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 2017-04-07.

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%
15325
15%
45333
11%
15283
43%
15283
21%
31600

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
29%
548
14%
1744
8%
548
37%
548
19%
1208
April16th to endNight
37%
495
18%
1485
8%
495
46%
495
24%
995
May1st to 15thNight
37%
495
12%
1485
7%
495
43%
495
17%
1103
May16th to endNight
53%
514
16%
1540
12%
513
57%
513
30%
954
June1st to 15thNight
54%
495
17%
1334
12%
495
59%
495
31%
869
June16th to endNight
59%
495
15%
1320
12%
495
62%
495
31%
856
July1st to 15thNight
64%
465
18%
1240
16%
465
65%
465
38%
753
July16th to endNight
69%
522
17%
1393
14%
489
72%
489
38%
816
August1st to 15thNight
71%
494
22%
1474
19%
491
73%
491
36%
852
August16th to endNight
67%
525
20%
1633
17%
525
71%
525
33%
959
September1st to 15thNight
61%
602
27%
1757
21%
602
65%
602
36%
1022
September16th to endNight
61%
657
24%
1815
20%
657
64%
657
34%
1134
October1st to 15thNight
49%
660
22%
1875
18%
660
54%
660
29%
1196
October16th to endNight
29%
704
17%
2211
12%
704
37%
704
19%
1515
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%46%6%35%45%7%33%
45891
Night
15%8%36%5%34446%35%
45512
Cloud CoverDay
14%8%36%6%35%45%7%33%
45901
Night
15%8%36%5%34446%36%
45516
TransparencyDay
49%6%12%18%11%1
45589
Night
48%5%12%19%12%1
45333
SeeingDay
17%7%24%23%18%8%
5134
Night
19%8%27%29%14%1
15329

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%34447%29%
2029
16th to endDay
17%6%35%5%34346%39%
2145
May1st to 15thDay
17%8%37%6%47%45%6%27%
2136
16th to endDay
11%5%25%5%35%6%6%7%39%
2223
June1st to 15thDay
11%5%26%6%35%5%6%8%38%
2293
16th to endDay
10%5%25%6%47%7%6%8%35%
2310
July1st to 15thDay
9%435%5%35%5%5%9%42%
2310
16th to endDay
8%425%5%35%5%8%9%39%
2360
August1st to 15thDay
6%425%5%46%6%7%9%42%
2145
16th to endDay
7%5%25%6%36%5%6%10%39%
2215
September1st to 15thDay
12%5%35%5%345%5%7%43%
1860
16th to endDay
14%5%24435%46%7%43%
1815
October1st to 15thDay
13%7%26%5%3445%7%40%
1755
16th to endDay
19%8%36%5%25%45%6%33%
1658
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
19%7%35%435%5%6%6%33%
1744
16th to endNight
16%7%25%5%245%47%39%
1485
May1st to 15thNight
18%6%46%6%45%5%5%7%29%
1485
16th to endNight
12%5%2442445%7%45%
1538
June1st to 15thNight
10%426%425%45%8%44%
1334
16th to endNight
8%4145%35%5%7%10%43%
1320
July1st to 15thNight
6%4245%25%36%9%50%
1320
16th to endNight
6%42442347%9%50%
1497
August1st to 15thNight
4413435%5%6%9%49%
1485
16th to endNight
9%315%33335%8%50%
1633
September1st to 15thNight
10%414323447%53%
1757
16th to endNight
12%414324447%48%
1815
October1st to 15thNight
12%6%35%423446%45%
1875
16th to endNight
20%7%345%24445%36%
2211
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%10%35%6%34446%29%
2029
16th to endDay
17%7%25%434446%39%
2145
May1st to 15thDay
18%8%37%7%36%5%5%6%27%
2136
16th to endDay
11%425%5%36%6%6%7%40%
2223
June1st to 15thDay
12%5%26%5%45%5%6%8%38%
2293
16th to endDay
10%5%25%6%46%6%6%8%36%
2310
July1st to 15thDay
9%5%25%5%25%5%6%9%41%
2310
16th to endDay
8%435%6%347%7%9%41%
2360
August1st to 15thDay
6%5%245%46%5%6%9%42%
2145
16th to endDay
9%425%5%46%6%6%10%39%
2215
September1st to 15thDay
12%5%25%4345%5%7%43%
1860
16th to endDay
13%6%2443446%6%42%
1815
October1st to 15thDay
13%7%25%5%2445%7%40%
1755
16th to endDay
19%8%445%25%45%6%33%
1658
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
19%7%35%4345%6%5%33%
1744
16th to endNight
16%6%25%4345%37%39%
1485
May1st to 15thNight
18%6%46%5%46%5%5%7%29%
1484
16th to endNight
12%5%24425%5%47%45%
1538
June1st to 15thNight
10%326%425%5%5%7%44%
1334
16th to endNight
9%4145%35%5%7%9%43%
1320
July1st to 15thNight
6%3145%2445%9%50%
1320
16th to endNight
6%32443347%9%50%
1497
August1st to 15thNight
44235%25%5%5%9%49%
1485
16th to endNight
10%41442345%7%50%
1633
September1st to 15thNight
10%424323437%53%
1757
16th to endNight
12%413424447%48%
1815
October1st to 15thNight
12%6%25%5%2345%6%46%
1875
16th to endNight
21%7%25%5%34345%36%
2211
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
54%5%11%16%11%
2029
16th to endDay
45%5%11%21%13%3
2145
May1st to 15thDay
55%7%11%17%8%
2136
16th to endDay
40%8%13%22%12%2
2227
June1st to 15thDay
42%7%11%23%13%1
2293
16th to endDay
43%9%12%15%16%2
2310
July1st to 15thDay
38%7%11%20%19%3
2161
16th to endDay
35%10%15%23%13%1
2202
August1st to 15thDay
34%9%15%23%16%1
2132
16th to endDay
38%9%12%20%15%3
2215
September1st to 15thDay
39%5%12%22%17%2
1860
16th to endDay
39%5%10%25%18%
1815
October1st to 15thDay
43%411%23%15%1
1755
16th to endDay
50%5%14%19%9%
1658
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%11%17%14%
1744
16th to endNight
44%5%10%18%17%3
1485
May1st to 15thNight
54%6%11%16%9%
1485
16th to endNight
37%5%11%26%15%3
1540
June1st to 15thNight
37%6%11%25%16%1
1334
16th to endNight
34%9%16%21%15%2
1320
July1st to 15thNight
30%6%13%25%19%3
1240
16th to endNight
27%8%16%24%18%4
1393
August1st to 15thNight
29%7%15%26%18%2
1474
16th to endNight
32%6%13%23%20%4
1633
September1st to 15thNight
31%412%24%22%3
1757
16th to endNight
34%6%9%25%21%1
1815
October1st to 15thNight
38%5%12%21%20%
1875
16th to endNight
48%411%24%8%1
2211
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
25%12%28%22%10%1
235
16th to endDay
20%10%29%19%12%8%
210
May1st to 15thDay
27%424%23%13%6%
228
16th to endDay
13%425%26%17%12%
267
June1st to 15thDay
12%429%30%16%5%
403
16th to endDay
15%5%22%29%20%7%
420
July1st to 15thDay
12%224%28%22%10%
400
16th to endDay
7%220%25%27%16%
346
August1st to 15thDay
12%12%27%27%19%
253
16th to endDay
11%114%22%29%20%
268
September1st to 15thDay
14%111%24%33%14%
255
16th to endDay
17%412%21%30%13%
254
October1st to 15thDay
15%7%21%24%25%5%
255
16th to endDay
21%11%32%27%6%
170
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
22%12%33%26%5%
548
16th to endNight
19%7%32%26%13%1
495
May1st to 15thNight
21%5%28%30%13%1
495
16th to endNight
14%223%34%21%3
515
June1st to 15thNight
11%222%43%19%
495
16th to endNight
10%121%40%23%2
495
July1st to 15thNight
7%217%41%28%3
465
16th to endNight
7%212%42%31%4
522
August1st to 15thNight
8%14%43%28%5%
494
16th to endNight
11%110%34%37%4
525
September1st to 15thNight
12%316%32%30%4
602
16th to endNight
14%314%33%30%4
657
October1st to 15thNight
16%6%23%30%20%2
660
16th to endNight
24%10%30%25%8%
704
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 2017-04-08 05:35:17. Version ac04

Copyright 2017 A. Danko


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