Wilson Coulee Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wilson Coulee Observatory 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
41%
15061
14%
46443
9%
15030
47%
15030
23%
30582

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
33%
898
12%
2685
7%
895
37%
895
18%
1920
January16th to endNight
36%
810
18%
2730
14%
810
44%
810
21%
1752
February1st to 15thNight
40%
701
14%
2411
11%
697
47%
697
20%
1562
February16th to endNight
38%
632
14%
1974
10%
632
45%
632
19%
1390
March1st to 15thNight
34%
720
15%
2117
9%
720
41%
720
22%
1452
March16th to endNight
32%
768
11%
2090
3%
768
38%
768
19%
1534
April1st to 15thNight
34%
629
12%
1709
5%
629
37%
629
18%
1257
April16th to endNight
36%
540
12%
1620
9%
540
39%
540
21%
1130
May1st to 15thNight
43%
428
11%
1431
10%
428
47%
428
22%
926
May16th to endNight
40%
374
5%
1309
3%
374
42%
374
16%
928
June1st to 15thNight
41%
360
1%
1260
0%
360
41%
360
19%
850
June16th to endNight
55%
360
1%
1260
0%
360
55%
360
28%
755
July1st to 15thNight
60%
340
3%
1190
0%
340
61%
340
29%
683
July16th to endNight
62%
376
11%
1288
13%
354
66%
354
33%
691
August1st to 15thNight
64%
393
12%
1441
14%
391
67%
391
28%
804
August16th to endNight
60%
525
19%
1575
15%
525
63%
525
42%
840
September1st to 15thNight
57%
610
19%
1663
13%
610
60%
610
39%
994
September16th to endNight
52%
656
21%
1815
13%
656
58%
656
39%
1071
October1st to 15thNight
43%
660
17%
1939
11%
660
49%
660
24%
1317
October16th to endNight
46%
704
21%
2288
14%
704
55%
704
27%
1400
November1st to 15thNight
33%
817
18%
2392
9%
817
41%
817
25%
1533
November16th to endNight
34%
900
15%
2676
7%
900
41%
900
23%
1778
December1st to 15thNight
38%
900
13%
2700
9%
900
41%
900
17%
1964
December16th to endNight
35%
960
15%
2880
8%
960
41%
960
19%
2051

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
11%8%36%5%35%5%6%8%36%
47567
Night
8%9%46%5%35%5%5%8%38%
46594
Cloud CoverDay
11%8%36%5%35%5%6%8%36%
47568
Night
8%8%46%5%345%5%8%37%
46597
TransparencyDay
44%7%17%21%8%1
47222
Night
42%6%16%22%10%1
46443
SeeingDay
15%9%29%27%14%3
5863
Night
12%6%29%34%14%2
15068

By Month

Percentage Cloud Cover NW (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
6%10%5%6%6%345%5%8%37%
1253
16th to endDay
411%5%7%5%35%46%9%35%
1503
February1st to 15thDay
5%10%48%5%36%5%6%8%34%
1452
16th to endDay
312%6%9%6%36%6%6%8%29%
1500
March1st to 15thDay
310%49%7%36%5%6%9%34%
1842
16th to endDay
9%13%49%7%35%47%6%27%
2132
April1st to 15thDay
12%13%6%7%6%345%5%8%27%
2239
16th to endDay
16%10%36%5%25%5%6%7%29%
2340
May1st to 15thDay
12%8%36%5%35%6%6%7%34%
2518
16th to endDay
23%6%35%6%345%6%7%25%
2802
June1st to 15thDay
21%7%35%5%35%5%5%7%27%
2700
16th to endDay
15%5%25%446%5%5%9%35%
2700
July1st to 15thDay
11%414435%5%7%8%43%
2700
16th to endDay
6%324435%5%7%9%48%
2792
August1st to 15thDay
13%4243245%7%9%42%
2425
16th to endDay
11%3143245%6%8%48%
2275
September1st to 15thDay
14%414423345%50%
1966
16th to endDay
10%6%1443445%9%46%
1815
October1st to 15thDay
13%11%27%6%3345%8%33%
1689
16th to endDay
6%10%26%435%6%6%9%37%
1584
November1st to 15thDay
8%9%46%6%35%5%5%7%36%
1455
16th to endDay
5%13%47%32345%9%39%
1281
December1st to 15thDay
49%5%12%8%5%5%6%5%7%29%
1260
16th to endDay
310%5%9%5%26%7%6%9%33%
1344
January1st to 15thNight
411%5%9%7%46%5%5%9%30%
2685
16th to endNight
5%9%5%7%6%35%46%9%37%
2730
February1st to 15thNight
410%5%6%5%446%6%8%37%
2400
16th to endNight
410%6%10%6%36%45%5%34%
1974
March1st to 15thNight
310%47%7%46%6%5%9%33%
2117
16th to endNight
6%12%6%8%7%35%47%8%28%
2087
April1st to 15thNight
12%13%5%7%5%25%5%47%30%
1709
16th to endNight
12%10%37%6%2445%7%34%
1620
May1st to 15thNight
10%9%37%5%34448%38%
1430
16th to endNight
20%6%25%5%35%6%5%7%30%
1309
June1st to 15thNight
16%7%46%5%35%5%5%7%32%
1260
16th to endNight
12%424325%5%7%8%42%
1260
July1st to 15thNight
8%315%5%3446%7%48%
1260
16th to endNight
7%32332346%8%53%
1376
August1st to 15thNight
10%41443446%9%46%
1449
16th to endNight
10%21232335%8%56%
1575
September1st to 15thNight
13%5%13213346%53%
1663
16th to endNight
10%5%1331346%7%52%
1815
October1st to 15thNight
12%8%37%5%3345%6%38%
1939
16th to endNight
8%9%245%245%6%8%42%
2288
November1st to 15thNight
6%8%35%5%345%5%8%42%
2392
16th to endNight
5%11%47%6%3436%9%36%
2676
December1st to 15thNight
311%49%8%47%5%5%8%30%
2700
16th to endNight
311%5%10%8%46%6%5%8%31%
2880

Percentage Cloud Cover SW (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
6%11%46%6%445%48%36%
1253
16th to endDay
5%11%47%6%35%5%6%7%35%
1503
February1st to 15thDay
5%10%5%8%6%26%5%7%8%33%
1452
16th to endDay
413%6%9%5%47%5%6%7%28%
1500
March1st to 15thDay
310%48%7%35%5%5%9%33%
1842
16th to endDay
9%15%5%7%6%445%6%7%26%
2133
April1st to 15thDay
12%13%5%7%7%35%45%7%26%
2239
16th to endDay
15%11%36%5%35%46%6%30%
2340
May1st to 15thDay
13%8%35%5%35%6%6%7%34%
2518
16th to endDay
23%6%26%6%445%5%7%26%
2802
June1st to 15thDay
21%6%36%6%35%5%5%8%28%
2700
16th to endDay
15%4245%36%5%7%8%35%
2700
July1st to 15thDay
11%4244246%6%8%43%
2700
16th to endDay
6%4244245%7%9%48%
2792
August1st to 15thDay
13%4243245%7%8%42%
2425
16th to endDay
10%413425%5%5%7%48%
2275
September1st to 15thDay
14%5%14423446%49%
1966
16th to endDay
9%6%25%434449%46%
1815
October1st to 15thDay
14%10%36%6%335%5%7%33%
1689
16th to endDay
7%9%36%5%346%6%9%37%
1584
November1st to 15thDay
9%10%37%5%35%6%48%35%
1455
16th to endDay
5%14%46%42346%9%38%
1281
December1st to 15thDay
410%5%12%8%5%6%5%5%6%28%
1260
16th to endDay
311%49%6%35%6%6%10%32%
1344
January1st to 15thNight
5%10%5%10%7%45%5%6%9%29%
2685
16th to endNight
5%9%48%6%345%6%9%36%
2730
February1st to 15thNight
6%9%48%5%35%5%5%8%36%
2400
16th to endNight
412%6%9%7%45%45%6%32%
1974
March1st to 15thNight
311%47%7%45%6%6%9%33%
2117
16th to endNight
7%11%5%9%7%35%5%6%8%28%
2090
April1st to 15thNight
13%13%5%5%5%35%5%46%31%
1709
16th to endNight
13%10%46%5%35%36%6%34%
1620
May1st to 15thNight
10%9%46%435%35%8%38%
1430
16th to endNight
20%7%25%5%35%5%6%7%30%
1309
June1st to 15thNight
17%7%25%6%45%46%7%31%
1260
16th to endNight
11%3245%3447%10%40%
1260
July1st to 15thNight
7%425%5%35%35%7%49%
1260
16th to endNight
7%3143235%5%8%53%
1376
August1st to 15thNight
9%4234335%6%9%46%
1449
16th to endNight
10%213222449%55%
1575
September1st to 15thNight
13%6%13212347%52%
1663
16th to endNight
10%42321446%6%52%
1815
October1st to 15thNight
13%9%26%5%3445%7%38%
1939
16th to endNight
9%8%2443446%8%42%
2288
November1st to 15thNight
7%9%35%5%35%45%7%41%
2392
16th to endNight
6%10%5%7%5%35%45%8%36%
2676
December1st to 15thNight
410%5%10%8%5%6%6%5%7%30%
2700
16th to endNight
310%5%10%7%46%6%6%7%30%
2880

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
45%5%15%24%6%2
1253
16th to endDay
43%7%15%19%10%3
1503
February1st to 15thDay
45%7%16%20%7%2
1452
16th to endDay
51%6%15%18%8%
1500
March1st to 15thDay
45%7%19%19%6%
1842
16th to endDay
54%7%14%17%5%
2133
April1st to 15thDay
54%6%14%16%5%1
2239
16th to endDay
52%5%15%18%7%1
2340
May1st to 15thDay
45%5%17%21%9%
2518
16th to endDay
54%7%15%16%5%
2807
June1st to 15thDay
53%7%15%16%5%1
2700
16th to endDay
42%8%18%21%7%1
2700
July1st to 15thDay
35%7%21%24%8%1
2541
16th to endDay
29%8%20%27%11%2
2617
August1st to 15thDay
36%8%24%23%6%1
2408
16th to endDay
31%7%19%29%11%1
2275
September1st to 15thDay
35%5%15%23%17%3
1966
16th to endDay
36%5%12%32%10%3
1815
October1st to 15thDay
46%7%15%19%9%
1689
16th to endDay
40%8%15%26%7%1
1584
November1st to 15thDay
45%8%14%21%8%1
1455
16th to endDay
41%5%18%22%8%2
1281
December1st to 15thDay
53%7%14%16%7%
1260
16th to endDay
45%5%17%20%9%1
1344
January1st to 15thNight
49%7%16%17%6%2
2685
16th to endNight
42%6%15%20%11%3
2730
February1st to 15thNight
43%6%15%22%10%1
2411
16th to endNight
50%5%12%19%10%
1974
March1st to 15thNight
44%7%19%21%5%
2117
16th to endNight
50%7%14%17%8%
2090
April1st to 15thNight
53%5%13%18%9%
1709
16th to endNight
48%5%15%22%6%1
1620
May1st to 15thNight
43%5%15%24%10%
1431
16th to endNight
51%7%17%17%5%1
1309
June1st to 15thNight
49%5%17%18%8%
1260
16th to endNight
36%6%22%24%9%
1260
July1st to 15thNight
34%6%20%27%11%
1190
16th to endNight
26%8%17%31%12%2
1288
August1st to 15thNight
32%7%22%27%9%1
1441
16th to endNight
25%418%31%16%3
1575
September1st to 15thNight
31%317%24%18%3
1663
16th to endNight
30%5%18%27%13%5%
1815
October1st to 15thNight
44%6%14%21%11%1
1939
16th to endNight
37%6%18%26%10%
2288
November1st to 15thNight
39%6%16%22%13%1
2392
16th to endNight
43%5%19%18%9%3
2676
December1st to 15thNight
51%7%14%19%6%
2700
16th to endNight
49%6%13%21%7%
2880

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
8%325%25%20%18%
60
16th to endDay
15%7%20%32%12%10%
64
February1st to 15thDay
8%8%37%28%14%1
69
16th to endDay
9%6%33%35%14%
159
March1st to 15thDay
7%18%50%19%3
270
16th to endDay
13%19%37%19%7%1
288
April1st to 15thDay
21%19%30%21%6%
269
16th to endDay
24%12%28%23%8%1
270
May1st to 15thDay
17%9%31%22%14%4
364
16th to endDay
23%5%21%27%17%3
517
June1st to 15thDay
20%9%27%27%13%2
495
16th to endDay
16%5%30%29%13%3
495
July1st to 15thDay
11%5%22%31%23%4
475
16th to endDay
8%7%30%31%18%3
461
August1st to 15thDay
11%6%30%30%17%4
300
16th to endDay
13%7%33%32%8%4
268
September1st to 15thDay
21%9%26%25%14%3
255
16th to endDay
11%15%26%32%10%2
255
October1st to 15thDay
17%13%25%26%16%1
156
16th to endDay
10%328%30%21%6%
96
November1st to 15thDay
23%12%21%33%5%4
90
16th to endDay
6%9%23%26%17%15%
63
December1st to 15thDay
5%5%36%31%20%1
60
16th to endDay
9%425%29%25%6%
64
January1st to 15thNight
10%11%32%33%11%1
900
16th to endNight
11%8%31%36%10%1
810
February1st to 15thNight
9%9%27%34%14%4
704
16th to endNight
9%5%30%35%16%2
632
March1st to 15thNight
9%7%38%32%10%1
720
16th to endNight
11%7%33%35%10%1
768
April1st to 15thNight
15%10%29%31%11%1
629
16th to endNight
19%6%28%33%12%
540
May1st to 15thNight
14%8%26%30%19%1
429
16th to endNight
22%5%22%31%18%
375
June1st to 15thNight
20%5%24%32%15%1
360
16th to endNight
12%420%39%21%
360
July1st to 15thNight
10%215%41%27%1
340
16th to endNight
8%220%45%21%2
376
August1st to 15thNight
11%213%38%30%3
393
16th to endNight
10%222%40%24%
525
September1st to 15thNight
16%220%30%24%4
610
16th to endNight
11%427%36%14%4
656
October1st to 15thNight
18%426%33%13%3
660
16th to endNight
13%5%27%39%12%2
704
November1st to 15thNight
10%11%37%31%7%1
817
16th to endNight
11%8%37%32%8%2
900
December1st to 15thNight
9%7%32%35%11%2
900
16th to endNight
8%6%34%36%11%2
960
Page generated at 2017-08-13 12:16:50. Version ac04

Copyright 2017 A. Danko


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