Belvédère du Lac de l'Est
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Belvédère du Lac de l'Est clear sky chart from 2005-11-06 to 2026-08-15.

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	16% 12% 4 10% 6% 5% 5% 4 5% 6% 28%	144009
	Night	14% 13% 5% 11% 6% 5% 5% 4 5% 5% 27%	138005
Transparency	Day	54% 7% 12% 17% 8% 1	147457
	Night	54% 8% 12% 17% 9% 1	142647
Seeing	Day	27% 21% 31% 15% 5% 1	17992
	Night	24% 18% 30% 21% 7% 1	26082

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	11% 16% 7% 15% 9% 7% 5% 4 4 4 17%	4355
	11th to 20th	Day	8% 18% 6% 22% 11% 7% 4 3 3 3 15%	4650
	21st to end	Day	5% 7% 5% 18% 8% 7% 6% 6% 7% 6% 26%	5124
February	1st to 10th	Day	8% 15% 5% 13% 9% 8% 6% 3 4 5% 23%	1760
	11th to 20th	Day	11% 19% 6% 13% 7% 6% 4 4 4 5% 22%	1937
	21st to end	Day	11% 15% 5% 11% 7% 6% 4 4 5% 5% 27%	1730
March	1st to 10th	Day	16% 18% 6% 13% 5% 4 4 3 3 4 23%	4576
	11th to 20th	Day	13% 18% 6% 12% 5% 4 5% 4 5% 6% 22%	5014
	21st to end	Day	15% 19% 7% 11% 5% 3 3 2 4 4 25%	5718
April	1st to 10th	Day	19% 17% 5% 11% 5% 4 3 3 4 5% 24%	2520
	11th to 20th	Day	18% 15% 4 8% 5% 4 4 3 4 4 31%	2678
	21st to end	Day	21% 14% 4 7% 4 4 3 3 4 5% 30%	2730
May	1st to 10th	Day	22% 14% 4 9% 5% 5% 5% 4 4 5% 23%	7639
	11th to 20th	Day	18% 12% 4 10% 5% 5% 5% 4 5% 6% 26%	8152
	21st to end	Day	19% 12% 3 7% 5% 5% 5% 4 5% 6% 29%	9716
June	1st to 10th	Day	22% 9% 3 8% 5% 5% 5% 4 6% 7% 28%	3150
	11th to 20th	Day	22% 7% 2 7% 5% 4 4 4 7% 7% 31%	3150
	21st to end	Day	23% 10% 4 9% 6% 5% 5% 3 5% 5% 25%	3150
July	1st to 10th	Day	14% 8% 3 8% 5% 5% 5% 4 6% 9% 32%	8880
	11th to 20th	Day	14% 8% 3 7% 5% 5% 5% 4 7% 8% 34%	8425
	21st to end	Day	11% 7% 2 8% 5% 5% 6% 5% 7% 8% 36%	8993
August	1st to 10th	Day	16% 8% 3 7% 5% 5% 6% 4 6% 9% 31%	4549
	11th to 20th	Day	18% 9% 3 9% 5% 5% 6% 4 7% 7% 27%	4227
	21st to end	Day	18% 8% 3 7% 5% 4 5% 3 6% 7% 35%	4656
September	1st to 10th	Day	17% 9% 3 6% 4 4 4 3 5% 7% 40%	2357
	11th to 20th	Day	16% 7% 3 5% 3 3 3 3 5% 6% 46%	2200
	21st to end	Day	19% 9% 3 7% 3 3 4 4 4 7% 37%	2200
October	1st to 10th	Day	18% 12% 4 6% 4 4 5% 3 5% 6% 33%	2155
	11th to 20th	Day	21% 16% 4 9% 5% 4 3 3 4 5% 26%	1886
	21st to end	Day	25% 17% 4 8% 4 3 4 2 3 4 25%	1980
November	1st to 10th	Day	17% 19% 5% 10% 5% 4 4 3 4 4 26%	1851
	11th to 20th	Day	17% 17% 6% 12% 5% 4 4 2 5% 4 23%	1756
	21st to end	Day	18% 19% 6% 12% 6% 5% 5% 3 2 4 21%	1554
December	1st to 10th	Day	15% 17% 6% 16% 6% 5% 4 3 4 5% 20%	2350
	11th to 20th	Day	16% 16% 7% 12% 8% 6% 4 3 4 5% 20%	2688
	21st to end	Day	16% 15% 6% 13% 8% 5% 5% 2 4 5% 23%	3553
January	1st to 10th	Night	9% 16% 7% 16% 9% 7% 6% 4 5% 5% 16%	8554
	11th to 20th	Night	8% 19% 7% 17% 11% 8% 5% 3 4 4 13%	8235
	21st to end	Night	4 8% 6% 16% 8% 7% 7% 6% 6% 6% 27%	9057
February	1st to 10th	Night	8% 15% 5% 11% 8% 6% 5% 4 5% 6% 26%	2858
	11th to 20th	Night	9% 17% 8% 14% 6% 5% 5% 3 4 5% 23%	2568
	21st to end	Night	10% 17% 4 9% 7% 5% 4 3 5% 4 31%	2076
March	1st to 10th	Night	16% 17% 4 9% 5% 5% 5% 3 4 5% 26%	5484
	11th to 20th	Night	12% 15% 5% 12% 5% 6% 6% 4 6% 6% 22%	5165
	21st to end	Night	17% 16% 5% 9% 5% 4 3 3 4 5% 28%	5453
April	1st to 10th	Night	20% 15% 4 8% 6% 4 4 3 4 4 27%	2100
	11th to 20th	Night	19% 12% 3 8% 5% 5% 4 4 5% 5% 29%	1890
	21st to end	Night	21% 12% 3 9% 4 4 4 3 5% 4 31%	1890
May	1st to 10th	Night	23% 12% 3 7% 4 4 4 4 5% 6% 28%	5259
	11th to 20th	Night	21% 12% 4 7% 4 4 4 3 4 6% 31%	4746
	21st to end	Night	16% 9% 3 6% 3 4 5% 4 6% 7% 37%	4491
June	1st to 10th	Night	20% 9% 4 6% 6% 5% 5% 5% 6% 6% 29%	1470
	11th to 20th	Night	17% 8% 3 7% 4 3 4 4 6% 7% 35%	1470
	21st to end	Night	22% 9% 3 7% 5% 5% 5% 3 5% 7% 29%	1470
July	1st to 10th	Night	14% 8% 3 8% 4 4 5% 4 6% 8% 36%	4110
	11th to 20th	Night	17% 8% 3 7% 4 4 4 4 6% 7% 36%	4526
	21st to end	Night	11% 7% 3 7% 5% 4 5% 4 5% 7% 42%	5084
August	1st to 10th	Night	19% 7% 3 7% 5% 4 5% 4 5% 6% 34%	2786
	11th to 20th	Night	14% 8% 4 11% 6% 5% 6% 4 6% 7% 30%	2909
	21st to end	Night	17% 9% 3 7% 4 4 3 3 4 6% 40%	3239
September	1st to 10th	Night	16% 8% 2 6% 4 4 4 2 6% 6% 41%	2042
	11th to 20th	Night	16% 8% 3 7% 4 3 4 3 4 5% 44%	2200
	21st to end	Night	15% 10% 3 7% 4 3 4 3 5% 6% 42%	2200
October	1st to 10th	Night	17% 10% 3 7% 3 4 4 3 5% 5% 39%	2245
	11th to 20th	Night	21% 13% 4 8% 4 4 4 3 4 5% 31%	2510
	21st to end	Night	22% 13% 4 8% 4 4 4 3 4 6% 27%	2860
November	1st to 10th	Night	19% 15% 5% 9% 5% 4 4 3 4 6% 27%	2667
	11th to 20th	Night	17% 16% 5% 10% 5% 4 3 3 5% 6% 26%	2862
	21st to end	Night	15% 18% 7% 13% 7% 4 5% 3 5% 4 19%	3061
December	1st to 10th	Night	12% 14% 7% 18% 11% 7% 5% 3 4 4 14%	5060
	11th to 20th	Night	17% 16% 6% 13% 8% 5% 5% 3 4 4 19%	5741
	21st to end	Night	15% 17% 6% 12% 7% 6% 5% 3 4 4 22%	7667

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	65% 8% 11% 12% 4	4356
	11th to 20th	Day	71% 6% 7% 11% 4 1	4680
	21st to end	Day	53% 8% 9% 15% 14%	5124
February	1st to 10th	Day	63% 6% 8% 13% 9% 2	1760
	11th to 20th	Day	63% 6% 10% 12% 7% 1	1945
	21st to end	Day	57% 6% 9% 18% 8% 2	1730
March	1st to 10th	Day	64% 5% 8% 9% 10% 4	4579
	11th to 20th	Day	60% 7% 14% 11% 7% 1	5014
	21st to end	Day	61% 4 6% 15% 11% 3	5718
April	1st to 10th	Day	63% 5% 8% 14% 8% 2	2520
	11th to 20th	Day	56% 5% 9% 18% 10% 2	2678
	21st to end	Day	55% 5% 9% 17% 12% 2	2730
May	1st to 10th	Day	60% 7% 9% 15% 10% 1	7651
	11th to 20th	Day	55% 8% 11% 17% 7% 2	8156
	21st to end	Day	51% 8% 11% 17% 12%	9717
June	1st to 10th	Day	54% 7% 11% 19% 8% 1	3150
	11th to 20th	Day	49% 7% 14% 19% 10% 1	3150
	21st to end	Day	59% 7% 10% 15% 7% 1	3150
July	1st to 10th	Day	46% 8% 15% 21% 11%	8805
	11th to 20th	Day	43% 9% 17% 24% 6%	8347
	21st to end	Day	41% 10% 19% 24% 5%	8795
August	1st to 10th	Day	48% 10% 18% 18% 6%	4535
	11th to 20th	Day	52% 9% 17% 18% 4	4266
	21st to end	Day	46% 8% 16% 18% 11%	4656
September	1st to 10th	Day	44% 6% 15% 25% 10%	2357
	11th to 20th	Day	39% 5% 14% 28% 13%	2200
	21st to end	Day	46% 7% 13% 23% 12%	2200
October	1st to 10th	Day	54% 8% 13% 19% 5%	3506
	11th to 20th	Day	53% 5% 15% 20% 6%	3050
	21st to end	Day	51% 6% 17% 18% 8%	3180
November	1st to 10th	Day	60% 6% 12% 17% 5%	1851
	11th to 20th	Day	62% 5% 12% 14% 6%	1756
	21st to end	Day	67% 6% 12% 12% 3	1554
December	1st to 10th	Day	64% 7% 12% 9% 8%	2350
	11th to 20th	Day	64% 7% 11% 11% 8%	2688
	21st to end	Day	64% 6% 9% 12% 8% 2	3553
January	1st to 10th	Night	63% 9% 12% 12% 5%	8554
	11th to 20th	Night	68% 10% 8% 9% 5%	8280
	21st to end	Night	50% 9% 9% 16% 16% 1	9057
February	1st to 10th	Night	56% 6% 12% 16% 9% 1	2858
	11th to 20th	Night	61% 6% 9% 14% 8% 1	2571
	21st to end	Night	54% 6% 9% 17% 12% 1	2076
March	1st to 10th	Night	60% 6% 8% 13% 12% 1	5494
	11th to 20th	Night	59% 8% 13% 12% 7% 1	5166
	21st to end	Night	57% 5% 6% 18% 12% 1	5453
April	1st to 10th	Night	59% 5% 8% 15% 12% 3	2100
	11th to 20th	Night	53% 7% 10% 17% 13% 1	1890
	21st to end	Night	55% 5% 8% 18% 12% 1	1890
May	1st to 10th	Night	53% 7% 11% 18% 9% 1	5265
	11th to 20th	Night	52% 8% 12% 20% 9%	4747
	21st to end	Night	42% 9% 14% 19% 14% 2	4492
June	1st to 10th	Night	53% 7% 12% 22% 6% 1	1470
	11th to 20th	Night	44% 7% 16% 20% 10% 2	1470
	21st to end	Night	55% 6% 15% 16% 8%	1470
July	1st to 10th	Night	42% 8% 19% 22% 9%	4075
	11th to 20th	Night	43% 9% 19% 25% 4	4481
	21st to end	Night	38% 9% 23% 23% 6%	4967
August	1st to 10th	Night	48% 8% 16% 23% 5%	2776
	11th to 20th	Night	48% 11% 20% 15% 5% 1	2936
	21st to end	Night	44% 7% 16% 21% 10% 2	3239
September	1st to 10th	Night	40% 8% 15% 26% 10% 1	2042
	11th to 20th	Night	42% 7% 17% 24% 10% 1	2200
	21st to end	Night	41% 8% 12% 27% 11% 1	2200
October	1st to 10th	Night	46% 5% 13% 28% 7%	3674
	11th to 20th	Night	50% 8% 13% 23% 6%	4085
	21st to end	Night	48% 6% 19% 18% 9%	4610
November	1st to 10th	Night	56% 7% 14% 17% 6%	2667
	11th to 20th	Night	58% 6% 12% 15% 9%	2862
	21st to end	Night	65% 7% 11% 11% 5%	3061
December	1st to 10th	Night	64% 10% 13% 10% 3	5060
	11th to 20th	Night	65% 7% 9% 13% 6%	5742
	21st to end	Night	63% 6% 10% 11% 10%	7667

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	28% 29% 34% 6% 2	220
	11th to 20th	Day	31% 26% 28% 11% 3 1	220
	21st to end	Day	22% 29% 34% 10% 5% 1	242
February	1st to 10th	Day	27% 23% 31% 13% 5% 1	300
	11th to 20th	Day	25% 26% 34% 12% 2	476
	21st to end	Day	25% 26% 32% 12% 4	446
March	1st to 10th	Day	29% 25% 30% 13% 3	540
	11th to 20th	Day	30% 24% 29% 12% 5% 1	540
	21st to end	Day	33% 25% 24% 14% 4 1	594
April	1st to 10th	Day	35% 24% 27% 10% 3 1	540
	11th to 20th	Day	33% 21% 30% 12% 3 1	532
	21st to end	Day	32% 20% 34% 10% 2 1	540
May	1st to 10th	Day	31% 17% 34% 13% 5%	543
	11th to 20th	Day	27% 22% 29% 16% 5% 1	567
	21st to end	Day	28% 23% 27% 17% 5%	845
June	1st to 10th	Day	27% 18% 30% 17% 6% 1	780
	11th to 20th	Day	26% 20% 28% 19% 7% 1	780
	21st to end	Day	28% 17% 30% 19% 6%	780
July	1st to 10th	Day	21% 18% 34% 20% 7% 1	770
	11th to 20th	Day	19% 19% 38% 17% 6% 1	615
	21st to end	Day	18% 15% 41% 20% 5% 1	620
August	1st to 10th	Day	20% 13% 38% 21% 6% 2	566
	11th to 20th	Day	19% 13% 31% 27% 9% 1	535
	21st to end	Day	23% 18% 28% 19% 10% 2	583
September	1st to 10th	Day	22% 21% 28% 18% 8% 2	530
	11th to 20th	Day	20% 15% 31% 21% 9% 3	530
	21st to end	Day	22% 18% 32% 15% 8% 5%	530
October	1st to 10th	Day	22% 21% 31% 15% 8% 3	505
	11th to 20th	Day	32% 20% 25% 13% 8% 1	420
	21st to end	Day	38% 19% 26% 12% 4	462
November	1st to 10th	Day	34% 22% 28% 13% 2	425
	11th to 20th	Day	29% 23% 27% 15% 6% 1	430
	21st to end	Day	33% 29% 27% 9% 3	304
December	1st to 10th	Day	35% 20% 30% 13% 2	220
	11th to 20th	Day	34% 27% 30% 5% 3	220
	21st to end	Day	31% 29% 23% 12% 4	242
January	1st to 10th	Night	24% 23% 36% 14% 3	900
	11th to 20th	Night	23% 24% 31% 16% 5%	840
	21st to end	Night	16% 22% 35% 22% 5% 1	924
February	1st to 10th	Night	17% 26% 33% 17% 6%	840
	11th to 20th	Night	21% 26% 34% 15% 5%	823
	21st to end	Night	23% 20% 37% 17% 4	692
March	1st to 10th	Night	25% 20% 33% 19% 2	840
	11th to 20th	Night	26% 22% 29% 17% 5% 1	840
	21st to end	Night	25% 22% 28% 19% 6%	924
April	1st to 10th	Night	33% 18% 27% 18% 4	840
	11th to 20th	Night	27% 19% 27% 20% 6%	646
	21st to end	Night	31% 16% 25% 20% 7%	630
May	1st to 10th	Night	27% 14% 29% 25% 5%	630
	11th to 20th	Night	23% 14% 29% 24% 9% 1	461
	21st to end	Night	25% 15% 30% 22% 7%	455
June	1st to 10th	Night	23% 9% 30% 30% 8%	420
	11th to 20th	Night	19% 11% 28% 33% 10%	420
	21st to end	Night	24% 10% 30% 26% 10% 1	420
July	1st to 10th	Night	18% 12% 33% 28% 9%	410
	11th to 20th	Night	17% 9% 34% 30% 8%	408
	21st to end	Night	15% 6% 31% 37% 10% 1	460
August	1st to 10th	Night	17% 7% 32% 30% 13% 1	486
	11th to 20th	Night	17% 8% 32% 32% 11% 1	605
	21st to end	Night	17% 12% 29% 30% 12% 1	663
September	1st to 10th	Night	19% 13% 31% 26% 10% 1	800
	11th to 20th	Night	20% 12% 28% 25% 13% 2	800
	21st to end	Night	20% 14% 29% 24% 13% 1	800
October	1st to 10th	Night	23% 17% 29% 23% 7% 1	800
	11th to 20th	Night	26% 18% 31% 17% 8% 1	800
	21st to end	Night	29% 20% 29% 17% 5%	880
November	1st to 10th	Night	31% 20% 28% 16% 5%	820
	11th to 20th	Night	27% 22% 27% 18% 6% 1	910
	21st to end	Night	28% 23% 29% 15% 4 1	950
December	1st to 10th	Night	29% 20% 30% 15% 5% 1	950
	11th to 20th	Night	27% 24% 29% 16% 4	950
	21st to end	Night	28% 26% 26% 16% 5%	1045

Page generated at 2026-08-12 03:37:15. Version ac07

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