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 2005-11-05 to 2018-03-11.

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
28%
15418
13%
49112
7%
15387
36%
15387
15%
34744

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
16%
780
9%
2716
3%
776
23%
776
8%
2111
January16th to endNight
18%
832
12%
2912
4%
832
28%
832
10%
2103
February1st to 15thNight
14%
764
9%
2465
2%
761
23%
761
9%
1909
February16th to endNight
19%
683
13%
2049
5%
683
31%
683
12%
1516
March1st to 15thNight
17%
764
12%
2291
5%
764
26%
764
12%
1735
March16th to endNight
23%
768
19%
1995
6%
768
33%
768
18%
1437
April1st to 15thNight
20%
718
15%
1796
4%
718
26%
718
16%
1344
April16th to endNight
27%
636
16%
1716
6%
636
33%
636
20%
1198
May1st to 15thNight
28%
423
16%
1503
11%
423
38%
423
15%
1021
May16th to endNight
36%
374
13%
1497
11%
374
46%
374
17%
958
June1st to 15thNight
31%
360
9%
1440
6%
360
41%
360
14%
974
June16th to endNight
45%
360
10%
1440
12%
360
53%
360
21%
882
July1st to 15thNight
46%
340
13%
1360
15%
340
54%
340
23%
784
July16th to endNight
54%
376
14%
1418
15%
354
60%
354
24%
812
August1st to 15thNight
50%
399
15%
1470
13%
397
56%
397
24%
881
August16th to endNight
53%
764
20%
1910
11%
764
56%
764
36%
1199
September1st to 15thNight
49%
720
15%
1800
8%
720
51%
720
31%
1213
September16th to endNight
46%
717
24%
1974
16%
717
52%
717
33%
1229
October1st to 15thNight
34%
720
17%
2112
10%
720
42%
720
20%
1445
October16th to endNight
26%
768
11%
2453
6%
768
34%
768
13%
1823
November1st to 15thNight
26%
760
14%
2472
9%
760
34%
760
13%
1781
November16th to endNight
24%
780
14%
2681
10%
780
32%
780
12%
1925
December1st to 15thNight
17%
780
8%
2730
1%
780
23%
780
7%
2145
December16th to endNight
11%
832
9%
2912
3%
832
19%
832
6%
2319

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%30%
49523
Night
13%8%37%6%35%5%5%7%33%
49282
Cloud CoverDay
14%8%47%6%35%5%5%6%30%
49533
Night
13%8%37%6%35%5%5%6%33%
49288
TransparencyDay
52%6%12%18%9%1
49211
Night
49%7%12%19%9%1
49112
SeeingDay
21%16%29%19%9%3
6140
Night
20%16%28%24%9%1
15419

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
9%10%5%11%8%45%6%6%8%22%
1552
16th to endDay
7%10%5%10%8%5%6%5%48%26%
1664
February1st to 15thDay
9%10%6%11%9%6%7%5%6%5%20%
1723
16th to endDay
11%12%5%9%8%45%5%5%426%
1710
March1st to 15thDay
13%13%6%9%8%47%45%423%
1896
16th to endDay
13%10%5%7%6%34445%34%
2226
April1st to 15thDay
17%9%5%6%5%345%46%32%
2152
16th to endDay
17%9%36%434346%35%
2244
May1st to 15thDay
17%9%37%6%4445%6%31%
2458
16th to endDay
16%8%36%5%35%5%5%7%31%
2618
June1st to 15thDay
23%8%25%435%5%5%6%27%
2520
16th to endDay
18%6%36%5%35%6%5%9%28%
2520
July1st to 15thDay
12%6%36%6%46%6%7%8%30%
2520
16th to endDay
12%5%36%7%37%6%7%8%31%
2654
August1st to 15thDay
11%7%38%8%46%5%6%9%28%
2466
16th to endDay
9%5%36%6%35%6%6%8%37%
2292
September1st to 15thDay
15%5%25%5%34447%40%
2160
16th to endDay
10%425%425%448%45%
1986
October1st to 15thDay
17%8%36%5%245%5%6%32%
1847
16th to endDay
18%12%37%6%345%45%28%
1770
November1st to 15thDay
11%11%5%6%6%35%5%5%7%30%
1716
16th to endDay
12%10%5%7%8%36%5%46%29%
1605
December1st to 15thDay
13%16%6%10%8%36%45%6%19%
1560
16th to endDay
16%15%7%10%7%3445%418%
1664
January1st to 15thNight
9%11%5%9%8%47%6%6%7%22%
2716
16th to endNight
8%10%49%8%46%6%6%7%28%
2912
February1st to 15thNight
9%11%5%9%9%5%7%6%7%6%21%
2464
16th to endNight
10%9%48%8%46%6%6%5%29%
2049
March1st to 15thNight
15%11%49%6%45%445%28%
2278
16th to endNight
12%8%47%6%34445%37%
1995
April1st to 15thNight
14%10%47%6%45%346%31%
1796
16th to endNight
17%8%145%34447%38%
1716
May1st to 15thNight
18%8%26%44445%8%33%
1503
16th to endNight
15%5%35%4345%5%9%37%
1495
June1st to 15thNight
22%6%245%245%49%32%
1440
16th to endNight
12%425%4345%7%9%41%
1440
July1st to 15thNight
8%5%26%4345%6%10%43%
1440
16th to endNight
11%3234245%6%7%47%
1514
August1st to 15thNight
8%5%245%2446%10%44%
1480
16th to endNight
9%41432447%9%48%
1910
September1st to 15thNight
13%6%15%43345%7%45%
1800
16th to endNight
14%323323447%49%
1974
October1st to 15thNight
15%8%26%5%2445%7%36%
2112
16th to endNight
19%9%36%6%35%45%6%28%
2453
November1st to 15thNight
13%10%37%6%45%5%5%6%31%
2472
16th to endNight
13%9%47%6%345%7%6%30%
2681
December1st to 15thNight
15%12%5%9%8%45%5%5%6%20%
2730
16th to endNight
13%14%5%9%8%45%5%46%21%
2912

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
11%10%7%11%8%45%6%6%7%22%
1552
16th to endDay
8%10%411%9%46%45%6%28%
1664
February1st to 15thDay
10%10%6%11%10%5%6%5%6%5%21%
1723
16th to endDay
11%12%5%10%7%35%5%5%427%
1710
March1st to 15thDay
14%14%5%9%7%37%44424%
1906
16th to endDay
13%10%47%7%35%34435%
2226
April1st to 15thDay
18%9%47%435%445%32%
2152
16th to endDay
17%10%37%424445%35%
2244
May1st to 15thDay
18%9%46%5%345%46%31%
2458
16th to endDay
16%7%26%6%446%6%7%31%
2618
June1st to 15thDay
22%7%35%6%345%5%7%27%
2520
16th to endDay
17%6%35%6%45%5%6%8%29%
2520
July1st to 15thDay
11%5%37%6%47%6%6%9%31%
2520
16th to endDay
12%436%7%37%5%8%7%32%
2654
August1st to 15thDay
10%6%38%8%45%6%7%8%29%
2466
16th to endDay
9%435%7%45%5%6%9%38%
2292
September1st to 15thDay
15%425%5%245%37%41%
2160
16th to endDay
10%425%4335%5%7%46%
1986
October1st to 15thDay
16%8%37%5%345%5%6%33%
1847
16th to endDay
17%10%37%7%345%5%428%
1770
November1st to 15thDay
13%10%47%5%35%46%6%31%
1716
16th to endDay
13%10%37%8%35%5%5%5%31%
1605
December1st to 15thDay
14%15%6%10%8%45%34421%
1560
16th to endDay
17%17%7%10%6%3444420%
1664
January1st to 15thNight
10%11%410%8%46%6%6%6%23%
2716
16th to endNight
8%10%49%7%46%6%6%6%29%
2912
February1st to 15thNight
9%11%411%9%47%6%6%5%23%
2457
16th to endNight
11%9%48%7%46%5%6%6%29%
2049
March1st to 15thNight
16%11%5%9%6%35%34428%
2291
16th to endNight
12%9%37%6%25%45%438%
1995
April1st to 15thNight
16%9%48%6%35%447%31%
1796
16th to endNight
18%7%145%33446%38%
1716
May1st to 15thNight
18%7%26%5%3436%6%33%
1503
16th to endNight
15%425%435%5%6%9%36%
1495
June1st to 15thNight
22%6%25%425%35%7%33%
1440
16th to endNight
13%5%14325%6%6%9%40%
1440
July1st to 15thNight
9%425%425%5%7%9%43%
1440
16th to endNight
11%423425%5%5%8%46%
1514
August1st to 15thNight
9%335%5%25%6%6%9%44%
1480
16th to endNight
9%32342446%9%48%
1910
September1st to 15thNight
14%425%5%23448%44%
1800
16th to endNight
13%423423447%49%
1974
October1st to 15thNight
16%7%26%5%24446%38%
2112
16th to endNight
20%8%37%5%35%5%45%29%
2453
November1st to 15thNight
14%9%38%6%45%45%7%31%
2472
16th to endNight
14%9%38%5%4445%6%31%
2681
December1st to 15thNight
16%12%5%9%7%45%5%5%5%22%
2730
16th to endNight
14%15%6%8%8%35%45%5%22%
2912

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
58%8%10%13%6%
1553
16th to endDay
56%6%13%15%8%
1664
February1st to 15thDay
62%8%7%15%5%
1726
16th to endDay
58%6%11%12%10%1
1710
March1st to 15thDay
63%5%10%11%7%1
1906
16th to endDay
52%48%14%15%4
2226
April1st to 15thDay
53%6%8%18%10%2
2152
16th to endDay
50%49%18%13%3
2244
May1st to 15thDay
52%5%10%17%13%1
2458
16th to endDay
50%7%12%17%11%1
2622
June1st to 15thDay
54%6%13%16%8%
2520
16th to endDay
50%7%13%19%8%
2520
July1st to 15thDay
46%7%13%22%8%
2371
16th to endDay
45%8%16%20%8%
2487
August1st to 15thDay
49%8%15%19%7%
2452
16th to endDay
40%7%16%25%10%
2292
September1st to 15thDay
42%5%12%27%11%1
2160
16th to endDay
35%6%15%27%13%1
1986
October1st to 15thDay
50%5%12%20%10%
1847
16th to endDay
56%6%13%16%5%
1770
November1st to 15thDay
50%8%13%17%8%2
1716
16th to endDay
54%6%12%16%9%1
1605
December1st to 15thDay
66%5%10%13%4
1560
16th to endDay
67%6%8%9%8%
1664
January1st to 15thNight
57%10%10%13%6%
2716
16th to endNight
53%8%10%17%9%
2912
February1st to 15thNight
59%8%12%12%6%
2465
16th to endNight
53%7%12%15%9%
2049
March1st to 15thNight
58%5%9%17%7%1
2291
16th to endNight
48%5%9%18%14%3
1995
April1st to 15thNight
52%5%9%17%13%
1796
16th to endNight
46%6%10%19%14%2
1716
May1st to 15thNight
49%5%8%16%17%2
1503
16th to endNight
42%9%14%21%11%1
1497
June1st to 15thNight
49%7%13%20%8%
1440
16th to endNight
37%10%15%25%11%
1440
July1st to 15thNight
34%8%15%29%11%
1360
16th to endNight
33%9%17%24%13%1
1418
August1st to 15thNight
34%10%19%24%10%
1470
16th to endNight
30%7%16%31%12%
1910
September1st to 15thNight
38%7%14%28%10%1
1800
16th to endNight
33%6%12%31%14%1
1974
October1st to 15thNight
46%6%13%21%12%
2112
16th to endNight
55%6%13%16%6%
2453
November1st to 15thNight
52%6%12%15%9%2
2472
16th to endNight
52%8%13%18%6%1
2681
December1st to 15thNight
63%7%12%13%3
2730
16th to endNight
63%8%9%12%6%
2912

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
20%26%31%12%10%
90
16th to endDay
20%29%36%9%31
96
February1st to 15thDay
30%29%32%32
155
16th to endDay
24%24%30%16%2
291
March1st to 15thDay
28%19%26%20%3
312
16th to endDay
22%25%26%15%7%2
288
April1st to 15thDay
27%20%27%17%5%1
270
16th to endDay
28%19%24%14%8%4
270
May1st to 15thDay
31%12%30%12%8%4
288
16th to endDay
19%19%32%20%5%2
331
June1st to 15thDay
28%14%29%18%7%1
315
16th to endDay
18%14%36%21%7%1
315
July1st to 15thDay
13%11%32%24%16%2
305
16th to endDay
14%6%33%33%8%3
326
August1st to 15thDay
12%9%33%24%16%4
313
16th to endDay
12%10%20%29%16%10%
332
September1st to 15thDay
14%9%24%23%19%8%
315
16th to endDay
9%11%26%21%16%14%
314
October1st to 15thDay
22%13%24%20%15%2
315
16th to endDay
28%16%28%21%5%
298
November1st to 15thDay
25%12%27%21%11%1
280
16th to endDay
28%24%24%15%5%1
135
December1st to 15thDay
17%24%37%10%8%1
90
16th to endDay
36%22%30%8%2
96
January1st to 15thNight
19%19%36%20%4
780
16th to endNight
18%21%34%20%4
832
February1st to 15thNight
18%19%40%19%2
764
16th to endNight
19%23%31%22%4
683
March1st to 15thNight
27%17%31%20%2
764
16th to endNight
21%22%27%21%5%1
768
April1st to 15thNight
22%22%29%20%4
718
16th to endNight
23%18%27%20%9%
636
May1st to 15thNight
25%13%28%22%8%
423
16th to endNight
15%14%28%29%10%
375
June1st to 15thNight
23%10%27%26%11%
360
16th to endNight
14%6%30%35%12%1
360
July1st to 15thNight
10%6%27%36%18%2
340
16th to endNight
13%323%42%16%
376
August1st to 15thNight
12%5%24%34%21%1
399
16th to endNight
11%6%21%36%21%2
764
September1st to 15thNight
14%7%22%34%17%2
720
16th to endNight
15%8%25%23%22%5%
717
October1st to 15thNight
21%12%24%25%15%1
720
16th to endNight
28%14%25%23%7%
768
November1st to 15thNight
20%18%28%21%10%1
760
16th to endNight
23%20%26%19%8%1
780
December1st to 15thNight
26%21%28%18%4
780
16th to endNight
25%21%33%15%2
832
Page generated at 2018-03-12 13:28:03. Version ac04

Copyright 2018 A. Danko


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