Celestial Exploration Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Celestial Exploration Observatory 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
35%
23165
19%
74694
10%
23122
45%
23122
23%
47942

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
20%
760
21%
2649
8%
757
38%
757
21%
1638
January11th to 20thNight
24%
744
18%
2582
7%
744
39%
744
17%
1707
January21st to endNight
21%
792
21%
2574
8%
792
37%
792
22%
1606
February1st to 10thNight
21%
720
17%
2340
6%
720
34%
720
19%
1540
February11th to 20thNight
16%
703
19%
2156
5%
700
34%
700
17%
1443
February21st to endNight
18%
592
24%
1776
9%
592
36%
592
20%
1162
March1st to 10thNight
26%
720
21%
2160
9%
720
41%
720
25%
1343
March11th to 20thNight
22%
720
22%
1980
8%
720
36%
720
23%
1328
March21st to endNight
23%
792
21%
2052
7%
792
34%
792
26%
1419
April1st to 10thNight
23%
720
18%
1800
4%
720
31%
720
24%
1256
April11th to 20thNight
29%
711
18%
1775
7%
711
33%
711
27%
1219
April21st to endNight
31%
720
19%
1800
5%
720
37%
720
29%
1203
May1st to 10thNight
31%
545
15%
1625
8%
545
36%
545
18%
1154
May11th to 20thNight
34%
354
18%
1416
12%
354
45%
354
18%
900
May21st to endNight
52%
388
14%
1551
15%
388
57%
388
19%
967
June1st to 10thNight
43%
360
17%
1440
16%
360
53%
360
21%
871
June11th to 20thNight
51%
360
14%
1440
14%
360
59%
360
22%
881
June21st to endNight
58%
360
15%
1440
19%
360
63%
360
24%
840
July1st to 10thNight
57%
350
13%
1400
18%
350
60%
350
19%
875
July11th to 20thNight
60%
348
16%
1392
20%
348
63%
348
23%
801
July21st to endNight
59%
406
16%
1498
17%
384
63%
384
24%
878
August1st to 10thNight
63%
537
16%
1600
12%
534
65%
534
27%
1042
August11th to 20thNight
54%
671
15%
1735
10%
671
56%
671
26%
1229
August21st to endNight
57%
792
17%
1980
8%
792
58%
792
31%
1339
September1st to 10thNight
49%
720
20%
1800
10%
720
53%
720
31%
1224
September11th to 20thNight
57%
720
28%
1825
19%
720
60%
720
36%
1150
September21st to endNight
49%
720
24%
1980
17%
720
56%
720
30%
1290
October1st to 10thNight
41%
720
16%
2160
13%
720
47%
720
25%
1417
October11th to 20thNight
41%
720
22%
2160
14%
720
52%
720
29%
1334
October21st to endNight
33%
792
23%
2450
14%
792
46%
792
26%
1562
November1st to 10thNight
37%
740
24%
2407
14%
740
52%
740
30%
1395
November11th to 20thNight
32%
760
24%
2470
13%
760
46%
760
23%
1526
November21st to endNight
29%
760
21%
2622
10%
760
43%
760
22%
1577
December1st to 10thNight
23%
760
17%
2660
8%
760
36%
760
17%
1749
December11th to 20thNight
25%
760
18%
3201
7%
759
39%
759
16%
2013
December21st to endNight
23%
828
12%
4798
7%
817
37%
817
11%
3064

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
16%6%35%5%35%5%6%8%39%
74766
Night
17%6%25%5%3445%7%42%
75039
TransparencyDay
42%7%12%22%14%2
74472
Night
41%7%12%22%15%2
74867
SeeingDay
20%13%28%23%12%4
13803
Night
19%9%31%30%10%1
23174

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
13%7%35%7%35%46%6%40%
1517
11th to 20thDay
16%7%38%6%5%5%5%5%7%33%
1504
21st to endDay
13%8%46%5%35%5%6%7%39%
1782
February1st to 10thDay
17%6%36%5%45%46%7%36%
1620
11th to 20thDay
15%8%35%5%445%6%7%39%
1691
21st to endDay
20%8%36%6%35%5%5%5%36%
1480
March1st to 10thDay
14%7%34445%36%7%43%
1797
11th to 20thDay
16%7%35%6%35%5%6%9%36%
1976
21st to endDay
21%7%35%42445%7%38%
2304
April1st to 10thDay
16%7%35%6%345%6%7%38%
2160
11th to 20thDay
16%6%36%5%345%6%7%39%
2134
21st to endDay
18%5%36%6%245%5%8%38%
2160
May1st to 10thDay
20%7%35%5%45%46%7%34%
2348
11th to 20thDay
21%6%245%36%46%6%36%
2478
21st to endDay
15%7%25%425%5%7%8%40%
2725
June1st to 10thDay
15%6%25%5%35%6%6%9%37%
2520
11th to 20thDay
15%5%35%6%46%5%7%9%36%
2520
21st to endDay
13%5%25%5%35%5%6%9%42%
2520
July1st to 10thDay
10%6%35%6%46%6%7%9%38%
2520
11th to 20thDay
9%325%5%46%6%7%12%41%
2520
21st to endDay
12%5%36%6%36%6%6%8%38%
2728
August1st to 10thDay
11%6%36%6%36%6%8%8%37%
2327
11th to 20thDay
12%5%36%6%35%6%6%7%40%
2148
21st to endDay
15%6%25%435%5%6%8%41%
2376
September1st to 10thDay
16%5%25%45%45%6%7%42%
2160
11th to 20thDay
14%42442345%7%51%
2134
21st to endDay
18%6%25%5%35%5%5%6%41%
1976
October1st to 10thDay
19%6%3443445%7%41%
1800
11th to 20thDay
17%5%25%43445%7%45%
1800
21st to endDay
21%6%25%44435%7%39%
1904
November1st to 10thDay
15%6%34323346%51%
1671
11th to 20thDay
17%6%244345%5%5%45%
1710
21st to endDay
17%6%245%2446%8%42%
1558
December1st to 10thDay
19%7%36%5%35%46%7%34%
1520
11th to 20thDay
21%7%3434445%7%39%
1906
21st to endDay
20%8%37%7%45%5%5%7%28%
2772
January1st to 10thNight
16%6%35%5%3345%7%43%
2649
11th to 20thNight
19%7%35%5%3445%7%37%
2582
21st to endNight
14%7%45%435%45%7%42%
2574
February1st to 10thNight
17%8%36%4245%5%7%39%
2340
11th to 20thNight
17%6%45%5%35%5%5%5%40%
2154
21st to endNight
18%8%345%345%45%41%
1776
March1st to 10thNight
16%43443445%7%45%
2150
11th to 20thNight
18%7%34434435%44%
1979
21st to endNight
18%7%25%5%345%47%40%
2052
April1st to 10thNight
18%6%35%6%345%5%8%38%
1800
11th to 20thNight
16%6%26%5%44347%41%
1775
21st to endNight
22%5%2332446%6%44%
1800
May1st to 10thNight
21%8%26%5%35%45%5%35%
1625
11th to 20thNight
19%5%26%6%335%6%6%40%
1415
21st to endNight
15%7%25%5%25%46%8%41%
1550
June1st to 10thNight
16%6%35%5%2445%8%43%
1440
11th to 20thNight
14%435%435%5%8%8%41%
1440
21st to endNight
11%4145%36%6%6%9%45%
1440
July1st to 10thNight
12%5%25%6%46%47%11%39%
1440
11th to 20thNight
10%425%5%36%5%6%10%44%
1440
21st to endNight
11%425%5%25%7%6%12%42%
1586
August1st to 10thNight
12%5%35%6%35%6%6%8%42%
1611
11th to 20thNight
12%6%36%7%45%7%5%8%37%
1735
21st to endNight
14%5%25%5%35%5%6%10%40%
1980
September1st to 10thNight
16%5%25%6%34346%46%
1800
11th to 20thNight
13%42443435%6%52%
1825
21st to endNight
16%6%25%33445%6%45%
1980
October1st to 10thNight
21%6%25%423446%43%
2160
11th to 20thNight
17%6%23424446%48%
2160
21st to endNight
22%6%23423446%45%
2450
November1st to 10thNight
13%5%2443445%5%51%
2407
11th to 20thNight
17%7%24424346%47%
2470
21st to endNight
15%5%25%5%345%6%7%44%
2622
December1st to 10thNight
21%6%26%5%35%5%46%38%
2660
11th to 20thNight
19%7%25%5%345%5%6%39%
3288
21st to endNight
20%10%36%5%34446%36%
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
44%6%12%23%12%3
1518
11th to 20thDay
50%7%14%18%10%2
1504
21st to endDay
44%6%11%23%14%2
1782
February1st to 10thDay
47%6%13%21%11%2
1620
11th to 20thDay
46%6%10%22%13%2
1700
21st to endDay
50%5%10%21%11%3
1480
March1st to 10thDay
40%5%13%27%13%3
1800
11th to 20thDay
45%7%12%20%14%3
1976
21st to endDay
46%5%10%18%16%4
2304
April1st to 10thDay
45%6%10%21%14%5%
2160
11th to 20thDay
41%7%12%22%16%4
2134
21st to endDay
43%6%11%20%15%5%
2160
May1st to 10thDay
48%8%9%17%15%3
2348
11th to 20thDay
47%7%11%19%14%2
2482
21st to endDay
41%8%14%22%14%2
2725
June1st to 10thDay
42%8%15%21%13%1
2520
11th to 20thDay
43%9%15%20%10%2
2520
21st to endDay
38%9%14%25%13%1
2520
July1st to 10thDay
41%9%13%21%15%1
2450
11th to 20thDay
32%10%16%26%14%2
2445
21st to endDay
41%9%12%21%15%3
2575
August1st to 10thDay
40%10%15%21%14%1
2314
11th to 20thDay
39%9%15%22%14%1
2148
21st to endDay
39%8%12%21%17%3
2376
September1st to 10thDay
41%8%11%21%18%2
2160
11th to 20thDay
32%6%13%22%24%3
2134
21st to endDay
44%5%10%19%20%2
1976
October1st to 10thDay
42%7%12%22%16%2
1800
11th to 20thDay
40%5%11%25%17%1
1800
21st to endDay
45%6%9%23%15%2
1904
November1st to 10thDay
35%5%13%24%19%3
1671
11th to 20thDay
39%6%10%25%18%2
1710
21st to endDay
38%7%14%28%11%2
1558
December1st to 10thDay
48%6%14%19%11%1
1520
11th to 20thDay
45%5%17%23%9%1
1906
21st to endDay
50%9%13%20%7%
2772
January1st to 10thNight
41%5%12%24%15%3
2649
11th to 20thNight
46%6%14%22%10%2
2582
21st to endNight
40%5%11%25%16%3
2574
February1st to 10thNight
45%6%14%23%11%2
2340
11th to 20thNight
46%5%10%19%15%4
2156
21st to endNight
44%5%10%22%17%3
1776
March1st to 10thNight
38%5%14%25%15%4
2160
11th to 20thNight
43%6%9%22%17%3
1980
21st to endNight
44%6%10%18%18%4
2052
April1st to 10thNight
43%7%12%21%14%4
1800
11th to 20thNight
41%7%11%20%20%2
1775
21st to endNight
40%5%12%20%18%5%
1800
May1st to 10thNight
49%7%10%16%16%2
1625
11th to 20thNight
43%8%13%16%17%3
1416
21st to endNight
39%10%16%18%13%3
1551
June1st to 10thNight
40%7%12%21%18%1
1440
11th to 20thNight
37%10%16%22%13%1
1440
21st to endNight
34%10%14%27%14%1
1440
July1st to 10thNight
40%10%14%21%13%2
1400
11th to 20thNight
33%11%16%26%12%2
1392
21st to endNight
31%12%18%20%15%2
1498
August1st to 10thNight
37%10%14%21%16%1
1600
11th to 20thNight
42%10%14%18%15%1
1735
21st to endNight
38%8%14%19%19%2
1980
September1st to 10thNight
40%6%11%22%19%2
1800
11th to 20thNight
32%7%10%21%26%4
1825
21st to endNight
39%6%9%22%22%1
1980
October1st to 10thNight
42%6%12%24%14%2
2160
11th to 20thNight
37%6%12%28%15%2
2160
21st to endNight
41%5%11%26%16%1
2450
November1st to 10thNight
34%6%13%24%20%4
2407
11th to 20thNight
40%410%24%17%4
2470
21st to endNight
38%6%14%27%14%2
2622
December1st to 10thNight
46%6%13%22%12%1
2660
11th to 20thNight
43%6%14%20%14%3
3288
21st to endNight
48%7%13%23%9%
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
26%23%28%21%21
180
11th to 20thDay
27%27%28%14%31
180
21st to endDay
21%26%34%13%6%1
264
February1st to 10thDay
27%25%37%9%3
240
11th to 20thDay
26%17%42%14%1
359
21st to endDay
31%19%28%20%1
346
March1st to 10thDay
21%22%32%21%4
420
11th to 20thDay
23%20%35%18%31
420
21st to endDay
27%21%29%15%7%1
462
April1st to 10thDay
21%24%31%17%6%1
420
11th to 20thDay
22%20%28%19%7%4
412
21st to endDay
29%16%30%18%5%1
420
May1st to 10thDay
29%19%24%18%7%3
423
11th to 20thDay
22%14%29%23%10%2
447
21st to endDay
20%7%23%24%21%5%
485
June1st to 10thDay
16%13%27%24%16%3
450
11th to 20thDay
18%12%25%26%16%4
450
21st to endDay
14%9%30%28%15%4
450
July1st to 10thDay
10%6%22%29%23%9%
445
11th to 20thDay
10%5%22%32%26%7%
444
21st to endDay
15%6%26%32%17%5%
488
August1st to 10thDay
11%6%23%31%22%8%
446
11th to 20thDay
15%5%18%33%22%8%
439
21st to endDay
13%5%25%28%18%11%
495
September1st to 10thDay
19%7%21%26%18%9%
450
11th to 20thDay
15%425%27%17%12%
450
21st to endDay
20%11%22%27%15%5%
450
October1st to 10thDay
27%6%24%24%14%6%
450
11th to 20thDay
19%12%30%24%12%2
450
21st to endDay
23%14%35%18%10%1
457
November1st to 10thDay
17%13%29%26%13%3
365
11th to 20thDay
21%18%29%25%6%1
370
21st to endDay
21%19%35%18%6%1
218
December1st to 10thDay
26%22%32%13%6%1
180
11th to 20thDay
32%21%26%16%6%
180
21st to endDay
25%19%30%20%5%2
198
January1st to 10thNight
19%14%42%22%3
760
11th to 20thNight
24%12%35%26%3
744
21st to endNight
17%14%44%24%1
792
February1st to 10thNight
21%13%40%25%2
720
11th to 20thNight
22%16%43%19%1
703
21st to endNight
21%17%39%21%2
592
March1st to 10thNight
21%13%36%27%3
720
11th to 20thNight
22%14%38%21%5%
720
21st to endNight
22%9%41%23%6%1
792
April1st to 10thNight
20%16%38%21%5%
720
11th to 20thNight
18%11%38%26%7%
711
21st to endNight
23%9%33%28%6%
720
May1st to 10thNight
25%9%31%28%6%1
545
11th to 20thNight
19%7%36%30%8%
354
21st to endNight
17%6%20%42%15%1
389
June1st to 10thNight
19%327%34%16%1
360
11th to 20thNight
14%5%26%41%14%
360
21st to endNight
13%320%50%14%
360
July1st to 10thNight
12%417%45%21%1
350
11th to 20thNight
8%420%46%21%1
348
21st to endNight
12%420%42%21%1
406
August1st to 10thNight
11%313%47%24%2
537
11th to 20thNight
14%317%36%28%2
671
21st to endNight
14%415%41%24%2
792
September1st to 10thNight
17%421%36%19%2
720
11th to 20thNight
15%5%16%39%22%4
720
21st to endNight
19%423%35%18%1
720
October1st to 10thNight
21%6%25%28%17%3
720
11th to 20thNight
18%8%29%35%10%
720
21st to endNight
24%7%32%28%8%
792
November1st to 10thNight
16%7%35%31%11%1
740
11th to 20thNight
21%12%31%29%7%1
760
21st to endNight
17%12%37%27%6%
760
December1st to 10thNight
24%11%34%25%5%1
760
11th to 20thNight
21%11%36%27%4
760
21st to endNight
22%12%38%27%2
836
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