Montreal River Harbour
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Montreal River Harbour clear sky chart from 2005-11-05 to 2017-11-30.

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%
15844
10%
47748
7%
15799
33%
15799
14%
36432

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
16%
900
3%
2568
2%
895
18%
895
6%
2307
January16th to endNight
20%
960
6%
2688
3%
960
23%
960
6%
2366
February1st to 15thNight
18%
779
6%
2360
3%
776
21%
776
9%
1970
February16th to endNight
25%
631
9%
1896
6%
631
28%
631
11%
1505
March1st to 15thNight
27%
720
15%
2121
8%
720
34%
720
20%
1493
March16th to endNight
36%
744
19%
2088
12%
744
43%
744
24%
1427
April1st to 15thNight
34%
539
14%
1752
9%
539
39%
539
18%
1207
April16th to endNight
35%
540
17%
1620
8%
540
42%
540
24%
1090
May1st to 15thNight
39%
540
12%
1584
10%
540
42%
540
20%
1109
May16th to endNight
47%
432
13%
1368
11%
431
51%
431
23%
888
June1st to 15thNight
45%
360
10%
1260
9%
360
48%
360
21%
812
June16th to endNight
48%
360
7%
1260
7%
360
49%
360
21%
820
July1st to 15thNight
55%
368
11%
1218
10%
368
57%
368
26%
758
July16th to endNight
55%
564
12%
1417
10%
531
55%
531
28%
960
August1st to 15thNight
59%
539
14%
1529
12%
536
61%
536
32%
949
August16th to endNight
49%
573
16%
1723
13%
573
53%
573
27%
1078
September1st to 15thNight
46%
612
11%
1872
8%
612
48%
612
24%
1240
September16th to endNight
44%
717
14%
1980
11%
717
45%
717
24%
1374
October1st to 15thNight
31%
720
14%
2076
8%
720
37%
720
18%
1529
October16th to endNight
18%
768
7%
2496
4%
768
23%
768
8%
2072
November1st to 15thNight
16%
760
9%
2486
6%
760
21%
760
8%
2040
November16th to endNight
16%
858
5%
2806
2%
858
18%
858
6%
2416
December1st to 15thNight
12%
900
3%
2700
2%
900
13%
900
4%
2446
December16th to endNight
12%
960
4%
2880
2%
960
15%
960
5%
2576

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%10%46%5%3445%6%31%
48667
Night
17%12%5%8%6%34445%26%
47910
Cloud CoverDay
17%11%46%5%3445%6%30%
48676
Night
16%12%5%8%6%34446%26%
47915
TransparencyDay
53%5%13%19%7%
48345
Night
59%5%11%16%6%
47750
SeeingDay
22%7%25%27%13%3
6268
Night
23%8%28%27%11%1
15844

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
16%19%7%13%7%445%7%5%8%
1367
16th to endDay
12%14%7%12%10%35%5%5%416%
1536
February1st to 15thDay
10%15%6%10%9%6%7%5%46%16%
1499
16th to endDay
9%12%8%11%7%45%5%5%6%22%
1575
March1st to 15thDay
13%12%48%6%35%35%5%31%
1828
16th to endDay
13%9%35%5%34445%37%
2146
April1st to 15thDay
19%10%25%42445%6%34%
2196
16th to endDay
17%8%35%5%1345%7%35%
2340
May1st to 15thDay
18%7%35%5%34446%35%
2365
16th to endDay
17%5%25%43445%7%37%
2747
June1st to 15thDay
18%6%24445%5%6%7%33%
2700
16th to endDay
16%6%35%5%25%45%9%35%
2700
July1st to 15thDay
15%5%25%43335%8%41%
2668
16th to endDay
17%5%24424447%42%
2655
August1st to 15thDay
12%5%2442445%8%42%
2421
16th to endDay
18%6%24423447%39%
2477
September1st to 15thDay
20%6%245%23347%38%
2076
16th to endDay
22%6%2442435%7%36%
1980
October1st to 15thDay
25%12%35%422335%30%
1881
16th to endDay
29%14%48%5%35%43317%
1728
November1st to 15thDay
21%20%47%5%24445%18%
1701
16th to endDay
20%19%6%8%7%44435%14%
1477
December1st to 15thDay
14%22%11%13%8%2243312%
1260
16th to endDay
17%26%6%11%6%35%32310%
1344
January1st to 15thNight
16%19%10%13%8%36%5%448%
2568
16th to endNight
12%16%9%12%9%46%5%5%412%
2688
February1st to 15thNight
10%16%8%14%10%35%46%415%
2360
16th to endNight
12%14%8%12%7%26%45%6%19%
1896
March1st to 15thNight
13%9%5%8%5%34445%35%
2108
16th to endNight
11%9%46%5%3445%6%38%
2088
April1st to 15thNight
20%8%37%424446%33%
1752
16th to endNight
15%9%26%414446%39%
1620
May1st to 15thNight
17%8%46%5%3446%7%31%
1584
16th to endNight
16%7%2343445%5%41%
1366
June1st to 15thNight
17%8%26%5%13447%38%
1260
16th to endNight
15%6%25%6%245%6%8%35%
1260
July1st to 15thNight
14%6%45%5%24447%41%
1290
16th to endNight
15%6%25%42436%7%41%
1513
August1st to 15thNight
11%6%15%4235%6%6%44%
1538
16th to endNight
16%424423447%44%
1723
September1st to 15thNight
18%6%25%424346%41%
1872
16th to endNight
22%5%34423347%38%
1980
October1st to 15thNight
24%9%25%5%23346%32%
2076
16th to endNight
30%15%37%5%23445%17%
2496
November1st to 15thNight
24%18%6%7%5%3432418%
2486
16th to endNight
20%19%7%10%6%36%5%4312%
2806
December1st to 15thNight
16%20%9%13%8%346%339%
2700
16th to endNight
18%22%7%13%8%343449%
2880

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
14%19%8%13%7%445%5%5%10%
1367
16th to endDay
11%14%8%13%9%45%44418%
1536
February1st to 15thDay
9%16%6%11%10%5%7%446%17%
1499
16th to endDay
9%14%8%11%8%45%45%5%21%
1575
March1st to 15thDay
13%12%49%5%34445%31%
1838
16th to endDay
13%11%46%5%33446%36%
2145
April1st to 15thDay
20%10%36%42345%7%31%
2196
16th to endDay
18%10%35%42345%7%34%
2340
May1st to 15thDay
18%8%36%5%34446%34%
2365
16th to endDay
17%6%25%4345%5%8%36%
2747
June1st to 15thDay
18%7%25%4345%6%8%33%
2700
16th to endDay
15%6%25%435%46%10%34%
2700
July1st to 15thDay
15%6%2442345%8%40%
2668
16th to endDay
16%6%2442345%7%42%
2655
August1st to 15thDay
13%6%25%3345%5%7%42%
2421
16th to endDay
19%7%2442335%7%38%
2477
September1st to 15thDay
19%8%245%23447%36%
2076
16th to endDay
22%7%245%2345%7%34%
1980
October1st to 15thDay
24%13%26%422336%29%
1881
16th to endDay
27%17%5%7%6%2433317%
1728
November1st to 15thDay
20%19%47%5%34445%18%
1701
16th to endDay
18%21%6%7%7%35%44415%
1477
December1st to 15thDay
13%21%12%12%8%2423413%
1260
16th to endDay
17%24%8%10%7%3434311%
1344
January1st to 15thNight
16%18%8%13%8%3445%411%
2568
16th to endNight
11%16%8%12%9%45%446%14%
2688
February1st to 15thNight
9%15%8%14%11%34445%17%
2353
16th to endNight
11%14%8%11%8%35%5%45%21%
1896
March1st to 15thNight
13%10%5%8%5%24346%34%
2121
16th to endNight
11%9%46%5%3445%6%38%
2088
April1st to 15thNight
19%9%36%42435%7%32%
1752
16th to endNight
14%10%27%424347%37%
1620
May1st to 15thNight
16%9%36%6%3446%7%31%
1583
16th to endNight
15%8%2343445%6%40%
1366
June1st to 15thNight
17%8%36%5%2335%7%37%
1260
16th to endNight
13%7%25%5%335%6%8%35%
1260
July1st to 15thNight
14%6%36%43345%7%41%
1290
16th to endNight
15%5%25%5%2445%7%41%
1513
August1st to 15thNight
10%6%25%5%235%5%7%45%
1538
16th to endNight
16%5%24423446%43%
1723
September1st to 15thNight
17%6%35%423347%40%
1872
16th to endNight
22%5%24423448%37%
1980
October1st to 15thNight
23%9%26%5%24446%31%
2076
16th to endNight
28%14%47%6%23335%18%
2496
November1st to 15thNight
22%19%6%7%5%34335%19%
2486
16th to endNight
19%18%6%10%6%35%45%414%
2806
December1st to 15thNight
14%20%9%13%8%34436%11%
2700
16th to endNight
16%22%7%13%8%2443411%
2880

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
74%7%9%6%1
1368
16th to endDay
69%7%7%9%5%
1536
February1st to 15thDay
68%5%12%8%5%
1501
16th to endDay
62%412%12%7%
1575
March1st to 15thDay
53%5%12%17%9%1
1838
16th to endDay
48%313%20%9%2
2146
April1st to 15thDay
50%312%22%9%1
2196
16th to endDay
48%39%22%13%2
2340
May1st to 15thDay
49%5%10%20%11%2
2365
16th to endDay
44%5%15%23%9%
2751
June1st to 15thDay
47%5%14%21%11%1
2700
16th to endDay
45%6%15%24%7%
2700
July1st to 15thDay
40%5%16%28%8%
2511
16th to endDay
41%5%15%27%9%
2488
August1st to 15thDay
38%6%19%26%7%
2406
16th to endDay
44%6%16%23%8%
2477
September1st to 15thDay
47%5%16%22%7%
2076
16th to endDay
46%5%18%24%4
1980
October1st to 15thDay
57%315%19%4
1881
16th to endDay
70%5%9%9%4
1728
November1st to 15thDay
67%5%10%12%3
1701
16th to endDay
72%6%10%7%2
1477
December1st to 15thDay
77%6%8%7%1
1260
16th to endDay
77%48%6%1
1344
January1st to 15thNight
76%7%8%5%1
2568
16th to endNight
73%7%6%7%3
2688
February1st to 15thNight
71%411%9%2
2362
16th to endNight
65%411%13%5%
1896
March1st to 15thNight
50%413%19%11%
2121
16th to endNight
46%412%23%11%2
2088
April1st to 15thNight
51%410%21%11%
1752
16th to endNight
46%312%19%15%2
1620
May1st to 15thNight
51%311%18%11%3
1584
16th to endNight
43%5%12%24%12%1
1368
June1st to 15thNight
46%412%20%14%2
1260
16th to endNight
43%7%15%25%7%
1260
July1st to 15thNight
39%6%13%28%11%
1218
16th to endNight
42%5%12%26%11%
1417
August1st to 15thNight
36%5%20%27%10%
1529
16th to endNight
40%417%29%8%
1723
September1st to 15thNight
43%6%16%25%7%
1872
16th to endNight
46%5%16%24%7%
1980
October1st to 15thNight
54%413%20%5%
2076
16th to endNight
68%6%9%11%3
2496
November1st to 15thNight
69%410%12%3
2486
16th to endNight
73%6%10%6%2
2806
December1st to 15thNight
78%7%6%5%1
2700
16th to endNight
78%5%8%5%1
2880

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
26%11%36%15%10%
79
16th to endDay
21%6%23%32%14%1
96
February1st to 15thDay
30%7%37%18%41
90
16th to endDay
24%18%37%19%
81
March1st to 15thDay
18%14%32%21%11%1
128
16th to endDay
22%7%31%26%9%2
288
April1st to 15thDay
26%432%26%8%1
270
16th to endDay
23%6%32%21%10%4
270
May1st to 15thDay
22%10%28%23%10%4
322
16th to endDay
24%5%26%29%12%2
517
June1st to 15thDay
22%7%28%26%12%2
495
16th to endDay
17%425%32%15%3
495
July1st to 15thDay
17%421%35%17%3
475
16th to endDay
19%220%36%15%4
515
August1st to 15thDay
14%420%34%20%5%
394
16th to endDay
28%318%26%16%6%
332
September1st to 15thDay
20%5%22%21%22%6%
315
16th to endDay
24%6%21%31%14%
314
October1st to 15thDay
30%8%22%27%10%
303
16th to endDay
29%15%30%18%4
144
November1st to 15thDay
29%13%28%22%6%
131
16th to endDay
31%17%31%16%3
90
December1st to 15thDay
28%18%28%18%6%
60
16th to endDay
32%23%37%41
64
January1st to 15thNight
23%15%33%22%5%
900
16th to endNight
20%8%35%28%6%
960
February1st to 15thNight
17%8%41%26%5%
779
16th to endNight
18%9%31%30%7%1
631
March1st to 15thNight
17%9%37%26%7%
720
16th to endNight
16%7%31%31%10%1
744
April1st to 15thNight
25%5%27%30%8%1
539
16th to endNight
21%6%30%25%15%2
540
May1st to 15thNight
22%323%34%13%2
540
16th to endNight
19%7%20%33%15%3
432
June1st to 15thNight
20%6%18%33%20%1
360
16th to endNight
16%5%22%33%20%2
360
July1st to 15thNight
16%316%37%23%2
368
16th to endNight
18%315%37%22%3
564
August1st to 15thNight
15%414%34%28%3
539
16th to endNight
19%220%33%20%3
573
September1st to 15thNight
20%5%23%25%18%5%
612
16th to endNight
24%6%19%32%13%2
717
October1st to 15thNight
29%7%27%23%11%
720
16th to endNight
37%11%24%21%5%
768
November1st to 15thNight
33%12%30%18%4
760
16th to endNight
30%13%29%20%6%
858
December1st to 15thNight
25%16%34%18%5%
900
16th to endNight
27%12%31%19%7%1
960
Page generated at 2017-12-01 12:13:41. Version ac04

Copyright 2017 A. Danko


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