Au Sable Forks Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Au Sable Forks Observatory clear sky chart from 2005-11-06 to 2024-01-31.

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
27%
22735
13%
74964
7%
22696
35%
22696
15%
53044

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
14%
760
10%
2649
3%
757
23%
757
7%
2054
January11th to 20thNight
15%
760
8%
2660
2%
760
22%
760
7%
2087
January21st to endNight
17%
835
12%
2919
5%
835
27%
835
11%
2098
February1st to 10thNight
13%
720
9%
2344
2%
720
21%
720
9%
1791
February11th to 20thNight
14%
703
12%
2157
3%
700
26%
700
12%
1591
February21st to endNight
16%
592
15%
1776
4%
592
30%
592
12%
1319
March1st to 10thNight
19%
720
14%
2160
6%
720
28%
720
12%
1645
March11th to 20thNight
17%
720
15%
2095
4%
720
28%
720
13%
1533
March21st to endNight
21%
792
20%
1980
6%
792
31%
792
18%
1443
April1st to 10thNight
19%
720
16%
1800
4%
720
27%
720
17%
1339
April11th to 20thNight
23%
711
13%
1775
3%
711
27%
711
17%
1321
April21st to endNight
24%
594
15%
1674
6%
594
31%
594
16%
1196
May1st to 10thNight
26%
455
15%
1535
9%
455
33%
455
14%
1067
May11th to 20thNight
28%
354
19%
1416
13%
354
43%
354
16%
885
May21st to endNight
38%
388
14%
1551
13%
388
48%
388
20%
946
June1st to 10thNight
35%
360
11%
1440
9%
360
46%
360
15%
955
June11th to 20thNight
39%
360
12%
1440
13%
360
47%
360
18%
887
June21st to endNight
39%
360
10%
1440
11%
360
48%
360
18%
921
July1st to 10thNight
45%
350
13%
1400
16%
350
54%
350
23%
814
July11th to 20thNight
52%
348
16%
1392
19%
348
60%
348
23%
802
July21st to endNight
51%
394
16%
1486
16%
372
57%
372
25%
842
August1st to 10thNight
53%
358
18%
1422
18%
356
59%
356
27%
793
August11th to 20thNight
53%
592
17%
1656
10%
592
56%
592
29%
1073
August21st to endNight
49%
792
18%
1980
8%
792
52%
792
31%
1312
September1st to 10thNight
50%
720
15%
1800
7%
720
52%
720
32%
1196
September11th to 20thNight
46%
720
21%
1880
11%
720
51%
720
33%
1184
September21st to endNight
39%
720
21%
1980
15%
720
45%
720
28%
1298
October1st to 10thNight
32%
720
15%
2087
9%
720
40%
720
19%
1464
October11th to 20thNight
32%
720
15%
2183
10%
720
40%
720
18%
1534
October21st to endNight
22%
792
12%
2574
6%
792
31%
792
13%
1898
November1st to 10thNight
24%
740
15%
2407
7%
740
34%
740
14%
1684
November11th to 20thNight
22%
760
17%
2493
10%
760
31%
760
14%
1764
November21st to endNight
20%
760
12%
2660
7%
760
28%
760
10%
1959
December1st to 10thNight
14%
760
8%
2660
2%
760
21%
760
7%
2126
December11th to 20thNight
15%
759
10%
3249
3%
759
23%
759
7%
2466
December21st to endNight
13%
826
5%
4844
2%
817
20%
817
4%
3757

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%48%7%45%5%6%7%31%
74908
Night
13%9%48%7%45%5%6%7%32%
75214
TransparencyDay
51%7%12%19%10%1
74613
Night
50%8%13%19%10%1
75043
SeeingDay
23%18%31%19%7%2
13591
Night
21%16%29%24%8%1
22747

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 10thDay
8%11%7%11%8%5%7%6%6%7%23%
1517
11th to 20thDay
10%13%6%13%9%445%5%7%24%
1520
21st to endDay
8%11%6%12%10%5%7%6%5%7%24%
1664
February1st to 10thDay
11%12%6%13%9%6%7%5%7%5%20%
1611
11th to 20thDay
8%10%5%10%10%7%7%5%6%6%26%
1691
21st to endDay
13%12%6%10%8%45%5%5%6%25%
1480
March1st to 10thDay
11%12%5%10%9%47%5%5%427%
1797
11th to 20thDay
12%13%5%8%9%36%5%5%6%28%
1862
21st to endDay
15%11%6%7%7%35%445%33%
2376
April1st to 10thDay
16%10%5%8%6%45%5%46%30%
2160
11th to 20thDay
16%10%48%6%34446%35%
2134
21st to endDay
21%10%37%5%35%446%30%
2285
May1st to 10thDay
17%10%38%6%45%5%5%6%32%
2440
11th to 20thDay
15%9%46%5%35%5%5%6%36%
2478
21st to endDay
15%7%36%7%45%6%6%8%34%
2725
June1st to 10thDay
22%8%25%6%45%6%6%8%28%
2520
11th to 20thDay
15%7%36%5%46%6%5%8%35%
2520
21st to endDay
19%7%37%7%45%6%6%8%28%
2520
July1st to 10thDay
12%6%37%6%46%6%7%9%35%
2520
11th to 20thDay
12%6%36%7%5%7%7%8%8%32%
2520
21st to endDay
13%5%36%6%47%6%7%9%33%
2744
August1st to 10thDay
11%6%38%8%46%6%7%8%32%
2506
11th to 20thDay
10%5%37%7%47%6%7%11%34%
2222
21st to endDay
11%6%37%6%45%6%7%8%37%
2376
September1st to 10thDay
14%6%25%5%345%5%9%42%
2160
11th to 20thDay
12%6%35%5%35%448%45%
2080
21st to endDay
11%6%37%6%36%6%6%8%38%
1980
October1st to 10thDay
20%8%37%5%35%5%6%7%31%
1872
11th to 20thDay
13%12%38%6%446%6%6%32%
1775
21st to endDay
20%12%38%6%346%5%6%27%
1782
November1st to 10thDay
10%11%5%7%8%45%6%6%6%31%
1671
11th to 20thDay
13%10%48%8%45%5%5%7%29%
1682
21st to endDay
13%12%5%9%8%36%5%5%6%27%
1520
December1st to 10thDay
14%18%8%12%8%46%45%6%17%
1520
11th to 20thDay
15%12%6%10%8%46%46%7%23%
1906
21st to endDay
19%16%5%10%7%34445%22%
2772
January1st to 10thNight
11%12%5%10%8%5%7%6%6%7%22%
2649
11th to 20thNight
10%13%6%12%9%47%6%5%6%22%
2660
21st to endNight
8%10%6%10%9%47%6%6%7%28%
2919
February1st to 10thNight
9%12%5%10%9%5%7%6%8%7%21%
2344
11th to 20thNight
9%10%5%9%9%5%7%6%6%6%28%
2155
21st to endNight
11%10%5%9%8%46%6%6%6%28%
1776
March1st to 10thNight
12%13%5%10%8%46%5%5%5%27%
2150
11th to 20thNight
12%11%5%9%8%45%45%6%30%
2094
21st to endNight
14%10%5%8%5%45%45%5%37%
1980
April1st to 10thNight
14%9%49%7%46%45%7%32%
1800
11th to 20thNight
17%10%26%6%5%5%5%5%7%32%
1775
21st to endNight
17%10%37%7%34446%35%
1674
May1st to 10thNight
19%10%27%5%45%45%8%31%
1535
11th to 20thNight
15%7%36%4435%6%8%38%
1415
21st to endNight
13%6%35%5%345%6%10%41%
1550
June1st to 10thNight
19%6%35%5%35%6%5%9%35%
1440
11th to 20thNight
15%6%36%5%35%46%8%40%
1440
21st to endNight
14%6%36%5%345%6%8%39%
1440
July1st to 10thNight
9%7%37%4345%6%9%44%
1440
11th to 20thNight
9%4245%36%6%6%9%46%
1440
21st to endNight
11%3245%35%5%7%8%46%
1574
August1st to 10thNight
9%425%435%5%6%10%47%
1432
11th to 20thNight
8%5%25%7%35%5%7%9%44%
1656
21st to endNight
10%5%25%5%35%5%6%8%44%
1980
September1st to 10thNight
11%5%25%5%4446%8%46%
1800
11th to 20thNight
13%6%24433448%48%
1880
21st to endNight
14%5%345%345%6%7%43%
1980
October1st to 10thNight
18%7%36%5%25%5%6%7%35%
2087
11th to 20thNight
15%8%36%7%45%5%5%7%35%
2183
21st to endNight
20%10%47%6%35%5%6%7%27%
2574
November1st to 10thNight
12%9%48%7%45%6%6%6%32%
2407
11th to 20thNight
12%10%5%9%7%45%5%6%6%32%
2493
21st to endNight
14%11%5%9%7%45%5%7%7%26%
2660
December1st to 10thNight
15%14%7%10%8%5%5%6%5%6%18%
2660
11th to 20thNight
15%13%6%10%8%46%46%6%24%
3288
21st to endNight
20%14%5%12%7%4445%5%21%
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
58%8%12%17%5%
1518
11th to 20thDay
59%7%10%13%10%1
1520
21st to endDay
58%7%12%13%9%1
1664
February1st to 10thDay
63%8%7%15%5%2
1611
11th to 20thDay
56%8%10%16%9%1
1700
21st to endDay
58%6%11%13%10%2
1480
March1st to 10thDay
58%6%10%14%9%3
1800
11th to 20thDay
56%6%10%13%12%3
1862
21st to endDay
53%5%7%15%14%4
2376
April1st to 10thDay
54%6%9%18%10%3
2160
11th to 20thDay
50%6%9%19%15%2
2134
21st to endDay
55%5%10%16%11%3
2285
May1st to 10thDay
52%6%9%18%14%2
2440
11th to 20thDay
47%6%10%19%16%2
2482
21st to endDay
46%8%14%19%11%2
2725
June1st to 10thDay
51%8%14%16%10%1
2520
11th to 20thDay
45%7%12%22%12%2
2520
21st to endDay
52%8%12%19%9%1
2520
July1st to 10thDay
43%8%13%24%12%1
2450
11th to 20thDay
44%9%15%25%7%
2445
21st to endDay
44%9%16%21%10%1
2591
August1st to 10thDay
45%9%16%22%9%
2492
11th to 20thDay
40%9%19%23%8%
2222
21st to endDay
42%7%14%24%11%1
2376
September1st to 10thDay
38%7%13%28%13%1
2160
11th to 20thDay
37%5%13%29%14%1
2080
21st to endDay
41%9%16%23%10%2
1980
October1st to 10thDay
51%6%12%19%11%
1872
11th to 20thDay
50%8%16%19%7%
1775
21st to endDay
57%7%12%16%7%1
1782
November1st to 10thDay
50%8%13%18%10%1
1671
11th to 20thDay
53%7%12%14%11%3
1682
21st to endDay
56%7%14%17%6%1
1520
December1st to 10thDay
68%6%10%12%3
1520
11th to 20thDay
60%7%12%14%6%
1906
21st to endDay
62%7%10%15%5%
2772
January1st to 10thNight
59%10%10%14%7%
2649
11th to 20thNight
60%10%10%13%6%
2660
21st to endNight
53%8%11%16%11%1
2919
February1st to 10thNight
58%9%14%11%8%1
2344
11th to 20thNight
53%8%12%17%9%1
2157
21st to endNight
54%7%11%17%9%1
1776
March1st to 10thNight
58%6%9%15%10%2
2160
11th to 20thNight
54%6%9%20%11%2
2095
21st to endNight
49%6%9%19%14%4
1980
April1st to 10thNight
52%6%9%19%13%1
1800
11th to 20thNight
51%7%11%18%13%1
1775
21st to endNight
50%6%11%18%12%3
1674
May1st to 10thNight
51%6%8%16%16%3
1535
11th to 20thNight
43%7%10%20%17%3
1416
21st to endNight
38%9%16%21%14%2
1551
June1st to 10thNight
46%9%13%21%10%2
1440
11th to 20thNight
40%9%14%22%13%2
1440
21st to endNight
42%9%14%24%10%
1440
July1st to 10thNight
35%8%16%26%15%1
1400
11th to 20thNight
33%11%15%30%11%
1392
21st to endNight
32%10%19%27%12%1
1486
August1st to 10thNight
31%9%21%28%11%
1422
11th to 20thNight
35%10%16%27%12%1
1656
21st to endNight
35%9%16%28%12%
1980
September1st to 10thNight
35%8%16%28%12%1
1800
11th to 20thNight
35%6%15%31%13%1
1880
21st to endNight
37%8%15%26%13%1
1980
October1st to 10thNight
48%7%13%20%12%1
2087
11th to 20thNight
48%7%15%21%8%
2183
21st to endNight
55%7%14%15%9%1
2574
November1st to 10thNight
50%7%14%17%10%2
2407
11th to 20thNight
50%8%13%18%8%3
2493
21st to endNight
54%9%14%16%6%
2660
December1st to 10thNight
65%7%12%14%3
2660
11th to 20thNight
60%8%10%13%8%
3288
21st to endNight
65%7%10%15%3
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
21%24%32%17%7%
180
11th to 20thDay
25%27%34%11%21
180
21st to endDay
21%24%37%14%21
196
February1st to 10thDay
39%31%26%31
236
11th to 20thDay
31%26%35%7%1
359
21st to endDay
31%22%31%14%2
346
March1st to 10thDay
27%24%30%15%3
420
11th to 20thDay
29%25%29%13%31
420
21st to endDay
27%28%24%13%6%1
462
April1st to 10thDay
33%19%28%15%41
420
11th to 20thDay
30%22%25%14%6%3
412
21st to endDay
35%20%26%11%6%2
420
May1st to 10thDay
30%19%32%11%6%2
423
11th to 20thDay
20%20%34%19%5%2
447
21st to endDay
18%19%32%22%8%1
485
June1st to 10thDay
28%16%32%18%42
450
11th to 20thDay
19%17%35%19%9%2
450
21st to endDay
20%18%33%21%7%2
450
July1st to 10thDay
14%13%34%26%12%1
445
11th to 20thDay
11%11%37%28%10%2
444
21st to endDay
14%11%35%30%8%2
488
August1st to 10thDay
11%10%33%28%15%3
446
11th to 20thDay
12%9%33%26%14%5%
439
21st to endDay
14%15%28%28%10%6%
495
September1st to 10thDay
16%12%29%23%14%6%
450
11th to 20thDay
14%14%26%23%14%8%
450
21st to endDay
15%13%34%23%11%5%
450
October1st to 10thDay
26%16%23%19%14%2
450
11th to 20thDay
21%22%28%20%8%1
437
21st to endDay
33%14%31%18%41
396
November1st to 10thDay
28%16%26%21%8%1
365
11th to 20thDay
30%22%28%13%5%1
342
21st to endDay
29%24%29%16%2
180
December1st to 10thDay
27%25%29%13%5%1
180
11th to 20thDay
34%21%34%9%2
180
21st to endDay
30%23%31%12%31
198
January1st to 10thNight
23%20%35%19%3
760
11th to 20thNight
25%20%34%18%3
760
21st to endNight
15%22%37%21%5%
835
February1st to 10thNight
19%23%38%18%3
720
11th to 20thNight
21%22%36%19%2
703
21st to endNight
20%23%34%19%3
592
March1st to 10thNight
26%18%31%22%3
720
11th to 20thNight
26%24%28%17%41
720
21st to endNight
23%19%29%21%5%1
792
April1st to 10thNight
25%21%29%21%5%
720
11th to 20thNight
23%24%26%19%7%1
711
21st to endNight
25%19%27%22%6%1
594
May1st to 10thNight
29%13%27%23%7%
455
11th to 20thNight
16%18%32%26%6%1
354
21st to endNight
13%15%29%29%13%1
389
June1st to 10thNight
21%11%28%29%11%
360
11th to 20thNight
16%9%27%35%13%1
360
21st to endNight
16%9%31%32%12%1
360
July1st to 10thNight
11%8%28%37%16%1
350
11th to 20thNight
10%5%26%41%15%2
348
21st to endNight
11%5%26%43%14%1
394
August1st to 10thNight
11%425%39%20%1
358
11th to 20thNight
11%6%21%39%20%3
592
21st to endNight
12%7%24%37%18%2
792
September1st to 10thNight
12%8%25%37%15%2
720
11th to 20thNight
14%8%26%29%20%3
720
21st to endNight
17%10%29%25%17%2
720
October1st to 10thNight
24%13%24%25%14%1
720
11th to 20thNight
22%15%25%27%10%1
720
21st to endNight
28%15%28%23%6%
792
November1st to 10thNight
21%19%30%22%8%1
740
11th to 20thNight
23%19%32%18%7%2
760
21st to endNight
24%21%29%19%6%1
760
December1st to 10thNight
26%22%30%17%4
760
11th to 20thNight
25%21%31%19%41
760
21st to endNight
26%23%32%16%3
836
Page generated at 2024-01-28 05:26:34. Version ac07

Copyright 2024 Attilla Danko


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