Montréal
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Montréal clear sky chart from 2005-11-05 to 2018-02-22.

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
33%
15271
14%
48916
9%
15240
38%
15240
17%
35086

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 15thNight
20%
780
9%
2716
4%
776
26%
776
9%
2141
January16th to endNight
23%
832
11%
2912
6%
832
30%
832
11%
2192
February1st to 15thNight
22%
764
9%
2506
5%
761
28%
761
11%
1995
February16th to endNight
26%
659
13%
1976
7%
659
34%
659
14%
1490
March1st to 15thNight
26%
720
14%
2160
10%
720
32%
720
15%
1632
March16th to endNight
33%
768
19%
1998
10%
768
39%
768
23%
1423
April1st to 15thNight
29%
718
16%
1796
6%
718
34%
718
20%
1366
April16th to endNight
30%
618
16%
1698
6%
618
37%
618
21%
1213
May1st to 15thNight
32%
401
17%
1481
14%
401
41%
401
18%
976
May16th to endNight
36%
374
13%
1497
14%
374
43%
374
17%
990
June1st to 15thNight
36%
360
9%
1440
9%
360
43%
360
13%
1011
June16th to endNight
45%
360
8%
1440
11%
360
49%
360
19%
917
July1st to 15thNight
54%
340
13%
1360
19%
340
58%
340
23%
799
July16th to endNight
56%
376
12%
1418
16%
354
59%
354
23%
831
August1st to 15thNight
58%
368
15%
1439
18%
366
59%
366
21%
882
August16th to endNight
55%
756
20%
1902
12%
756
58%
756
35%
1229
September1st to 15thNight
52%
720
15%
1800
8%
720
53%
720
30%
1246
September16th to endNight
51%
717
22%
1974
15%
717
55%
717
31%
1251
October1st to 15thNight
36%
720
19%
2115
11%
720
46%
720
23%
1465
October16th to endNight
29%
768
12%
2466
9%
768
35%
768
15%
1816
November1st to 15thNight
27%
760
17%
2472
12%
760
35%
760
16%
1766
November16th to endNight
24%
780
13%
2708
9%
780
31%
780
12%
2027
December1st to 15thNight
18%
780
8%
2730
4%
780
23%
780
9%
2138
December16th to endNight
14%
832
11%
2912
4%
832
23%
832
9%
2290

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%5%3445%6%33%
49353
Night
19%9%36%5%34445%32%
49085
Cloud CoverDay
18%8%36%5%3445%7%32%
49363
Night
19%9%46%5%34446%31%
49090
TransparencyDay
50%5%12%20%9%1
49040
Night
53%5%10%19%10%1
48916
SeeingDay
21%8%26%24%14%4
6025
Night
23%7%27%29%11%
15272

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 15thDay
21%13%7%8%6%45%32321%
1552
16th to endDay
14%13%47%6%46%446%26%
1664
February1st to 15thDay
15%12%5%10%7%45%445%24%
1686
16th to endDay
18%12%5%7%7%3435%427%
1644
March1st to 15thDay
17%10%5%8%7%4445%5%27%
1790
16th to endDay
18%8%46%424345%37%
2225
April1st to 15thDay
22%8%37%5%3433432%
2152
16th to endDay
20%6%36%5%24345%37%
2261
May1st to 15thDay
21%6%35%435%5%46%33%
2481
16th to endDay
19%6%35%5%345%5%7%33%
2618
June1st to 15thDay
22%6%345%3445%7%31%
2520
16th to endDay
18%5%35%5%36%45%8%32%
2520
July1st to 15thDay
12%5%345%45%5%6%9%37%
2520
16th to endDay
11%5%25%5%445%7%10%37%
2654
August1st to 15thDay
11%5%37%6%35%5%6%9%35%
2499
16th to endDay
9%5%14435%5%6%9%45%
2299
September1st to 15thDay
15%5%245%2345%7%42%
2160
16th to endDay
13%5%1441335%7%49%
1986
October1st to 15thDay
20%6%36%5%335%5%6%34%
1845
16th to endDay
23%9%36%5%34445%28%
1758
November1st to 15thDay
18%10%45%43446%7%30%
1716
16th to endDay
23%9%37%5%24346%28%
1579
December1st to 15thDay
25%13%47%5%345%46%19%
1560
16th to endDay
26%15%36%6%24335%21%
1664
January1st to 15thNight
19%15%5%9%6%3444422%
2716
16th to endNight
15%12%5%8%7%45%5%4426%
2912
February1st to 15thNight
14%14%6%11%7%35%445%21%
2504
16th to endNight
19%11%5%7%5%45%43428%
1976
March1st to 15thNight
21%12%36%6%24335%28%
2147
16th to endNight
17%10%35%5%2433438%
1998
April1st to 15thNight
26%8%45%5%24335%31%
1796
16th to endNight
22%7%245%24345%36%
1698
May1st to 15thNight
21%6%36%5%33345%36%
1481
16th to endNight
19%7%25%435%45%6%34%
1495
June1st to 15thNight
26%6%25%5%245%47%29%
1440
16th to endNight
17%425%4346%7%8%35%
1440
July1st to 15thNight
11%325%5%45%5%7%9%39%
1440
16th to endNight
11%425%5%3448%8%41%
1514
August1st to 15thNight
13%425%6%35%5%5%8%39%
1449
16th to endNight
12%42343345%8%46%
1902
September1st to 15thNight
17%5%25%5%23446%42%
1800
16th to endNight
18%323312347%48%
1974
October1st to 15thNight
18%6%35%5%33446%38%
2115
16th to endNight
25%8%37%5%24335%30%
2466
November1st to 15thNight
21%9%25%6%24445%32%
2472
16th to endNight
23%12%47%5%3434427%
2708
December1st to 15thNight
23%15%5%8%423345%22%
2730
16th to endNight
24%15%5%7%5%2334422%
2912

Percentage Cloud Cover SE (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 15thDay
21%15%5%9%6%3434321%
1552
16th to endDay
14%13%48%6%45%6%47%24%
1664
February1st to 15thDay
16%12%5%10%8%45%435%23%
1686
16th to endDay
18%12%5%7%6%3444427%
1644
March1st to 15thDay
17%11%47%8%35%445%26%
1800
16th to endDay
18%9%45%5%13446%35%
2225
April1st to 15thDay
22%9%35%5%34335%32%
2152
16th to endDay
20%6%35%5%2345%5%36%
2261
May1st to 15thDay
20%7%25%5%35%45%6%33%
2481
16th to endDay
19%5%35%5%345%5%7%34%
2618
June1st to 15thDay
22%6%345%35%448%31%
2520
16th to endDay
18%6%25%6%35%5%5%8%33%
2520
July1st to 15thDay
12%5%346%45%5%5%9%38%
2520
16th to endDay
12%425%6%346%7%10%36%
2654
August1st to 15thDay
11%5%26%6%35%6%6%9%35%
2499
16th to endDay
10%4144245%6%8%46%
2299
September1st to 15thDay
15%5%2442445%6%43%
2160
16th to endDay
12%5%14423348%48%
1986
October1st to 15thDay
20%7%26%5%4435%6%34%
1845
16th to endDay
24%9%35%6%44345%28%
1758
November1st to 15thDay
18%9%36%5%245%5%7%29%
1716
16th to endDay
22%10%46%6%34445%26%
1579
December1st to 15thDay
25%12%5%8%6%35%446%17%
1560
16th to endDay
26%15%47%6%25%43419%
1664
January1st to 15thNight
19%15%6%9%6%34445%21%
2716
16th to endNight
14%13%5%8%6%45%5%4425%
2912
February1st to 15thNight
15%14%6%11%8%45%44420%
2497
16th to endNight
18%11%5%8%5%45%43428%
1976
March1st to 15thNight
21%12%36%7%24345%28%
2160
16th to endNight
17%10%35%5%33345%37%
1997
April1st to 15thNight
27%8%35%5%33336%30%
1796
16th to endNight
21%7%35%425%445%36%
1698
May1st to 15thNight
20%7%46%5%24345%36%
1481
16th to endNight
20%5%35%435%447%34%
1495
June1st to 15thNight
26%6%35%424446%30%
1440
16th to endNight
16%5%25%5%25%6%7%8%35%
1440
July1st to 15thNight
12%3245%35%5%7%9%39%
1440
16th to endNight
11%434435%5%6%10%40%
1514
August1st to 15thNight
13%5%245%35%5%6%9%38%
1449
16th to endNight
12%42433445%7%46%
1902
September1st to 15thNight
17%5%25%5%24446%41%
1800
16th to endNight
17%423323346%47%
1974
October1st to 15thNight
17%7%26%6%24346%37%
2115
16th to endNight
25%8%36%424345%29%
2466
November1st to 15thNight
21%8%36%5%34346%31%
2472
16th to endNight
23%11%47%5%2434427%
2708
December1st to 15thNight
23%14%5%8%434346%20%
2730
16th to endNight
23%17%6%7%5%2333422%
2912

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 15thDay
67%47%13%6%
1553
16th to endDay
56%7%12%15%7%
1664
February1st to 15thDay
63%310%17%3
1688
16th to endDay
59%311%15%8%1
1644
March1st to 15thDay
58%412%15%7%1
1800
16th to endDay
48%5%11%17%14%3
2225
April1st to 15thDay
55%37%19%11%2
2152
16th to endDay
49%48%19%14%3
2261
May1st to 15thDay
50%5%9%18%14%1
2481
16th to endDay
47%6%11%20%11%1
2622
June1st to 15thDay
50%6%11%19%10%1
2520
16th to endDay
49%5%12%22%9%1
2520
July1st to 15thDay
40%7%13%26%11%
2371
16th to endDay
40%8%17%24%8%
2487
August1st to 15thDay
44%8%16%23%8%
2485
16th to endDay
33%6%18%27%13%
2299
September1st to 15thDay
40%5%14%27%12%
2160
16th to endDay
34%5%12%32%13%
1986
October1st to 15thDay
49%6%11%23%8%
1845
16th to endDay
57%413%18%6%
1758
November1st to 15thDay
51%7%12%18%9%
1716
16th to endDay
57%6%11%15%7%
1579
December1st to 15thDay
67%5%11%12%3
1560
16th to endDay
66%5%10%9%6%
1664
January1st to 15thNight
64%5%10%14%4
2716
16th to endNight
59%5%9%16%8%
2912
February1st to 15thNight
65%5%9%15%4
2506
16th to endNight
58%49%15%10%
1976
March1st to 15thNight
58%48%17%9%1
2160
16th to endNight
49%38%18%15%3
1998
April1st to 15thNight
57%2419%14%1
1796
16th to endNight
50%47%18%15%4
1698
May1st to 15thNight
50%37%18%15%4
1481
16th to endNight
48%6%9%20%13%2
1497
June1st to 15thNight
54%5%8%20%9%
1440
16th to endNight
43%7%13%20%14%1
1440
July1st to 15thNight
37%7%12%26%15%
1360
16th to endNight
37%7%17%23%13%
1418
August1st to 15thNight
40%7%16%23%11%
1439
16th to endNight
35%5%15%29%13%
1902
September1st to 15thNight
42%5%11%25%13%1
1800
16th to endNight
36%6%10%30%15%
1974
October1st to 15thNight
46%6%9%26%10%
2115
16th to endNight
56%5%11%19%7%
2466
November1st to 15thNight
54%410%19%8%2
2472
16th to endNight
59%49%18%6%
2708
December1st to 15thNight
65%411%15%3
2730
16th to endNight
65%49%12%6%
2912

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 15thDay
23%13%23%28%11%
90
16th to endDay
29%10%33%19%6%1
96
February1st to 15thDay
30%13%35%17%2
137
16th to endDay
27%7%31%25%6%
265
March1st to 15thDay
24%10%30%28%6%
270
16th to endDay
24%7%28%22%13%3
288
April1st to 15thDay
29%12%27%19%8%3
270
16th to endDay
18%12%25%22%15%3
270
May1st to 15thDay
26%6%27%20%13%4
288
16th to endDay
20%8%31%20%16%3
331
June1st to 15thDay
27%8%21%27%9%4
315
16th to endDay
19%8%24%29%16%2
315
July1st to 15thDay
12%6%27%28%19%6%
305
16th to endDay
14%218%34%24%5%
326
August1st to 15thDay
14%220%30%23%8%
313
16th to endDay
9%5%21%28%20%14%
332
September1st to 15thDay
16%320%26%19%14%
315
16th to endDay
13%5%26%20%21%12%
314
October1st to 15thDay
20%8%27%21%18%2
315
16th to endDay
31%10%25%22%9%
295
November1st to 15thDay
25%10%26%22%13%1
280
16th to endDay
32%11%31%17%8%
109
December1st to 15thDay
28%5%30%26%5%3
90
16th to endDay
35%15%30%15%3
96
January1st to 15thNight
25%11%31%24%6%
780
16th to endNight
21%9%34%25%7%
832
February1st to 15thNight
22%7%34%28%7%
764
16th to endNight
25%7%32%27%6%
659
March1st to 15thNight
26%8%29%27%6%
720
16th to endNight
22%5%30%30%10%
768
April1st to 15thNight
29%8%25%30%5%
718
16th to endNight
24%10%29%25%9%
618
May1st to 15thNight
23%430%29%10%1
401
16th to endNight
22%5%28%33%10%
375
June1st to 15thNight
28%422%32%11%
360
16th to endNight
17%226%38%14%
360
July1st to 15thNight
11%424%37%21%
340
16th to endNight
11%121%46%17%1
376
August1st to 15thNight
15%213%45%21%1
368
16th to endNight
13%221%36%24%2
756
September1st to 15thNight
19%218%40%17%1
720
16th to endNight
19%5%19%31%21%2
717
October1st to 15thNight
21%6%28%29%13%1
720
16th to endNight
29%9%26%27%6%
768
November1st to 15thNight
27%7%29%24%11%
760
16th to endNight
28%10%27%20%11%
780
December1st to 15thNight
31%9%30%23%5%
780
16th to endNight
32%9%31%19%5%1
832
Page generated at 2018-02-23 11:21:32. Version ac04

Copyright 2018 A. Danko


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