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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 2005-11-06 to 2024-01-15.

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
35%
23227
20%
74614
11%
23183
46%
23183
24%
46943

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 10thNight
22%
760
24%
2649
10%
757
41%
757
23%
1562
January11th to 20thNight
23%
740
20%
2588
7%
740
41%
740
19%
1626
January21st to endNight
20%
792
24%
2610
8%
792
40%
792
23%
1581
February1st to 10thNight
21%
720
16%
2312
6%
720
34%
720
21%
1478
February11th to 20thNight
15%
703
21%
2099
5%
699
35%
699
20%
1370
February21st to endNight
19%
592
26%
1776
9%
592
41%
592
22%
1129
March1st to 10thNight
23%
720
23%
2160
10%
720
41%
720
27%
1328
March11th to 20thNight
22%
720
21%
2061
9%
720
35%
720
23%
1374
March21st to endNight
24%
792
23%
1998
7%
792
36%
792
27%
1370
April1st to 10thNight
25%
720
20%
1800
6%
720
33%
720
26%
1240
April11th to 20thNight
33%
711
19%
1775
7%
711
38%
711
28%
1207
April21st to endNight
32%
716
20%
1796
7%
716
39%
716
28%
1226
May1st to 10thNight
29%
540
16%
1620
7%
540
36%
540
18%
1148
May11th to 20thNight
30%
418
18%
1480
10%
418
40%
418
19%
966
May21st to endNight
50%
388
15%
1551
15%
388
55%
388
19%
989
June1st to 10thNight
46%
360
17%
1440
17%
360
55%
360
20%
898
June11th to 20thNight
49%
360
15%
1440
17%
360
54%
360
20%
885
June21st to endNight
59%
360
15%
1440
16%
360
64%
360
24%
816
July1st to 10thNight
55%
350
14%
1400
18%
350
58%
350
20%
856
July11th to 20thNight
62%
348
17%
1392
21%
348
65%
348
25%
792
July21st to endNight
58%
394
19%
1486
18%
372
65%
372
25%
847
August1st to 10thNight
61%
520
16%
1584
12%
518
63%
518
29%
987
August11th to 20thNight
59%
710
17%
1774
10%
710
61%
710
31%
1190
August21st to endNight
59%
792
17%
1980
9%
792
61%
792
33%
1319
September1st to 10thNight
51%
720
20%
1800
11%
720
55%
720
31%
1221
September11th to 20thNight
57%
720
26%
1879
17%
720
61%
720
38%
1156
September21st to endNight
45%
720
24%
1980
18%
720
51%
720
27%
1323
October1st to 10thNight
40%
720
17%
2070
13%
720
46%
720
25%
1375
October11th to 20thNight
42%
720
25%
2160
16%
720
54%
720
30%
1299
October21st to endNight
29%
792
23%
2506
12%
792
43%
792
25%
1578
November1st to 10thNight
37%
740
25%
2407
14%
740
52%
740
31%
1385
November11th to 20thNight
30%
760
25%
2470
13%
760
46%
760
23%
1522
November21st to endNight
30%
760
24%
2512
11%
760
47%
760
26%
1468
December1st to 10thNight
22%
760
20%
2660
7%
760
39%
760
19%
1682
December11th to 20thNight
23%
760
21%
3176
7%
759
39%
759
18%
1867
December21st to endNight
23%
829
14%
4783
9%
817
40%
817
13%
2883

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%6%25%5%35%5%5%8%41%
74786
Night
16%6%25%5%3445%7%43%
74999
TransparencyDay
41%6%12%23%16%2
74491
Night
41%5%11%23%17%3
74828
SeeingDay
19%11%30%25%12%4
13943
Night
19%8%31%30%11%1
23235

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 10thDay
14%7%35%5%36%45%5%43%
1517
11th to 20thDay
15%9%345%345%5%6%41%
1478
21st to endDay
16%7%3443445%7%42%
1745
February1st to 10thDay
16%9%35%5%34447%39%
1647
11th to 20thDay
16%8%35%425%446%42%
1748
21st to endDay
18%9%36%5%35%445%39%
1480
March1st to 10thDay
15%6%36%5%25%447%45%
1797
11th to 20thDay
15%6%26%6%345%5%7%41%
1897
21st to endDay
19%8%35%5%34445%41%
2356
April1st to 10thDay
17%8%35%5%3445%7%41%
2160
11th to 20thDay
15%5%25%5%25%5%6%7%42%
2134
21st to endDay
19%5%245%35%5%6%7%39%
2164
May1st to 10thDay
20%7%35%435%5%5%8%34%
2340
11th to 20thDay
21%5%25%5%35%5%5%7%37%
2428
21st to endDay
17%6%245%25%45%9%41%
2725
June1st to 10thDay
16%5%245%46%6%7%10%37%
2520
11th to 20thDay
15%5%35%5%35%6%6%9%38%
2520
21st to endDay
10%335%5%36%7%7%9%40%
2520
July1st to 10thDay
11%436%5%5%6%6%7%11%38%
2520
11th to 20thDay
9%5%245%46%7%6%10%41%
2520
21st to endDay
11%5%36%6%47%5%7%10%35%
2744
August1st to 10thDay
9%5%36%6%36%6%8%9%40%
2322
11th to 20thDay
12%5%35%5%45%5%6%10%40%
2126
21st to endDay
14%5%25%5%35%5%7%8%41%
2376
September1st to 10thDay
16%425%4345%5%8%44%
2160
11th to 20thDay
13%5%25%4345%47%49%
2080
21st to endDay
18%6%25%5%35%45%6%40%
1980
October1st to 10thDay
22%5%14325%45%6%43%
1886
11th to 20thDay
16%5%24423446%49%
1800
21st to endDay
19%7%25%32445%6%44%
1850
November1st to 10thDay
14%5%25%42335%6%51%
1671
11th to 20thDay
17%5%245%3345%6%47%
1710
21st to endDay
16%5%245%35%45%7%46%
1667
December1st to 10thDay
17%7%36%5%3345%7%40%
1520
11th to 20thDay
19%7%2442335%6%45%
1906
21st to endDay
17%7%35%5%36%5%5%7%37%
2772
January1st to 10thNight
16%6%24423446%47%
2649
11th to 20thNight
19%7%2442445%6%41%
2588
21st to endNight
15%7%24425%45%7%45%
2610
February1st to 10thNight
17%9%35%43445%6%40%
2312
11th to 20thNight
18%7%35%424446%41%
2098
21st to endNight
19%6%25%433446%44%
1776
March1st to 10thNight
16%6%2442435%7%47%
2150
11th to 20thNight
17%7%36%5%3445%5%43%
2060
21st to endNight
18%7%36%5%24346%42%
1998
April1st to 10thNight
17%8%45%425%445%41%
1800
11th to 20thNight
16%6%36%5%335%47%42%
1775
21st to endNight
19%7%2443446%7%41%
1796
May1st to 10thNight
21%9%36%5%25%447%34%
1620
11th to 20thNight
19%8%35%435%45%8%36%
1479
21st to endNight
17%7%25%435%45%8%39%
1550
June1st to 10thNight
16%5%36%5%3445%9%40%
1440
11th to 20thNight
15%6%35%6%345%5%9%40%
1440
21st to endNight
9%425%6%46%6%8%10%41%
1440
July1st to 10thNight
10%6%36%6%35%5%6%10%40%
1440
11th to 20thNight
8%6%35%5%45%6%7%9%43%
1440
21st to endNight
9%435%6%35%7%7%9%42%
1574
August1st to 10thNight
8%5%36%5%36%6%7%10%42%
1594
11th to 20thNight
11%6%36%6%35%5%7%8%41%
1774
21st to endNight
12%7%26%5%35%46%9%42%
1980
September1st to 10thNight
14%6%25%5%45%5%46%44%
1800
11th to 20thNight
13%5%2443445%6%51%
1879
21st to endNight
18%8%25%43335%7%42%
1980
October1st to 10thNight
20%6%25%434446%43%
2070
11th to 20thNight
15%5%2442345%6%49%
2160
21st to endNight
19%8%35%323445%45%
2506
November1st to 10thNight
13%4245%24346%52%
2407
11th to 20thNight
18%6%25%423435%47%
2470
21st to endNight
14%4245%4445%6%48%
2512
December1st to 10thNight
20%7%25%434447%40%
2660
11th to 20thNight
19%5%25%43345%7%44%
3288
21st to endNight
18%8%35%43445%6%39%
4884

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 10thDay
42%5%11%23%15%5%
1518
11th to 20thDay
43%5%13%23%13%3
1478
21st to endDay
41%410%26%15%4
1745
February1st to 10thDay
46%412%24%13%2
1647
11th to 20thDay
43%5%9%25%15%3
1757
21st to endDay
47%49%21%13%5%
1480
March1st to 10thDay
40%5%12%25%15%3
1800
11th to 20thDay
42%411%24%15%3
1897
21st to endDay
47%5%7%20%17%4
2356
April1st to 10thDay
44%411%19%17%5%
2160
11th to 20thDay
39%6%13%23%16%3
2134
21st to endDay
43%6%11%19%18%4
2164
May1st to 10thDay
47%6%10%20%14%2
2340
11th to 20thDay
46%6%11%21%15%1
2432
21st to endDay
41%6%17%22%13%2
2725
June1st to 10thDay
41%8%14%21%13%2
2520
11th to 20thDay
41%9%14%22%12%2
2520
21st to endDay
37%8%15%23%16%1
2520
July1st to 10thDay
40%9%15%20%15%2
2450
11th to 20thDay
35%7%17%25%14%2
2445
21st to endDay
40%8%11%25%14%2
2591
August1st to 10thDay
36%8%17%24%14%1
2308
11th to 20thDay
39%8%16%22%14%2
2126
21st to endDay
38%6%14%22%17%3
2376
September1st to 10thDay
38%6%15%21%19%2
2160
11th to 20thDay
35%5%10%23%24%3
2080
21st to endDay
43%5%10%18%21%3
1980
October1st to 10thDay
43%5%11%21%18%2
1886
11th to 20thDay
37%410%24%24%2
1800
21st to endDay
41%410%23%20%2
1850
November1st to 10thDay
35%412%27%20%2
1671
11th to 20thDay
39%49%22%24%3
1710
21st to endDay
39%411%30%13%3
1667
December1st to 10thDay
44%415%22%15%1
1520
11th to 20thDay
41%412%26%15%2
1906
21st to endDay
44%8%11%24%13%1
2772
January1st to 10thNight
40%310%25%18%5%
2649
11th to 20thNight
44%414%24%12%2
2588
21st to endNight
39%49%26%19%3
2610
February1st to 10thNight
44%415%22%13%2
2312
11th to 20thNight
44%49%19%18%5%
2100
21st to endNight
42%39%23%19%4
1776
March1st to 10thNight
39%310%25%18%5%
2160
11th to 20thNight
44%49%20%18%5%
2061
21st to endNight
45%39%19%19%6%
1998
April1st to 10thNight
44%49%19%18%5%
1800
11th to 20thNight
43%410%19%21%3
1775
21st to endNight
42%5%9%19%20%5%
1796
May1st to 10thNight
49%7%8%18%16%2
1620
11th to 20thNight
46%5%11%16%18%3
1480
21st to endNight
45%6%15%19%13%2
1551
June1st to 10thNight
43%7%10%21%18%1
1440
11th to 20thNight
42%7%13%24%13%2
1440
21st to endNight
34%8%16%24%15%2
1440
July1st to 10thNight
41%8%15%22%13%2
1400
11th to 20thNight
35%7%14%27%14%2
1392
21st to endNight
34%8%15%26%14%3
1486
August1st to 10thNight
36%8%18%21%15%1
1584
11th to 20thNight
38%7%16%24%14%1
1774
21st to endNight
38%7%14%20%18%3
1980
September1st to 10thNight
41%6%12%22%18%2
1800
11th to 20thNight
33%412%22%25%4
1879
21st to endNight
43%5%6%23%21%2
1980
October1st to 10thNight
43%6%10%22%17%2
2070
11th to 20thNight
35%5%11%28%17%3
2160
21st to endNight
42%49%23%20%2
2506
November1st to 10thNight
34%411%25%21%4
2407
11th to 20thNight
41%48%23%20%5%
2470
21st to endNight
36%413%27%18%2
2512
December1st to 10thNight
45%412%23%15%1
2660
11th to 20thNight
40%413%20%18%4
3288
21st to endNight
45%5%13%24%12%1
4884

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 10thDay
22%16%42%15%41
180
11th to 20thDay
27%28%26%15%4
170
21st to endDay
23%19%37%17%32
248
February1st to 10thDay
25%22%36%15%21
267
11th to 20thDay
25%17%42%15%1
416
21st to endDay
29%18%33%18%1
346
March1st to 10thDay
22%17%37%19%4
420
11th to 20thDay
20%18%40%16%5%1
420
21st to endDay
27%20%29%18%5%1
462
April1st to 10thDay
22%20%34%16%7%1
420
11th to 20thDay
19%15%34%21%9%2
412
21st to endDay
26%14%35%17%5%2
420
May1st to 10thDay
27%12%32%19%8%2
423
11th to 20thDay
22%9%36%23%8%2
447
21st to endDay
22%5%23%28%17%6%
485
June1st to 10thDay
17%6%27%30%15%4
450
11th to 20thDay
15%7%34%28%13%4
450
21st to endDay
13%429%34%17%4
450
July1st to 10thDay
13%222%33%21%8%
445
11th to 20thDay
9%320%36%24%8%
444
21st to endDay
13%5%26%34%18%5%
488
August1st to 10thDay
11%323%37%20%7%
446
11th to 20thDay
13%418%34%23%8%
439
21st to endDay
12%323%32%19%10%
495
September1st to 10thDay
18%6%26%24%17%10%
450
11th to 20thDay
13%425%30%16%11%
450
21st to endDay
23%7%26%26%14%5%
450
October1st to 10thDay
26%8%20%25%16%6%
450
11th to 20thDay
17%11%29%27%14%3
450
21st to endDay
21%11%34%21%10%3
430
November1st to 10thDay
15%11%32%25%13%2
365
11th to 20thDay
19%16%33%22%10%
370
21st to endDay
19%10%36%24%8%2
327
December1st to 10thDay
24%19%36%11%8%1
180
11th to 20thDay
29%19%31%15%6%
180
21st to endDay
26%13%32%23%5%1
198
January1st to 10thNight
20%12%42%21%4
760
11th to 20thNight
25%11%35%24%4
740
21st to endNight
19%14%42%22%3
792
February1st to 10thNight
23%11%39%25%3
720
11th to 20thNight
24%16%42%17%1
703
21st to endNight
23%17%37%20%3
592
March1st to 10thNight
21%12%39%23%4
720
11th to 20thNight
22%10%40%22%41
720
21st to endNight
22%9%39%24%6%
792
April1st to 10thNight
22%12%36%24%6%
720
11th to 20thNight
20%8%34%32%6%
711
21st to endNight
21%8%34%31%5%1
716
May1st to 10thNight
25%8%29%29%9%1
540
11th to 20thNight
23%7%33%30%6%
418
21st to endNight
21%218%39%18%2
389
June1st to 10thNight
19%421%37%18%1
360
11th to 20thNight
15%421%41%19%
360
21st to endNight
9%220%53%16%
360
July1st to 10thNight
14%415%45%21%3
350
11th to 20thNight
12%314%43%26%2
348
21st to endNight
10%220%45%22%1
394
August1st to 10thNight
12%214%48%23%3
520
11th to 20thNight
13%314%41%25%3
710
21st to endNight
14%314%41%24%4
792
September1st to 10thNight
16%321%36%21%4
720
11th to 20thNight
16%318%35%23%6%
720
21st to endNight
22%421%32%19%2
720
October1st to 10thNight
23%5%24%26%17%4
720
11th to 20thNight
17%8%27%35%12%1
720
21st to endNight
23%7%36%24%10%1
792
November1st to 10thNight
15%8%34%29%12%1
740
11th to 20thNight
20%12%32%26%10%1
760
21st to endNight
16%11%38%26%8%1
760
December1st to 10thNight
25%13%35%19%8%1
760
11th to 20thNight
21%10%39%26%4
760
21st to endNight
21%10%40%26%3
836
Page generated at 2024-01-12 16:17:47. Version ac07

Copyright 2024 Attilla Danko


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