Observatoire astronomique du bois de Belle-Rivière
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire astronomique du bois de Belle-Rivière clear sky chart from 2005-11-06 to 2025-05-26.

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
30%
24105
11%
114994
8%
23733
37%
23733
11%
80937

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
16%
794
7%
6282
4%
757
23%
757
3%
4810
January11th to 20thNight
18%
783
5%
6242
5%
759
25%
759
4%
4720
January21st to endNight
23%
865
11%
6776
8%
836
31%
836
5%
4970
February1st to 10thNight
18%
800
11%
2625
5%
800
27%
800
12%
1992
February11th to 20thNight
20%
783
12%
2450
5%
780
29%
780
15%
1786
February21st to endNight
23%
660
15%
1980
7%
660
33%
660
16%
1457
March1st to 10thNight
22%
792
13%
5007
9%
763
30%
763
7%
3649
March11th to 20thNight
23%
789
10%
4846
6%
760
32%
760
8%
3317
March21st to endNight
28%
871
11%
4654
8%
836
37%
836
10%
3265
April1st to 10thNight
26%
800
15%
2000
4%
800
32%
800
20%
1487
April11th to 20thNight
26%
791
14%
1975
4%
791
31%
791
21%
1467
April21st to endNight
27%
653
17%
1853
7%
653
35%
653
19%
1320
May1st to 10thNight
28%
430
13%
2629
10%
426
37%
426
9%
1760
May11th to 20thNight
34%
387
12%
2545
15%
384
46%
384
10%
1589
May21st to endNight
31%
420
9%
2769
10%
411
43%
411
11%
1658
June1st to 10thNight
37%
380
9%
1520
10%
380
45%
380
15%
1047
June11th to 20thNight
39%
380
11%
1520
13%
380
47%
380
20%
945
June21st to endNight
41%
380
10%
1520
13%
380
46%
380
16%
1016
July1st to 10thNight
48%
364
10%
2433
17%
360
56%
360
13%
1505
July11th to 20thNight
52%
364
10%
2290
19%
358
56%
358
14%
1328
July21st to endNight
52%
410
10%
2413
15%
383
56%
383
15%
1381
August1st to 10thNight
55%
372
15%
2303
19%
365
60%
365
13%
1476
August11th to 20thNight
51%
552
12%
2672
10%
545
56%
545
17%
1723
August21st to endNight
49%
822
14%
3287
8%
814
52%
814
20%
2212
September1st to 10thNight
51%
760
16%
1900
8%
760
53%
760
32%
1282
September11th to 20thNight
53%
760
20%
1966
12%
760
56%
760
35%
1258
September21st to endNight
46%
760
21%
2090
15%
760
51%
760
28%
1387
October1st to 10thNight
38%
760
12%
3175
12%
740
46%
740
15%
2216
October11th to 20thNight
32%
760
11%
3072
9%
740
39%
740
13%
2219
October21st to endNight
25%
836
7%
3763
7%
814
31%
814
11%
2645
November1st to 10thNight
27%
780
15%
2537
9%
780
37%
780
16%
1772
November11th to 20thNight
24%
800
15%
2702
9%
800
33%
800
15%
1913
November21st to endNight
19%
800
11%
2800
5%
800
27%
800
10%
2116
December1st to 10thNight
17%
794
8%
4524
4%
780
24%
780
5%
3518
December11th to 20thNight
16%
795
8%
5093
4%
779
25%
779
5%
3771
December21st to endNight
15%
858
11%
6781
3%
839
23%
839
4%
4960

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
16%10%38%5%5%5%45%7%32%
114009
Night
17%11%49%5%4435%6%31%
115266
TransparencyDay
49%8%13%20%10%1
117502
Night
52%7%12%18%10%1
119937
SeeingDay
20%14%29%23%11%3
15176
Night
22%10%31%28%9%1
24260

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
16%18%6%14%5%4434423%
3597
11th to 20thDay
13%15%6%11%7%5%435%6%26%
3570
21st to endDay
10%17%5%11%5%5%6%45%6%26%
3960
February1st to 10thDay
13%16%5%10%6%5%6%35%5%26%
1772
11th to 20thDay
14%12%5%10%7%6%45%6%6%27%
1838
21st to endDay
18%15%5%8%5%44445%27%
1650
March1st to 10thDay
19%14%5%11%6%5%434425%
4476
11th to 20thDay
10%14%410%5%4446%7%32%
4743
21st to endDay
19%9%49%5%4434435%
5939
April1st to 10thDay
21%11%37%5%44445%33%
2400
11th to 20thDay
21%8%36%5%5%435%5%36%
2374
21st to endDay
22%10%37%5%5%435%6%32%
2545
May1st to 10thDay
21%9%38%5%5%5%45%7%28%
4552
11th to 20thDay
18%8%39%5%4445%7%32%
4538
21st to endDay
16%6%27%5%5%446%8%36%
4907
June1st to 10thDay
21%8%27%5%5%5%46%7%30%
2660
11th to 20thDay
14%6%27%5%5%5%5%6%7%38%
2660
21st to endDay
19%8%37%6%5%5%5%6%8%29%
2660
July1st to 10thDay
11%6%37%6%6%6%46%8%36%
4440
11th to 20thDay
13%6%26%5%5%5%5%7%9%37%
4440
21st to endDay
11%5%25%445%46%8%45%
4814
August1st to 10thDay
14%6%37%5%6%5%5%7%9%34%
4423
11th to 20thDay
14%7%38%445%46%8%38%
3994
21st to endDay
15%5%26%5%5%5%46%9%39%
4180
September1st to 10thDay
12%5%26%45%5%46%9%41%
2280
11th to 20thDay
12%5%3435%4347%50%
2214
21st to endDay
17%5%27%44345%7%42%
2090
October1st to 10thDay
19%7%36%5%4445%6%37%
1938
11th to 20thDay
19%7%38%7%5%6%45%6%30%
1872
21st to endDay
23%9%37%5%4446%6%29%
1881
November1st to 10thDay
15%9%37%5%5%5%36%7%34%
1761
11th to 20thDay
18%9%5%7%5%46%45%7%31%
1695
21st to endDay
22%11%38%5%7%5%46%7%24%
1600
December1st to 10thDay
20%18%6%12%44445%419%
2600
11th to 20thDay
18%15%5%10%5%4335%428%
2986
21st to endDay
23%13%5%9%5%45%44424%
3960
January1st to 10thNight
13%20%7%14%5%44345%21%
6349
11th to 20thNight
10%15%6%16%7%6%5%35%5%21%
6315
21st to endNight
12%15%5%12%7%5%5%45%5%25%
6996
February1st to 10thNight
14%14%5%11%6%5%5%46%6%26%
2625
11th to 20thNight
13%11%49%6%6%5%46%6%30%
2448
21st to endNight
14%16%5%9%5%44345%32%
1980
March1st to 10thNight
22%14%37%5%44345%29%
5364
11th to 20thNight
13%14%48%5%5%5%36%7%30%
5214
21st to endNight
15%11%39%6%5%5%35%433%
4992
April1st to 10thNight
23%10%36%5%3435%6%32%
2000
11th to 20thNight
21%9%36%5%4335%6%35%
1975
21st to endNight
21%8%47%334446%35%
1853
May1st to 10thNight
22%9%38%5%5%5%35%6%30%
2637
11th to 20thNight
22%7%36%44435%6%37%
2575
21st to endNight
17%8%37%5%4435%8%36%
2784
June1st to 10thNight
20%7%27%46%5%38%8%31%
1520
11th to 20thNight
15%8%26%5%3445%8%39%
1520
21st to endNight
19%7%36%5%5%5%46%6%35%
1520
July1st to 10thNight
14%6%38%5%6%6%47%7%35%
2520
11th to 20thNight
14%6%26%5%45%46%8%42%
2520
21st to endNight
11%6%36%44446%9%43%
2739
August1st to 10thNight
15%7%37%5%4446%7%39%
2506
11th to 20thNight
15%7%37%44445%6%40%
2799
21st to endNight
17%6%27%445%45%6%40%
3476
September1st to 10thNight
10%5%37%45%445%8%45%
1900
11th to 20thNight
14%6%2433335%8%49%
1966
21st to endNight
16%5%26%33445%7%44%
2090
October1st to 10thNight
19%7%36%445%35%5%40%
2237
11th to 20thNight
21%8%36%5%4435%6%36%
2306
21st to endNight
21%9%48%5%5%4445%32%
2717
November1st to 10thNight
19%9%37%45%446%7%33%
2537
11th to 20thNight
17%10%38%5%45%45%6%34%
2702
21st to endNight
21%13%39%5%43445%28%
2800
December1st to 10thNight
17%15%5%10%7%6%5%45%5%20%
4580
11th to 20thNight
24%13%49%5%4424426%
5208
21st to endNight
25%16%49%43335%5%24%
6996

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
62%8%9%16%4
3598
11th to 20thDay
58%7%11%16%7%1
3600
21st to endDay
57%8%11%13%10%1
3960
February1st to 10thDay
59%6%10%18%6%2
1772
11th to 20thDay
57%7%12%14%8%1
1847
21st to endDay
59%5%10%15%9%2
1650
March1st to 10thDay
60%6%8%12%10%3
4479
11th to 20thDay
48%9%18%13%10%2
4743
21st to endDay
50%6%8%15%18%2
5939
April1st to 10thDay
53%6%9%18%12%2
2400
11th to 20thDay
48%6%8%21%15%2
2374
21st to endDay
53%5%10%16%13%3
2545
May1st to 10thDay
51%9%11%19%9%1
4566
11th to 20thDay
47%11%16%17%8%2
4542
21st to endDay
41%9%14%21%13%1
4907
June1st to 10thDay
50%10%10%18%12%1
2660
11th to 20thDay
42%8%13%20%13%3
2660
21st to endDay
51%9%13%17%9%1
2660
July1st to 10thDay
42%8%14%25%10%1
4370
11th to 20thDay
39%9%16%28%8%
4365
21st to endDay
35%8%15%33%10%
4661
August1st to 10thDay
45%8%17%21%8%
4409
11th to 20thDay
41%8%17%27%6%
4036
21st to endDay
40%8%17%21%14%1
4180
September1st to 10thDay
37%8%16%26%13%
2280
11th to 20thDay
34%8%14%30%13%1
2214
21st to endDay
41%7%14%26%10%1
2090
October1st to 10thDay
45%7%13%26%9%
3224
11th to 20thDay
44%7%17%26%7%
3088
21st to endDay
43%6%21%21%9%1
3081
November1st to 10thDay
48%7%15%22%7%1
1761
11th to 20thDay
51%8%13%18%10%
1695
21st to endDay
58%10%12%14%5%1
1600
December1st to 10thDay
69%6%9%14%2
2600
11th to 20thDay
60%6%10%16%9%
2986
21st to endDay
62%6%10%15%6%
3960
January1st to 10thNight
65%7%11%12%4
6349
11th to 20thNight
61%9%12%12%4
6360
21st to endNight
59%7%10%10%13%1
6996
February1st to 10thNight
58%8%11%15%7%1
2625
11th to 20thNight
52%8%13%20%7%1
2450
21st to endNight
54%6%10%17%12%1
1980
March1st to 10thNight
57%6%8%13%12%4
5374
11th to 20thNight
49%8%14%16%10%3
5215
21st to endNight
52%6%7%21%12%2
4992
April1st to 10thNight
52%6%10%18%13%2
2000
11th to 20thNight
51%6%8%19%14%2
1975
21st to endNight
50%6%8%18%14%4
1853
May1st to 10thNight
51%9%12%17%9%2
2643
11th to 20thNight
45%10%13%19%11%2
2576
21st to endNight
44%8%12%17%17%1
2785
June1st to 10thNight
48%10%12%18%12%1
1520
11th to 20thNight
41%8%12%22%15%2
1520
21st to endNight
47%9%12%19%13%1
1520
July1st to 10thNight
45%8%15%19%13%
2480
11th to 20thNight
39%7%18%27%8%
2472
21st to endNight
37%7%18%25%13%
2651
August1st to 10thNight
45%6%14%27%9%
2496
11th to 20thNight
42%8%18%24%7%
2823
21st to endNight
43%8%15%21%13%1
3476
September1st to 10thNight
36%8%14%25%16%1
1900
11th to 20thNight
35%6%14%33%12%1
1966
21st to endNight
39%8%12%27%14%
2090
October1st to 10thNight
44%6%14%26%10%1
3731
11th to 20thNight
43%6%13%29%9%
3829
21st to endNight
46%6%18%17%12%1
4467
November1st to 10thNight
50%7%14%20%8%1
2537
11th to 20thNight
51%7%14%17%10%2
2702
21st to endNight
58%8%12%17%5%
2800
December1st to 10thNight
66%6%13%12%3
4580
11th to 20thNight
61%6%7%15%10%
5208
21st to endNight
62%5%8%14%11%
6996

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
21%17%34%24%5%1
200
11th to 20thDay
25%21%30%19%6%1
200
21st to endDay
19%19%32%22%7%
220
February1st to 10thDay
29%24%33%12%2
287
11th to 20thDay
23%19%39%18%2
385
21st to endDay
27%15%33%22%2
414
March1st to 10thDay
25%14%32%24%5%
500
11th to 20thDay
19%20%36%19%5%1
500
21st to endDay
26%17%31%17%9%1
550
April1st to 10thDay
27%18%27%19%7%2
500
11th to 20thDay
25%20%26%18%9%2
492
21st to endDay
27%18%30%17%7%1
500
May1st to 10thDay
24%13%32%23%7%2
503
11th to 20thDay
19%10%33%23%11%2
527
21st to endDay
19%13%32%23%10%2
549
June1st to 10thDay
22%12%28%27%10%2
490
11th to 20thDay
15%13%27%30%13%2
490
21st to endDay
23%10%29%23%13%3
490
July1st to 10thDay
11%8%29%32%16%4
485
11th to 20thDay
14%8%27%33%14%3
484
21st to endDay
14%8%27%33%16%3
532
August1st to 10thDay
15%6%23%34%19%3
486
11th to 20thDay
11%7%24%31%18%9%
479
21st to endDay
14%8%28%26%17%7%
539
September1st to 10thDay
13%8%28%28%14%7%
490
11th to 20thDay
11%9%23%24%22%10%
490
21st to endDay
17%11%29%21%17%5%
490
October1st to 10thDay
20%13%27%23%14%3
490
11th to 20thDay
19%17%29%23%11%1
475
21st to endDay
28%15%28%21%7%
429
November1st to 10thDay
27%16%26%21%9%1
395
11th to 20thDay
23%18%36%18%5%
295
21st to endDay
25%23%28%20%41
200
December1st to 10thDay
30%13%27%24%7%1
200
11th to 20thDay
29%17%35%16%31
200
21st to endDay
30%19%28%17%5%2
220
January1st to 10thNight
24%13%34%25%4
800
11th to 20thNight
24%15%32%24%5%
800
21st to endNight
17%11%39%27%6%1
880
February1st to 10thNight
20%13%39%23%5%
800
11th to 20thNight
20%13%41%22%4
783
21st to endNight
22%12%35%28%3
660
March1st to 10thNight
23%13%34%26%4
800
11th to 20thNight
23%15%32%24%6%
800
21st to endNight
23%11%32%28%6%
880
April1st to 10thNight
27%13%29%27%5%
800
11th to 20thNight
24%13%31%26%5%
791
21st to endNight
27%10%31%24%8%
653
May1st to 10thNight
25%8%34%25%7%2
430
11th to 20thNight
23%6%29%32%9%1
394
21st to endNight
16%7%39%29%9%
423
June1st to 10thNight
23%6%28%33%9%1
380
11th to 20thNight
18%6%30%33%12%1
380
21st to endNight
20%6%27%32%16%1
380
July1st to 10thNight
10%6%30%38%16%1
370
11th to 20thNight
13%324%44%17%
368
21st to endNight
11%425%43%16%1
416
August1st to 10thNight
14%418%45%18%1
378
11th to 20thNight
14%322%35%24%2
562
21st to endNight
14%5%25%35%20%2
836
September1st to 10thNight
12%5%26%41%16%1
760
11th to 20thNight
16%5%20%35%21%2
760
21st to endNight
18%5%27%30%17%2
760
October1st to 10thNight
21%9%27%31%13%1
760
11th to 20thNight
22%9%30%28%10%1
760
21st to endNight
26%11%32%26%5%
836
November1st to 10thNight
24%15%28%26%7%
780
11th to 20thNight
23%13%34%21%9%
800
21st to endNight
28%16%31%19%6%
800
December1st to 10thNight
29%12%33%21%5%
800
11th to 20thNight
28%16%32%20%41
800
21st to endNight
33%13%31%18%5%
880
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