CMOR
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the CMOR clear sky chart from 2005-11-05 to 2017-10-31.

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%
15072
14%
47098
10%
15036
40%
15036
18%
33152

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
14%
716
9%
2401
4%
716
20%
716
8%
1944
January16th to endNight
14%
768
9%
2496
3%
768
20%
768
8%
2035
February1st to 15thNight
17%
701
7%
2287
3%
701
23%
701
9%
1821
February16th to endNight
23%
631
11%
1973
4%
631
30%
631
12%
1496
March1st to 15thNight
24%
720
13%
2002
7%
720
29%
720
16%
1523
March16th to endNight
32%
768
20%
2112
11%
768
39%
768
23%
1465
April1st to 15thNight
26%
694
15%
1832
7%
694
32%
694
21%
1324
April16th to endNight
38%
540
20%
1620
10%
540
46%
540
25%
1056
May1st to 15thNight
42%
540
16%
1620
11%
540
47%
540
25%
1075
May16th to endNight
45%
396
17%
1519
14%
396
54%
396
25%
879
June1st to 15thNight
49%
360
13%
1413
13%
360
57%
360
24%
825
June16th to endNight
53%
360
15%
1260
15%
360
60%
360
28%
737
July1st to 15thNight
64%
350
19%
1247
23%
350
68%
350
37%
637
July16th to endNight
62%
564
15%
1595
11%
531
65%
531
33%
949
August1st to 15thNight
68%
539
18%
1609
15%
536
70%
536
35%
948
August16th to endNight
62%
592
24%
1738
16%
592
67%
592
36%
1018
September1st to 15thNight
54%
720
21%
1869
13%
720
57%
720
34%
1196
September16th to endNight
56%
717
22%
1980
17%
717
59%
717
32%
1228
October1st to 15thNight
42%
720
17%
2148
15%
720
47%
720
23%
1436
October16th to endNight
25%
768
15%
2310
9%
768
34%
768
16%
1697
November1st to 15thNight
34%
700
17%
2339
15%
700
39%
700
19%
1586
November16th to endNight
23%
720
9%
2520
7%
720
28%
720
11%
1917
December1st to 15thNight
13%
720
5%
2520
2%
720
17%
720
6%
2089
December16th to endNight
11%
768
6%
2688
2%
768
17%
768
5%
2271

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
14%9%47%6%35%5%5%7%29%
48639
Night
14%9%47%5%35%45%7%32%
47275
Cloud CoverDay
14%9%47%6%35%5%5%7%30%
48649
Night
14%8%47%5%35%45%7%33%
47279
TransparencyDay
51%7%12%18%9%
48335
Night
49%7%12%19%10%1
47098
SeeingDay
17%8%27%23%15%7%
5799
Night
18%9%29%28%12%1
15080

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
18%15%5%10%8%44447%15%
1534
16th to endDay
12%18%8%13%9%36%445%13%
1728
February1st to 15thDay
14%17%8%10%8%47%45%6%13%
1575
16th to endDay
15%14%6%10%6%47%5%46%19%
1499
March1st to 15thDay
15%13%6%10%7%24436%24%
1945
16th to endDay
15%10%5%7%6%45%35%5%29%
2112
April1st to 15thDay
19%11%46%4345%5%6%28%
2124
16th to endDay
17%9%36%5%22347%37%
2340
May1st to 15thDay
18%7%36%5%3445%7%34%
2331
16th to endDay
12%6%35%6%25%5%5%7%38%
2594
June1st to 15thDay
13%5%25%5%246%6%8%37%
2542
16th to endDay
12%5%25%5%45%6%6%10%35%
2700
July1st to 15thDay
8%5%246%35%6%7%9%39%
2633
16th to endDay
9%5%35%6%46%6%6%9%35%
2465
August1st to 15thDay
7%5%36%7%46%6%6%9%35%
2340
16th to endDay
11%6%25%5%35%6%6%7%37%
2451
September1st to 15thDay
13%7%35%6%35%46%9%34%
2090
16th to endDay
15%5%25%4245%5%7%40%
1980
October1st to 15thDay
20%8%37%5%34347%32%
1812
16th to endDay
22%10%5%6%6%44446%22%
1911
November1st to 15thDay
13%9%46%6%445%5%5%32%
1517
16th to endDay
18%14%6%8%6%4445%6%18%
1440
December1st to 15thDay
16%17%9%11%7%46%445%13%
1440
16th to endDay
20%17%8%12%8%445%45%9%
1536
January1st to 15thNight
20%12%7%8%8%45%5%5%5%17%
2401
16th to endNight
13%14%9%11%8%46%445%17%
2496
February1st to 15thNight
13%13%7%10%8%36%446%20%
2285
16th to endNight
15%10%5%9%8%35%5%5%6%24%
1973
March1st to 15thNight
16%10%37%6%46%446%29%
1990
16th to endNight
13%9%46%43435%6%38%
2112
April1st to 15thNight
19%8%35%6%25%35%7%32%
1832
16th to endNight
11%7%26%5%25%46%7%39%
1620
May1st to 15thNight
14%6%46%5%245%5%7%38%
1620
16th to endNight
10%5%25%425%447%47%
1517
June1st to 15thNight
10%425%5%345%7%9%42%
1413
16th to endNight
8%4245%346%6%8%45%
1260
July1st to 15thNight
431442445%8%55%
1321
16th to endNight
7%414435%47%10%47%
1703
August1st to 15thNight
5%315%4346%6%9%47%
1620
16th to endNight
7%42443445%7%51%
1738
September1st to 15thNight
11%5%2432435%7%48%
1869
16th to endNight
11%5%15%4245%5%7%47%
1980
October1st to 15thNight
17%7%2443445%6%39%
2148
16th to endNight
21%7%37%5%3446%7%28%
2310
November1st to 15thNight
13%9%37%435%46%7%33%
2339
16th to endNight
19%11%5%9%6%25%45%7%22%
2520
December1st to 15thNight
18%16%7%10%6%45%5%4416%
2520
16th to endNight
19%15%8%12%6%445%45%12%
2688

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
19%13%6%10%7%35%447%16%
1534
16th to endDay
12%17%8%12%9%45%445%13%
1728
February1st to 15thDay
14%17%7%9%8%45%46%5%15%
1575
16th to endDay
15%14%6%9%7%37%45%5%20%
1499
March1st to 15thDay
16%12%5%10%6%3445%6%23%
1956
16th to endDay
15%9%5%8%6%4445%5%30%
2111
April1st to 15thDay
18%10%47%43446%6%28%
2124
16th to endDay
18%9%35%413346%37%
2340
May1st to 15thDay
17%6%36%5%25%45%7%34%
2331
16th to endDay
12%6%25%6%35%5%6%7%38%
2594
June1st to 15thDay
13%5%35%5%25%46%9%37%
2542
16th to endDay
12%5%25%6%35%6%6%9%36%
2700
July1st to 15thDay
8%5%245%36%6%6%9%39%
2633
16th to endDay
9%5%36%6%36%6%6%9%35%
2465
August1st to 15thDay
8%5%26%6%46%6%7%9%36%
2340
16th to endDay
11%6%26%5%35%5%5%8%37%
2451
September1st to 15thDay
13%6%36%5%35%5%5%8%35%
2090
16th to endDay
14%5%25%5%35%45%7%40%
1980
October1st to 15thDay
19%8%36%6%24346%32%
1812
16th to endDay
22%10%36%7%45%45%6%23%
1911
November1st to 15thDay
13%8%46%6%35%5%5%6%32%
1517
16th to endDay
18%13%6%8%7%35%47%6%18%
1440
December1st to 15thDay
16%17%8%9%7%45%5%45%13%
1440
16th to endDay
20%15%8%12%7%46%45%49%
1536
January1st to 15thNight
20%12%6%9%6%4446%6%17%
2401
16th to endNight
13%13%9%11%7%46%45%5%18%
2496
February1st to 15thNight
13%13%6%11%7%36%45%6%20%
2278
16th to endNight
15%11%48%8%4445%7%24%
1973
March1st to 15thNight
17%10%37%6%35%45%6%28%
2002
16th to endNight
14%8%46%5%23445%39%
2112
April1st to 15thNight
19%7%45%6%25%347%33%
1832
16th to endNight
11%8%25%5%345%5%7%39%
1620
May1st to 15thNight
14%6%36%43446%7%37%
1619
16th to endNight
10%4245%145%47%48%
1517
June1st to 15thNight
10%5%15%425%5%7%8%42%
1413
16th to endNight
8%4245%35%5%6%8%45%
1260
July1st to 15thNight
42234245%5%9%55%
1321
16th to endNight
7%414335%5%6%9%47%
1703
August1st to 15thNight
5%3245%346%6%10%48%
1620
16th to endNight
7%4145%2445%6%52%
1738
September1st to 15thNight
11%5%24324447%47%
1869
16th to endNight
11%42443345%7%47%
1980
October1st to 15thNight
17%6%25%5%2445%7%39%
2148
16th to endNight
21%7%36%6%35%36%7%28%
2310
November1st to 15thNight
13%8%36%6%345%6%8%34%
2339
16th to endNight
19%10%5%8%7%35%447%22%
2520
December1st to 15thNight
18%15%6%9%7%36%5%5%5%16%
2520
16th to endNight
19%15%7%11%7%3445%5%13%
2688

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
67%6%10%10%3
1535
16th to endDay
72%6%9%8%3
1728
February1st to 15thDay
67%7%9%12%3
1577
16th to endDay
64%6%10%12%4
1499
March1st to 15thDay
60%5%11%15%5%
1956
16th to endDay
53%6%11%16%10%1
2112
April1st to 15thDay
54%6%12%17%9%
2124
16th to endDay
47%5%10%20%13%2
2340
May1st to 15thDay
48%6%11%21%10%
2331
16th to endDay
42%6%13%21%13%1
2598
June1st to 15thDay
41%7%14%22%11%1
2542
16th to endDay
41%8%14%23%12%
2700
July1st to 15thDay
36%9%12%23%16%1
2479
16th to endDay
41%8%15%22%10%2
2310
August1st to 15thDay
39%11%17%19%11%1
2327
16th to endDay
41%8%14%23%11%1
2451
September1st to 15thDay
44%6%15%20%11%
2090
16th to endDay
41%7%13%26%10%
1980
October1st to 15thDay
52%5%11%16%12%1
1812
16th to endDay
60%7%13%12%5%
1911
November1st to 15thDay
50%8%14%17%8%
1517
16th to endDay
63%8%12%12%3
1440
December1st to 15thDay
70%9%12%5%2
1440
16th to endDay
74%8%7%7%1
1536
January1st to 15thNight
65%7%9%10%6%
2401
16th to endNight
65%7%10%12%3
2496
February1st to 15thNight
63%6%10%13%4
2287
16th to endNight
57%7%12%14%6%
1973
March1st to 15thNight
54%7%11%18%6%
2002
16th to endNight
46%5%9%22%12%2
2112
April1st to 15thNight
50%410%20%12%
1832
16th to endNight
41%6%10%19%19%3
1620
May1st to 15thNight
43%5%11%23%13%2
1620
16th to endNight
34%7%14%25%13%3
1519
June1st to 15thNight
37%6%13%25%15%1
1413
16th to endNight
34%6%16%22%18%
1260
July1st to 15thNight
24%6%13%29%22%3
1247
16th to endNight
31%8%16%24%17%2
1595
August1st to 15thNight
29%8%16%30%13%1
1609
16th to endNight
30%6%12%31%16%2
1738
September1st to 15thNight
35%6%13%27%15%1
1869
16th to endNight
34%6%13%30%14%
1980
October1st to 15thNight
43%6%10%23%14%
2148
16th to endNight
53%6%14%17%8%
2310
November1st to 15thNight
46%7%13%18%12%1
2339
16th to endNight
59%6%14%13%4
2520
December1st to 15thNight
66%9%11%8%3
2520
16th to endNight
71%7%10%8%2
2688

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
18%24%41%7%6%1
77
16th to endDay
35%15%37%11%
96
February1st to 15thDay
24%18%46%10%
90
16th to endDay
22%23%43%8%2
81
March1st to 15thDay
23%13%33%22%6%
246
16th to endDay
23%8%31%25%7%2
288
April1st to 15thDay
24%12%30%19%11%1
270
16th to endDay
21%11%27%21%12%5%
270
May1st to 15thDay
20%8%28%22%12%6%
288
16th to endDay
15%7%30%25%15%6%
331
June1st to 15thDay
16%7%25%28%17%4
337
16th to endDay
13%8%29%31%12%4
495
July1st to 15thDay
12%6%22%28%22%8%
425
16th to endDay
9%321%29%24%11%
326
August1st to 15thDay
9%117%28%25%17%
313
16th to endDay
14%219%21%22%20%
332
September1st to 15thDay
11%318%23%28%13%
315
16th to endDay
17%317%19%23%18%
314
October1st to 15thDay
22%7%23%24%15%6%
315
16th to endDay
24%10%33%24%5%1
327
November1st to 15thDay
15%15%31%24%10%3
79
16th to endDay
28%13%38%10%10%
60
December1st to 15thDay
26%31%31%5%5%
60
16th to endDay
29%23%40%6%
64
January1st to 15thNight
25%18%34%16%4
720
16th to endNight
21%12%39%21%4
768
February1st to 15thNight
21%16%36%21%2
704
16th to endNight
22%13%32%25%5%
631
March1st to 15thNight
22%12%35%23%5%
720
16th to endNight
17%11%33%25%11%
768
April1st to 15thNight
23%12%31%26%5%
694
16th to endNight
15%8%31%32%10%1
540
May1st to 15thNight
17%5%27%34%14%1
540
16th to endNight
12%430%33%17%1
397
June1st to 15thNight
13%326%42%13%
360
16th to endNight
11%326%42%15%
360
July1st to 15thNight
5%122%48%20%2
350
16th to endNight
8%220%44%21%2
564
August1st to 15thNight
7%16%43%28%3
539
16th to endNight
9%117%37%29%4
592
September1st to 15thNight
13%420%30%24%5%
720
16th to endNight
13%417%30%26%7%
717
October1st to 15thNight
19%6%25%28%17%2
720
16th to endNight
25%10%32%24%6%
768
November1st to 15thNight
18%10%31%26%11%2
700
16th to endNight
25%14%29%21%7%
720
December1st to 15thNight
28%16%32%18%3
720
16th to endNight
26%16%35%17%4
768
Page generated at 2017-11-01 17:23:38. Version ac04

Copyright 2017 A. Danko


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