Windy Hill 5 Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Windy Hill 5 Observatory clear sky chart from 2005-11-06 to 2024-01-15.

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
61%
24416
20%
74558
16%
24361
66%
24361
29%
46457

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
47%
758
20%
2459
16%
757
55%
757
26%
1504
January11th to 20thNight
52%
737
24%
2393
20%
737
60%
737
30%
1386
January21st to endNight
42%
792
23%
2385
16%
792
50%
792
26%
1529
February1st to 10thNight
45%
720
22%
2160
16%
720
52%
720
31%
1322
February11th to 20thNight
54%
700
23%
2099
16%
700
60%
700
35%
1194
February21st to endNight
58%
592
28%
1736
21%
592
65%
592
37%
1001
March1st to 10thNight
52%
720
31%
1980
19%
720
62%
720
48%
1050
March11th to 20thNight
57%
720
28%
1980
17%
720
64%
720
40%
1136
March21st to endNight
57%
792
30%
2178
21%
792
63%
792
42%
1215
April1st to 10thNight
60%
720
23%
1980
16%
720
65%
720
43%
1105
April11th to 20thNight
54%
711
20%
1953
13%
711
60%
711
37%
1168
April21st to endNight
61%
698
30%
1842
20%
698
66%
698
47%
1052
May1st to 10thNight
76%
540
32%
1620
26%
540
81%
540
54%
780
May11th to 20thNight
68%
531
18%
1592
13%
531
71%
531
33%
970
May21st to endNight
75%
582
24%
1745
20%
582
76%
582
37%
1018
June1st to 10thNight
72%
540
14%
1620
13%
540
73%
540
27%
1081
June11th to 20thNight
80%
540
12%
1620
10%
540
81%
540
30%
1022
June21st to endNight
77%
540
10%
1620
9%
540
77%
540
24%
1121
July1st to 10thNight
75%
525
6%
1575
6%
525
75%
525
21%
1134
July11th to 20thNight
77%
522
4%
1566
5%
522
77%
522
19%
1159
July21st to endNight
78%
591
7%
1672
8%
558
79%
558
23%
1172
August1st to 10thNight
80%
537
3%
1657
4%
534
80%
534
25%
1135
August11th to 20thNight
75%
534
6%
1776
6%
534
75%
534
20%
1254
August21st to endNight
65%
769
8%
2155
8%
769
66%
769
17%
1635
September1st to 10thNight
71%
720
7%
1980
8%
720
71%
720
20%
1449
September11th to 20thNight
66%
720
7%
1980
7%
720
67%
720
19%
1465
September21st to endNight
65%
720
15%
1980
14%
720
66%
720
22%
1419
October1st to 10thNight
63%
720
20%
1980
18%
720
67%
720
28%
1309
October11th to 20thNight
66%
720
27%
2097
26%
720
70%
720
35%
1238
October21st to endNight
58%
792
26%
2376
25%
792
63%
792
34%
1391
November1st to 10thNight
55%
740
26%
2221
20%
740
64%
740
36%
1276
November11th to 20thNight
54%
760
27%
2280
22%
760
61%
760
33%
1370
November21st to endNight
54%
760
25%
2427
22%
760
60%
760
31%
1435
December1st to 10thNight
56%
760
25%
2470
21%
760
64%
760
31%
1421
December11th to 20thNight
54%
760
24%
2939
21%
758
60%
758
25%
1695
December21st to endNight
52%
833
15%
4465
23%
817
57%
817
15%
2846

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
7%425%6%46%6%7%10%42%
74843
Night
7%5%25%5%35%6%7%10%44%
74935
TransparencyDay
34%11%18%19%13%4
74566
Night
33%10%18%20%14%5%
74731
SeeingDay
8%418%28%27%16%
14324
Night
8%418%33%28%10%
24426

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
9%5%36%5%25%6%6%9%44%
1706
11th to 20thDay
7%5%25%435%5%6%10%49%
1656
21st to endDay
11%5%36%5%2446%7%47%
1967
February1st to 10thDay
10%5%26%435%5%6%8%45%
1800
11th to 20thDay
5%5%2442445%8%57%
1748
21st to endDay
8%32443346%8%54%
1519
March1st to 10thDay
331333445%9%61%
1980
11th to 20thDay
6%31332446%8%59%
1980
21st to endDay
7%3234235%5%9%57%
2178
April1st to 10thDay
6%214435%5%6%10%53%
1980
11th to 20thDay
8%425%6%35%5%6%9%47%
1956
21st to endDay
42144346%6%8%59%
2131
May1st to 10thDay
321232346%11%63%
2340
11th to 20thDay
8%4245%35%6%7%10%46%
2301
21st to endDay
5%4245%36%7%8%10%43%
2531
June1st to 10thDay
10%6%36%6%46%7%8%11%33%
2340
11th to 20thDay
6%5%25%6%5%8%7%10%14%33%
2340
21st to endDay
7%436%7%48%9%10%11%31%
2340
July1st to 10thDay
9%426%6%5%9%10%11%12%27%
2340
11th to 20thDay
5%427%9%6%9%10%10%11%26%
2340
21st to endDay
6%5%37%8%6%9%10%9%13%24%
2547
August1st to 10thDay
6%426%8%6%9%9%11%13%26%
2264
11th to 20thDay
6%5%37%8%6%9%10%10%13%24%
2125
21st to endDay
9%6%36%8%6%8%8%10%13%24%
2182
September1st to 10thDay
7%5%36%8%5%9%9%10%12%27%
1980
11th to 20thDay
9%5%46%7%5%8%8%8%12%29%
1980
21st to endDay
7%5%27%7%47%7%9%12%34%
1980
October1st to 10thDay
7%5%27%8%5%5%7%7%9%39%
1980
11th to 20thDay
6%4245%45%5%6%9%50%
1860
21st to endDay
7%5%24435%5%5%9%51%
1980
November1st to 10thDay
7%425%4345%6%8%52%
1857
11th to 20thDay
8%5%25%5%35%5%5%8%49%
1900
21st to endDay
8%5%24445%5%5%9%49%
1748
December1st to 10thDay
6%425%445%5%5%11%47%
1710
11th to 20thDay
9%5%45%5%35%46%7%46%
2153
21st to endDay
11%8%38%8%45%5%5%7%36%
3124
January1st to 10thNight
9%6%26%6%35%5%5%10%42%
2459
11th to 20thNight
8%6%25%5%35%46%9%46%
2393
21st to endNight
12%5%35%6%35%5%6%7%43%
2385
February1st to 10thNight
10%7%36%5%2445%8%46%
2160
11th to 20thNight
9%5%2442445%7%52%
2098
21st to endNight
6%4245%35%6%7%8%50%
1736
March1st to 10thNight
42134345%5%8%60%
1980
11th to 20thNight
6%4245%345%7%9%53%
1980
21st to endNight
5%425%4345%47%57%
2178
April1st to 10thNight
5%3145%245%6%9%55%
1980
11th to 20thNight
6%4245%347%6%10%49%
1953
21st to endNight
4324435%5%5%9%57%
1842
May1st to 10thNight
211332446%9%65%
1620
11th to 20thNight
6%5%25%6%45%5%6%9%47%
1592
21st to endNight
4335%6%35%47%9%52%
1744
June1st to 10thNight
10%5%36%5%45%5%7%11%39%
1620
11th to 20thNight
5%4245%5%5%7%9%14%41%
1620
21st to endNight
7%5%25%5%46%7%8%14%36%
1620
July1st to 10thNight
6%5%36%5%47%8%9%14%34%
1620
11th to 20thNight
4427%6%5%7%8%11%14%31%
1620
21st to endNight
4437%7%48%8%10%13%32%
1771
August1st to 10thNight
4425%5%47%8%11%15%35%
1668
11th to 20thNight
5%5%26%7%47%9%9%14%31%
1776
21st to endNight
9%5%37%7%5%7%8%9%12%28%
2155
September1st to 10thNight
45%36%8%5%8%8%9%14%31%
1980
11th to 20thNight
8%5%37%8%6%7%7%7%12%29%
1980
21st to endNight
8%6%37%7%5%7%6%7%11%32%
1980
October1st to 10thNight
6%5%35%6%46%6%8%9%41%
1980
11th to 20thNight
7%5%345%35%45%9%51%
2097
21st to endNight
8%5%245%345%7%9%48%
2376
November1st to 10thNight
6%325%5%35%5%5%9%51%
2221
11th to 20thNight
8%6%35%5%3445%8%49%
2280
21st to endNight
8%445%5%35%5%5%9%47%
2427
December1st to 10thNight
7%435%5%35%6%6%8%48%
2470
11th to 20thNight
12%5%25%5%345%5%8%46%
3042
21st to endNight
13%8%37%6%46%5%6%8%34%
4532

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
34%7%13%24%15%7%
1707
11th to 20thDay
30%6%10%27%20%7%
1656
21st to endDay
36%6%9%19%23%7%
1967
February1st to 10thDay
35%7%12%20%17%9%
1800
11th to 20thDay
25%6%13%20%27%9%
1758
21st to endDay
27%6%14%19%27%7%
1519
March1st to 10thDay
21%6%13%27%26%8%
1980
11th to 20thDay
22%6%15%30%18%8%
1980
21st to endDay
24%5%13%28%23%6%
2178
April1st to 10thDay
25%9%21%23%18%6%
1980
11th to 20thDay
32%8%16%18%22%5%
1956
21st to endDay
21%7%15%26%26%5%
2131
May1st to 10thDay
16%5%18%29%24%8%
2340
11th to 20thDay
30%10%19%22%17%2
2305
21st to endDay
32%11%17%23%15%2
2531
June1st to 10thDay
40%13%24%18%4
2340
11th to 20thDay
36%14%28%19%3
2340
21st to endDay
39%17%27%14%3
2340
July1st to 10thDay
41%20%30%7%2
2275
11th to 20thDay
45%19%27%8%1
2271
21st to endDay
43%19%27%11%1
2405
August1st to 10thDay
40%21%31%8%
2251
11th to 20thDay
42%22%27%8%
2125
21st to endDay
46%18%25%10%1
2182
September1st to 10thDay
44%18%26%12%1
1980
11th to 20thDay
45%14%25%13%3
1980
21st to endDay
39%14%19%18%8%2
1980
October1st to 10thDay
38%11%14%17%13%7%
1980
11th to 20thDay
30%8%11%23%24%4
1860
21st to endDay
29%6%13%21%20%11%
1980
November1st to 10thDay
28%7%13%23%18%10%
1857
11th to 20thDay
33%6%11%22%20%7%
1900
21st to endDay
31%7%14%21%19%7%
1748
December1st to 10thDay
32%7%15%26%16%4
1710
11th to 20thDay
35%6%12%19%17%11%
2150
21st to endDay
45%8%12%18%14%3
3124
January1st to 10thNight
37%6%13%22%15%6%
2459
11th to 20thNight
34%6%11%24%19%6%
2393
21st to endNight
39%6%11%18%18%7%
2385
February1st to 10thNight
36%5%12%19%20%8%
2160
11th to 20thNight
29%6%11%20%23%10%
2099
21st to endNight
29%7%13%20%25%6%
1736
March1st to 10thNight
20%7%13%30%23%7%
1980
11th to 20thNight
26%7%15%27%18%7%
1980
21st to endNight
26%6%12%27%23%6%
2178
April1st to 10thNight
24%7%21%27%15%6%
1980
11th to 20thNight
27%10%17%21%21%4
1953
21st to endNight
23%7%13%27%26%4
1842
May1st to 10thNight
16%6%14%31%24%9%
1620
11th to 20thNight
31%10%20%23%16%1
1593
21st to endNight
28%9%18%26%19%1
1745
June1st to 10thNight
38%10%24%21%6%
1620
11th to 20thNight
30%13%30%22%4
1620
21st to endNight
35%17%28%14%6%
1620
July1st to 10thNight
36%20%32%10%2
1575
11th to 20thNight
38%22%31%9%1
1566
21st to endNight
35%18%34%11%1
1672
August1st to 10thNight
32%19%37%10%1
1657
11th to 20thNight
37%20%33%10%
1776
21st to endNight
44%18%23%12%2
2155
September1st to 10thNight
38%20%26%14%2
1980
11th to 20thNight
46%14%25%13%2
1980
21st to endNight
42%13%19%16%8%1
1980
October1st to 10thNight
34%13%15%18%14%6%
1980
11th to 20thNight
30%8%13%23%22%4
2097
21st to endNight
31%7%13%19%21%9%
2376
November1st to 10thNight
28%8%14%20%19%10%
2221
11th to 20thNight
33%7%12%22%19%8%
2280
21st to endNight
32%8%12%23%18%7%
2427
December1st to 10thNight
31%8%14%28%17%3
2470
11th to 20thNight
34%7%10%21%18%10%
3044
21st to endNight
43%10%13%16%14%3
4532

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
11%12%37%30%9%
270
11th to 20thDay
9%12%33%33%12%2
252
21st to endDay
14%11%45%25%5%
264
February1st to 10thDay
7%12%33%33%14%1
240
11th to 20thDay
6%6%35%33%18%3
240
21st to endDay
6%10%28%37%16%2
237
March1st to 10thDay
5%7%41%34%13%1
420
11th to 20thDay
8%8%30%32%20%2
420
21st to endDay
6%8%32%34%18%3
462
April1st to 10thDay
5%7%34%34%18%2
420
11th to 20thDay
8%8%26%37%16%3
412
21st to endDay
5%423%39%25%5%
420
May1st to 10thDay
4421%39%24%8%
423
11th to 20thDay
9%316%34%30%10%
447
21st to endDay
6%111%27%36%19%
485
June1st to 10thDay
15%38%26%30%17%
450
11th to 20thDay
7%17%26%34%25%
450
21st to endDay
5%15%15%35%40%
450
July1st to 10thDay
6%129%39%42%
445
11th to 20thDay
41313%39%41%
444
21st to endDay
10%15%12%37%34%
488
August1st to 10thDay
7%1213%38%38%
446
11th to 20thDay
7%1411%35%41%
439
21st to endDay
8%16%15%35%34%
495
September1st to 10thDay
9%1416%34%36%
450
11th to 20thDay
10%1425%34%27%
450
21st to endDay
6%15%23%38%27%
450
October1st to 10thDay
8%414%34%32%8%
450
11th to 20thDay
8%217%33%30%10%
450
21st to endDay
8%317%38%28%5%
495
November1st to 10thDay
8%5%19%35%28%5%
455
11th to 20thDay
12%6%23%36%20%4
460
21st to endDay
8%6%27%36%20%3
308
December1st to 10thDay
6%9%29%35%16%4
270
11th to 20thDay
8%7%36%31%17%1
270
21st to endDay
5%11%29%36%15%3
297
January1st to 10thNight
11%8%26%37%16%1
760
11th to 20thNight
12%7%23%40%17%1
737
21st to endNight
12%11%29%36%13%
792
February1st to 10thNight
13%6%30%34%16%
720
11th to 20thNight
10%8%22%39%20%1
703
21st to endNight
8%423%47%18%1
592
March1st to 10thNight
5%6%34%43%12%1
720
11th to 20thNight
6%6%25%41%21%1
720
21st to endNight
6%425%42%21%2
792
April1st to 10thNight
5%7%24%43%20%1
720
11th to 20thNight
7%5%26%43%17%2
711
21st to endNight
5%325%46%20%1
698
May1st to 10thNight
3114%45%33%4
540
11th to 20thNight
7%213%40%32%6%
531
21st to endNight
5%19%35%42%8%
584
June1st to 10thNight
11%1424%45%14%
540
11th to 20thNight
6%2416%45%28%
540
21st to endNight
7%1411%43%34%
540
July1st to 10thNight
7%47%43%39%
525
11th to 20thNight
439%40%43%
522
21st to endNight
41310%45%37%
591
August1st to 10thNight
41211%45%37%
537
11th to 20thNight
6%39%37%44%
534
21st to endNight
11%15%19%38%25%
769
September1st to 10thNight
6%15%18%44%25%
720
11th to 20thNight
9%27%25%39%18%
720
21st to endNight
10%18%28%39%14%
720
October1st to 10thNight
10%115%37%32%6%
720
11th to 20thNight
8%414%37%34%4
720
21st to endNight
9%420%39%25%3
792
November1st to 10thNight
7%327%40%20%3
740
11th to 20thNight
9%5%23%40%22%2
760
21st to endNight
8%5%26%42%18%1
760
December1st to 10thNight
8%5%23%38%24%2
760
11th to 20thNight
10%6%24%37%21%3
760
21st to endNight
10%7%24%38%21%1
836
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