WWIN Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the WWIN Observatory clear sky chart from 2005-11-05 to 2017-09-24.

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
52%
15671
26%
47052
19%
15626
59%
15626
33%
27894

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
34%
899
28%
2327
11%
895
45%
895
33%
1484
January16th to endNight
32%
960
27%
2496
10%
960
42%
960
32%
1610
February1st to 15thNight
30%
839
21%
2247
8%
836
38%
836
30%
1452
February16th to endNight
30%
631
28%
1893
11%
631
44%
631
30%
1132
March1st to 15thNight
34%
546
22%
1986
16%
546
43%
546
23%
1213
March16th to endNight
42%
576
21%
2094
18%
576
50%
576
25%
1284
April1st to 15thNight
41%
539
26%
1797
18%
539
54%
539
33%
997
April16th to endNight
43%
540
26%
1800
19%
540
56%
540
32%
1028
May1st to 15thNight
53%
540
20%
1785
18%
540
60%
540
27%
1096
May16th to endNight
60%
563
23%
1636
20%
561
64%
561
32%
1002
June1st to 15thNight
79%
540
25%
1440
21%
540
81%
540
49%
780
June16th to endNight
78%
540
28%
1462
25%
540
79%
540
47%
820
July1st to 15thNight
77%
510
18%
1530
20%
510
78%
510
36%
887
July16th to endNight
84%
564
25%
1594
28%
531
84%
531
41%
881
August1st to 15thNight
82%
539
24%
1682
28%
536
83%
536
41%
905
August16th to endNight
76%
573
25%
1910
30%
573
76%
573
31%
1120
September1st to 15thNight
71%
540
25%
1800
28%
540
73%
540
33%
1029
September16th to endNight
72%
591
34%
1884
31%
591
75%
591
38%
1024
October1st to 15thNight
61%
660
32%
1980
26%
660
65%
660
39%
1105
October16th to endNight
56%
704
35%
2112
25%
704
65%
704
41%
1143
November1st to 15thNight
51%
700
32%
2118
23%
700
59%
700
38%
1160
November16th to endNight
44%
720
29%
2340
21%
720
54%
720
30%
1376
December1st to 15thNight
38%
897
21%
2517
12%
897
46%
897
27%
1637
December16th to endNight
34%
960
23%
2622
11%
960
43%
960
28%
1729

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
12%5%2443445%7%44%
47855
Night
12%424423446%50%
47249
TransparencyDay
37%6%10%22%18%4
47556
Night
33%49%23%22%6%
47053
SeeingDay
11%315%25%27%14%
5727
Night
14%423%33%21%2
15672

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 15thDay
19%6%23322335%47%
1611
16th to endDay
17%5%34423235%46%
1728
February1st to 15thDay
17%6%24312245%47%
1615
16th to endDay
18%6%35%5%23336%40%
1583
March1st to 15thDay
19%5%245%24335%40%
1980
16th to endDay
16%6%36%434345%42%
2126
April1st to 15thDay
13%5%25%424346%48%
2151
16th to endDay
15%5%25%435%346%42%
2160
May1st to 15thDay
16%6%26%5%34447%38%
2163
16th to endDay
8%437%6%45%6%7%9%36%
2474
June1st to 15thDay
5%415%5%46%5%6%9%44%
2520
16th to endDay
5%3345%35%6%7%9%43%
2493
July1st to 15thDay
7%435%7%48%7%7%10%34%
2340
16th to endDay
6%3245%46%7%6%10%43%
2466
August1st to 15thDay
7%4145%45%6%7%10%40%
2267
16th to endDay
8%4245%46%6%7%9%39%
2292
September1st to 15thDay
12%5%24435%5%5%6%44%
2160
16th to endDay
11%413423347%52%
1920
October1st to 15thDay
12%42441334453%
1650
16th to endDay
15%31221123459%
1760
November1st to 15thDay
11%5%13212235%57%
1737
16th to endDay
18%6%24323325%48%
1620
December1st to 15thDay
18%6%25%413345%44%
1440
16th to endDay
19%6%3441344442%
1599
January1st to 15thNight
18%5%2431223450%
2327
16th to endNight
16%5%2432343350%
2496
February1st to 15thNight
18%5%2431243447%
2238
16th to endNight
15%5%23314245%51%
1893
March1st to 15thNight
16%6%34424345%44%
1986
16th to endNight
15%5%25%424346%45%
2094
April1st to 15thNight
10%32442335%8%51%
1797
16th to endNight
10%3235%235%48%49%
1800
May1st to 15thNight
14%42342445%7%45%
1784
16th to endNight
7%425%435%45%8%46%
1635
June1st to 15thNight
221332447%8%58%
1440
16th to endNight
322343445%9%56%
1462
July1st to 15thNight
42246%26%5%7%12%45%
1620
16th to endNight
422435%5%6%11%53%
1702
August1st to 15thNight
32145%3447%11%52%
1692
16th to endNight
6%3245%36%5%6%10%44%
1910
September1st to 15thNight
9%42442345%7%51%
1800
16th to endNight
7%41323435%6%55%
1884
October1st to 15thNight
10%424324345%57%
1980
16th to endNight
13%2232323362%
2112
November1st to 15thNight
10%324312247%55%
2118
16th to endNight
16%5%1332333451%
2340
December1st to 15thNight
18%6%2432334445%
2517
16th to endNight
18%7%34323335%45%
2622

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
39%46%25%19%5%
1612
16th to endDay
39%37%24%20%3
1728
February1st to 15thDay
39%410%24%17%3
1617
16th to endDay
45%46%21%18%3
1583
March1st to 15thDay
45%49%18%16%6%
1980
16th to endDay
44%411%25%12%1
2128
April1st to 15thDay
37%5%10%23%18%5%
2151
16th to endDay
41%5%9%21%19%3
2160
May1st to 15thDay
44%7%10%15%18%3
2163
16th to endDay
40%8%15%22%12%1
2478
June1st to 15thDay
34%7%11%27%19%
2520
16th to endDay
32%7%12%24%18%3
2493
July1st to 15thDay
39%10%12%22%12%2
2201
16th to endDay
31%9%15%25%16%2
2311
August1st to 15thDay
34%9%13%24%15%2
2253
16th to endDay
36%9%14%21%14%3
2292
September1st to 15thDay
37%7%10%18%18%7%
2160
16th to endDay
31%49%21%25%7%
1920
October1st to 15thDay
33%38%20%25%8%
1650
16th to endDay
28%3424%28%10%
1760
November1st to 15thDay
30%37%24%26%8%
1737
16th to endDay
40%37%19%22%6%
1620
December1st to 15thDay
41%5%9%22%15%5%
1440
16th to endDay
44%311%18%16%4
1599
January1st to 15thNight
38%36%20%27%4
2327
16th to endNight
38%45%23%21%6%
2496
February1st to 15thNight
40%38%23%19%5%
2247
16th to endNight
35%37%25%19%7%
1893
March1st to 15thNight
42%39%16%19%7%
1986
16th to endNight
40%5%8%24%19%2
2094
April1st to 15thNight
31%410%23%22%7%
1797
16th to endNight
32%5%9%23%24%4
1800
May1st to 15thNight
38%5%9%21%18%6%
1785
16th to endNight
34%6%14%23%18%1
1637
June1st to 15thNight
20%6%14%30%25%2
1440
16th to endNight
24%5%12%27%25%5%
1462
July1st to 15thNight
28%8%17%27%14%3
1530
16th to endNight
22%9%14%29%20%3
1594
August1st to 15thNight
23%7%17%29%18%3
1682
16th to endNight
32%7%12%24%17%3
1910
September1st to 15thNight
31%6%10%23%19%8%
1800
16th to endNight
27%5%8%22%26%9%
1884
October1st to 15thNight
29%48%21%23%12%
1980
16th to endNight
28%2418%33%11%
2112
November1st to 15thNight
29%36%23%25%11%
2118
16th to endNight
36%35%19%28%6%
2340
December1st to 15thNight
41%38%21%17%6%
2517
16th to endNight
42%38%21%19%4
2622

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
26%5%37%21%5%3
90
16th to endDay
16%8%48%19%6%
96
February1st to 15thDay
13%8%48%20%6%2
90
16th to endDay
16%7%46%18%9%1
81
March1st to 15thDay
28%7%34%21%6%1
90
16th to endDay
10%15%18%37%17%
112
April1st to 15thDay
14%8%35%22%17%1
270
16th to endDay
20%5%24%28%17%4
270
May1st to 15thDay
17%5%23%31%17%4
300
16th to endDay
12%418%31%24%9%
517
June1st to 15thDay
6%212%24%35%18%
495
16th to endDay
6%28%31%32%18%
495
July1st to 15thDay
6%17%33%35%16%
475
16th to endDay
4220%39%32%
515
August1st to 15thDay
9%5%23%37%23%
420
16th to endDay
12%1319%38%23%
332
September1st to 15thDay
9%6%21%36%25%
315
16th to endDay
10%18%18%37%23%
212
October1st to 15thDay
11%124%31%15%16%
90
16th to endDay
16%215%32%26%7%
96
November1st to 15thDay
15%222%30%22%7%
90
16th to endDay
30%11%27%15%11%4
90
December1st to 15thDay
16%5%38%17%14%6%
90
16th to endDay
29%11%32%21%5%
96
January1st to 15thNight
21%7%33%29%8%
900
16th to endNight
20%5%38%31%4
960
February1st to 15thNight
21%7%36%30%4
839
16th to endNight
17%10%38%29%3
631
March1st to 15thNight
19%7%33%34%4
546
16th to endNight
17%431%35%10%
576
April1st to 15thNight
12%5%34%34%11%1
539
16th to endNight
12%5%33%32%13%1
540
May1st to 15thNight
15%222%42%15%1
540
16th to endNight
10%118%40%24%4
563
June1st to 15thNight
29%38%43%5%
540
16th to endNight
316%38%44%5%
540
July1st to 15thNight
45%33%48%7%
510
16th to endNight
4226%52%13%
564
August1st to 15thNight
5%330%48%11%
539
16th to endNight
8%427%52%8%
573
September1st to 15thNight
11%7%26%46%5%
540
16th to endNight
9%19%35%39%4
591
October1st to 15thNight
11%217%36%27%5%
660
16th to endNight
13%322%36%22%1
704
November1st to 15thNight
11%427%34%19%2
700
16th to endNight
19%5%26%33%15%
720
December1st to 15thNight
22%6%27%35%8%
897
16th to endNight
22%6%31%33%6%
960
Page generated at 2017-09-25 08:02:22. Version ac04

Copyright 2017 A. Danko


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