C.E.K. Mees Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the C.E.K. Mees Observatory clear sky chart from 2005-11-05 to 2018-02-14.

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
28%
15482
12%
48840
8%
15447
34%
15447
15%
35713

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
12%
779
6%
2716
4%
776
16%
776
6%
2260
January16th to endNight
12%
832
7%
2723
3%
832
17%
832
6%
2253
February1st to 15thNight
9%
760
6%
2468
1%
757
14%
757
6%
2039
February16th to endNight
14%
631
9%
1968
3%
631
21%
631
9%
1572
March1st to 15thNight
16%
720
11%
2024
4%
720
23%
720
11%
1600
March16th to endNight
22%
768
15%
2082
7%
768
29%
768
16%
1561
April1st to 15thNight
21%
718
13%
1796
5%
718
25%
718
18%
1360
April16th to endNight
32%
666
17%
1746
7%
666
38%
666
26%
1208
May1st to 15thNight
41%
435
15%
1515
10%
435
48%
435
16%
1038
May16th to endNight
43%
374
16%
1497
16%
374
53%
374
21%
908
June1st to 15thNight
42%
360
12%
1440
12%
360
51%
360
18%
914
June16th to endNight
47%
360
12%
1440
15%
360
53%
360
21%
856
July1st to 15thNight
58%
340
13%
1360
18%
340
63%
340
26%
782
July16th to endNight
53%
426
15%
1464
14%
400
57%
400
26%
864
August1st to 15thNight
53%
539
15%
1609
11%
536
56%
536
30%
1001
August16th to endNight
56%
697
21%
1843
13%
697
59%
697
35%
1165
September1st to 15thNight
48%
720
19%
1800
10%
720
52%
720
30%
1206
September16th to endNight
51%
717
22%
1980
17%
717
54%
717
29%
1300
October1st to 15thNight
35%
720
14%
2160
12%
720
40%
720
20%
1500
October16th to endNight
19%
768
10%
2310
5%
768
26%
768
13%
1757
November1st to 15thNight
24%
760
15%
2527
10%
760
32%
760
15%
1770
November16th to endNight
20%
780
11%
2730
7%
780
26%
780
11%
2067
December1st to 15thNight
13%
780
5%
2730
2%
780
17%
780
6%
2228
December16th to endNight
10%
832
4%
2912
1%
832
14%
832
5%
2504

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%10%48%7%35%45%6%28%
49235
Night
14%10%48%7%35%45%6%29%
49015
Cloud CoverDay
14%11%5%8%7%35%45%6%27%
49245
Night
13%10%48%7%35%5%5%6%29%
49020
TransparencyDay
55%7%11%16%8%
48928
Night
52%7%12%16%8%
48840
SeeingDay
19%16%28%20%10%4
5921
Night
20%17%28%22%9%1
15484

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
11%15%7%13%12%5%7%435%13%
1552
16th to endDay
8%15%8%16%12%46%5%3413%
1849
February1st to 15thDay
14%15%9%13%11%5%5%33314%
1695
16th to endDay
14%16%7%12%9%4443418%
1503
March1st to 15thDay
14%16%7%10%7%3434421%
1924
16th to endDay
14%13%6%9%6%3435%6%26%
2142
April1st to 15thDay
16%13%5%8%6%24345%28%
2152
16th to endDay
15%11%36%424445%36%
2223
May1st to 15thDay
15%9%37%6%345%46%32%
2436
16th to endDay
14%6%25%6%35%45%9%35%
2618
June1st to 15thDay
20%6%36%5%35%46%6%31%
2520
16th to endDay
14%5%16%6%45%5%6%8%34%
2520
July1st to 15thDay
10%5%25%6%45%7%7%8%36%
2520
16th to endDay
12%5%26%7%47%5%7%9%31%
2602
August1st to 15thDay
12%6%37%6%5%6%5%5%9%32%
2340
16th to endDay
13%7%26%6%5%5%5%7%7%32%
2345
September1st to 15thDay
18%6%25%5%45%446%36%
2160
16th to endDay
15%5%25%5%35%5%5%6%39%
1977
October1st to 15thDay
19%8%36%5%2435%6%33%
1800
16th to endDay
23%14%47%5%43445%23%
1914
November1st to 15thDay
12%16%37%6%44445%29%
1659
16th to endDay
14%16%6%8%5%44446%22%
1560
December1st to 15thDay
13%21%7%13%7%3344417%
1560
16th to endDay
15%15%11%14%9%45%5%349%
1664
January1st to 15thNight
13%15%6%13%10%5%6%445%13%
2716
16th to endNight
9%14%7%12%13%6%6%5%5%415%
2723
February1st to 15thNight
12%15%7%14%9%35%5%4416%
2466
16th to endNight
11%11%7%14%11%35%35%6%18%
1968
March1st to 15thNight
14%12%6%10%8%34445%24%
2012
16th to endNight
15%11%5%8%7%34345%30%
2082
April1st to 15thNight
16%13%45%6%25%445%31%
1796
16th to endNight
14%8%27%424446%39%
1746
May1st to 15thNight
16%6%25%6%35%5%5%7%33%
1515
16th to endNight
10%6%26%4245%5%7%43%
1495
June1st to 15thNight
15%5%25%5%25%5%6%7%37%
1440
16th to endNight
11%424425%5%6%8%42%
1440
July1st to 15thNight
5%5%345%25%6%5%11%44%
1440
16th to endNight
10%4245%35%6%7%8%43%
1564
August1st to 15thNight
9%415%6%345%5%8%45%
1620
16th to endNight
9%425%42345%7%48%
1843
September1st to 15thNight
16%425%424447%44%
1800
16th to endNight
14%424325%6%6%7%41%
1980
October1st to 15thNight
18%8%36%5%24346%36%
2160
16th to endNight
23%11%37%5%335%45%27%
2310
November1st to 15thNight
15%13%26%5%34447%32%
2527
16th to endNight
14%15%5%8%6%4445%5%24%
2730
December1st to 15thNight
16%16%6%10%7%35%5%45%16%
2730
16th to endNight
15%14%10%13%9%5%5%45%412%
2912

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
11%15%7%14%10%5%6%5%4413%
1552
16th to endDay
7%15%9%15%13%47%44413%
1849
February1st to 15thDay
13%15%9%13%11%46%43314%
1695
16th to endDay
15%15%7%12%10%3443319%
1503
March1st to 15thDay
14%16%7%11%6%2435%5%22%
1935
16th to endDay
14%13%6%9%5%4445%6%25%
2141
April1st to 15thDay
16%13%6%8%6%2335%5%28%
2152
16th to endDay
14%12%35%5%24346%36%
2223
May1st to 15thDay
14%9%47%6%35%446%32%
2436
16th to endDay
13%7%36%6%35%5%5%7%34%
2618
June1st to 15thDay
19%7%36%6%35%47%6%30%
2520
16th to endDay
12%5%26%7%46%5%6%9%32%
2520
July1st to 15thDay
8%436%7%46%6%7%9%34%
2520
16th to endDay
11%5%36%7%47%6%7%9%30%
2602
August1st to 15thDay
11%7%36%7%47%5%7%8%30%
2340
16th to endDay
12%6%36%7%46%6%5%8%31%
2345
September1st to 15thDay
17%7%25%6%4436%6%35%
2160
16th to endDay
15%6%25%5%35%5%5%6%38%
1977
October1st to 15thDay
18%9%37%6%23347%31%
1800
16th to endDay
21%15%5%6%6%43445%22%
1914
November1st to 15thDay
12%16%38%7%45%45%5%28%
1659
16th to endDay
14%16%6%9%6%3445%6%22%
1560
December1st to 15thDay
12%20%9%13%7%3434416%
1560
16th to endDay
15%15%10%14%10%5%5%435%9%
1664
January1st to 15thNight
13%14%6%12%10%5%5%6%5%5%13%
2716
16th to endNight
8%14%8%11%12%6%7%5%5%5%14%
2723
February1st to 15thNight
11%15%6%13%10%46%5%45%16%
2459
16th to endNight
11%11%6%14%11%5%5%446%19%
1968
March1st to 15thNight
14%12%5%11%7%35%34425%
2024
16th to endNight
15%10%5%8%8%34435%30%
2082
April1st to 15thNight
16%12%45%6%3445%6%30%
1796
16th to endNight
13%8%37%5%24446%39%
1746
May1st to 15thNight
15%7%26%6%46%6%5%7%32%
1515
16th to endNight
10%6%25%5%35%46%7%42%
1495
June1st to 15thNight
14%6%25%5%35%5%5%8%38%
1440
16th to endNight
10%5%25%425%5%7%8%42%
1440
July1st to 15thNight
5%5%25%5%35%5%6%9%45%
1440
16th to endNight
9%3245%35%6%6%8%43%
1564
August1st to 15thNight
8%415%5%346%7%7%44%
1620
16th to endNight
9%425%43445%6%48%
1843
September1st to 15thNight
15%5%1442445%6%44%
1800
16th to endNight
13%5%144346%5%7%41%
1980
October1st to 15thNight
17%9%36%5%3335%6%35%
2160
16th to endNight
22%11%36%6%3445%5%26%
2310
November1st to 15thNight
14%11%37%6%245%46%33%
2527
16th to endNight
14%14%5%8%7%35%5%5%6%24%
2730
December1st to 15thNight
16%15%6%10%8%46%5%5%5%16%
2730
16th to endNight
14%14%9%14%9%5%5%44411%
2912

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
71%6%7%9%4
1553
16th to endDay
71%7%10%7%2
1849
February1st to 15thDay
73%5%8%8%3
1697
16th to endDay
68%49%12%4
1503
March1st to 15thDay
63%5%11%12%5%
1935
16th to endDay
57%6%9%16%8%
2142
April1st to 15thDay
58%49%15%10%1
2152
16th to endDay
48%5%8%18%16%2
2223
May1st to 15thDay
51%6%10%19%10%1
2436
16th to endDay
46%8%12%18%12%1
2622
June1st to 15thDay
50%7%12%18%10%
2520
16th to endDay
45%9%13%20%11%
2520
July1st to 15thDay
42%9%11%23%12%
2371
16th to endDay
46%9%14%18%9%1
2439
August1st to 15thDay
47%9%13%18%9%
2327
16th to endDay
46%8%12%21%9%1
2345
September1st to 15thDay
47%6%11%22%11%
2160
16th to endDay
44%7%11%21%14%1
1977
October1st to 15thDay
51%5%11%16%12%1
1800
16th to endDay
63%414%13%3
1914
November1st to 15thDay
56%6%12%15%8%1
1659
16th to endDay
60%6%13%15%3
1560
December1st to 15thDay
70%6%11%9%1
1560
16th to endDay
75%7%9%5%1
1664
January1st to 15thNight
68%7%9%8%4
2716
16th to endNight
66%8%11%10%3
2723
February1st to 15thNight
67%7%10%10%3
2468
16th to endNight
64%5%12%11%5%
1968
March1st to 15thNight
60%6%11%15%5%
2024
16th to endNight
55%5%10%15%12%
2082
April1st to 15thNight
53%5%11%17%11%
1796
16th to endNight
44%5%11%20%15%2
1746
May1st to 15thNight
47%8%11%19%12%1
1515
16th to endNight
38%8%15%22%13%1
1497
June1st to 15thNight
42%8%15%21%12%
1440
16th to endNight
35%10%13%23%15%1
1440
July1st to 15thNight
32%9%15%22%18%1
1360
16th to endNight
34%8%15%25%13%2
1464
August1st to 15thNight
34%8%17%27%11%
1609
16th to endNight
33%6%13%29%14%1
1843
September1st to 15thNight
38%7%14%23%13%2
1800
16th to endNight
38%7%13%24%15%
1980
October1st to 15thNight
48%6%12%18%13%
2160
16th to endNight
56%6%17%13%4
2310
November1st to 15thNight
50%6%13%17%8%3
2527
16th to endNight
58%7%13%15%4
2730
December1st to 15thNight
67%6%13%9%2
2730
16th to endNight
73%6%9%8%1
2912

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
15%34%36%7%41
90
16th to endDay
17%30%42%7%
139
February1st to 15thDay
25%40%28%5%
130
16th to endDay
25%23%35%12%1
162
March1st to 15thDay
27%22%27%17%4
270
16th to endDay
22%22%31%14%7%1
288
April1st to 15thDay
27%21%29%14%41
270
16th to endDay
19%19%27%21%9%3
270
May1st to 15thDay
26%18%24%16%11%3
288
16th to endDay
14%13%36%19%10%5%
331
June1st to 15thDay
20%11%30%25%10%2
315
16th to endDay
15%12%32%26%9%3
315
July1st to 15thDay
10%5%29%35%13%5%
305
16th to endDay
13%9%27%30%14%5%
326
August1st to 15thDay
12%7%29%23%16%11%
313
16th to endDay
12%7%23%23%16%16%
332
September1st to 15thDay
16%10%19%20%21%10%
315
16th to endDay
15%10%19%21%19%13%
314
October1st to 15thDay
19%13%25%21%14%5%
315
16th to endDay
28%21%27%17%4
334
November1st to 15thDay
20%17%31%17%12%
223
16th to endDay
17%37%28%14%1
90
December1st to 15thDay
22%30%25%16%41
90
16th to endDay
26%41%25%7%
96
January1st to 15thNight
22%30%31%12%2
780
16th to endNight
19%26%34%16%2
832
February1st to 15thNight
21%28%35%13%1
760
16th to endNight
20%28%31%17%2
631
March1st to 15thNight
24%26%29%16%2
720
16th to endNight
22%19%30%20%6%
768
April1st to 15thNight
23%19%31%21%2
718
16th to endNight
18%12%32%25%9%1
666
May1st to 15thNight
19%8%24%34%11%
435
16th to endNight
12%7%31%31%16%
375
June1st to 15thNight
15%8%26%33%15%
360
16th to endNight
11%6%29%40%10%
360
July1st to 15thNight
8%223%42%21%1
340
16th to endNight
11%325%36%20%3
426
August1st to 15thNight
11%224%35%21%4
539
16th to endNight
11%422%32%27%2
697
September1st to 15thNight
18%7%19%29%22%3
720
16th to endNight
15%8%21%22%25%6%
717
October1st to 15thNight
22%11%24%23%15%1
720
16th to endNight
29%16%29%19%4
768
November1st to 15thNight
22%15%33%20%6%1
760
16th to endNight
23%25%26%17%6%1
780
December1st to 15thNight
26%25%30%13%3
780
16th to endNight
25%26%32%12%2
832
Page generated at 2018-02-15 10:58:45. Version ac04

Copyright 2018 A. Danko


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