The Winter-Hawk Memorial Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Winter-Hawk Memorial Observatory clear sky chart from 2005-11-05 to 2017-09-22.

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
48%
15591
18%
46978
14%
15549
52%
15549
23%
31584

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
27%
719
17%
2327
11%
716
36%
716
15%
1688
January16th to endNight
25%
768
18%
2496
10%
768
36%
768
16%
1764
February1st to 15thNight
30%
704
17%
2166
9%
701
39%
701
18%
1492
February16th to endNight
23%
631
18%
1893
9%
631
32%
631
16%
1366
March1st to 15thNight
30%
720
19%
2029
11%
720
36%
720
21%
1409
March16th to endNight
36%
768
14%
2112
10%
768
38%
768
20%
1503
April1st to 15thNight
38%
685
20%
1943
12%
685
45%
685
26%
1247
April16th to endNight
46%
540
20%
1629
14%
540
51%
540
24%
1099
May1st to 15thNight
50%
540
15%
1620
10%
540
53%
540
22%
1098
May16th to endNight
61%
561
15%
1683
11%
561
63%
561
25%
1123
June1st to 15thNight
69%
540
13%
1620
11%
540
70%
540
26%
1072
June16th to endNight
69%
540
16%
1620
14%
540
71%
540
28%
1040
July1st to 15thNight
69%
510
9%
1530
9%
510
69%
510
23%
1067
July16th to endNight
73%
564
13%
1595
11%
531
75%
531
26%
1074
August1st to 15thNight
72%
539
16%
1609
15%
536
72%
536
25%
1087
August16th to endNight
72%
585
17%
1827
17%
585
72%
585
23%
1218
September1st to 15thNight
61%
720
17%
1980
16%
720
62%
720
25%
1364
September16th to endNight
61%
685
24%
1892
21%
685
63%
685
30%
1210
October1st to 15thNight
55%
660
29%
1876
26%
660
59%
660
33%
1138
October16th to endNight
48%
704
27%
2112
22%
704
56%
704
30%
1275
November1st to 15thNight
53%
700
26%
2243
24%
700
59%
700
30%
1323
November16th to endNight
43%
720
23%
2340
18%
720
52%
720
25%
1459
December1st to 15thNight
37%
720
17%
2340
15%
720
42%
720
17%
1643
December16th to endNight
31%
768
17%
2496
11%
768
38%
768
14%
1825

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
13%7%35%5%35%5%5%7%37%
47897
Night
13%7%35%42445%7%39%
47176
TransparencyDay
44%8%12%17%13%2
47598
Night
42%7%12%19%14%2
46979
SeeingDay
16%8%18%24%21%11%
5446
Night
16%8%20%30%20%3
15594

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
16%10%49%5%23446%31%
1611
16th to endDay
15%11%345%2445%6%36%
1728
February1st to 15thDay
16%10%5%8%5%2344433%
1693
16th to endDay
17%12%47%323346%34%
1580
March1st to 15thDay
16%11%34324346%38%
1929
16th to endDay
17%9%36%435%45%6%33%
2111
April1st to 15thDay
13%6%2442446%7%43%
2014
16th to endDay
15%5%35%5%3445%7%39%
2331
May1st to 15thDay
15%5%26%6%345%6%7%35%
2331
16th to endDay
12%6%36%6%36%6%6%8%35%
2431
June1st to 15thDay
8%5%25%6%49%7%8%9%32%
2340
16th to endDay
6%5%25%6%47%6%7%10%36%
2340
July1st to 15thDay
11%5%36%7%47%5%7%9%30%
2340
16th to endDay
10%6%26%7%37%7%8%10%29%
2465
August1st to 15thDay
9%5%25%7%5%8%7%7%10%29%
2340
16th to endDay
11%6%36%6%36%6%7%9%33%
2359
September1st to 15thDay
13%5%25%5%35%6%6%8%37%
1980
16th to endDay
14%5%344245%5%6%42%
1881
October1st to 15thDay
13%5%14323246%52%
1752
16th to endDay
16%6%23223235%50%
1760
November1st to 15thDay
13%5%13323437%51%
1613
16th to endDay
13%8%35%32435%6%45%
1620
December1st to 15thDay
15%10%25%3245%6%7%35%
1620
16th to endDay
19%11%35%414445%34%
1728
January1st to 15thNight
16%9%5%8%5%25%34434%
2327
16th to endNight
16%12%46%5%23445%34%
2496
February1st to 15thNight
15%10%46%423445%37%
2157
16th to endNight
17%11%46%5%24346%32%
1893
March1st to 15thNight
17%10%35%323445%40%
2029
16th to endNight
16%6%35%5%2446%7%36%
2112
April1st to 15thNight
12%6%2441346%8%44%
1943
16th to endNight
13%6%26%43445%7%40%
1629
May1st to 15thNight
15%6%35%43446%8%37%
1619
16th to endNight
9%425%5%35%6%9%10%37%
1682
June1st to 15thNight
7%3245%46%5%9%12%37%
1620
16th to endNight
5%5%35%6%25%46%10%44%
1620
July1st to 15thNight
9%5%35%6%36%6%7%10%34%
1620
16th to endNight
6%326%5%47%7%9%12%34%
1703
August1st to 15thNight
7%425%6%36%6%6%10%39%
1620
16th to endNight
7%425%6%37%7%8%8%38%
1827
September1st to 15thNight
12%5%36%5%35%5%6%8%38%
1980
16th to endNight
11%42433345%7%48%
1892
October1st to 15thNight
13%423413347%52%
1876
16th to endNight
13%5%24423336%51%
2112
November1st to 15thNight
14%6%23222335%51%
2243
16th to endNight
13%7%24333346%47%
2340
December1st to 15thNight
15%10%47%42445%6%34%
2340
16th to endNight
19%11%36%424445%31%
2496

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
54%49%16%11%3
1612
16th to endDay
47%49%23%12%1
1728
February1st to 15thDay
53%5%8%15%16%1
1695
16th to endDay
50%411%17%12%2
1580
March1st to 15thDay
47%5%9%19%15%3
1929
16th to endDay
50%7%11%17%10%1
2112
April1st to 15thDay
37%7%11%22%17%3
2014
16th to endDay
43%6%10%19%13%5%
2331
May1st to 15thDay
46%9%12%19%9%2
2331
16th to endDay
44%10%14%18%10%2
2435
June1st to 15thDay
43%14%17%15%8%
2340
16th to endDay
41%12%13%16%13%2
2340
July1st to 15thDay
47%13%14%12%9%1
2201
16th to endDay
45%14%16%13%8%1
2310
August1st to 15thDay
45%14%15%15%8%
2327
16th to endDay
45%11%14%16%10%1
2359
September1st to 15thDay
43%10%13%16%11%3
1980
16th to endDay
41%7%13%17%17%3
1881
October1st to 15thDay
35%5%10%20%22%5%
1752
16th to endDay
36%38%23%22%5%
1760
November1st to 15thDay
34%47%19%28%5%
1613
16th to endDay
39%5%9%22%19%4
1620
December1st to 15thDay
46%7%10%19%13%2
1620
16th to endDay
51%6%12%16%11%1
1728
January1st to 15thNight
53%5%8%14%14%2
2327
16th to endNight
52%5%8%17%14%1
2496
February1st to 15thNight
48%410%18%14%2
2166
16th to endNight
52%5%9%18%11%2
1893
March1st to 15thNight
46%6%10%18%15%3
2029
16th to endNight
47%7%13%19%10%1
2112
April1st to 15thNight
38%6%11%23%17%3
1943
16th to endNight
43%7%10%19%15%3
1629
May1st to 15thNight
42%9%15%20%10%1
1620
16th to endNight
37%12%16%22%9%1
1684
June1st to 15thNight
36%12%22%18%9%
1620
16th to endNight
34%10%16%22%12%3
1620
July1st to 15thNight
40%12%18%15%10%1
1530
16th to endNight
35%14%20%18%9%1
1595
August1st to 15thNight
37%12%17%19%11%1
1609
16th to endNight
38%12%16%22%9%
1827
September1st to 15thNight
42%8%14%18%12%3
1980
16th to endNight
35%9%11%20%21%2
1892
October1st to 15thNight
34%5%10%20%23%5%
1876
16th to endNight
35%47%22%23%6%
2112
November1st to 15thNight
35%47%19%24%8%
2243
16th to endNight
39%5%8%24%18%3
2340
December1st to 15thNight
49%7%10%16%13%3
2340
16th to endNight
54%6%9%15%12%1
2496

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%23%34%10%5%
90
16th to endDay
25%28%28%15%3
96
February1st to 15thDay
20%27%43%8%
90
16th to endDay
37%17%37%6%2
81
March1st to 15thDay
19%17%26%29%6%
219
16th to endDay
20%11%29%25%12%
288
April1st to 15thDay
16%17%15%31%15%3
270
16th to endDay
14%8%22%27%21%5%
270
May1st to 15thDay
19%12%22%22%14%9%
288
16th to endDay
16%417%24%19%16%
331
June1st to 15thDay
8%313%29%30%14%
315
16th to endDay
9%219%26%24%18%
315
July1st to 15thDay
16%117%23%21%19%
305
16th to endDay
10%18%24%31%23%
326
August1st to 15thDay
14%13%23%26%22%
313
16th to endDay
14%27%22%30%22%
332
September1st to 15thDay
14%310%20%34%15%
315
16th to endDay
16%214%24%33%10%
278
October1st to 15thDay
19%7%17%24%23%8%
255
16th to endDay
22%8%16%26%22%3
272
November1st to 15thDay
12%13%26%23%19%4
121
16th to endDay
14%13%32%26%12%1
90
December1st to 15thDay
23%23%23%25%4
90
16th to endDay
25%25%29%19%1
96
January1st to 15thNight
21%17%28%24%6%
720
16th to endNight
23%14%30%27%2
768
February1st to 15thNight
21%16%27%30%2
704
16th to endNight
23%21%29%23%2
631
March1st to 15thNight
23%13%29%29%5%
720
16th to endNight
19%12%26%29%11%
768
April1st to 15thNight
16%15%26%29%10%1
685
16th to endNight
17%6%23%35%15%1
540
May1st to 15thNight
16%7%20%35%17%1
540
16th to endNight
10%216%33%32%5%
563
June1st to 15thNight
7%111%36%35%7%
540
16th to endNight
6%111%33%39%7%
540
July1st to 15thNight
12%26%34%37%6%
510
16th to endNight
6%8%26%44%13%
564
August1st to 15thNight
7%16%30%46%7%
539
16th to endNight
9%8%31%44%6%
585
September1st to 15thNight
16%29%28%37%6%
720
16th to endNight
14%314%32%31%4
685
October1st to 15thNight
14%6%19%30%23%5%
660
16th to endNight
16%7%22%31%19%2
704
November1st to 15thNight
17%7%17%34%19%4
700
16th to endNight
17%13%22%32%13%1
720
December1st to 15thNight
21%12%23%33%9%
720
16th to endNight
25%12%25%29%6%
768
Page generated at 2017-09-23 06:43:42. Version ac04

Copyright 2017 A. Danko


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