White Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the White Lake Observatory clear sky chart from 2005-11-05 to 2017-09-24.

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%
15484
23%
47023
15%
15441
55%
15441
27%
29209

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
24%
720
23%
2327
9%
716
41%
716
19%
1469
January16th to endNight
25%
768
24%
2432
10%
768
41%
768
20%
1568
February1st to 15thNight
27%
704
25%
2112
9%
701
43%
701
25%
1304
February16th to endNight
22%
631
23%
1893
8%
631
36%
631
23%
1200
March1st to 15thNight
29%
720
22%
2079
11%
720
39%
720
25%
1342
March16th to endNight
36%
768
21%
2112
11%
768
43%
768
29%
1334
April1st to 15thNight
42%
611
25%
1869
15%
611
53%
611
31%
1083
April16th to endNight
48%
540
26%
1716
18%
540
57%
540
32%
983
May1st to 15thNight
50%
540
21%
1620
12%
540
58%
540
29%
1011
May16th to endNight
62%
561
21%
1682
14%
561
67%
561
32%
1022
June1st to 15thNight
74%
540
16%
1620
14%
540
75%
540
32%
1018
June16th to endNight
76%
540
17%
1620
15%
540
77%
540
35%
970
July1st to 15thNight
70%
510
14%
1530
12%
510
71%
510
27%
1002
July16th to endNight
72%
564
16%
1595
15%
531
74%
531
27%
1030
August1st to 15thNight
73%
539
19%
1663
21%
536
74%
536
28%
1047
August16th to endNight
65%
573
19%
1910
21%
573
67%
573
22%
1278
September1st to 15thNight
62%
690
18%
1950
17%
690
63%
690
27%
1323
September16th to endNight
60%
693
26%
1914
19%
693
65%
693
32%
1203
October1st to 15thNight
54%
660
33%
1815
25%
660
61%
660
38%
1066
October16th to endNight
50%
704
33%
2112
25%
704
62%
704
36%
1186
November1st to 15thNight
48%
700
30%
2276
23%
700
60%
700
35%
1221
November16th to endNight
36%
720
27%
2340
17%
720
50%
720
27%
1372
December1st to 15thNight
31%
720
23%
2340
13%
720
43%
720
22%
1472
December16th to endNight
29%
768
20%
2496
14%
768
38%
768
18%
1705

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
12%5%25%5%35%5%6%7%40%
47901
Night
11%5%2442445%7%45%
47222
TransparencyDay
40%7%12%18%17%4
47602
Night
36%6%11%20%19%5%
47025
SeeingDay
15%7%19%22%22%13%
5368
Night
14%9%23%27%21%4
15486

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%8%25%424336%41%
1611
16th to endDay
16%8%34324445%42%
1791
February1st to 15thDay
15%7%3432345%7%41%
1750
16th to endDay
19%5%2442445%5%41%
1580
March1st to 15thDay
15%6%25%424447%40%
1881
16th to endDay
15%5%245%25%5%47%40%
2111
April1st to 15thDay
11%5%26%4345%46%44%
2088
16th to endDay
10%425%43445%7%46%
2241
May1st to 15thDay
11%5%25%5%25%5%6%7%42%
2331
16th to endDay
8%5%35%5%446%6%9%40%
2431
June1st to 15thDay
8%5%26%6%46%7%8%10%34%
2340
16th to endDay
6%2135%36%6%8%11%43%
2340
July1st to 15thDay
9%5%25%7%48%7%8%9%30%
2340
16th to endDay
7%435%6%48%7%9%10%31%
2465
August1st to 15thDay
8%425%6%37%8%10%9%32%
2283
16th to endDay
11%7%35%8%5%7%7%7%9%26%
2292
September1st to 15thDay
13%6%246%25%5%6%8%37%
1998
16th to endDay
14%6%145%2445%7%43%
1905
October1st to 15thDay
12%5%23323335%53%
1815
16th to endDay
12%41332333357%
1758
November1st to 15thDay
13%5%2321324454%
1582
16th to endDay
14%5%25%323345%48%
1620
December1st to 15thDay
18%6%26%423446%39%
1620
16th to endDay
24%8%34424335%34%
1728
January1st to 15thNight
18%6%34324336%43%
2327
16th to endNight
17%7%34324345%42%
2432
February1st to 15thNight
14%6%24423436%46%
2103
16th to endNight
17%5%25%323445%44%
1893
March1st to 15thNight
13%7%2441445%6%45%
2079
16th to endNight
10%6%35%5%14446%47%
2112
April1st to 15thNight
11%42332445%7%49%
1869
16th to endNight
8%42443446%8%49%
1716
May1st to 15thNight
8%4345%36%5%6%7%45%
1619
16th to endNight
6%4245%35%5%5%10%46%
1682
June1st to 15thNight
43245%35%6%8%12%41%
1620
16th to endNight
42245%35%5%8%12%44%
1620
July1st to 15thNight
5%435%6%37%6%7%10%38%
1620
16th to endNight
5%435%5%46%6%8%12%37%
1703
August1st to 15thNight
5%5%246%35%6%6%12%41%
1674
16th to endNight
10%5%36%5%36%5%6%10%36%
1910
September1st to 15thNight
9%425%6%445%6%8%41%
1950
16th to endNight
12%414434447%47%
1914
October1st to 15thNight
10%423323236%55%
1815
16th to endNight
9%42442233359%
2112
November1st to 15thNight
10%5%23323336%56%
2276
16th to endNight
13%6%24423346%50%
2340
December1st to 15thNight
15%7%25%424346%42%
2340
16th to endNight
20%8%345%24346%35%
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
43%48%15%22%4
1612
16th to endDay
42%46%18%21%5%
1791
February1st to 15thDay
41%49%19%21%3
1752
16th to endDay
43%48%19%18%5%
1580
March1st to 15thDay
43%410%17%19%4
1881
16th to endDay
42%6%11%19%15%3
2112
April1st to 15thDay
39%5%10%20%19%5%
2088
16th to endDay
35%6%9%22%21%4
2241
May1st to 15thDay
38%7%12%19%18%3
2331
16th to endDay
36%9%14%23%13%2
2435
June1st to 15thDay
39%11%17%21%8%1
2340
16th to endDay
31%10%16%25%14%2
2340
July1st to 15thDay
42%12%19%17%7%1
2201
16th to endDay
41%13%17%18%8%1
2310
August1st to 15thDay
39%12%17%19%8%1
2270
16th to endDay
49%11%14%13%9%1
2292
September1st to 15thDay
40%9%14%16%14%3
1998
16th to endDay
39%5%12%19%18%3
1905
October1st to 15thDay
33%48%17%25%9%
1815
16th to endDay
31%36%17%30%10%
1758
November1st to 15thDay
33%26%16%32%9%
1582
16th to endDay
38%37%15%26%7%
1620
December1st to 15thDay
44%48%20%15%6%
1620
16th to endDay
53%38%16%14%4
1728
January1st to 15thNight
42%47%18%22%4
2327
16th to endNight
43%35%18%21%6%
2432
February1st to 15thNight
39%37%20%20%8%
2112
16th to endNight
41%37%20%22%4
1893
March1st to 15thNight
39%5%9%19%18%7%
2079
16th to endNight
36%5%10%24%18%3
2112
April1st to 15thNight
33%49%23%23%6%
1869
16th to endNight
31%5%11%23%20%7%
1716
May1st to 15thNight
35%7%13%19%20%2
1620
16th to endNight
31%9%14%25%15%3
1684
June1st to 15thNight
30%12%22%22%11%1
1620
16th to endNight
29%9%20%22%15%2
1620
July1st to 15thNight
36%11%18%21%9%2
1530
16th to endNight
34%12%20%19%10%2
1595
August1st to 15thNight
33%10%17%23%12%1
1663
16th to endNight
40%11%16%17%13%1
1910
September1st to 15thNight
38%10%14%17%14%4
1950
16th to endNight
35%7%11%23%17%5%
1914
October1st to 15thNight
30%410%18%27%8%
1815
16th to endNight
31%3416%31%13%
2112
November1st to 15thNight
30%36%17%30%12%
2276
16th to endNight
36%46%17%26%8%
2340
December1st to 15thNight
41%5%8%20%18%6%
2340
16th to endNight
49%48%16%17%4
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
17%20%37%16%5%2
90
16th to endDay
18%29%42%5%4
96
February1st to 15thDay
17%27%37%14%2
90
16th to endDay
25%17%43%13%
81
March1st to 15thDay
18%19%33%22%5%
171
16th to endDay
17%12%32%23%12%1
288
April1st to 15thDay
15%14%29%22%17%1
270
16th to endDay
13%5%24%26%23%5%
270
May1st to 15thDay
11%9%29%19%15%13%
288
16th to endDay
15%315%28%22%14%
331
June1st to 15thDay
13%19%22%29%24%
315
16th to endDay
11%12%23%27%24%
315
July1st to 15thDay
11%16%21%25%33%
305
16th to endDay
10%17%14%38%27%
326
August1st to 15thDay
14%8%23%28%24%
313
16th to endDay
15%17%27%27%20%
332
September1st to 15thDay
15%5%9%20%28%20%
315
16th to endDay
15%316%26%27%11%
287
October1st to 15thDay
19%321%23%24%7%
255
16th to endDay
16%8%18%23%27%6%
264
November1st to 15thDay
24%16%22%21%13%2
90
16th to endDay
11%15%37%21%11%3
90
December1st to 15thDay
21%16%37%17%6%
90
16th to endDay
31%17%31%15%4
96
January1st to 15thNight
22%18%29%21%6%
720
16th to endNight
20%18%32%24%3
768
February1st to 15thNight
19%16%33%26%4
704
16th to endNight
19%19%35%23%2
631
March1st to 15thNight
16%16%35%24%6%
720
16th to endNight
13%11%32%28%13%
768
April1st to 15thNight
13%12%30%28%15%
611
16th to endNight
12%8%26%33%17%1
540
May1st to 15thNight
9%6%27%30%23%2
540
16th to endNight
9%217%31%31%6%
563
June1st to 15thNight
6%12%32%36%11%
540
16th to endNight
417%32%42%12%
540
July1st to 15thNight
6%17%24%45%13%
510
16th to endNight
6%18%22%48%12%
564
August1st to 15thNight
7%8%28%43%11%
539
16th to endNight
12%9%25%40%10%
573
September1st to 15thNight
12%210%26%37%10%
690
16th to endNight
15%116%31%32%2
693
October1st to 15thNight
13%5%22%29%23%5%
660
16th to endNight
11%8%24%30%20%3
704
November1st to 15thNight
12%7%27%26%23%1
700
16th to endNight
17%14%28%26%12%
720
December1st to 15thNight
18%15%30%25%9%
720
16th to endNight
26%14%27%25%6%
768
Page generated at 2017-09-25 09:02:17. Version ac04

Copyright 2017 A. Danko


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