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 2019-06-19.

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
47%
17909
18%
53993
14%
17867
52%
17867
22%
36516

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%
839
17%
2717
11%
836
36%
836
15%
1978
January16th to endNight
27%
896
18%
2912
11%
896
37%
896
17%
2024
February1st to 15thNight
30%
824
17%
2535
10%
821
38%
821
17%
1779
February16th to endNight
23%
735
17%
2205
9%
735
31%
735
15%
1608
March1st to 15thNight
29%
840
18%
2367
11%
840
35%
840
20%
1670
March16th to endNight
36%
896
14%
2464
10%
896
39%
896
20%
1757
April1st to 15thNight
38%
800
20%
2268
13%
800
44%
800
25%
1467
April16th to endNight
46%
624
19%
1881
13%
624
51%
624
23%
1264
May1st to 15thNight
53%
630
16%
1890
11%
630
56%
630
23%
1267
May16th to endNight
62%
657
15%
1971
11%
657
63%
657
24%
1321
June1st to 15thNight
68%
630
13%
1890
11%
630
70%
630
25%
1255
June16th to endNight
69%
597
15%
1791
13%
597
70%
597
27%
1168
July1st to 15thNight
70%
555
10%
1665
10%
555
70%
555
23%
1156
July16th to endNight
72%
612
12%
1739
10%
579
73%
579
24%
1191
August1st to 15thNight
72%
575
16%
1715
15%
572
72%
572
25%
1157
August16th to endNight
72%
634
16%
1980
16%
634
73%
634
24%
1317
September1st to 15thNight
61%
780
16%
2145
15%
780
62%
780
25%
1489
September16th to endNight
62%
777
24%
2145
21%
777
64%
777
29%
1384
October1st to 15thNight
56%
780
27%
2218
24%
780
60%
780
33%
1352
October16th to endNight
48%
832
27%
2496
23%
832
56%
832
30%
1508
November1st to 15thNight
51%
820
24%
2627
23%
820
57%
820
27%
1622
November16th to endNight
45%
840
24%
2730
19%
840
53%
840
26%
1689
December1st to 15thNight
35%
840
16%
2730
14%
840
40%
840
16%
1943
December16th to endNight
32%
896
15%
2912
10%
896
38%
896
14%
2150

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%6%7%36%
54721
Night
13%7%35%5%2445%7%39%
54191
TransparencyDay
45%8%12%17%13%2
54422
Night
43%7%12%19%14%2
53994
SeeingDay
17%9%20%23%19%9%
7719
Night
17%8%19%30%20%3
17912

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%
1881
16th to endDay
15%11%35%5%24446%36%
2016
February1st to 15thDay
18%10%48%5%2444432%
1983
16th to endDay
19%12%37%323345%32%
1840
March1st to 15thDay
17%11%34324345%36%
2251
16th to endDay
16%9%36%425%45%7%34%
2463
April1st to 15thDay
13%6%244245%6%7%42%
2351
16th to endDay
15%6%25%5%3445%7%39%
2684
May1st to 15thDay
14%5%26%6%346%7%7%35%
2721
16th to endDay
12%5%35%6%35%5%6%8%35%
2847
June1st to 15thDay
8%5%25%7%48%6%7%9%33%
2730
16th to endDay
6%425%6%5%7%6%7%10%35%
2577
July1st to 15thDay
11%5%36%7%47%5%8%9%30%
2535
16th to endDay
9%6%27%7%48%6%8%10%28%
2673
August1st to 15thDay
10%5%25%7%48%7%8%10%29%
2487
16th to endDay
10%6%35%6%35%6%7%10%33%
2557
September1st to 15thDay
12%5%25%5%35%6%6%8%36%
2145
16th to endDay
14%5%35%5%345%5%6%41%
2145
October1st to 15thDay
13%414323246%50%
2070
16th to endDay
16%6%13223235%50%
2080
November1st to 15thDay
15%5%14324437%46%
1889
16th to endDay
12%8%35%32435%6%46%
1890
December1st to 15thDay
16%11%36%3245%5%6%34%
1890
16th to endDay
19%11%35%5%24445%33%
2016
January1st to 15thNight
16%9%5%8%5%2434433%
2717
16th to endNight
16%12%46%5%2344435%
2912
February1st to 15thNight
17%10%46%423445%36%
2526
16th to endNight
19%10%46%5%24346%31%
2205
March1st to 15thNight
18%10%25%423445%38%
2367
16th to endNight
16%7%35%5%2446%7%35%
2464
April1st to 15thNight
13%6%2441446%8%43%
2268
16th to endNight
14%6%26%43445%7%40%
1881
May1st to 15thNight
14%5%25%5%3446%9%38%
1889
16th to endNight
9%426%5%35%5%8%10%36%
1970
June1st to 15thNight
7%4245%46%5%8%12%37%
1890
16th to endNight
5%5%35%6%36%5%6%10%42%
1791
July1st to 15thNight
9%435%6%36%6%8%10%34%
1755
16th to endNight
6%326%6%37%7%8%12%34%
1847
August1st to 15thNight
8%425%6%36%6%6%10%39%
1726
16th to endNight
7%425%6%47%7%8%9%37%
1980
September1st to 15thNight
12%5%26%5%35%5%6%8%38%
2145
16th to endNight
12%42433445%7%46%
2145
October1st to 15thNight
12%424423347%50%
2218
16th to endNight
14%5%13423336%50%
2496
November1st to 15thNight
16%6%24322345%47%
2627
16th to endNight
13%7%24323346%47%
2730
December1st to 15thNight
16%10%47%42445%6%33%
2730
16th to endNight
20%12%35%5%24446%30%
2912

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
1882
16th to endDay
48%49%22%13%1
2016
February1st to 15thDay
54%5%8%15%14%
1985
16th to endDay
52%5%10%17%11%2
1840
March1st to 15thDay
49%49%18%14%3
2251
16th to endDay
49%6%11%18%11%1
2464
April1st to 15thDay
38%8%11%22%16%2
2351
16th to endDay
43%6%10%19%13%5%
2684
May1st to 15thDay
45%10%13%19%9%1
2721
16th to endDay
43%11%13%18%10%2
2851
June1st to 15thDay
43%13%17%15%9%
2730
16th to endDay
41%13%13%16%12%2
2577
July1st to 15thDay
46%13%15%13%9%1
2396
16th to endDay
46%14%16%13%7%1
2518
August1st to 15thDay
45%14%15%15%8%
2474
16th to endDay
44%12%15%15%10%1
2557
September1st to 15thDay
44%11%14%15%10%3
2145
16th to endDay
42%7%13%17%16%2
2145
October1st to 15thDay
35%6%10%20%21%4
2070
16th to endDay
36%38%23%22%5%
2080
November1st to 15thDay
39%5%7%18%25%4
1889
16th to endDay
38%5%9%22%19%4
1890
December1st to 15thDay
48%7%9%20%11%2
1890
16th to endDay
52%6%12%15%11%1
2016
January1st to 15thNight
54%5%8%15%14%2
2717
16th to endNight
51%49%17%15%1
2912
February1st to 15thNight
50%410%18%13%2
2535
16th to endNight
53%5%9%18%10%2
2205
March1st to 15thNight
48%6%10%17%14%3
2367
16th to endNight
47%7%12%19%11%
2464
April1st to 15thNight
38%6%11%23%16%2
2268
16th to endNight
43%7%10%20%15%3
1881
May1st to 15thNight
40%9%15%21%9%1
1890
16th to endNight
37%12%15%22%9%1
1972
June1st to 15thNight
36%12%21%18%9%
1890
16th to endNight
35%11%16%21%11%3
1791
July1st to 15thNight
39%13%18%16%10%1
1665
16th to endNight
36%14%19%17%9%1
1739
August1st to 15thNight
37%12%17%19%11%1
1715
16th to endNight
38%12%17%22%9%
1980
September1st to 15thNight
42%9%16%16%11%3
2145
16th to endNight
36%8%12%19%21%1
2145
October1st to 15thNight
34%5%12%20%21%4
2218
16th to endNight
35%47%21%24%6%
2496
November1st to 15thNight
38%5%7%18%21%7%
2627
16th to endNight
38%5%8%24%19%3
2730
December1st to 15thNight
50%7%10%16%12%2
2730
16th to endNight
55%6%10%14%11%1
2912

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
25%21%33%14%4
180
16th to endDay
21%32%26%13%6%
192
February1st to 15thDay
27%23%35%11%1
180
16th to endDay
40%19%29%9%1
159
March1st to 15thDay
22%23%26%22%4
331
16th to endDay
21%14%28%23%10%
416
April1st to 15thDay
17%16%22%29%11%2
390
16th to endDay
16%11%23%25%19%4
379
May1st to 15thDay
17%11%23%24%15%7%
408
16th to endDay
17%419%24%19%15%
459
June1st to 15thDay
10%317%28%27%12%
435
16th to endDay
9%219%26%26%15%
388
July1st to 15thDay
14%114%22%26%19%
365
16th to endDay
10%110%27%29%20%
390
August1st to 15thDay
15%113%23%25%21%
358
16th to endDay
13%27%22%31%22%
396
September1st to 15thDay
14%39%20%32%18%
375
16th to endDay
15%213%25%32%9%
374
October1st to 15thDay
17%5%17%25%26%7%
375
16th to endDay
22%9%19%25%20%3
400
November1st to 15thDay
22%10%26%23%14%2
217
16th to endDay
15%11%31%27%12%1
180
December1st to 15thDay
26%20%26%23%3
180
16th to endDay
27%20%35%15%1
192
January1st to 15thNight
22%17%27%25%6%
840
16th to endNight
23%15%29%28%4
896
February1st to 15thNight
23%15%26%30%3
824
16th to endNight
25%20%28%23%2
735
March1st to 15thNight
24%13%28%28%4
840
16th to endNight
19%14%24%30%11%
896
April1st to 15thNight
16%14%26%30%10%1
800
16th to endNight
17%7%22%36%15%1
624
May1st to 15thNight
15%6%18%35%21%1
630
16th to endNight
10%114%34%34%4
659
June1st to 15thNight
7%111%36%35%6%
630
16th to endNight
6%110%33%39%7%
597
July1st to 15thNight
11%16%32%39%7%
555
16th to endNight
6%8%27%43%12%
612
August1st to 15thNight
7%16%30%45%8%
575
16th to endNight
9%8%30%44%7%
634
September1st to 15thNight
15%29%27%37%7%
780
16th to endNight
14%214%31%32%4
777
October1st to 15thNight
13%5%19%30%25%6%
780
16th to endNight
17%8%21%31%19%2
832
November1st to 15thNight
20%7%16%34%18%3
820
16th to endNight
17%12%20%32%15%
840
December1st to 15thNight
22%12%23%32%8%
840
16th to endNight
26%11%25%30%6%
896
Page generated at 2019-06-20 08:02:29. Version ac04

Copyright 2019 A. Danko


The Winter-Hawk Memorial Observatory Clear Sky Chart |Charts Home