Beman Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Beman Observatory clear sky chart from 2005-11-05 to 2017-09-24.

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
37%
15965
15%
46879
10%
15923
42%
15923
20%
33111

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
15%
900
8%
2506
3%
895
19%
895
10%
2051
January16th to endNight
18%
930
6%
2658
2%
930
22%
930
9%
2238
February1st to 15thNight
18%
701
9%
2208
3%
701
24%
701
11%
1733
February16th to endNight
23%
631
14%
1893
6%
631
31%
631
14%
1419
March1st to 15thNight
29%
720
14%
2115
9%
720
33%
720
18%
1508
March16th to endNight
31%
759
18%
2103
9%
759
39%
759
22%
1491
April1st to 15thNight
29%
539
13%
1797
8%
539
35%
539
19%
1240
April16th to endNight
35%
540
19%
1626
9%
540
43%
540
23%
1080
May1st to 15thNight
36%
540
13%
1620
7%
540
42%
540
21%
1139
May16th to endNight
48%
562
15%
1606
10%
561
53%
561
29%
1018
June1st to 15thNight
53%
540
15%
1440
10%
540
57%
540
34%
905
June16th to endNight
57%
540
15%
1440
13%
540
59%
540
34%
910
July1st to 15thNight
67%
510
17%
1360
14%
510
69%
510
40%
816
July16th to endNight
68%
564
21%
1443
17%
531
71%
531
40%
865
August1st to 15thNight
67%
539
21%
1609
18%
536
69%
536
38%
932
August16th to endNight
64%
573
21%
1803
19%
573
68%
573
33%
1054
September1st to 15thNight
60%
630
26%
1890
22%
630
64%
630
34%
1100
September16th to endNight
59%
693
24%
1914
19%
693
62%
693
34%
1185
October1st to 15thNight
46%
660
22%
1859
17%
660
51%
660
27%
1236
October16th to endNight
28%
704
15%
2255
9%
704
37%
704
17%
1593
November1st to 15thNight
37%
700
19%
2276
17%
700
42%
700
20%
1523
November16th to endNight
26%
720
12%
2340
9%
720
31%
720
13%
1761
December1st to 15thNight
17%
810
7%
2430
3%
810
22%
810
10%
2000
December16th to endNight
13%
960
7%
2688
1%
960
18%
960
7%
2314

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
13%8%47%6%35%45%7%33%
48050
Night
15%9%46%5%3445%6%34%
47051
Cloud CoverDay
13%9%47%6%35%5%5%7%32%
48059
Night
15%9%46%6%3445%7%34%
47056
TransparencyDay
49%6%11%20%11%1
47740
Night
49%5%11%20%11%1
46879
SeeingDay
16%7%26%25%15%7%
5958
Night
18%7%28%30%12%1
15969

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
17%15%8%9%9%45%45%5%14%
1432
16th to endDay
13%19%9%11%10%46%345%12%
1566
February1st to 15thDay
13%13%7%12%9%5%6%43419%
1651
16th to endDay
13%14%6%10%9%35%5%5%5%20%
1580
March1st to 15thDay
13%11%5%9%6%345%5%6%28%
1833
16th to endDay
17%9%46%6%2436%6%32%
2131
April1st to 15thDay
19%11%46%5%23445%31%
2151
16th to endDay
16%7%25%434447%38%
2334
May1st to 15thDay
19%6%36%6%3445%6%32%
2331
16th to endDay
12%7%35%6%345%5%7%39%
2506
June1st to 15thDay
10%5%345%45%5%7%8%40%
2520
16th to endDay
8%425%6%36%6%8%9%36%
2520
July1st to 15thDay
7%3245%35%5%6%7%46%
2520
16th to endDay
7%425%5%36%5%8%9%41%
2625
August1st to 15thDay
8%5%25%5%46%5%6%9%40%
2340
16th to endDay
11%5%26%5%35%5%6%9%38%
2396
September1st to 15thDay
12%5%245%35%35%7%43%
2058
16th to endDay
11%5%245%345%5%9%41%
1905
October1st to 15thDay
14%7%36%5%345%5%5%39%
1770
16th to endDay
20%9%47%5%35%446%30%
1616
November1st to 15thDay
13%10%36%6%34336%39%
1582
16th to endDay
16%15%6%9%6%24446%22%
1620
December1st to 15thDay
14%15%9%11%5%45%446%18%
1527
16th to endDay
19%18%8%12%6%4333413%
1536
January1st to 15thNight
20%14%6%10%7%3344419%
2506
16th to endNight
12%13%9%12%10%5%5%5%45%15%
2658
February1st to 15thNight
14%14%6%10%6%45%44424%
2206
16th to endNight
14%12%5%7%6%45%45%7%25%
1893
March1st to 15thNight
16%11%36%5%34346%34%
2102
16th to endNight
14%7%46%5%3445%7%35%
2103
April1st to 15thNight
18%9%345%25%45%7%33%
1797
16th to endNight
16%7%26%425%35%6%39%
1626
May1st to 15thNight
19%6%25%5%3445%7%33%
1620
16th to endNight
12%4245%25%45%9%42%
1604
June1st to 15thNight
10%5%245%134410%46%
1440
16th to endNight
7%4145%35%5%6%11%42%
1440
July1st to 15thNight
6%2234245%7%8%51%
1440
16th to endNight
6%31442445%9%53%
1541
August1st to 15thNight
6%3145%4446%8%49%
1620
16th to endNight
10%42433345%7%50%
1803
September1st to 15thNight
12%413313447%51%
1890
16th to endNight
11%5%2443345%7%47%
1914
October1st to 15thNight
17%6%25%433346%41%
1859
16th to endNight
20%8%35%5%34345%33%
2255
November1st to 15thNight
14%9%36%4245%46%37%
2276
16th to endNight
18%13%5%7%5%335%47%25%
2340
December1st to 15thNight
19%15%7%9%6%35%445%18%
2430
16th to endNight
21%17%7%9%7%3434413%
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
18%15%7%9%9%46%445%14%
1432
16th to endDay
12%19%9%10%11%45%435%12%
1566
February1st to 15thDay
12%14%6%12%9%5%6%43419%
1651
16th to endDay
14%14%6%11%8%46%5%4420%
1580
March1st to 15thDay
14%11%5%8%6%35%45%6%27%
1843
16th to endDay
17%10%46%5%2445%7%31%
2130
April1st to 15thDay
19%11%36%5%24445%30%
2151
16th to endDay
16%7%25%434447%38%
2334
May1st to 15thDay
18%7%36%6%3445%6%31%
2331
16th to endDay
12%7%25%6%3445%8%38%
2506
June1st to 15thDay
10%425%5%35%5%7%8%40%
2520
16th to endDay
8%5%25%6%37%7%8%9%35%
2520
July1st to 15thDay
7%4145%35%5%7%8%46%
2520
16th to endDay
7%425%5%36%5%7%10%40%
2625
August1st to 15thDay
7%5%25%5%45%6%6%10%39%
2340
16th to endDay
11%5%25%5%45%6%5%8%38%
2396
September1st to 15thDay
12%5%15%5%35%45%8%42%
2058
16th to endDay
11%6%245%345%5%9%40%
1905
October1st to 15thDay
14%7%36%5%245%46%39%
1770
16th to endDay
20%10%46%5%35%445%30%
1616
November1st to 15thDay
13%10%36%6%24435%39%
1582
16th to endDay
16%15%6%8%6%26%346%23%
1620
December1st to 15thDay
15%14%9%11%6%35%446%18%
1527
16th to endDay
19%18%9%12%7%3333414%
1536
January1st to 15thNight
21%13%7%10%7%34345%19%
2506
16th to endNight
13%12%9%12%11%45%5%45%14%
2658
February1st to 15thNight
14%15%7%9%7%45%34424%
2199
16th to endNight
14%11%6%7%7%345%5%6%25%
1893
March1st to 15thNight
17%11%36%6%24346%34%
2115
16th to endNight
15%7%46%6%335%5%6%35%
2103
April1st to 15thNight
18%9%35%435%45%7%33%
1797
16th to endNight
16%7%26%42435%7%38%
1626
May1st to 15thNight
20%7%25%5%3445%7%33%
1619
16th to endNight
11%5%3443445%9%43%
1604
June1st to 15thNight
10%5%2442435%9%46%
1440
16th to endNight
7%4246%25%5%7%10%43%
1440
July1st to 15thNight
6%2234245%6%10%50%
1440
16th to endNight
6%32432346%9%52%
1541
August1st to 15thNight
6%315%6%3346%8%49%
1620
16th to endNight
10%425%323448%50%
1803
September1st to 15thNight
12%423323348%51%
1890
16th to endNight
11%5%35%42435%7%47%
1914
October1st to 15thNight
16%6%25%424346%41%
1859
16th to endNight
20%7%35%6%33446%33%
2255
November1st to 15thNight
14%10%36%5%345%46%37%
2276
16th to endNight
19%13%5%7%5%3345%6%25%
2340
December1st to 15thNight
19%14%6%10%7%34436%18%
2430
16th to endNight
22%16%7%10%7%34445%13%
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
71%5%11%9%2
1433
16th to endDay
74%49%8%2
1566
February1st to 15thDay
68%5%5%13%5%
1653
16th to endDay
65%5%10%12%5%
1580
March1st to 15thDay
55%6%12%16%7%1
1843
16th to endDay
52%5%11%21%8%1
2131
April1st to 15thDay
55%49%19%11%
2151
16th to endDay
45%6%12%17%14%3
2334
May1st to 15thDay
51%5%12%19%9%1
2331
16th to endDay
42%6%12%25%11%1
2510
June1st to 15thDay
38%7%12%25%15%1
2520
16th to endDay
39%9%13%20%15%1
2520
July1st to 15thDay
34%7%11%23%20%2
2371
16th to endDay
35%8%14%22%16%2
2460
August1st to 15thDay
37%8%12%26%12%2
2327
16th to endDay
40%7%11%25%13%2
2396
September1st to 15thDay
39%5%12%25%15%1
2058
16th to endDay
38%6%11%27%15%
1905
October1st to 15thDay
45%5%10%24%12%1
1770
16th to endDay
55%5%12%18%6%
1616
November1st to 15thDay
47%5%10%21%13%1
1582
16th to endDay
62%5%12%15%4
1620
December1st to 15thDay
67%411%13%3
1527
16th to endDay
75%49%7%2
1536
January1st to 15thNight
67%410%12%4
2506
16th to endNight
69%6%11%9%2
2658
February1st to 15thNight
63%5%9%15%5%1
2208
16th to endNight
57%5%12%18%5%1
1893
March1st to 15thNight
52%412%19%9%1
2115
16th to endNight
48%5%11%22%10%1
2103
April1st to 15thNight
49%6%11%18%14%
1797
16th to endNight
44%5%12%18%15%3
1626
May1st to 15thNight
49%412%19%11%2
1620
16th to endNight
37%6%14%24%15%2
1606
June1st to 15thNight
34%5%12%28%16%1
1440
16th to endNight
33%7%17%23%16%1
1440
July1st to 15thNight
28%7%12%27%22%2
1360
16th to endNight
27%8%13%25%21%3
1443
August1st to 15thNight
29%5%14%28%18%2
1609
16th to endNight
33%5%10%27%19%3
1803
September1st to 15thNight
32%5%9%29%21%1
1890
16th to endNight
35%411%28%18%1
1914
October1st to 15thNight
43%410%22%18%
1859
16th to endNight
51%5%10%22%8%1
2255
November1st to 15thNight
46%5%10%21%13%2
2276
16th to endNight
58%6%12%18%5%
2340
December1st to 15thNight
66%6%10%11%5%
2430
16th to endNight
72%5%8%9%2
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
18%13%51%14%2
90
16th to endDay
29%8%44%14%3
96
February1st to 15thDay
20%23%43%13%
90
16th to endDay
19%18%34%22%4
81
March1st to 15thDay
30%11%33%18%7%
133
16th to endDay
25%9%30%22%10%1
288
April1st to 15thDay
24%12%29%25%7%
270
16th to endDay
20%7%33%21%12%4
270
May1st to 15thDay
23%9%24%25%9%6%
288
16th to endDay
17%8%26%26%13%7%
406
June1st to 15thDay
12%5%28%32%14%6%
495
16th to endDay
12%7%30%28%14%5%
495
July1st to 15thDay
8%424%29%21%10%
475
16th to endDay
10%322%30%23%9%
485
August1st to 15thDay
10%114%26%25%21%
313
16th to endDay
13%318%21%27%15%
332
September1st to 15thDay
13%316%23%28%14%
315
16th to endDay
14%412%25%28%14%
287
October1st to 15thDay
15%7%20%36%14%5%
255
16th to endDay
25%13%30%25%5%
128
November1st to 15thDay
8%13%26%36%8%5%
90
16th to endDay
31%18%34%11%4
90
December1st to 15thDay
24%22%36%14%2
90
16th to endDay
26%34%35%31
96
January1st to 15thNight
25%14%34%19%5%
900
16th to endNight
17%11%36%30%5%
930
February1st to 15thNight
24%10%38%23%3
704
16th to endNight
20%12%34%28%4
631
March1st to 15thNight
23%10%31%26%6%1
720
16th to endNight
17%9%34%28%8%
759
April1st to 15thNight
20%10%34%28%5%
539
16th to endNight
19%7%35%27%9%1
540
May1st to 15thNight
24%428%30%10%1
540
16th to endNight
14%227%36%16%2
563
June1st to 15thNight
12%224%42%17%
540
16th to endNight
8%124%41%21%2
540
July1st to 15thNight
8%116%45%24%3
510
16th to endNight
7%115%44%28%2
564
August1st to 15thNight
7%113%45%28%3
539
16th to endNight
12%114%35%30%5%
573
September1st to 15thNight
13%216%33%26%6%
630
16th to endNight
13%416%30%28%5%
693
October1st to 15thNight
18%6%21%33%18%1
660
16th to endNight
23%11%32%24%7%
704
November1st to 15thNight
20%9%28%30%10%1
700
16th to endNight
25%12%29%25%6%
720
December1st to 15thNight
26%13%35%21%4
810
16th to endNight
28%11%37%19%2
960
Page generated at 2017-09-25 09:02:30. Version ac04

Copyright 2017 A. Danko


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