Observatoire Magenta
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire Magenta clear sky chart from 2005-11-06 to 2024-01-27.

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
29%
22627
11%
74926
8%
22586
34%
22586
14%
56052

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
15%
760
6%
2649
3%
757
19%
757
6%
2239
January11th to 20thNight
14%
760
7%
2660
4%
760
18%
760
7%
2207
January21st to endNight
21%
820
9%
2868
6%
820
26%
820
10%
2231
February1st to 10thNight
15%
720
7%
2411
3%
720
22%
720
7%
2007
February11th to 20thNight
18%
703
9%
2140
4%
700
25%
700
10%
1721
February21st to endNight
23%
592
12%
1776
7%
592
31%
592
12%
1383
March1st to 10thNight
24%
720
13%
2160
9%
720
30%
720
13%
1672
March11th to 20thNight
24%
720
13%
2109
7%
720
31%
720
14%
1603
March21st to endNight
28%
792
19%
1980
8%
792
34%
792
18%
1493
April1st to 10thNight
24%
720
12%
1800
4%
720
28%
720
16%
1412
April11th to 20thNight
27%
711
14%
1775
4%
711
32%
711
19%
1343
April21st to endNight
25%
545
16%
1625
7%
545
32%
545
17%
1182
May1st to 10thNight
28%
468
14%
1548
10%
468
35%
468
16%
1105
May11th to 20thNight
31%
354
17%
1416
17%
354
40%
354
16%
936
May21st to endNight
37%
388
12%
1551
11%
388
47%
388
17%
1022
June1st to 10thNight
33%
360
10%
1440
11%
360
41%
360
14%
999
June11th to 20thNight
40%
360
11%
1440
13%
360
46%
360
18%
922
June21st to endNight
40%
360
9%
1440
12%
360
46%
360
15%
966
July1st to 10thNight
46%
350
12%
1400
16%
350
52%
350
20%
872
July11th to 20thNight
56%
348
13%
1392
19%
348
60%
348
21%
862
July21st to endNight
49%
394
12%
1486
16%
372
52%
372
19%
963
August1st to 10thNight
55%
358
15%
1422
17%
356
57%
356
20%
885
August11th to 20thNight
52%
533
15%
1597
10%
533
54%
533
24%
1079
August21st to endNight
51%
792
16%
1980
9%
792
52%
792
27%
1379
September1st to 10thNight
46%
720
13%
1800
6%
720
47%
720
28%
1253
September11th to 20thNight
51%
720
17%
1908
12%
720
53%
720
31%
1230
September21st to endNight
40%
720
19%
1980
14%
720
43%
720
26%
1347
October1st to 10thNight
34%
720
17%
2051
10%
720
41%
720
20%
1460
October11th to 20thNight
29%
720
13%
2229
10%
720
35%
720
15%
1671
October21st to endNight
22%
792
10%
2574
6%
792
28%
792
12%
1986
November1st to 10thNight
23%
740
13%
2407
8%
740
31%
740
13%
1771
November11th to 20thNight
23%
760
15%
2488
11%
760
30%
760
13%
1891
November21st to endNight
19%
760
9%
2660
6%
760
25%
760
9%
2096
December1st to 10thNight
15%
760
5%
2660
2%
760
19%
760
6%
2271
December11th to 20thNight
15%
760
7%
3256
3%
759
19%
759
5%
2665
December21st to endNight
13%
827
4%
4848
2%
817
17%
817
3%
3928

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%10%47%6%35%45%7%30%
74882
Night
20%12%48%6%34446%29%
75165
TransparencyDay
54%7%13%18%8%1
74587
Night
57%6%11%17%8%1
74994
SeeingDay
25%14%28%21%10%2
13558
Night
26%11%27%26%9%1
22637

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
22%21%7%10%6%4434415%
1517
11th to 20thDay
19%19%7%10%7%35%44417%
1520
21st to endDay
12%14%5%10%9%5%7%5%46%22%
1632
February1st to 10thDay
17%17%6%11%7%5%6%45%419%
1548
11th to 20thDay
16%16%7%11%6%35%445%23%
1708
21st to endDay
17%16%6%8%8%45%446%23%
1480
March1st to 10thDay
16%14%5%9%6%46%45%5%26%
1797
11th to 20thDay
19%12%5%8%6%34436%31%
1845
21st to endDay
20%12%5%8%6%34345%32%
2376
April1st to 10thDay
24%12%5%6%6%2445%5%27%
2160
11th to 20thDay
22%9%35%5%34445%36%
2134
21st to endDay
25%9%35%6%34446%30%
2335
May1st to 10thDay
21%8%46%6%33447%34%
2426
11th to 20thDay
19%6%37%5%35%5%5%6%35%
2478
21st to endDay
19%6%36%6%45%5%6%8%33%
2725
June1st to 10thDay
25%7%35%5%35%5%6%7%30%
2520
11th to 20thDay
17%5%36%5%35%5%6%9%37%
2520
21st to endDay
23%7%37%5%35%45%7%31%
2520
July1st to 10thDay
15%5%36%5%35%5%6%9%38%
2520
11th to 20thDay
15%5%25%5%46%6%7%9%35%
2520
21st to endDay
16%6%25%5%35%5%8%9%35%
2744
August1st to 10thDay
15%5%36%7%45%6%6%10%33%
2506
11th to 20thDay
14%6%35%6%35%6%6%9%38%
2283
21st to endDay
16%6%25%5%35%5%6%9%39%
2376
September1st to 10thDay
15%6%25%5%35%5%6%7%41%
2160
11th to 20thDay
18%5%24324447%46%
2052
21st to endDay
17%7%25%5%3447%9%38%
1980
October1st to 10thDay
25%7%36%6%35%45%8%28%
1908
11th to 20thDay
22%9%37%7%35%5%5%7%28%
1730
21st to endDay
28%13%26%5%43436%25%
1782
November1st to 10thDay
20%12%45%5%445%5%5%31%
1671
11th to 20thDay
20%13%6%9%7%25%446%24%
1691
21st to endDay
23%16%47%6%345%6%5%21%
1520
December1st to 10thDay
25%18%6%10%7%35%33416%
1520
11th to 20thDay
24%15%6%8%5%4445%5%21%
1906
21st to endDay
26%17%5%10%7%4444316%
2772
January1st to 10thNight
21%19%7%11%7%4443416%
2649
11th to 20thNight
18%18%7%12%7%45%44419%
2660
21st to endNight
17%13%6%10%8%45%445%24%
2868
February1st to 10thNight
18%16%6%13%8%45%445%18%
2411
11th to 20thNight
16%14%6%11%9%35%445%23%
2138
21st to endNight
18%15%5%9%7%35%335%28%
1776
March1st to 10thNight
18%15%6%8%6%34445%27%
2150
11th to 20thNight
21%13%5%7%6%44345%29%
2108
21st to endNight
20%14%45%42444434%
1980
April1st to 10thNight
25%11%47%6%34445%27%
1800
11th to 20thNight
24%9%36%5%33435%34%
1775
21st to endNight
23%10%37%5%34346%33%
1625
May1st to 10thNight
22%10%36%5%34346%32%
1548
11th to 20thNight
20%8%36%6%3446%6%35%
1415
21st to endNight
18%6%35%5%35%45%7%38%
1550
June1st to 10thNight
26%6%345%35%46%7%30%
1440
11th to 20thNight
19%6%25%435%45%7%38%
1440
21st to endNight
17%7%46%6%35%5%5%8%34%
1440
July1st to 10thNight
13%6%35%5%36%5%7%8%38%
1440
11th to 20thNight
11%5%35%6%37%6%7%8%39%
1440
21st to endNight
14%5%26%5%46%6%7%8%37%
1574
August1st to 10thNight
15%5%246%445%8%9%38%
1432
11th to 20thNight
14%6%36%6%345%5%8%39%
1597
21st to endNight
14%6%35%5%35%5%6%7%40%
1980
September1st to 10thNight
16%6%36%5%2446%6%41%
1800
11th to 20thNight
15%5%245%24447%46%
1908
21st to endNight
20%6%25%5%34347%41%
1980
October1st to 10thNight
20%7%36%5%345%5%7%35%
2051
11th to 20thNight
23%9%38%6%3445%6%29%
2229
21st to endNight
27%11%36%5%45%445%26%
2574
November1st to 10thNight
21%13%46%435%5%46%30%
2407
11th to 20thNight
22%12%47%6%34445%28%
2488
21st to endNight
23%16%5%9%5%34435%24%
2660
December1st to 10thNight
25%18%8%9%8%34335%15%
2660
11th to 20thNight
25%16%5%11%6%3433420%
3288
21st to endNight
26%18%6%9%6%3333419%
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
73%5%10%10%2
1518
11th to 20thDay
71%5%10%9%5%
1520
21st to endDay
63%7%12%12%5%1
1632
February1st to 10thDay
70%6%9%11%41
1548
11th to 20thDay
65%5%14%12%41
1717
21st to endDay
64%6%10%12%6%1
1480
March1st to 10thDay
60%5%12%15%6%2
1800
11th to 20thDay
56%6%13%14%9%1
1845
21st to endDay
57%410%18%9%2
2376
April1st to 10thDay
60%6%9%17%8%1
2160
11th to 20thDay
52%5%10%20%12%1
2134
21st to endDay
57%6%10%16%9%3
2335
May1st to 10thDay
51%5%9%19%13%2
2426
11th to 20thDay
49%7%11%18%13%2
2482
21st to endDay
49%9%12%18%11%1
2725
June1st to 10thDay
53%7%12%18%9%1
2520
11th to 20thDay
44%7%12%23%11%2
2520
21st to endDay
53%8%11%19%8%1
2520
July1st to 10thDay
41%8%15%26%10%
2450
11th to 20thDay
43%8%16%27%6%
2445
21st to endDay
44%10%17%23%7%
2591
August1st to 10thDay
46%9%17%22%5%
2492
11th to 20thDay
41%9%19%21%10%
2283
21st to endDay
42%8%15%24%11%
2376
September1st to 10thDay
42%8%14%25%11%1
2160
11th to 20thDay
39%5%13%31%12%
2052
21st to endDay
43%7%16%25%9%1
1980
October1st to 10thDay
55%7%13%17%8%
1908
11th to 20thDay
54%8%16%16%6%
1730
21st to endDay
63%5%11%14%5%1
1782
November1st to 10thDay
55%7%12%18%7%
1671
11th to 20thDay
62%6%12%12%8%1
1691
21st to endDay
65%7%15%9%3
1520
December1st to 10thDay
73%6%11%8%2
1520
11th to 20thDay
66%6%10%13%4
1906
21st to endDay
72%7%11%7%3
2772
January1st to 10thNight
73%5%10%9%2
2649
11th to 20thNight
71%5%9%10%4
2660
21st to endNight
64%5%11%12%7%1
2868
February1st to 10thNight
70%6%8%11%5%
2411
11th to 20thNight
65%5%9%15%5%
2140
21st to endNight
62%49%14%10%1
1776
March1st to 10thNight
61%5%10%15%8%1
2160
11th to 20thNight
59%49%16%10%2
2109
21st to endNight
54%5%7%19%11%3
1980
April1st to 10thNight
60%5%9%16%10%1
1800
11th to 20thNight
54%5%8%19%13%1
1775
21st to endNight
54%5%10%17%12%3
1625
May1st to 10thNight
54%5%7%17%14%4
1548
11th to 20thNight
48%6%9%18%16%3
1416
21st to endNight
46%8%10%20%13%2
1551
June1st to 10thNight
52%7%11%20%9%1
1440
11th to 20thNight
45%7%12%20%13%3
1440
21st to endNight
48%8%14%18%11%
1440
July1st to 10thNight
40%9%14%22%14%1
1400
11th to 20thNight
38%10%14%27%10%
1392
21st to endNight
41%11%15%24%9%
1486
August1st to 10thNight
40%9%18%24%9%
1422
11th to 20thNight
43%7%16%23%11%
1597
21st to endNight
42%8%15%24%11%1
1980
September1st to 10thNight
42%8%12%25%12%1
1800
11th to 20thNight
38%6%16%29%11%1
1908
21st to endNight
44%6%12%24%14%1
1980
October1st to 10thNight
49%7%12%21%11%
2051
11th to 20thNight
56%7%11%20%6%
2229
21st to endNight
61%6%10%14%8%1
2574
November1st to 10thNight
56%6%12%18%7%1
2407
11th to 20thNight
59%6%12%14%8%2
2488
21st to endNight
65%6%12%13%4
2660
December1st to 10thNight
74%5%9%9%2
2660
11th to 20thNight
70%5%9%11%4
3288
21st to endNight
72%5%9%12%2
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
30%16%28%18%8%1
180
11th to 20thDay
31%21%31%13%41
180
21st to endDay
23%17%36%17%6%1
188
February1st to 10thDay
34%27%27%11%1
208
11th to 20thDay
27%20%34%16%3
376
21st to endDay
25%21%28%23%4
346
March1st to 10thDay
27%18%27%22%5%
420
11th to 20thDay
26%19%33%15%6%1
420
21st to endDay
30%18%22%21%7%1
462
April1st to 10thDay
33%14%28%17%7%1
420
11th to 20thDay
32%18%23%16%8%3
412
21st to endDay
33%11%32%14%9%2
420
May1st to 10thDay
30%13%30%18%8%2
423
11th to 20thDay
21%13%30%25%10%3
447
21st to endDay
19%12%34%23%10%2
485
June1st to 10thDay
27%13%29%22%7%2
450
11th to 20thDay
19%11%29%29%11%2
450
21st to endDay
24%9%31%23%11%2
450
July1st to 10thDay
16%7%28%32%14%3
445
11th to 20thDay
17%7%30%31%12%4
444
21st to endDay
20%7%28%30%14%2
488
August1st to 10thDay
17%7%25%29%18%3
446
11th to 20thDay
17%7%24%29%18%5%
439
21st to endDay
18%11%24%24%15%8%
495
September1st to 10thDay
17%9%30%23%15%7%
450
11th to 20thDay
17%10%22%23%18%10%
450
21st to endDay
18%12%25%23%17%5%
450
October1st to 10thDay
24%14%28%18%13%4
450
11th to 20thDay
28%18%23%20%11%1
414
21st to endDay
36%15%24%19%6%
396
November1st to 10thDay
30%17%28%18%7%
365
11th to 20thDay
30%21%25%15%9%1
351
21st to endDay
29%21%31%17%3
180
December1st to 10thDay
37%14%23%19%5%1
180
11th to 20thDay
28%24%31%13%41
180
21st to endDay
33%23%26%13%41
198
January1st to 10thNight
30%15%30%21%4
760
11th to 20thNight
27%16%32%19%6%
760
21st to endNight
25%13%30%25%7%
820
February1st to 10thNight
28%12%34%21%4
720
11th to 20thNight
24%15%33%23%4
703
21st to endNight
27%14%30%26%3
592
March1st to 10thNight
26%14%30%26%4
720
11th to 20thNight
30%14%27%23%7%
720
21st to endNight
28%13%26%25%7%1
792
April1st to 10thNight
30%13%28%24%5%
720
11th to 20thNight
29%14%26%23%7%
711
21st to endNight
28%14%28%24%7%
545
May1st to 10thNight
27%9%31%23%9%1
468
11th to 20thNight
24%8%30%28%10%1
354
21st to endNight
21%6%32%32%8%1
389
June1st to 10thNight
30%7%27%27%9%1
360
11th to 20thNight
21%5%27%33%14%
360
21st to endNight
17%8%26%36%12%1
360
July1st to 10thNight
13%5%30%40%11%1
350
11th to 20thNight
12%324%42%18%1
348
21st to endNight
14%426%41%15%
394
August1st to 10thNight
17%418%40%20%1
358
11th to 20thNight
16%420%36%22%2
533
21st to endNight
17%6%21%35%19%2
792
September1st to 10thNight
17%8%23%36%15%1
720
11th to 20thNight
18%8%19%33%21%3
720
21st to endNight
23%6%27%25%15%2
720
October1st to 10thNight
24%10%25%28%12%1
720
11th to 20thNight
28%11%25%25%9%2
720
21st to endNight
35%10%29%21%5%
792
November1st to 10thNight
29%13%30%21%6%1
740
11th to 20thNight
27%17%27%19%9%1
760
21st to endNight
33%16%28%18%5%1
760
December1st to 10thNight
36%14%26%20%4
760
11th to 20thNight
32%14%30%17%6%1
760
21st to endNight
34%16%27%19%4
836
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