Laval-West
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Laval-West clear sky chart from 2005-11-05 to 2017-08-12.

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
34%
14495
13%
46477
9%
14464
40%
14464
18%
32988

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%
720
9%
2506
5%
716
26%
716
10%
1957
January16th to endNight
25%
768
11%
2688
7%
768
31%
768
12%
1986
February1st to 15thNight
24%
704
9%
2308
6%
701
29%
701
12%
1791
February16th to endNight
27%
631
14%
1893
7%
631
37%
631
15%
1417
March1st to 15thNight
27%
720
14%
2160
10%
720
33%
720
15%
1607
March16th to endNight
36%
768
19%
1995
10%
768
41%
768
24%
1406
April1st to 15thNight
31%
718
16%
1796
6%
718
36%
718
20%
1347
April16th to endNight
31%
627
17%
1707
6%
627
38%
627
23%
1206
May1st to 15thNight
32%
389
16%
1469
13%
389
42%
389
17%
976
May16th to endNight
40%
374
13%
1497
13%
374
48%
374
17%
988
June1st to 15thNight
40%
360
9%
1440
10%
360
46%
360
15%
1000
June16th to endNight
47%
360
8%
1440
11%
360
51%
360
18%
924
July1st to 15thNight
55%
340
13%
1360
19%
340
59%
340
25%
776
July16th to endNight
58%
376
13%
1418
18%
354
61%
354
25%
821
August1st to 15thNight
60%
351
15%
1400
17%
349
64%
349
22%
849
August16th to endNight
58%
700
18%
1750
10%
700
60%
700
36%
1124
September1st to 15thNight
54%
660
14%
1650
8%
660
55%
660
29%
1148
September16th to endNight
50%
657
19%
1804
13%
657
54%
657
32%
1157
October1st to 15thNight
36%
660
19%
1947
12%
660
45%
660
22%
1339
October16th to endNight
30%
704
11%
2253
8%
704
35%
704
15%
1650
November1st to 15thNight
31%
700
17%
2277
11%
700
39%
700
18%
1613
November16th to endNight
26%
720
13%
2511
9%
720
33%
720
13%
1844
December1st to 15thNight
21%
720
8%
2520
4%
720
27%
720
10%
1954
December16th to endNight
15%
768
10%
2688
4%
768
23%
768
9%
2108

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%7%36%5%35%45%7%33%
47502
Night
18%9%36%5%34446%32%
46646
Cloud CoverDay
17%8%36%5%3445%7%33%
47511
Night
19%9%36%5%34446%32%
46652
TransparencyDay
49%6%12%20%10%1
47189
Night
52%5%11%19%10%1
46477
SeeingDay
21%5%24%26%16%5%
5426
Night
23%5%26%31%11%
14496

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
22%12%47%7%35%44323%
1432
16th to endDay
13%13%5%8%7%36%446%28%
1536
February1st to 15thDay
13%12%5%11%6%36%5%45%24%
1553
16th to endDay
16%12%5%8%7%24445%28%
1578
March1st to 15thDay
17%9%5%9%6%35%44427%
1790
16th to endDay
19%7%25%5%23345%38%
2226
April1st to 15thDay
22%8%45%6%24445%32%
2152
16th to endDay
19%8%36%5%14445%37%
2253
May1st to 15thDay
20%6%25%6%36%446%32%
2493
16th to endDay
19%6%25%5%3445%8%33%
2618
June1st to 15thDay
21%7%35%5%3445%7%31%
2520
16th to endDay
17%5%35%5%35%5%6%8%31%
2520
July1st to 15thDay
11%5%246%36%6%6%8%39%
2520
16th to endDay
11%5%25%436%6%6%10%36%
2654
August1st to 15thDay
11%6%26%6%45%5%6%9%35%
2450
16th to endDay
9%4145%25%5%6%9%45%
2100
September1st to 15thDay
15%5%245%3446%8%39%
1980
16th to endDay
14%5%24423346%47%
1826
October1st to 15thDay
20%7%345%345%46%34%
1680
16th to endDay
23%9%36%6%35%45%5%26%
1618
November1st to 15thDay
16%9%45%5%245%6%7%32%
1581
16th to endDay
23%8%36%5%3445%6%29%
1446
December1st to 15thDay
25%11%5%7%5%245%5%5%20%
1440
16th to endDay
26%12%5%7%43444422%
1536
January1st to 15thNight
18%14%6%9%6%3445%5%21%
2506
16th to endNight
13%12%5%8%7%45%445%27%
2688
February1st to 15thNight
13%13%5%10%7%46%5%5%5%22%
2306
16th to endNight
16%12%5%7%5%35%445%29%
1893
March1st to 15thNight
19%11%48%5%24445%28%
2147
16th to endNight
16%9%5%6%423245%39%
1995
April1st to 15thNight
25%8%45%433345%32%
1796
16th to endNight
21%7%25%5%2345%5%36%
1707
May1st to 15thNight
21%8%36%424345%35%
1469
16th to endNight
19%6%35%42445%7%35%
1495
June1st to 15thNight
23%7%35%5%2446%7%29%
1440
16th to endNight
16%5%25%5%345%6%8%35%
1440
July1st to 15thNight
10%3245%35%5%6%10%41%
1440
16th to endNight
10%435%33447%9%41%
1514
August1st to 15thNight
12%5%25%42447%9%41%
1410
16th to endNight
12%42433345%8%47%
1750
September1st to 15thNight
15%5%35%5%2445%7%40%
1650
16th to endNight
17%324323346%47%
1804
October1st to 15thNight
18%6%25%425%447%37%
1947
16th to endNight
23%9%36%5%24345%30%
2253
November1st to 15thNight
20%8%36%5%25%446%32%
2277
16th to endNight
22%10%47%6%23445%28%
2511
December1st to 15thNight
23%14%47%5%24435%24%
2520
16th to endNight
24%17%47%5%3334423%
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%13%5%8%6%35%44322%
1432
16th to endDay
12%13%5%7%7%45%446%27%
1536
February1st to 15thDay
13%12%5%10%6%45%5%45%24%
1553
16th to endDay
16%13%6%6%7%33445%27%
1578
March1st to 15thDay
18%11%49%7%35%44427%
1800
16th to endDay
19%7%35%424345%37%
2225
April1st to 15thDay
21%8%35%6%2434432%
2152
16th to endDay
19%7%36%5%33445%38%
2253
May1st to 15thDay
19%6%36%5%35%446%33%
2493
16th to endDay
19%6%25%5%3445%9%33%
2618
June1st to 15thDay
21%7%35%5%35%45%7%31%
2520
16th to endDay
17%6%26%445%5%6%8%31%
2520
July1st to 15thDay
11%425%5%35%5%6%9%39%
2520
16th to endDay
11%425%5%346%7%9%37%
2654
August1st to 15thDay
12%5%27%6%35%5%5%9%35%
2450
16th to endDay
10%3145%25%5%6%9%46%
2100
September1st to 15thDay
15%425%4245%6%8%40%
1980
16th to endDay
15%4245%23347%47%
1826
October1st to 15thDay
20%7%35%5%35%446%34%
1680
16th to endDay
23%9%35%6%33446%27%
1618
November1st to 15thDay
16%9%45%4245%6%6%31%
1581
16th to endDay
22%9%36%5%3445%5%29%
1446
December1st to 15thDay
25%12%5%7%4345%5%5%19%
1440
16th to endDay
26%13%37%6%35%44421%
1536
January1st to 15thNight
18%13%6%9%6%3445%5%21%
2506
16th to endNight
13%13%5%8%7%45%445%27%
2688
February1st to 15thNight
14%14%5%10%7%35%5%5%5%22%
2299
16th to endNight
17%12%5%8%5%35%43429%
1893
March1st to 15thNight
20%11%47%5%34345%28%
2160
16th to endNight
17%9%36%42334439%
1995
April1st to 15thNight
25%7%45%433336%32%
1796
16th to endNight
21%6%25%5%33445%37%
1707
May1st to 15thNight
21%6%37%423346%35%
1469
16th to endNight
20%5%25%6%25%45%7%34%
1495
June1st to 15thNight
24%7%35%5%3445%7%29%
1440
16th to endNight
16%427%4346%6%8%35%
1440
July1st to 15thNight
10%324436%5%6%10%42%
1440
16th to endNight
11%425%425%5%6%11%41%
1514
August1st to 15thNight
13%425%42446%10%40%
1410
16th to endNight
12%32442436%8%46%
1750
September1st to 15thNight
16%5%35%424446%41%
1650
16th to endNight
18%413423345%47%
1804
October1st to 15thNight
18%5%25%5%2445%6%37%
1947
16th to endNight
24%8%37%5%3434430%
2253
November1st to 15thNight
20%8%36%5%245%46%32%
2277
16th to endNight
22%12%47%5%2443428%
2511
December1st to 15thNight
23%15%47%5%3335%5%22%
2520
16th to endNight
24%16%47%423345%21%
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
65%5%8%14%6%
1433
16th to endDay
56%5%12%16%8%
1536
February1st to 15thDay
60%5%10%19%3
1555
16th to endDay
58%410%15%9%1
1578
March1st to 15thDay
58%411%16%7%1
1800
16th to endDay
47%410%18%15%3
2226
April1st to 15thDay
54%47%19%12%2
2152
16th to endDay
48%48%19%15%3
2253
May1st to 15thDay
51%5%8%18%14%2
2493
16th to endDay
47%6%11%20%12%1
2622
June1st to 15thDay
51%6%10%19%10%1
2520
16th to endDay
49%7%10%22%9%1
2520
July1st to 15thDay
38%8%13%26%12%
2371
16th to endDay
39%8%17%25%8%
2487
August1st to 15thDay
43%8%16%23%8%
2436
16th to endDay
32%7%18%26%14%
2100
September1st to 15thDay
40%5%14%26%12%
1980
16th to endDay
37%411%33%11%
1826
October1st to 15thDay
50%411%23%9%
1680
16th to endDay
58%5%11%17%6%
1618
November1st to 15thDay
49%6%13%20%9%
1581
16th to endDay
55%6%12%17%7%
1446
December1st to 15thDay
64%5%14%12%2
1440
16th to endDay
65%5%11%11%6%
1536
January1st to 15thNight
63%5%10%15%4
2506
16th to endNight
58%410%16%8%
2688
February1st to 15thNight
62%5%11%16%4
2308
16th to endNight
57%49%17%10%
1893
March1st to 15thNight
58%38%18%9%1
2160
16th to endNight
48%48%18%16%3
1995
April1st to 15thNight
55%25%19%14%1
1796
16th to endNight
49%48%18%15%4
1707
May1st to 15thNight
51%37%17%15%4
1469
16th to endNight
47%6%9%20%13%1
1497
June1st to 15thNight
52%6%10%19%10%
1440
16th to endNight
43%8%12%19%14%
1440
July1st to 15thNight
35%7%13%27%15%
1360
16th to endNight
35%7%18%23%13%
1418
August1st to 15thNight
39%7%17%23%12%
1400
16th to endNight
34%5%16%28%13%
1750
September1st to 15thNight
43%5%12%25%13%
1650
16th to endNight
38%412%29%14%
1804
October1st to 15thNight
46%5%10%25%11%
1947
16th to endNight
57%312%18%6%
2253
November1st to 15thNight
52%412%18%8%2
2277
16th to endNight
58%411%18%6%
2511
December1st to 15thNight
63%5%12%15%3
2520
16th to endNight
65%410%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
18%16%23%26%15%
60
16th to endDay
32%6%28%21%7%3
64
February1st to 15thDay
31%14%28%22%2
87
16th to endDay
27%331%30%6%
237
March1st to 15thDay
22%9%28%31%7%
270
16th to endDay
24%427%26%12%4
288
April1st to 15thDay
28%9%27%21%9%3
270
16th to endDay
20%6%28%23%16%4
270
May1st to 15thDay
27%426%22%11%7%
288
16th to endDay
21%6%29%21%16%5%
331
June1st to 15thDay
27%6%22%27%12%3
315
16th to endDay
17%420%35%19%3
315
July1st to 15thDay
12%5%21%30%21%7%
305
16th to endDay
13%215%34%27%6%
326
August1st to 15thDay
13%116%29%26%12%
297
16th to endDay
9%218%29%24%15%
268
September1st to 15thDay
15%316%26%23%14%
255
16th to endDay
18%5%23%20%19%11%
254
October1st to 15thDay
20%5%24%23%20%4
255
16th to endDay
30%6%25%24%11%
246
November1st to 15thDay
24%5%27%28%11%2
235
16th to endDay
33%7%25%21%12%
66
December1st to 15thDay
31%130%26%6%3
60
16th to endDay
35%10%39%12%1
64
January1st to 15thNight
24%10%31%27%6%
720
16th to endNight
20%8%35%27%8%
768
February1st to 15thNight
21%6%34%29%8%
704
16th to endNight
22%7%31%30%6%
631
March1st to 15thNight
28%6%29%29%5%
720
16th to endNight
21%5%27%34%10%
768
April1st to 15thNight
28%6%25%33%5%
718
16th to endNight
25%7%29%26%10%
627
May1st to 15thNight
23%429%30%9%1
389
16th to endNight
22%425%37%9%
375
June1st to 15thNight
28%320%34%12%
360
16th to endNight
17%223%41%14%
360
July1st to 15thNight
10%224%39%22%1
340
16th to endNight
11%217%47%19%1
376
August1st to 15thNight
16%211%43%24%1
351
16th to endNight
15%117%37%26%1
700
September1st to 15thNight
19%317%40%18%1
660
16th to endNight
20%321%30%22%1
657
October1st to 15thNight
21%5%28%32%11%
660
16th to endNight
29%5%27%28%8%
704
November1st to 15thNight
25%5%29%27%11%
700
16th to endNight
28%9%25%23%11%1
720
December1st to 15thNight
32%7%28%26%6%
720
16th to endNight
32%7%32%21%41
768
Page generated at 2017-08-13 14:16:47. Version ac04

Copyright 2017 A. Danko


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