Windy Hills Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Windy Hills Observatory clear sky chart from 2005-11-05 to 2017-09-19.

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
42%
15909
23%
47103
14%
15862
51%
15862
32%
27978

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%
900
23%
2327
9%
895
44%
895
34%
1458
January16th to endNight
29%
960
26%
2496
10%
960
40%
960
32%
1569
February1st to 15thNight
28%
880
16%
2288
6%
876
34%
876
24%
1592
February16th to endNight
28%
663
25%
1925
7%
663
41%
663
30%
1174
March1st to 15thNight
34%
540
22%
1980
13%
540
47%
540
25%
1139
March16th to endNight
27%
576
15%
2112
10%
576
35%
576
19%
1352
April1st to 15thNight
32%
539
20%
1881
13%
539
45%
539
28%
1067
April16th to endNight
31%
540
22%
1659
13%
540
44%
540
24%
1086
May1st to 15thNight
38%
539
19%
1620
15%
539
46%
539
26%
1030
May16th to endNight
44%
563
18%
1685
13%
561
51%
561
33%
1010
June1st to 15thNight
55%
540
19%
1512
11%
540
59%
540
39%
863
June16th to endNight
60%
540
25%
1558
15%
540
65%
540
51%
784
July1st to 15thNight
67%
510
18%
1530
14%
510
70%
510
41%
828
July16th to endNight
68%
564
25%
1594
23%
531
72%
531
42%
863
August1st to 15thNight
76%
539
23%
1610
27%
536
79%
536
41%
876
August16th to endNight
67%
573
27%
1779
30%
573
71%
573
41%
949
September1st to 15thNight
60%
540
25%
1899
26%
540
67%
540
32%
1056
September16th to endNight
61%
504
29%
1857
26%
504
69%
504
36%
947
October1st to 15thNight
43%
630
28%
1950
20%
630
49%
630
31%
1157
October16th to endNight
40%
704
29%
2112
14%
704
51%
704
39%
1136
November1st to 15thNight
44%
805
30%
2205
15%
805
54%
805
41%
1225
November16th to endNight
34%
900
26%
2436
9%
900
46%
900
36%
1440
December1st to 15thNight
30%
900
19%
2520
8%
900
39%
900
26%
1653
December16th to endNight
31%
960
23%
2568
9%
960
41%
960
27%
1724

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
23%5%24423346%39%
47686
Night
23%414323345%44%
47298
Cloud CoverDay
11%5%25%42445%7%45%
47684
Night
10%5%24423347%50%
47298
TransparencyDay
37%5%12%25%15%2
47384
Night
33%412%27%18%3
47103
SeeingDay
13%7%27%30%17%3
5920
Night
13%7%31%33%12%
15910

By Month

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
25%425%433335%38%
1611
16th to endDay
25%8%3431233438%
1728
February1st to 15thDay
25%7%35%322346%34%
1575
16th to endDay
23%8%35%322335%37%
1557
March1st to 15thDay
26%7%15%323435%33%
1980
16th to endDay
31%8%3442223432%
2112
April1st to 15thDay
29%6%14323335%35%
2067
16th to endDay
31%7%25%5%32335%28%
2298
May1st to 15thDay
28%5%25%423336%35%
2331
16th to endDay
29%5%14323446%32%
2430
June1st to 15thDay
23%41342435%7%39%
2439
16th to endDay
19%21332346%7%46%
2392
July1st to 15thDay
24%3134235%6%7%38%
2340
16th to endDay
21%21342345%7%41%
2466
August1st to 15thDay
15%31342446%8%45%
2340
16th to endDay
15%323413447%47%
2421
September1st to 15thDay
17%425%5%2335%6%44%
2058
16th to endDay
15%313433447%48%
1848
October1st to 15thDay
20%414312345%47%
1669
16th to endDay
18%413312245%51%
1760
November1st to 15thDay
21%2231333451%
1650
16th to endDay
29%31322222445%
1521
December1st to 15thDay
30%6%25%412335%33%
1440
16th to endDay
27%6%36%42333434%
1653
January1st to 15thNight
22%5%2442334442%
2327
16th to endNight
24%6%25%41323441%
2496
February1st to 15thNight
24%8%25%5%2333434%
2278
16th to endNight
23%5%24424335%41%
1925
March1st to 15thNight
25%5%25%32323440%
1980
16th to endNight
31%5%13413336%34%
2112
April1st to 15thNight
25%5%13422335%41%
1881
16th to endNight
30%5%2442344432%
1659
May1st to 15thNight
27%5%14322336%38%
1619
16th to endNight
27%313313338%39%
1683
June1st to 15thNight
21%213313346%47%
1512
16th to endNight
18%1121235%8%53%
1558
July1st to 15thNight
21%21231335%8%47%
1620
16th to endNight
20%213323447%45%
1702
August1st to 15thNight
12%11332346%9%51%
1620
16th to endNight
13%414212345%56%
1779
September1st to 15thNight
16%413433347%47%
1899
16th to endNight
14%213433346%52%
1857
October1st to 15thNight
21%41431333449%
1950
16th to endNight
17%33212225%56%
2112
November1st to 15thNight
20%312212235%53%
2205
16th to endNight
27%4221224448%
2436
December1st to 15thNight
28%6%1442233436%
2520
16th to endNight
28%7%25%31233437%
2568

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
10%435%5%34346%47%
1611
16th to endDay
11%9%45%313345%46%
1728
February1st to 15thDay
11%8%5%6%32335%7%40%
1575
16th to endDay
8%9%45%42335%7%43%
1557
March1st to 15thDay
12%8%26%435%5%48%39%
1980
16th to endDay
19%9%35%434335%37%
2110
April1st to 15thDay
15%7%25%424346%43%
2067
16th to endDay
18%8%35%5%33446%36%
2298
May1st to 15thDay
16%6%36%5%24446%39%
2331
16th to endDay
14%6%244245%5%8%39%
2430
June1st to 15thDay
8%424435%5%6%8%45%
2439
16th to endDay
5%2143345%6%10%52%
2392
July1st to 15thDay
9%3135%35%5%7%9%44%
2340
16th to endDay
6%2245%25%5%6%8%49%
2466
August1st to 15thDay
7%323425%46%9%48%
2340
16th to endDay
8%42442445%9%49%
2421
September1st to 15thDay
10%5%25%5%2435%6%47%
2058
16th to endDay
7%32443445%7%52%
1848
October1st to 15thDay
12%5%14322346%51%
1669
16th to endDay
12%414313345%54%
1760
November1st to 15thDay
7%323324435%59%
1650
16th to endDay
15%423322235%52%
1521
December1st to 15thDay
14%7%35%5%23446%41%
1440
16th to endDay
13%7%5%6%5%34346%38%
1653
January1st to 15thNight
7%6%345%3445%6%50%
2327
16th to endNight
8%6%36%423346%51%
2496
February1st to 15thNight
10%10%46%5%34446%39%
2278
16th to endNight
9%6%25%424446%49%
1925
March1st to 15thNight
10%5%35%325%346%48%
1980
16th to endNight
19%6%2442335%7%40%
2112
April1st to 15thNight
10%5%24424346%50%
1881
16th to endNight
17%6%24433445%42%
1659
May1st to 15thNight
13%6%25%424348%43%
1619
16th to endNight
11%4243234410%47%
1683
June1st to 15thNight
6%314325%35%9%55%
1512
16th to endNight
311221346%10%61%
1558
July1st to 15thNight
6%31231446%8%55%
1620
16th to endNight
5%21343445%9%53%
1702
August1st to 15thNight
31143345%7%10%54%
1620
16th to endNight
7%42431235%6%59%
1779
September1st to 15thNight
10%423343448%50%
1899
16th to endNight
6%313433447%56%
1857
October1st to 15thNight
13%5%24313435%52%
1950
16th to endNight
10%413312225%60%
2112
November1st to 15thNight
7%413223236%60%
2205
16th to endNight
13%41231334455%
2436
December1st to 15thNight
13%7%25%423445%44%
2520
16th to endNight
14%8%36%313345%43%
2568

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%314%25%15%1
1612
16th to endDay
39%415%25%12%1
1728
February1st to 15thDay
44%5%15%23%9%2
1576
16th to endDay
40%5%12%24%14%2
1557
March1st to 15thDay
44%5%11%23%12%2
1980
16th to endDay
50%412%20%9%1
2112
April1st to 15thDay
43%410%23%18%
2067
16th to endDay
49%5%10%22%11%
2298
May1st to 15thDay
46%5%11%23%13%
2331
16th to endDay
42%8%14%21%11%1
2434
June1st to 15thDay
34%7%14%25%15%1
2439
16th to endDay
26%7%15%29%18%2
2392
July1st to 15thDay
32%8%13%28%13%3
2201
16th to endDay
28%6%13%31%16%2
2311
August1st to 15thDay
30%8%13%27%17%2
2326
16th to endDay
32%6%11%25%18%6%
2421
September1st to 15thDay
36%5%11%23%17%5%
2058
16th to endDay
31%5%11%27%22%1
1848
October1st to 15thDay
34%49%24%23%3
1669
16th to endDay
32%311%27%21%4
1760
November1st to 15thDay
28%310%28%23%5%
1650
16th to endDay
35%39%29%19%1
1521
December1st to 15thDay
43%414%26%10%
1440
16th to endDay
46%5%12%21%12%1
1653
January1st to 15thNight
34%415%26%18%1
2327
16th to endNight
35%413%26%17%2
2496
February1st to 15thNight
45%5%11%24%11%2
2288
16th to endNight
36%412%24%18%3
1925
March1st to 15thNight
37%411%25%16%4
1980
16th to endNight
44%5%14%21%11%2
2112
April1st to 15thNight
34%410%26%21%2
1881
16th to endNight
43%5%9%24%16%1
1659
May1st to 15thNight
40%5%11%23%17%1
1620
16th to endNight
33%6%20%23%15%1
1685
June1st to 15thNight
26%6%15%32%15%3
1512
16th to endNight
18%5%13%34%23%3
1558
July1st to 15thNight
25%6%14%31%17%4
1530
16th to endNight
25%5%12%32%21%2
1594
August1st to 15thNight
23%8%14%31%18%3
1610
16th to endNight
26%49%28%23%6%
1779
September1st to 15thNight
32%5%10%25%19%7%
1899
16th to endNight
27%410%28%25%3
1857
October1st to 15thNight
36%36%23%23%6%
1950
16th to endNight
28%29%30%24%4
2112
November1st to 15thNight
26%412%25%23%7%
2205
16th to endNight
32%310%31%19%3
2436
December1st to 15thNight
41%5%12%28%12%
2520
16th to endNight
43%413%23%13%2
2568

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
24%16%38%15%4
90
16th to endDay
17%13%45%18%31
96
February1st to 15thDay
14%21%41%21%2
90
16th to endDay
12%23%41%9%11%1
81
March1st to 15thDay
21%18%41%16%2
90
16th to endDay
26%13%41%15%3
96
April1st to 15thDay
20%12%29%27%9%
186
16th to endDay
24%12%37%16%8%1
408
May1st to 15thDay
18%10%32%23%12%1
468
16th to endDay
19%7%31%26%11%2
517
June1st to 15thDay
9%5%26%35%19%4
495
16th to endDay
4332%37%16%4
495
July1st to 15thDay
12%219%36%24%4
475
16th to endDay
6%112%40%32%6%
515
August1st to 15thDay
9%114%39%30%4
493
16th to endDay
9%316%37%26%7%
461
September1st to 15thDay
8%222%37%22%7%
213
16th to endDay
12%123%44%13%6%
99
October1st to 15thDay
12%8%28%33%5%11%
90
16th to endDay
9%9%38%30%12%
96
November1st to 15thDay
7%325%41%15%6%
90
16th to endDay
35%12%37%10%4
90
December1st to 15thDay
13%20%45%12%5%3
90
16th to endDay
22%20%28%25%3
96
January1st to 15thNight
11%12%36%31%7%
900
16th to endNight
12%11%40%29%5%
960
February1st to 15thNight
16%11%37%30%3
880
16th to endNight
12%12%41%27%5%
663
March1st to 15thNight
12%10%37%31%6%
540
16th to endNight
22%10%35%26%4
576
April1st to 15thNight
14%10%39%28%6%
539
16th to endNight
21%7%36%26%7%
540
May1st to 15thNight
16%8%32%31%10%
540
16th to endNight
12%6%34%33%11%1
563
June1st to 15thNight
7%228%41%19%
540
16th to endNight
5%230%44%16%1
540
July1st to 15thNight
8%18%47%23%1
510
16th to endNight
5%15%46%29%1
564
August1st to 15thNight
311%51%31%2
539
16th to endNight
7%116%38%31%4
573
September1st to 15thNight
12%219%37%24%2
540
16th to endNight
7%223%39%24%2
504
October1st to 15thNight
15%6%29%29%17%1
630
16th to endNight
12%7%37%30%11%
704
November1st to 15thNight
9%11%31%34%12%
805
16th to endNight
15%11%36%28%7%
900
December1st to 15thNight
18%11%36%28%5%
900
16th to endNight
19%8%34%31%6%
960
Page generated at 2017-09-20 03:49:52. Version ac04

Copyright 2017 A. Danko


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