Observatoire Astronomique Jean-Marc-Richard
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire Astronomique Jean-Marc-Richard 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
33%
22545
14%
74739
9%
22504
40%
22504
17%
52622

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
19%
760
10%
2649
5%
757
26%
757
9%
2069
January11th to 20thNight
22%
741
11%
2591
6%
741
28%
741
11%
2003
January21st to endNight
27%
792
13%
2772
8%
792
35%
792
15%
1969
February1st to 10thNight
20%
720
11%
2382
5%
720
29%
720
12%
1839
February11th to 20thNight
25%
703
14%
2179
6%
700
35%
700
16%
1568
February21st to endNight
26%
592
16%
1776
8%
592
37%
592
16%
1305
March1st to 10thNight
27%
720
16%
2160
11%
720
34%
720
16%
1581
March11th to 20thNight
27%
720
16%
2097
8%
720
36%
720
17%
1523
March21st to endNight
32%
792
21%
1980
9%
792
40%
792
24%
1438
April1st to 10thNight
28%
720
16%
1800
5%
720
34%
720
20%
1347
April11th to 20thNight
31%
711
17%
1775
5%
711
37%
711
23%
1282
April21st to endNight
28%
571
18%
1651
7%
571
37%
571
21%
1173
May1st to 10thNight
31%
414
16%
1494
11%
414
41%
414
17%
1000
May11th to 20thNight
33%
354
19%
1416
17%
354
45%
354
18%
904
May21st to endNight
35%
389
13%
1551
11%
388
47%
388
19%
979
June1st to 10thNight
40%
360
10%
1440
11%
360
48%
360
16%
971
June11th to 20thNight
43%
360
11%
1440
13%
360
50%
360
20%
891
June21st to endNight
43%
360
10%
1440
13%
360
48%
360
16%
946
July1st to 10thNight
51%
350
13%
1400
18%
350
58%
350
24%
815
July11th to 20thNight
54%
348
14%
1392
20%
348
58%
348
24%
820
July21st to endNight
55%
394
14%
1486
17%
372
58%
372
22%
869
August1st to 10thNight
60%
358
17%
1422
20%
356
62%
356
22%
844
August11th to 20thNight
54%
526
17%
1590
13%
526
57%
526
28%
1022
August21st to endNight
52%
792
18%
1980
10%
792
54%
792
32%
1333
September1st to 10thNight
52%
720
15%
1800
7%
720
55%
720
33%
1209
September11th to 20thNight
54%
720
20%
1876
13%
720
57%
720
34%
1196
September21st to endNight
46%
720
22%
1980
15%
720
52%
720
29%
1303
October1st to 10thNight
39%
720
21%
2096
14%
720
48%
720
24%
1417
October11th to 20thNight
34%
720
17%
2202
10%
720
42%
720
19%
1545
October21st to endNight
28%
792
12%
2574
8%
792
35%
792
15%
1864
November1st to 10thNight
30%
740
17%
2407
11%
740
39%
740
17%
1669
November11th to 20thNight
27%
760
18%
2541
12%
760
37%
760
18%
1778
November21st to endNight
23%
760
13%
2660
6%
760
32%
760
12%
1966
December1st to 10thNight
20%
760
9%
2660
4%
760
26%
760
10%
2074
December11th to 20thNight
18%
760
13%
3239
6%
759
28%
759
9%
2414
December21st to endNight
17%
826
7%
4841
3%
817
25%
817
6%
3696

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
18%8%36%6%35%5%5%7%34%
74784
Night
19%10%47%5%3445%6%33%
75003
TransparencyDay
50%6%12%21%11%1
74489
Night
52%5%11%20%11%1
74832
SeeingDay
21%10%27%25%13%4
13463
Night
23%7%29%30%11%1
22555

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
18%17%5%9%7%5%444423%
1517
11th to 20thDay
19%14%5%8%7%35%445%28%
1480
21st to endDay
11%13%48%7%47%5%5%7%29%
1584
February1st to 10thDay
16%15%6%8%7%335%46%28%
1575
11th to 20thDay
14%13%5%8%6%46%5%5%6%28%
1667
21st to endDay
18%15%6%8%6%25%45%427%
1480
March1st to 10thDay
16%12%48%7%5%6%445%30%
1797
11th to 20thDay
17%11%46%6%35%45%6%33%
1859
21st to endDay
19%9%47%6%2444436%
2376
April1st to 10thDay
22%10%46%7%35%44432%
2160
11th to 20thDay
21%8%36%6%34345%38%
2134
21st to endDay
22%9%37%5%34446%32%
2308
May1st to 10thDay
20%6%47%5%35%46%6%35%
2482
11th to 20thDay
19%6%26%5%45%46%7%37%
2478
21st to endDay
18%5%36%5%35%5%6%8%36%
2725
June1st to 10thDay
21%8%36%5%45%5%5%7%31%
2520
11th to 20thDay
15%6%26%6%35%6%5%8%38%
2520
21st to endDay
20%7%37%6%35%5%5%8%30%
2520
July1st to 10thDay
12%5%25%6%46%6%6%8%41%
2520
11th to 20thDay
13%435%6%35%7%7%9%37%
2520
21st to endDay
11%5%36%445%6%7%9%39%
2744
August1st to 10thDay
13%5%27%6%46%6%6%8%38%
2506
11th to 20thDay
10%5%36%5%45%5%7%8%41%
2288
21st to endDay
12%5%35%5%35%46%8%44%
2376
September1st to 10thDay
12%5%26%5%35%5%6%9%41%
2160
11th to 20thDay
15%424424446%49%
2083
21st to endDay
16%5%25%5%35%448%42%
1980
October1st to 10thDay
21%6%36%5%345%5%6%36%
1863
11th to 20thDay
20%7%47%8%46%5%6%6%29%
1757
21st to endDay
26%8%36%5%3445%6%30%
1782
November1st to 10thDay
17%9%36%5%25%5%5%7%35%
1671
11th to 20thDay
18%11%47%5%35%5%47%30%
1634
21st to endDay
22%11%35%6%36%5%5%6%28%
1520
December1st to 10thDay
25%11%7%9%6%34445%22%
1520
11th to 20thDay
22%13%5%6%6%2445%429%
1906
21st to endDay
27%15%410%5%33335%21%
2772
January1st to 10thNight
18%16%6%10%7%44445%21%
2649
11th to 20thNight
16%16%6%9%6%45%445%25%
2591
21st to endNight
12%12%6%8%8%35%45%6%31%
2772
February1st to 10thNight
14%14%6%11%7%45%45%6%23%
2382
11th to 20thNight
16%11%5%8%6%45%5%5%5%31%
2177
21st to endNight
16%13%5%8%7%35%35%432%
1776
March1st to 10thNight
18%12%5%7%6%34446%30%
2150
11th to 20thNight
18%12%47%5%34446%32%
2097
21st to endNight
18%10%36%5%3444438%
1980
April1st to 10thNight
25%7%47%5%345%5%5%31%
1800
11th to 20thNight
23%7%36%434345%37%
1775
21st to endNight
23%8%36%5%3345%5%35%
1651
May1st to 10thNight
21%7%37%5%25%447%35%
1494
11th to 20thNight
20%6%27%5%3445%6%38%
1415
21st to endNight
16%7%35%5%46%45%7%39%
1550
June1st to 10thNight
22%7%45%5%345%6%7%33%
1440
11th to 20thNight
17%6%36%4345%6%7%40%
1440
21st to endNight
18%5%36%5%35%5%5%8%35%
1440
July1st to 10thNight
11%5%25%6%35%5%7%8%43%
1440
11th to 20thNight
12%5%345%46%6%6%9%40%
1440
21st to endNight
12%5%25%6%445%6%9%42%
1574
August1st to 10thNight
12%5%35%5%345%5%9%43%
1432
11th to 20thNight
13%6%25%5%345%6%8%43%
1590
21st to endNight
14%5%25%5%35%46%8%43%
1980
September1st to 10thNight
12%427%5%35%5%5%7%45%
1800
11th to 20thNight
15%5%35%32335%7%49%
1876
21st to endNight
16%5%36%5%3445%6%44%
1980
October1st to 10thNight
18%6%26%5%345%5%5%40%
2096
11th to 20thNight
21%8%36%5%34446%35%
2202
21st to endNight
23%9%37%6%35%45%5%31%
2574
November1st to 10thNight
19%8%46%5%345%5%6%34%
2407
11th to 20thNight
19%9%47%5%345%5%6%34%
2541
21st to endNight
22%12%47%6%33345%29%
2660
December1st to 10thNight
21%13%6%9%6%345%45%22%
2660
11th to 20thNight
23%15%48%6%33445%27%
3288
21st to endNight
28%15%5%8%43333423%
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
65%5%9%16%5%
1518
11th to 20thDay
60%5%10%14%11%1
1480
21st to endDay
54%6%11%18%10%1
1584
February1st to 10thDay
59%410%18%6%2
1575
11th to 20thDay
57%6%12%15%9%1
1676
21st to endDay
60%39%16%10%2
1480
March1st to 10thDay
56%5%10%17%10%2
1800
11th to 20thDay
52%412%16%13%3
1859
21st to endDay
51%410%18%14%3
2376
April1st to 10thDay
56%47%18%12%2
2160
11th to 20thDay
49%47%22%15%2
2134
21st to endDay
54%5%8%17%13%3
2308
May1st to 10thDay
49%5%7%21%15%2
2482
11th to 20thDay
46%5%10%20%15%3
2482
21st to endDay
44%8%13%18%15%2
2725
June1st to 10thDay
51%7%11%19%11%2
2520
11th to 20thDay
44%5%11%24%13%3
2520
21st to endDay
52%6%13%18%10%1
2520
July1st to 10thDay
39%8%13%27%13%1
2450
11th to 20thDay
40%7%16%28%10%
2445
21st to endDay
40%7%17%26%9%
2591
August1st to 10thDay
42%7%18%25%8%
2492
11th to 20thDay
38%7%19%26%10%
2288
21st to endDay
37%6%16%26%14%
2376
September1st to 10thDay
39%6%14%28%12%1
2160
11th to 20thDay
35%5%13%32%15%1
2083
21st to endDay
42%5%14%27%11%1
1980
October1st to 10thDay
47%6%13%22%11%
1863
11th to 20thDay
54%7%13%20%7%
1757
21st to endDay
55%412%19%8%1
1782
November1st to 10thDay
48%5%14%23%9%1
1671
11th to 20thDay
53%6%11%18%11%
1634
21st to endDay
57%6%14%16%6%1
1520
December1st to 10thDay
66%5%11%14%5%
1520
11th to 20thDay
59%5%11%19%7%
1906
21st to endDay
69%312%10%6%
2772
January1st to 10thNight
65%49%16%5%
2649
11th to 20thNight
62%6%10%13%8%1
2591
21st to endNight
54%5%10%18%12%1
2772
February1st to 10thNight
63%48%17%7%1
2382
11th to 20thNight
55%411%21%9%1
2179
21st to endNight
55%5%8%17%14%1
1776
March1st to 10thNight
56%49%17%11%2
2160
11th to 20thNight
54%49%16%13%3
2098
21st to endNight
50%47%20%15%4
1980
April1st to 10thNight
54%48%19%14%2
1800
11th to 20thNight
50%47%22%15%2
1775
21st to endNight
52%48%20%13%4
1651
May1st to 10thNight
50%5%7%19%15%5%
1494
11th to 20thNight
48%49%18%17%4
1416
21st to endNight
45%5%11%20%17%2
1551
June1st to 10thNight
50%6%10%21%13%1
1440
11th to 20thNight
43%6%12%22%14%4
1440
21st to endNight
46%8%12%19%14%
1440
July1st to 10thNight
36%7%14%26%16%1
1400
11th to 20thNight
37%7%16%27%12%
1392
21st to endNight
37%8%17%25%12%
1486
August1st to 10thNight
39%7%18%25%12%
1422
11th to 20thNight
38%8%18%25%12%
1590
21st to endNight
38%7%15%26%13%1
1980
September1st to 10thNight
38%6%14%26%15%1
1800
11th to 20thNight
36%5%13%33%12%1
1876
21st to endNight
40%6%11%28%15%
1980
October1st to 10thNight
44%6%10%26%13%1
2096
11th to 20thNight
51%5%12%25%8%
2202
21st to endNight
55%5%12%18%9%1
2574
November1st to 10thNight
51%5%12%22%9%1
2407
11th to 20thNight
52%5%12%20%10%1
2541
21st to endNight
59%5%11%18%7%
2660
December1st to 10thNight
64%6%11%15%5%
2660
11th to 20thNight
61%49%18%8%1
3288
21st to endNight
67%39%15%5%
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
22%15%24%29%10%
180
11th to 20thDay
28%11%33%22%5%1
170
21st to endDay
17%13%35%26%7%1
176
February1st to 10thDay
35%17%32%16%
220
11th to 20thDay
23%12%36%25%5%
334
21st to endDay
28%12%31%25%4
346
March1st to 10thDay
23%11%33%24%9%
420
11th to 20thDay
22%13%32%26%6%1
420
21st to endDay
26%10%31%21%10%2
462
April1st to 10thDay
26%15%26%22%8%2
420
11th to 20thDay
27%15%23%22%10%3
412
21st to endDay
27%13%28%22%8%3
420
May1st to 10thDay
23%9%31%24%10%3
423
11th to 20thDay
19%8%31%25%12%4
447
21st to endDay
18%10%31%25%13%2
485
June1st to 10thDay
22%11%25%26%12%3
450
11th to 20thDay
17%10%24%30%15%4
450
21st to endDay
20%9%25%27%16%4
450
July1st to 10thDay
13%6%22%32%22%6%
445
11th to 20thDay
14%327%32%19%5%
444
21st to endDay
14%5%23%34%19%6%
488
August1st to 10thDay
14%424%31%21%7%
446
11th to 20thDay
10%420%31%22%12%
439
21st to endDay
14%7%25%24%20%10%
495
September1st to 10thDay
12%5%26%28%19%9%
450
11th to 20thDay
14%7%22%27%18%12%
450
21st to endDay
18%8%26%22%20%7%
450
October1st to 10thDay
21%10%26%22%15%6%
450
11th to 20thDay
20%11%32%23%11%3
428
21st to endDay
32%10%24%25%8%
396
November1st to 10thDay
26%12%26%23%12%1
365
11th to 20thDay
24%14%32%19%9%1
294
21st to endDay
28%13%27%22%8%2
180
December1st to 10thDay
29%11%25%23%10%2
180
11th to 20thDay
25%12%39%19%41
180
21st to endDay
32%16%28%16%7%1
198
January1st to 10thNight
27%10%30%27%6%
760
11th to 20thNight
24%10%33%26%7%
741
21st to endNight
19%7%34%31%8%1
792
February1st to 10thNight
21%8%37%28%6%1
720
11th to 20thNight
21%9%35%28%5%1
703
21st to endNight
24%8%31%33%4
592
March1st to 10thNight
24%7%33%29%6%
720
11th to 20thNight
25%9%32%26%8%
720
21st to endNight
22%8%30%32%8%
792
April1st to 10thNight
27%10%26%30%7%
720
11th to 20thNight
25%10%30%29%6%1
711
21st to endNight
28%7%32%25%9%
571
May1st to 10thNight
23%6%32%29%8%1
414
11th to 20thNight
22%5%33%32%8%1
354
21st to endNight
19%435%33%9%1
389
June1st to 10thNight
25%425%34%11%
360
11th to 20thNight
19%428%36%13%1
360
21st to endNight
19%426%34%16%1
360
July1st to 10thNight
11%5%25%41%17%1
350
11th to 20thNight
11%324%45%16%1
348
21st to endNight
13%319%47%17%1
394
August1st to 10thNight
15%413%46%22%1
358
11th to 20thNight
14%221%35%25%2
526
21st to endNight
16%222%35%22%2
792
September1st to 10thNight
15%323%41%18%1
720
11th to 20thNight
17%5%18%36%21%2
720
21st to endNight
18%5%26%33%17%2
720
October1st to 10thNight
21%6%27%33%13%1
720
11th to 20thNight
25%8%26%30%11%1
720
21st to endNight
27%8%29%29%7%
792
November1st to 10thNight
24%10%28%29%9%
740
11th to 20thNight
23%9%32%25%10%1
760
21st to endNight
29%10%29%23%9%1
760
December1st to 10thNight
28%9%31%24%7%
760
11th to 20thNight
28%10%32%23%6%1
760
21st to endNight
32%11%30%21%6%
836
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