Sommet du Mont Tremblant
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sommet du Mont Tremblant clear sky chart from 2005-11-06 to 2026-08-30.

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 Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(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

By Month

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 Forecast	Data Points
Cloud Cover	Day	18% 12% 4 9% 5% 5% 4 3 5% 6% 28%	144425
	Night	17% 14% 5% 11% 6% 5% 4 3 4 5% 26%	137775
Transparency	Day	56% 6% 11% 18% 9% 1	147858
	Night	59% 5% 11% 16% 8% 1	142431
Seeing	Day	27% 19% 29% 17% 6% 2	16740
	Night	25% 15% 26% 23% 9% 1	25647

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
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	12% 16% 7% 21% 8% 6% 6% 3 4 4 13%	4661
	11th to 20th	Day	10% 21% 8% 20% 11% 4 3 2 2 4 16%	4650
	21st to end	Day	7% 13% 8% 17% 9% 6% 7% 4 5% 6% 18%	5124
February	1st to 10th	Day	10% 19% 7% 14% 9% 5% 3 3 4 5% 21%	1866
	11th to 20th	Day	11% 19% 6% 14% 6% 5% 3 3 4 5% 23%	1895
	21st to end	Day	15% 19% 5% 11% 7% 5% 5% 3 4 4 22%	1730
March	1st to 10th	Day	18% 17% 6% 14% 6% 5% 3 2 3 4 21%	4576
	11th to 20th	Day	15% 16% 6% 11% 5% 4 4 3 4 6% 26%	4901
	21st to end	Day	18% 14% 4 9% 5% 4 3 3 4 5% 31%	6026
April	1st to 10th	Day	21% 17% 5% 9% 4 3 2 3 4 5% 27%	2520
	11th to 20th	Day	24% 12% 4 7% 5% 4 3 2 4 4 30%	2494
	21st to end	Day	21% 12% 4 8% 5% 4 4 4 4 5% 30%	2703
May	1st to 10th	Day	24% 13% 4 8% 5% 5% 5% 4 5% 6% 22%	8237
	11th to 20th	Day	21% 9% 3 7% 5% 5% 5% 3 6% 7% 29%	8221
	21st to end	Day	23% 10% 3 7% 5% 5% 4 3 5% 6% 30%	9060
June	1st to 10th	Day	26% 9% 3 6% 5% 5% 4 4 6% 6% 27%	2940
	11th to 20th	Day	19% 7% 3 7% 6% 5% 6% 4 5% 8% 31%	2940
	21st to end	Day	25% 7% 2 7% 5% 5% 5% 3 6% 7% 27%	2940
July	1st to 10th	Day	19% 7% 2 7% 5% 5% 5% 4 6% 8% 32%	8280
	11th to 20th	Day	15% 6% 2 5% 4 4 5% 4 7% 10% 38%	8280
	21st to end	Day	14% 7% 2 6% 4 4 5% 4 7% 10% 36%	8993
August	1st to 10th	Day	18% 8% 3 8% 5% 5% 6% 4 6% 8% 29%	4703
	11th to 20th	Day	19% 8% 3 6% 4 5% 5% 4 6% 7% 34%	4292
	21st to end	Day	18% 6% 2 6% 5% 5% 5% 4 6% 9% 35%	4420
September	1st to 10th	Day	19% 6% 2 6% 4 4 5% 3 6% 6% 39%	2400
	11th to 20th	Day	18% 7% 2 6% 3 3 4 4 6% 6% 41%	2350
	21st to end	Day	24% 8% 2 5% 4 3 3 3 5% 6% 38%	2200
October	1st to 10th	Day	25% 10% 3 5% 4 4 4 3 4 7% 32%	2008
	11th to 20th	Day	27% 14% 3 8% 4 3 3 3 4 4 25%	1983
	21st to end	Day	27% 17% 4 7% 5% 3 3 2 3 5% 23%	1980
November	1st to 10th	Day	19% 19% 5% 8% 3 3 4 3 3 5% 27%	1851
	11th to 20th	Day	21% 18% 7% 11% 6% 4 3 4 3 4 20%	1727
	21st to end	Day	21% 21% 7% 14% 5% 3 3 2 3 3 17%	1680
December	1st to 10th	Day	18% 23% 10% 13% 7% 4 3 3 3 4 12%	2680
	11th to 20th	Day	18% 21% 7% 14% 7% 4 4 3 3 3 16%	3066
	21st to end	Day	18% 18% 6% 12% 5% 5% 5% 3 4 4 21%	4048
January	1st to 10th	Night	10% 21% 9% 17% 7% 5% 4 3 4 4 15%	8234
	11th to 20th	Night	10% 19% 9% 21% 13% 5% 4 2 3 3 11%	8235
	21st to end	Night	6% 13% 8% 18% 9% 9% 7% 4 6% 4 16%	9057
February	1st to 10th	Night	11% 17% 6% 13% 9% 5% 5% 3 4 4 22%	2751
	11th to 20th	Night	13% 16% 8% 13% 8% 6% 4 3 4 4 22%	2610
	21st to end	Night	13% 17% 6% 12% 6% 4 5% 3 4 5% 23%	2076
March	1st to 10th	Night	20% 16% 5% 13% 6% 4 5% 2 3 4 23%	5484
	11th to 20th	Night	14% 16% 5% 10% 5% 4 5% 3 4 6% 27%	5263
	21st to end	Night	18% 14% 5% 10% 5% 5% 4 3 4 5% 26%	5148
April	1st to 10th	Night	23% 14% 4 7% 5% 3 3 3 4 6% 28%	2100
	11th to 20th	Night	21% 12% 3 6% 4 4 3 4 5% 5% 34%	2075
	21st to end	Night	21% 11% 3 8% 4 4 3 3 4 5% 34%	1933
May	1st to 10th	Night	18% 12% 4 9% 5% 5% 5% 4 5% 7% 26%	4660
	11th to 20th	Night	23% 9% 3 7% 4 4 4 3 5% 7% 32%	4639
	21st to end	Night	23% 11% 3 7% 4 4 4 4 5% 6% 30%	5114
June	1st to 10th	Night	19% 9% 3 7% 5% 5% 5% 4 5% 7% 32%	1680
	11th to 20th	Night	20% 8% 2 6% 4 4 4 4 5% 7% 36%	1680
	21st to end	Night	21% 8% 2 5% 5% 5% 4 4 5% 5% 35%	1680
July	1st to 10th	Night	17% 8% 3 7% 5% 5% 5% 4 7% 9% 32%	4680
	11th to 20th	Night	16% 8% 3 5% 3 3 4 3 5% 7% 43%	4680
	21st to end	Night	16% 5% 2 6% 4 5% 5% 4 6% 7% 40%	5084
August	1st to 10th	Night	16% 8% 2 6% 5% 4 5% 4 5% 7% 38%	2666
	11th to 20th	Night	22% 7% 3 6% 3 4 4 3 4 6% 38%	2938
	21st to end	Night	22% 7% 2 6% 4 4 4 3 4 7% 38%	3677
September	1st to 10th	Night	18% 8% 2 6% 3 4 4 3 5% 6% 43%	2000
	11th to 20th	Night	18% 6% 2 4 3 4 3 3 4 6% 47%	2049
	21st to end	Night	19% 8% 2 6% 3 3 4 3 5% 8% 41%	2200
October	1st to 10th	Night	22% 8% 3 6% 3 5% 4 3 4 6% 38%	2390
	11th to 20th	Night	25% 14% 4 7% 4 4 3 2 4 5% 29%	2416
	21st to end	Night	27% 15% 4 7% 5% 4 4 3 4 5% 24%	2860
November	1st to 10th	Night	22% 15% 5% 7% 4 4 4 4 4 6% 25%	2667
	11th to 20th	Night	18% 18% 7% 11% 6% 4 4 3 4 5% 21%	2891
	21st to end	Night	22% 21% 7% 12% 6% 4 4 3 3 3 16%	2940
December	1st to 10th	Night	17% 19% 9% 18% 8% 4 3 2 3 4 12%	4720
	11th to 20th	Night	22% 19% 6% 11% 7% 4 3 2 2 3 19%	5348
	21st to end	Night	19% 22% 5% 12% 6% 3 3 2 3 4 22%	7150

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	73% 4 7% 12% 4	4662
	11th to 20th	Day	76% 2 3 9% 8% 1	4680
	21st to end	Day	65% 6% 6% 10% 11% 1	5124
February	1st to 10th	Day	66% 4 6% 15% 7% 2	1866
	11th to 20th	Day	64% 4 9% 12% 10% 1	1904
	21st to end	Day	65% 5% 6% 13% 10% 2	1730
March	1st to 10th	Day	68% 4 5% 9% 11% 3	4579
	11th to 20th	Day	60% 4 14% 10% 11% 2	4901
	21st to end	Day	56% 4 7% 15% 17% 2	6026
April	1st to 10th	Day	60% 3 9% 15% 11% 2	2520
	11th to 20th	Day	57% 4 9% 18% 11% 2	2494
	21st to end	Day	58% 5% 7% 15% 12% 3	2703
May	1st to 10th	Day	60% 6% 8% 18% 8% 1	8249
	11th to 20th	Day	53% 7% 13% 19% 7% 1	8225
	21st to end	Day	55% 5% 9% 18% 12% 1	9061
June	1st to 10th	Day	56% 7% 10% 17% 10% 1	2940
	11th to 20th	Day	50% 7% 11% 20% 9% 2	2940
	21st to end	Day	56% 8% 10% 17% 8%	2940
July	1st to 10th	Day	48% 7% 13% 23% 10%	8210
	11th to 20th	Day	40% 6% 17% 28% 9%	8205
	21st to end	Day	42% 7% 16% 27% 7%	8795
August	1st to 10th	Day	51% 7% 16% 20% 5%	4689
	11th to 20th	Day	47% 7% 16% 24% 5%	4334
	21st to end	Day	45% 7% 14% 21% 12% 1	4420
September	1st to 10th	Day	44% 7% 15% 24% 11%	2400
	11th to 20th	Day	41% 7% 13% 29% 10%	2350
	21st to end	Day	48% 7% 11% 24% 11%	2200
October	1st to 10th	Day	53% 5% 10% 25% 7%	3268
	11th to 20th	Day	55% 6% 11% 20% 7% 1	3211
	21st to end	Day	59% 5% 18% 12% 6% 1	3180
November	1st to 10th	Day	60% 6% 11% 17% 6% 1	1851
	11th to 20th	Day	68% 5% 8% 10% 7% 1	1727
	21st to end	Day	74% 5% 8% 9% 4 1	1680
December	1st to 10th	Day	78% 4 6% 9% 3	2680
	11th to 20th	Day	73% 4 4 13% 6%	3066
	21st to end	Day	67% 5% 6% 14% 8%	4048
January	1st to 10th	Night	72% 4 8% 12% 3 1	8234
	11th to 20th	Night	78% 5% 6% 7% 4 1	8280
	21st to end	Night	68% 5% 6% 8% 11% 1	9057
February	1st to 10th	Night	65% 5% 8% 14% 6% 1	2751
	11th to 20th	Night	65% 4 8% 13% 8% 1	2612
	21st to end	Night	62% 5% 8% 15% 9% 1	2076
March	1st to 10th	Night	65% 4 9% 9% 10% 3	5494
	11th to 20th	Night	58% 6% 11% 14% 9% 3	5264
	21st to end	Night	59% 4 8% 17% 9% 3	5148
April	1st to 10th	Night	58% 5% 9% 15% 12% 2	2100
	11th to 20th	Night	50% 7% 9% 20% 13% 2	2075
	21st to end	Night	52% 6% 9% 18% 14% 2	1933
May	1st to 10th	Night	55% 7% 11% 18% 8% 1	4666
	11th to 20th	Night	51% 7% 13% 18% 9% 1	4640
	21st to end	Night	55% 5% 9% 19% 11% 1	5115
June	1st to 10th	Night	50% 8% 11% 20% 11% 1	1680
	11th to 20th	Night	46% 7% 12% 21% 11% 2	1680
	21st to end	Night	50% 7% 12% 19% 12% 1	1680
July	1st to 10th	Night	47% 7% 16% 20% 9%	4640
	11th to 20th	Night	41% 5% 17% 30% 6%	4632
	21st to end	Night	41% 8% 17% 26% 8%	4967
August	1st to 10th	Night	45% 8% 15% 25% 7%	2656
	11th to 20th	Night	46% 6% 19% 22% 7%	2962
	21st to end	Night	46% 6% 15% 22% 9% 2	3677
September	1st to 10th	Night	40% 7% 15% 25% 12% 1	2000
	11th to 20th	Night	37% 6% 16% 31% 9% 1	2049
	21st to end	Night	42% 7% 13% 27% 11%	2200
October	1st to 10th	Night	47% 5% 14% 21% 11% 1	3910
	11th to 20th	Night	54% 5% 12% 20% 8%	3927
	21st to end	Night	57% 4 15% 14% 8% 1	4610
November	1st to 10th	Night	60% 6% 12% 16% 5%	2667
	11th to 20th	Night	65% 5% 10% 12% 7% 1	2891
	21st to end	Night	72% 6% 8% 10% 4	2940
December	1st to 10th	Night	76% 5% 9% 7% 3	4720
	11th to 20th	Night	72% 4 5% 12% 8%	5348
	21st to end	Night	68% 4 4 10% 13% 1	7150

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
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	19% 26% 40% 13% 3	220
	11th to 20th	Day	31% 20% 34% 11% 4	220
	21st to end	Day	22% 24% 34% 17% 4	242
February	1st to 10th	Day	28% 33% 30% 7% 2	318
	11th to 20th	Day	28% 29% 32% 10% 1	382
	21st to end	Day	30% 26% 30% 11% 2	446
March	1st to 10th	Day	29% 23% 32% 13% 3	540
	11th to 20th	Day	31% 24% 30% 13% 2 1	540
	21st to end	Day	33% 24% 24% 12% 5% 1	594
April	1st to 10th	Day	35% 19% 27% 12% 5% 1	540
	11th to 20th	Day	38% 18% 23% 12% 8% 2	532
	21st to end	Day	33% 23% 28% 12% 4 1	540
May	1st to 10th	Day	33% 21% 28% 13% 4 1	543
	11th to 20th	Day	28% 19% 28% 17% 7% 1	567
	21st to end	Day	29% 22% 27% 15% 6% 1	617
June	1st to 10th	Day	31% 15% 33% 16% 5% 1	570
	11th to 20th	Day	25% 20% 29% 16% 8% 1	570
	21st to end	Day	28% 15% 32% 18% 6% 1	570
July	1st to 10th	Day	19% 15% 34% 23% 8% 1	565
	11th to 20th	Day	19% 16% 33% 24% 7% 1	564
	21st to end	Day	17% 15% 33% 24% 9% 2	620
August	1st to 10th	Day	20% 12% 28% 28% 10% 2	566
	11th to 20th	Day	18% 9% 31% 26% 10% 5%	559
	21st to end	Day	22% 15% 28% 18% 11% 5%	619
September	1st to 10th	Day	22% 15% 28% 19% 11% 5%	530
	11th to 20th	Day	16% 12% 25% 23% 15% 8%	530
	21st to end	Day	24% 17% 22% 21% 11% 5%	530
October	1st to 10th	Day	27% 17% 23% 20% 10% 3	530
	11th to 20th	Day	33% 22% 24% 14% 6% 1	520
	21st to end	Day	37% 18% 25% 16% 5%	462
November	1st to 10th	Day	37% 16% 25% 17% 4 1	425
	11th to 20th	Day	31% 23% 27% 13% 6%	267
	21st to end	Day	33% 28% 29% 9% 2	220
December	1st to 10th	Day	33% 19% 31% 14% 4	220
	11th to 20th	Day	32% 27% 28% 10% 2	220
	21st to end	Day	33% 21% 30% 11% 3 2	242
January	1st to 10th	Night	26% 20% 34% 16% 4	840
	11th to 20th	Night	28% 20% 27% 20% 5%	840
	21st to end	Night	18% 17% 36% 22% 7% 1	924
February	1st to 10th	Night	18% 23% 34% 19% 6% 1	840
	11th to 20th	Night	22% 23% 34% 17% 3	823
	21st to end	Night	24% 21% 29% 23% 3	692
March	1st to 10th	Night	27% 18% 32% 20% 4	840
	11th to 20th	Night	28% 21% 28% 18% 4 1	840
	21st to end	Night	25% 18% 29% 21% 6%	924
April	1st to 10th	Night	31% 16% 27% 22% 4	840
	11th to 20th	Night	28% 16% 27% 21% 7%	831
	21st to end	Night	27% 17% 28% 19% 8%	673
May	1st to 10th	Night	24% 11% 28% 24% 10% 2	420
	11th to 20th	Night	25% 10% 29% 27% 9%	414
	21st to end	Night	23% 11% 32% 26% 7%	455
June	1st to 10th	Night	22% 9% 30% 29% 9%	420
	11th to 20th	Night	22% 10% 23% 32% 13% 1	420
	21st to end	Night	24% 4 20% 37% 15% 1	420
July	1st to 10th	Night	16% 7% 24% 41% 11% 1	410
	11th to 20th	Night	16% 7% 19% 40% 17%	408
	21st to end	Night	15% 7% 23% 39% 15% 1	460
August	1st to 10th	Night	17% 3 19% 42% 18%	418
	11th to 20th	Night	18% 5% 19% 34% 23% 2	594
	21st to end	Night	20% 9% 23% 28% 17% 3	917
September	1st to 10th	Night	21% 8% 23% 31% 16% 1	800
	11th to 20th	Night	21% 7% 18% 31% 22% 2	800
	21st to end	Night	23% 11% 22% 25% 18% 2	800
October	1st to 10th	Night	26% 12% 22% 25% 14% 1	800
	11th to 20th	Night	31% 13% 25% 22% 8% 1	800
	21st to end	Night	33% 16% 24% 21% 5%	880
November	1st to 10th	Night	29% 17% 26% 20% 6% 1	820
	11th to 20th	Night	26% 20% 28% 16% 9% 1	840
	21st to end	Night	33% 22% 23% 17% 5% 1	840
December	1st to 10th	Night	30% 20% 26% 18% 6%	840
	11th to 20th	Night	30% 21% 27% 15% 5% 1	840
	21st to end	Night	34% 18% 25% 18% 5%	924

Page generated at 2026-08-27 04:07:14. Version ac07

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