Washington Island
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Washington Island clear sky chart from 2005-11-06 to 2024-01-12.

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%
24821
14%
74725
9%
24764
42%
24764
20%
52927

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
21%
950
9%
2648
2%
946
26%
946
15%
2039
January11th to 20thNight
21%
910
8%
2547
3%
910
26%
910
13%
2015
January21st to endNight
29%
990
10%
2772
5%
990
34%
990
17%
2095
February1st to 10thNight
26%
893
13%
2455
4%
893
33%
893
19%
1816
February11th to 20thNight
28%
702
17%
2098
7%
699
37%
699
19%
1469
February21st to endNight
27%
592
15%
1776
7%
592
34%
592
16%
1295
March1st to 10thNight
35%
719
18%
2160
10%
719
41%
719
23%
1438
March11th to 20thNight
36%
720
20%
2092
11%
720
45%
720
25%
1394
March21st to endNight
40%
645
20%
2031
15%
645
47%
645
22%
1348
April1st to 10thNight
34%
540
12%
1800
10%
540
39%
540
16%
1288
April11th to 20thNight
41%
533
19%
1736
14%
533
47%
533
21%
1196
April21st to endNight
40%
540
16%
1620
9%
540
46%
540
22%
1122
May1st to 10thNight
43%
540
16%
1603
11%
540
47%
540
24%
1083
May11th to 20thNight
44%
531
17%
1416
12%
531
47%
531
22%
1018
May21st to endNight
59%
583
13%
1552
10%
582
62%
582
33%
995
June1st to 10thNight
55%
540
14%
1440
9%
540
58%
540
32%
929
June11th to 20thNight
53%
540
12%
1440
9%
540
54%
540
29%
970
June21st to endNight
59%
540
15%
1440
10%
540
60%
540
35%
907
July1st to 10thNight
71%
525
16%
1400
11%
525
72%
525
42%
813
July11th to 20thNight
63%
522
18%
1392
12%
522
65%
522
38%
836
July21st to endNight
65%
591
18%
1487
13%
558
67%
558
40%
898
August1st to 10thNight
67%
537
21%
1427
17%
534
69%
534
39%
855
August11th to 20thNight
69%
534
21%
1598
17%
534
73%
534
39%
894
August21st to endNight
59%
594
19%
1958
17%
594
63%
594
30%
1148
September1st to 10thNight
56%
540
20%
1800
18%
540
61%
540
30%
1043
September11th to 20thNight
56%
666
23%
1926
20%
666
59%
666
33%
1172
September21st to endNight
47%
720
18%
1980
12%
720
52%
720
26%
1327
October1st to 10thNight
41%
720
17%
1996
11%
720
46%
720
24%
1379
October11th to 20thNight
29%
720
14%
2272
8%
720
36%
720
18%
1637
October21st to endNight
25%
792
11%
2574
7%
792
30%
792
13%
1929
November1st to 10thNight
31%
740
18%
2406
13%
740
38%
740
18%
1644
November11th to 20thNight
20%
760
11%
2470
6%
760
26%
760
10%
1899
November21st to endNight
20%
915
9%
2625
4%
915
24%
915
11%
2075
December1st to 10thNight
17%
950
7%
2660
2%
950
21%
950
10%
2155
December11th to 20thNight
16%
948
7%
3260
2%
948
21%
948
8%
2616
December21st to endNight
14%
1039
5%
4868
2%
1026
20%
1026
5%
4190

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%36%6%35%5%6%8%37%
74801
Night
15%10%47%6%3445%6%33%
74937
TransparencyDay
46%5%14%23%11%1
74508
Night
52%413%21%9%1
74765
SeeingDay
16%5%25%31%18%5%
14823
Night
19%7%26%31%15%2
24832

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 10thDay
11%12%7%10%8%5%6%6%6%6%25%
1517
11th to 20thDay
16%12%6%12%7%46%5%6%7%21%
1453
21st to endDay
14%12%5%9%6%35%5%6%7%28%
1584
February1st to 10thDay
9%11%39%8%45%5%6%7%33%
1501
11th to 20thDay
11%11%46%6%45%5%6%8%34%
1748
21st to endDay
12%11%5%9%8%45%5%6%6%31%
1480
March1st to 10thDay
13%9%45%6%35%46%8%36%
1798
11th to 20thDay
10%9%48%7%35%45%7%38%
1867
21st to endDay
16%9%46%6%35%5%6%7%34%
2340
April1st to 10thDay
17%9%47%6%36%5%6%8%29%
2160
11th to 20thDay
19%7%36%5%345%5%6%36%
2173
21st to endDay
16%8%26%5%35%5%6%8%37%
2340
May1st to 10thDay
14%6%36%5%35%5%6%8%40%
2353
11th to 20thDay
14%6%35%5%345%5%8%42%
2479
21st to endDay
10%6%25%435%5%6%10%43%
2725
June1st to 10thDay
10%5%25%6%35%5%6%9%46%
2520
11th to 20thDay
11%6%345%35%5%6%8%44%
2520
21st to endDay
12%5%35%4345%6%9%44%
2520
July1st to 10thDay
7%2144245%7%11%51%
2520
11th to 20thDay
7%325%4345%6%9%52%
2520
21st to endDay
7%424335%6%7%9%52%
2743
August1st to 10thDay
7%4245%35%6%6%10%47%
2503
11th to 20thDay
10%5%25%4445%6%9%48%
2303
21st to endDay
12%4244345%5%8%49%
2394
September1st to 10thDay
13%5%35%5%4445%8%44%
2160
11th to 20thDay
12%6%245%35%5%6%9%44%
2015
21st to endDay
14%6%36%5%346%8%8%36%
1980
October1st to 10thDay
18%7%26%5%34448%39%
1962
11th to 20thDay
23%11%47%6%335%46%27%
1688
21st to endDay
22%12%47%7%4445%5%24%
1782
November1st to 10thDay
15%9%36%6%45%45%7%34%
1672
11th to 20thDay
17%14%5%9%7%45%5%5%6%22%
1710
21st to endDay
20%14%7%9%6%45%446%21%
1554
December1st to 10thDay
16%13%8%11%8%45%5%5%6%20%
1520
11th to 20thDay
18%16%6%13%8%5%5%445%17%
1914
21st to endDay
21%22%7%11%7%35%44414%
2783
January1st to 10thNight
13%13%6%10%9%45%45%6%26%
2648
11th to 20thNight
16%15%7%9%8%45%5%46%22%
2547
21st to endNight
12%14%6%8%7%46%5%5%7%27%
2772
February1st to 10thNight
11%12%6%8%8%45%5%46%31%
2455
11th to 20thNight
11%11%5%8%5%45%5%6%7%32%
2098
21st to endNight
16%12%48%7%45%5%5%7%27%
1776
March1st to 10thNight
12%10%37%5%3445%7%40%
2149
11th to 20thNight
12%8%37%5%45%45%7%40%
2092
21st to endNight
16%8%36%5%345%5%6%38%
2031
April1st to 10thNight
19%11%5%7%5%345%5%6%31%
1800
11th to 20thNight
20%7%36%5%445%5%6%36%
1736
21st to endNight
16%8%36%7%45%46%5%35%
1620
May1st to 10thNight
17%7%27%6%345%5%9%34%
1603
11th to 20thNight
16%9%47%6%35%6%5%6%34%
1416
21st to endNight
12%425%5%36%5%7%9%42%
1551
June1st to 10thNight
13%5%25%5%35%5%5%7%44%
1440
11th to 20thNight
13%5%45%6%45%48%8%38%
1440
21st to endNight
12%6%245%2446%8%47%
1440
July1st to 10thNight
8%324435%5%6%9%52%
1440
11th to 20thNight
10%5%25%433449%51%
1440
21st to endNight
8%5%344345%5%8%53%
1575
August1st to 10thNight
6%5%26%435%5%7%9%48%
1436
11th to 20thNight
8%3234346%6%9%52%
1598
21st to endNight
12%6%35%434446%50%
1958
September1st to 10thNight
11%6%25%5%3345%5%51%
1800
11th to 20thNight
15%5%245%2345%7%48%
1926
21st to endNight
16%8%36%5%34447%40%
1980
October1st to 10thNight
18%9%36%5%345%47%38%
1996
11th to 20thNight
22%10%36%6%445%5%5%31%
2272
21st to endNight
24%13%47%5%34346%26%
2574
November1st to 10thNight
15%12%36%5%345%5%7%34%
2406
11th to 20thNight
18%16%6%9%8%44345%24%
2470
21st to endNight
19%14%8%8%6%35%5%5%5%21%
2625
December1st to 10thNight
17%16%8%10%7%35%45%5%20%
2660
11th to 20thNight
16%15%7%14%7%46%5%5%418%
3283
21st to endNight
24%20%9%11%6%3333314%
4884

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
58%5%15%16%5%1
1518
11th to 20thDay
64%5%13%12%5%
1453
21st to endDay
56%316%18%7%1
1584
February1st to 10thDay
50%5%15%24%6%
1501
11th to 20thDay
48%5%17%20%10%1
1758
21st to endDay
54%412%19%10%1
1480
March1st to 10thDay
46%5%14%22%12%2
1800
11th to 20thDay
47%412%24%11%2
1867
21st to endDay
48%6%14%21%10%1
2340
April1st to 10thDay
52%412%20%11%1
2160
11th to 20thDay
48%5%9%24%13%2
2173
21st to endDay
46%411%21%16%2
2340
May1st to 10thDay
42%6%11%27%12%2
2353
11th to 20thDay
41%5%11%26%15%2
2483
21st to endDay
37%6%15%27%13%2
2725
June1st to 10thDay
34%5%15%30%14%2
2520
11th to 20thDay
38%5%14%25%17%1
2520
21st to endDay
36%7%17%25%13%1
2520
July1st to 10thDay
25%6%17%34%17%1
2451
11th to 20thDay
28%5%16%32%16%3
2445
21st to endDay
28%7%17%29%18%1
2591
August1st to 10thDay
30%6%20%30%12%2
2488
11th to 20thDay
33%5%17%32%13%1
2303
21st to endDay
34%5%17%29%14%1
2394
September1st to 10thDay
39%5%15%28%12%1
2160
11th to 20thDay
36%5%23%29%6%
2015
21st to endDay
43%6%18%26%8%
1980
October1st to 10thDay
45%5%16%26%8%
1962
11th to 20thDay
59%414%19%41
1688
21st to endDay
61%5%13%16%5%
1782
November1st to 10thDay
50%414%21%10%
1672
11th to 20thDay
63%5%15%12%5%
1710
21st to endDay
66%5%15%12%2
1554
December1st to 10thDay
66%413%14%3
1520
11th to 20thDay
71%310%11%4
1915
21st to endDay
76%38%10%3
2783
January1st to 10thNight
61%313%16%5%
2648
11th to 20thNight
64%314%14%3
2547
21st to endNight
57%414%16%8%1
2772
February1st to 10thNight
56%311%22%8%1
2455
11th to 20thNight
50%6%13%21%8%2
2099
21st to endNight
57%313%18%8%1
1776
March1st to 10thNight
45%5%13%25%10%2
2160
11th to 20thNight
44%5%11%25%14%2
2093
21st to endNight
46%5%12%24%13%1
2031
April1st to 10thNight
55%48%18%13%2
1800
11th to 20thNight
49%5%9%20%14%3
1736
21st to endNight
49%410%19%14%3
1620
May1st to 10thNight
47%411%23%12%3
1603
11th to 20thNight
51%46%21%15%2
1417
21st to endNight
38%5%15%26%14%3
1552
June1st to 10thNight
38%5%11%30%14%2
1440
11th to 20thNight
42%6%13%20%17%2
1440
21st to endNight
35%5%16%26%15%2
1440
July1st to 10thNight
28%5%14%33%18%2
1400
11th to 20thNight
32%5%14%27%19%3
1392
21st to endNight
31%5%17%30%15%3
1487
August1st to 10thNight
30%6%18%31%12%2
1427
11th to 20thNight
27%7%18%34%13%2
1598
21st to endNight
36%414%27%17%2
1958
September1st to 10thNight
35%5%14%28%16%2
1800
11th to 20thNight
37%316%33%10%1
1926
21st to endNight
45%417%25%9%1
1980
October1st to 10thNight
47%413%25%9%1
1996
11th to 20thNight
54%5%13%20%7%
2272
21st to endNight
61%313%17%6%
2574
November1st to 10thNight
50%413%22%9%1
2406
11th to 20thNight
64%312%13%8%
2470
21st to endNight
64%416%14%2
2625
December1st to 10thNight
67%313%14%2
2660
11th to 20thNight
69%313%12%3
3281
21st to endNight
76%48%9%2
4884

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
17%10%32%28%11%1
270
11th to 20thDay
22%10%33%24%8%2
245
21st to endDay
23%5%25%32%14%2
264
February1st to 10thDay
13%7%40%29%9%1
240
11th to 20thDay
13%8%45%25%8%1
240
21st to endDay
18%10%42%24%6%
198
March1st to 10thDay
13%7%38%30%11%1
240
11th to 20thDay
15%7%28%34%13%3
307
21st to endDay
22%7%27%29%14%2
462
April1st to 10thDay
22%6%27%29%14%1
420
11th to 20thDay
21%7%27%28%12%4
412
21st to endDay
19%5%28%28%17%3
420
May1st to 10thDay
19%327%35%12%4
436
11th to 20thDay
16%324%36%17%4
625
21st to endDay
13%322%35%20%7%
679
June1st to 10thDay
11%221%39%23%4
630
11th to 20thDay
15%317%37%23%4
630
21st to endDay
13%319%35%24%6%
630
July1st to 10thDay
8%215%37%30%9%
621
11th to 20thDay
8%219%37%26%7%
618
21st to endDay
6%217%36%29%10%
684
August1st to 10thDay
8%214%36%31%10%
622
11th to 20thDay
13%5%11%28%31%12%
439
21st to endDay
15%217%29%27%9%
495
September1st to 10thDay
18%417%30%22%9%
450
11th to 20thDay
13%319%32%26%7%
450
21st to endDay
17%8%22%26%19%8%
450
October1st to 10thDay
21%6%24%29%16%4
432
11th to 20thDay
25%10%33%23%9%1
270
21st to endDay
28%9%34%23%6%
297
November1st to 10thDay
15%12%33%28%11%1
270
11th to 20thDay
19%13%38%22%7%
270
21st to endDay
23%14%37%21%6%
270
December1st to 10thDay
22%13%36%20%8%1
270
11th to 20thDay
26%12%39%18%41
270
21st to endDay
31%10%34%19%5%
297
January1st to 10thNight
19%9%35%27%8%1
950
11th to 20thNight
23%9%33%26%9%1
910
21st to endNight
18%6%31%32%11%1
990
February1st to 10thNight
17%6%37%31%8%1
893
11th to 20thNight
18%8%35%30%9%
703
21st to endNight
22%6%35%33%5%
592
March1st to 10thNight
17%6%33%32%12%2
720
11th to 20thNight
15%6%36%33%10%1
720
21st to endNight
19%6%25%36%13%2
645
April1st to 10thNight
23%6%27%35%8%2
540
11th to 20thNight
22%424%34%14%1
533
21st to endNight
18%425%38%14%1
540
May1st to 10thNight
19%424%37%15%2
540
11th to 20thNight
18%421%37%17%2
531
21st to endNight
13%315%39%25%5%
584
June1st to 10thNight
15%218%39%23%3
540
11th to 20thNight
16%317%37%24%3
540
21st to endNight
13%314%39%27%4
540
July1st to 10thNight
9%211%40%34%4
525
11th to 20thNight
11%214%36%31%6%
522
21st to endNight
9%415%38%29%6%
591
August1st to 10thNight
9%111%41%32%6%
537
11th to 20thNight
9%212%32%36%8%
534
21st to endNight
13%414%39%28%2
594
September1st to 10thNight
12%419%33%24%8%
540
11th to 20thNight
16%320%33%21%7%
666
21st to endNight
18%7%18%29%23%5%
720
October1st to 10thNight
22%8%21%27%19%3
720
11th to 20thNight
28%6%29%25%11%
720
21st to endNight
32%8%25%25%9%1
792
November1st to 10thNight
23%10%28%30%9%
740
11th to 20thNight
26%14%30%22%8%
760
21st to endNight
26%15%29%22%8%
915
December1st to 10thNight
25%14%32%22%6%1
950
11th to 20thNight
25%12%34%20%8%2
950
21st to endNight
28%11%34%24%4
1045
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