Observatoire du Mont-Cosmos
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire du Mont-Cosmos clear sky chart from 2005-11-05 to 2017-08-12.

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
25%
14516
11%
46504
6%
14484
31%
14484
13%
34879

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
11%
720
9%
2506
4%
716
18%
716
6%
2050
January16th to endNight
15%
768
9%
2688
3%
768
23%
768
8%
2096
February1st to 15thNight
16%
704
8%
2343
3%
701
23%
701
7%
1887
February16th to endNight
15%
631
11%
1893
3%
631
25%
631
10%
1479
March1st to 15thNight
18%
720
14%
2156
6%
720
26%
720
13%
1627
March16th to endNight
26%
768
16%
2030
6%
768
33%
768
17%
1504
April1st to 15thNight
22%
718
14%
1796
5%
718
28%
718
17%
1383
April16th to endNight
23%
540
15%
1620
6%
540
30%
540
16%
1151
May1st to 15thNight
28%
474
12%
1554
10%
474
33%
474
15%
1125
May16th to endNight
28%
375
10%
1494
9%
374
37%
374
12%
1063
June1st to 15thNight
31%
360
7%
1260
5%
360
35%
360
13%
938
June16th to endNight
40%
360
8%
1260
8%
360
43%
360
18%
867
July1st to 15thNight
41%
340
8%
1354
10%
340
45%
340
17%
905
July16th to endNight
46%
376
10%
1418
12%
354
48%
354
17%
922
August1st to 15thNight
45%
417
11%
1466
10%
415
48%
415
18%
989
August16th to endNight
45%
588
15%
1638
8%
588
49%
588
26%
1103
September1st to 15thNight
36%
660
11%
1699
4%
660
38%
660
24%
1221
September16th to endNight
38%
657
18%
1815
11%
657
44%
657
27%
1197
October1st to 15thNight
28%
660
16%
1901
9%
660
35%
660
18%
1385
October16th to endNight
19%
704
9%
2288
4%
704
26%
704
10%
1791
November1st to 15thNight
25%
700
15%
2277
10%
700
33%
700
13%
1690
November16th to endNight
21%
735
12%
2522
7%
735
28%
735
10%
1927
December1st to 15thNight
14%
750
5%
2700
1%
750
18%
750
6%
2236
December16th to endNight
14%
791
8%
2826
4%
791
20%
791
5%
2343

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
20%11%47%6%34446%26%
47465
Night
18%11%47%6%34445%28%
46674
TransparencyDay
58%6%10%16%7%
47153
Night
57%6%10%17%7%
46504
SeeingDay
24%15%29%19%9%2
5903
Night
24%15%28%23%8%
14516

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
16%14%7%14%8%45%425%17%
1432
16th to endDay
10%14%7%11%9%45%5%4422%
1536
February1st to 15thDay
11%18%8%11%10%35%335%18%
1516
16th to endDay
13%18%6%11%8%3444321%
1580
March1st to 15thDay
17%14%6%8%6%33335%26%
1793
16th to endDay
16%11%5%8%5%3443431%
2193
April1st to 15thDay
22%11%47%42333430%
2152
16th to endDay
23%11%25%423335%32%
2340
May1st to 15thDay
23%9%47%5%34435%28%
2406
16th to endDay
22%10%47%5%3446%5%24%
2618
June1st to 15thDay
26%7%35%5%35%46%7%24%
2700
16th to endDay
23%7%46%6%35%45%7%24%
2700
July1st to 15thDay
17%6%36%6%35%5%5%8%29%
2523
16th to endDay
19%7%36%6%36%5%6%7%26%
2654
August1st to 15thDay
20%8%36%6%36%5%5%8%24%
2386
16th to endDay
16%6%36%5%34448%37%
2209
September1st to 15thDay
22%7%25%42345%6%34%
1931
16th to endDay
18%7%25%323347%39%
1815
October1st to 15thDay
22%11%26%425%346%29%
1727
16th to endDay
26%15%37%6%3433319%
1584
November1st to 15thDay
22%13%46%6%3434426%
1581
16th to endDay
20%17%5%9%42332424%
1434
December1st to 15thDay
22%19%7%9%6%3323217%
1260
16th to endDay
23%16%9%10%5%3334317%
1395
January1st to 15thNight
16%14%7%11%8%35%43419%
2506
16th to endNight
10%13%7%11%9%36%6%45%20%
2688
February1st to 15thNight
9%14%6%11%12%5%6%45%420%
2342
16th to endNight
14%15%7%10%7%35%33424%
1893
March1st to 15thNight
18%12%46%6%3433429%
2143
16th to endNight
14%12%5%7%5%3444433%
2030
April1st to 15thNight
21%13%36%5%245%45%27%
1796
16th to endNight
21%8%36%5%23335%36%
1620
May1st to 15thNight
23%9%35%5%24445%30%
1554
16th to endNight
23%7%47%5%23445%29%
1492
June1st to 15thNight
23%9%36%6%25%45%5%26%
1260
16th to endNight
17%6%36%5%35%5%7%6%31%
1260
July1st to 15thNight
17%5%26%5%35%45%8%34%
1434
16th to endNight
14%5%35%6%35%5%5%7%37%
1514
August1st to 15thNight
16%7%35%435%35%9%35%
1476
16th to endNight
15%424435%46%9%39%
1638
September1st to 15thNight
21%6%25%3235%46%37%
1699
16th to endNight
19%5%14223345%45%
1815
October1st to 15thNight
21%8%35%5%2445%433%
1901
16th to endNight
25%13%37%5%24335%24%
2288
November1st to 15thNight
19%10%47%6%35%435%29%
2277
16th to endNight
19%15%6%8%5%2433427%
2522
December1st to 15thNight
20%16%6%11%7%3433318%
2700
16th to endNight
20%18%6%9%6%35%33317%
2826

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
70%48%10%6%
1433
16th to endDay
63%6%7%16%6%
1536
February1st to 15thDay
68%5%7%11%5%
1519
16th to endDay
66%37%13%7%1
1580
March1st to 15thDay
61%39%13%10%1
1803
16th to endDay
55%5%7%17%12%1
2193
April1st to 15thDay
57%38%17%9%3
2152
16th to endDay
54%48%17%12%2
2340
May1st to 15thDay
57%5%8%17%9%1
2406
16th to endDay
59%7%9%15%7%
2622
June1st to 15thDay
58%6%11%15%7%
2700
16th to endDay
58%6%9%17%7%
2700
July1st to 15thDay
50%7%15%19%7%
2374
16th to endDay
55%8%12%17%4
2487
August1st to 15thDay
55%8%17%14%4
2372
16th to endDay
45%7%15%24%8%
2209
September1st to 15thDay
48%6%12%21%10%
1931
16th to endDay
44%5%12%27%9%
1815
October1st to 15thDay
55%5%12%21%6%
1727
16th to endDay
68%47%16%2
1584
November1st to 15thDay
59%6%11%14%7%
1581
16th to endDay
63%410%15%5%
1434
December1st to 15thDay
73%47%11%2
1260
16th to endDay
73%45%8%6%
1395
January1st to 15thNight
68%5%7%13%4
2506
16th to endNight
63%5%9%14%5%
2688
February1st to 15thNight
65%6%7%13%5%
2343
16th to endNight
63%38%12%10%
1893
March1st to 15thNight
57%5%8%17%9%1
2156
16th to endNight
52%5%9%17%12%2
2030
April1st to 15thNight
56%47%17%10%2
1796
16th to endNight
50%6%9%16%13%3
1620
May1st to 15thNight
54%5%9%15%13%1
1554
16th to endNight
55%6%10%17%9%
1494
June1st to 15thNight
58%5%10%16%7%1
1260
16th to endNight
47%7%14%20%8%
1260
July1st to 15thNight
45%8%16%20%7%
1354
16th to endNight
44%9%17%19%9%
1418
August1st to 15thNight
46%8%18%23%3
1466
16th to endNight
40%8%18%25%7%
1638
September1st to 15thNight
46%7%13%23%8%
1699
16th to endNight
40%5%13%28%10%
1815
October1st to 15thNight
51%6%10%22%8%
1901
16th to endNight
62%5%10%16%4
2288
November1st to 15thNight
55%6%13%15%7%
2277
16th to endNight
61%49%17%6%
2522
December1st to 15thNight
71%5%9%11%2
2700
16th to endNight
70%5%8%9%5%
2826

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%21%45%13%1
60
16th to endDay
23%28%34%10%11
64
February1st to 15thDay
24%19%31%18%5%
137
16th to endDay
20%19%34%19%5%
239
March1st to 15thDay
24%20%30%18%41
270
16th to endDay
22%19%26%16%12%2
288
April1st to 15thDay
30%17%27%18%41
270
16th to endDay
24%19%32%12%8%2
270
May1st to 15thDay
33%12%28%15%7%1
288
16th to endDay
21%16%35%17%6%1
331
June1st to 15thDay
29%13%25%21%9%
495
16th to endDay
26%10%30%22%8%
495
July1st to 15thDay
19%12%32%23%11%1
308
16th to endDay
19%8%31%28%10%1
326
August1st to 15thDay
19%9%30%19%15%5%
297
16th to endDay
19%8%26%23%16%5%
268
September1st to 15thDay
21%7%27%22%13%7%
255
16th to endDay
16%18%27%18%12%7%
254
October1st to 15thDay
26%15%26%14%12%5%
248
16th to endDay
34%17%26%15%5%1
240
November1st to 15thDay
26%20%22%20%9%
235
16th to endDay
32%18%17%20%9%1
141
December1st to 15thDay
41%13%30%11%11
60
16th to endDay
29%35%26%7%
64
January1st to 15thNight
24%24%31%15%3
720
16th to endNight
19%18%34%21%5%
768
February1st to 15thNight
15%22%35%20%5%
704
16th to endNight
24%19%32%18%4
631
March1st to 15thNight
25%18%33%18%3
720
16th to endNight
21%17%29%24%6%
768
April1st to 15thNight
27%15%29%21%5%
718
16th to endNight
25%15%28%22%8%
540
May1st to 15thNight
26%12%25%25%8%
474
16th to endNight
24%9%29%28%8%
375
June1st to 15thNight
28%6%26%27%11%
360
16th to endNight
20%6%27%35%10%
360
July1st to 15thNight
19%5%27%34%12%
340
16th to endNight
15%325%43%11%
376
August1st to 15thNight
20%423%30%19%
417
16th to endNight
17%5%25%33%15%1
588
September1st to 15thNight
22%8%26%29%11%1
660
16th to endNight
22%9%26%26%13%1
657
October1st to 15thNight
21%13%30%23%10%1
660
16th to endNight
33%16%25%17%7%
704
November1st to 15thNight
25%17%25%23%8%
700
16th to endNight
27%19%26%16%8%1
735
December1st to 15thNight
30%19%28%15%5%
750
16th to endNight
30%20%26%17%41
791
Page generated at 2017-08-13 14:16:48. Version ac04

Copyright 2017 A. Danko


Observatoire du Mont-Cosmos Clear Sky Chart | Charts Home