Detroit
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Detroit clear sky chart from 2005-11-05 to 2018-02-22.

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%
16258
15%
48912
9%
16220
41%
16220
19%
33792

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
19%
971
10%
2716
4%
970
24%
970
13%
2103
January16th to endNight
17%
877
9%
2749
3%
877
24%
877
10%
2167
February1st to 15thNight
18%
761
9%
2465
3%
761
24%
761
11%
1892
February16th to endNight
23%
659
13%
1977
6%
659
29%
659
13%
1468
March1st to 15thNight
25%
720
14%
2062
8%
720
31%
720
16%
1502
March16th to endNight
31%
768
18%
2112
10%
768
38%
768
19%
1474
April1st to 15thNight
29%
611
15%
1821
8%
611
37%
611
19%
1266
April16th to endNight
32%
540
21%
1620
7%
540
44%
540
21%
1054
May1st to 15thNight
34%
540
13%
1620
6%
540
41%
540
18%
1114
May16th to endNight
43%
562
16%
1684
9%
561
51%
561
25%
1071
June1st to 15thNight
48%
414
16%
1351
12%
414
56%
414
24%
821
June16th to endNight
48%
437
18%
1337
14%
437
55%
437
27%
808
July1st to 15thNight
59%
510
17%
1360
13%
510
62%
510
36%
815
July16th to endNight
59%
564
19%
1534
15%
531
67%
531
36%
878
August1st to 15thNight
62%
539
19%
1609
15%
536
66%
536
32%
962
August16th to endNight
63%
573
23%
1719
16%
573
68%
573
35%
989
September1st to 15thNight
57%
683
23%
1943
18%
683
60%
683
32%
1188
September16th to endNight
56%
717
25%
1980
18%
717
61%
717
32%
1219
October1st to 15thNight
44%
720
18%
2082
16%
720
48%
720
24%
1346
October16th to endNight
27%
768
17%
2382
9%
768
39%
768
17%
1647
November1st to 15thNight
33%
760
20%
2471
16%
760
40%
760
20%
1617
November16th to endNight
21%
780
15%
2618
7%
780
31%
780
13%
1842
December1st to 15thNight
17%
780
9%
2730
4%
780
23%
780
10%
2082
December16th to endNight
13%
1004
7%
2970
2%
1004
19%
1004
9%
2467

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%36%6%35%5%5%7%33%
49311
Night
15%8%36%5%3445%6%35%
49093
Cloud CoverDay
14%8%46%6%35%45%7%33%
49321
Night
15%8%36%5%3445%6%35%
49097
TransparencyDay
48%6%13%20%10%1
49011
Night
48%5%12%20%11%1
48912
SeeingDay
15%12%23%24%15%7%
6263
Night
16%19%23%27%12%1
16266

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
19%14%48%8%46%45%419%
1552
16th to endDay
15%16%8%9%8%3445%5%17%
1823
February1st to 15thDay
16%14%6%8%8%45%45%5%20%
1725
16th to endDay
16%12%6%10%6%35%45%5%22%
1643
March1st to 15thDay
18%11%48%6%34436%27%
1885
16th to endDay
18%10%47%6%34345%29%
2112
April1st to 15thDay
18%10%45%5%2445%6%30%
2137
16th to endDay
17%8%35%5%2445%6%37%
2340
May1st to 15thDay
17%8%37%5%35%45%6%31%
2331
16th to endDay
13%5%25%5%3445%8%41%
2431
June1st to 15thDay
9%5%25%7%35%5%5%8%40%
2603
16th to endDay
9%5%25%6%35%6%7%11%34%
2618
July1st to 15thDay
7%435%5%35%5%6%8%44%
2520
16th to endDay
7%5%25%6%45%5%7%10%39%
2525
August1st to 15thDay
8%5%26%6%36%6%8%8%38%
2340
16th to endDay
10%4245%45%5%7%9%40%
2480
September1st to 15thDay
12%6%25%435%46%7%41%
2004
16th to endDay
12%5%244245%6%8%43%
1980
October1st to 15thDay
14%6%26%5%3445%7%39%
1878
16th to endDay
20%8%25%7%34446%33%
1839
November1st to 15thDay
14%7%35%5%345%5%7%38%
1717
16th to endDay
16%10%46%6%3445%7%29%
1669
December1st to 15thDay
16%11%6%10%7%35%45%5%22%
1560
16th to endDay
21%15%6%10%7%4445%5%14%
1599
January1st to 15thNight
21%13%46%6%34445%24%
2716
16th to endNight
13%13%7%10%8%4445%5%22%
2749
February1st to 15thNight
15%14%49%7%35%34425%
2463
16th to endNight
17%12%5%7%6%33445%28%
1977
March1st to 15thNight
18%9%47%6%2445%5%32%
2050
16th to endNight
15%7%36%5%3445%7%35%
2112
April1st to 15thNight
18%9%35%5%2445%6%34%
1821
16th to endNight
14%7%25%4245%5%8%39%
1620
May1st to 15thNight
17%6%35%6%345%5%6%35%
1620
16th to endNight
12%5%2443435%7%44%
1682
June1st to 15thNight
10%5%244245%6%8%45%
1351
16th to endNight
9%4245%246%6%7%46%
1337
July1st to 15thNight
7%323325%447%53%
1440
16th to endNight
4323425%5%6%9%52%
1640
August1st to 15thNight
5%3245%345%5%8%49%
1620
16th to endNight
10%333424448%52%
1719
September1st to 15thNight
9%42442445%6%50%
1943
16th to endNight
11%4244335%48%47%
1980
October1st to 15thNight
15%6%35%42345%7%42%
2082
16th to endNight
20%7%25%5%34346%36%
2382
November1st to 15thNight
14%7%25%425%45%6%39%
2471
16th to endNight
21%9%36%5%2345%7%29%
2618
December1st to 15thNight
19%12%5%8%6%34445%24%
2730
16th to endNight
21%14%6%10%6%35%45%5%17%
2970

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
19%13%5%8%8%45%5%4418%
1552
16th to endDay
15%16%8%9%8%35%5%5%5%16%
1823
February1st to 15thDay
16%14%6%9%8%4445%5%19%
1725
16th to endDay
16%12%5%10%7%45%45%6%21%
1643
March1st to 15thDay
19%11%5%7%7%35%446%25%
1896
16th to endDay
18%11%5%7%6%33346%29%
2111
April1st to 15thDay
19%9%45%5%25%45%6%30%
2137
16th to endDay
17%9%25%424447%37%
2340
May1st to 15thDay
18%8%35%5%36%45%6%31%
2331
16th to endDay
13%5%25%5%3445%7%41%
2431
June1st to 15thDay
10%5%25%6%35%5%5%7%40%
2603
16th to endDay
9%5%35%5%35%6%8%10%35%
2618
July1st to 15thDay
8%4245%35%5%5%8%45%
2520
16th to endDay
8%425%5%35%5%7%10%39%
2525
August1st to 15thDay
8%5%25%6%36%5%7%9%38%
2340
16th to endDay
10%4245%35%5%7%9%40%
2480
September1st to 15thDay
12%5%35%5%25%46%8%41%
2004
16th to endDay
12%5%244235%5%8%43%
1980
October1st to 15thDay
15%5%25%6%3345%7%39%
1878
16th to endDay
20%7%35%7%34345%33%
1839
November1st to 15thDay
13%7%45%5%35%447%38%
1717
16th to endDay
15%10%47%6%45%45%7%28%
1669
December1st to 15thDay
16%12%6%10%7%4445%5%21%
1560
16th to endDay
21%15%7%10%8%44446%14%
1599
January1st to 15thNight
20%12%47%6%35%35%5%24%
2716
16th to endNight
13%14%7%10%8%35%5%45%22%
2749
February1st to 15thNight
15%14%49%7%35%435%25%
2456
16th to endNight
17%11%5%7%6%245%5%5%27%
1977
March1st to 15thNight
18%10%46%6%34445%31%
2062
16th to endNight
15%6%36%5%25%5%5%6%36%
2112
April1st to 15thNight
18%9%35%5%24447%34%
1821
16th to endNight
14%7%25%5%25%46%8%38%
1620
May1st to 15thNight
17%7%25%6%3445%7%35%
1619
16th to endNight
12%5%26%43346%7%43%
1682
June1st to 15thNight
11%4245%245%5%8%45%
1351
16th to endNight
9%3245%245%6%9%45%
1337
July1st to 15thNight
8%324335%447%53%
1440
16th to endNight
43234245%6%9%52%
1640
August1st to 15thNight
5%4245%345%6%8%49%
1620
16th to endNight
9%42332335%7%52%
1719
September1st to 15thNight
9%42442445%6%50%
1943
16th to endNight
12%4143235%5%7%48%
1980
October1st to 15thNight
15%6%245%3335%7%42%
2082
16th to endNight
19%7%35%5%34446%36%
2382
November1st to 15thNight
14%6%25%42445%7%39%
2471
16th to endNight
21%10%36%5%2445%7%29%
2618
December1st to 15thNight
19%13%5%7%6%34445%24%
2730
16th to endNight
21%13%6%9%6%35%445%17%
2970

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
66%5%11%10%5%
1553
16th to endDay
67%5%12%9%4
1823
February1st to 15thDay
63%5%10%14%5%
1727
16th to endDay
61%5%12%16%4
1643
March1st to 15thDay
58%6%11%16%5%1
1896
16th to endDay
55%411%20%7%
2112
April1st to 15thDay
52%5%11%18%11%
2137
16th to endDay
45%5%14%17%14%2
2340
May1st to 15thDay
51%5%10%18%10%2
2331
16th to endDay
41%5%12%25%13%1
2435
June1st to 15thDay
39%6%13%25%13%1
2603
16th to endDay
38%9%14%19%15%1
2618
July1st to 15thDay
34%5%11%26%19%2
2371
16th to endDay
35%7%16%23%14%2
2369
August1st to 15thDay
36%7%15%28%11%1
2327
16th to endDay
35%7%14%25%15%1
2480
September1st to 15thDay
38%5%15%27%12%
2004
16th to endDay
37%414%30%12%
1980
October1st to 15thDay
42%5%13%23%12%1
1878
16th to endDay
51%414%19%8%
1839
November1st to 15thDay
44%6%13%22%11%1
1717
16th to endDay
53%6%15%17%6%
1669
December1st to 15thDay
62%6%12%13%5%
1560
16th to endDay
71%411%9%3
1599
January1st to 15thNight
60%412%14%7%
2716
16th to endNight
64%413%12%4
2749
February1st to 15thNight
61%5%11%15%6%
2465
16th to endNight
57%411%18%7%
1977
March1st to 15thNight
53%411%18%9%1
2062
16th to endNight
46%6%12%22%10%1
2112
April1st to 15thNight
50%310%21%13%
1821
16th to endNight
42%5%11%20%16%4
1620
May1st to 15thNight
47%5%13%18%12%2
1620
16th to endNight
38%6%11%25%15%3
1684
June1st to 15thNight
36%6%13%27%15%1
1351
16th to endNight
33%6%14%24%18%1
1337
July1st to 15thNight
31%5%10%30%20%2
1360
16th to endNight
26%7%16%25%20%4
1534
August1st to 15thNight
30%7%14%28%15%2
1609
16th to endNight
30%5%14%28%18%2
1719
September1st to 15thNight
32%7%11%27%18%2
1943
16th to endNight
34%5%11%29%17%1
1980
October1st to 15thNight
41%5%12%21%17%1
2082
16th to endNight
49%5%12%23%9%
2382
November1st to 15thNight
43%6%11%24%12%1
2471
16th to endNight
53%5%13%20%6%
2618
December1st to 15thNight
60%5%12%14%6%
2730
16th to endNight
68%5%10%11%3
2970

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
20%9%45%14%8%1
135
16th to endDay
28%8%38%22%2
144
February1st to 15thDay
25%11%36%25%1
135
16th to endDay
22%12%43%20%3
100
March1st to 15thDay
25%20%21%23%8%
186
16th to endDay
20%17%26%24%9%2
288
April1st to 15thDay
17%20%25%26%7%2
270
16th to endDay
20%16%28%18%8%7%
270
May1st to 15thDay
19%15%26%21%12%4
288
16th to endDay
15%14%22%27%15%6%
331
June1st to 15thDay
10%13%23%33%15%3
455
16th to endDay
10%15%28%25%13%5%
495
July1st to 15thDay
8%10%21%27%24%8%
475
16th to endDay
8%11%13%27%25%12%
385
August1st to 15thDay
9%7%10%33%22%17%
313
16th to endDay
11%7%13%20%28%18%
332
September1st to 15thDay
12%6%18%22%25%15%
315
16th to endDay
15%6%13%18%28%17%
314
October1st to 15thDay
15%9%20%25%19%9%
315
16th to endDay
19%13%30%29%6%1
255
November1st to 15thDay
16%10%24%29%16%2
135
16th to endDay
16%21%34%21%5%
115
December1st to 15thDay
21%18%34%16%8%
90
16th to endDay
27%19%36%14%1
122
January1st to 15thNight
20%24%28%21%5%
975
16th to endNight
15%23%31%24%4
877
February1st to 15thNight
20%22%29%23%3
764
16th to endNight
19%22%26%27%4
659
March1st to 15thNight
19%22%24%26%7%
720
16th to endNight
16%22%23%28%8%1
768
April1st to 15thNight
18%22%24%28%5%
611
16th to endNight
15%21%26%25%9%1
540
May1st to 15thNight
16%18%22%30%10%1
540
16th to endNight
11%17%19%32%16%2
563
June1st to 15thNight
9%17%18%40%13%
414
16th to endNight
9%17%16%37%16%2
437
July1st to 15thNight
8%12%12%37%24%3
510
16th to endNight
417%11%40%21%4
564
August1st to 15thNight
7%10%10%39%26%5%
539
16th to endNight
8%10%10%30%33%5%
573
September1st to 15thNight
10%12%13%31%24%7%
683
16th to endNight
11%10%15%27%27%6%
717
October1st to 15thNight
16%12%20%27%20%3
720
16th to endNight
21%16%29%25%7%
768
November1st to 15thNight
15%18%26%23%14%1
760
16th to endNight
21%24%27%18%7%
780
December1st to 15thNight
23%23%28%19%4
780
16th to endNight
23%22%32%17%3
1004
Page generated at 2018-02-23 11:21:39. Version ac04

Copyright 2018 A. Danko


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