Longueuil
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Longueuil clear sky chart from 2005-11-06 to 2024-01-22.

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%
22579
14%
74844
9%
22537
38%
22537
16%
53551

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
17%
760
9%
2649
4%
757
24%
757
8%
2119
January11th to 20thNight
17%
760
10%
2660
4%
760
25%
760
10%
2069
January21st to endNight
23%
800
13%
2798
7%
800
32%
800
13%
2035
February1st to 10thNight
18%
720
10%
2389
4%
720
26%
720
10%
1895
February11th to 20thNight
22%
703
13%
2173
5%
700
32%
700
14%
1611
February21st to endNight
24%
592
16%
1776
7%
592
36%
592
16%
1302
March1st to 10thNight
25%
720
15%
2160
10%
720
33%
720
15%
1604
March11th to 20thNight
24%
720
15%
2100
7%
720
32%
720
16%
1538
March21st to endNight
29%
792
21%
1980
9%
792
37%
792
23%
1441
April1st to 10thNight
27%
720
16%
1800
5%
720
32%
720
19%
1365
April11th to 20thNight
28%
711
16%
1775
4%
711
34%
711
22%
1302
April21st to endNight
28%
566
17%
1646
8%
566
35%
566
18%
1192
May1st to 10thNight
29%
424
16%
1504
11%
424
39%
424
17%
1028
May11th to 20thNight
31%
354
19%
1416
17%
354
42%
354
18%
905
May21st to endNight
36%
388
13%
1551
12%
388
46%
388
18%
979
June1st to 10thNight
33%
360
11%
1440
10%
360
43%
360
15%
983
June11th to 20thNight
40%
360
11%
1440
13%
360
48%
360
19%
904
June21st to endNight
42%
360
10%
1440
13%
360
47%
360
17%
964
July1st to 10thNight
48%
350
13%
1400
18%
350
54%
350
21%
833
July11th to 20thNight
54%
348
14%
1392
20%
348
58%
348
24%
825
July21st to endNight
50%
394
14%
1486
14%
372
56%
372
20%
891
August1st to 10thNight
60%
358
17%
1422
21%
356
62%
356
21%
847
August11th to 20thNight
53%
527
18%
1591
13%
527
56%
527
28%
1016
August21st to endNight
51%
792
19%
1980
10%
792
54%
792
31%
1337
September1st to 10thNight
49%
720
16%
1800
8%
720
52%
720
31%
1217
September11th to 20thNight
51%
720
20%
1883
12%
720
54%
720
33%
1202
September21st to endNight
43%
720
21%
1980
14%
720
49%
720
27%
1326
October1st to 10thNight
36%
720
20%
2088
12%
720
45%
720
23%
1438
October11th to 20thNight
32%
720
16%
2207
10%
720
40%
720
17%
1596
October21st to endNight
25%
792
12%
2574
7%
792
33%
792
14%
1912
November1st to 10thNight
24%
740
17%
2407
10%
740
35%
740
16%
1695
November11th to 20thNight
25%
760
18%
2531
12%
760
35%
760
16%
1800
November21st to endNight
21%
760
12%
2660
6%
760
30%
760
11%
2029
December1st to 10thNight
18%
760
8%
2660
4%
760
23%
760
8%
2132
December11th to 20thNight
15%
760
12%
3243
4%
759
25%
759
8%
2468
December21st to endNight
14%
828
6%
4843
3%
817
22%
817
5%
3751

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
17%9%36%6%35%5%5%7%33%
74830
Night
19%10%47%6%3445%6%32%
75102
TransparencyDay
50%6%12%20%10%1
74535
Night
53%6%10%20%10%1
74931
SeeingDay
21%12%28%24%12%3
13491
Night
23%9%29%28%10%1
22588

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
20%17%6%11%7%35%43321%
1517
11th to 20thDay
20%13%6%9%8%34445%23%
1520
21st to endDay
13%14%47%6%46%7%6%6%28%
1592
February1st to 10thDay
16%15%5%9%7%46%445%25%
1570
11th to 20thDay
15%11%5%9%8%45%5%5%6%28%
1674
21st to endDay
18%15%6%7%7%34445%27%
1480
March1st to 10thDay
15%12%49%8%45%446%28%
1797
11th to 20thDay
17%11%46%7%35%45%6%32%
1856
21st to endDay
19%10%46%5%245%5%6%34%
2376
April1st to 10thDay
22%10%36%6%445%45%31%
2160
11th to 20thDay
20%8%36%5%34346%38%
2134
21st to endDay
21%10%37%6%3445%6%31%
2313
May1st to 10thDay
20%7%27%5%35%5%47%34%
2470
11th to 20thDay
17%7%36%5%345%5%7%38%
2478
21st to endDay
17%6%36%5%35%6%5%8%36%
2725
June1st to 10thDay
21%7%35%6%45%5%5%8%31%
2520
11th to 20thDay
15%6%25%6%35%46%8%40%
2520
21st to endDay
19%7%36%6%45%5%5%7%33%
2520
July1st to 10thDay
12%5%35%6%45%5%6%9%41%
2520
11th to 20thDay
12%5%25%5%46%5%7%10%38%
2520
21st to endDay
12%6%25%6%35%6%7%9%38%
2744
August1st to 10thDay
12%6%26%5%36%6%7%9%38%
2506
11th to 20thDay
9%5%35%6%35%6%7%9%42%
2287
21st to endDay
13%5%25%445%5%6%9%42%
2376
September1st to 10thDay
11%5%26%6%35%6%6%8%43%
2160
11th to 20thDay
15%5%2432345%8%49%
2076
21st to endDay
15%5%25%5%35%46%8%41%
1980
October1st to 10thDay
20%6%36%6%45%5%5%6%33%
1871
11th to 20thDay
18%9%37%8%45%5%6%6%28%
1751
21st to endDay
27%10%35%5%3445%5%30%
1782
November1st to 10thDay
20%10%36%5%346%5%8%32%
1671
11th to 20thDay
18%11%5%7%6%36%6%6%6%28%
1646
21st to endDay
22%12%46%7%35%5%5%7%24%
1520
December1st to 10thDay
24%15%6%8%8%34445%19%
1520
11th to 20thDay
23%13%5%8%5%246%46%25%
1906
21st to endDay
28%15%49%7%3444419%
2772
January1st to 10thNight
19%16%6%10%6%45%44421%
2649
11th to 20thNight
17%15%6%9%6%45%445%23%
2660
21st to endNight
14%12%6%9%7%45%5%45%29%
2798
February1st to 10thNight
16%15%6%11%8%46%5%45%21%
2389
11th to 20thNight
16%10%6%8%7%45%5%5%6%29%
2171
21st to endNight
17%12%5%9%5%4444432%
1776
March1st to 10thNight
18%14%47%7%3445%5%29%
2150
11th to 20thNight
19%13%46%6%44445%31%
2100
21st to endNight
18%10%46%6%3444438%
1980
April1st to 10thNight
25%8%46%5%25%447%30%
1800
11th to 20thNight
23%7%36%434447%34%
1775
21st to endNight
22%9%46%5%34445%34%
1646
May1st to 10thNight
21%8%47%5%34446%35%
1504
11th to 20thNight
19%8%36%5%25%45%6%37%
1415
21st to endNight
16%6%345%35%5%5%6%40%
1550
June1st to 10thNight
23%7%36%5%346%47%32%
1440
11th to 20thNight
17%5%26%5%345%6%6%39%
1440
21st to endNight
17%6%36%6%46%6%5%8%34%
1440
July1st to 10thNight
12%5%25%6%45%5%6%8%41%
1440
11th to 20thNight
10%5%25%6%35%6%8%9%40%
1440
21st to endNight
12%5%36%5%35%47%10%39%
1574
August1st to 10thNight
13%4246%45%5%6%10%42%
1432
11th to 20thNight
13%6%25%5%36%5%5%8%42%
1591
21st to endNight
13%7%26%5%35%46%8%42%
1980
September1st to 10thNight
13%5%27%6%3445%7%43%
1800
11th to 20thNight
16%6%24423446%49%
1883
21st to endNight
17%6%35%43445%7%42%
1980
October1st to 10thNight
18%6%36%5%345%5%6%38%
2088
11th to 20thNight
22%8%37%5%45%45%5%33%
2207
21st to endNight
25%9%38%5%345%45%30%
2574
November1st to 10thNight
20%9%46%6%445%5%6%32%
2407
11th to 20thNight
20%10%47%6%4445%6%32%
2531
21st to endNight
23%13%37%6%3445%5%26%
2660
December1st to 10thNight
22%16%7%9%5%3445%6%19%
2660
11th to 20thNight
23%15%5%7%6%34445%25%
3288
21st to endNight
28%15%5%8%5%2334421%
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
68%5%8%14%5%
1518
11th to 20thDay
63%6%10%12%10%
1520
21st to endDay
54%8%11%17%10%1
1592
February1st to 10thDay
62%49%17%6%1
1570
11th to 20thDay
58%5%11%17%8%1
1683
21st to endDay
60%410%15%10%1
1480
March1st to 10thDay
57%6%9%17%9%2
1800
11th to 20thDay
52%5%13%15%13%3
1856
21st to endDay
51%5%10%18%13%3
2376
April1st to 10thDay
56%5%7%19%11%2
2160
11th to 20thDay
48%49%23%14%2
2134
21st to endDay
54%5%9%18%12%3
2313
May1st to 10thDay
49%6%8%20%15%2
2470
11th to 20thDay
45%6%10%20%16%3
2482
21st to endDay
45%8%13%19%13%2
2725
June1st to 10thDay
50%7%11%19%11%2
2520
11th to 20thDay
42%6%10%24%14%3
2520
21st to endDay
51%6%13%19%10%1
2520
July1st to 10thDay
38%8%13%28%12%1
2450
11th to 20thDay
40%8%15%29%9%
2445
21st to endDay
40%9%15%26%9%
2591
August1st to 10thDay
41%9%16%26%8%
2492
11th to 20thDay
37%8%18%26%11%1
2287
21st to endDay
38%7%15%26%14%1
2376
September1st to 10thDay
38%8%14%28%12%
2160
11th to 20thDay
35%6%12%32%14%1
2076
21st to endDay
41%7%14%27%10%1
1980
October1st to 10thDay
49%8%11%22%10%
1871
11th to 20thDay
53%7%13%19%7%
1751
21st to endDay
57%5%11%19%8%1
1782
November1st to 10thDay
49%7%13%20%9%1
1671
11th to 20thDay
55%8%11%16%11%
1646
21st to endDay
59%8%13%14%6%
1520
December1st to 10thDay
69%5%9%12%4
1520
11th to 20thDay
59%7%11%17%5%
1906
21st to endDay
69%6%11%9%5%
2772
January1st to 10thNight
67%5%9%14%5%
2649
11th to 20thNight
63%6%10%13%7%1
2660
21st to endNight
56%5%9%17%11%1
2798
February1st to 10thNight
65%5%8%15%6%1
2389
11th to 20thNight
56%5%10%19%8%1
2173
21st to endNight
56%49%17%13%1
1776
March1st to 10thNight
57%5%9%17%11%2
2160
11th to 20thNight
55%49%16%13%3
2101
21st to endNight
50%47%20%15%4
1980
April1st to 10thNight
55%47%18%14%2
1800
11th to 20thNight
51%46%21%15%2
1775
21st to endNight
52%5%7%19%13%4
1646
May1st to 10thNight
52%46%18%15%5%
1504
11th to 20thNight
46%5%8%19%17%4
1416
21st to endNight
44%7%11%20%16%3
1551
June1st to 10thNight
51%6%9%22%12%1
1440
11th to 20thNight
43%7%10%22%14%3
1440
21st to endNight
48%7%12%20%13%
1440
July1st to 10thNight
38%8%12%25%16%1
1400
11th to 20thNight
37%8%15%27%13%
1392
21st to endNight
38%9%16%25%11%
1486
August1st to 10thNight
38%8%16%26%11%
1422
11th to 20thNight
37%8%17%24%13%1
1591
21st to endNight
39%7%13%27%13%1
1980
September1st to 10thNight
39%7%11%27%15%1
1800
11th to 20thNight
36%6%13%32%13%1
1883
21st to endNight
41%7%10%27%14%
1980
October1st to 10thNight
45%6%10%25%12%1
2088
11th to 20thNight
53%6%10%24%8%
2207
21st to endNight
57%6%11%16%9%1
2574
November1st to 10thNight
52%5%11%21%9%1
2407
11th to 20thNight
53%5%11%19%10%1
2531
21st to endNight
60%6%10%17%7%
2660
December1st to 10thNight
67%5%10%14%4
2660
11th to 20thNight
63%5%9%17%7%
3288
21st to endNight
67%5%10%14%4
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
26%17%26%21%10%
180
11th to 20thDay
25%14%35%19%5%1
180
21st to endDay
22%13%36%19%10%1
178
February1st to 10thDay
33%19%36%12%
218
11th to 20thDay
23%16%37%20%41
342
21st to endDay
27%13%30%25%4
346
March1st to 10thDay
24%13%34%23%6%
420
11th to 20thDay
21%17%31%23%7%1
420
21st to endDay
26%15%28%20%9%2
462
April1st to 10thDay
28%15%29%19%9%2
420
11th to 20thDay
28%20%21%17%11%3
412
21st to endDay
26%13%29%20%10%2
420
May1st to 10thDay
23%11%32%21%11%2
423
11th to 20thDay
17%11%32%25%11%4
447
21st to endDay
18%11%34%23%12%2
485
June1st to 10thDay
22%14%24%28%10%3
450
11th to 20thDay
16%11%26%30%13%3
450
21st to endDay
20%10%25%26%16%3
450
July1st to 10thDay
11%9%24%30%20%5%
445
11th to 20thDay
13%6%28%31%17%5%
444
21st to endDay
13%7%25%33%19%4
488
August1st to 10thDay
15%425%29%22%5%
446
11th to 20thDay
11%5%22%33%18%10%
439
21st to endDay
13%10%24%25%18%11%
495
September1st to 10thDay
11%8%26%28%18%8%
450
11th to 20thDay
16%10%20%26%16%12%
450
21st to endDay
17%8%28%23%17%7%
450
October1st to 10thDay
21%12%28%21%15%4
450
11th to 20thDay
20%18%29%20%12%2
426
21st to endDay
33%14%24%23%6%
396
November1st to 10thDay
25%16%25%25%8%1
365
11th to 20thDay
25%19%32%15%8%1
306
21st to endDay
29%14%32%19%6%1
180
December1st to 10thDay
34%13%21%23%7%2
180
11th to 20thDay
26%22%34%14%31
180
21st to endDay
30%20%25%18%5%2
198
January1st to 10thNight
27%13%31%24%6%
760
11th to 20thNight
25%11%35%23%6%
760
21st to endNight
20%10%35%27%8%1
800
February1st to 10thNight
23%9%35%27%6%1
720
11th to 20thNight
22%10%38%24%6%
703
21st to endNight
25%10%32%28%4
592
March1st to 10thNight
25%11%31%27%7%
720
11th to 20thNight
26%10%33%24%7%
720
21st to endNight
23%9%32%28%8%1
792
April1st to 10thNight
28%10%28%28%6%
720
11th to 20thNight
27%11%29%26%6%1
711
21st to endNight
25%11%30%25%9%
566
May1st to 10thNight
22%9%32%27%8%2
424
11th to 20thNight
23%5%33%30%9%1
354
21st to endNight
18%10%30%32%10%
389
June1st to 10thNight
25%5%27%32%11%
360
11th to 20thNight
18%5%29%33%13%1
360
21st to endNight
18%428%35%15%1
360
July1st to 10thNight
12%7%27%36%18%
350
11th to 20thNight
11%225%45%16%1
348
21st to endNight
12%324%43%17%1
394
August1st to 10thNight
15%314%48%19%1
358
11th to 20thNight
13%420%36%24%2
527
21st to endNight
15%323%36%21%2
792
September1st to 10thNight
15%5%23%39%17%1
720
11th to 20thNight
18%6%19%35%19%2
720
21st to endNight
19%7%26%29%16%3
720
October1st to 10thNight
20%9%28%29%13%1
720
11th to 20thNight
25%9%27%29%9%
720
21st to endNight
27%11%29%28%5%
792
November1st to 10thNight
25%11%31%24%9%
740
11th to 20thNight
24%13%31%22%10%1
760
21st to endNight
30%14%28%20%8%
760
December1st to 10thNight
31%11%29%23%5%
760
11th to 20thNight
31%12%33%18%6%1
760
21st to endNight
34%12%31%19%4
836
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