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 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
37%
15908
15%
46719
10%
15866
42%
15866
21%
32575

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
9%
2506
4%
895
20%
895
11%
2031
January16th to endNight
20%
915
7%
2643
3%
915
24%
915
10%
2153
February1st to 15thNight
19%
701
10%
2229
3%
701
25%
701
11%
1722
February16th to endNight
23%
631
14%
1893
5%
631
32%
631
15%
1388
March1st to 15thNight
29%
720
15%
2105
10%
720
34%
720
19%
1506
March16th to endNight
33%
768
18%
2112
10%
768
39%
768
21%
1490
April1st to 15thNight
28%
546
13%
1795
9%
546
34%
546
19%
1219
April16th to endNight
35%
540
19%
1620
9%
540
44%
540
25%
1056
May1st to 15thNight
37%
540
14%
1620
7%
540
44%
540
22%
1103
May16th to endNight
48%
562
16%
1618
11%
561
53%
561
30%
1029
June1st to 15thNight
52%
540
15%
1440
11%
540
56%
540
33%
907
June16th to endNight
55%
540
16%
1440
11%
540
59%
540
35%
902
July1st to 15thNight
64%
510
17%
1360
14%
510
67%
510
41%
809
July16th to endNight
67%
564
21%
1454
18%
531
70%
531
42%
853
August1st to 15thNight
67%
539
20%
1609
17%
536
70%
536
37%
922
August16th to endNight
60%
573
22%
1779
17%
573
65%
573
33%
1051
September1st to 15thNight
60%
620
26%
1845
22%
620
65%
620
35%
1071
September16th to endNight
57%
657
22%
1815
16%
657
61%
657
34%
1112
October1st to 15thNight
46%
660
21%
1873
17%
660
51%
660
27%
1239
October16th to endNight
27%
704
15%
2241
8%
704
36%
704
18%
1579
November1st to 15thNight
35%
700
19%
2276
17%
700
41%
700
21%
1493
November16th to endNight
25%
720
14%
2340
8%
720
32%
720
14%
1721
December1st to 15thNight
18%
798
7%
2418
3%
798
22%
798
11%
1925
December16th to endNight
14%
960
8%
2688
2%
960
20%
960
8%
2294

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%8%46%6%35%45%7%33%
47905
Night
15%9%46%5%3445%6%34%
46892
Cloud CoverDay
13%9%47%6%35%45%7%33%
47914
Night
15%9%46%5%3445%6%34%
46897
TransparencyDay
49%5%11%20%11%1
47596
Night
49%411%20%11%1
46719
SeeingDay
16%7%26%24%16%7%
5903
Night
19%7%28%30%12%1
15912

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%15%7%9%8%5%5%5%5%5%15%
1432
16th to endDay
14%19%8%9%9%44335%14%
1580
February1st to 15thDay
13%14%6%12%8%46%435%20%
1630
16th to endDay
14%14%6%11%6%35%446%21%
1580
March1st to 15thDay
15%9%5%8%6%35%45%7%28%
1844
16th to endDay
18%9%5%6%5%3435%7%30%
2115
April1st to 15thDay
20%12%36%5%24445%30%
2160
16th to endDay
16%6%26%5%245%47%37%
2340
May1st to 15thDay
19%7%36%6%25%347%33%
2331
16th to endDay
13%6%26%5%3445%7%39%
2494
June1st to 15thDay
11%435%6%35%46%6%42%
2520
16th to endDay
9%425%6%46%6%6%9%38%
2520
July1st to 15thDay
7%414425%5%7%8%46%
2520
16th to endDay
8%4245%25%6%7%9%42%
2613
August1st to 15thDay
9%425%5%45%5%6%8%40%
2340
16th to endDay
11%6%25%5%3446%8%40%
2420
September1st to 15thDay
12%5%25%5%345%6%7%42%
1989
16th to endDay
11%6%25%6%345%6%9%39%
1815
October1st to 15thDay
14%7%26%6%34447%37%
1757
16th to endDay
22%9%36%6%34335%30%
1628
November1st to 15thDay
14%10%26%5%23446%38%
1582
16th to endDay
17%15%5%7%5%34346%25%
1620
December1st to 15thDay
16%14%9%12%6%34435%20%
1539
16th to endDay
19%20%7%9%5%25%35%416%
1536
January1st to 15thNight
21%13%6%9%7%3444419%
2506
16th to endNight
13%13%9%11%8%5%5%446%17%
2643
February1st to 15thNight
16%14%5%8%7%35%44424%
2227
16th to endNight
15%10%5%8%8%35%5%5%6%25%
1893
March1st to 15thNight
14%11%46%5%33346%34%
2092
16th to endNight
16%7%36%5%25%45%7%35%
2112
April1st to 15thNight
19%8%35%5%3345%6%33%
1795
16th to endNight
16%7%25%42445%6%39%
1620
May1st to 15thNight
19%7%25%5%35%448%34%
1620
16th to endNight
13%5%25%3245%49%43%
1616
June1st to 15thNight
12%325%5%2435%7%46%
1440
16th to endNight
8%425%4345%6%10%43%
1440
July1st to 15thNight
7%42342446%8%52%
1440
16th to endNight
7%31442345%10%51%
1553
August1st to 15thNight
6%325%43446%9%49%
1620
16th to endNight
11%425%433247%50%
1779
September1st to 15thNight
11%413323446%52%
1845
16th to endNight
11%5%2442445%7%46%
1815
October1st to 15thNight
17%6%25%5%2335%6%41%
1873
16th to endNight
21%8%26%5%34346%32%
2241
November1st to 15thNight
15%9%36%424445%38%
2276
16th to endNight
19%12%5%6%5%35%445%27%
2340
December1st to 15thNight
19%15%7%9%5%34335%21%
2418
16th to endNight
21%16%7%10%7%3444414%
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
17%16%7%9%8%5%45%45%14%
1432
16th to endDay
14%19%9%8%10%5%5%335%14%
1580
February1st to 15thDay
13%14%7%11%9%46%435%19%
1630
16th to endDay
15%13%6%11%6%26%5%5%5%21%
1580
March1st to 15thDay
15%10%5%7%6%345%5%7%27%
1854
16th to endDay
16%10%47%5%34347%29%
2114
April1st to 15thDay
19%11%36%5%24445%30%
2160
16th to endDay
16%7%27%5%24447%37%
2340
May1st to 15thDay
18%7%46%5%35%446%32%
2331
16th to endDay
13%6%25%6%3445%7%39%
2494
June1st to 15thDay
10%5%26%5%45%5%5%7%41%
2520
16th to endDay
9%425%6%45%6%6%9%37%
2520
July1st to 15thDay
7%424435%5%7%8%46%
2520
16th to endDay
7%425%6%35%5%7%9%41%
2613
August1st to 15thDay
9%5%16%6%45%5%6%9%40%
2340
16th to endDay
11%5%35%5%345%6%8%40%
2420
September1st to 15thDay
11%426%5%345%6%7%41%
1989
16th to endDay
11%6%26%6%2446%9%39%
1815
October1st to 15thDay
14%6%37%6%3445%6%38%
1757
16th to endDay
21%10%36%5%35%345%30%
1628
November1st to 15thDay
14%9%36%5%33446%37%
1582
16th to endDay
17%15%5%8%5%24446%25%
1620
December1st to 15thDay
15%14%8%12%7%34436%18%
1539
16th to endDay
19%18%8%9%6%25%44416%
1536
January1st to 15thNight
21%13%6%8%8%3444419%
2506
16th to endNight
13%13%9%11%8%5%5%445%18%
2643
February1st to 15thNight
15%14%5%9%7%35%44424%
2220
16th to endNight
15%10%5%8%8%345%5%6%25%
1893
March1st to 15thNight
15%11%46%5%34346%33%
2105
16th to endNight
16%7%36%5%35%45%6%34%
2112
April1st to 15thNight
19%8%35%5%2445%6%33%
1795
16th to endNight
15%7%25%5%2445%6%39%
1620
May1st to 15thNight
18%7%25%5%34447%35%
1619
16th to endNight
13%5%25%4245%5%8%43%
1616
June1st to 15thNight
11%4145%25%348%46%
1440
16th to endNight
7%425%4345%7%10%42%
1440
July1st to 15thNight
7%42332445%9%52%
1440
16th to endNight
7%22442346%10%51%
1553
August1st to 15thNight
6%315%4245%7%10%48%
1620
16th to endNight
10%5%245%23347%50%
1779
September1st to 15thNight
10%413334447%52%
1845
16th to endNight
10%425%42445%8%46%
1815
October1st to 15thNight
16%7%25%5%2335%6%41%
1873
16th to endNight
20%8%36%6%34346%32%
2241
November1st to 15thNight
14%9%35%4245%45%38%
2276
16th to endNight
18%13%47%5%25%45%5%27%
2340
December1st to 15thNight
19%15%7%9%6%34435%21%
2418
16th to endNight
21%15%7%11%7%35%34414%
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
70%410%11%2
1433
16th to endDay
73%39%9%3
1580
February1st to 15thDay
68%38%14%5%
1632
16th to endDay
64%49%15%5%
1580
March1st to 15thDay
55%413%17%8%
1854
16th to endDay
54%311%21%8%1
2115
April1st to 15thDay
55%49%19%11%
2160
16th to endDay
46%413%17%14%3
2340
May1st to 15thDay
51%5%10%21%10%1
2331
16th to endDay
42%5%12%26%11%1
2498
June1st to 15thDay
40%5%12%24%15%
2520
16th to endDay
40%7%13%21%16%
2520
July1st to 15thDay
32%6%11%26%20%2
2371
16th to endDay
35%6%13%25%15%2
2449
August1st to 15thDay
39%5%12%26%12%2
2327
16th to endDay
39%6%11%25%15%2
2420
September1st to 15thDay
39%6%11%26%14%1
1989
16th to endDay
41%412%27%13%
1815
October1st to 15thDay
45%5%11%23%13%1
1757
16th to endDay
55%414%18%6%
1628
November1st to 15thDay
46%5%11%22%12%1
1582
16th to endDay
59%412%17%5%
1620
December1st to 15thDay
66%312%13%2
1539
16th to endDay
71%5%10%9%3
1536
January1st to 15thNight
67%310%13%5%
2506
16th to endNight
66%5%12%11%3
2643
February1st to 15thNight
61%5%10%15%6%
2229
16th to endNight
56%413%17%6%1
1893
March1st to 15thNight
52%411%19%9%1
2105
16th to endNight
48%5%11%22%10%1
2112
April1st to 15thNight
49%411%18%15%
1795
16th to endNight
44%312%18%17%3
1620
May1st to 15thNight
49%310%22%10%3
1620
16th to endNight
38%5%12%24%15%3
1618
June1st to 15thNight
36%412%28%16%1
1440
16th to endNight
33%6%16%26%15%1
1440
July1st to 15thNight
29%5%10%31%20%3
1360
16th to endNight
27%6%15%26%22%2
1454
August1st to 15thNight
29%6%14%30%16%2
1609
16th to endNight
33%5%10%28%18%3
1779
September1st to 15thNight
32%49%30%21%1
1845
16th to endNight
35%413%28%18%
1815
October1st to 15thNight
43%310%24%16%1
1873
16th to endNight
53%312%21%7%
2241
November1st to 15thNight
46%411%22%12%1
2276
16th to endNight
57%412%19%5%
2340
December1st to 15thNight
65%412%11%5%
2418
16th to endNight
72%49%10%3
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
15%12%48%17%5%
90
16th to endDay
29%11%37%16%32
96
February1st to 15thDay
20%20%51%7%1
90
16th to endDay
22%16%34%18%8%
81
March1st to 15thDay
29%10%31%20%7%
144
16th to endDay
25%6%31%22%11%2
288
April1st to 15thDay
24%9%30%25%8%2
270
16th to endDay
21%7%30%19%15%5%
270
May1st to 15thDay
24%9%27%23%10%5%
288
16th to endDay
18%7%26%24%15%7%
394
June1st to 15thDay
13%430%29%16%5%
495
16th to endDay
12%6%31%26%16%5%
495
July1st to 15thDay
8%422%30%22%11%
475
16th to endDay
9%323%30%23%10%
473
August1st to 15thDay
9%216%26%20%23%
313
16th to endDay
15%316%20%27%16%
332
September1st to 15thDay
12%219%24%25%15%
294
16th to endDay
16%415%23%27%12%
254
October1st to 15thDay
19%5%19%32%17%5%
255
16th to endDay
26%11%30%25%6%
140
November1st to 15thDay
8%12%27%35%13%2
90
16th to endDay
30%15%35%10%8%
90
December1st to 15thDay
21%25%31%18%21
90
16th to endDay
26%31%35%7%
96
January1st to 15thNight
27%12%34%19%5%1
900
16th to endNight
18%10%34%30%5%
915
February1st to 15thNight
22%13%36%23%3
704
16th to endNight
22%12%32%27%5%
631
March1st to 15thNight
22%10%32%28%6%
720
16th to endNight
17%10%31%28%9%1
768
April1st to 15thNight
22%8%34%26%6%
546
16th to endNight
21%6%35%27%9%1
540
May1st to 15thNight
22%429%32%8%1
540
16th to endNight
15%326%34%18%1
563
June1st to 15thNight
12%223%44%16%
540
16th to endNight
9%125%40%21%1
540
July1st to 15thNight
9%116%43%27%2
510
16th to endNight
7%216%45%26%2
564
August1st to 15thNight
8%13%47%25%4
539
16th to endNight
13%115%34%30%5%
573
September1st to 15thNight
14%317%36%24%5%
620
16th to endNight
14%416%30%28%4
657
October1st to 15thNight
18%423%34%16%2
660
16th to endNight
24%10%33%25%7%
704
November1st to 15thNight
19%10%29%28%11%1
700
16th to endNight
25%11%30%24%7%
720
December1st to 15thNight
28%10%35%20%4
798
16th to endNight
29%10%36%19%3
960
Page generated at 2017-09-11 19:35:20. Version ac04

Copyright 2017 A. Danko


MSU Observatory Clear Sky Chart | Charts Home