This page made possible by the sponsorship of: Ralph E. Taggart, Horace Smith.

MSU Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the MSU Observatory clear sky chart from 2005-11-05 to 2019-07-11.

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
36%
18408
15%
54069
10%
18366
41%
18366
21%
37866

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
18%
1050
10%
2926
4%
1045
23%
1045
12%
2338
January16th to endNight
20%
1067
7%
3083
3%
1067
24%
1067
11%
2489
February1st to 15thNight
18%
821
9%
2609
3%
821
24%
821
10%
2047
February16th to endNight
22%
735
13%
2205
5%
735
30%
735
14%
1634
March1st to 15thNight
29%
840
17%
2456
10%
840
34%
840
19%
1751
March16th to endNight
34%
896
19%
2464
10%
896
40%
896
22%
1714
April1st to 15thNight
26%
638
13%
2096
8%
638
33%
638
18%
1448
April16th to endNight
36%
624
19%
1870
9%
624
44%
624
24%
1232
May1st to 15thNight
37%
630
15%
1890
8%
630
44%
630
22%
1289
May16th to endNight
48%
658
16%
1896
11%
657
54%
657
30%
1211
June1st to 15thNight
53%
630
16%
1680
12%
630
56%
630
33%
1059
June16th to endNight
54%
630
15%
1680
11%
630
58%
630
34%
1058
July1st to 15thNight
67%
588
19%
1568
16%
588
69%
588
42%
929
July16th to endNight
67%
612
20%
1585
17%
579
69%
579
42%
929
August1st to 15thNight
68%
575
21%
1715
18%
572
71%
572
37%
984
August16th to endNight
60%
621
21%
1928
16%
621
64%
621
32%
1143
September1st to 15thNight
60%
693
26%
2058
22%
693
64%
693
34%
1211
September16th to endNight
58%
777
24%
2145
18%
777
61%
777
34%
1308
October1st to 15thNight
44%
780
19%
2213
15%
780
48%
780
25%
1513
October16th to endNight
28%
832
16%
2649
9%
832
37%
832
19%
1840
November1st to 15thNight
33%
820
18%
2666
15%
820
38%
820
19%
1813
November16th to endNight
24%
840
14%
2730
8%
840
31%
840
14%
2018
December1st to 15thNight
19%
931
8%
2821
3%
931
24%
931
11%
2237
December16th to endNight
14%
1120
8%
3136
2%
1120
20%
1120
9%
2671

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%36%6%3445%7%33%
55133
Night
15%9%46%5%3445%6%34%
54242
Cloud CoverDay
14%9%47%6%3445%7%33%
55142
Night
15%9%46%5%3445%6%34%
54247
TransparencyDay
49%5%11%20%11%1
54824
Night
49%411%20%11%1
54069
SeeingDay
18%8%26%23%15%7%
8375
Night
19%7%28%30%12%1
18412

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
17%16%7%9%8%45%445%15%
1672
16th to endDay
15%18%8%9%9%45%335%16%
1844
February1st to 15thDay
15%14%6%12%8%46%435%19%
1910
16th to endDay
15%14%6%11%6%34446%21%
1840
March1st to 15thDay
15%10%48%6%35%45%7%27%
2153
16th to endDay
17%9%5%7%5%3435%7%32%
2467
April1st to 15thDay
19%11%36%6%24446%29%
2521
16th to endDay
17%7%26%5%24446%36%
2695
May1st to 15thDay
19%7%36%6%34447%32%
2721
16th to endDay
13%6%26%5%3445%8%38%
2920
June1st to 15thDay
12%425%6%3446%7%42%
2940
16th to endDay
11%425%6%46%5%6%9%38%
2940
July1st to 15thDay
7%414425%5%7%8%48%
2874
16th to endDay
8%4345%25%6%7%8%42%
2834
August1st to 15thDay
9%425%6%35%5%6%8%40%
2487
16th to endDay
11%6%35%5%3446%8%39%
2623
September1st to 15thDay
12%5%25%5%345%5%7%42%
2217
16th to endDay
11%6%25%6%345%5%8%41%
2145
October1st to 15thDay
16%7%26%6%34447%36%
2077
16th to endDay
22%9%36%5%35%34430%
1924
November1st to 15thDay
16%11%26%5%23345%36%
1852
16th to endDay
17%15%47%5%34346%26%
1890
December1st to 15thDay
16%14%9%11%6%34435%20%
1795
16th to endDay
19%19%7%9%6%25%35%416%
1792
January1st to 15thNight
20%13%6%9%7%34445%20%
2926
16th to endNight
13%13%9%11%7%45%446%18%
3083
February1st to 15thNight
17%15%5%8%8%3444423%
2607
16th to endNight
17%11%5%8%7%345%5%5%25%
2205
March1st to 15thNight
14%11%46%6%33445%34%
2443
16th to endNight
15%7%36%5%2445%7%36%
2464
April1st to 15thNight
19%9%35%5%3345%6%33%
2096
16th to endNight
16%7%25%42445%6%39%
1870
May1st to 15thNight
20%7%245%24448%34%
1890
16th to endNight
13%5%25%4245%49%42%
1894
June1st to 15thNight
12%325%42435%7%46%
1680
16th to endNight
9%425%4345%6%10%43%
1680
July1st to 15thNight
6%3234245%6%8%52%
1648
16th to endNight
7%31442345%10%52%
1684
August1st to 15thNight
6%325%33446%9%49%
1726
16th to endNight
10%425%5%33347%50%
1928
September1st to 15thNight
10%5%13423446%51%
2058
16th to endNight
11%42442445%7%47%
2145
October1st to 15thNight
19%7%25%5%2435%5%38%
2213
16th to endNight
20%9%26%5%24346%33%
2649
November1st to 15thNight
17%9%36%424445%35%
2666
16th to endNight
18%13%5%7%5%35%446%26%
2730
December1st to 15thNight
17%15%7%10%6%3434422%
2821
16th to endNight
21%16%7%10%7%4444415%
3136

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
16%16%7%9%9%5%5%445%15%
1672
16th to endDay
15%18%8%8%10%45%335%16%
1844
February1st to 15thDay
15%14%6%11%9%46%435%18%
1910
16th to endDay
16%13%6%11%7%25%445%21%
1840
March1st to 15thDay
15%10%5%7%7%345%5%7%27%
2163
16th to endDay
16%10%47%5%34347%31%
2466
April1st to 15thDay
19%11%36%6%34445%30%
2521
16th to endDay
16%7%36%5%24447%36%
2695
May1st to 15thDay
18%7%46%5%35%446%32%
2721
16th to endDay
13%6%26%6%3445%8%38%
2920
June1st to 15thDay
11%5%25%5%35%5%5%7%41%
2940
16th to endDay
10%425%6%45%6%6%9%37%
2940
July1st to 15thDay
6%424435%5%7%8%48%
2874
16th to endDay
7%5%25%6%35%5%7%8%41%
2834
August1st to 15thDay
8%5%16%6%45%5%6%9%40%
2487
16th to endDay
11%5%35%5%345%6%8%39%
2623
September1st to 15thDay
12%5%26%5%345%6%7%41%
2217
16th to endDay
10%6%26%5%245%6%8%41%
2145
October1st to 15thDay
15%7%36%6%33446%36%
2077
16th to endDay
21%10%36%5%35%345%30%
1924
November1st to 15thDay
16%10%36%5%33445%35%
1852
16th to endDay
17%14%48%6%24446%26%
1890
December1st to 15thDay
15%14%8%12%7%34346%19%
1795
16th to endDay
19%17%8%9%6%24445%16%
1792
January1st to 15thNight
20%13%6%8%8%3444421%
2926
16th to endNight
13%13%9%11%8%45%445%18%
3083
February1st to 15thNight
16%15%5%9%8%35%44423%
2600
16th to endNight
16%11%47%8%345%46%25%
2205
March1st to 15thNight
15%11%46%5%34346%33%
2456
16th to endNight
15%7%36%5%3445%7%35%
2464
April1st to 15thNight
20%9%36%5%245%5%6%32%
2096
16th to endNight
15%7%25%5%2445%6%39%
1870
May1st to 15thNight
19%6%25%5%34447%35%
1889
16th to endNight
13%5%25%42445%8%42%
1894
June1st to 15thNight
11%4245%25%449%45%
1680
16th to endNight
9%5%25%4345%7%10%42%
1680
July1st to 15thNight
6%32332446%9%52%
1648
16th to endNight
6%22442346%9%52%
1684
August1st to 15thNight
6%316%4245%7%10%48%
1726
16th to endNight
10%5%245%23347%49%
1928
September1st to 15thNight
10%5%13334347%51%
2058
16th to endNight
11%425%42445%7%47%
2145
October1st to 15thNight
18%7%25%5%3335%5%38%
2213
16th to endNight
20%8%36%5%34346%33%
2649
November1st to 15thNight
16%10%36%4345%45%35%
2666
16th to endNight
17%13%47%6%2445%5%26%
2730
December1st to 15thNight
17%14%6%10%7%34435%21%
2821
16th to endNight
20%15%7%10%7%35%44415%
3136

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
70%49%11%3
1673
16th to endDay
71%39%10%4
1844
February1st to 15thDay
68%38%13%5%
1912
16th to endDay
64%49%15%5%
1840
March1st to 15thDay
55%412%17%8%
2163
16th to endDay
52%310%21%10%1
2467
April1st to 15thDay
55%49%18%10%
2521
16th to endDay
47%412%16%15%2
2695
May1st to 15thDay
51%6%10%20%9%1
2721
16th to endDay
43%6%12%25%11%1
2924
June1st to 15thDay
40%5%11%25%15%1
2940
16th to endDay
40%7%12%22%15%
2940
July1st to 15thDay
31%6%10%26%20%4
2725
16th to endDay
36%6%13%24%16%2
2670
August1st to 15thDay
38%6%13%26%13%2
2474
16th to endDay
39%6%11%25%14%2
2623
September1st to 15thDay
39%6%11%25%15%1
2217
16th to endDay
40%413%27%15%
2145
October1st to 15thDay
47%5%11%22%12%1
2077
16th to endDay
54%414%18%7%
1924
November1st to 15thDay
49%5%11%21%10%1
1852
16th to endDay
58%413%17%5%
1890
December1st to 15thDay
65%312%14%3
1795
16th to endDay
70%5%10%10%3
1792
January1st to 15thNight
65%310%14%5%
2926
16th to endNight
65%5%12%12%4
3083
February1st to 15thNight
63%5%9%14%6%
2609
16th to endNight
57%412%17%6%
2205
March1st to 15thNight
52%410%20%11%1
2456
16th to endNight
47%410%23%11%1
2464
April1st to 15thNight
50%410%18%14%
2096
16th to endNight
44%412%17%17%3
1870
May1st to 15thNight
48%311%23%10%2
1890
16th to endNight
39%5%12%25%15%2
1896
June1st to 15thNight
36%5%12%27%16%1
1680
16th to endNight
34%6%15%27%14%
1680
July1st to 15thNight
27%6%10%30%20%4
1568
16th to endNight
27%6%15%26%22%2
1585
August1st to 15thNight
29%6%14%30%17%2
1715
16th to endNight
34%5%10%28%18%2
1928
September1st to 15thNight
33%5%9%28%20%2
2058
16th to endNight
34%412%29%18%
2145
October1st to 15thNight
46%49%23%15%1
2213
16th to endNight
51%312%22%8%
2649
November1st to 15thNight
49%411%21%11%1
2666
16th to endNight
58%412%18%5%
2730
December1st to 15thNight
65%411%12%5%
2821
16th to endNight
71%48%10%3
3136

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
19%8%42%22%5%1
180
16th to endDay
28%15%39%12%31
192
February1st to 15thDay
30%18%37%11%1
180
16th to endDay
27%16%32%17%5%
159
March1st to 15thDay
26%12%32%19%8%
243
16th to endDay
24%7%30%25%10%2
416
April1st to 15thDay
26%13%31%21%6%1
390
16th to endDay
24%7%28%18%16%4
379
May1st to 15thDay
25%8%26%23%11%4
408
16th to endDay
19%6%25%24%16%7%
532
June1st to 15thDay
14%5%29%28%16%4
645
16th to endDay
13%6%27%28%18%5%
645
July1st to 15thDay
7%320%29%25%13%
602
16th to endDay
9%321%30%23%11%
550
August1st to 15thDay
8%216%27%20%23%
358
16th to endDay
16%317%21%25%15%
396
September1st to 15thDay
14%116%23%25%18%
375
16th to endDay
14%5%15%22%26%14%
374
October1st to 15thDay
24%6%22%26%16%4
375
16th to endDay
26%13%30%23%6%
244
November1st to 15thDay
27%10%25%27%8%1
180
16th to endDay
28%15%36%14%5%
180
December1st to 15thDay
23%20%29%17%8%
180
16th to endDay
26%23%35%9%21
192
January1st to 15thNight
26%12%33%20%5%1
1050
16th to endNight
18%11%36%29%4
1067
February1st to 15thNight
24%13%36%22%3
824
16th to endNight
24%11%31%27%4
735
March1st to 15thNight
21%9%33%27%7%
840
16th to endNight
17%10%31%29%9%1
896
April1st to 15thNight
23%9%34%25%6%
638
16th to endNight
21%6%34%27%9%1
624
May1st to 15thNight
23%428%31%9%1
630
16th to endNight
15%326%33%18%1
659
June1st to 15thNight
13%224%43%15%
630
16th to endNight
12%122%39%22%1
630
July1st to 15thNight
8%115%41%29%2
588
16th to endNight
7%216%44%27%2
612
August1st to 15thNight
8%13%48%26%3
575
16th to endNight
12%115%34%30%5%
621
September1st to 15thNight
13%316%34%25%6%
693
16th to endNight
14%417%30%28%5%
777
October1st to 15thNight
20%422%34%15%2
780
16th to endNight
23%10%33%25%7%
832
November1st to 15thNight
21%9%28%29%10%
820
16th to endNight
26%11%31%24%6%
840
December1st to 15thNight
26%10%34%22%5%
931
16th to endNight
29%10%36%20%3
1120
Page generated at 2019-07-12 07:32:32. Version ac04

Copyright 2019 A. Danko


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