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 2025-04-11.

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% 13% 4 10% 6% 5% 5% 4 5% 6% 27%	112868
	Night	15% 13% 5% 11% 6% 5% 5% 4 5% 5% 27%	115476
Transparency	Day	55% 7% 12% 16% 8% 1	116362
	Night	55% 7% 13% 16% 8% 1	120147
Seeing	Day	27% 20% 30% 16% 6% 1	16125
	Night	24% 18% 30% 21% 7% 1	24508

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% 18% 8% 17% 10% 7% 5% 3 4 4 13%	3354
	11th to 20th	Day	8% 16% 6% 22% 11% 6% 4 3 3 3 16%	3570
	21st to end	Day	6% 7% 4 19% 7% 5% 6% 5% 6% 5% 27%	3960
February	1st to 10th	Day	9% 16% 5% 13% 9% 8% 6% 4 5% 5% 21%	1676
	11th to 20th	Day	11% 20% 6% 12% 7% 6% 4 4 4 5% 21%	1842
	21st to end	Day	11% 15% 4 11% 7% 6% 4 4 4 5% 27%	1650
March	1st to 10th	Day	16% 19% 6% 13% 5% 4 4 3 3 4 23%	4476
	11th to 20th	Day	13% 17% 6% 12% 5% 5% 5% 4 5% 6% 22%	4906
	21st to end	Day	15% 19% 7% 11% 5% 3 3 3 4 4 25%	5594
April	1st to 10th	Day	19% 18% 4 10% 6% 4 3 3 4 5% 24%	2400
	11th to 20th	Day	18% 15% 4 7% 5% 4 4 3 4 4 32%	2420
	21st to end	Day	22% 14% 4 7% 4 4 3 3 4 5% 30%	2470
May	1st to 10th	Day	17% 12% 4 9% 6% 5% 5% 4 4 6% 28%	4106
	11th to 20th	Day	18% 12% 3 8% 5% 5% 5% 4 6% 7% 27%	4356
	21st to end	Day	18% 10% 3 7% 5% 6% 6% 4 6% 7% 29%	5185
June	1st to 10th	Day	23% 8% 3 8% 5% 5% 5% 4 6% 7% 27%	2850
	11th to 20th	Day	22% 7% 2 7% 5% 4 4 4 6% 7% 32%	2850
	21st to end	Day	24% 11% 4 8% 6% 4 4 3 5% 5% 26%	2850
July	1st to 10th	Day	16% 8% 3 9% 5% 5% 6% 5% 6% 8% 29%	4760
	11th to 20th	Day	16% 7% 2 7% 5% 5% 5% 5% 7% 8% 33%	4515
	21st to end	Day	14% 6% 2 7% 4 5% 5% 5% 6% 7% 39%	4814
August	1st to 10th	Day	17% 8% 3 7% 5% 5% 6% 4 7% 9% 29%	4278
	11th to 20th	Day	18% 9% 3 9% 5% 5% 6% 4 7% 7% 27%	4045
	21st to end	Day	18% 8% 3 7% 5% 4 4 3 6% 7% 35%	4514
September	1st to 10th	Day	17% 9% 2 6% 4 4 4 3 5% 7% 40%	2239
	11th to 20th	Day	17% 8% 3 5% 3 3 3 3 5% 5% 45%	2090
	21st to end	Day	20% 10% 3 7% 3 3 4 4 4 7% 36%	2090
October	1st to 10th	Day	19% 13% 4 6% 4 4 4 3 5% 6% 32%	2047
	11th to 20th	Day	22% 16% 4 9% 5% 4 3 3 4 4 25%	1792
	21st to end	Day	25% 17% 4 8% 4 4 4 2 3 4 25%	1881
November	1st to 10th	Day	17% 18% 4 10% 5% 4 4 2 3 4 27%	1761
	11th to 20th	Day	18% 17% 5% 11% 5% 4 4 2 5% 4 23%	1673
	21st to end	Day	18% 20% 5% 11% 6% 5% 5% 3 2 4 21%	1480
December	1st to 10th	Day	16% 17% 6% 16% 6% 5% 4 3 4 5% 19%	2280
	11th to 20th	Day	16% 16% 7% 11% 8% 6% 5% 3 4 5% 21%	2618
	21st to end	Day	16% 15% 6% 12% 8% 5% 5% 2 4 5% 23%	3476
January	1st to 10th	Night	10% 17% 8% 17% 10% 7% 6% 4 5% 4 13%	6601
	11th to 20th	Night	8% 18% 7% 17% 12% 9% 5% 3 4 4 13%	6315
	21st to end	Night	5% 10% 6% 13% 8% 6% 6% 6% 6% 6% 29%	6996
February	1st to 10th	Night	8% 15% 5% 11% 8% 6% 6% 4 5% 6% 25%	2722
	11th to 20th	Night	9% 18% 8% 14% 7% 6% 5% 3 4 5% 22%	2443
	21st to end	Night	10% 17% 5% 9% 7% 5% 4 3 5% 4 31%	1980
March	1st to 10th	Night	17% 17% 4 9% 5% 5% 5% 3 4 5% 25%	5364
	11th to 20th	Night	12% 16% 5% 11% 6% 6% 6% 4 6% 6% 22%	5053
	21st to end	Night	18% 16% 5% 9% 5% 4 3 3 4 5% 29%	5335
April	1st to 10th	Night	20% 15% 4 8% 6% 4 4 4 4 4 28%	2000
	11th to 20th	Night	19% 12% 3 7% 5% 5% 4 3 6% 5% 30%	1715
	21st to end	Night	22% 12% 3 9% 5% 4 4 3 5% 4 31%	1710
May	1st to 10th	Night	20% 9% 3 6% 4 4 4 4 6% 6% 33%	2834
	11th to 20th	Night	18% 11% 4 8% 5% 4 4 3 4 6% 31%	2548
	21st to end	Night	17% 7% 2 6% 4 4 5% 4 7% 9% 36%	2401
June	1st to 10th	Night	21% 9% 4 7% 5% 5% 5% 5% 6% 5% 28%	1330
	11th to 20th	Night	17% 7% 3 7% 4 3 5% 4 6% 7% 37%	1330
	21st to end	Night	23% 9% 3 7% 5% 4 5% 3 5% 7% 29%	1330
July	1st to 10th	Night	13% 7% 3 8% 5% 5% 6% 5% 7% 8% 33%	2210
	11th to 20th	Night	18% 8% 3 7% 5% 5% 5% 4 5% 7% 33%	2444
	21st to end	Night	12% 7% 2 5% 4 4 4 4 5% 8% 45%	2739
August	1st to 10th	Night	20% 8% 3 7% 5% 4 5% 4 5% 7% 33%	2620
	11th to 20th	Night	15% 8% 4 11% 6% 5% 6% 4 6% 7% 29%	2782
	21st to end	Night	17% 9% 3 6% 4 4 3 3 4 6% 41%	3140
September	1st to 10th	Night	17% 8% 3 5% 4 4 4 2 6% 6% 40%	1940
	11th to 20th	Night	17% 8% 3 7% 4 3 4 3 4 5% 43%	2090
	21st to end	Night	15% 10% 3 6% 4 3 4 3 5% 6% 41%	2090
October	1st to 10th	Night	18% 10% 3 7% 3 4 4 3 5% 5% 38%	2133
	11th to 20th	Night	22% 13% 4 8% 5% 4 4 2 4 5% 30%	2384
	21st to end	Night	22% 13% 4 8% 4 4 4 3 4 6% 27%	2717
November	1st to 10th	Night	18% 14% 5% 8% 5% 4 4 3 4 6% 28%	2537
	11th to 20th	Night	17% 16% 5% 10% 5% 4 4 3 5% 6% 26%	2725
	21st to end	Night	16% 18% 6% 13% 7% 5% 5% 3 5% 4 20%	2915
December	1st to 10th	Night	13% 14% 7% 18% 11% 7% 5% 3 4 4 14%	4910
	11th to 20th	Night	18% 16% 6% 13% 8% 5% 5% 3 4 4 19%	5591
	21st to end	Night	15% 17% 6% 12% 7% 6% 5% 3 4 4 23%	7502

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	71% 8% 11% 8% 2	3355
	11th to 20th	Day	69% 7% 8% 12% 4 1	3600
	21st to end	Day	54% 8% 9% 13% 17%	3960
February	1st to 10th	Day	64% 6% 8% 11% 9% 2	1676
	11th to 20th	Day	64% 7% 10% 11% 7% 1	1850
	21st to end	Day	57% 6% 9% 18% 8% 2	1650
March	1st to 10th	Day	65% 5% 8% 9% 10% 4	4479
	11th to 20th	Day	60% 7% 14% 11% 7% 1	4906
	21st to end	Day	61% 4 6% 15% 11% 3	5594
April	1st to 10th	Day	62% 5% 8% 14% 9% 3	2400
	11th to 20th	Day	55% 5% 9% 18% 11% 2	2420
	21st to end	Day	56% 5% 8% 16% 13% 2	2470
May	1st to 10th	Day	54% 8% 11% 17% 10% 1	4120
	11th to 20th	Day	53% 8% 14% 17% 8%	4360
	21st to end	Day	50% 9% 12% 19% 11%	5185
June	1st to 10th	Day	54% 8% 11% 18% 8% 1	2850
	11th to 20th	Day	49% 7% 15% 18% 10% 1	2850
	21st to end	Day	60% 7% 10% 15% 7% 1	2850
July	1st to 10th	Day	50% 8% 15% 20% 8%	4685
	11th to 20th	Day	45% 9% 19% 22% 4	4437
	21st to end	Day	42% 9% 16% 24% 8%	4661
August	1st to 10th	Day	49% 10% 18% 18% 6%	4264
	11th to 20th	Day	53% 9% 17% 17% 4	4084
	21st to end	Day	46% 8% 16% 18% 11%	4514
September	1st to 10th	Day	44% 5% 14% 25% 11%	2239
	11th to 20th	Day	40% 5% 14% 27% 13%	2090
	21st to end	Day	47% 7% 13% 22% 11%	2090
October	1st to 10th	Day	55% 8% 13% 19% 5%	3398
	11th to 20th	Day	54% 6% 15% 20% 5%	2956
	21st to end	Day	51% 6% 17% 17% 8%	3081
November	1st to 10th	Day	60% 6% 12% 17% 5%	1761
	11th to 20th	Day	63% 5% 12% 14% 6%	1673
	21st to end	Day	67% 7% 12% 13% 2	1480
December	1st to 10th	Day	65% 7% 12% 8% 8%	2280
	11th to 20th	Day	63% 7% 11% 11% 8%	2618
	21st to end	Day	64% 6% 9% 12% 8% 2	3476
January	1st to 10th	Night	66% 9% 12% 10% 3	6601
	11th to 20th	Night	67% 10% 9% 9% 4	6360
	21st to end	Night	48% 8% 10% 16% 17% 1	6996
February	1st to 10th	Night	57% 6% 11% 14% 10% 1	2722
	11th to 20th	Night	62% 7% 10% 13% 8% 1	2446
	21st to end	Night	55% 6% 9% 16% 12% 1	1980
March	1st to 10th	Night	60% 5% 8% 13% 12% 1	5374
	11th to 20th	Night	58% 8% 13% 12% 7% 1	5054
	21st to end	Night	57% 5% 6% 18% 12% 1	5335
April	1st to 10th	Night	58% 5% 7% 15% 12% 3	2000
	11th to 20th	Night	52% 6% 10% 17% 14% 1	1715
	21st to end	Night	56% 5% 8% 17% 13% 1	1710
May	1st to 10th	Night	48% 8% 14% 20% 8% 3	2840
	11th to 20th	Night	51% 9% 13% 18% 9% 1	2549
	21st to end	Night	41% 9% 15% 22% 12% 1	2402
June	1st to 10th	Night	54% 8% 12% 22% 5% 1	1330
	11th to 20th	Night	42% 7% 16% 21% 11% 2	1330
	21st to end	Night	55% 6% 15% 15% 9%	1330
July	1st to 10th	Night	42% 9% 21% 23% 4	2175
	11th to 20th	Night	47% 8% 20% 20% 3 1	2399
	21st to end	Night	36% 10% 25% 21% 8%	2651
August	1st to 10th	Night	49% 8% 16% 23% 4	2610
	11th to 20th	Night	50% 11% 20% 14% 5%	2809
	21st to end	Night	44% 7% 16% 21% 10% 2	3140
September	1st to 10th	Night	41% 8% 15% 24% 10% 1	1940
	11th to 20th	Night	43% 7% 17% 22% 10% 1	2090
	21st to end	Night	42% 8% 12% 27% 11% 1	2090
October	1st to 10th	Night	47% 6% 13% 27% 6%	3562
	11th to 20th	Night	51% 8% 13% 22% 6%	3959
	21st to end	Night	48% 6% 19% 18% 9%	4467
November	1st to 10th	Night	56% 7% 14% 17% 6%	2537
	11th to 20th	Night	57% 6% 12% 15% 9% 1	2725
	21st to end	Night	65% 7% 11% 11% 5%	2915
December	1st to 10th	Night	65% 10% 13% 10% 3	4910
	11th to 20th	Night	65% 7% 9% 13% 7%	5592
	21st to end	Night	63% 6% 10% 11% 10%	7502

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	29% 30% 34% 6% 2 1	200
	11th to 20th	Day	30% 26% 29% 12% 3 1	200
	21st to end	Day	22% 28% 35% 10% 5% 1	220
February	1st to 10th	Day	29% 24% 31% 12% 4	276
	11th to 20th	Day	27% 26% 34% 12% 2	441
	21st to end	Day	25% 26% 32% 12% 4	414
March	1st to 10th	Day	29% 23% 31% 13% 3	500
	11th to 20th	Day	28% 23% 29% 12% 6% 1	500
	21st to end	Day	33% 24% 25% 14% 5% 1	550
April	1st to 10th	Day	35% 23% 27% 11% 3 1	500
	11th to 20th	Day	31% 20% 30% 14% 3 1	452
	21st to end	Day	31% 21% 34% 10% 2 1	460
May	1st to 10th	Day	29% 16% 35% 14% 6%	463
	11th to 20th	Day	26% 21% 30% 17% 6% 1	487
	21st to end	Day	27% 23% 27% 17% 5%	735
June	1st to 10th	Day	28% 19% 29% 17% 6% 1	680
	11th to 20th	Day	25% 19% 27% 20% 8% 1	680
	21st to end	Day	28% 17% 30% 20% 6%	680
July	1st to 10th	Day	21% 16% 35% 21% 7% 1	670
	11th to 20th	Day	19% 17% 39% 18% 7% 1	530
	21st to end	Day	18% 14% 42% 21% 5% 1	532
August	1st to 10th	Day	22% 14% 36% 20% 6% 1	486
	11th to 20th	Day	20% 14% 30% 27% 8% 1	479
	21st to end	Day	22% 18% 27% 20% 10% 2	539
September	1st to 10th	Day	21% 21% 29% 18% 8% 2	490
	11th to 20th	Day	21% 15% 32% 21% 9% 2	490
	21st to end	Day	22% 18% 32% 16% 8% 5%	490
October	1st to 10th	Day	22% 21% 30% 16% 8% 4	467
	11th to 20th	Day	33% 21% 24% 13% 7% 2	390
	21st to end	Day	38% 19% 26% 12% 4	429
November	1st to 10th	Day	33% 21% 28% 14% 2 1	395
	11th to 20th	Day	29% 23% 27% 15% 6% 1	400
	21st to end	Day	33% 28% 27% 9% 3	280
December	1st to 10th	Day	36% 19% 29% 14% 3 1	200
	11th to 20th	Day	34% 25% 32% 6% 3 1	200
	21st to end	Day	32% 29% 22% 12% 4	220
January	1st to 10th	Night	25% 23% 36% 14% 2	855
	11th to 20th	Night	23% 24% 31% 16% 6%	800
	21st to end	Night	16% 21% 35% 22% 5% 1	880
February	1st to 10th	Night	18% 27% 34% 17% 4	800
	11th to 20th	Night	21% 26% 34% 14% 4	783
	21st to end	Night	23% 19% 36% 17% 4	660
March	1st to 10th	Night	23% 20% 34% 20% 3	800
	11th to 20th	Night	25% 22% 30% 17% 6% 1	800
	21st to end	Night	25% 21% 27% 20% 6%	880
April	1st to 10th	Night	32% 19% 27% 18% 4	800
	11th to 20th	Night	26% 19% 28% 20% 7%	587
	21st to end	Night	32% 16% 25% 19% 7% 1	570
May	1st to 10th	Night	26% 13% 29% 26% 5% 1	570
	11th to 20th	Night	23% 12% 29% 25% 9% 1	417
	21st to end	Night	26% 15% 30% 22% 7%	411
June	1st to 10th	Night	24% 9% 30% 29% 8%	380
	11th to 20th	Night	18% 11% 28% 33% 10%	380
	21st to end	Night	24% 9% 30% 27% 9% 1	380
July	1st to 10th	Night	18% 12% 33% 28% 9% 1	370
	11th to 20th	Night	17% 8% 34% 31% 9% 1	368
	21st to end	Night	15% 5% 31% 38% 10% 1	416
August	1st to 10th	Night	17% 7% 33% 30% 12% 1	440
	11th to 20th	Night	18% 8% 31% 32% 11% 1	562
	21st to end	Night	17% 11% 29% 30% 12% 1	630
September	1st to 10th	Night	19% 13% 32% 25% 10% 1	760
	11th to 20th	Night	21% 12% 29% 24% 12% 2	760
	21st to end	Night	20% 14% 29% 23% 13% 1	760
October	1st to 10th	Night	23% 17% 28% 23% 8% 1	760
	11th to 20th	Night	27% 18% 30% 17% 8% 1	760
	21st to end	Night	29% 20% 29% 17% 4	836
November	1st to 10th	Night	30% 19% 28% 17% 5%	780
	11th to 20th	Night	27% 22% 26% 18% 5% 1	863
	21st to end	Night	28% 22% 30% 15% 3 1	900
December	1st to 10th	Night	30% 20% 30% 15% 5% 1	900
	11th to 20th	Night	27% 23% 29% 16% 4	900
	21st to end	Night	28% 25% 25% 16% 6%	990

Page generated at 2025-04-08 09:17:25. Version ac07

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