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 2024-03-01.

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 8% 7% 4 5% 4 5% 6% 28%	78022
	Night	16% 12% 5% 9% 7% 4 5% 5% 5% 5% 27%	81390
Transparency	Day	56% 6% 11% 17% 8% 1	77718
	Night	56% 7% 12% 16% 8% 1	81229
Seeing	Day	27% 20% 31% 16% 6% 1	14653
	Night	24% 18% 30% 21% 7% 1	23058

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% 15% 8% 11% 10% 6% 5% 6% 5% 5% 17%	2339
	11th to 20th	Day	11% 15% 5% 16% 10% 5% 5% 4 4 4 22%	2520
	21st to end	Day	9% 9% 4 15% 10% 4 6% 6% 6% 5% 27%	2772
February	1st to 10th	Day	9% 15% 6% 11% 9% 6% 6% 5% 4 5% 21%	1592
	11th to 20th	Day	12% 19% 7% 11% 8% 4 5% 5% 4 5% 21%	1747
	21st to end	Day	12% 14% 5% 9% 9% 4 6% 5% 4 5% 26%	1570
March	1st to 10th	Day	14% 14% 6% 11% 6% 4 5% 6% 5% 5% 24%	1797
	11th to 20th	Day	15% 15% 6% 10% 7% 3 5% 6% 4 4 25%	1948
	21st to end	Day	15% 16% 5% 10% 7% 3 4 4 5% 5% 27%	2224
April	1st to 10th	Day	20% 16% 6% 9% 7% 3 4 4 4 5% 22%	2160
	11th to 20th	Day	18% 15% 4 6% 6% 3 4 4 4 4 33%	2291
	21st to end	Day	23% 14% 4 6% 5% 3 4 4 4 5% 29%	2340
May	1st to 10th	Day	22% 12% 4 6% 5% 2 4 5% 4 5% 31%	2340
	11th to 20th	Day	20% 12% 4 6% 5% 3 4 4 5% 5% 32%	2450
	21st to end	Day	22% 9% 4 6% 5% 3 5% 5% 5% 6% 30%	2919
June	1st to 10th	Day	23% 8% 3 7% 6% 4 5% 5% 5% 7% 26%	2700
	11th to 20th	Day	23% 7% 2 6% 6% 3 4 4 6% 7% 32%	2700
	21st to end	Day	24% 10% 4 8% 6% 3 5% 4 5% 6% 26%	2700
July	1st to 10th	Day	19% 8% 3 7% 6% 4 5% 5% 6% 9% 29%	2700
	11th to 20th	Day	17% 7% 3 6% 5% 4 6% 5% 7% 9% 31%	2567
	21st to end	Day	18% 8% 3 7% 5% 4 5% 7% 6% 7% 31%	2744
August	1st to 10th	Day	19% 9% 4 7% 6% 4 5% 5% 6% 8% 26%	2430
	11th to 20th	Day	17% 9% 3 7% 6% 4 5% 5% 6% 6% 33%	2304
	21st to end	Day	17% 8% 3 6% 6% 3 4 4 6% 8% 35%	2570
September	1st to 10th	Day	18% 8% 3 5% 5% 3 4 4 5% 7% 39%	2122
	11th to 20th	Day	18% 8% 3 4 4 3 3 3 5% 5% 44%	1980
	21st to end	Day	20% 9% 3 6% 4 2 4 4 4 6% 37%	1980
October	1st to 10th	Day	20% 12% 4 6% 4 3 5% 4 5% 6% 33%	1940
	11th to 20th	Day	23% 15% 4 8% 6% 3 4 4 4 4 25%	1698
	21st to end	Day	27% 17% 4 7% 6% 3 4 3 3 4 23%	1782
November	1st to 10th	Day	18% 16% 6% 8% 7% 3 4 3 3 5% 28%	1671
	11th to 20th	Day	19% 15% 6% 11% 7% 3 4 3 5% 5% 24%	1590
	21st to end	Day	18% 18% 5% 10% 8% 4 5% 5% 2 4 22%	1406
December	1st to 10th	Day	21% 19% 8% 12% 7% 3 4 3 4 3 17%	1330
	11th to 20th	Day	18% 16% 6% 11% 7% 4 4 4 3 4 22%	1668
	21st to end	Day	20% 12% 6% 12% 10% 5% 5% 2 3 4 22%	2431
January	1st to 10th	Night	11% 14% 7% 13% 11% 6% 7% 5% 5% 5% 16%	4611
	11th to 20th	Night	10% 16% 7% 12% 13% 6% 6% 5% 5% 4 18%	4440
	21st to end	Night	7% 11% 7% 12% 9% 5% 6% 6% 5% 6% 26%	4884
February	1st to 10th	Night	9% 15% 5% 10% 9% 4 6% 6% 5% 6% 25%	2586
	11th to 20th	Night	10% 17% 8% 14% 8% 4 5% 4 4 5% 22%	2318
	21st to end	Night	11% 15% 5% 8% 8% 5% 4 4 5% 5% 30%	1884
March	1st to 10th	Night	13% 12% 6% 8% 7% 4 5% 5% 4 7% 28%	2157
	11th to 20th	Night	14% 14% 6% 9% 6% 4 5% 4 5% 5% 29%	2011
	21st to end	Night	14% 15% 5% 9% 7% 4 5% 4 5% 5% 29%	2129
April	1st to 10th	Night	21% 15% 5% 6% 7% 3 4 4 4 4 26%	1800
	11th to 20th	Night	19% 11% 3 6% 6% 4 5% 4 5% 6% 31%	1617
	21st to end	Night	23% 11% 4 7% 5% 3 4 3 5% 4 30%	1620
May	1st to 10th	Night	22% 10% 5% 7% 4 3 5% 4 5% 4 31%	1620
	11th to 20th	Night	22% 8% 4 5% 5% 3 4 4 4 6% 36%	1453
	21st to end	Night	21% 9% 3 6% 5% 3 5% 4 5% 5% 34%	1356
June	1st to 10th	Night	21% 9% 4 7% 6% 3 6% 5% 5% 5% 28%	1260
	11th to 20th	Night	17% 7% 3 6% 5% 2 5% 5% 6% 7% 37%	1260
	21st to end	Night	22% 8% 3 6% 6% 4 5% 4 5% 7% 30%	1260
July	1st to 10th	Night	18% 7% 3 6% 5% 3 5% 6% 7% 8% 34%	1260
	11th to 20th	Night	17% 6% 2 5% 5% 4 6% 6% 7% 8% 34%	1390
	21st to end	Night	15% 7% 3 5% 5% 3 6% 7% 6% 7% 36%	1574
August	1st to 10th	Night	15% 6% 2 5% 6% 3 5% 6% 6% 9% 38%	1490
	11th to 20th	Night	16% 7% 4 7% 6% 4 6% 5% 6% 8% 32%	1596
	21st to end	Night	15% 6% 3 5% 6% 4 4 4 5% 8% 39%	1784
September	1st to 10th	Night	17% 7% 3 5% 5% 3 5% 4 6% 6% 40%	1837
	11th to 20th	Night	18% 8% 3 6% 5% 2 4 5% 4 4 42%	1980
	21st to end	Night	15% 9% 3 5% 4 2 4 4 5% 6% 42%	1980
October	1st to 10th	Night	18% 9% 3 6% 4 3 4 4 5% 5% 38%	2020
	11th to 20th	Night	22% 13% 4 6% 7% 3 4 4 4 5% 29%	2258
	21st to end	Night	23% 13% 5% 7% 5% 3 4 5% 4 6% 27%	2574
November	1st to 10th	Night	19% 13% 5% 8% 6% 3 5% 4 4 6% 27%	2407
	11th to 20th	Night	18% 14% 6% 8% 6% 3 4 4 5% 6% 26%	2588
	21st to end	Night	16% 15% 7% 11% 9% 4 5% 4 5% 4 21%	2769
December	1st to 10th	Night	19% 18% 8% 11% 8% 5% 4 4 4 4 16%	2850
	11th to 20th	Night	20% 14% 6% 10% 8% 4 5% 5% 5% 5% 19%	3531
	21st to end	Night	18% 18% 6% 10% 9% 4 5% 4 4 4 19%	5236

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	63% 9% 14% 11% 3	2340
	11th to 20th	Day	63% 7% 8% 16% 5% 1	2520
	21st to end	Day	55% 9% 10% 13% 12%	2772
February	1st to 10th	Day	65% 6% 8% 11% 8% 2	1592
	11th to 20th	Day	64% 6% 10% 11% 7% 1	1755
	21st to end	Day	58% 6% 10% 17% 8% 2	1570
March	1st to 10th	Day	61% 6% 9% 12% 10% 2	1800
	11th to 20th	Day	60% 6% 10% 12% 10% 1	1948
	21st to end	Day	59% 5% 9% 16% 9% 2	2224
April	1st to 10th	Day	64% 5% 9% 13% 8% 2	2160
	11th to 20th	Day	55% 5% 9% 18% 11% 2	2291
	21st to end	Day	57% 5% 8% 16% 13% 2	2340
May	1st to 10th	Day	54% 6% 9% 16% 13% 2	2340
	11th to 20th	Day	54% 5% 9% 19% 12%	2454
	21st to end	Day	53% 7% 10% 19% 9%	2919
June	1st to 10th	Day	55% 8% 11% 17% 8% 1	2700
	11th to 20th	Day	50% 7% 14% 19% 10% 1	2700
	21st to end	Day	60% 7% 10% 15% 7% 1	2700
July	1st to 10th	Day	50% 8% 16% 20% 6%	2625
	11th to 20th	Day	48% 8% 15% 21% 8%	2489
	21st to end	Day	52% 9% 14% 18% 6% 1	2591
August	1st to 10th	Day	54% 9% 16% 17% 4	2416
	11th to 20th	Day	50% 8% 16% 20% 7%	2304
	21st to end	Day	46% 7% 15% 24% 8%	2570
September	1st to 10th	Day	45% 5% 14% 25% 10% 1	2122
	11th to 20th	Day	42% 5% 14% 25% 13%	1980
	21st to end	Day	47% 6% 13% 21% 12%	1980
October	1st to 10th	Day	51% 5% 12% 22% 9%	1940
	11th to 20th	Day	62% 6% 13% 15% 4	1698
	21st to end	Day	65% 5% 10% 13% 6% 1	1782
November	1st to 10th	Day	60% 6% 12% 18% 6%	1671
	11th to 20th	Day	62% 5% 12% 14% 6%	1590
	21st to end	Day	65% 7% 12% 13% 2	1406
December	1st to 10th	Day	72% 4 9% 10% 4	1330
	11th to 20th	Day	66% 5% 8% 11% 10%	1668
	21st to end	Day	66% 6% 10% 13% 4 1	2431
January	1st to 10th	Night	65% 8% 12% 10% 4	4611
	11th to 20th	Night	63% 9% 10% 12% 5% 1	4440
	21st to end	Night	53% 9% 10% 14% 13% 1	4884
February	1st to 10th	Night	58% 6% 11% 14% 9% 1	2586
	11th to 20th	Night	63% 7% 9% 13% 8% 1	2321
	21st to end	Night	55% 6% 9% 16% 12% 1	1884
March	1st to 10th	Night	56% 5% 11% 18% 9% 1	2167
	11th to 20th	Night	55% 6% 11% 16% 11% 1	2012
	21st to end	Night	56% 5% 10% 17% 9% 2	2129
April	1st to 10th	Night	60% 5% 8% 14% 11% 3	1800
	11th to 20th	Night	51% 6% 10% 17% 14% 1	1617
	21st to end	Night	57% 5% 8% 17% 12% 2	1620
May	1st to 10th	Night	54% 6% 10% 16% 11% 2	1620
	11th to 20th	Night	50% 6% 11% 20% 12% 1	1454
	21st to end	Night	51% 8% 9% 19% 12% 1	1357
June	1st to 10th	Night	55% 7% 11% 21% 5% 1	1260
	11th to 20th	Night	43% 7% 14% 22% 11% 2	1260
	21st to end	Night	54% 6% 15% 15% 9%	1260
July	1st to 10th	Night	45% 8% 19% 22% 6%	1225
	11th to 20th	Night	44% 10% 17% 22% 6% 1	1345
	21st to end	Night	43% 11% 19% 20% 6%	1486
August	1st to 10th	Night	41% 10% 19% 26% 3	1480
	11th to 20th	Night	46% 11% 18% 18% 6% 1	1596
	21st to end	Night	42% 8% 16% 27% 7%	1784
September	1st to 10th	Night	42% 8% 15% 24% 10% 1	1837
	11th to 20th	Night	44% 7% 17% 21% 10% 1	1980
	21st to end	Night	42% 8% 12% 26% 11% 1	1980
October	1st to 10th	Night	47% 6% 12% 25% 10% 1	2020
	11th to 20th	Night	56% 7% 12% 20% 4	2258
	21st to end	Night	58% 6% 14% 15% 7% 1	2574
November	1st to 10th	Night	57% 7% 14% 16% 6%	2407
	11th to 20th	Night	57% 7% 12% 15% 9%	2588
	21st to end	Night	63% 7% 12% 12% 6%	2769
December	1st to 10th	Night	71% 6% 9% 9% 4	2850
	11th to 20th	Night	64% 6% 11% 12% 6%	3532
	21st to end	Night	65% 7% 11% 11% 6%	5236

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% 33% 6% 2 1	180
	11th to 20th	Day	32% 26% 28% 11% 3 1	180
	21st to end	Day	22% 26% 34% 11% 6% 1	198
February	1st to 10th	Day	29% 23% 31% 12% 4	252
	11th to 20th	Day	26% 26% 34% 12% 2	406
	21st to end	Day	25% 26% 32% 13% 4	382
March	1st to 10th	Day	27% 23% 32% 14% 3	420
	11th to 20th	Day	29% 20% 31% 12% 6% 1	420
	21st to end	Day	29% 24% 25% 16% 5% 1	462
April	1st to 10th	Day	34% 23% 26% 12% 4 1	420
	11th to 20th	Day	30% 21% 30% 14% 4 1	412
	21st to end	Day	32% 19% 34% 11% 3 1	420
May	1st to 10th	Day	30% 16% 34% 15% 5%	423
	11th to 20th	Day	28% 21% 31% 16% 4 1	447
	21st to end	Day	28% 22% 27% 18% 5%	680
June	1st to 10th	Day	28% 19% 29% 17% 6% 1	630
	11th to 20th	Day	27% 18% 26% 20% 8% 1	630
	21st to end	Day	27% 16% 31% 21% 7%	630
July	1st to 10th	Day	20% 15% 35% 21% 8% 1	620
	11th to 20th	Day	19% 16% 39% 18% 7% 1	488
	21st to end	Day	18% 13% 42% 21% 5% 1	488
August	1st to 10th	Day	21% 13% 37% 21% 7% 2	446
	11th to 20th	Day	19% 13% 31% 27% 8% 1	439
	21st to end	Day	23% 19% 27% 19% 10% 2	495
September	1st to 10th	Day	21% 21% 28% 18% 9% 2	450
	11th to 20th	Day	23% 16% 32% 19% 8% 2	450
	21st to end	Day	23% 18% 33% 15% 8% 5%	450
October	1st to 10th	Day	20% 21% 31% 16% 8% 4	430
	11th to 20th	Day	33% 20% 24% 13% 8% 2	360
	21st to end	Day	39% 18% 26% 12% 4 1	396
November	1st to 10th	Day	33% 21% 29% 15% 2 1	365
	11th to 20th	Day	28% 22% 27% 16% 6% 1	370
	21st to end	Day	31% 28% 28% 10% 3	256
December	1st to 10th	Day	35% 18% 29% 14% 3 1	180
	11th to 20th	Day	33% 26% 31% 6% 3 1	180
	21st to end	Day	34% 30% 20% 13% 3	198
January	1st to 10th	Night	25% 23% 36% 14% 2	810
	11th to 20th	Night	24% 25% 32% 16% 4	760
	21st to end	Night	16% 20% 35% 23% 5% 1	836
February	1st to 10th	Night	18% 27% 34% 17% 5%	760
	11th to 20th	Night	21% 26% 34% 15% 5%	743
	21st to end	Night	24% 20% 35% 16% 4	628
March	1st to 10th	Night	23% 19% 34% 21% 3	723
	11th to 20th	Night	25% 21% 31% 15% 6% 1	720
	21st to end	Night	24% 21% 28% 21% 7% 1	792
April	1st to 10th	Night	32% 18% 27% 18% 4	720
	11th to 20th	Night	26% 19% 28% 20% 7%	553
	21st to end	Night	32% 15% 25% 20% 7% 1	540
May	1st to 10th	Night	27% 13% 29% 26% 5% 1	540
	11th to 20th	Night	24% 13% 29% 25% 8% 1	395
	21st to end	Night	26% 15% 29% 22% 7% 1	389
June	1st to 10th	Night	24% 9% 31% 29% 7%	360
	11th to 20th	Night	18% 11% 28% 33% 10%	360
	21st to end	Night	23% 9% 30% 28% 9% 1	360
July	1st to 10th	Night	18% 11% 34% 28% 9% 1	350
	11th to 20th	Night	16% 7% 34% 32% 9% 1	348
	21st to end	Night	15% 5% 30% 38% 10% 1	394
August	1st to 10th	Night	16% 7% 32% 31% 12% 1	416
	11th to 20th	Night	18% 7% 31% 32% 11% 1	532
	21st to end	Night	16% 11% 29% 30% 12% 1	596
September	1st to 10th	Night	19% 13% 32% 26% 10% 1	720
	11th to 20th	Night	22% 13% 29% 24% 11% 2	720
	21st to end	Night	20% 15% 30% 23% 12% 1	720
October	1st to 10th	Night	23% 18% 28% 23% 7% 2	720
	11th to 20th	Night	27% 18% 30% 17% 8% 1	720
	21st to end	Night	29% 20% 28% 17% 5%	792
November	1st to 10th	Night	30% 19% 29% 17% 6%	740
	11th to 20th	Night	27% 22% 26% 18% 6% 1	816
	21st to end	Night	27% 22% 31% 16% 4 1	850
December	1st to 10th	Night	31% 20% 29% 15% 5% 1	850
	11th to 20th	Night	26% 24% 30% 16% 5%	850
	21st to end	Night	29% 26% 24% 16% 5%	935

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