15thNight
10%
720
4%
2520
2%
720
13%
720
4%
2184
December16th to endNight
6%
768
3%
2688
1%
768
9%
768
3%
2395

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%12%5%8%6%34446%26%
47808
Night
15%12%5%9%6%34445%27%
46997
Cloud CoverDay
16%12%5%8%6%34446%26%
47818
Night
15%12%5%9%6%34445%27%
47002
TransparencyDay
57%5%10%16%8%
47505
Night
57%5%11%16%8%
46818
SeeingDay
24%15%28%18%9%3
5419
Night
23%18%28%20%8%
14870

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 15thDay
15%20%8%15%10%35%33310%
1450
16th to endDay
10%18%11%19%11%45%2338%
1728
February1st to 15thDay
13%22%10%13%12%4331210%
1575
16th to endDay
16%16%8%11%10%3334416%
1476
March1st to 15thDay
16%16%8%11%7%33335%21%
1960
16th to endDay
16%17%6%7%6%24445%25%
2115
April1st to 15thDay
19%15%5%6%43443427%
2152
16th to endDay
19%12%35%424335%36%
2262
May1st to 15thDay
20%10%36%5%34347%30%
2398
16th to endDay
16%8%25%6%35%5%46%37%
2618
June1st to 15thDay
22%8%25%42445%7%32%
2520
16th to endDay
17%5%25%5%346%6%8%33%
2520
July1st to 15thDay
13%6%26%6%35%5%5%9%35%
2520
16th to endDay
14%6%25%6%36%6%7%8%30%
2556
August1st to 15thDay
14%6%26%6%35%5%6%8%31%
2340
16th to endDay
15%6%25%6%35%5%6%8%34%
2375
September1st to 15thDay
21%6%35%424447%33%
2098
16th to endDay
19%7%245%25%46%7%35%
1797
October1st to 15thDay
25%8%36%42435%430%
1650
16th to endDay
27%18%36%5%2433419%
1760
November1st to 15thDay
14%17%6%6%424445%29%
1522
16th to endDay
20%22%6%7%5%2435%417%
1440
December1st to 15thDay
17%25%9%13%6%3342310%
1440
16th to endDay
18%21%13%16%6%333237%
1536
January1st to 15thNight
14%20%9%16%10%4433310%
2487
16th to endNight
10%19%11%16%10%5%5%32310%
2496
February1st to 15thNight
13%19%8%15%10%46%32311%
2285
16th to endNight
12%15%7%17%9%3444416%
1997
March1st to 15thNight
16%14%6%11%6%44335%22%
1975
16th to endNight
15%13%6%9%5%33335%30%
2109
April1st to 15thNight
21%12%46%5%24345%30%
1796
16th to endNight
15%10%245%2445%6%38%
1707
May1st to 15thNight
18%6%36%6%45%5%5%6%31%
1551
16th to endNight
12%6%35%425%45%7%42%
1495
June1st to 15thNight
16%5%25%435%46%7%36%
1440
16th to endNight
14%6%245%35%46%7%39%
1440
July1st to 15thNight
8%5%25%6%245%6%8%44%
1440
16th to endNight
10%415%425%6%6%7%44%
1609
August1st to 15thNight
9%425%4345%5%9%43%
1620
16th to endNight
10%5%24425%5%6%6%44%
1815
September1st to 15thNight
17%6%24323446%43%
1750
16th to endNight
17%6%244345%46%40%
1831
October1st to 15thNight
21%8%25%5%34346%33%
1980
16th to endNight
28%13%35%424435%21%
2112
November1st to 15thNight
17%13%36%434345%32%
2334
16th to endNight
16%19%6%10%6%24445%19%
2520
December1st to 15thNight
19%21%10%11%6%3433311%
2520
16th to endNight
16%22%11%14%7%343338%
2688

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
14%19%7%15%10%35%34410%
1450
16th to endDay
10%17%10%17%13%5%5%3339%
1728
February1st to 15thDay
12%21%10%13%12%4442211%
1575
16th to endDay
15%15%8%12%10%34335%17%
1476
March1st to 15thDay
16%15%8%12%6%33335%21%
1971
16th to endDay
15%17%6%8%5%24445%25%
2114
April1st to 15thDay
19%14%5%6%5%3344428%
2152
16th to endDay
18%12%35%413335%36%
2262
May1st to 15thDay
19%10%36%6%2435%6%30%
2398
16th to endDay
15%7%25%5%35%45%7%35%
2618
June1st to 15thDay
21%8%35%43445%7%31%
2520
16th to endDay
17%6%25%5%35%6%6%8%33%
2520
July1st to 15thDay
12%5%36%5%36%5%6%8%35%
2520
16th to endDay
14%6%26%7%46%6%6%9%29%
2556
August1st to 15thDay
14%8%26%6%35%5%6%9%31%
2340
16th to endDay
15%6%26%5%35%6%6%8%33%
2375
September1st to 15thDay
20%6%36%5%3445%7%33%
2098
16th to endDay
18%7%35%5%3445%8%34%
1797
October1st to 15thDay
24%9%26%5%2444431%
1650
16th to endDay
25%18%47%42433420%
1760
November1st to 15thDay
13%17%6%5%5%2445%6%28%
1522
16th to endDay
19%20%7%8%5%2444418%
1440
December1st to 15thDay
16%23%10%13%7%2342410%
1440
16th to endDay
16%20%13%17%8%233337%
1536
January1st to 15thNight
14%17%9%16%9%45%43310%
2487
16th to endNight
10%18%11%16%12%45%33310%
2496
February1st to 15thNight
13%16%9%14%11%46%43212%
2278
16th to endNight
11%14%7%15%11%4433418%
1997
March1st to 15thNight
16%13%7%10%7%35%335%23%
1987
16th to endNight
14%12%6%9%5%3423430%
2109
April1st to 15thNight
20%12%35%6%24445%30%
1796
16th to endNight
14%10%25%42445%6%38%
1707
May1st to 15thNight
17%6%26%6%36%5%5%7%31%
1551
16th to endNight
11%6%245%25%46%7%42%
1495
June1st to 15thNight
16%5%25%5%35%5%6%7%37%
1440
16th to endNight
13%6%25%5%25%46%8%39%
1440
July1st to 15thNight
8%425%5%345%5%9%45%
1440
16th to endNight
9%5%24435%5%6%8%44%
1609
August1st to 15thNight
8%4245%345%5%9%44%
1620
16th to endNight
10%425%4345%6%7%44%
1815
September1st to 15thNight
17%5%24324347%44%
1750
16th to endNight
17%6%245%345%46%40%
1831
October1st to 15thNight
21%7%25%5%24446%33%
1980
16th to endNight
28%13%36%423446%22%
2112
November1st to 15thNight
17%12%36%444345%33%
2334
16th to endNight
15%17%6%11%6%34445%21%
2520
December1st to 15thNight
18%20%9%12%7%3433411%
2520
16th to endNight
16%20%10%15%8%344339%
2688

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
77%48%6%3
1451
16th to endDay
80%38%41
1728
February1st to 15thDay
80%46%5%2
1577
16th to endDay
69%211%12%3
1476
March1st to 15thDay
66%311%13%4
1971
16th to endDay
60%47%17%8%1
2115
April1st to 15thDay
59%49%16%9%
2152
16th to endDay
49%49%18%15%2
2262
May1st to 15thDay
53%5%9%20%10%
2398
16th to endDay
46%6%13%19%12%1
2622
June1st to 15thDay
51%5%11%20%10%
2520
16th to endDay
46%7%13%20%11%
2520
July1st to 15thDay
44%7%9%22%13%1
2371
16th to endDay
47%9%14%18%10%
2397
August1st to 15thDay
46%8%12%20%11%
2327
16th to endDay
45%7%11%23%10%1
2375
September1st to 15thDay
49%6%10%22%10%
2098
16th to endDay
47%5%10%21%13%
1797
October1st to 15thDay
55%5%9%16%11%1
1650
16th to endDay
67%411%11%3
1760
November1st to 15thDay
55%6%11%15%9%2
1522
16th to endDay
68%410%10%41
1440
December1st to 15thDay
77%39%6%
1440
16th to endDay
81%5%7%4
1536
January1st to 15thNight
77%5%7%5%4
2487
16th to endNight
79%37%7%2
2496
February1st to 15thNight
76%5%8%7%3
2287
16th to endNight
68%49%12%4
1997
March1st to 15thNight
64%410%15%4
1987
16th to endNight
57%48%15%11%1
2109
April1st to 15thNight
56%410%17%11%
1796
16th to endNight
45%411%20%15%2
1707
May1st to 15thNight
50%6%9%22%10%
1551
16th to endNight
38%7%15%22%15%1
1497
June1st to 15thNight
42%6%15%21%13%
1440
16th to endNight
41%6%14%22%13%1
1440
July1st to 15thNight
35%7%14%22%18%1
1360
16th to endNight
36%6%15%25%13%2
1505
August1st to 15thNight
34%8%17%27%11%
1609
16th to endNight
35%7%14%28%13%1
1815
September1st to 15thNight
41%413%26%12%1
1750
16th to endNight
42%6%11%24%13%1
1831
October1st to 15thNight
50%6%10%17%13%
1980
16th to endNight
62%6%14%12%3
2112
November1st to 15thNight
52%5%12%17%8%4
2334
16th to endNight
65%412%12%4
2520
December1st to 15thNight
76%49%7%2
2520
16th to endNight
79%5%7%6%
2688

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
26%36%25%7%3
63
16th to endDay
27%36%28%7%1
96
February1st to 15thDay
33%42%18%5%
90
16th to endDay
29%25%33%9%1
135
March1st to 15thDay
32%22%26%13%4
270
16th to endDay
26%25%28%13%5%
288
April1st to 15thDay
37%16%28%11%41
270
16th to endDay
24%17%31%16%7%4
270
May1st to 15thDay
36%13%22%17%8%1
288
16th to endDay
19%15%33%18%8%4
331
June1st to 15thDay
26%12%31%19%9%1
315
16th to endDay
23%10%34%21%7%1
315
July1st to 15thDay
15%9%27%30%13%5%
305
16th to endDay
13%8%34%25%12%5%
326
August1st to 15thDay
15%7%26%24%16%7%
313
16th to endDay
16%7%24%25%14%11%
332
September1st to 15thDay
20%6%25%23%17%6%
294
16th to endDay
18%9%22%21%18%8%
254
October1st to 15thDay
26%8%28%19%12%4
255
16th to endDay
37%19%25%14%3
272
November1st to 15thDay
24%11%33%18%9%1
153
16th to endDay
33%25%25%16%
60
December1st to 15thDay
36%33%15%11%3
60
16th to endDay
42%29%26%1
64
January1st to 15thNight
28%29%29%10%2
720
16th to endNight
23%33%29%11%2
768
February1st to 15thNight
28%29%31%8%
704
16th to endNight
25%30%30%11%2
631
March1st to 15thNight
27%28%25%15%2
720
16th to endNight
23%20%34%15%6%
768
April1st to 15thNight
29%18%30%18%2
718
16th to endNight
21%13%29%27%7%
627
May1st to 15thNight
19%9%25%33%10%1
471
16th to endNight
13%9%36%25%13%1
375
June1st to 15thNight
17%8%31%32%9%
360
16th to endNight
16%6%36%32%8%
360
July1st to 15thNight
8%5%31%36%18%1
340
16th to endNight
10%431%32%19%1
471
August1st to 15thNight
10%429%32%19%3
539
16th to endNight
11%6%23%30%25%2
669
September1st to 15thNight
20%8%22%29%17%1
700
16th to endNight
19%9%21%25%21%3
657
October1st to 15thNight
26%11%25%21%13%1
660
16th to endNight
36%14%29%16%2
704
November1st to 15thNight
24%17%30%18%7%1
700
16th to endNight
27%26%25%13%6%
720
December1st to 15thNight
31%28%25%10%2
720
16th to endNight
28%32%27%10%1
768
Page generated at 2017-09-11 19:35:29. Version ac04

Copyright 2017 A. Danko


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