Bois Blanc Island Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bois Blanc Island 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
30%
15776
12%
47351
7%
15731
35%
15731
15%
34463

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
5%
2509
2%
895
18%
895
6%
2146
January16th to endNight
16%
960
8%
2688
2%
960
22%
960
9%
2226
February1st to 15thNight
18%
742
8%
2312
3%
740
23%
740
10%
1793
February16th to endNight
23%
631
11%
1893
4%
631
30%
631
12%
1458
March1st to 15thNight
26%
720
15%
2115
8%
720
32%
720
19%
1471
March16th to endNight
33%
756
19%
2100
10%
756
42%
756
21%
1435
April1st to 15thNight
31%
539
15%
1761
10%
539
38%
539
17%
1212
April16th to endNight
31%
540
18%
1620
7%
540
41%
540
19%
1075
May1st to 15thNight
34%
540
13%
1620
7%
540
39%
540
18%
1110
May16th to endNight
43%
491
16%
1439
10%
489
51%
489
27%
890
June1st to 15thNight
40%
360
12%
1260
7%
360
47%
360
20%
772
June16th to endNight
50%
360
12%
1260
10%
360
54%
360
23%
764
July1st to 15thNight
55%
434
14%
1284
10%
434
59%
434
31%
749
July16th to endNight
52%
564
15%
1417
10%
531
59%
531
32%
882
August1st to 15thNight
56%
539
19%
1567
15%
536
60%
536
35%
881
August16th to endNight
54%
573
19%
1737
12%
573
60%
573
31%
1011
September1st to 15thNight
48%
624
16%
1884
11%
624
52%
624
27%
1181
September16th to endNight
49%
717
18%
1980
13%
717
53%
717
29%
1303
October1st to 15thNight
38%
720
15%
2061
11%
720
42%
720
21%
1433
October16th to endNight
23%
768
9%
2483
5%
768
28%
768
10%
1972
November1st to 15thNight
24%
700
14%
2276
10%
700
30%
700
12%
1700
November16th to endNight
14%
738
6%
2505
3%
738
18%
738
6%
2106
December1st to 15thNight
9%
900
3%
2700
1%
900
11%
900
4%
2377
December16th to endNight
11%
960
5%
2880
2%
960
14%
960
5%
2516

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%3445%7%34%
48400
Night
15%10%48%6%34446%30%
47517
Cloud CoverDay
14%9%46%5%3445%7%34%
48409
Night
15%10%48%6%34446%29%
47522
TransparencyDay
48%413%22%9%
48084
Night
54%412%19%8%
47351
SeeingDay
16%13%22%28%14%3
6152
Night
17%21%21%25%12%2
15777

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
16%14%7%13%9%47%445%10%
1427
16th to endDay
12%14%7%14%10%5%6%446%14%
1536
February1st to 15thDay
11%14%5%10%9%35%45%6%24%
1547
16th to endDay
12%11%48%9%45%46%6%25%
1580
March1st to 15thDay
12%9%47%6%34446%35%
1835
16th to endDay
12%7%36%43445%6%39%
2133
April1st to 15thDay
18%8%35%5%25%45%7%32%
2187
16th to endDay
15%8%36%5%3435%7%36%
2340
May1st to 15thDay
15%7%35%434446%38%
2331
16th to endDay
12%6%245%25%5%48%43%
2673
June1st to 15thDay
13%5%25%5%345%7%9%38%
2700
16th to endDay
12%5%25%5%245%6%9%40%
2700
July1st to 15thDay
8%424425%35%8%49%
2594
16th to endDay
8%4244245%5%8%48%
2655
August1st to 15thDay
9%4144235%5%8%49%
2382
16th to endDay
10%425%43445%8%47%
2464
September1st to 15thDay
13%5%25%4335%5%7%42%
2064
16th to endDay
13%5%35%5%2445%8%42%
1980
October1st to 15thDay
20%9%26%4335%37%32%
1899
16th to endDay
23%12%47%6%45%5%6%5%18%
1738
November1st to 15thDay
17%12%49%6%35%45%7%23%
1582
16th to endDay
21%17%8%12%7%45%43311%
1449
December1st to 15thDay
17%19%8%14%11%35%3248%
1260
16th to endDay
20%19%7%11%9%4433311%
1344
January1st to 15thNight
18%14%7%12%9%4434414%
2509
16th to endNight
14%13%7%10%10%45%45%5%17%
2688
February1st to 15thNight
10%14%7%8%9%36%6%5%6%21%
2310
16th to endNight
14%12%6%9%9%46%5%46%22%
1893
March1st to 15thNight
13%8%48%6%24445%36%
2102
16th to endNight
13%8%46%6%35%35%5%39%
2100
April1st to 15thNight
19%8%345%35%5%46%33%
1761
16th to endNight
15%8%35%5%25%5%46%38%
1620
May1st to 15thNight
15%8%37%6%3446%6%33%
1620
16th to endNight
13%425%32445%7%45%
1437
June1st to 15thNight
13%6%25%5%25%5%6%9%38%
1260
16th to endNight
11%3345%35%5%6%9%41%
1260
July1st to 15thNight
9%315%5%34347%49%
1362
16th to endNight
8%424425%46%7%48%
1513
August1st to 15thNight
7%325%423448%53%
1576
16th to endNight
9%5%24424448%49%
1737
September1st to 15thNight
15%6%14423446%45%
1884
16th to endNight
16%5%35%42345%7%40%
1980
October1st to 15thNight
21%7%25%5%3445%5%35%
2061
16th to endNight
24%11%48%6%35%5%45%20%
2483
November1st to 15thNight
17%13%48%5%2445%6%24%
2276
16th to endNight
21%18%6%11%6%4444412%
2505
December1st to 15thNight
19%17%8%13%10%4433310%
2700
16th to endNight
20%17%9%12%8%3443312%
2880

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
16%13%8%14%9%6%6%45%410%
1427
16th to endDay
12%15%7%13%10%5%5%5%35%13%
1536
February1st to 15thDay
12%14%6%10%8%45%45%7%22%
1547
16th to endDay
12%12%49%8%45%45%6%25%
1580
March1st to 15thDay
13%9%46%7%3445%5%35%
1845
16th to endDay
12%8%36%5%25%5%5%7%38%
2132
April1st to 15thDay
18%9%36%43445%7%32%
2187
16th to endDay
15%8%36%43345%7%36%
2340
May1st to 15thDay
14%8%35%5%35%5%46%37%
2331
16th to endDay
12%6%245%25%5%48%42%
2673
June1st to 15thDay
13%5%245%35%47%9%38%
2700
16th to endDay
12%5%25%425%46%8%41%
2700
July1st to 15thDay
8%423425%5%5%8%48%
2594
16th to endDay
8%4244245%6%8%48%
2655
August1st to 15thDay
9%42342345%8%49%
2382
16th to endDay
11%5%1443345%7%47%
2464
September1st to 15thDay
13%5%26%5%2445%7%42%
2064
16th to endDay
13%6%2442445%8%41%
1980
October1st to 15thDay
21%8%35%434447%32%
1899
16th to endDay
23%13%46%6%35%46%6%18%
1738
November1st to 15thDay
18%12%5%8%6%34447%22%
1582
16th to endDay
20%18%9%10%8%35%33311%
1449
December1st to 15thDay
17%18%10%15%11%343237%
1260
16th to endDay
20%19%8%12%9%4433211%
1344
January1st to 15thNight
18%14%6%12%10%45%44413%
2509
16th to endNight
14%13%7%12%10%46%445%16%
2688
February1st to 15thNight
11%14%6%9%9%36%5%5%5%21%
2303
16th to endNight
14%11%6%10%9%45%446%22%
1893
March1st to 15thNight
13%9%5%8%6%2435%5%35%
2115
16th to endNight
13%8%37%5%25%446%38%
2100
April1st to 15thNight
19%9%25%5%345%45%33%
1761
16th to endNight
15%8%25%5%35%446%38%
1620
May1st to 15thNight
14%7%37%6%35%46%6%33%
1619
16th to endNight
13%425%42345%7%46%
1437
June1st to 15thNight
13%6%25%5%3445%9%38%
1260
16th to endNight
12%425%435%5%6%9%41%
1260
July1st to 15thNight
9%415%5%34447%49%
1362
16th to endNight
8%424435%6%5%6%49%
1513
August1st to 15thNight
7%325%423448%53%
1576
16th to endNight
10%424424447%49%
1737
September1st to 15thNight
15%6%25%5%2335%6%44%
1884
16th to endNight
15%6%35%42345%8%40%
1980
October1st to 15thNight
20%7%36%433346%35%
2061
16th to endNight
24%13%37%6%4445%5%19%
2483
November1st to 15thNight
17%14%5%7%6%2445%7%23%
2276
16th to endNight
22%18%7%11%7%3434413%
2505
December1st to 15thNight
18%18%9%15%9%45%3339%
2700
16th to endNight
20%18%9%13%7%4433311%
2880

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
74%6%9%8%1
1428
16th to endDay
69%6%9%10%3
1536
February1st to 15thDay
61%5%14%13%5%
1549
16th to endDay
56%315%18%5%
1580
March1st to 15thDay
49%413%21%9%1
1845
16th to endDay
44%413%24%9%2
2133
April1st to 15thDay
52%310%21%11%
2187
16th to endDay
46%211%20%15%2
2340
May1st to 15thDay
45%49%24%11%3
2331
16th to endDay
39%414%26%13%1
2677
June1st to 15thDay
40%414%27%11%1
2700
16th to endDay
39%5%16%25%12%1
2700
July1st to 15thDay
32%415%32%14%1
2443
16th to endDay
33%5%15%29%16%
2488
August1st to 15thDay
31%418%30%13%
2367
16th to endDay
34%418%30%10%1
2464
September1st to 15thDay
39%5%15%30%9%
2064
16th to endDay
38%418%30%7%
1980
October1st to 15thDay
50%5%12%24%8%
1899
16th to endDay
63%6%12%13%4
1738
November1st to 15thDay
59%5%12%17%5%
1582
16th to endDay
77%311%6%2
1449
December1st to 15thDay
78%47%7%2
1260
16th to endDay
77%38%7%2
1344
January1st to 15thNight
73%39%9%2
2509
16th to endNight
68%5%10%11%4
2688
February1st to 15thNight
62%412%15%4
2312
16th to endNight
61%413%14%5%
1893
March1st to 15thNight
49%313%22%10%
2115
16th to endNight
45%312%23%12%1
2100
April1st to 15thNight
50%38%24%11%1
1761
16th to endNight
46%310%21%15%3
1620
May1st to 15thNight
50%310%18%13%3
1620
16th to endNight
37%412%28%14%2
1439
June1st to 15thNight
40%412%23%17%
1260
16th to endNight
38%5%15%28%10%1
1260
July1st to 15thNight
33%313%29%17%2
1284
16th to endNight
34%5%14%27%17%1
1417
August1st to 15thNight
30%317%33%12%1
1567
16th to endNight
32%5%20%27%13%
1737
September1st to 15thNight
40%315%26%12%1
1884
16th to endNight
41%417%28%7%
1980
October1st to 15thNight
48%413%23%9%
2061
16th to endNight
65%411%14%4
2483
November1st to 15thNight
58%5%12%18%5%
2276
16th to endNight
73%410%8%3
2505
December1st to 15thNight
77%48%7%1
2700
16th to endNight
76%48%7%2
2880

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%11%37%20%31
89
16th to endDay
32%5%17%34%10%
96
February1st to 15thDay
24%18%33%16%6%
90
16th to endDay
19%12%38%23%6%
81
March1st to 15thDay
17%15%27%25%14%
135
16th to endDay
23%17%20%25%9%3
288
April1st to 15thDay
21%20%21%24%12%
270
16th to endDay
21%14%31%20%10%2
270
May1st to 15thDay
20%15%28%22%11%2
288
16th to endDay
15%16%22%30%12%2
501
June1st to 15thDay
15%15%26%29%11%1
495
16th to endDay
15%16%18%30%15%3
495
July1st to 15thDay
9%10%20%34%21%3
475
16th to endDay
11%15%16%31%19%4
515
August1st to 15thDay
10%8%14%38%21%6%
355
16th to endDay
15%8%16%32%20%5%
332
September1st to 15thDay
13%7%15%28%23%12%
315
16th to endDay
11%11%17%32%21%6%
314
October1st to 15thDay
20%12%24%28%13%1
315
16th to endDay
31%5%33%22%5%1
154
November1st to 15thDay
15%11%36%24%10%2
90
16th to endDay
26%16%36%16%3
65
December1st to 15thDay
30%21%33%11%11
60
16th to endDay
28%28%37%6%
64
January1st to 15thNight
20%29%24%19%6%
900
16th to endNight
17%25%26%22%6%1
960
February1st to 15thNight
15%25%29%23%6%
743
16th to endNight
16%22%25%25%11%
631
March1st to 15thNight
15%23%26%24%9%
720
16th to endNight
16%21%21%29%9%1
756
April1st to 15thNight
17%21%22%28%8%1
539
16th to endNight
17%20%24%22%13%1
540
May1st to 15thNight
15%19%20%29%13%2
540
16th to endNight
13%19%17%29%18%1
491
June1st to 15thNight
14%20%16%30%16%
360
16th to endNight
13%20%12%27%23%3
360
July1st to 15thNight
9%14%11%36%22%5%
434
16th to endNight
8%17%13%34%21%4
564
August1st to 15thNight
11%10%13%33%26%4
539
16th to endNight
11%10%14%35%24%4
573
September1st to 15thNight
14%12%18%25%21%7%
624
16th to endNight
16%11%14%29%20%6%
717
October1st to 15thNight
22%13%19%28%14%1
720
16th to endNight
28%20%20%24%5%1
768
November1st to 15thNight
20%22%25%22%8%1
700
16th to endNight
27%27%23%16%4
738
December1st to 15thNight
23%30%28%13%3
900
16th to endNight
23%29%24%16%41
960
Page generated at 2017-11-01 17:23:42. Version ac04

Copyright 2017 A. Danko


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