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 2025-04-26.

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	19% 12% 4 10% 6% 5% 4 3 5% 6% 27%	113601
	Night	18% 14% 5% 11% 6% 4 4 3 4 5% 26%	114992
Transparency	Day	57% 6% 11% 17% 9% 1	117080
	Night	59% 6% 11% 15% 8% 1	119677
Seeing	Day	27% 19% 29% 17% 7% 2	14978
	Night	25% 15% 26% 23% 9% 1	24130

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% 19% 7% 20% 8% 7% 6% 2 3 3 12%	3597
	11th to 20th	Day	12% 16% 6% 21% 12% 4 3 2 3 4 17%	3570
	21st to end	Day	8% 15% 9% 16% 7% 5% 6% 4 5% 5% 20%	3960
February	1st to 10th	Day	11% 19% 6% 14% 10% 5% 3 2 4 5% 20%	1777
	11th to 20th	Day	12% 19% 6% 14% 6% 6% 3 3 4 4 22%	1802
	21st to end	Day	16% 20% 4 11% 7% 6% 4 3 4 4 22%	1650
March	1st to 10th	Day	18% 17% 6% 14% 6% 5% 3 2 3 4 21%	4476
	11th to 20th	Day	15% 15% 6% 11% 5% 4 4 3 4 6% 26%	4795
	21st to end	Day	18% 14% 4 9% 5% 4 3 3 4 5% 31%	5896
April	1st to 10th	Day	20% 17% 4 9% 4 3 2 3 4 5% 27%	2400
	11th to 20th	Day	23% 12% 4 7% 5% 4 3 3 4 4 31%	2374
	21st to end	Day	21% 13% 4 8% 5% 4 4 3 4 4 29%	2507
May	1st to 10th	Day	22% 11% 3 7% 5% 5% 4 4 5% 5% 28%	4426
	11th to 20th	Day	20% 8% 2 7% 5% 5% 5% 3 7% 7% 31%	4398
	21st to end	Day	21% 8% 3 7% 5% 5% 4 3 5% 6% 33%	4837
June	1st to 10th	Day	26% 9% 3 6% 5% 5% 5% 4 6% 6% 26%	2660
	11th to 20th	Day	19% 7% 3 7% 6% 5% 5% 4 5% 8% 31%	2660
	21st to end	Day	26% 8% 2 7% 6% 5% 5% 3 6% 6% 26%	2660
July	1st to 10th	Day	18% 8% 3 8% 5% 5% 5% 5% 7% 8% 29%	4440
	11th to 20th	Day	18% 8% 3 6% 4 5% 5% 5% 7% 8% 32%	4440
	21st to end	Day	15% 7% 3 6% 4 4 3 4 6% 7% 42%	4814
August	1st to 10th	Day	18% 8% 3 8% 6% 5% 6% 4 6% 8% 28%	4423
	11th to 20th	Day	19% 8% 3 6% 4 5% 5% 4 6% 7% 33%	4031
	21st to end	Day	18% 6% 2 6% 5% 5% 5% 4 6% 9% 35%	4180
September	1st to 10th	Day	20% 6% 2 6% 4 4 4 3 5% 6% 39%	2280
	11th to 20th	Day	19% 7% 2 6% 3 3 4 4 6% 6% 40%	2233
	21st to end	Day	24% 8% 2 5% 4 3 3 3 5% 6% 37%	2090
October	1st to 10th	Day	26% 10% 3 5% 4 4 4 3 4 7% 30%	1908
	11th to 20th	Day	28% 15% 3 9% 4 4 3 3 4 4 24%	1884
	21st to end	Day	27% 17% 4 6% 5% 3 4 2 4 5% 22%	1881
November	1st to 10th	Day	19% 18% 4 7% 3 3 4 3 3 6% 29%	1761
	11th to 20th	Day	21% 18% 6% 10% 6% 4 3 4 4 4 20%	1645
	21st to end	Day	21% 21% 7% 13% 6% 3 3 2 3 4 18%	1600
December	1st to 10th	Day	19% 23% 10% 13% 7% 4 3 2 3 4 11%	2600
	11th to 20th	Day	18% 21% 7% 14% 7% 4 4 3 3 3 16%	2986
	21st to end	Day	18% 18% 6% 12% 5% 5% 5% 3 4 4 21%	3960
January	1st to 10th	Night	11% 24% 10% 16% 7% 4 4 2 4 3 14%	6349
	11th to 20th	Night	10% 15% 8% 20% 14% 5% 4 3 4 3 13%	6315
	21st to end	Night	7% 14% 9% 19% 8% 8% 6% 4 4 4 17%	6996
February	1st to 10th	Night	12% 18% 6% 12% 9% 5% 5% 3 4 4 21%	2620
	11th to 20th	Night	13% 16% 8% 13% 8% 6% 4 3 4 4 21%	2483
	21st to end	Night	14% 17% 6% 11% 6% 4 5% 3 5% 5% 23%	1980
March	1st to 10th	Night	20% 16% 5% 13% 6% 4 5% 2 3 4 23%	5364
	11th to 20th	Night	14% 16% 5% 10% 5% 4 4 3 4 6% 27%	5149
	21st to end	Night	18% 14% 5% 10% 5% 5% 4 3 4 5% 26%	5036
April	1st to 10th	Night	22% 14% 4 7% 5% 4 3 3 4 6% 28%	2000
	11th to 20th	Night	21% 12% 3 6% 4 4 3 4 5% 5% 34%	1975
	21st to end	Night	21% 12% 3 8% 4 4 3 3 5% 5% 33%	1804
May	1st to 10th	Night	21% 11% 3 7% 5% 4 4 4 5% 6% 30%	2514
	11th to 20th	Night	21% 8% 3 7% 4 3 4 2 4 7% 37%	2495
	21st to end	Night	22% 8% 2 6% 5% 5% 5% 4 4 7% 32%	2738
June	1st to 10th	Night	20% 8% 3 7% 5% 5% 5% 4 6% 7% 30%	1520
	11th to 20th	Night	19% 8% 2 6% 4 4 4 4 5% 7% 37%	1520
	21st to end	Night	21% 8% 2 5% 5% 5% 4 4 5% 5% 35%	1520
July	1st to 10th	Night	17% 8% 3 8% 6% 5% 5% 3 6% 7% 33%	2520
	11th to 20th	Night	20% 7% 3 6% 3 4 4 3 6% 6% 37%	2520
	21st to end	Night	13% 4 2 5% 4 4 4 4 7% 7% 46%	2739
August	1st to 10th	Night	16% 8% 3 7% 5% 4 4 4 5% 7% 37%	2506
	11th to 20th	Night	23% 7% 3 6% 3 4 4 3 5% 6% 37%	2761
	21st to end	Night	21% 7% 2 6% 4 4 4 3 4 7% 38%	3476
September	1st to 10th	Night	19% 8% 2 5% 3 4 4 3 4 6% 43%	1900
	11th to 20th	Night	18% 7% 2 4 3 4 3 3 4 6% 46%	1946
	21st to end	Night	20% 8% 2 6% 3 2 3 2 5% 8% 40%	2090
October	1st to 10th	Night	22% 9% 3 6% 3 5% 4 3 4 5% 36%	2270
	11th to 20th	Night	26% 14% 4 7% 4 4 3 3 3 4 28%	2295
	21st to end	Night	28% 15% 3 7% 5% 4 4 3 3 5% 24%	2717
November	1st to 10th	Night	22% 15% 4 7% 5% 4 4 4 4 6% 26%	2537
	11th to 20th	Night	18% 18% 6% 10% 6% 5% 4 3 4 5% 21%	2753
	21st to end	Night	22% 20% 6% 12% 5% 4 4 3 3 4 17%	2800
December	1st to 10th	Night	17% 19% 9% 18% 8% 4 3 2 3 4 11%	4580
	11th to 20th	Night	23% 20% 6% 11% 7% 4 3 2 2 3 19%	5208
	21st to end	Night	19% 22% 5% 12% 5% 3 3 2 3 4 22%	6996

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	77% 4 6% 10% 3	3598
	11th to 20th	Day	74% 2 4 11% 8% 1	3600
	21st to end	Day	65% 6% 7% 10% 11% 1	3960
February	1st to 10th	Day	67% 4 6% 14% 7% 2	1777
	11th to 20th	Day	65% 5% 9% 11% 9% 1	1811
	21st to end	Day	65% 5% 6% 13% 9% 2	1650
March	1st to 10th	Day	68% 4 5% 9% 11% 3	4479
	11th to 20th	Day	59% 4 14% 10% 11% 2	4795
	21st to end	Day	56% 4 7% 15% 17% 2	5896
April	1st to 10th	Day	60% 3 9% 15% 11% 2	2400
	11th to 20th	Day	57% 4 9% 18% 11% 2	2374
	21st to end	Day	59% 5% 7% 14% 11% 3	2507
May	1st to 10th	Day	54% 8% 9% 20% 8% 1	4440
	11th to 20th	Day	49% 9% 16% 16% 8% 1	4402
	21st to end	Day	50% 7% 10% 18% 14% 1	4837
June	1st to 10th	Day	56% 7% 11% 15% 10% 1	2660
	11th to 20th	Day	49% 8% 11% 20% 10% 2	2660
	21st to end	Day	58% 8% 10% 16% 8%	2660
July	1st to 10th	Day	49% 8% 13% 22% 7%	4370
	11th to 20th	Day	47% 8% 18% 23% 5%	4365
	21st to end	Day	41% 7% 15% 28% 9%	4661
August	1st to 10th	Day	53% 7% 15% 20% 5%	4409
	11th to 20th	Day	48% 7% 16% 23% 5%	4073
	21st to end	Day	45% 7% 14% 20% 12% 1	4180
September	1st to 10th	Day	45% 6% 14% 23% 11%	2280
	11th to 20th	Day	42% 7% 14% 28% 9%	2233
	21st to end	Day	48% 7% 11% 24% 10%	2090
October	1st to 10th	Day	54% 5% 10% 24% 6%	3168
	11th to 20th	Day	56% 6% 11% 20% 6%	3112
	21st to end	Day	59% 5% 18% 11% 6% 1	3081
November	1st to 10th	Day	57% 6% 11% 18% 6% 1	1761
	11th to 20th	Day	68% 6% 8% 10% 7% 1	1645
	21st to end	Day	72% 5% 8% 10% 4 1	1600
December	1st to 10th	Day	79% 4 6% 9% 3	2600
	11th to 20th	Day	72% 5% 5% 13% 6%	2986
	21st to end	Day	67% 5% 6% 14% 8%	3960
January	1st to 10th	Night	74% 5% 9% 10% 2	6349
	11th to 20th	Night	73% 6% 8% 8% 4 1	6360
	21st to end	Night	69% 5% 7% 7% 11% 1	6996
February	1st to 10th	Night	65% 5% 9% 14% 6% 1	2620
	11th to 20th	Night	66% 5% 8% 13% 7% 1	2485
	21st to end	Night	62% 5% 9% 15% 9% 1	1980
March	1st to 10th	Night	66% 4 8% 9% 10% 3	5374
	11th to 20th	Night	57% 6% 11% 14% 9% 3	5150
	21st to end	Night	58% 4 8% 18% 9% 3	5036
April	1st to 10th	Night	57% 5% 9% 15% 12% 2	2000
	11th to 20th	Night	50% 7% 9% 20% 13% 2	1975
	21st to end	Night	52% 6% 10% 17% 13% 2	1804
May	1st to 10th	Night	50% 9% 14% 17% 8% 2	2520
	11th to 20th	Night	46% 8% 17% 16% 12% 2	2496
	21st to end	Night	50% 7% 10% 19% 12% 1	2739
June	1st to 10th	Night	51% 8% 12% 19% 9%	1520
	11th to 20th	Night	45% 7% 13% 21% 11% 3	1520
	21st to end	Night	51% 7% 11% 18% 12% 1	1520
July	1st to 10th	Night	50% 7% 16% 19% 8%	2480
	11th to 20th	Night	46% 7% 18% 23% 5%	2472
	21st to end	Night	35% 9% 19% 27% 11%	2651
August	1st to 10th	Night	45% 9% 14% 25% 6%	2496
	11th to 20th	Night	47% 6% 19% 22% 6%	2785
	21st to end	Night	46% 7% 15% 21% 9% 2	3476
September	1st to 10th	Night	41% 7% 14% 25% 13% 1	1900
	11th to 20th	Night	38% 6% 16% 30% 9% 1	1946
	21st to end	Night	42% 7% 13% 27% 10%	2090
October	1st to 10th	Night	48% 5% 14% 21% 11%	3790
	11th to 20th	Night	54% 5% 12% 20% 8%	3806
	21st to end	Night	57% 4 15% 13% 8% 1	4467
November	1st to 10th	Night	59% 7% 13% 16% 5% 1	2537
	11th to 20th	Night	64% 6% 10% 12% 7% 2	2753
	21st to end	Night	72% 6% 8% 10% 4	2800
December	1st to 10th	Night	77% 5% 9% 6% 2	4580
	11th to 20th	Night	72% 4 5% 12% 8%	5208
	21st to end	Night	68% 4 4 10% 13% 1	6996

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% 2	200
	11th to 20th	Day	30% 18% 35% 13% 4 1	200
	21st to end	Day	21% 24% 36% 15% 4	220
February	1st to 10th	Day	30% 35% 28% 5% 2	289
	11th to 20th	Day	29% 30% 32% 9%	349
	21st to end	Day	31% 27% 28% 12% 2	414
March	1st to 10th	Day	28% 22% 32% 14% 3	500
	11th to 20th	Day	29% 24% 30% 14% 2 1	500
	21st to end	Day	33% 24% 24% 13% 5% 1	550
April	1st to 10th	Day	34% 19% 27% 13% 6% 1	500
	11th to 20th	Day	36% 18% 23% 11% 9% 2	492
	21st to end	Day	32% 22% 29% 12% 4 1	480
May	1st to 10th	Day	32% 21% 28% 14% 5% 1	463
	11th to 20th	Day	24% 19% 30% 18% 8% 1	487
	21st to end	Day	26% 20% 29% 16% 6% 1	529
June	1st to 10th	Day	30% 16% 33% 16% 4 1	490
	11th to 20th	Day	23% 21% 29% 18% 9% 1	490
	21st to end	Day	29% 15% 31% 18% 6% 1	490
July	1st to 10th	Day	17% 14% 35% 24% 8% 1	485
	11th to 20th	Day	19% 14% 33% 26% 7% 1	484
	21st to end	Day	17% 12% 34% 26% 9% 2	532
August	1st to 10th	Day	20% 13% 28% 28% 10% 1	486
	11th to 20th	Day	19% 8% 30% 27% 11% 6%	479
	21st to end	Day	21% 15% 29% 18% 12% 6%	539
September	1st to 10th	Day	22% 15% 28% 19% 11% 6%	490
	11th to 20th	Day	18% 13% 25% 22% 15% 8%	490
	21st to end	Day	23% 18% 21% 21% 11% 6%	490
October	1st to 10th	Day	29% 18% 22% 20% 9% 3	490
	11th to 20th	Day	35% 22% 22% 14% 6% 1	481
	21st to end	Day	37% 18% 24% 15% 5%	429
November	1st to 10th	Day	36% 16% 25% 18% 4 1	395
	11th to 20th	Day	31% 24% 27% 12% 6%	245
	21st to end	Day	31% 28% 32% 9% 2	200
December	1st to 10th	Day	34% 18% 30% 15% 4 1	200
	11th to 20th	Day	33% 28% 26% 12% 2 1	200
	21st to end	Day	33% 22% 30% 10% 4 2	220
January	1st to 10th	Night	26% 21% 33% 15% 4	800
	11th to 20th	Night	27% 20% 28% 21% 5%	800
	21st to end	Night	17% 16% 37% 22% 6% 1	880
February	1st to 10th	Night	19% 24% 34% 18% 5%	800
	11th to 20th	Night	22% 23% 34% 16% 3	783
	21st to end	Night	25% 20% 29% 23% 3	660
March	1st to 10th	Night	26% 18% 31% 20% 4	800
	11th to 20th	Night	27% 21% 29% 19% 4 1	800
	21st to end	Night	25% 17% 29% 22% 7%	880
April	1st to 10th	Night	31% 16% 26% 23% 4	800
	11th to 20th	Night	28% 17% 26% 21% 7% 1	791
	21st to end	Night	27% 17% 28% 20% 8%	630
May	1st to 10th	Night	25% 10% 28% 25% 11% 2	380
	11th to 20th	Night	24% 10% 28% 28% 9%	374
	21st to end	Night	22% 10% 33% 27% 8%	411
June	1st to 10th	Night	22% 10% 29% 29% 9%	380
	11th to 20th	Night	21% 9% 23% 32% 14% 1	380
	21st to end	Night	24% 4 19% 37% 15% 1	380
July	1st to 10th	Night	16% 8% 24% 41% 12% 1	370
	11th to 20th	Night	16% 7% 19% 40% 18% 1	368
	21st to end	Night	14% 6% 24% 39% 15% 1	416
August	1st to 10th	Night	17% 3 20% 40% 19%	378
	11th to 20th	Night	18% 5% 18% 33% 23% 2	537
	21st to end	Night	19% 10% 23% 28% 17% 3	836
September	1st to 10th	Night	22% 8% 23% 30% 16% 1	760
	11th to 20th	Night	22% 7% 18% 30% 22% 2	760
	21st to end	Night	22% 11% 22% 24% 18% 2	760
October	1st to 10th	Night	26% 13% 21% 25% 13% 1	760
	11th to 20th	Night	32% 13% 24% 21% 9% 1	760
	21st to end	Night	33% 17% 23% 20% 5%	836
November	1st to 10th	Night	29% 17% 26% 20% 6% 1	780
	11th to 20th	Night	26% 20% 28% 16% 9% 1	800
	21st to end	Night	33% 22% 23% 16% 5% 1	800
December	1st to 10th	Night	31% 20% 26% 17% 6%	800
	11th to 20th	Night	31% 21% 26% 16% 5% 1	800
	21st to end	Night	34% 18% 26% 18% 5%	880

Page generated at 2025-04-23 09:25:05. Version ac07

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