St-Jean-Sur-Richelieu
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the St-Jean-Sur-Richelieu 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
31%
22623
13%
74914
9%
22581
37%
22581
15%
54790

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
7%
2649
4%
757
24%
757
6%
2195
January11th to 20thNight
18%
760
9%
2660
5%
760
23%
760
8%
2155
January21st to endNight
23%
820
11%
2868
7%
820
30%
820
11%
2185
February1st to 10thNight
17%
720
8%
2394
3%
720
23%
720
9%
1942
February11th to 20thNight
22%
703
10%
2157
5%
700
30%
700
12%
1661
February21st to endNight
26%
592
15%
1776
7%
592
36%
592
15%
1338
March1st to 10thNight
27%
720
15%
2160
11%
720
33%
720
14%
1627
March11th to 20thNight
26%
720
14%
2104
7%
720
33%
720
15%
1566
March21st to endNight
31%
792
20%
1980
9%
792
37%
792
22%
1462
April1st to 10thNight
27%
720
14%
1800
4%
720
31%
720
18%
1379
April11th to 20thNight
28%
711
15%
1775
4%
711
34%
711
21%
1319
April21st to endNight
29%
558
17%
1638
9%
558
35%
558
18%
1190
May1st to 10thNight
30%
446
15%
1526
10%
446
38%
446
18%
1062
May11th to 20thNight
35%
354
19%
1416
17%
354
45%
354
18%
916
May21st to endNight
38%
388
13%
1551
12%
388
48%
388
18%
998
June1st to 10thNight
35%
360
10%
1440
11%
360
43%
360
15%
997
June11th to 20thNight
40%
360
11%
1440
12%
360
47%
360
19%
900
June21st to endNight
42%
360
10%
1440
14%
360
49%
360
15%
963
July1st to 10thNight
50%
350
13%
1400
17%
350
56%
350
22%
859
July11th to 20thNight
56%
348
14%
1392
20%
348
59%
348
23%
838
July21st to endNight
53%
394
14%
1486
17%
372
58%
372
19%
923
August1st to 10thNight
59%
358
16%
1422
20%
356
61%
356
22%
850
August11th to 20thNight
54%
537
16%
1601
12%
537
56%
537
26%
1060
August21st to endNight
51%
792
18%
1980
11%
792
52%
792
28%
1368
September1st to 10thNight
50%
720
15%
1800
7%
720
52%
720
29%
1244
September11th to 20thNight
52%
720
19%
1894
12%
720
55%
720
32%
1223
September21st to endNight
41%
720
21%
1980
14%
720
45%
720
25%
1357
October1st to 10thNight
36%
720
18%
2070
11%
720
43%
720
22%
1435
October11th to 20thNight
30%
720
15%
2214
10%
720
38%
720
16%
1633
October21st to endNight
23%
792
11%
2574
7%
792
30%
792
13%
1942
November1st to 10thNight
25%
740
15%
2407
9%
740
35%
740
15%
1705
November11th to 20thNight
24%
760
17%
2508
12%
760
32%
760
14%
1825
November21st to endNight
20%
760
11%
2660
6%
760
27%
760
10%
2057
December1st to 10thNight
17%
760
6%
2660
3%
760
21%
760
7%
2202
December11th to 20thNight
17%
760
10%
3251
4%
759
25%
759
7%
2557
December21st to endNight
14%
828
5%
4841
3%
817
20%
817
5%
3857

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%9%37%6%35%5%5%7%32%
74880
Night
20%10%47%6%34446%31%
75166
TransparencyDay
51%7%12%20%10%1
74585
Night
55%6%10%18%10%1
74995
SeeingDay
22%11%27%24%13%3
13534
Night
24%9%28%28%10%1
22632

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
21%18%7%10%7%4433420%
1517
11th to 20thDay
20%15%6%10%7%45%435%21%
1520
21st to endDay
13%14%5%9%7%46%5%5%6%26%
1632
February1st to 10thDay
18%14%6%12%7%45%445%22%
1564
11th to 20thDay
15%13%5%10%7%35%5%5%6%26%
1691
21st to endDay
17%15%6%6%7%45%446%25%
1480
March1st to 10thDay
16%11%5%8%7%46%445%29%
1797
11th to 20thDay
17%10%48%6%35%446%32%
1853
21st to endDay
19%10%36%6%35%446%33%
2376
April1st to 10thDay
23%9%47%6%3435%5%30%
2160
11th to 20thDay
21%8%35%5%3445%6%37%
2134
21st to endDay
23%9%36%6%35%447%31%
2322
May1st to 10thDay
20%7%38%5%3445%6%35%
2449
11th to 20thDay
18%7%36%5%35%5%47%37%
2478
21st to endDay
16%7%36%6%35%6%6%8%34%
2725
June1st to 10thDay
22%6%36%6%36%5%5%8%30%
2520
11th to 20thDay
16%6%35%5%35%46%8%39%
2520
21st to endDay
22%6%36%6%35%45%7%33%
2520
July1st to 10thDay
14%5%25%5%45%46%10%40%
2520
11th to 20thDay
13%5%35%6%46%6%7%10%37%
2520
21st to endDay
14%6%25%5%36%6%6%9%38%
2744
August1st to 10thDay
13%6%26%6%45%6%6%9%38%
2506
11th to 20thDay
10%6%35%5%35%5%6%11%41%
2280
21st to endDay
15%425%6%35%5%6%8%41%
2376
September1st to 10thDay
13%5%26%5%345%6%7%43%
2160
11th to 20thDay
16%6%2432345%7%48%
2066
21st to endDay
15%6%25%6%345%7%8%40%
1980
October1st to 10thDay
22%6%26%5%45%6%5%7%32%
1886
11th to 20thDay
20%8%36%8%45%6%7%6%28%
1745
21st to endDay
27%10%36%6%3345%5%28%
1782
November1st to 10thDay
19%10%36%5%445%46%33%
1671
11th to 20thDay
18%10%5%7%7%46%5%5%6%27%
1668
21st to endDay
23%12%47%7%445%5%5%23%
1520
December1st to 10thDay
25%14%8%8%7%35%345%18%
1520
11th to 20thDay
23%12%49%6%345%5%6%23%
1906
21st to endDay
28%15%5%9%7%3433319%
2772
January1st to 10thNight
20%17%6%10%8%35%44419%
2649
11th to 20thNight
18%16%7%11%7%35%5%4421%
2660
21st to endNight
16%13%6%9%8%45%445%27%
2868
February1st to 10thNight
18%15%7%11%8%45%445%19%
2394
11th to 20thNight
16%11%5%10%8%45%5%5%5%26%
2155
21st to endNight
19%12%49%6%44345%30%
1776
March1st to 10thNight
18%14%5%8%6%44445%28%
2150
11th to 20thNight
20%13%47%6%34336%31%
2104
21st to endNight
20%10%46%435%44437%
1980
April1st to 10thNight
24%9%46%6%35%446%29%
1800
11th to 20thNight
23%9%37%5%24445%34%
1775
21st to endNight
21%11%26%5%34445%35%
1638
May1st to 10thNight
21%9%37%6%24447%33%
1526
11th to 20thNight
19%7%46%5%3435%7%36%
1415
21st to endNight
18%436%5%35%5%47%40%
1550
June1st to 10thNight
24%7%35%5%35%5%5%7%31%
1440
11th to 20thNight
18%5%27%6%3447%7%38%
1440
21st to endNight
17%5%47%7%35%5%5%7%35%
1440
July1st to 10thNight
12%5%35%6%345%7%9%41%
1440
11th to 20thNight
11%5%26%5%46%7%6%8%41%
1440
21st to endNight
13%5%35%6%45%5%6%8%39%
1574
August1st to 10thNight
15%425%5%445%6%10%42%
1432
11th to 20thNight
13%6%25%5%35%5%6%7%42%
1601
21st to endNight
13%7%35%5%345%5%7%42%
1980
September1st to 10thNight
14%6%26%5%345%5%6%43%
1800
11th to 20thNight
16%5%24433447%47%
1894
21st to endNight
18%6%35%435%45%6%42%
1980
October1st to 10thNight
19%6%36%43446%7%37%
2070
11th to 20thNight
22%8%36%6%3446%6%31%
2214
21st to endNight
26%9%28%6%35%445%29%
2574
November1st to 10thNight
21%10%36%435%5%6%6%31%
2407
11th to 20thNight
20%10%38%5%345%46%31%
2508
21st to endNight
23%12%39%6%44445%26%
2660
December1st to 10thNight
23%17%7%9%7%34445%17%
2660
11th to 20thNight
24%14%5%9%6%3443323%
3288
21st to endNight
28%15%6%9%5%3333421%
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
70%5%9%13%4
1518
11th to 20thDay
67%6%9%11%8%
1520
21st to endDay
59%7%11%16%7%1
1632
February1st to 10thDay
65%5%8%15%5%1
1564
11th to 20thDay
60%5%11%16%6%1
1700
21st to endDay
60%5%12%14%8%1
1480
March1st to 10thDay
58%5%10%17%9%2
1800
11th to 20thDay
53%6%12%15%12%2
1853
21st to endDay
54%49%19%11%2
2376
April1st to 10thDay
56%6%9%17%10%2
2160
11th to 20thDay
49%5%9%22%14%1
2134
21st to endDay
54%6%10%17%10%3
2322
May1st to 10thDay
50%5%9%19%15%2
2449
11th to 20thDay
46%6%10%20%15%2
2482
21st to endDay
47%7%12%19%12%2
2725
June1st to 10thDay
51%8%11%19%10%1
2520
11th to 20thDay
43%7%11%23%13%2
2520
21st to endDay
50%8%11%20%9%1
2520
July1st to 10thDay
38%9%13%28%12%1
2450
11th to 20thDay
40%9%13%29%8%
2445
21st to endDay
42%9%16%25%8%1
2591
August1st to 10thDay
42%10%15%25%8%
2492
11th to 20thDay
37%10%17%25%11%
2280
21st to endDay
38%8%15%25%12%
2376
September1st to 10thDay
38%10%13%27%12%1
2160
11th to 20thDay
36%6%11%32%14%
2066
21st to endDay
41%8%14%26%10%1
1980
October1st to 10thDay
52%8%12%20%9%
1886
11th to 20thDay
53%9%13%18%6%
1745
21st to endDay
58%6%11%17%7%1
1782
November1st to 10thDay
51%7%13%19%8%1
1671
11th to 20thDay
57%8%12%14%9%
1668
21st to endDay
62%9%11%13%5%
1520
December1st to 10thDay
69%7%11%10%3
1520
11th to 20thDay
62%8%10%15%6%
1906
21st to endDay
71%6%11%8%4
2772
January1st to 10thNight
68%8%8%12%4
2649
11th to 20thNight
66%7%8%12%6%1
2660
21st to endNight
60%6%9%14%10%1
2868
February1st to 10thNight
68%5%8%13%5%1
2394
11th to 20thNight
60%7%9%17%7%
2157
21st to endNight
58%5%8%16%12%1
1776
March1st to 10thNight
58%5%9%16%10%2
2160
11th to 20thNight
57%49%16%11%2
2105
21st to endNight
51%5%8%19%13%4
1980
April1st to 10thNight
57%5%8%16%13%1
1800
11th to 20thNight
52%5%7%21%14%2
1775
21st to endNight
52%6%8%18%13%4
1638
May1st to 10thNight
52%5%8%16%15%5%
1526
11th to 20thNight
47%5%8%18%17%4
1416
21st to endNight
45%7%11%20%15%2
1551
June1st to 10thNight
52%7%8%22%10%1
1440
11th to 20thNight
44%6%12%21%14%3
1440
21st to endNight
48%8%11%20%12%
1440
July1st to 10thNight
38%10%12%25%15%1
1400
11th to 20thNight
38%8%13%29%12%
1392
21st to endNight
41%9%14%25%10%1
1486
August1st to 10thNight
38%8%17%25%11%
1422
11th to 20thNight
40%9%15%23%13%
1601
21st to endNight
40%9%12%25%12%1
1980
September1st to 10thNight
41%8%11%25%15%1
1800
11th to 20thNight
37%6%14%30%13%1
1894
21st to endNight
42%8%9%25%14%1
1980
October1st to 10thNight
46%7%11%23%12%
2070
11th to 20thNight
53%8%9%22%7%
2214
21st to endNight
58%6%10%15%9%1
2574
November1st to 10thNight
53%6%12%20%8%1
2407
11th to 20thNight
55%6%11%17%10%1
2508
21st to endNight
62%6%11%15%6%
2660
December1st to 10thNight
70%6%10%11%3
2660
11th to 20thNight
65%6%9%15%6%
3288
21st to endNight
69%6%9%13%3
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
29%12%29%18%10%2
180
11th to 20thDay
28%15%33%17%7%1
180
21st to endDay
20%18%32%18%11%1
188
February1st to 10thDay
32%21%30%15%2
216
11th to 20thDay
27%13%35%20%5%1
359
21st to endDay
26%12%29%28%5%
346
March1st to 10thDay
25%11%30%27%7%
420
11th to 20thDay
23%13%35%19%8%1
420
21st to endDay
28%14%26%22%9%1
462
April1st to 10thDay
31%13%25%20%9%2
420
11th to 20thDay
28%18%24%17%10%4
412
21st to endDay
28%11%30%17%12%3
420
May1st to 10thDay
24%12%31%19%12%2
423
11th to 20thDay
18%10%32%25%12%4
447
21st to endDay
18%8%34%24%12%2
485
June1st to 10thDay
24%9%26%28%10%3
450
11th to 20thDay
17%10%25%29%17%3
450
21st to endDay
22%8%28%24%16%2
450
July1st to 10thDay
14%5%24%33%19%5%
445
11th to 20thDay
14%7%29%29%16%5%
444
21st to endDay
16%6%23%32%22%2
488
August1st to 10thDay
14%6%23%29%22%6%
446
11th to 20thDay
10%7%22%33%19%8%
439
21st to endDay
15%8%24%24%19%9%
495
September1st to 10thDay
13%9%24%27%18%9%
450
11th to 20thDay
17%8%20%26%19%11%
450
21st to endDay
16%7%29%23%19%6%
450
October1st to 10thDay
22%10%29%19%16%5%
450
11th to 20thDay
24%15%27%20%12%2
422
21st to endDay
35%13%23%22%7%
396
November1st to 10thDay
29%13%27%23%8%
365
11th to 20thDay
24%20%28%18%9%2
328
21st to endDay
32%14%28%18%7%1
180
December1st to 10thDay
33%15%21%21%8%2
180
11th to 20thDay
27%18%35%13%6%
180
21st to endDay
33%17%28%17%42
198
January1st to 10thNight
28%11%31%25%5%1
760
11th to 20thNight
26%12%33%23%6%
760
21st to endNight
22%10%31%28%7%1
820
February1st to 10thNight
26%9%34%26%5%1
720
11th to 20thNight
23%10%35%27%4
703
21st to endNight
25%10%29%30%5%
592
March1st to 10thNight
25%12%30%29%5%
720
11th to 20thNight
28%11%29%24%8%
720
21st to endNight
26%9%29%28%7%1
792
April1st to 10thNight
28%9%28%28%6%
720
11th to 20thNight
27%12%28%24%8%1
711
21st to endNight
28%10%28%25%8%1
558
May1st to 10thNight
25%7%30%26%11%1
446
11th to 20thNight
22%6%31%32%8%1
354
21st to endNight
19%7%30%34%10%1
389
June1st to 10thNight
28%6%26%31%10%1
360
11th to 20thNight
20%428%34%14%
360
21st to endNight
16%8%24%36%15%1
360
July1st to 10thNight
13%228%40%15%1
350
11th to 20thNight
10%320%48%17%1
348
21st to endNight
14%221%46%16%1
394
August1st to 10thNight
15%316%44%21%1
358
11th to 20thNight
13%420%36%24%2
537
21st to endNight
16%5%19%38%21%2
792
September1st to 10thNight
16%5%21%39%17%2
720
11th to 20thNight
18%6%19%34%21%3
720
21st to endNight
20%6%28%28%15%3
720
October1st to 10thNight
22%6%29%28%14%1
720
11th to 20thNight
28%8%28%28%8%1
720
21st to endNight
29%9%31%25%6%
792
November1st to 10thNight
26%12%31%23%8%1
740
11th to 20thNight
26%13%30%21%9%1
760
21st to endNight
30%12%30%20%7%
760
December1st to 10thNight
33%13%27%22%5%
760
11th to 20thNight
31%12%31%19%6%1
760
21st to endNight
34%11%31%19%4
836
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