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 2005-11-06 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
41%
24497
23%
74775
14%
24436
50%
24436
31%
44765

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
33%
950
23%
2458
9%
946
43%
946
33%
1550
January11th to 20thNight
31%
910
24%
2366
10%
910
40%
910
29%
1563
January21st to endNight
28%
990
23%
2574
8%
990
37%
990
28%
1695
February1st to 10thNight
26%
900
17%
2340
5%
900
33%
900
25%
1601
February11th to 20thNight
27%
852
19%
2247
6%
848
35%
848
27%
1478
February21st to endNight
26%
579
26%
1763
8%
579
41%
579
28%
1079
March1st to 10thNight
28%
540
26%
1980
12%
540
45%
540
25%
1119
March11th to 20thNight
30%
540
20%
1980
13%
540
41%
540
22%
1201
March21st to endNight
24%
594
14%
2178
8%
594
33%
594
16%
1469
April1st to 10thNight
28%
540
21%
1926
12%
540
44%
540
28%
1060
April11th to 20thNight
28%
533
23%
1748
12%
533
44%
533
25%
1064
April21st to endNight
29%
540
22%
1620
12%
540
44%
540
25%
1042
May1st to 10thNight
34%
540
17%
1620
12%
540
42%
540
24%
1062
May11th to 20thNight
42%
531
20%
1594
16%
531
50%
531
31%
974
May21st to endNight
46%
584
17%
1746
12%
582
52%
582
31%
1062
June1st to 10thNight
62%
540
23%
1550
15%
540
66%
540
43%
843
June11th to 20thNight
57%
540
23%
1440
13%
540
62%
540
42%
844
June21st to endNight
55%
540
24%
1618
15%
540
61%
540
47%
823
July1st to 10thNight
69%
525
18%
1575
15%
525
72%
525
40%
875
July11th to 20thNight
73%
522
24%
1566
21%
522
76%
522
51%
764
July21st to endNight
68%
591
25%
1673
24%
558
71%
558
39%
936
August1st to 10thNight
72%
537
22%
1601
23%
534
76%
534
41%
865
August11th to 20thNight
69%
534
29%
1600
31%
534
74%
534
42%
873
August21st to endNight
70%
594
29%
1872
33%
594
73%
594
44%
961
September1st to 10thNight
60%
540
27%
1858
27%
540
66%
540
35%
1000
September11th to 20thNight
60%
540
28%
1980
27%
540
69%
540
36%
1017
September21st to endNight
57%
540
31%
1980
28%
540
65%
540
37%
985
October1st to 10thNight
48%
669
26%
2109
20%
669
53%
669
33%
1213
October11th to 20thNight
33%
720
30%
2160
13%
720
46%
720
37%
1206
October21st to endNight
34%
792
27%
2376
13%
792
44%
792
31%
1402
November1st to 10thNight
43%
811
32%
2291
15%
811
55%
811
41%
1240
November11th to 20thNight
34%
950
28%
2470
9%
950
47%
950
39%
1451
November21st to endNight
36%
950
25%
2622
11%
950
46%
950
35%
1563
December1st to 10thNight
34%
950
22%
2660
9%
950
44%
950
30%
1656
December11th to 20thNight
30%
949
23%
3120
8%
948
40%
948
23%
1931
December21st to endNight
26%
1040
16%
4514
9%
1026
39%
1026
14%
3298

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%6%35%5%3445%7%46%
74518
Night
11%6%35%43445%7%50%
75188
TransparencyDay
38%6%12%25%17%3
74241
Night
35%5%11%27%19%4
74985
SeeingDay
13%9%29%29%15%3
14507
Night
13%9%33%34%11%1
24503

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 10thDay
12%7%36%5%3445%7%45%
1707
11th to 20thDay
12%9%5%6%5%33446%44%
1634
21st to endDay
10%8%5%7%5%3445%7%41%
1782
February1st to 10thDay
13%10%47%5%33446%42%
1620
11th to 20thDay
10%9%5%5%5%3446%8%41%
1615
21st to endDay
9%10%36%43436%7%44%
1493
March1st to 10thDay
11%7%37%5%345%47%45%
1980
11th to 20thDay
21%10%25%324447%38%
1980
21st to endDay
17%11%46%6%4445%6%33%
2178
April1st to 10thDay
14%6%35%43435%7%47%
2034
11th to 20thDay
14%7%36%5%345%47%42%
2159
21st to endDay
19%7%36%5%44446%39%
2340
May1st to 10thDay
18%7%37%6%24447%38%
2340
11th to 20thDay
15%7%36%435%5%6%7%41%
2302
21st to endDay
15%8%35%5%35%6%6%8%36%
2531
June1st to 10thDay
6%4245%36%6%6%10%50%
2398
11th to 20thDay
7%5%25%5%35%5%6%9%50%
2508
21st to endDay
6%425%43446%10%52%
2340
July1st to 10thDay
9%4145%35%6%7%9%46%
2340
11th to 20thDay
43245%35%6%7%9%53%
2340
21st to endDay
7%435%5%35%47%8%49%
2546
August1st to 10thDay
8%4245%35%6%7%10%46%
2328
11th to 20thDay
8%5%345%3445%8%52%
2301
21st to endDay
8%42442445%9%55%
2482
September1st to 10thDay
12%42443435%7%52%
2099
11th to 20thDay
9%5%26%5%3446%7%49%
1980
21st to endDay
8%423424447%56%
1980
October1st to 10thDay
12%5%2442345%7%52%
1832
11th to 20thDay
11%5%25%42334458%
1800
21st to endDay
15%6%24323346%51%
1980
November1st to 10thDay
8%424433446%58%
1782
11th to 20thDay
12%5%2433334457%
1710
21st to endDay
15%6%34333346%51%
1554
December1st to 10thDay
9%5%36%5%3445%7%48%
1520
11th to 20thDay
11%8%47%7%34445%44%
1918
21st to endDay
15%13%8%11%6%34445%26%
3085
January1st to 10thNight
7%8%36%5%2445%7%49%
2458
11th to 20thNight
11%8%5%6%43445%6%45%
2366
21st to endNight
10%7%37%6%34446%46%
2574
February1st to 10thNight
10%12%46%5%4345%7%41%
2340
11th to 20thNight
11%7%37%5%24447%44%
2246
21st to endNight
11%7%25%5%345%5%5%49%
1763
March1st to 10thNight
11%6%35%33445%6%50%
1980
11th to 20thNight
15%6%35%5%35%35%6%44%
1980
21st to endNight
21%8%35%43445%7%36%
2178
April1st to 10thNight
10%5%2442445%6%53%
1926
11th to 20thNight
13%7%35%5%34447%46%
1748
21st to endNight
16%6%35%4335%5%6%44%
1620
May1st to 10thNight
15%7%25%5%35%45%8%41%
1620
11th to 20thNight
14%5%24434348%49%
1593
21st to endNight
10%6%35%4245%5%9%47%
1745
June1st to 10thNight
431442445%9%58%
1550
11th to 20thNight
6%324435%46%9%54%
1440
21st to endNight
431342345%10%60%
1618
July1st to 10thNight
7%4234345%6%8%55%
1620
11th to 20thNight
21234245%6%10%61%
1620
21st to endNight
6%424435%45%11%51%
1772
August1st to 10thNight
32244345%7%10%55%
1611
11th to 20thNight
5%5%25%33435%7%58%
1600
21st to endNight
6%32432345%7%62%
1872
September1st to 10thNight
11%423333347%56%
1858
11th to 20thNight
9%42333445%8%55%
1980
21st to endNight
7%424433446%61%
1980
October1st to 10thNight
12%5%25%424445%54%
2109
11th to 20thNight
13%414423335%58%
2160
21st to endNight
14%7%24323335%54%
2376
November1st to 10thNight
8%424323345%63%
2291
11th to 20thNight
10%5%23424446%57%
2470
21st to endNight
13%6%2332335%6%54%
2622
December1st to 10thNight
9%7%344345%5%6%49%
2660
11th to 20thNight
11%7%36%5%3445%5%47%
3279
21st to endNight
18%14%6%8%5%2333433%
4563

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
40%412%26%16%2
1708
11th to 20thDay
43%414%25%14%1
1634
21st to endDay
43%5%16%24%12%1
1782
February1st to 10thDay
46%5%13%22%11%3
1620
11th to 20thDay
42%6%12%25%13%2
1624
21st to endDay
40%412%24%17%3
1493
March1st to 10thDay
41%411%23%16%4
1980
11th to 20thDay
48%49%22%15%3
1980
21st to endDay
52%6%14%18%8%2
2178
April1st to 10thDay
39%412%23%20%3
2034
11th to 20thDay
43%5%12%23%16%1
2159
21st to endDay
47%5%10%26%11%1
2340
May1st to 10thDay
48%6%11%21%14%1
2340
11th to 20thDay
42%7%14%24%13%
2306
21st to endDay
45%8%13%22%9%2
2531
June1st to 10thDay
27%9%16%30%17%2
2398
11th to 20thDay
31%7%13%29%18%2
2508
21st to endDay
28%7%14%30%17%4
2340
July1st to 10thDay
32%8%13%27%16%4
2276
11th to 20thDay
25%8%15%26%20%5%
2271
21st to endDay
30%6%13%32%16%2
2405
August1st to 10thDay
31%11%14%28%15%2
2314
11th to 20thDay
32%6%10%32%19%2
2301
21st to endDay
28%6%11%26%22%7%
2482
September1st to 10thDay
32%5%12%26%18%7%
2099
11th to 20thDay
34%6%10%25%22%3
1980
21st to endDay
29%5%9%29%25%3
1980
October1st to 10thDay
32%5%11%27%22%3
1832
11th to 20thDay
32%47%25%27%6%
1800
21st to endDay
37%310%25%20%6%
1980
November1st to 10thDay
30%412%29%20%5%
1782
11th to 20thDay
33%49%28%23%4
1710
21st to endDay
37%49%26%22%2
1554
December1st to 10thDay
35%5%14%31%14%1
1520
11th to 20thDay
44%5%12%25%13%1
1915
21st to endDay
61%5%9%17%8%1
3085
January1st to 10thNight
35%414%26%18%2
2458
11th to 20thNight
40%412%26%16%2
2366
21st to endNight
40%5%14%25%14%2
2574
February1st to 10thNight
45%5%11%22%15%3
2340
11th to 20thNight
41%411%24%16%4
2247
21st to endNight
38%49%23%20%7%
1763
March1st to 10thNight
36%49%26%20%5%
1980
11th to 20thNight
41%5%12%23%15%4
1980
21st to endNight
49%6%12%19%11%3
2178
April1st to 10thNight
33%411%25%23%4
1926
11th to 20thNight
38%6%9%26%18%3
1748
21st to endNight
41%5%11%26%16%1
1620
May1st to 10thNight
43%6%13%21%16%2
1620
11th to 20thNight
36%5%14%26%18%1
1594
21st to endNight
35%6%19%25%12%2
1746
June1st to 10thNight
23%7%17%35%16%3
1550
11th to 20thNight
26%7%12%32%19%4
1440
21st to endNight
20%6%14%34%22%4
1618
July1st to 10thNight
27%6%15%30%18%4
1575
11th to 20thNight
17%7%15%33%24%5%
1566
21st to endNight
27%6%11%33%21%1
1673
August1st to 10thNight
22%9%17%35%15%3
1601
11th to 20thNight
25%6%11%33%23%3
1600
21st to endNight
23%6%11%30%24%7%
1872
September1st to 10thNight
30%49%28%20%8%
1858
11th to 20thNight
28%411%26%25%5%
1980
21st to endNight
26%48%26%31%4
1980
October1st to 10thNight
34%48%25%25%5%
2109
11th to 20thNight
31%36%27%24%9%
2160
21st to endNight
36%38%22%26%4
2376
November1st to 10thNight
25%411%28%25%7%
2291
11th to 20thNight
29%411%28%24%4
2470
21st to endNight
33%310%29%21%3
2622
December1st to 10thNight
36%5%12%28%17%1
2660
11th to 20thNight
39%5%9%30%16%1
3281
21st to endNight
56%48%21%9%2
4563

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
20%16%34%23%8%
270
11th to 20thDay
22%16%41%18%2
245
21st to endDay
12%13%51%22%2
264
February1st to 10thDay
20%20%41%16%3
240
11th to 20thDay
18%19%44%13%7%
240
21st to endDay
15%24%41%16%31
198
March1st to 10thDay
16%20%41%20%3
240
11th to 20thDay
27%13%35%20%5%
240
21st to endDay
28%20%39%11%11
264
April1st to 10thDay
22%16%34%23%5%
294
11th to 20thDay
18%15%38%23%5%1
437
21st to endDay
22%15%36%18%9%1
600
May1st to 10thDay
17%14%37%23%8%1
603
11th to 20thDay
19%9%30%28%12%2
625
21st to endDay
19%8%31%25%14%3
679
June1st to 10thDay
5%6%22%33%28%6%
630
11th to 20thDay
6%429%38%18%5%
630
21st to endDay
7%6%33%41%11%2
630
July1st to 10thDay
10%315%32%31%9%
621
11th to 20thDay
4317%41%28%7%
618
21st to endDay
7%317%40%27%6%
684
August1st to 10thDay
8%217%40%29%4
626
11th to 20thDay
8%218%42%25%5%
615
21st to endDay
10%215%33%32%7%
601
September1st to 10thDay
13%219%36%25%5%
389
11th to 20thDay
6%422%39%25%5%
270
21st to endDay
14%7%27%35%14%3
270
October1st to 10thDay
17%7%29%27%15%6%
270
11th to 20thDay
9%16%45%20%9%1
270
21st to endDay
20%15%34%23%7%1
297
November1st to 10thDay
13%12%36%29%10%1
270
11th to 20thDay
15%16%36%25%7%1
270
21st to endDay
22%9%38%22%8%1
270
December1st to 10thDay
8%15%40%27%7%2
270
11th to 20thDay
19%14%37%23%7%
270
21st to endDay
19%22%37%21%1
297
January1st to 10thNight
12%12%38%31%7%
950
11th to 20thNight
15%13%35%31%5%1
910
21st to endNight
13%12%41%29%5%
990
February1st to 10thNight
17%13%40%27%4
900
11th to 20thNight
15%13%40%30%3
852
21st to endNight
15%13%42%24%6%
579
March1st to 10thNight
14%13%42%26%6%
540
11th to 20thNight
19%11%35%28%6%1
540
21st to endNight
23%13%38%23%4
594
April1st to 10thNight
13%12%44%26%5%
540
11th to 20thNight
16%13%39%26%6%
533
21st to endNight
19%10%39%25%6%1
540
May1st to 10thNight
17%9%35%32%6%1
540
11th to 20thNight
15%8%31%35%11%
531
21st to endNight
11%7%32%34%15%1
584
June1st to 10thNight
5%225%43%24%1
540
11th to 20thNight
6%329%44%16%1
540
21st to endNight
5%432%46%12%1
540
July1st to 10thNight
8%214%45%30%1
525
11th to 20thNight
2218%52%26%2
522
21st to endNight
7%116%49%27%1
591
August1st to 10thNight
3118%50%27%2
537
11th to 20thNight
6%116%47%27%3
534
21st to endNight
6%215%42%32%3
594
September1st to 10thNight
13%221%42%20%2
540
11th to 20thNight
9%223%42%21%3
540
21st to endNight
8%426%44%18%1
540
October1st to 10thNight
14%6%29%33%17%1
669
11th to 20thNight
14%10%40%28%8%
720
21st to endNight
18%10%35%27%9%
792
November1st to 10thNight
9%10%34%35%12%
811
11th to 20thNight
12%12%39%30%7%
950
21st to endNight
16%11%34%31%7%
950
December1st to 10thNight
13%11%38%31%6%1
950
11th to 20thNight
18%9%38%30%5%
950
21st to endNight
18%14%38%27%4
1045
Page generated at 2024-01-09 15:24:24. Version ac07

Copyright 2024 Attilla Danko


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