Washington(MI)
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Washington(MI) clear sky chart from 2005-11-05 to 2017-09-23.

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%
15570
16%
46907
10%
15533
44%
15533
22%
31769

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
17%
896
10%
2506
4%
895
22%
895
13%
1962
January16th to endNight
22%
831
11%
2559
5%
831
28%
831
13%
1943
February1st to 15thNight
18%
701
10%
2279
3%
701
26%
701
11%
1720
February16th to endNight
24%
631
16%
1893
6%
631
33%
631
15%
1365
March1st to 15thNight
27%
720
15%
2064
9%
720
32%
720
18%
1479
March16th to endNight
34%
768
19%
2112
10%
768
41%
768
22%
1462
April1st to 15thNight
29%
608
15%
1815
7%
608
36%
608
20%
1246
April16th to endNight
37%
540
21%
1620
8%
540
48%
540
26%
1044
May1st to 15thNight
41%
540
15%
1620
10%
540
46%
540
24%
1086
May16th to endNight
51%
561
16%
1684
12%
561
57%
561
31%
1036
June1st to 15thNight
55%
372
18%
1290
17%
372
61%
372
29%
759
June16th to endNight
59%
391
19%
1291
18%
391
65%
391
32%
744
July1st to 15thNight
63%
510
17%
1360
14%
510
66%
510
41%
800
July16th to endNight
68%
564
19%
1520
15%
531
72%
531
42%
853
August1st to 15thNight
65%
539
20%
1609
15%
536
69%
536
38%
917
August16th to endNight
63%
573
24%
1719
17%
573
69%
573
37%
985
September1st to 15thNight
58%
681
24%
1935
18%
681
61%
681
34%
1163
September16th to endNight
61%
689
25%
1903
19%
689
65%
689
36%
1149
October1st to 15thNight
46%
660
21%
1911
15%
660
52%
660
29%
1212
October16th to endNight
25%
704
15%
2189
9%
704
35%
704
17%
1538
November1st to 15thNight
38%
700
22%
2276
17%
700
46%
700
23%
1447
November16th to endNight
25%
720
14%
2439
10%
720
32%
720
15%
1714
December1st to 15thNight
16%
720
9%
2520
3%
720
24%
720
11%
1876
December16th to endNight
15%
951
8%
2793
2%
951
21%
951
10%
2269

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
13%8%47%6%35%5%5%7%33%
47985
Night
14%8%36%5%3445%6%36%
47087
Cloud CoverDay
13%8%47%6%35%45%7%33%
47995
Night
14%8%36%5%3445%6%36%
47091
TransparencyDay
49%412%21%11%1
47683
Night
47%412%22%12%1
46907
SeeingDay
15%7%26%24%16%8%
5828
Night
18%8%27%30%13%1
15579

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
16%14%5%10%8%45%5%45%19%
1432
16th to endDay
14%16%8%11%8%46%446%15%
1664
February1st to 15thDay
15%13%6%11%8%45%5%5%6%18%
1583
16th to endDay
12%14%6%9%9%35%35%6%23%
1580
March1st to 15thDay
16%12%5%8%6%34446%27%
1885
16th to endDay
17%10%5%8%6%35%345%29%
2112
April1st to 15thDay
17%10%46%5%245%5%6%31%
2144
16th to endDay
16%7%36%5%3335%7%37%
2340
May1st to 15thDay
17%7%36%5%35%45%6%33%
2331
16th to endDay
12%6%25%5%3446%8%38%
2431
June1st to 15thDay
10%5%35%5%45%5%6%9%40%
2665
16th to endDay
8%5%35%5%46%6%7%9%35%
2664
July1st to 15thDay
7%425%5%36%5%6%8%44%
2520
16th to endDay
7%426%5%46%7%8%9%37%
2543
August1st to 15thDay
8%426%6%46%6%7%8%37%
2340
16th to endDay
10%436%6%25%5%6%8%40%
2483
September1st to 15thDay
11%5%35%5%3446%8%40%
2010
16th to endDay
12%6%25%5%345%5%9%39%
1894
October1st to 15thDay
12%8%26%5%25%45%7%39%
1719
16th to endDay
19%11%36%5%34435%31%
1680
November1st to 15thDay
14%7%37%5%3445%6%38%
1582
16th to endDay
17%11%5%6%6%35%5%46%28%
1518
December1st to 15thDay
15%12%7%10%7%45%445%22%
1440
16th to endDay
19%16%7%9%6%34445%18%
1425
January1st to 15thNight
21%10%5%8%6%34445%23%
2506
16th to endNight
12%12%7%9%7%45%5%45%23%
2559
February1st to 15thNight
14%14%48%6%45%45%427%
2277
16th to endNight
15%11%48%7%44446%29%
1893
March1st to 15thNight
16%10%46%5%34446%33%
2052
16th to endNight
15%7%36%435%447%36%
2112
April1st to 15thNight
18%8%35%5%2445%7%34%
1815
16th to endNight
15%6%25%5%235%5%7%41%
1620
May1st to 15thNight
16%5%26%5%245%5%8%36%
1620
16th to endNight
11%425%42445%7%45%
1682
June1st to 15thNight
8%326%5%25%6%6%7%45%
1290
16th to endNight
9%4245%25%5%6%9%45%
1291
July1st to 15thNight
7%324434349%53%
1440
16th to endNight
5%3134245%7%9%51%
1625
August1st to 15thNight
5%3145%35%5%6%10%48%
1620
16th to endNight
9%424323347%52%
1719
September1st to 15thNight
10%424424347%50%
1935
16th to endNight
11%325%423448%48%
1903
October1st to 15thNight
15%5%24433447%43%
1911
16th to endNight
20%8%27%5%35%5%5%5%32%
2189
November1st to 15thNight
13%7%35%5%245%5%6%39%
2276
16th to endNight
20%9%36%6%345%5%6%29%
2439
December1st to 15thNight
20%12%6%7%5%34446%25%
2520
16th to endNight
21%14%6%9%6%3444419%
2793

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%14%5%10%7%45%5%46%18%
1432
16th to endDay
14%16%8%11%8%45%45%5%14%
1664
February1st to 15thDay
15%13%6%11%7%46%5%5%6%18%
1583
16th to endDay
12%14%6%9%8%45%35%6%23%
1580
March1st to 15thDay
16%12%5%8%7%25%346%26%
1896
16th to endDay
17%11%48%6%35%345%28%
2111
April1st to 15thDay
17%10%46%4345%5%6%31%
2144
16th to endDay
17%7%26%6%3335%7%36%
2340
May1st to 15thDay
17%8%36%5%345%5%7%32%
2331
16th to endDay
12%6%25%5%345%5%8%39%
2431
June1st to 15thDay
9%5%35%5%45%46%9%40%
2665
16th to endDay
7%5%35%6%37%7%7%9%35%
2664
July1st to 15thDay
6%5%25%5%36%5%5%8%44%
2520
16th to endDay
6%4345%37%6%8%10%37%
2543
August1st to 15thDay
7%5%26%6%46%5%7%9%37%
2340
16th to endDay
10%435%5%35%5%7%8%39%
2483
September1st to 15thDay
11%5%35%5%345%6%9%39%
2010
16th to endDay
12%6%25%4345%5%9%39%
1894
October1st to 15thDay
12%8%26%5%35%35%7%39%
1719
16th to endDay
19%11%36%5%24445%31%
1680
November1st to 15thDay
13%7%36%435%45%6%38%
1582
16th to endDay
16%11%47%6%34446%28%
1518
December1st to 15thDay
15%12%7%10%6%35%45%6%21%
1440
16th to endDay
19%16%8%8%7%34445%18%
1425
January1st to 15thNight
21%11%48%7%34445%23%
2506
16th to endNight
13%12%7%10%7%45%45%5%23%
2559
February1st to 15thNight
13%13%48%7%45%5%5%426%
2270
16th to endNight
15%11%48%6%44446%29%
1893
March1st to 15thNight
17%10%36%5%35%446%32%
2064
16th to endNight
15%7%35%5%35%447%36%
2112
April1st to 15thNight
18%8%25%43445%7%34%
1815
16th to endNight
15%6%245%3345%8%40%
1620
May1st to 15thNight
15%6%27%5%345%6%7%36%
1619
16th to endNight
11%435%43445%7%45%
1682
June1st to 15thNight
8%426%435%6%6%8%45%
1290
16th to endNight
8%5%25%43447%8%45%
1291
July1st to 15thNight
7%314424449%52%
1440
16th to endNight
5%3233345%7%9%51%
1625
August1st to 15thNight
43245%25%5%6%9%48%
1620
16th to endNight
9%424423447%52%
1719
September1st to 15thNight
9%5%34324447%49%
1935
16th to endNight
10%415%42345%7%48%
1903
October1st to 15thNight
14%5%245%23447%43%
1911
16th to endNight
20%7%37%5%3445%6%31%
2189
November1st to 15thNight
13%7%35%4345%5%6%39%
2276
16th to endNight
19%9%46%6%245%5%6%29%
2439
December1st to 15thNight
20%11%5%7%5%3445%6%24%
2520
16th to endNight
21%14%6%9%5%3444418%
2793

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
65%411%12%5%
1433
16th to endDay
70%39%10%4
1664
February1st to 15thDay
65%48%14%6%
1585
16th to endDay
62%210%16%6%1
1580
March1st to 15thDay
58%412%16%6%
1896
16th to endDay
57%310%19%7%1
2112
April1st to 15thDay
53%39%21%11%
2144
16th to endDay
47%313%18%14%2
2340
May1st to 15thDay
51%211%20%11%2
2331
16th to endDay
42%412%24%13%2
2435
June1st to 15thDay
39%413%25%14%1
2665
16th to endDay
41%6%13%21%15%1
2664
July1st to 15thDay
36%5%9%27%19%2
2371
16th to endDay
37%6%15%22%14%2
2385
August1st to 15thDay
39%5%13%26%13%1
2327
16th to endDay
39%5%11%25%15%1
2483
September1st to 15thDay
39%5%12%28%13%
2010
16th to endDay
40%412%30%11%
1894
October1st to 15thDay
42%313%25%13%1
1719
16th to endDay
54%414%19%7%
1680
November1st to 15thDay
45%411%23%12%1
1582
16th to endDay
57%312%18%6%
1518
December1st to 15thDay
64%312%15%4
1440
16th to endDay
69%212%11%4
1425
January1st to 15thNight
62%310%15%7%
2506
16th to endNight
61%313%15%5%
2559
February1st to 15thNight
59%5%10%16%7%
2279
16th to endNight
56%211%20%8%
1893
March1st to 15thNight
52%310%20%10%1
2064
16th to endNight
48%311%24%10%1
2112
April1st to 15thNight
49%311%20%13%
1815
16th to endNight
42%310%21%17%4
1620
May1st to 15thNight
45%311%21%13%2
1620
16th to endNight
37%412%25%16%3
1684
June1st to 15thNight
35%5%11%29%16%1
1290
16th to endNight
34%414%24%19%1
1291
July1st to 15thNight
30%49%32%21%2
1360
16th to endNight
26%5%18%26%19%3
1520
August1st to 15thNight
29%5%14%33%14%2
1609
16th to endNight
31%413%30%18%2
1719
September1st to 15thNight
33%5%11%30%18%1
1935
16th to endNight
34%311%33%15%
1903
October1st to 15thNight
39%412%23%19%
1911
16th to endNight
52%312%23%7%
2189
November1st to 15thNight
42%411%25%13%1
2276
16th to endNight
54%314%20%6%
2439
December1st to 15thNight
60%313%15%6%
2520
16th to endNight
67%311%12%4
2793

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
18%18%40%14%6%1
90
16th to endDay
27%14%35%17%5%
96
February1st to 15thDay
21%16%47%13%1
90
16th to endDay
19%14%43%18%3
81
March1st to 15thDay
27%13%27%22%8%
186
16th to endDay
25%9%27%26%8%3
288
April1st to 15thDay
20%11%31%22%11%3
270
16th to endDay
21%9%30%18%11%9%
270
May1st to 15thDay
22%7%25%24%14%5%
288
16th to endDay
14%7%27%24%17%9%
331
June1st to 15thDay
11%7%30%28%17%4
475
16th to endDay
11%6%32%25%17%6%
495
July1st to 15thDay
8%423%32%20%11%
475
16th to endDay
6%422%29%24%12%
403
August1st to 15thDay
9%217%28%21%20%
313
16th to endDay
13%315%25%22%19%
332
September1st to 15thDay
10%318%22%26%17%
315
16th to endDay
15%313%22%29%15%
283
October1st to 15thDay
14%6%26%22%21%8%
255
16th to endDay
25%8%36%23%42
192
November1st to 15thDay
11%14%26%32%13%2
90
16th to endDay
20%21%36%15%5%
73
December1st to 15thDay
21%18%41%13%5%
60
16th to endDay
28%22%38%9%1
77
January1st to 15thNight
25%13%33%21%41
900
16th to endNight
19%11%32%29%5%
831
February1st to 15thNight
19%15%36%24%3
704
16th to endNight
22%12%31%28%5%
631
March1st to 15thNight
22%11%32%27%6%
720
16th to endNight
18%10%29%29%10%1
768
April1st to 15thNight
23%10%30%29%5%
608
16th to endNight
18%6%31%30%11%1
540
May1st to 15thNight
19%425%35%13%1
540
16th to endNight
13%223%38%19%3
563
June1st to 15thNight
9%224%51%12%
372
16th to endNight
10%120%47%18%
391
July1st to 15thNight
9%117%40%28%3
510
16th to endNight
6%215%48%24%3
564
August1st to 15thNight
6%117%38%32%4
539
16th to endNight
10%115%34%32%4
573
September1st to 15thNight
11%5%17%31%27%5%
681
16th to endNight
12%314%33%28%7%
689
October1st to 15thNight
18%423%32%18%3
660
16th to endNight
23%11%33%26%5%
704
November1st to 15thNight
17%10%29%26%14%1
700
16th to endNight
25%12%29%23%9%
720
December1st to 15thNight
26%11%35%20%5%
720
16th to endNight
28%10%33%23%3
951
Page generated at 2017-09-24 09:15:57. Version ac04

Copyright 2017 A. Danko


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