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 2024-10-25.

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	17% 12% 4 9% 5% 5% 5% 4 5% 6% 28%	101464
	Night	16% 13% 4 10% 6% 5% 5% 4 5% 5% 28%	97380
Transparency	Day	55% 7% 12% 17% 8% 1	101213
	Night	55% 7% 13% 17% 8% 1	97252
Seeing	Day	27% 20% 31% 16% 6% 1	15644
	Night	24% 18% 30% 21% 7% 1	23784

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	10% 16% 8% 12% 9% 7% 6% 4 5% 5% 17%	2339
	11th to 20th	Day	11% 16% 4 19% 8% 6% 4 3 4 4 22%	2520
	21st to end	Day	9% 10% 4 17% 7% 6% 5% 5% 6% 5% 27%	2772
February	1st to 10th	Day	9% 17% 6% 12% 9% 8% 6% 4 5% 5% 21%	1592
	11th to 20th	Day	12% 19% 6% 12% 7% 6% 4 4 4 5% 21%	1747
	21st to end	Day	12% 15% 4 11% 8% 6% 4 4 4 5% 26%	1570
March	1st to 10th	Day	15% 18% 5% 10% 5% 4 5% 4 4 5% 25%	3116
	11th to 20th	Day	14% 23% 7% 13% 5% 4 4 3 4 4 18%	3434
	21st to end	Day	15% 19% 6% 10% 4 3 3 3 4 4 30%	3902
April	1st to 10th	Day	19% 18% 4 10% 6% 3 3 3 4 5% 24%	2280
	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% 18% 4 8% 4 4 4 2 3 4 24%	1825
November	1st to 10th	Day	17% 18% 4 10% 5% 4 4 3 4 4 28%	1671
	11th to 20th	Day	18% 16% 5% 12% 6% 4 4 2 5% 5% 23%	1590
	21st to end	Day	18% 19% 5% 11% 6% 5% 5% 3 3 4 22%	1406
December	1st to 10th	Day	20% 21% 6% 13% 6% 4 3 3 4 3 16%	1330
	11th to 20th	Day	17% 17% 6% 12% 7% 5% 3 3 3 4 22%	1668
	21st to end	Day	20% 13% 5% 13% 8% 6% 4 2 3 4 21%	2431
January	1st to 10th	Night	10% 15% 7% 15% 9% 8% 6% 4 5% 5% 16%	4611
	11th to 20th	Night	10% 17% 6% 14% 10% 7% 5% 4 5% 4 18%	4440
	21st to end	Night	7% 12% 7% 13% 8% 6% 5% 5% 5% 6% 26%	4884
February	1st to 10th	Night	8% 16% 5% 11% 8% 6% 5% 4 5% 6% 24%	2586
	11th to 20th	Night	9% 18% 8% 15% 7% 6% 5% 3 4 5% 22%	2318
	21st to end	Night	11% 17% 5% 9% 7% 5% 4 3 5% 4 30%	1884
March	1st to 10th	Night	16% 16% 4 8% 5% 4 6% 4 4 5% 28%	3724
	11th to 20th	Night	12% 18% 6% 13% 6% 5% 5% 4 5% 6% 21%	3525
	21st to end	Night	18% 16% 4 9% 5% 4 3 3 4 5% 28%	3727
April	1st to 10th	Night	20% 16% 4 8% 6% 4 4 3 4 4 28%	1900
	11th to 20th	Night	19% 12% 3 7% 5% 5% 4 3 6% 5% 30%	1708
	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%	2637
November	1st to 10th	Night	18% 15% 5% 8% 5% 4 4 3 4 6% 27%	2407
	11th to 20th	Night	17% 15% 5% 10% 5% 4 4 3 5% 6% 26%	2588
	21st to end	Night	16% 16% 6% 13% 7% 5% 5% 3 5% 4 21%	2769
December	1st to 10th	Night	19% 19% 7% 12% 7% 5% 4 3 4 3 16%	2850
	11th to 20th	Night	19% 15% 5% 11% 7% 5% 5% 3 5% 5% 19%	3531
	21st to end	Night	17% 18% 6% 12% 7% 6% 4 3 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% 10% 12% 9% 3	3119
	11th to 20th	Day	68% 7% 10% 9% 6% 1	3434
	21st to end	Day	57% 4 7% 17% 11% 4	3902
April	1st to 10th	Day	63% 5% 8% 14% 8% 3	2280
	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	51% 6% 12% 22% 9%	2047
	11th to 20th	Day	61% 6% 14% 15% 4	1792
	21st to end	Day	64% 5% 11% 14% 6% 1	1825
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% 10% 16% 12% 1	1884
March	1st to 10th	Night	59% 6% 10% 16% 8% 1	3734
	11th to 20th	Night	61% 8% 12% 12% 6% 1	3526
	21st to end	Night	58% 5% 7% 20% 9% 1	3727
April	1st to 10th	Night	59% 4 7% 15% 12% 3	1900
	11th to 20th	Night	52% 6% 10% 17% 14% 1	1708
	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% 12% 26% 10% 1	2133
	11th to 20th	Night	55% 7% 12% 20% 4	2384
	21st to end	Night	57% 6% 15% 15% 7% 1	2637
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% 27% 32% 13% 4	382
March	1st to 10th	Day	27% 23% 32% 14% 3	460
	11th to 20th	Day	28% 22% 30% 13% 6% 1	460
	21st to end	Day	32% 23% 24% 15% 5% 1	506
April	1st to 10th	Day	34% 23% 27% 12% 3 1	460
	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% 5%	411
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% 20% 34% 21% 3	760
	11th to 20th	Night	25% 21% 31% 17% 6% 1	760
	21st to end	Night	25% 21% 28% 20% 6%	836
April	1st to 10th	Night	31% 18% 28% 19% 4	760
	11th to 20th	Night	26% 19% 28% 20% 7%	584
	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% 28% 18% 5%	812
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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