Kresge Environmental Education Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Kresge Environmental Education Center clear sky chart from 2005-11-06 to 2024-02-10.

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
34%
24088
14%
80584
9%
23989
40%
23989
17%
56985

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 10thNight
17%
941
9%
4390
4%
926
24%
926
8%
3270
January11th to 20thNight
16%
947
6%
4417
2%
930
21%
930
6%
3657
January21st to endNight
20%
885
5%
4592
4%
867
26%
867
6%
3685
February1st to 10thNight
16%
759
9%
2464
3%
759
23%
759
10%
1937
February11th to 20thNight
20%
700
14%
2167
6%
699
28%
699
12%
1643
February21st to endNight
17%
592
14%
1776
4%
592
27%
592
13%
1329
March1st to 10thNight
24%
720
17%
2117
9%
720
32%
720
17%
1505
March11th to 20thNight
28%
720
20%
1980
9%
720
38%
720
22%
1371
March21st to endNight
30%
792
17%
2178
8%
792
36%
792
20%
1580
April1st to 10thNight
24%
626
14%
1886
6%
626
33%
626
19%
1311
April11th to 20thNight
30%
533
19%
1615
8%
533
40%
533
23%
1076
April21st to endNight
32%
540
18%
1620
7%
540
41%
540
23%
1082
May1st to 10thNight
36%
540
14%
1620
8%
540
41%
540
22%
1114
May11th to 20thNight
40%
531
19%
1593
12%
531
47%
531
25%
1024
May21st to endNight
54%
582
15%
1723
10%
582
59%
582
31%
1048
June1st to 10thNight
49%
360
18%
1260
17%
360
57%
360
28%
732
June11th to 20thNight
50%
360
19%
1260
19%
360
56%
360
29%
720
June21st to endNight
53%
384
20%
1284
18%
384
61%
384
30%
733
July1st to 10thNight
64%
525
17%
1400
14%
525
66%
525
41%
831
July11th to 20thNight
62%
522
20%
1392
17%
522
66%
522
39%
837
July21st to endNight
63%
591
16%
1610
13%
558
67%
558
36%
955
August1st to 10thNight
67%
537
19%
1600
16%
534
70%
534
36%
931
August11th to 20thNight
63%
534
22%
1598
17%
534
68%
534
34%
940
August21st to endNight
60%
594
23%
1782
17%
594
65%
594
35%
1043
September1st to 10thNight
55%
648
18%
1906
14%
648
58%
648
28%
1201
September11th to 20thNight
58%
720
26%
1980
19%
720
62%
720
36%
1200
September21st to endNight
49%
720
22%
1980
16%
720
53%
720
28%
1307
October1st to 10thNight
42%
720
20%
2039
15%
720
48%
720
27%
1335
October11th to 20thNight
29%
720
14%
2160
7%
720
38%
720
18%
1554
October21st to endNight
23%
792
14%
2524
9%
792
32%
792
15%
1840
November1st to 10thNight
34%
740
22%
2406
16%
740
44%
740
23%
1517
November11th to 20thNight
24%
760
15%
2470
9%
760
33%
760
15%
1754
November21st to endNight
21%
760
12%
2636
7%
760
28%
760
13%
1937
December1st to 10thNight
17%
760
8%
2660
4%
760
22%
760
9%
2084
December11th to 20thNight
14%
896
9%
3442
2%
895
22%
895
9%
2595
December21st to endNight
13%
1037
4%
5057
1%
1026
19%
1026
5%
4307

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%10%47%6%45%5%5%7%32%
78088
Night
15%11%47%6%35%45%6%33%
80902
TransparencyDay
50%6%12%19%11%1
77796
Night
51%6%12%19%10%1
80715
SeeingDay
18%11%29%23%13%6%
14325
Night
19%10%30%29%11%1
24118

By Month

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 10thDay
15%18%9%10%7%35%44421%
2527
11th to 20thDay
15%19%7%13%11%6%5%5%4411%
2530
21st to endDay
25%19%6%10%7%34335%15%
3033
February1st to 10thDay
13%14%6%13%9%5%5%445%21%
1701
11th to 20thDay
13%13%6%10%9%47%446%23%
1675
21st to endDay
15%15%5%10%8%3445%5%25%
1480
March1st to 10thDay
15%10%6%9%8%35%5%46%30%
1842
11th to 20thDay
11%15%5%8%6%35%5%5%6%31%
1980
21st to endDay
19%12%5%8%7%35%445%28%
2178
April1st to 10thDay
16%12%5%7%6%3445%7%30%
2090
11th to 20thDay
17%10%36%6%35%46%7%34%
2294
21st to endDay
17%9%47%6%35%45%6%34%
2340
May1st to 10thDay
17%8%36%6%35%5%5%7%34%
2340
11th to 20thDay
19%7%27%4345%47%37%
2301
21st to endDay
13%6%36%5%445%5%9%40%
2549
June1st to 10thDay
11%6%35%6%45%5%6%9%41%
2695
11th to 20thDay
11%6%26%5%35%5%6%8%43%
2700
21st to endDay
10%6%35%5%45%6%8%9%38%
2670
July1st to 10thDay
7%5%25%5%35%6%7%8%47%
2520
11th to 20thDay
9%5%25%6%36%5%7%9%42%
2520
21st to endDay
9%5%245%46%6%7%9%42%
2612
August1st to 10thDay
9%6%26%6%45%6%7%9%39%
2327
11th to 20thDay
10%5%35%6%46%6%6%9%40%
2303
21st to endDay
12%6%35%5%45%5%5%8%42%
2574
September1st to 10thDay
10%7%37%6%5%6%6%6%9%36%
2034
11th to 20thDay
11%6%245%346%6%8%45%
1980
21st to endDay
15%7%36%6%45%6%6%8%35%
1980
October1st to 10thDay
15%7%36%6%35%5%6%6%39%
1919
11th to 20thDay
19%9%47%6%45%5%5%6%31%
1800
21st to endDay
21%12%36%5%35%45%6%29%
1831
November1st to 10thDay
13%10%47%6%35%5%5%7%35%
1672
11th to 20thDay
14%11%6%9%8%445%5%7%28%
1710
21st to endDay
18%14%6%8%7%345%46%26%
1539
December1st to 10thDay
13%16%7%12%9%45%5%5%5%20%
1520
11th to 20thDay
15%15%6%8%5%35%5%5%6%25%
1723
21st to endDay
25%20%7%10%7%34445%11%
2599
January1st to 10thNight
16%14%7%10%6%45%45%6%24%
4428
11th to 20thNight
13%16%7%12%10%7%7%445%15%
4440
21st to endNight
21%16%10%9%7%34445%19%
4624
February1st to 10thNight
15%14%6%9%8%36%5%5%5%23%
2464
11th to 20thNight
13%14%5%9%7%45%5%5%5%27%
2167
21st to endNight
19%11%5%8%6%35%445%28%
1776
March1st to 10thNight
15%12%5%8%6%34446%34%
2117
11th to 20thNight
13%9%47%6%35%5%47%38%
1980
21st to endNight
19%9%47%5%345%5%6%33%
2178
April1st to 10thNight
18%10%47%5%3445%6%35%
1886
11th to 20thNight
18%7%26%5%4445%7%38%
1615
21st to endNight
18%8%26%5%345%5%7%37%
1620
May1st to 10thNight
15%7%36%6%45%5%6%8%34%
1620
11th to 20thNight
19%6%25%5%24447%42%
1592
21st to endNight
10%5%25%435%5%5%8%47%
1722
June1st to 10thNight
12%435%3345%6%9%46%
1260
11th to 20thNight
10%5%25%435%5%6%9%47%
1260
21st to endNight
9%6%25%4345%6%7%49%
1284
July1st to 10thNight
7%4345%2446%8%54%
1440
11th to 20thNight
9%4243445%6%8%50%
1440
21st to endNight
6%325%5%35%5%7%8%50%
1705
August1st to 10thNight
8%425%5%345%7%10%49%
1611
11th to 20thNight
8%4245%345%8%8%49%
1598
21st to endNight
9%5%35%3335%5%8%51%
1782
September1st to 10thNight
11%436%5%45%5%5%7%45%
1906
11th to 20thNight
10%5%2442445%5%53%
1980
21st to endNight
14%6%36%5%3445%6%44%
1980
October1st to 10thNight
16%6%36%5%335%5%6%43%
2039
11th to 20thNight
19%9%46%5%35%5%5%6%33%
2160
21st to endNight
22%9%48%6%445%5%5%29%
2524
November1st to 10thNight
14%8%35%43445%8%42%
2406
11th to 20thNight
15%11%5%7%6%35%6%6%7%29%
2470
21st to endNight
19%14%37%5%35%5%5%6%27%
2636
December1st to 10thNight
17%15%7%10%7%45%45%6%21%
2660
11th to 20thNight
14%13%6%11%7%35%5%6%6%24%
3469
21st to endNight
25%22%7%10%5%3333414%
5063

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 10thDay
66%6%10%13%5%
2528
11th to 20thDay
75%5%12%6%2
2530
21st to endDay
74%5%11%7%31
3033
February1st to 10thDay
64%6%8%14%7%
1701
11th to 20thDay
64%49%14%8%1
1684
21st to endDay
61%6%9%15%7%2
1480
March1st to 10thDay
54%8%12%17%9%1
1842
11th to 20thDay
53%6%9%19%12%3
1980
21st to endDay
58%5%10%18%8%1
2178
April1st to 10thDay
54%6%11%19%10%1
2090
11th to 20thDay
49%6%12%18%13%2
2294
21st to endDay
50%6%14%17%12%1
2340
May1st to 10thDay
48%6%11%22%10%2
2340
11th to 20thDay
47%5%11%21%14%2
2305
21st to endDay
42%6%13%21%15%3
2549
June1st to 10thDay
38%8%12%25%15%2
2695
11th to 20thDay
38%8%13%23%17%2
2700
21st to endDay
39%9%12%23%16%1
2670
July1st to 10thDay
33%7%12%27%18%3
2451
11th to 20thDay
35%8%13%26%17%2
2445
21st to endDay
36%7%14%21%18%3
2467
August1st to 10thDay
39%8%14%23%14%1
2314
11th to 20thDay
39%7%16%23%14%2
2303
21st to endDay
38%8%12%27%14%1
2574
September1st to 10thDay
42%8%14%23%11%2
2034
11th to 20thDay
35%6%13%32%13%1
1980
21st to endDay
44%7%14%23%11%1
1980
October1st to 10thDay
44%6%12%25%13%2
1919
11th to 20thDay
53%6%13%19%9%1
1800
21st to endDay
56%6%13%18%8%
1831
November1st to 10thDay
47%7%11%24%11%1
1672
11th to 20thDay
55%5%14%17%9%
1710
21st to endDay
59%414%16%6%1
1539
December1st to 10thDay
66%5%12%13%3
1520
11th to 20thDay
59%7%14%15%5%
1719
21st to endDay
76%410%6%3
2599
January1st to 10thNight
60%6%13%14%5%1
4428
11th to 20thNight
70%6%11%10%3
4440
21st to endNight
69%5%10%13%3
4624
February1st to 10thNight
62%7%9%14%7%1
2464
11th to 20thNight
59%6%9%17%9%1
2169
21st to endNight
58%411%18%8%1
1776
March1st to 10thNight
52%5%10%22%10%1
2117
11th to 20thNight
47%5%10%23%13%2
1980
21st to endNight
52%5%9%21%11%2
2178
April1st to 10thNight
50%5%11%20%13%1
1886
11th to 20thNight
46%5%12%18%18%2
1615
21st to endNight
44%6%12%19%15%4
1620
May1st to 10thNight
47%6%11%22%11%3
1620
11th to 20thNight
43%49%21%18%4
1593
21st to endNight
35%7%14%25%16%4
1723
June1st to 10thNight
36%6%10%29%18%2
1260
11th to 20thNight
33%7%16%23%19%3
1260
21st to endNight
33%6%13%26%20%2
1284
July1st to 10thNight
28%7%11%28%23%4
1400
11th to 20thNight
30%7%15%30%17%2
1392
21st to endNight
28%10%17%23%20%2
1610
August1st to 10thNight
30%7%17%31%14%2
1600
11th to 20thNight
29%9%16%30%13%3
1598
21st to endNight
30%7%14%29%18%1
1782
September1st to 10thNight
36%8%12%27%15%2
1906
11th to 20thNight
31%7%12%32%18%1
1980
21st to endNight
40%6%11%29%13%1
1980
October1st to 10thNight
41%5%11%24%17%1
2039
11th to 20thNight
52%6%12%20%10%1
2160
21st to endNight
55%5%12%19%8%1
2524
November1st to 10thNight
41%5%13%26%14%1
2406
11th to 20thNight
53%6%14%19%8%1
2470
21st to endNight
57%6%15%17%6%
2636
December1st to 10thNight
64%6%12%14%4
2660
11th to 20thNight
60%6%13%14%6%
3472
21st to endNight
75%5%10%7%3
5063

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 10thDay
26%17%36%14%7%1
270
11th to 20thDay
19%14%46%16%41
270
21st to endDay
29%15%33%17%41
297
February1st to 10thDay
24%19%39%13%41
267
11th to 20thDay
24%21%38%16%1
240
21st to endDay
26%31%31%11%2
198
March1st to 10thDay
28%17%38%13%31
282
11th to 20thDay
20%15%34%23%8%
420
21st to endDay
29%11%31%22%7%1
462
April1st to 10thDay
21%15%33%20%10%1
420
11th to 20thDay
27%12%30%17%8%5%
412
21st to endDay
22%13%29%24%10%3
420
May1st to 10thDay
23%11%29%23%10%3
423
11th to 20thDay
20%9%29%23%13%6%
447
21st to endDay
16%6%23%28%17%9%
503
June1st to 10thDay
13%8%30%31%13%5%
630
11th to 20thDay
14%8%28%29%17%5%
630
21st to endDay
12%7%29%29%17%5%
630
July1st to 10thDay
9%422%30%23%12%
621
11th to 20thDay
10%7%26%30%19%9%
618
21st to endDay
9%425%30%22%10%
553
August1st to 10thDay
10%5%20%27%24%15%
446
11th to 20thDay
12%5%17%27%25%14%
439
21st to endDay
12%8%19%26%22%12%
495
September1st to 10thDay
11%8%23%26%18%14%
450
11th to 20thDay
11%419%24%26%15%
450
21st to endDay
16%13%20%23%19%9%
450
October1st to 10thDay
18%9%27%23%15%8%
450
11th to 20thDay
21%17%32%22%7%1
450
21st to endDay
29%14%33%17%5%1
346
November1st to 10thDay
15%19%34%22%8%1
270
11th to 20thDay
20%20%37%15%6%2
270
21st to endDay
26%21%34%15%4
189
December1st to 10thDay
24%17%38%14%7%1
180
11th to 20thDay
25%23%37%11%31
180
21st to endDay
27%21%36%12%3
247
January1st to 10thNight
22%15%36%20%6%1
950
11th to 20thNight
24%15%33%23%41
950
21st to endNight
21%11%34%28%6%
889
February1st to 10thNight
23%13%38%22%31
759
11th to 20thNight
24%16%32%23%5%
703
21st to endNight
25%18%33%21%2
592
March1st to 10thNight
21%13%34%25%6%
720
11th to 20thNight
17%14%35%27%6%1
720
21st to endNight
23%10%30%29%8%1
792
April1st to 10thNight
23%12%35%24%5%
626
11th to 20thNight
22%9%35%25%7%2
533
21st to endNight
20%9%33%30%8%
540
May1st to 10thNight
18%7%31%33%10%1
540
11th to 20thNight
23%5%26%34%12%1
531
21st to endNight
11%424%39%20%2
584
June1st to 10thNight
11%428%45%12%
360
11th to 20thNight
12%5%29%39%14%
360
21st to endNight
10%424%45%15%1
384
July1st to 10thNight
8%317%43%27%3
525
11th to 20thNight
11%317%44%21%4
522
21st to endNight
7%320%46%22%2
591
August1st to 10thNight
9%314%44%29%2
537
11th to 20thNight
9%217%39%29%4
534
21st to endNight
10%319%37%28%3
594
September1st to 10thNight
13%5%20%35%22%6%
648
11th to 20thNight
12%5%18%36%26%4
720
21st to endNight
17%6%22%32%19%4
720
October1st to 10thNight
19%7%25%30%18%1
720
11th to 20thNight
23%12%31%25%9%
720
21st to endNight
26%12%32%26%5%
792
November1st to 10thNight
19%12%31%26%12%1
740
11th to 20thNight
19%15%34%23%7%1
760
21st to endNight
25%14%35%20%6%
760
December1st to 10thNight
24%15%35%20%5%
760
11th to 20thNight
21%15%39%21%3
897
21st to endNight
30%12%35%21%2
1045
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