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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 2017-02-18.

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%
14016
13%
44896
9%
13985
38%
13985
17%
32290

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
19%
720
9%
2506
5%
716
25%
716
9%
1981
January16th to endNight
24%
768
11%
2688
7%
768
31%
768
11%
2020
February1st to 15thNight
22%
704
8%
2310
5%
701
27%
701
11%
1837
February16th to endNight
26%
588
11%
1762
6%
588
32%
588
13%
1346
March1st to 15thNight
27%
660
14%
1980
11%
660
32%
660
15%
1500
March16th to endNight
33%
704
19%
1831
10%
704
40%
704
24%
1299
April1st to 15thNight
29%
658
17%
1646
6%
658
34%
658
20%
1246
April16th to endNight
31%
567
16%
1557
7%
567
38%
567
22%
1102
May1st to 15thNight
34%
368
18%
1358
15%
368
43%
368
18%
879
May16th to endNight
38%
342
13%
1369
14%
342
46%
342
17%
903
June1st to 15thNight
35%
330
9%
1320
10%
330
42%
330
12%
946
June16th to endNight
48%
330
8%
1320
12%
330
51%
330
20%
832
July1st to 15thNight
54%
310
14%
1240
20%
310
59%
310
24%
720
July16th to endNight
55%
348
11%
1306
14%
326
58%
326
23%
767
August1st to 15thNight
60%
337
16%
1318
19%
335
61%
335
21%
808
August16th to endNight
57%
693
18%
1743
11%
693
59%
693
35%
1134
September1st to 15thNight
51%
660
15%
1650
8%
660
53%
660
29%
1152
September16th to endNight
48%
657
20%
1809
13%
657
53%
657
30%
1167
October1st to 15thNight
34%
660
19%
1939
11%
660
43%
660
22%
1360
October16th to endNight
28%
704
11%
2260
8%
704
34%
704
14%
1681
November1st to 15thNight
27%
700
17%
2277
12%
700
36%
700
16%
1635
November16th to endNight
25%
720
14%
2499
9%
720
32%
720
12%
1862
December1st to 15thNight
19%
720
8%
2520
4%
720
24%
720
9%
1980
December16th to endNight
13%
768
10%
2688
3%
768
22%
768
9%
2133

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%
45286
Night
19%9%36%5%34445%31%
45065
Cloud CoverDay
18%8%36%5%3445%7%32%
45296
Night
19%9%46%5%34446%31%
45070
TransparencyDay
50%5%12%20%10%1
44973
Night
53%5%10%19%10%1
44896
SeeingDay
21%7%25%25%15%5%
4753
Night
23%7%27%29%11%
14017

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%14%6%8%6%45%32421%
1432
16th to endDay
14%13%47%5%46%45%7%26%
1536
February1st to 15thDay
14%12%5%10%7%45%445%24%
1552
16th to endDay
17%12%5%7%7%3435%427%
1470
March1st to 15thDay
17%11%47%7%3445%5%27%
1640
16th to endDay
17%8%46%424445%37%
2040
April1st to 15thDay
20%9%37%6%3434432%
1972
16th to endDay
19%6%36%424345%38%
2072
May1st to 15thDay
20%6%35%435%5%46%35%
2273
16th to endDay
19%5%35%5%345%5%7%34%
2394
June1st to 15thDay
22%7%345%35%45%7%30%
2310
16th to endDay
18%6%35%5%35%45%8%32%
2310
July1st to 15thDay
11%5%345%35%5%6%9%38%
2310
16th to endDay
11%5%25%5%445%7%10%36%
2458
August1st to 15thDay
12%6%37%6%35%5%6%8%34%
2291
16th to endDay
9%5%14435%5%6%9%44%
2107
September1st to 15thDay
16%5%245%2345%7%41%
1980
16th to endDay
14%5%1441335%7%46%
1821
October1st to 15thDay
20%6%36%5%3345%6%33%
1691
16th to endDay
23%9%36%5%34445%27%
1612
November1st to 15thDay
17%11%4443446%7%30%
1581
16th to endDay
23%10%37%5%24345%29%
1458
December1st to 15thDay
26%13%5%7%5%3445%6%18%
1440
16th to endDay
27%15%36%6%24335%20%
1536
January1st to 15thNight
18%15%5%9%6%3444422%
2506
16th to endNight
14%13%5%7%7%45%5%45%26%
2688
February1st to 15thNight
14%14%6%11%7%45%445%21%
2308
16th to endNight
18%11%5%8%5%45%43427%
1762
March1st to 15thNight
21%12%46%6%25%335%29%
1967
16th to endNight
16%10%35%5%2433438%
1831
April1st to 15thNight
26%8%445%24335%31%
1646
16th to endNight
21%7%35%5%24345%37%
1557
May1st to 15thNight
19%6%36%5%33345%37%
1358
16th to endNight
20%7%25%425%45%6%35%
1367
June1st to 15thNight
26%7%25%5%245%46%28%
1320
16th to endNight
16%425%4346%6%8%36%
1320
July1st to 15thNight
10%325%5%45%5%6%10%39%
1320
16th to endNight
11%425%43448%9%40%
1402
August1st to 15thNight
14%425%6%35%5%5%9%39%
1328
16th to endNight
13%42443346%8%45%
1743
September1st to 15thNight
17%5%25%6%23446%41%
1650
16th to endNight
19%323322346%47%
1809
October1st to 15thNight
18%6%35%5%33446%36%
1939
16th to endNight
26%8%37%5%23335%29%
2260
November1st to 15thNight
21%9%26%6%34445%31%
2277
16th to endNight
23%12%46%5%3434427%
2499
December1st to 15thNight
23%15%5%8%423345%22%
2520
16th to endNight
25%16%5%7%5%2333422%
2688

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%14%49%7%3433321%
1432
16th to endDay
14%13%48%5%45%6%5%7%24%
1536
February1st to 15thDay
15%12%5%10%9%36%435%23%
1552
16th to endDay
17%13%5%7%7%34445%26%
1470
March1st to 15thDay
18%11%47%7%35%445%27%
1650
16th to endDay
18%10%45%5%14447%35%
2040
April1st to 15thDay
20%9%46%5%34335%32%
1972
16th to endDay
19%6%35%5%2345%5%37%
2072
May1st to 15thDay
20%6%25%5%35%447%35%
2273
16th to endDay
19%5%35%5%3445%7%34%
2394
June1st to 15thDay
22%6%345%35%448%30%
2310
16th to endDay
18%6%25%5%35%45%8%33%
2310
July1st to 15thDay
11%5%346%35%5%5%9%38%
2310
16th to endDay
11%5%25%6%35%6%7%10%35%
2458
August1st to 15thDay
12%6%36%6%45%5%6%8%34%
2291
16th to endDay
10%414325%5%6%9%45%
2107
September1st to 15thDay
15%5%25%42445%6%43%
1980
16th to endDay
13%5%24424348%46%
1821
October1st to 15thDay
20%7%26%5%3435%6%33%
1691
16th to endDay
24%9%35%6%4444427%
1612
November1st to 15thDay
18%10%36%5%25%5%5%7%30%
1581
16th to endDay
22%10%46%6%24445%27%
1458
December1st to 15thDay
26%12%5%8%6%3445%6%16%
1440
16th to endDay
27%15%47%6%2443419%
1536
January1st to 15thNight
18%15%6%9%6%345%45%21%
2506
16th to endNight
13%13%5%8%6%45%5%4426%
2688
February1st to 15thNight
15%13%6%11%8%45%44420%
2301
16th to endNight
18%11%5%8%5%45%43426%
1762
March1st to 15thNight
21%13%46%6%24335%28%
1980
16th to endNight
16%9%35%6%34345%37%
1830
April1st to 15thNight
26%8%35%5%33336%30%
1646
16th to endNight
21%7%35%325%345%37%
1557
May1st to 15thNight
18%7%46%5%14345%38%
1358
16th to endNight
21%5%35%435%447%35%
1367
June1st to 15thNight
27%6%35%424446%28%
1320
16th to endNight
16%5%35%425%6%7%8%36%
1320
July1st to 15thNight
11%3245%35%5%7%9%40%
1320
16th to endNight
11%434435%5%6%10%39%
1402
August1st to 15thNight
13%5%246%35%6%6%9%38%
1328
16th to endNight
12%42433445%8%45%
1743
September1st to 15thNight
17%5%25%5%24447%40%
1650
16th to endNight
19%423323435%47%
1809
October1st to 15thNight
18%7%26%6%24446%36%
1939
16th to endNight
26%8%36%424345%28%
2260
November1st to 15thNight
21%8%36%5%35%346%30%
2277
16th to endNight
23%11%37%6%2434427%
2499
December1st to 15thNight
24%14%5%7%434346%20%
2520
16th to endNight
24%17%6%7%5%2333421%
2688

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%48%13%5%
1433
16th to endDay
57%8%11%15%7%
1536
February1st to 15thDay
63%310%18%3
1554
16th to endDay
60%310%15%8%
1470
March1st to 15thDay
58%412%16%7%
1650
16th to endDay
48%5%12%18%12%3
2040
April1st to 15thDay
54%38%18%11%2
1972
16th to endDay
48%48%19%15%4
2072
May1st to 15thDay
48%49%19%15%1
2273
16th to endDay
47%6%10%21%12%2
2398
June1st to 15thDay
51%6%11%18%10%1
2310
16th to endDay
48%5%11%23%9%1
2310
July1st to 15thDay
39%7%13%27%12%
2161
16th to endDay
40%8%17%24%8%
2291
August1st to 15thDay
45%7%15%23%8%
2277
16th to endDay
34%6%19%25%13%
2107
September1st to 15thDay
40%5%14%26%12%
1980
16th to endDay
37%5%12%31%12%
1821
October1st to 15thDay
49%7%11%22%8%
1691
16th to endDay
58%412%17%6%
1612
November1st to 15thDay
51%7%12%18%9%
1581
16th to endDay
57%6%11%16%7%
1458
December1st to 15thDay
67%5%11%12%3
1440
16th to endDay
67%5%11%9%6%
1536
January1st to 15thNight
64%5%9%14%4
2506
16th to endNight
59%5%9%16%8%
2688
February1st to 15thNight
65%49%15%4
2310
16th to endNight
60%49%14%10%
1762
March1st to 15thNight
59%48%18%8%1
1980
16th to endNight
49%39%18%15%3
1831
April1st to 15thNight
56%2419%14%1
1646
16th to endNight
49%37%17%16%4
1557
May1st to 15thNight
48%38%18%15%5%
1358
16th to endNight
48%5%7%21%13%2
1369
June1st to 15thNight
56%5%8%18%9%
1320
16th to endNight
42%7%12%20%15%1
1320
July1st to 15thNight
36%6%12%27%14%
1240
16th to endNight
37%7%18%22%13%
1306
August1st to 15thNight
40%7%16%23%11%
1318
16th to endNight
36%5%15%28%13%1
1743
September1st to 15thNight
43%5%11%25%13%
1650
16th to endNight
38%5%10%30%14%
1809
October1st to 15thNight
47%6%9%24%10%
1939
16th to endNight
57%411%18%7%
2260
November1st to 15thNight
54%410%18%8%2
2277
16th to endNight
59%49%18%7%
2499
December1st to 15thNight
65%411%15%3
2520
16th to endNight
67%310%12%6%
2688

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%16%18%26%15%
60
16th to endDay
35%428%21%7%1
64
February1st to 15thDay
29%15%36%15%4
93
16th to endDay
28%5%29%26%8%1
195
March1st to 15thDay
26%9%29%28%7%
210
16th to endDay
22%8%27%23%13%4
224
April1st to 15thDay
25%13%28%19%9%3
210
16th to endDay
14%10%25%27%18%4
210
May1st to 15thDay
24%5%27%23%15%4
228
16th to endDay
18%9%28%22%17%3
267
June1st to 15thDay
29%9%20%25%10%5%
255
16th to endDay
19%6%20%31%19%2
255
July1st to 15thDay
11%6%25%29%20%6%
245
16th to endDay
13%220%34%22%5%
270
August1st to 15thDay
15%219%30%23%8%
253
16th to endDay
9%420%30%20%14%
268
September1st to 15thDay
16%318%28%18%14%
255
16th to endDay
16%7%28%16%18%11%
254
October1st to 15thDay
21%8%25%23%18%2
255
16th to endDay
32%9%22%24%9%
245
November1st to 15thDay
23%10%28%22%13%1
235
16th to endDay
35%8%25%19%10%
78
December1st to 15thDay
30%5%31%26%33
60
16th to endDay
37%15%32%14%
64
January1st to 15thNight
24%12%31%24%6%
720
16th to endNight
21%8%35%25%8%
768
February1st to 15thNight
22%7%33%28%7%
704
16th to endNight
25%7%32%27%7%
588
March1st to 15thNight
27%8%28%27%7%
660
16th to endNight
21%6%31%30%10%
704
April1st to 15thNight
29%8%26%30%5%
658
16th to endNight
24%9%29%26%9%
567
May1st to 15thNight
21%431%30%10%2
368
16th to endNight
23%5%26%33%10%
343
June1st to 15thNight
28%5%21%32%11%
330
16th to endNight
16%224%40%15%
330
July1st to 15thNight
10%424%37%21%
310
16th to endNight
11%122%47%15%1
348
August1st to 15thNight
15%213%44%21%1
337
16th to endNight
13%220%37%24%2
693
September1st to 15thNight
20%218%39%17%1
660
16th to endNight
21%5%20%31%19%1
657
October1st to 15thNight
22%6%28%29%11%1
660
16th to endNight
30%8%25%27%7%
704
November1st to 15thNight
26%7%30%24%11%
700
16th to endNight
28%10%27%20%12%
720
December1st to 15thNight
31%9%30%23%5%
720
16th to endNight
34%9%30%18%5%1
768
Page generated at 2017-02-18 16:04:30. Version ac04

Copyright 2017 A. Danko


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