BGSU Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the BGSU Observatory clear sky chart from 2005-11-06 to 2024-01-27.

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
36%
24356
16%
74730
11%
24299
43%
24299
21%
51775

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 10thNight
17%
950
13%
2648
4%
946
25%
946
13%
2054
January11th to 20thNight
15%
912
9%
2622
4%
912
21%
912
11%
2112
January21st to endNight
18%
820
11%
2664
5%
820
25%
820
11%
2081
February1st to 10thNight
17%
720
8%
2340
3%
720
24%
720
11%
1810
February11th to 20thNight
20%
701
14%
2107
7%
699
28%
699
14%
1570
February21st to endNight
16%
592
14%
1776
4%
592
25%
592
15%
1317
March1st to 10thNight
27%
720
15%
2124
9%
720
33%
720
18%
1533
March11th to 20thNight
27%
720
20%
1980
10%
720
36%
720
24%
1348
March21st to endNight
29%
792
18%
2178
10%
792
36%
792
20%
1565
April1st to 10thNight
27%
622
15%
1882
7%
622
36%
622
20%
1271
April11th to 20thNight
32%
533
20%
1655
10%
533
41%
533
21%
1107
April21st to endNight
33%
540
18%
1620
7%
540
41%
540
24%
1093
May1st to 10thNight
36%
540
12%
1620
7%
540
41%
540
19%
1179
May11th to 20thNight
40%
531
18%
1592
11%
531
47%
531
23%
1069
May21st to endNight
53%
583
16%
1745
13%
582
57%
582
31%
1076
June1st to 10thNight
53%
540
16%
1514
12%
540
58%
540
32%
947
June11th to 20thNight
55%
540
19%
1440
16%
540
60%
540
34%
903
June21st to endNight
56%
540
20%
1440
14%
540
62%
540
35%
894
July1st to 10thNight
65%
525
17%
1400
16%
525
66%
525
37%
860
July11th to 20thNight
62%
522
21%
1396
17%
522
65%
522
40%
825
July21st to endNight
66%
591
19%
1672
15%
558
70%
558
38%
967
August1st to 10thNight
67%
537
21%
1600
18%
534
69%
534
37%
917
August11th to 20thNight
66%
534
23%
1598
19%
534
70%
534
35%
946
August21st to endNight
65%
594
23%
1842
19%
594
68%
594
34%
1064
September1st to 10thNight
61%
648
22%
1908
18%
648
64%
648
31%
1163
September11th to 20thNight
63%
720
29%
1980
22%
720
66%
720
38%
1164
September21st to endNight
51%
720
24%
1980
18%
720
56%
720
31%
1266
October1st to 10thNight
50%
720
22%
2008
18%
720
54%
720
31%
1261
October11th to 20thNight
34%
720
19%
2160
11%
720
43%
720
22%
1453
October21st to endNight
29%
792
19%
2506
14%
792
37%
792
19%
1718
November1st to 10thNight
36%
740
22%
2406
16%
740
45%
740
25%
1502
November11th to 20thNight
26%
760
19%
2470
11%
760
38%
760
18%
1685
November21st to endNight
25%
760
15%
2470
10%
760
31%
760
14%
1817
December1st to 10thNight
19%
760
10%
2470
5%
760
25%
760
12%
1887
December11th to 20thNight
19%
778
11%
3049
4%
777
27%
777
10%
2262
December21st to endNight
17%
1039
4%
4868
3%
1026
21%
1026
5%
4089

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%9%47%6%35%5%5%7%33%
75087
Night
15%9%47%6%3445%7%35%
74968
TransparencyDay
49%5%12%21%12%2
74800
Night
49%5%11%21%13%2
74775
SeeingDay
18%9%27%25%15%7%
14432
Night
20%8%28%30%13%2
24366

By Month

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 10thDay
17%16%6%10%9%46%5%45%18%
1517
11th to 20thDay
17%19%7%10%9%45%346%16%
1553
21st to endDay
18%16%8%10%8%45%445%18%
1836
February1st to 10thDay
16%16%6%10%10%45%445%21%
1620
11th to 20thDay
16%11%6%9%9%47%5%46%22%
1736
21st to endDay
17%14%5%8%6%35%45%7%27%
1480
March1st to 10thDay
17%11%6%8%7%345%6%6%25%
1836
11th to 20thDay
17%11%48%6%34446%32%
1980
21st to endDay
23%12%5%9%5%35%45%6%25%
2178
April1st to 10thDay
13%11%5%7%7%45%6%5%7%30%
2092
11th to 20thDay
17%8%46%5%35%5%6%8%34%
2253
21st to endDay
19%9%36%6%345%47%34%
2340
May1st to 10thDay
17%8%36%7%45%6%6%7%31%
2340
11th to 20thDay
18%8%36%6%45%5%6%7%33%
2301
21st to endDay
10%5%36%7%46%6%7%8%39%
2531
June1st to 10thDay
13%5%25%7%46%6%6%7%39%
2440
11th to 20thDay
9%6%26%6%36%5%5%8%43%
2520
21st to endDay
11%5%26%6%36%6%6%10%38%
2520
July1st to 10thDay
9%5%26%5%45%6%5%10%43%
2520
11th to 20thDay
8%425%5%35%6%8%11%43%
2512
21st to endDay
8%5%26%6%46%5%7%9%42%
2547
August1st to 10thDay
7%5%25%5%37%6%8%10%43%
2327
11th to 20thDay
8%5%25%6%46%7%8%10%39%
2303
21st to endDay
9%5%345%36%5%7%10%44%
2511
September1st to 10thDay
13%7%25%5%36%5%5%7%42%
2034
11th to 20thDay
8%6%26%5%345%6%8%47%
1980
21st to endDay
15%6%35%4345%5%7%43%
1980
October1st to 10thDay
12%7%36%6%45%5%5%7%42%
1951
11th to 20thDay
17%8%36%6%35%46%6%37%
1800
21st to endDay
19%9%37%6%35%5%6%6%31%
1846
November1st to 10thDay
11%9%35%5%3445%8%42%
1672
11th to 20thDay
17%11%47%5%44446%34%
1710
21st to endDay
19%13%47%6%25%35%8%27%
1710
December1st to 10thDay
16%16%8%11%8%34445%20%
1710
11th to 20thDay
14%14%7%10%7%45%5%5%7%23%
2118
21st to endDay
22%22%8%11%7%3443412%
2783
January1st to 10thNight
18%12%6%10%7%45%45%5%25%
2648
11th to 20thNight
19%15%7%10%7%35%45%5%21%
2622
21st to endNight
17%15%8%10%8%35%445%23%
2664
February1st to 10thNight
19%14%6%9%7%35%45%6%23%
2340
11th to 20thNight
15%13%5%7%7%45%5%5%6%27%
2107
21st to endNight
21%11%5%7%6%35%35%5%28%
1776
March1st to 10thNight
16%10%48%7%35%45%5%32%
2124
11th to 20thNight
14%9%35%6%35%5%5%7%39%
1980
21st to endNight
20%10%37%6%34346%35%
2178
April1st to 10thNight
15%9%36%6%35%5%6%8%34%
1882
11th to 20thNight
17%8%36%5%45%5%5%6%36%
1655
21st to endNight
17%8%36%5%25%45%7%37%
1620
May1st to 10thNight
17%8%48%7%45%5%5%6%32%
1620
11th to 20thNight
18%6%45%425%45%7%39%
1592
21st to endNight
9%5%35%5%35%6%6%10%42%
1744
June1st to 10thNight
11%5%25%446%5%5%8%45%
1514
11th to 20thNight
9%5%26%5%35%5%6%10%45%
1440
21st to endNight
10%425%5%35%5%7%10%45%
1440
July1st to 10thNight
8%5%15%6%335%7%8%50%
1440
11th to 20thNight
8%4245%345%7%9%50%
1444
21st to endNight
6%425%6%35%6%7%9%49%
1771
August1st to 10thNight
6%4146%345%6%9%50%
1611
11th to 20thNight
8%5%25%5%35%6%7%9%47%
1598
21st to endNight
8%325%5%45%5%6%7%50%
1842
September1st to 10thNight
11%5%25%5%3445%8%47%
1908
11th to 20thNight
9%5%36%42335%7%53%
1980
21st to endNight
12%6%346%34446%46%
1980
October1st to 10thNight
13%6%35%6%2445%6%47%
2008
11th to 20thNight
17%9%36%5%3435%6%38%
2160
21st to endNight
21%7%36%5%245%46%35%
2506
November1st to 10thNight
13%8%35%4345%5%7%43%
2406
11th to 20thNight
16%11%46%6%345%5%7%33%
2470
21st to endNight
20%12%5%8%6%34447%27%
2470
December1st to 10thNight
18%12%5%10%8%35%447%23%
2470
11th to 20thNight
17%15%6%8%6%35%5%46%25%
3074
21st to endNight
25%18%7%10%7%44445%12%
4884

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 10thDay
68%5%10%14%4
1518
11th to 20thDay
72%411%9%4
1553
21st to endDay
70%38%12%6%1
1836
February1st to 10thDay
67%410%12%6%1
1620
11th to 20thDay
62%5%10%15%8%1
1746
21st to endDay
57%413%17%7%2
1480
March1st to 10thDay
59%5%12%18%6%
1836
11th to 20thDay
54%411%20%10%2
1980
21st to endDay
61%48%20%6%1
2178
April1st to 10thDay
53%5%11%19%12%1
2092
11th to 20thDay
48%5%12%20%13%2
2253
21st to endDay
50%411%22%10%2
2340
May1st to 10thDay
50%6%13%19%12%1
2340
11th to 20thDay
50%5%10%19%14%2
2305
21st to endDay
41%7%14%25%12%2
2531
June1st to 10thDay
41%6%12%25%14%3
2440
11th to 20thDay
38%6%14%22%17%3
2520
21st to endDay
39%7%14%21%14%4
2520
July1st to 10thDay
37%6%11%24%19%3
2451
11th to 20thDay
32%7%14%27%18%2
2437
21st to endDay
37%6%12%24%18%3
2405
August1st to 10thDay
33%7%15%29%16%1
2314
11th to 20thDay
37%7%15%25%13%2
2303
21st to endDay
34%6%12%25%18%3
2511
September1st to 10thDay
41%5%12%22%17%3
2034
11th to 20thDay
35%5%11%29%20%1
1980
21st to endDay
40%5%12%25%18%1
1980
October1st to 10thDay
41%5%10%27%15%2
1951
11th to 20thDay
47%410%23%15%1
1800
21st to endDay
53%412%19%11%1
1846
November1st to 10thDay
41%6%11%24%17%1
1672
11th to 20thDay
53%312%19%12%1
1710
21st to endDay
57%313%19%8%
1710
December1st to 10thDay
68%410%14%4
1710
11th to 20thDay
61%5%12%18%5%
2115
21st to endDay
77%48%8%3
2783
January1st to 10thNight
62%49%17%8%
2648
11th to 20thNight
66%411%14%5%
2622
21st to endNight
65%410%15%6%1
2664
February1st to 10thNight
63%411%16%5%1
2340
11th to 20thNight
57%5%9%19%9%1
2108
21st to endNight
58%410%18%9%1
1776
March1st to 10thNight
54%411%20%10%1
2124
11th to 20thNight
44%6%12%20%16%2
1980
21st to endNight
52%48%25%10%2
2178
April1st to 10thNight
48%5%11%20%14%2
1882
11th to 20thNight
47%410%19%18%2
1655
21st to endNight
46%411%22%14%3
1620
May1st to 10thNight
53%5%11%17%12%2
1620
11th to 20thNight
45%6%9%20%17%2
1593
21st to endNight
36%6%13%28%14%3
1745
June1st to 10thNight
37%5%11%26%17%3
1514
11th to 20thNight
34%7%13%27%17%3
1440
21st to endNight
34%6%14%26%17%2
1440
July1st to 10thNight
33%6%12%26%21%4
1400
11th to 20thNight
29%6%15%28%20%2
1396
21st to endNight
29%7%16%25%18%4
1672
August1st to 10thNight
29%7%13%33%17%1
1600
11th to 20thNight
32%6%15%28%17%2
1598
21st to endNight
31%6%13%23%23%4
1842
September1st to 10thNight
36%5%12%26%17%5%
1908
11th to 20thNight
31%5%11%27%26%1
1980
21st to endNight
39%411%24%19%2
1980
October1st to 10thNight
38%411%25%20%1
2008
11th to 20thNight
47%39%24%15%1
2160
21st to endNight
50%49%24%11%2
2506
November1st to 10thNight
41%411%25%17%2
2406
11th to 20thNight
50%5%11%21%12%1
2470
21st to endNight
58%412%19%7%
2470
December1st to 10thNight
62%411%16%7%
2470
11th to 20thNight
60%5%13%15%6%1
3076
21st to endNight
74%411%8%2
4884

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 10thDay
24%18%30%22%5%1
270
11th to 20thDay
24%15%42%13%5%1
270
21st to endDay
29%12%31%22%41
282
February1st to 10thDay
30%18%37%15%
240
11th to 20thDay
24%17%39%17%4
240
21st to endDay
29%17%41%12%1
198
March1st to 10thDay
24%16%37%18%5%1
276
11th to 20thDay
25%10%36%20%8%1
420
21st to endDay
32%12%31%18%8%
462
April1st to 10thDay
20%12%30%23%13%1
420
11th to 20thDay
19%16%31%20%9%4
412
21st to endDay
26%10%31%22%9%2
420
May1st to 10thDay
24%8%32%21%12%3
423
11th to 20thDay
21%9%25%26%13%7%
447
21st to endDay
13%5%24%27%19%12%
485
June1st to 10thDay
13%5%27%31%18%6%
550
11th to 20thDay
13%5%29%27%20%6%
630
21st to endDay
12%7%25%31%18%6%
630
July1st to 10thDay
11%218%33%22%15%
621
11th to 20thDay
9%422%32%21%12%
610
21st to endDay
10%322%25%27%13%
488
August1st to 10thDay
11%212%30%26%18%
446
11th to 20thDay
12%415%31%25%13%
439
21st to endDay
9%318%28%27%16%
495
September1st to 10thDay
17%414%30%23%12%
450
11th to 20thDay
10%214%27%29%18%
450
21st to endDay
16%8%21%24%20%10%
450
October1st to 10thDay
14%6%24%27%20%10%
450
11th to 20thDay
20%13%30%24%11%2
450
21st to endDay
24%12%35%22%6%1
361
November1st to 10thDay
13%13%34%22%13%4
270
11th to 20thDay
24%16%31%21%7%1
270
21st to endDay
27%11%38%20%4
270
December1st to 10thDay
21%17%34%17%9%
270
11th to 20thDay
20%19%37%19%41
270
21st to endDay
27%16%36%18%3
297
January1st to 10thNight
24%13%35%21%6%
950
11th to 20thNight
28%12%35%19%5%1
912
21st to endNight
24%13%35%24%5%
820
February1st to 10thNight
27%12%34%23%4
720
11th to 20thNight
24%12%36%25%3
703
21st to endNight
28%13%37%19%3
592
March1st to 10thNight
22%10%32%29%7%
720
11th to 20thNight
19%13%36%25%7%1
720
21st to endNight
24%10%31%27%8%
792
April1st to 10thNight
20%11%36%27%41
622
11th to 20thNight
22%9%32%27%8%1
533
21st to endNight
23%7%33%28%9%1
540
May1st to 10thNight
21%6%29%34%10%1
540
11th to 20thNight
21%5%27%31%16%1
531
21st to endNight
11%324%38%22%3
584
June1st to 10thNight
11%422%45%17%
540
11th to 20thNight
12%322%44%18%2
540
21st to endNight
11%223%41%21%2
540
July1st to 10thNight
10%115%40%29%4
525
11th to 20thNight
9%217%42%24%5%
522
21st to endNight
7%213%44%31%3
591
August1st to 10thNight
9%111%41%33%4
537
11th to 20thNight
10%14%36%34%4
534
21st to endNight
9%213%36%35%5%
594
September1st to 10thNight
15%413%33%29%5%
648
11th to 20thNight
10%414%36%33%5%
720
21st to endNight
14%5%21%33%23%3
720
October1st to 10thNight
15%6%23%33%21%3
720
11th to 20thNight
20%12%29%28%10%2
720
21st to endNight
25%11%30%26%8%
792
November1st to 10thNight
17%10%32%28%11%1
740
11th to 20thNight
24%13%31%24%8%1
760
21st to endNight
26%11%32%25%7%
760
December1st to 10thNight
25%13%35%22%5%
760
11th to 20thNight
26%11%35%24%4
779
21st to endNight
31%11%32%23%3
1045
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