Muskegon Astronomical Society
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Muskegon Astronomical Society clear sky chart from 2005-11-05 to 2017-09-17.

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%
16007
14%
46821
9%
15965
40%
15965
19%
33446

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%
900
6%
2506
3%
895
19%
895
7%
2171
January16th to endNight
20%
960
5%
2688
3%
960
21%
960
8%
2324
February1st to 15thNight
18%
742
8%
2225
3%
742
23%
742
9%
1821
February16th to endNight
24%
631
10%
1893
5%
631
29%
631
12%
1476
March1st to 15thNight
31%
720
15%
2148
10%
720
36%
720
19%
1508
March16th to endNight
34%
708
18%
2052
12%
708
40%
708
23%
1391
April1st to 15thNight
30%
539
14%
1797
11%
539
36%
539
18%
1239
April16th to endNight
35%
540
21%
1650
11%
540
44%
540
24%
1079
May1st to 15thNight
35%
540
16%
1620
9%
540
42%
540
23%
1094
May16th to endNight
41%
562
16%
1525
8%
561
48%
561
28%
1021
June1st to 15thNight
48%
540
15%
1440
10%
540
53%
540
36%
889
June16th to endNight
54%
540
15%
1440
9%
540
59%
540
34%
900
July1st to 15thNight
64%
510
17%
1360
13%
510
65%
510
44%
784
July16th to endNight
63%
564
19%
1417
13%
531
65%
531
42%
831
August1st to 15thNight
68%
539
23%
1571
19%
536
71%
536
40%
876
August16th to endNight
62%
573
22%
1838
21%
573
66%
573
33%
1065
September1st to 15thNight
61%
596
25%
1856
23%
596
66%
596
35%
1048
September16th to endNight
56%
665
23%
1837
17%
665
60%
665
34%
1129
October1st to 15thNight
44%
660
22%
1852
16%
660
49%
660
27%
1222
October16th to endNight
28%
704
13%
2288
8%
704
36%
704
17%
1608
November1st to 15thNight
31%
700
18%
2276
14%
700
39%
700
19%
1562
November16th to endNight
23%
720
9%
2340
6%
720
27%
720
10%
1858
December1st to 15thNight
15%
894
4%
2514
2%
894
17%
894
6%
2223
December16th to endNight
14%
960
6%
2688
1%
960
18%
960
8%
2327

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%46%6%3445%7%34%
47961
Night
14%9%47%6%34446%33%
46989
Cloud CoverDay
14%8%46%6%35%45%7%34%
47970
Night
14%9%47%6%34446%33%
46994
TransparencyDay
48%412%21%10%1
47647
Night
52%411%20%10%1
46821
SeeingDay
17%9%28%24%13%6%
6001
Night
19%8%27%30%12%1
16011

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
18%14%9%12%10%5%6%33411%
1432
16th to endDay
13%19%11%12%12%5%5%32310%
1536
February1st to 15thDay
11%17%8%11%12%46%34415%
1634
16th to endDay
14%13%7%11%8%5%6%5%4417%
1580
March1st to 15thDay
15%12%47%7%345%5%6%27%
1802
16th to endDay
15%9%37%5%245%5%6%33%
2181
April1st to 15thDay
20%12%35%424446%31%
2151
16th to endDay
18%7%2443445%7%36%
2309
May1st to 15thDay
19%6%25%42445%8%36%
2331
16th to endDay
11%5%244335%6%9%44%
2587
June1st to 15thDay
11%5%246%35%5%5%9%40%
2520
16th to endDay
10%4245%25%46%9%43%
2520
July1st to 15thDay
6%414425%45%8%52%
2520
16th to endDay
8%4244245%6%10%47%
2655
August1st to 15thDay
8%325%5%35%6%5%9%43%
2379
16th to endDay
12%5%244245%5%8%43%
2362
September1st to 15thDay
11%425%435%447%46%
2091
16th to endDay
11%5%25%6%35%5%5%9%39%
1829
October1st to 15thDay
16%7%25%6%24446%37%
1777
16th to endDay
22%8%48%7%44446%25%
1584
November1st to 15thDay
14%10%46%6%2435%6%34%
1582
16th to endDay
21%20%46%6%34346%17%
1620
December1st to 15thDay
16%19%10%14%8%4332412%
1443
16th to endDay
19%21%9%12%7%2334310%
1536
January1st to 15thNight
18%17%7%11%8%3443315%
2506
16th to endNight
12%14%9%12%10%46%5%3414%
2688
February1st to 15thNight
11%16%8%10%10%45%34419%
2223
16th to endNight
15%12%6%10%7%36%5%45%22%
1893
March1st to 15thNight
16%8%46%6%24447%33%
2135
16th to endNight
15%8%36%6%2435%6%36%
2052
April1st to 15thNight
19%9%45%5%34347%32%
1797
16th to endNight
16%8%25%324446%41%
1650
May1st to 15thNight
16%5%25%6%35%448%36%
1620
16th to endNight
10%6%36%4345%47%42%
1523
June1st to 15thNight
10%43442445%9%45%
1440
16th to endNight
9%424435%46%9%45%
1440
July1st to 15thNight
5%3234245%6%9%52%
1440
16th to endNight
6%224425%37%8%52%
1513
August1st to 15thNight
5%315%3345%6%9%51%
1580
16th to endNight
10%42443445%6%50%
1838
September1st to 15thNight
10%32332445%7%52%
1856
16th to endNight
10%4245%34336%50%
1837
October1st to 15thNight
17%6%25%324335%43%
1852
16th to endNight
21%8%36%424347%32%
2288
November1st to 15thNight
15%10%46%4245%5%6%34%
2276
16th to endNight
20%16%48%7%3445%6%19%
2340
December1st to 15thNight
20%17%8%12%8%3434411%
2514
16th to endNight
21%18%8%9%7%3444413%
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
18%13%9%12%9%5%6%43411%
1432
16th to endDay
13%19%11%13%10%6%5%33210%
1536
February1st to 15thDay
11%17%8%11%11%5%5%44415%
1634
16th to endDay
13%14%7%11%7%5%6%6%45%18%
1580
March1st to 15thDay
16%11%47%6%345%5%7%27%
1812
16th to endDay
16%8%37%5%2445%6%33%
2180
April1st to 15thDay
20%11%46%423436%31%
2151
16th to endDay
18%6%34425%448%36%
2309
May1st to 15thDay
19%6%25%42445%8%36%
2331
16th to endDay
10%5%15%4345%6%8%43%
2587
June1st to 15thDay
11%5%245%36%5%5%9%40%
2520
16th to endDay
10%4145%36%45%9%43%
2520
July1st to 15thDay
6%414425%45%8%52%
2520
16th to endDay
9%324425%5%6%9%47%
2655
August1st to 15thDay
8%315%5%35%5%6%9%43%
2379
16th to endDay
12%5%244245%5%8%44%
2362
September1st to 15thDay
12%4145%3445%6%46%
2091
16th to endDay
12%425%6%35%5%6%8%40%
1829
October1st to 15thDay
16%7%25%5%2435%6%38%
1777
16th to endDay
22%9%46%7%45%437%25%
1584
November1st to 15thDay
14%10%36%6%25%35%5%35%
1582
16th to endDay
21%19%47%6%34346%18%
1620
December1st to 15thDay
16%18%10%14%8%3422413%
1443
16th to endDay
20%20%9%11%7%2335%310%
1536
January1st to 15thNight
19%16%7%11%8%45%33315%
2506
16th to endNight
12%15%9%13%9%5%5%5%3414%
2688
February1st to 15thNight
12%15%9%10%9%36%345%18%
2216
16th to endNight
15%12%6%9%7%45%446%22%
1893
March1st to 15thNight
16%9%36%6%2445%7%34%
2148
16th to endNight
14%8%45%6%25%35%7%36%
2052
April1st to 15thNight
19%10%45%5%25%347%32%
1797
16th to endNight
17%8%25%325%346%41%
1650
May1st to 15thNight
17%5%25%6%35%448%36%
1619
16th to endNight
11%6%36%435%447%42%
1523
June1st to 15thNight
10%42442446%9%45%
1440
16th to endNight
9%424435%46%9%44%
1440
July1st to 15thNight
5%3134235%6%10%52%
1440
16th to endNight
6%32343446%8%52%
1513
August1st to 15thNight
6%225%3245%5%9%52%
1580
16th to endNight
10%324424446%50%
1838
September1st to 15thNight
10%313324446%53%
1856
16th to endNight
9%5%24444436%50%
1837
October1st to 15thNight
17%6%35%333345%43%
1852
16th to endNight
22%7%36%424347%32%
2288
November1st to 15thNight
16%9%45%5%2445%6%35%
2276
16th to endNight
20%15%48%6%3445%7%19%
2340
December1st to 15thNight
20%17%8%11%8%4443411%
2514
16th to endNight
21%19%7%9%8%3344413%
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
75%5%9%8%1
1433
16th to endDay
80%36%7%2
1536
February1st to 15thDay
71%5%7%14%1
1636
16th to endDay
67%5%9%13%4
1580
March1st to 15thDay
55%5%14%17%7%
1812
16th to endDay
48%414%23%6%1
2181
April1st to 15thDay
53%49%21%11%
2151
16th to endDay
45%413%19%13%2
2309
May1st to 15thDay
45%412%25%11%1
2331
16th to endDay
35%5%14%27%14%1
2591
June1st to 15thDay
38%5%14%25%16%
2520
16th to endDay
35%416%24%17%1
2520
July1st to 15thDay
28%414%31%19%2
2371
16th to endDay
31%5%14%28%17%2
2488
August1st to 15thDay
34%5%13%32%12%1
2364
16th to endDay
36%412%27%16%2
2362
September1st to 15thDay
36%411%30%15%2
2091
16th to endDay
39%413%26%15%
1829
October1st to 15thDay
47%310%25%12%
1777
16th to endDay
59%415%15%5%
1584
November1st to 15thDay
50%412%21%10%
1582
16th to endDay
67%411%12%3
1620
December1st to 15thDay
77%38%8%2
1443
16th to endDay
77%410%6%1
1536
January1st to 15thNight
74%46%10%3
2506
16th to endNight
74%410%8%2
2688
February1st to 15thNight
68%37%14%4
2225
16th to endNight
62%411%14%5%
1893
March1st to 15thNight
49%5%12%20%9%1
2148
16th to endNight
47%212%24%10%1
2052
April1st to 15thNight
52%38%19%15%
1797
16th to endNight
44%310%20%15%5%
1650
May1st to 15thNight
46%312%22%12%2
1620
16th to endNight
41%5%10%24%15%2
1525
June1st to 15thNight
35%313%30%15%2
1440
16th to endNight
34%5%16%25%16%1
1440
July1st to 15thNight
26%5%12%31%21%2
1360
16th to endNight
28%5%17%26%19%3
1417
August1st to 15thNight
28%413%34%17%1
1571
16th to endNight
33%5%10%27%20%2
1838
September1st to 15thNight
30%5%11%31%19%1
1856
16th to endNight
35%311%34%13%
1837
October1st to 15thNight
44%39%27%14%
1852
16th to endNight
53%315%19%7%
2288
November1st to 15thNight
49%5%11%20%11%1
2276
16th to endNight
65%412%13%2
2340
December1st to 15thNight
78%47%7%3
2514
16th to endNight
74%411%7%1
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%14%38%22%1
90
16th to endDay
28%10%32%20%5%3
96
February1st to 15thDay
17%28%37%13%2
90
16th to endDay
22%17%39%12%7%1
81
March1st to 15thDay
32%20%26%12%7%
102
16th to endDay
29%6%24%26%10%2
288
April1st to 15thDay
28%10%30%22%7%1
270
16th to endDay
24%12%27%18%13%3
270
May1st to 15thDay
24%10%27%23%10%4
288
16th to endDay
14%12%31%23%13%5%
487
June1st to 15thDay
12%8%37%27%9%4
495
16th to endDay
14%9%36%23%11%5%
495
July1st to 15thDay
7%6%29%31%16%8%
475
16th to endDay
9%6%26%31%16%9%
515
August1st to 15thDay
8%321%27%22%15%
352
16th to endDay
20%5%14%26%21%12%
332
September1st to 15thDay
11%320%28%26%9%
315
16th to endDay
11%5%20%27%23%10%
259
October1st to 15thDay
17%9%19%30%18%3
239
16th to endDay
25%15%40%18%
96
November1st to 15thDay
13%17%33%21%8%5%
90
16th to endDay
30%16%35%11%6%
90
December1st to 15thDay
27%33%24%10%4
90
16th to endDay
30%35%26%8%
96
January1st to 15thNight
27%13%30%21%7%
900
16th to endNight
20%10%33%30%6%
960
February1st to 15thNight
17%15%33%26%6%
745
16th to endNight
22%13%29%27%6%
631
March1st to 15thNight
20%10%30%28%9%
720
16th to endNight
18%7%31%29%11%1
708
April1st to 15thNight
23%8%32%28%6%
539
16th to endNight
22%7%31%26%10%
540
May1st to 15thNight
20%6%30%31%10%
540
16th to endNight
13%6%28%33%15%1
563
June1st to 15thNight
12%429%38%14%
540
16th to endNight
11%423%41%17%1
540
July1st to 15thNight
7%119%44%25%2
510
16th to endNight
7%221%38%28%2
564
August1st to 15thNight
6%114%47%26%2
539
16th to endNight
11%213%39%27%4
573
September1st to 15thNight
10%5%16%36%24%6%
596
16th to endNight
12%7%18%31%25%4
665
October1st to 15thNight
20%423%31%18%1
660
16th to endNight
25%11%28%25%8%
704
November1st to 15thNight
21%9%30%26%10%
700
16th to endNight
27%13%25%25%5%
720
December1st to 15thNight
29%14%29%21%4
894
16th to endNight
28%11%35%20%3
960
Page generated at 2017-09-18 08:38:25. Version ac04

Copyright 2017 A. Danko


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