CCK's Universe
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the CCK's Universe clear sky chart from 2005-11-06 to 2024-01-16.

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%
24055
22%
74452
14%
23999
55%
23999
27%
46182

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
23%
759
23%
2459
9%
757
41%
757
21%
1505
January11th to 20thNight
31%
744
26%
2417
13%
744
47%
744
23%
1460
January21st to endNight
25%
792
25%
2529
10%
792
42%
792
22%
1558
February1st to 10thNight
30%
720
24%
2160
11%
720
42%
720
25%
1346
February11th to 20thNight
24%
703
23%
2098
6%
699
41%
699
24%
1316
February21st to endNight
26%
592
24%
1776
10%
592
40%
592
23%
1129
March1st to 10thNight
34%
720
28%
2039
14%
720
46%
720
31%
1227
March11th to 20thNight
33%
720
22%
1980
8%
720
45%
720
27%
1259
March21st to endNight
33%
792
23%
2178
9%
792
44%
792
29%
1342
April1st to 10thNight
36%
720
25%
1980
14%
720
46%
720
32%
1220
April11th to 20thNight
41%
627
26%
1865
15%
627
51%
627
34%
1074
April21st to endNight
52%
540
32%
1620
20%
540
63%
540
37%
907
May1st to 10thNight
49%
540
26%
1620
14%
540
59%
540
39%
882
May11th to 20thNight
54%
531
16%
1592
11%
531
58%
531
29%
999
May21st to endNight
61%
582
21%
1744
15%
582
64%
582
29%
1091
June1st to 10thNight
61%
540
15%
1620
12%
540
62%
540
23%
1093
June11th to 20thNight
68%
540
16%
1620
13%
540
70%
540
32%
989
June21st to endNight
66%
540
13%
1620
10%
540
67%
540
26%
1081
July1st to 10thNight
69%
525
11%
1575
9%
525
70%
525
23%
1084
July11th to 20thNight
73%
522
9%
1566
9%
522
73%
522
25%
1069
July21st to endNight
73%
591
14%
1672
13%
558
74%
558
26%
1119
August1st to 10thNight
71%
537
12%
1600
13%
534
72%
534
25%
1079
August11th to 20thNight
68%
534
14%
1678
14%
534
68%
534
21%
1174
August21st to endNight
61%
643
15%
2029
14%
643
62%
643
21%
1395
September1st to 10thNight
65%
720
16%
1980
14%
720
65%
720
26%
1332
September11th to 20thNight
60%
720
18%
1980
16%
720
62%
720
27%
1344
September21st to endNight
58%
720
24%
1980
19%
720
63%
720
30%
1298
October1st to 10thNight
56%
720
28%
1980
22%
720
63%
720
37%
1194
October11th to 20thNight
51%
720
32%
2123
24%
720
62%
720
37%
1186
October21st to endNight
50%
792
32%
2376
26%
792
60%
792
35%
1328
November1st to 10thNight
53%
740
29%
2259
23%
740
63%
740
35%
1273
November11th to 20thNight
41%
760
28%
2470
19%
760
55%
760
30%
1380
November21st to endNight
38%
760
26%
2470
18%
760
50%
760
27%
1478
December1st to 10thNight
36%
760
27%
2470
16%
760
51%
760
25%
1498
December11th to 20thNight
33%
759
26%
2912
16%
758
46%
758
21%
1705
December21st to endNight
34%
830
15%
4415
15%
817
44%
817
12%
2768

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%35%5%35%5%6%8%42%
74912
Night
12%5%25%5%35%5%6%8%45%
74908
TransparencyDay
38%7%12%18%18%6%
74635
Night
37%7%11%18%20%8%
74704
SeeingDay
14%10%23%24%19%9%
13961
Night
14%9%23%30%20%3
24065

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 10thDay
16%5%25%5%24446%47%
1706
11th to 20thDay
14%6%246%23446%49%
1671
21st to endDay
18%6%35%434447%44%
1822
February1st to 10thDay
16%7%35%5%35%5%6%6%40%
1800
11th to 20thDay
17%6%35%333447%45%
1748
21st to endDay
16%7%35%5%2445%8%41%
1480
March1st to 10thDay
13%424433346%53%
1921
11th to 20thDay
14%5%35%5%3445%7%44%
1980
21st to endDay
13%6%25%4345%6%6%45%
2178
April1st to 10thDay
11%5%25%5%3445%5%49%
1980
11th to 20thDay
13%6%3443445%7%49%
2055
21st to endDay
7%3244245%6%8%54%
2340
May1st to 10thDay
7%4235%35%36%8%53%
2340
11th to 20thDay
9%5%35%5%5%5%6%5%9%42%
2301
21st to endDay
10%425%6%47%5%7%9%41%
2531
June1st to 10thDay
11%6%36%6%5%6%6%8%9%35%
2340
11th to 20thDay
5%426%6%47%6%8%12%40%
2340
21st to endDay
6%5%35%7%5%7%8%8%11%35%
2340
July1st to 10thDay
8%5%27%8%5%7%8%9%12%29%
2340
11th to 20thDay
7%5%37%7%5%7%8%10%10%30%
2340
21st to endDay
6%5%36%7%5%8%8%9%13%29%
2547
August1st to 10thDay
8%6%26%6%5%8%8%10%13%27%
2327
11th to 20thDay
10%5%29%8%5%8%8%8%10%27%
2218
21st to endDay
14%6%48%7%5%7%6%6%9%28%
2309
September1st to 10thDay
9%6%26%5%48%6%7%9%38%
1980
11th to 20thDay
13%5%26%7%45%46%9%39%
1980
21st to endDay
12%7%26%6%45%46%7%41%
1980
October1st to 10thDay
12%5%2433345%5%52%
1980
11th to 20thDay
11%3133235%6%6%55%
1836
21st to endDay
10%4234245%5%6%56%
1980
November1st to 10thDay
11%6%245%235%45%53%
1815
11th to 20thDay
13%5%24423336%54%
1710
21st to endDay
14%5%35%4245%5%8%46%
1710
December1st to 10thDay
16%6%35%5%345%5%6%42%
1710
11th to 20thDay
17%6%24433346%46%
2153
21st to endDay
19%8%36%433345%42%
3124
January1st to 10thNight
16%6%25%434346%46%
2459
11th to 20thNight
14%7%35%42445%6%47%
2417
21st to endNight
17%6%35%424445%47%
2529
February1st to 10thNight
16%6%36%42445%7%44%
2160
11th to 20thNight
18%5%245%23445%47%
2098
21st to endNight
14%7%345%35%5%5%7%42%
1776
March1st to 10thNight
10%5%25%5%3445%6%52%
2039
11th to 20thNight
13%5%25%435%46%7%46%
1980
21st to endNight
11%5%35%5%3445%7%50%
2178
April1st to 10thNight
11%425%43445%7%51%
1980
11th to 20thNight
10%5%244245%5%8%52%
1865
21st to endNight
6%315%435%45%7%56%
1620
May1st to 10thNight
5%42443446%9%54%
1620
11th to 20thNight
7%5%25%6%45%6%7%8%44%
1592
21st to endNight
9%6%25%5%35%5%8%9%43%
1744
June1st to 10thNight
10%5%27%8%47%6%7%11%33%
1620
11th to 20thNight
5%435%6%46%5%8%12%43%
1620
21st to endNight
7%5%25%6%46%8%7%12%36%
1620
July1st to 10thNight
8%435%7%45%7%9%12%34%
1620
11th to 20thNight
6%5%26%5%48%8%11%14%31%
1620
21st to endNight
5%425%8%5%7%8%9%14%33%
1771
August1st to 10thNight
6%5%36%6%47%8%9%13%33%
1611
11th to 20thNight
10%5%26%6%37%7%9%12%31%
1678
21st to endNight
11%7%38%5%46%7%8%10%32%
2029
September1st to 10thNight
9%6%36%6%45%6%7%10%38%
1980
11th to 20thNight
11%6%36%7%46%5%5%6%43%
1980
21st to endNight
10%6%26%6%346%5%8%44%
1980
October1st to 10thNight
12%5%24434346%53%
1980
11th to 20thNight
12%423323346%57%
2123
21st to endNight
10%42442435%6%55%
2376
November1st to 10thNight
10%5%25%43335%5%56%
2259
11th to 20thNight
14%6%34323346%54%
2470
21st to endNight
14%435%5%34447%48%
2470
December1st to 10thNight
14%5%345%3445%6%47%
2470
11th to 20thNight
16%6%35%424345%49%
3042
21st to endNight
17%9%36%6%34446%37%
4532

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
39%47%19%26%6%
1707
11th to 20thDay
37%48%18%25%8%
1671
21st to endDay
42%45%17%24%9%
1822
February1st to 10thDay
45%48%17%19%8%
1800
11th to 20thDay
40%5%6%18%25%7%
1758
21st to endDay
42%5%7%17%19%11%
1480
March1st to 10thDay
34%48%18%23%14%
1921
11th to 20thDay
39%7%11%17%18%9%
1980
21st to endDay
39%5%11%19%20%6%
2178
April1st to 10thDay
36%5%11%20%18%10%
1980
11th to 20thDay
34%5%8%20%21%12%
2055
21st to endDay
26%5%12%24%27%6%
2340
May1st to 10thDay
28%6%12%23%25%6%
2340
11th to 20thDay
37%7%15%23%15%3
2305
21st to endDay
37%8%13%22%17%3
2531
June1st to 10thDay
41%10%16%18%13%2
2340
11th to 20thDay
33%10%18%25%14%1
2340
21st to endDay
38%11%19%18%12%2
2340
July1st to 10thDay
42%13%20%17%6%3
2275
11th to 20thDay
41%13%23%16%5%2
2271
21st to endDay
40%13%20%21%6%
2405
August1st to 10thDay
42%13%22%18%4
2314
11th to 20thDay
46%14%16%17%7%
2218
21st to endDay
50%11%15%14%9%2
2309
September1st to 10thDay
40%10%16%16%14%4
1980
11th to 20thDay
41%7%11%18%18%5%
1980
21st to endDay
42%6%8%19%19%6%
1980
October1st to 10thDay
34%5%9%19%24%10%
1980
11th to 20thDay
28%5%8%24%26%9%
1836
21st to endDay
28%48%13%30%16%
1980
November1st to 10thDay
33%5%7%13%27%15%
1815
11th to 20thDay
33%36%20%24%15%
1710
21st to endDay
36%5%9%18%22%9%
1710
December1st to 10thDay
42%5%11%15%19%8%
1710
11th to 20thDay
40%36%15%26%9%
2150
21st to endDay
44%5%6%15%24%4
3124
January1st to 10thNight
40%47%18%24%7%
2459
11th to 20thNight
39%46%18%25%8%
2417
21st to endNight
41%45%15%26%10%
2529
February1st to 10thNight
40%49%17%21%10%
2160
11th to 20thNight
41%36%16%23%11%
2099
21st to endNight
40%5%8%16%16%14%
1776
March1st to 10thNight
34%5%7%19%23%13%
2039
11th to 20thNight
37%6%14%15%19%10%
1980
21st to endNight
35%5%11%18%22%10%
2178
April1st to 10thNight
33%6%10%19%20%12%
1980
11th to 20thNight
31%5%8%22%23%11%
1865
21st to endNight
27%6%10%25%23%9%
1620
May1st to 10thNight
26%6%13%23%24%8%
1620
11th to 20thNight
34%10%18%18%17%3
1593
21st to endNight
34%9%12%23%19%3
1745
June1st to 10thNight
41%10%17%19%13%
1620
11th to 20thNight
31%11%20%25%12%2
1620
21st to endNight
38%11%21%15%11%3
1620
July1st to 10thNight
38%14%22%17%6%2
1575
11th to 20thNight
36%15%28%15%6%1
1566
21st to endNight
35%14%23%21%6%1
1672
August1st to 10thNight
36%14%24%22%4
1600
11th to 20thNight
41%14%20%17%8%1
1678
21st to endNight
43%12%19%16%8%2
2029
September1st to 10thNight
38%11%18%15%14%4
1980
11th to 20thNight
41%8%12%16%17%5%
1980
21st to endNight
37%8%11%18%21%6%
1980
October1st to 10thNight
32%5%9%19%25%10%
1980
11th to 20thNight
30%48%19%29%11%
2123
21st to endNight
30%45%17%28%16%
2376
November1st to 10thNight
31%48%14%27%15%
2259
11th to 20thNight
33%46%16%26%15%
2470
21st to endNight
38%46%18%23%11%
2470
December1st to 10thNight
38%5%10%18%22%6%
2470
11th to 20thNight
38%47%14%26%10%
3044
21st to endNight
47%5%6%18%20%4
4532

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
20%24%41%13%1
270
11th to 20thDay
19%22%34%18%6%1
257
21st to endDay
24%30%33%11%3
264
February1st to 10thDay
22%25%35%15%3
240
11th to 20thDay
28%23%34%15%
240
21st to endDay
21%25%39%12%3
198
March1st to 10thDay
13%22%35%22%8%1
361
11th to 20thDay
18%19%33%21%9%
420
21st to endDay
19%17%34%22%8%
462
April1st to 10thDay
18%19%28%23%11%1
420
11th to 20thDay
13%17%31%21%16%3
412
21st to endDay
10%12%28%29%17%5%
420
May1st to 10thDay
8%14%28%28%15%6%
423
11th to 20thDay
11%6%19%32%21%11%
447
21st to endDay
12%6%13%31%24%14%
485
June1st to 10thDay
13%217%28%28%12%
450
11th to 20thDay
8%414%25%27%22%
450
21st to endDay
7%416%32%27%15%
450
July1st to 10thDay
8%28%26%32%23%
445
11th to 20thDay
8%35%22%38%24%
444
21st to endDay
6%211%26%35%20%
488
August1st to 10thDay
12%213%24%29%20%
446
11th to 20thDay
10%26%21%37%23%
439
21st to endDay
15%211%28%28%15%
495
September1st to 10thDay
12%410%27%31%16%
450
11th to 20thDay
14%415%29%27%11%
450
21st to endDay
17%214%31%24%11%
450
October1st to 10thDay
15%425%29%18%9%
450
11th to 20thDay
12%7%24%29%21%7%
450
21st to endDay
14%9%25%29%19%4
495
November1st to 10thDay
20%8%26%26%16%3
413
11th to 20thDay
14%20%41%18%6%1
270
21st to endDay
13%18%33%27%9%
270
December1st to 10thDay
23%17%33%18%8%1
270
11th to 20thDay
26%17%39%14%4
270
21st to endDay
27%14%31%20%7%1
297
January1st to 10thNight
21%18%33%23%5%
760
11th to 20thNight
18%16%29%27%9%
744
21st to endNight
20%19%34%24%4
792
February1st to 10thNight
18%16%31%28%7%
720
11th to 20thNight
21%15%36%25%3
703
21st to endNight
17%18%35%27%4
592
March1st to 10thNight
13%15%35%30%8%
720
11th to 20thNight
16%16%30%27%10%1
720
21st to endNight
13%18%32%26%10%
792
April1st to 10thNight
13%12%35%27%12%
720
11th to 20thNight
12%12%32%29%14%1
627
21st to endNight
8%9%28%39%16%1
540
May1st to 10thNight
9%7%30%34%18%2
540
11th to 20thNight
10%424%35%24%3
531
21st to endNight
11%313%37%30%5%
584
June1st to 10thNight
12%114%37%32%4
540
11th to 20thNight
6%314%32%34%11%
540
21st to endNight
9%212%32%37%8%
540
July1st to 10thNight
10%26%33%35%15%
525
11th to 20thNight
9%16%28%42%15%
522
21st to endNight
6%17%33%41%11%
591
August1st to 10thNight
8%17%33%41%10%
537
11th to 20thNight
12%35%29%43%7%
534
21st to endNight
13%29%29%34%13%
643
September1st to 10thNight
11%39%31%38%9%
720
11th to 20thNight
15%310%34%33%5%
720
21st to endNight
13%315%32%34%4
720
October1st to 10thNight
15%320%33%23%5%
720
11th to 20thNight
16%5%23%29%23%4
720
21st to endNight
13%8%23%33%21%2
792
November1st to 10thNight
13%9%21%34%22%1
740
11th to 20thNight
16%13%26%30%14%1
760
21st to endNight
16%11%29%29%14%1
760
December1st to 10thNight
15%14%29%27%13%1
760
11th to 20thNight
20%13%28%28%11%1
760
21st to endNight
24%15%22%31%8%
836
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