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Computer Deconstruction Laboratory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Computer Deconstruction Laboratory clear sky chart from 2005-11-05 to 2019-09-17.

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
36%
17621
20%
54749
11%
17590
46%
17590
22%
35027

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
23%
840
21%
2926
10%
836
39%
836
20%
1805
January16th to endNight
19%
896
21%
3010
7%
896
38%
896
20%
1855
February1st to 15thNight
20%
824
18%
2590
6%
821
35%
821
20%
1663
February16th to endNight
21%
735
24%
2205
9%
735
40%
735
21%
1396
March1st to 15thNight
23%
840
21%
2512
10%
840
38%
840
22%
1634
March16th to endNight
29%
896
23%
2324
10%
896
40%
896
25%
1558
April1st to 15thNight
32%
838
19%
2096
6%
838
39%
838
25%
1442
April16th to endNight
36%
828
17%
2074
6%
828
41%
828
24%
1438
May1st to 15thNight
32%
610
16%
1870
8%
610
38%
610
17%
1323
May16th to endNight
45%
438
15%
1753
14%
438
51%
438
15%
1133
June1st to 15thNight
45%
420
16%
1680
17%
420
50%
420
17%
1088
June16th to endNight
60%
420
15%
1680
17%
420
64%
420
21%
949
July1st to 15thNight
57%
400
15%
1600
19%
400
59%
400
20%
939
July16th to endNight
57%
440
17%
1674
17%
418
64%
418
22%
972
August1st to 15thNight
60%
674
17%
1905
12%
672
62%
672
29%
1207
August16th to endNight
64%
892
18%
2230
10%
892
66%
892
32%
1466
September1st to 15thNight
53%
840
21%
2100
13%
840
55%
840
29%
1421
September16th to endNight
50%
782
23%
2151
17%
782
55%
782
27%
1405
October1st to 15thNight
43%
780
20%
2275
16%
780
49%
780
25%
1473
October16th to endNight
32%
832
23%
2590
13%
832
46%
832
26%
1580
November1st to 15thNight
31%
820
22%
2667
13%
820
44%
820
22%
1670
November16th to endNight
29%
840
21%
2761
10%
840
42%
840
21%
1726
December1st to 15thNight
25%
840
18%
2940
8%
840
38%
840
16%
1901
December16th to endNight
18%
896
20%
3136
6%
896
36%
896
18%
1983

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
15%5%2442445%7%41%
55954
Night
16%6%2442445%6%42%
54919
Cloud CoverDay
15%5%2442445%7%41%
55963
Night
16%6%2442445%6%42%
54925
TransparencyDay
40%6%12%22%15%2
55642
Night
41%5%11%22%16%2
54749
SeeingDay
18%8%20%28%18%5%
8394
Night
18%15%23%26%13%2
17622

By Month

Percentage Cloud Cover NE (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
14%6%25%435%446%42%
1672
16th to endDay
16%8%23323447%43%
1917
February1st to 15thDay
16%7%35%423445%41%
1931
16th to endDay
15%6%26%5%24445%41%
1840
March1st to 15thDay
17%425%4245%5%7%39%
2096
16th to endDay
18%6%25%5%2334443%
2604
April1st to 15thDay
18%6%2442335%6%40%
2512
16th to endDay
15%4244345%5%6%41%
2491
May1st to 15thDay
20%6%24435%45%7%35%
2752
16th to endDay
19%5%2432446%8%38%
3066
June1st to 15thDay
16%5%24425%5%6%9%36%
2940
16th to endDay
10%425%5%35%5%6%8%41%
2940
July1st to 15thDay
9%425%5%36%5%6%10%41%
2940
16th to endDay
10%5%25%5%36%6%7%9%38%
3102
August1st to 15thDay
9%425%4345%7%10%41%
2611
16th to endDay
12%42442446%8%44%
2676
September1st to 15thDay
14%42442345%7%45%
2520
16th to endDay
14%6%25%4345%5%6%41%
2164
October1st to 15thDay
19%5%24423447%41%
2012
16th to endDay
15%5%24322447%48%
1986
November1st to 15thDay
17%6%24423445%43%
1851
16th to endDay
15%5%24424346%46%
1859
December1st to 15thDay
16%6%25%423447%41%
1680
16th to endDay
19%6%34424445%39%
1792
January1st to 15thNight
18%6%24323446%43%
2926
16th to endNight
17%7%23323346%44%
3010
February1st to 15thNight
17%7%25%423445%41%
2589
16th to endNight
18%6%24323445%44%
2205
March1st to 15thNight
18%6%25%423246%43%
2499
16th to endNight
17%7%25%413335%44%
2324
April1st to 15thNight
17%6%35%324446%41%
2096
16th to endNight
18%5%25%434447%40%
2074
May1st to 15thNight
21%8%25%5%14446%34%
1870
16th to endNight
19%7%2432445%9%36%
1751
June1st to 15thNight
19%5%25%424449%36%
1680
16th to endNight
9%5%24435%45%9%43%
1680
July1st to 15thNight
8%5%25%6%335%6%10%41%
1680
16th to endNight
9%4245%35%6%7%8%42%
1770
August1st to 15thNight
8%426%5%2446%9%45%
1915
16th to endNight
10%5%145%3446%8%43%
2230
September1st to 15thNight
15%4145%3445%6%43%
2100
16th to endNight
15%6%24423346%44%
2151
October1st to 15thNight
17%5%14424446%43%
2275
16th to endNight
17%5%24323345%48%
2590
November1st to 15thNight
17%5%25%42333446%
2667
16th to endNight
15%5%25%42345%7%43%
2761
December1st to 15thNight
19%6%25%5%24446%38%
2940
16th to endNight
18%6%25%32345%6%41%
3136

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
14%7%244345%5%5%41%
1672
16th to endDay
16%7%23324346%44%
1917
February1st to 15thDay
16%8%34423345%41%
1931
16th to endDay
15%6%36%4345%46%40%
1840
March1st to 15thDay
16%5%35%42445%7%39%
2106
16th to endDay
17%6%24423445%42%
2603
April1st to 15thDay
17%6%245%3435%6%40%
2512
16th to endDay
15%5%235%3446%6%41%
2491
May1st to 15thDay
20%7%24325%45%7%35%
2752
16th to endDay
19%5%234245%5%8%38%
3066
June1st to 15thDay
16%5%14435%5%6%8%36%
2940
16th to endDay
9%4245%36%6%6%9%40%
2940
July1st to 15thDay
9%425%5%36%6%6%9%41%
2940
16th to endDay
10%5%245%36%6%7%9%38%
3102
August1st to 15thDay
9%425%5%345%6%9%42%
2611
16th to endDay
12%42442446%8%44%
2676
September1st to 15thDay
13%5%2432435%8%44%
2520
16th to endDay
14%6%35%5%2445%7%41%
2164
October1st to 15thDay
19%5%24423446%41%
2012
16th to endDay
16%5%24313346%48%
1986
November1st to 15thDay
18%5%2431435%5%43%
1851
16th to endDay
15%5%24425%436%46%
1859
December1st to 15thDay
15%6%25%42445%7%41%
1680
16th to endDay
19%7%244235%46%39%
1792
January1st to 15thNight
18%5%23424337%43%
2926
16th to endNight
17%7%23323346%44%
3010
February1st to 15thNight
16%7%35%424346%41%
2582
16th to endNight
18%6%2441335%5%44%
2205
March1st to 15thNight
18%6%25%423246%43%
2512
16th to endNight
18%6%25%423335%45%
2324
April1st to 15thNight
17%7%34323446%41%
2096
16th to endNight
17%6%35%32445%7%39%
2074
May1st to 15thNight
20%8%35%43345%7%33%
1870
16th to endNight
20%6%1442446%8%36%
1751
June1st to 15thNight
19%6%2442445%8%36%
1680
16th to endNight
9%425%5%25%5%6%10%43%
1680
July1st to 15thNight
8%5%35%5%345%6%10%41%
1680
16th to endNight
8%5%25%5%45%5%8%8%41%
1770
August1st to 15thNight
7%5%25%43446%8%45%
1915
16th to endNight
10%5%1442447%8%44%
2230
September1st to 15thNight
15%5%15%4245%5%6%43%
2100
16th to endNight
15%6%34423447%44%
2151
October1st to 15thNight
18%5%24424346%43%
2275
16th to endNight
16%5%24422335%49%
2590
November1st to 15thNight
17%5%245%23245%46%
2667
16th to endNight
15%5%2442445%6%43%
2761
December1st to 15thNight
19%6%25%5%23447%38%
2940
16th to endNight
18%5%25%32445%6%41%
3136

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
42%5%12%22%12%3
1673
16th to endDay
41%313%25%13%2
1917
February1st to 15thDay
43%5%13%22%13%1
1934
16th to endDay
43%410%25%13%1
1840
March1st to 15thDay
42%5%13%22%13%2
2106
16th to endDay
43%49%22%16%3
2604
April1st to 15thDay
43%5%10%21%14%4
2512
16th to endDay
40%6%11%18%20%2
2491
May1st to 15thDay
46%7%10%19%13%1
2752
16th to endDay
43%7%13%21%12%1
3070
June1st to 15thDay
42%9%13%21%12%1
2940
16th to endDay
36%9%13%22%16%1
2940
July1st to 15thDay
35%9%11%24%16%1
2791
16th to endDay
35%9%13%25%13%2
2935
August1st to 15thDay
34%8%15%26%15%
2597
16th to endDay
33%7%13%22%19%2
2676
September1st to 15thDay
36%6%13%21%19%1
2520
16th to endDay
40%6%9%19%21%1
2164
October1st to 15thDay
42%5%12%19%17%1
2012
16th to endDay
35%5%10%26%20%1
1986
November1st to 15thDay
43%312%23%16%1
1851
16th to endDay
39%411%25%16%2
1859
December1st to 15thDay
43%316%22%13%1
1680
16th to endDay
46%414%20%12%
1792
January1st to 15thNight
41%412%23%14%2
2926
16th to endNight
42%311%26%15%1
3010
February1st to 15thNight
43%314%22%14%1
2590
16th to endNight
41%39%24%17%3
2205
March1st to 15thNight
43%312%21%15%3
2512
16th to endNight
43%38%21%18%4
2324
April1st to 15thNight
43%411%20%17%2
2096
16th to endNight
43%5%8%17%21%3
2074
May1st to 15thNight
50%5%8%17%14%2
1870
16th to endNight
44%7%13%19%13%2
1753
June1st to 15thNight
45%7%11%18%16%
1680
16th to endNight
35%6%13%26%16%1
1680
July1st to 15thNight
37%7%14%21%16%2
1600
16th to endNight
35%7%15%27%11%2
1674
August1st to 15thNight
34%8%15%23%15%1
1905
16th to endNight
35%7%12%23%18%2
2230
September1st to 15thNight
39%6%11%23%17%1
2100
16th to endNight
41%46%22%22%2
2151
October1st to 15thNight
42%412%21%16%2
2275
16th to endNight
39%310%26%18%1
2590
November1st to 15thNight
42%310%21%18%4
2667
16th to endNight
40%5%12%24%14%1
2761
December1st to 15thNight
45%415%21%12%1
2940
16th to endNight
43%5%12%24%12%1
3136

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
16%450%18%9%1
120
16th to endDay
27%5%34%25%7%
164
February1st to 15thDay
22%11%32%29%2
267
16th to endDay
19%13%34%27%4
343
March1st to 15thDay
19%11%35%28%5%
390
16th to endDay
21%13%27%28%7%1
416
April1st to 15thDay
17%10%30%29%11%1
390
16th to endDay
20%10%23%30%12%2
379
May1st to 15thDay
26%9%20%29%12%2
408
16th to endDay
25%8%10%29%21%4
459
June1st to 15thDay
18%7%15%28%23%7%
435
16th to endDay
12%7%12%37%25%4
435
July1st to 15thDay
12%5%6%29%34%12%
425
16th to endDay
11%7%7%31%33%8%
454
August1st to 15thDay
12%45%36%31%10%
418
16th to endDay
10%47%31%32%13%
460
September1st to 15thDay
17%412%29%24%12%
435
16th to endDay
22%412%27%23%10%
378
October1st to 15thDay
25%5%14%22%24%6%
375
16th to endDay
14%9%31%25%16%2
371
November1st to 15thDay
19%12%24%24%16%1
325
16th to endDay
15%13%33%22%13%1
299
December1st to 15thDay
20%6%38%21%11%
120
16th to endDay
26%6%34%27%5%
128
January1st to 15thNight
17%21%33%23%4
840
16th to endNight
19%20%35%20%2
896
February1st to 15thNight
19%20%34%23%2
824
16th to endNight
20%20%32%23%2
735
March1st to 15thNight
19%17%34%23%5%
840
16th to endNight
19%17%27%26%7%1
896
April1st to 15thNight
19%18%25%29%6%
838
16th to endNight
17%16%23%32%9%1
828
May1st to 15thNight
25%16%17%28%11%1
610
16th to endNight
21%15%10%30%18%3
439
June1st to 15thNight
20%14%13%27%22%1
420
16th to endNight
9%15%8%40%25%
420
July1st to 15thNight
9%10%10%35%30%3
400
16th to endNight
12%14%8%30%32%2
440
August1st to 15thNight
11%8%9%36%30%3
674
16th to endNight
12%7%7%33%31%7%
892
September1st to 15thNight
16%8%14%29%25%6%
840
16th to endNight
19%9%12%27%24%7%
782
October1st to 15thNight
20%10%18%26%20%3
780
16th to endNight
18%13%30%25%11%
832
November1st to 15thNight
18%16%28%21%13%1
820
16th to endNight
15%20%29%24%9%
840
December1st to 15thNight
22%20%26%21%8%1
840
16th to endNight
19%20%36%21%1
896
Page generated at 2019-09-17 21:12:17. Version ac04

Copyright 2019 A. Danko


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