Windsor
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Windsor clear sky chart from 2005-11-05 to 2017-08-12.

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
34%
15465
15%
46503
9%
15427
41%
15427
19%
32141

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
12%
1961
January16th to endNight
17%
810
9%
2538
3%
810
24%
810
9%
2005
February1st to 15thNight
18%
701
9%
2273
3%
701
24%
701
11%
1741
February16th to endNight
23%
631
13%
1893
6%
631
30%
631
13%
1398
March1st to 15thNight
25%
720
14%
2061
8%
720
31%
720
16%
1501
March16th to endNight
31%
768
18%
2112
10%
768
38%
768
19%
1474
April1st to 15thNight
29%
611
15%
1821
8%
611
36%
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
42%
562
16%
1684
9%
561
50%
561
25%
1071
June1st to 15thNight
48%
411
16%
1350
12%
411
56%
411
24%
818
June16th to endNight
48%
434
18%
1334
14%
434
56%
434
27%
805
July1st to 15thNight
59%
510
17%
1360
13%
510
62%
510
36%
815
July16th to endNight
59%
564
19%
1535
15%
531
67%
531
36%
879
August1st to 15thNight
61%
527
19%
1575
15%
524
65%
524
32%
947
August16th to endNight
63%
525
21%
1575
15%
525
68%
525
35%
911
September1st to 15thNight
58%
627
24%
1782
19%
627
61%
627
32%
1087
September16th to endNight
55%
657
23%
1815
16%
657
60%
657
31%
1127
October1st to 15thNight
43%
660
19%
1908
17%
660
48%
660
25%
1224
October16th to endNight
26%
704
15%
2183
7%
704
37%
704
17%
1520
November1st to 15thNight
33%
700
21%
2276
16%
700
41%
700
21%
1468
November16th to endNight
21%
720
14%
2418
7%
720
30%
720
12%
1723
December1st to 15thNight
16%
720
8%
2520
4%
720
22%
720
9%
1947
December16th to endNight
14%
927
7%
2744
2%
927
19%
927
8%
2285

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%
47442
Night
15%8%36%5%3445%6%36%
46684
Cloud CoverDay
14%8%36%6%345%5%7%33%
47452
Night
15%8%36%5%3445%6%35%
46688
TransparencyDay
48%6%13%20%10%1
47142
Night
47%5%12%20%11%1
46503
SeeingDay
14%13%23%25%16%7%
5634
Night
15%19%22%27%12%1
15473

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%13%48%8%45%5%5%5%18%
1432
16th to endDay
14%16%8%9%9%45%45%5%16%
1683
February1st to 15thDay
15%15%6%8%8%45%5%5%5%20%
1589
16th to endDay
15%12%6%10%6%45%45%6%23%
1580
March1st to 15thDay
18%11%48%6%34436%27%
1886
16th to endDay
18%10%47%6%34345%29%
2112
April1st to 15thDay
18%10%45%5%2445%6%30%
2136
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%
2601
16th to endDay
9%5%25%6%35%6%7%10%34%
2620
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%5%8%8%38%
2288
16th to endDay
10%4245%35%5%7%9%40%
2274
September1st to 15thDay
13%6%25%435%46%6%42%
1837
16th to endDay
13%5%244245%6%8%41%
1815
October1st to 15thDay
13%6%26%5%2445%7%39%
1722
16th to endDay
21%8%25%6%24446%32%
1686
November1st to 15thDay
13%7%344345%5%7%39%
1582
16th to endDay
16%10%47%7%345%5%7%28%
1539
December1st to 15thDay
17%11%6%10%7%36%5%5%6%20%
1440
16th to endDay
21%15%6%11%7%4445%5%14%
1473
January1st to 15thNight
21%13%47%6%34445%23%
2506
16th to endNight
13%13%7%10%8%4445%5%21%
2538
February1st to 15thNight
15%14%49%7%35%34426%
2271
16th to endNight
16%11%5%7%6%3445%5%29%
1893
March1st to 15thNight
18%9%47%6%2445%5%32%
2049
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%
1350
16th to endNight
9%4245%246%6%7%46%
1334
July1st to 15thNight
7%323325%447%53%
1440
16th to endNight
4323425%5%6%9%52%
1641
August1st to 15thNight
5%3245%345%5%8%49%
1586
16th to endNight
10%433423348%52%
1575
September1st to 15thNight
10%42442445%6%51%
1782
16th to endNight
11%5%244235%47%47%
1815
October1st to 15thNight
14%5%3432345%7%43%
1908
16th to endNight
20%7%35%5%34346%34%
2183
November1st to 15thNight
13%6%25%425%45%6%41%
2276
16th to endNight
21%10%46%42345%6%29%
2418
December1st to 15thNight
20%13%5%8%6%34445%24%
2520
16th to endNight
22%14%6%10%5%35%445%17%
2744

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%12%5%8%8%46%5%5%5%18%
1432
16th to endDay
15%16%7%9%8%45%45%6%15%
1683
February1st to 15thDay
15%14%6%8%8%45%45%6%20%
1589
16th to endDay
15%11%6%10%6%4446%6%22%
1580
March1st to 15thDay
18%10%47%7%44446%26%
1897
16th to endDay
18%11%48%6%3335%5%29%
2111
April1st to 15thDay
18%10%46%5%345%5%7%30%
2136
16th to endDay
17%8%25%5%23447%36%
2340
May1st to 15thDay
17%8%36%6%45%45%6%31%
2331
16th to endDay
13%5%35%5%3445%8%41%
2431
June1st to 15thDay
9%5%25%6%446%5%8%40%
2601
16th to endDay
9%5%36%5%36%6%7%10%35%
2620
July1st to 15thDay
8%4245%35%6%6%8%45%
2520
16th to endDay
7%435%5%36%6%7%10%39%
2525
August1st to 15thDay
8%5%25%6%45%6%7%9%38%
2288
16th to endDay
10%4245%35%5%6%10%40%
2274
September1st to 15thDay
13%5%25%5%245%5%7%42%
1837
16th to endDay
13%6%245%235%5%8%42%
1815
October1st to 15thDay
13%5%26%5%335%5%7%40%
1722
16th to endDay
20%9%26%6%33446%32%
1686
November1st to 15thDay
13%7%35%5%3445%7%39%
1582
16th to endDay
16%10%47%5%35%5%5%7%28%
1539
December1st to 15thDay
17%11%6%9%7%45%5%5%5%20%
1440
16th to endDay
21%15%7%10%7%4435%5%14%
1473
January1st to 15thNight
21%12%47%5%35%445%23%
2506
16th to endNight
13%13%7%10%8%45%445%21%
2538
February1st to 15thNight
15%13%49%6%45%44426%
2264
16th to endNight
16%12%5%7%6%345%5%5%28%
1893
March1st to 15thNight
18%9%47%5%34445%31%
2061
16th to endNight
15%7%36%5%25%46%7%35%
2112
April1st to 15thNight
18%9%35%43445%7%34%
1821
16th to endNight
14%7%25%42446%6%39%
1620
May1st to 15thNight
17%5%35%5%245%5%7%35%
1619
16th to endNight
12%5%25%43445%7%43%
1682
June1st to 15thNight
10%5%244345%5%8%45%
1350
16th to endNight
8%425%5%25%5%6%8%45%
1334
July1st to 15thNight
7%414335%447%53%
1440
16th to endNight
43134245%6%9%52%
1641
August1st to 15thNight
6%3246%345%5%8%49%
1586
16th to endNight
10%5%1341435%8%51%
1575
September1st to 15thNight
10%424423446%51%
1782
16th to endNight
12%4244235%5%6%47%
1815
October1st to 15thNight
15%5%25%5%24347%43%
1908
16th to endNight
20%8%25%6%34345%35%
2183
November1st to 15thNight
13%6%25%5%35%45%6%41%
2276
16th to endNight
21%10%46%5%2435%7%28%
2418
December1st to 15thNight
19%13%5%7%6%245%45%24%
2520
16th to endNight
22%13%6%8%6%35%445%17%
2744

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%12%11%4
1433
16th to endDay
69%5%11%8%4
1683
February1st to 15thDay
63%5%10%14%5%
1591
16th to endDay
60%5%12%16%5%
1580
March1st to 15thDay
58%6%11%16%5%1
1897
16th to endDay
55%411%20%7%
2112
April1st to 15thDay
52%5%11%18%11%
2136
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
2601
16th to endDay
38%9%14%19%15%1
2620
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%27%11%1
2275
16th to endDay
35%7%14%25%14%2
2274
September1st to 15thDay
39%415%25%13%
1837
16th to endDay
38%414%29%12%
1815
October1st to 15thDay
41%5%14%23%12%1
1722
16th to endDay
52%415%19%7%
1686
November1st to 15thDay
43%6%13%22%12%1
1582
16th to endDay
54%6%15%17%5%
1539
December1st to 15thDay
63%6%12%12%4
1440
16th to endDay
71%411%9%2
1473
January1st to 15thNight
61%412%14%6%
2506
16th to endNight
64%412%13%4
2538
February1st to 15thNight
60%5%11%15%5%
2273
16th to endNight
56%412%18%7%
1893
March1st to 15thNight
53%411%18%9%1
2061
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
1350
16th to endNight
33%6%14%24%18%1
1334
July1st to 15thNight
31%5%10%30%20%2
1360
16th to endNight
26%7%16%25%20%4
1535
August1st to 15thNight
31%7%14%27%16%2
1575
16th to endNight
30%5%14%28%17%3
1575
September1st to 15thNight
32%7%12%26%19%2
1782
16th to endNight
35%5%11%29%16%1
1815
October1st to 15thNight
40%5%13%21%18%1
1908
16th to endNight
49%5%13%22%7%
2183
November1st to 15thNight
42%6%11%24%13%1
2276
16th to endNight
54%413%20%6%
2418
December1st to 15thNight
62%5%12%14%5%
2520
16th to endNight
68%6%10%11%3
2744

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
21%12%44%13%7%1
90
16th to endDay
29%8%35%23%3
96
February1st to 15thDay
20%14%38%25%1
90
16th to endDay
18%12%43%22%3
81
March1st to 15thDay
25%20%21%23%8%
187
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
453
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%32%21%18%
297
16th to endDay
10%8%11%18%28%21%
268
September1st to 15thDay
13%7%15%20%26%16%
255
16th to endDay
17%7%12%20%28%12%
254
October1st to 15thDay
13%9%20%26%20%9%
255
16th to endDay
21%13%31%26%7%
198
November1st to 15thDay
11%12%22%34%15%4
90
16th to endDay
18%23%28%23%6%
77
December1st to 15thDay
23%18%33%18%6%
60
16th to endDay
24%20%40%13%
81
January1st to 15thNight
20%25%28%20%4
900
16th to endNight
15%24%29%25%5%
810
February1st to 15thNight
19%23%29%23%3
704
16th to endNight
17%22%25%28%5%
631
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%39%13%
411
16th to endNight
9%17%15%38%16%2
434
July1st to 15thNight
8%12%12%37%24%3
510
16th to endNight
417%11%40%21%4
564
August1st to 15thNight
7%11%10%38%26%5%
527
16th to endNight
9%11%9%29%33%6%
525
September1st to 15thNight
10%14%12%31%24%6%
627
16th to endNight
12%11%15%28%27%5%
657
October1st to 15thNight
15%13%20%27%20%3
660
16th to endNight
21%17%29%25%6%
704
November1st to 15thNight
14%20%27%22%14%1
700
16th to endNight
22%26%25%18%6%
720
December1st to 15thNight
23%24%28%18%4
720
16th to endNight
23%24%30%17%3
927
Page generated at 2017-08-13 14:16:53. Version ac04

Copyright 2017 A. Danko


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