Black Swamp Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Black Swamp Observatory clear sky chart from 2005-11-05 to 2017-10-31.

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
38%
15996
16%
47287
11%
15954
43%
15954
21%
32758

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
17%
900
11%
2506
5%
895
23%
895
13%
1968
January16th to endNight
17%
843
9%
2571
4%
843
23%
843
11%
2029
February1st to 15thNight
20%
701
9%
2220
4%
701
26%
701
12%
1687
February16th to endNight
23%
631
14%
1893
6%
631
30%
631
14%
1416
March1st to 15thNight
28%
720
13%
2090
9%
720
31%
720
17%
1531
March16th to endNight
31%
768
17%
2112
10%
768
38%
768
21%
1498
April1st to 15thNight
30%
572
14%
1823
8%
572
37%
572
19%
1258
April16th to endNight
37%
540
20%
1620
8%
540
46%
540
24%
1069
May1st to 15thNight
37%
540
12%
1620
6%
540
43%
540
18%
1187
May16th to endNight
50%
562
17%
1684
12%
561
55%
561
29%
1051
June1st to 15thNight
56%
540
16%
1455
11%
540
61%
540
33%
929
June16th to endNight
57%
540
16%
1440
12%
540
61%
540
32%
926
July1st to 15thNight
63%
510
17%
1360
14%
510
65%
510
38%
825
July16th to endNight
70%
564
19%
1513
16%
531
73%
531
40%
868
August1st to 15thNight
71%
539
21%
1609
18%
536
73%
536
37%
926
August16th to endNight
67%
573
21%
1782
18%
573
71%
573
33%
1046
September1st to 15thNight
60%
657
26%
1917
20%
657
64%
657
35%
1125
September16th to endNight
62%
717
26%
1980
21%
717
65%
717
35%
1221
October1st to 15thNight
48%
720
21%
2046
17%
720
53%
720
28%
1323
October16th to endNight
30%
768
19%
2411
14%
768
38%
768
19%
1636
November1st to 15thNight
38%
700
22%
2276
18%
700
46%
700
24%
1439
November16th to endNight
26%
720
13%
2340
11%
720
30%
720
13%
1739
December1st to 15thNight
20%
720
9%
2340
5%
720
25%
720
11%
1837
December16th to endNight
16%
951
7%
2679
2%
951
21%
951
10%
2224

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
14%8%36%6%35%5%5%7%33%
48453
Night
15%8%36%5%34446%36%
47466
Cloud CoverDay
14%8%36%6%35%5%5%7%33%
48463
Night
15%8%36%5%34446%36%
47470
TransparencyDay
48%6%12%19%11%1
48151
Night
47%5%12%20%12%1
47287
SeeingDay
17%7%24%24%17%8%
5998
Night
19%7%27%29%14%1
16000

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
19%16%6%8%8%33345%20%
1432
16th to endDay
15%16%7%9%7%445%45%17%
1651
February1st to 15thDay
14%14%5%11%7%45%346%22%
1640
16th to endDay
15%11%5%9%7%35%5%45%23%
1580
March1st to 15thDay
20%12%5%7%7%23445%25%
1858
16th to endDay
20%9%47%6%24446%29%
2112
April1st to 15thDay
19%9%36%6%3445%7%29%
2135
16th to endDay
16%7%35%5%34346%39%
2340
May1st to 15thDay
18%8%37%6%46%45%6%29%
2331
16th to endDay
11%5%35%5%35%6%6%7%39%
2431
June1st to 15thDay
11%5%26%5%35%5%6%8%40%
2502
16th to endDay
9%5%25%6%46%7%6%9%35%
2520
July1st to 15thDay
8%5%35%5%35%5%5%9%41%
2520
16th to endDay
8%425%5%35%6%8%9%40%
2548
August1st to 15thDay
6%425%5%46%6%7%9%42%
2340
16th to endDay
8%425%6%36%5%6%9%40%
2417
September1st to 15thDay
12%5%35%5%345%5%7%42%
2029
16th to endDay
13%424335%45%6%44%
1980
October1st to 15thDay
14%7%26%6%3445%7%39%
1914
16th to endDay
18%7%36%5%35%446%33%
1809
November1st to 15thDay
12%9%3443435%6%41%
1582
16th to endDay
19%13%48%6%23436%26%
1620
December1st to 15thDay
18%15%6%10%6%35%335%21%
1620
16th to endDay
20%15%8%9%6%4445%415%
1542
January1st to 15thNight
21%13%5%7%5%3434426%
2506
16th to endNight
14%14%6%9%7%45%445%21%
2571
February1st to 15thNight
15%13%6%8%5%34446%26%
2218
16th to endNight
17%10%48%7%34346%28%
1893
March1st to 15thNight
18%10%36%6%34446%31%
2078
16th to endNight
15%9%46%5%34446%35%
2112
April1st to 15thNight
18%7%35%435%5%6%6%33%
1823
16th to endNight
15%6%25%5%245%47%40%
1620
May1st to 15thNight
18%6%46%5%45%5%5%6%31%
1620
16th to endNight
12%5%2443445%7%44%
1682
June1st to 15thNight
9%326%425%45%8%46%
1455
16th to endNight
8%4145%25%5%7%10%43%
1440
July1st to 15thNight
5%4145%25%36%9%50%
1440
16th to endNight
6%32442347%8%52%
1617
August1st to 15thNight
4413435%5%6%10%50%
1620
16th to endNight
9%315%33345%8%50%
1782
September1st to 15thNight
10%424323437%53%
1917
16th to endNight
11%414324447%50%
1980
October1st to 15thNight
13%6%35%423446%44%
2046
16th to endNight
19%7%345%24445%37%
2411
November1st to 15thNight
14%7%34434446%43%
2276
16th to endNight
22%10%47%5%34346%27%
2340
December1st to 15thNight
20%13%5%8%5%44346%22%
2340
16th to endNight
24%15%5%8%5%34445%18%
2679

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
20%15%7%8%7%43335%20%
1432
16th to endDay
15%17%6%9%7%45%445%17%
1651
February1st to 15thDay
14%15%6%10%8%34446%22%
1640
16th to endDay
15%12%5%9%7%45%5%5%6%23%
1580
March1st to 15thDay
20%12%6%8%6%23345%25%
1869
16th to endDay
20%10%37%5%33446%28%
2111
April1st to 15thDay
19%9%35%6%34447%30%
2135
16th to endDay
16%7%25%5%34446%39%
2340
May1st to 15thDay
18%7%36%7%36%5%5%6%28%
2331
16th to endDay
11%5%25%5%36%6%6%7%39%
2431
June1st to 15thDay
11%426%5%45%5%6%8%40%
2502
16th to endDay
10%5%25%6%46%6%6%8%36%
2520
July1st to 15thDay
8%5%25%5%35%5%6%9%41%
2520
16th to endDay
8%425%5%346%7%8%41%
2548
August1st to 15thDay
6%425%5%46%6%7%9%42%
2340
16th to endDay
9%425%5%46%6%6%9%40%
2417
September1st to 15thDay
12%6%25%4345%5%7%42%
2029
16th to endDay
13%5%2443446%7%44%
1980
October1st to 15thDay
14%7%26%6%34447%39%
1914
16th to endDay
18%8%346%35%445%34%
1809
November1st to 15thDay
13%8%3443345%6%41%
1582
16th to endDay
19%12%5%8%6%24346%26%
1620
December1st to 15thDay
18%15%7%10%6%24335%21%
1620
16th to endDay
20%15%8%9%6%35%445%15%
1542
January1st to 15thNight
22%13%5%7%5%33345%26%
2506
16th to endNight
15%14%6%9%7%345%46%21%
2571
February1st to 15thNight
15%14%6%8%5%34446%26%
2211
16th to endNight
17%11%5%7%6%43446%28%
1893
March1st to 15thNight
19%9%36%6%34346%31%
2090
16th to endNight
15%8%36%5%33447%35%
2112
April1st to 15thNight
18%7%35%4345%6%5%33%
1823
16th to endNight
16%6%25%434448%39%
1620
May1st to 15thNight
18%6%46%5%46%5%5%6%31%
1619
16th to endNight
12%5%244245%5%7%44%
1682
June1st to 15thNight
9%326%425%45%7%47%
1455
16th to endNight
8%4145%35%5%7%10%43%
1440
July1st to 15thNight
6%3145%2445%9%50%
1440
16th to endNight
5%32443337%9%52%
1617
August1st to 15thNight
44235%25%5%6%9%50%
1620
16th to endNight
9%41442445%7%50%
1782
September1st to 15thNight
11%324324436%53%
1917
16th to endNight
11%413424447%50%
1980
October1st to 15thNight
13%6%25%42345%5%44%
2046
16th to endNight
20%6%25%5%34445%37%
2411
November1st to 15thNight
15%7%24434437%43%
2276
16th to endNight
22%11%37%5%34346%27%
2340
December1st to 15thNight
20%13%6%8%6%34346%22%
2340
16th to endNight
24%15%5%8%5%34445%18%
2679

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
67%5%12%11%3
1433
16th to endDay
66%7%10%9%5%
1651
February1st to 15thDay
64%5%8%15%5%
1642
16th to endDay
61%5%12%15%41
1580
March1st to 15thDay
61%5%11%15%5%
1869
16th to endDay
55%5%11%21%5%
2112
April1st to 15thDay
53%5%11%16%11%
2135
16th to endDay
45%5%11%20%12%3
2340
May1st to 15thDay
54%6%11%17%9%
2331
16th to endDay
41%8%12%22%12%1
2435
June1st to 15thDay
40%7%11%24%14%1
2502
16th to endDay
42%9%12%16%15%2
2520
July1st to 15thDay
37%7%11%21%18%2
2371
16th to endDay
34%10%15%23%13%1
2390
August1st to 15thDay
35%9%15%23%15%1
2327
16th to endDay
37%8%12%21%15%3
2417
September1st to 15thDay
40%5%12%22%17%2
2029
16th to endDay
37%5%10%25%19%
1980
October1st to 15thDay
44%411%22%14%1
1914
16th to endDay
50%5%14%19%9%
1809
November1st to 15thDay
43%5%11%21%17%1
1582
16th to endDay
59%412%16%6%
1620
December1st to 15thDay
65%6%10%13%4
1620
16th to endDay
69%7%11%8%2
1542
January1st to 15thNight
61%410%15%8%
2506
16th to endNight
63%5%14%12%4
2571
February1st to 15thNight
58%6%11%16%5%
2220
16th to endNight
57%5%10%19%6%
1893
March1st to 15thNight
54%412%17%9%1
2090
16th to endNight
48%6%11%23%8%2
2112
April1st to 15thNight
49%5%12%18%14%
1823
16th to endNight
43%5%11%19%17%3
1620
May1st to 15thNight
52%6%11%17%10%1
1620
16th to endNight
37%6%11%26%14%3
1684
June1st to 15thNight
35%7%11%25%18%1
1455
16th to endNight
33%9%16%22%16%2
1440
July1st to 15thNight
30%6%14%25%19%3
1360
16th to endNight
25%7%16%26%19%4
1513
August1st to 15thNight
28%7%15%27%18%2
1609
16th to endNight
31%7%12%23%20%4
1782
September1st to 15thNight
32%412%25%21%3
1917
16th to endNight
33%5%9%26%22%2
1980
October1st to 15thNight
39%5%11%21%20%
2046
16th to endNight
47%410%25%9%1
2411
November1st to 15thNight
41%5%11%22%16%2
2276
16th to endNight
58%411%18%6%
2340
December1st to 15thNight
63%5%10%13%6%
2340
16th to endNight
67%6%11%10%4
2679

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
22%17%36%13%7%2
90
16th to endDay
32%9%40%13%4
96
February1st to 15thDay
22%23%43%11%
90
16th to endDay
19%18%34%19%7%
81
March1st to 15thDay
33%12%21%23%8%
159
16th to endDay
28%9%31%18%9%2
288
April1st to 15thDay
23%12%30%22%9%1
270
16th to endDay
19%10%31%20%12%6%
270
May1st to 15thDay
27%5%24%24%12%5%
288
16th to endDay
14%6%28%23%16%10%
331
June1st to 15thDay
10%429%31%18%6%
477
16th to endDay
15%5%25%29%17%6%
495
July1st to 15thDay
11%225%31%20%9%
475
16th to endDay
7%219%26%27%15%
408
August1st to 15thDay
10%213%27%25%20%
313
16th to endDay
11%215%23%26%18%
332
September1st to 15thDay
14%114%24%30%13%
315
16th to endDay
15%411%20%29%18%
314
October1st to 15thDay
18%7%19%25%24%5%
315
16th to endDay
19%12%30%30%6%
225
November1st to 15thDay
12%11%25%25%18%6%
90
16th to endDay
24%14%40%14%6%
90
December1st to 15thDay
23%23%34%13%5%
90
16th to endDay
29%20%39%9%1
96
January1st to 15thNight
27%12%34%19%3
900
16th to endNight
20%13%37%23%5%
843
February1st to 15thNight
22%13%35%24%3
704
16th to endNight
22%12%34%27%3
631
March1st to 15thNight
24%8%31%27%7%
720
16th to endNight
18%10%35%24%10%
768
April1st to 15thNight
21%12%33%26%5%
572
16th to endNight
18%7%33%26%12%1
540
May1st to 15thNight
21%5%28%30%12%
540
16th to endNight
14%325%34%19%2
563
June1st to 15thNight
10%222%44%20%
540
16th to endNight
10%124%39%22%1
540
July1st to 15thNight
7%118%41%27%2
510
16th to endNight
6%112%42%32%4
564
August1st to 15thNight
7%14%43%28%5%
539
16th to endNight
10%110%35%37%4
573
September1st to 15thNight
12%317%32%29%4
657
16th to endNight
13%314%31%31%4
717
October1st to 15thNight
17%6%22%29%20%2
720
16th to endNight
24%10%31%25%8%
768
November1st to 15thNight
18%9%29%27%12%1
700
16th to endNight
28%12%26%24%7%
720
December1st to 15thNight
28%10%34%21%4
720
16th to endNight
29%11%35%19%3
951
Page generated at 2017-11-01 17:23:39. Version ac04

Copyright 2017 A. Danko


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