White Mills Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the White Mills 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
47%
15573
21%
46773
16%
15530
52%
15530
26%
30132

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
25%
899
16%
2506
7%
895
33%
895
19%
1824
January16th to endNight
25%
792
18%
2472
10%
792
34%
792
20%
1689
February1st to 15thNight
23%
704
15%
2112
6%
701
32%
701
18%
1508
February16th to endNight
21%
631
17%
1893
7%
631
30%
631
19%
1337
March1st to 15thNight
28%
720
17%
2136
10%
720
33%
720
19%
1507
March16th to endNight
36%
732
16%
2076
10%
732
41%
732
21%
1451
April1st to 15thNight
39%
539
23%
1797
15%
539
51%
539
28%
1072
April16th to endNight
43%
540
21%
1723
15%
540
50%
540
25%
1104
May1st to 15thNight
45%
539
17%
1619
11%
539
50%
539
22%
1124
May16th to endNight
62%
561
19%
1684
15%
561
65%
561
30%
1069
June1st to 15thNight
70%
540
21%
1530
17%
540
73%
540
39%
898
June16th to endNight
73%
540
22%
1440
17%
540
75%
540
38%
875
July1st to 15thNight
67%
510
17%
1360
14%
510
68%
510
33%
878
July16th to endNight
78%
564
22%
1554
19%
531
80%
531
38%
899
August1st to 15thNight
78%
539
24%
1658
24%
536
79%
536
38%
935
August16th to endNight
77%
573
23%
1910
27%
573
77%
573
36%
1048
September1st to 15thNight
66%
621
24%
1881
23%
621
69%
621
31%
1143
September16th to endNight
62%
673
28%
1858
23%
673
65%
673
35%
1133
October1st to 15thNight
59%
660
34%
1815
28%
660
64%
660
39%
1054
October16th to endNight
46%
704
27%
2213
23%
704
54%
704
31%
1312
November1st to 15thNight
47%
700
29%
2276
25%
700
56%
700
32%
1298
November16th to endNight
40%
720
23%
2340
18%
720
48%
720
25%
1474
December1st to 15thNight
31%
720
15%
2340
12%
720
36%
720
17%
1656
December16th to endNight
28%
852
17%
2580
10%
852
36%
852
18%
1844

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%6%25%5%345%5%7%39%
48029
Night
13%6%25%42445%7%42%
46960
TransparencyDay
43%6%10%21%15%2
47719
Night
41%5%10%22%17%3
46774
SeeingDay
14%5%20%24%22%12%
5642
Night
16%5%24%30%20%2
15577

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
19%9%38%5%23335%32%
1432
16th to endDay
14%8%47%5%2435%6%37%
1745
February1st to 15thDay
16%10%5%7%424345%34%
1750
16th to endDay
14%8%37%6%345%5%6%32%
1580
March1st to 15thDay
20%9%35%424435%37%
1822
16th to endDay
17%8%36%5%34446%33%
2156
April1st to 15thDay
13%6%25%5%245%5%7%40%
2151
16th to endDay
15%5%26%6%245%46%39%
2235
May1st to 15thDay
18%6%25%435%45%7%35%
2331
16th to endDay
10%5%26%6%36%5%6%9%36%
2431
June1st to 15thDay
8%3246%36%5%7%9%42%
2427
16th to endDay
6%325%5%46%7%6%11%41%
2520
July1st to 15thDay
11%5%26%6%35%6%6%9%36%
2520
16th to endDay
8%4246%36%6%8%10%38%
2504
August1st to 15thDay
7%5%25%5%45%6%6%11%39%
2289
16th to endDay
9%425%6%35%5%6%9%42%
2292
September1st to 15thDay
14%5%25%6%345%6%7%37%
2065
16th to endDay
13%4245%3445%7%45%
1848
October1st to 15thDay
11%5%24223445%53%
1815
16th to endDay
17%415%42333449%
1656
November1st to 15thDay
13%434324325%50%
1582
16th to endDay
17%7%34323335%45%
1620
December1st to 15thDay
23%9%35%5%2344432%
1620
16th to endDay
18%10%35%5%24345%36%
1638
January1st to 15thNight
17%9%38%6%34345%33%
2506
16th to endNight
17%9%36%5%2435%5%35%
2472
February1st to 15thNight
19%9%37%42435%5%33%
2103
16th to endNight
16%9%47%424346%34%
1893
March1st to 15thNight
17%9%37%42434436%
2136
16th to endNight
15%9%36%43445%6%36%
2076
April1st to 15thNight
13%4244245%5%8%44%
1797
16th to endNight
14%6%25%5%2445%6%42%
1723
May1st to 15thNight
16%6%35%6%35%45%6%37%
1619
16th to endNight
6%426%5%36%5%6%9%43%
1682
June1st to 15thNight
6%425%32446%8%51%
1530
16th to endNight
4323425%6%8%12%46%
1440
July1st to 15thNight
11%43343436%9%44%
1440
16th to endNight
6%114435%5%7%10%47%
1661
August1st to 15thNight
6%31343446%9%52%
1669
16th to endNight
5%315%325%5%7%10%50%
1910
September1st to 15thNight
13%41432345%8%47%
1881
16th to endNight
10%5%24423445%51%
1858
October1st to 15thNight
12%5%12323446%54%
1815
16th to endNight
16%414413335%49%
2213
November1st to 15thNight
12%5%2342434453%
2276
16th to endNight
18%6%24324446%43%
2340
December1st to 15thNight
20%10%45%5%24345%32%
2340
16th to endNight
23%9%35%423435%34%
2580

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%38%20%11%
1433
16th to endDay
47%410%27%8%1
1745
February1st to 15thDay
52%48%22%10%1
1752
16th to endDay
51%5%11%19%10%1
1580
March1st to 15thDay
49%5%8%19%14%1
1822
16th to endDay
51%5%9%23%8%
2157
April1st to 15thDay
41%6%9%22%18%2
2151
16th to endDay
43%5%9%23%14%2
2235
May1st to 15thDay
47%7%12%20%11%
2331
16th to endDay
43%7%13%20%12%2
2435
June1st to 15thDay
36%8%11%24%17%1
2427
16th to endDay
34%8%13%19%20%3
2520
July1st to 15thDay
42%8%12%18%12%4
2371
16th to endDay
36%10%16%22%11%2
2348
August1st to 15thDay
37%9%13%20%16%2
2276
16th to endDay
36%7%13%21%17%4
2292
September1st to 15thDay
42%7%11%18%15%4
2065
16th to endDay
37%5%8%20%24%3
1848
October1st to 15thDay
33%38%24%26%3
1815
16th to endDay
39%37%25%21%2
1656
November1st to 15thDay
37%36%23%20%7%
1582
16th to endDay
42%36%27%18%2
1620
December1st to 15thDay
54%49%19%10%2
1620
16th to endDay
50%412%22%8%1
1638
January1st to 15thNight
53%47%18%14%1
2506
16th to endNight
50%310%22%11%1
2472
February1st to 15thNight
52%5%8%21%10%1
2112
16th to endNight
51%410%20%10%1
1893
March1st to 15thNight
50%5%8%18%13%3
2136
16th to endNight
47%6%11%23%9%1
2076
April1st to 15thNight
36%5%11%21%21%3
1797
16th to endNight
41%5%7%25%15%4
1723
May1st to 15thNight
47%6%9%23%10%1
1620
16th to endNight
34%9%14%21%16%3
1684
June1st to 15thNight
28%7%13%26%20%3
1530
16th to endNight
27%9%14%21%21%5%
1440
July1st to 15thNight
36%6%13%23%16%4
1360
16th to endNight
27%8%17%27%16%2
1554
August1st to 15thNight
27%7%14%26%20%3
1658
16th to endNight
27%7%14%25%20%3
1910
September1st to 15thNight
34%7%10%22%20%5%
1881
16th to endNight
34%5%7%21%26%5%
1858
October1st to 15thNight
30%37%24%28%5%
1815
16th to endNight
37%36%25%21%5%
2213
November1st to 15thNight
34%36%23%25%7%
2276
16th to endNight
42%48%24%18%2
2340
December1st to 15thNight
53%410%17%11%2
2340
16th to endNight
53%410%19%10%1
2580

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
31%18%33%7%6%2
90
16th to endDay
18%15%52%11%2
96
February1st to 15thDay
22%18%40%16%2
90
16th to endDay
19%14%40%19%4
81
March1st to 15thDay
25%14%38%17%3
112
16th to endDay
19%10%33%25%9%1
288
April1st to 15thDay
14%13%27%26%15%2
270
16th to endDay
18%7%24%25%18%5%
270
May1st to 15thDay
21%6%28%23%12%7%
288
16th to endDay
14%319%30%19%13%
331
June1st to 15thDay
7%114%26%32%17%
402
16th to endDay
6%318%31%26%13%
495
July1st to 15thDay
14%215%26%27%13%
475
16th to endDay
8%17%24%29%29%
364
August1st to 15thDay
10%7%21%34%25%
313
16th to endDay
12%25%24%35%20%
332
September1st to 15thDay
16%19%19%33%20%
315
16th to endDay
17%10%22%32%16%
266
October1st to 15thDay
12%121%27%25%10%
255
16th to endDay
20%223%32%18%2
143
November1st to 15thDay
13%5%24%25%24%6%
90
16th to endDay
24%11%30%22%12%
90
December1st to 15thDay
16%11%38%23%7%2
90
16th to endDay
26%19%36%15%2
96
January1st to 15thNight
21%12%35%26%5%
900
16th to endNight
22%11%36%27%2
792
February1st to 15thNight
25%7%37%28%1
704
16th to endNight
22%8%41%24%3
631
March1st to 15thNight
20%12%33%28%5%
720
16th to endNight
19%8%30%31%9%1
732
April1st to 15thNight
15%7%34%29%12%
539
16th to endNight
16%5%28%32%15%1
540
May1st to 15thNight
19%324%33%16%2
540
16th to endNight
6%216%39%29%6%
563
June1st to 15thNight
7%12%38%36%3
540
16th to endNight
5%112%39%38%3
540
July1st to 15thNight
12%8%29%45%3
510
16th to endNight
7%432%42%11%
564
August1st to 15thNight
7%5%30%47%8%
539
16th to endNight
6%5%32%47%6%
573
September1st to 15thNight
14%19%27%40%5%
621
16th to endNight
12%312%27%37%6%
673
October1st to 15thNight
14%317%31%26%7%
660
16th to endNight
18%327%33%15%1
704
November1st to 15thNight
13%7%27%28%21%2
700
16th to endNight
19%8%28%31%10%
720
December1st to 15thNight
25%7%29%27%9%
720
16th to endNight
27%9%29%28%4
852
Page generated at 2017-09-20 04:49:45. Version ac04

Copyright 2017 A. Danko


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