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 2017-09-10.

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%
14690
13%
46767
7%
14659
36%
14659
16%
33090

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%
720
9%
2506
3%
716
23%
716
8%
1952
January16th to endNight
18%
768
12%
2688
4%
768
28%
768
10%
1930
February1st to 15thNight
14%
704
9%
2272
2%
701
23%
701
9%
1759
February16th to endNight
19%
631
13%
1893
5%
631
31%
631
12%
1402
March1st to 15thNight
18%
720
13%
2160
5%
720
27%
720
13%
1615
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
48%
700
14%
1750
7%
700
50%
700
30%
1190
September16th to endNight
44%
657
21%
1809
14%
657
49%
657
31%
1147
October1st to 15thNight
33%
660
17%
1936
10%
660
42%
660
19%
1335
October16th to endNight
26%
704
9%
2248
4%
704
33%
704
13%
1692
November1st to 15thNight
26%
700
15%
2277
9%
700
34%
700
14%
1636
November16th to endNight
24%
720
14%
2475
10%
720
31%
720
12%
1790
December1st to 15thNight
16%
720
7%
2520
2%
720
23%
720
7%
1982
December16th to endNight
12%
768
8%
2688
2%
768
18%
768
6%
2170

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%
47868
Night
13%8%37%6%35%5%5%7%33%
46937
Cloud CoverDay
14%8%47%6%35%5%5%6%30%
47878
Night
14%8%37%6%35%5%5%6%33%
46943
TransparencyDay
52%6%12%18%9%1
47556
Night
49%7%12%19%9%1
46767
SeeingDay
21%15%29%20%9%3
5605
Night
20%15%28%24%9%1
14691

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
10%9%6%11%8%45%6%6%8%21%
1432
16th to endDay
8%10%5%10%7%5%6%5%48%26%
1536
February1st to 15thDay
10%10%5%11%9%6%7%6%6%5%21%
1586
16th to endDay
10%12%5%9%8%46%5%5%426%
1580
March1st to 15thDay
12%12%6%9%8%47%5%5%425%
1790
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%39%
2098
16th to endDay
11%5%26%425%448%43%
1821
October1st to 15thDay
17%9%37%5%245%5%6%31%
1693
16th to endDay
18%12%37%6%345%45%26%
1623
November1st to 15thDay
11%10%5%6%6%36%5%6%8%29%
1581
16th to endDay
12%9%5%7%8%36%5%45%30%
1482
December1st to 15thDay
13%16%5%9%8%36%45%7%19%
1440
16th to endDay
16%16%8%10%7%35%45%417%
1536
January1st to 15thNight
9%11%5%9%8%46%6%6%7%22%
2506
16th to endNight
8%10%5%8%8%46%6%6%6%28%
2688
February1st to 15thNight
9%10%5%9%9%5%7%6%8%5%21%
2271
16th to endNight
10%9%48%8%46%5%6%5%29%
1893
March1st to 15thNight
14%10%49%6%45%445%29%
2147
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%43%
1750
16th to endNight
14%324323447%47%
1809
October1st to 15thNight
16%8%36%5%2445%6%36%
1936
16th to endNight
20%9%36%6%36%45%6%27%
2248
November1st to 15thNight
13%9%37%6%45%5%5%6%31%
2277
16th to endNight
14%9%47%7%345%6%6%30%
2475
December1st to 15thNight
16%12%5%9%7%5%5%5%5%6%20%
2520
16th to endNight
14%15%5%9%8%45%5%46%20%
2688

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%9%7%11%8%45%6%6%7%21%
1432
16th to endDay
8%10%411%8%47%5%5%5%28%
1536
February1st to 15thDay
10%10%6%11%11%5%6%5%6%5%21%
1586
16th to endDay
10%12%5%10%8%35%5%5%427%
1580
March1st to 15thDay
13%13%5%9%8%37%5%4425%
1800
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%5%25%6%25%5%47%40%
2098
16th to endDay
11%425%5%335%5%7%44%
1821
October1st to 15thDay
16%9%38%5%345%5%6%31%
1693
16th to endDay
17%11%48%7%35%45%427%
1623
November1st to 15thDay
12%10%47%5%35%5%6%7%31%
1581
16th to endDay
13%10%47%8%35%5%45%31%
1482
December1st to 15thDay
15%15%6%9%8%45%345%21%
1440
16th to endDay
17%17%7%10%6%3444419%
1536
January1st to 15thNight
10%11%5%10%8%46%6%6%6%22%
2506
16th to endNight
8%10%49%7%45%5%6%6%29%
2688
February1st to 15thNight
9%11%411%9%47%6%6%5%23%
2264
16th to endNight
11%9%49%7%46%5%6%6%28%
1893
March1st to 15thNight
15%10%5%8%6%35%345%30%
2160
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%43%
1750
16th to endNight
14%423423447%48%
1809
October1st to 15thNight
17%7%26%5%25%45%6%37%
1936
16th to endNight
21%9%37%5%35%5%45%28%
2248
November1st to 15thNight
14%9%37%5%45%45%7%31%
2277
16th to endNight
14%9%48%5%4445%6%31%
2475
December1st to 15thNight
17%12%5%10%7%45%5%45%22%
2520
16th to endNight
14%16%6%8%8%35%44420%
2688

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
59%9%10%13%6%
1433
16th to endDay
55%6%12%15%8%
1536
February1st to 15thDay
61%9%7%15%5%
1589
16th to endDay
57%7%11%11%10%1
1580
March1st to 15thDay
61%5%11%11%7%1
1800
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
43%5%12%26%11%
2098
16th to endDay
37%6%14%26%13%
1821
October1st to 15thDay
51%5%13%19%9%
1693
16th to endDay
58%6%13%14%5%
1623
November1st to 15thDay
50%8%13%17%8%2
1581
16th to endDay
54%6%11%16%9%1
1482
December1st to 15thDay
66%5%10%13%3
1440
16th to endDay
68%6%8%8%7%
1536
January1st to 15thNight
57%11%10%14%5%
2506
16th to endNight
53%7%10%17%9%
2688
February1st to 15thNight
59%8%13%12%6%
2272
16th to endNight
54%6%12%15%9%
1893
March1st to 15thNight
56%5%9%18%8%1
2160
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
39%7%14%28%9%
1750
16th to endNight
35%7%13%29%13%1
1809
October1st to 15thNight
47%5%13%20%12%
1936
16th to endNight
56%6%14%15%6%
2248
November1st to 15thNight
52%6%13%15%9%2
2277
16th to endNight
52%8%12%18%6%1
2475
December1st to 15thNight
62%7%12%13%3
2520
16th to endNight
64%8%10%11%4
2688

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
23%28%25%10%13%
60
16th to endDay
23%28%31%10%41
64
February1st to 15thDay
34%26%30%43
108
16th to endDay
23%23%32%17%3
239
March1st to 15thDay
24%20%27%22%3
270
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
15%10%24%23%17%8%
294
16th to endDay
12%11%27%21%13%12%
254
October1st to 15thDay
23%12%24%20%16%3
255
16th to endDay
27%16%28%21%4
247
November1st to 15thDay
22%12%28%22%11%2
235
16th to endDay
25%23%26%14%7%1
102
December1st to 15thDay
20%23%40%6%8%1
60
16th to endDay
35%28%26%7%1
64
January1st to 15thNight
19%18%37%20%4
720
16th to endNight
19%21%34%20%4
768
February1st to 15thNight
18%18%40%20%2
704
16th to endNight
18%22%30%22%4
631
March1st to 15thNight
26%18%32%20%2
720
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
15%7%23%34%16%2
700
16th to endNight
16%8%26%24%20%3
657
October1st to 15thNight
22%12%24%24%14%1
660
16th to endNight
28%14%25%23%7%
704
November1st to 15thNight
19%17%29%21%9%1
700
16th to endNight
23%20%26%19%8%1
720
December1st to 15thNight
26%22%29%17%4
720
16th to endNight
27%20%33%14%2
768
Page generated at 2017-09-11 19:35:29. Version ac04

Copyright 2017 A. Danko


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