Lac Echo
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lac Echo clear sky chart from 2005-11-06 to 2026-03-03.

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 9% 5% 5% 4 4 5% 6% 29%	131198
	Night	15% 14% 5% 10% 6% 5% 4 3 5% 6% 28%	129944
Transparency	Day	54% 5% 11% 20% 9% 1	134650
	Night	56% 5% 11% 18% 9% 1	134579
Seeing	Day	25% 17% 30% 18% 7% 2	15994
	Night	23% 14% 28% 24% 9% 1	25187

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% 7% 18% 8% 6% 5% 3 4 4 16%	4661
	11th to 20th	Day	10% 21% 8% 18% 8% 4 4 2 4 5% 16%	4650
	21st to end	Day	7% 13% 7% 18% 10% 8% 6% 4 4 5% 19%	5226
February	1st to 10th	Day	11% 18% 6% 14% 8% 4 4 4 5% 5% 21%	1890
	11th to 20th	Day	11% 18% 6% 13% 6% 5% 4 3 4 5% 25%	1854
	21st to end	Day	16% 16% 7% 9% 8% 5% 4 3 4 4 23%	1730
March	1st to 10th	Day	17% 16% 5% 14% 6% 4 4 3 4 5% 22%	4496
	11th to 20th	Day	11% 15% 6% 11% 6% 5% 5% 3 5% 7% 26%	4927
	21st to end	Day	16% 15% 3 7% 5% 4 4 3 5% 5% 33%	5804
April	1st to 10th	Day	21% 14% 4 8% 4 4 3 3 4 5% 30%	2400
	11th to 20th	Day	22% 11% 4 8% 5% 3 3 3 3 6% 33%	2374
	21st to end	Day	21% 12% 4 8% 5% 4 4 3 4 5% 29%	2570
May	1st to 10th	Day	21% 13% 4 9% 5% 5% 4 4 5% 6% 24%	6346
	11th to 20th	Day	17% 9% 3 9% 5% 5% 5% 4 5% 7% 30%	6318
	21st to end	Day	22% 9% 3 8% 4 4 4 3 5% 7% 31%	6949
June	1st to 10th	Day	22% 9% 3 8% 5% 5% 4 4 5% 7% 28%	2800
	11th to 20th	Day	16% 6% 2 6% 5% 5% 5% 4 7% 9% 35%	2800
	21st to end	Day	21% 7% 3 7% 6% 4 5% 4 7% 8% 29%	2800
July	1st to 10th	Day	15% 7% 3 8% 6% 6% 5% 5% 7% 9% 30%	6360
	11th to 20th	Day	12% 7% 3 7% 4 4 5% 4 6% 8% 39%	6360
	21st to end	Day	10% 6% 2 6% 4 3 5% 4 6% 10% 45%	6926
August	1st to 10th	Day	14% 7% 3 8% 6% 5% 5% 4 7% 9% 32%	4563
	11th to 20th	Day	16% 8% 3 6% 4 5% 4 4 6% 8% 36%	4121
	21st to end	Day	14% 7% 3 6% 4 5% 4 4 6% 9% 37%	4312
September	1st to 10th	Day	15% 7% 2 6% 4 4 4 3 5% 7% 42%	2400
	11th to 20th	Day	14% 6% 2 6% 4 4 5% 3 6% 8% 44%	2388
	21st to end	Day	20% 8% 2 5% 3 3 3 3 5% 8% 38%	2153
October	1st to 10th	Day	19% 10% 3 7% 4 4 5% 3 5% 6% 34%	2000
	11th to 20th	Day	24% 13% 4 8% 5% 4 5% 3 5% 6% 25%	2000
	21st to end	Day	25% 14% 3 8% 4 4 5% 3 4 5% 24%	2010
November	1st to 10th	Day	17% 14% 4 8% 5% 3 3 3 5% 7% 31%	1851
	11th to 20th	Day	18% 17% 5% 10% 7% 5% 5% 4 4 5% 20%	1685
	21st to end	Day	21% 18% 7% 12% 6% 4 4 4 4 4 16%	1680
December	1st to 10th	Day	18% 23% 9% 11% 6% 5% 4 4 5% 4 11%	2680
	11th to 20th	Day	17% 17% 8% 15% 6% 4 4 3 4 4 20%	3066
	21st to end	Day	18% 20% 6% 11% 6% 4 5% 3 3 4 19%	4048
January	1st to 10th	Night	11% 20% 9% 16% 7% 5% 4 3 4 4 17%	8234
	11th to 20th	Night	10% 19% 8% 17% 9% 6% 5% 3 3 4 16%	8235
	21st to end	Night	7% 15% 8% 15% 8% 8% 7% 4 5% 5% 18%	8938
February	1st to 10th	Night	11% 16% 5% 13% 9% 6% 5% 4 5% 5% 23%	2730
	11th to 20th	Night	11% 15% 7% 13% 6% 6% 4 3 4 5% 26%	2650
	21st to end	Night	12% 17% 6% 11% 5% 5% 4 4 5% 6% 25%	2076
March	1st to 10th	Night	19% 16% 5% 11% 5% 4 4 3 4 4 26%	5389
	11th to 20th	Night	11% 15% 5% 9% 5% 5% 5% 4 6% 7% 28%	5030
	21st to end	Night	17% 12% 5% 10% 5% 5% 4 4 5% 5% 29%	5114
April	1st to 10th	Night	21% 13% 3 7% 4 4 4 4 4 6% 30%	2000
	11th to 20th	Night	19% 10% 4 7% 4 4 4 3 4 5% 35%	1975
	21st to end	Night	20% 11% 4 8% 3 4 4 3 4 6% 33%	1846
May	1st to 10th	Night	18% 13% 4 9% 6% 5% 5% 4 6% 7% 24%	3594
	11th to 20th	Night	16% 8% 3 8% 4 5% 4 4 6% 6% 36%	3575
	21st to end	Night	19% 10% 3 8% 5% 5% 5% 3 5% 6% 29%	3926
June	1st to 10th	Night	18% 8% 2 6% 5% 4 5% 4 6% 10% 32%	1600
	11th to 20th	Night	15% 7% 2 7% 5% 4 4 4 5% 8% 40%	1600
	21st to end	Night	18% 7% 3 6% 5% 4 6% 4 5% 8% 34%	1600
July	1st to 10th	Night	15% 8% 3 7% 5% 5% 5% 5% 6% 8% 34%	3600
	11th to 20th	Night	14% 7% 2 6% 4 3 4 4 6% 8% 43%	3600
	21st to end	Night	9% 6% 2 6% 4 4 5% 4 6% 8% 47%	3926
August	1st to 10th	Night	12% 7% 3 8% 5% 5% 5% 4 6% 7% 38%	2586
	11th to 20th	Night	16% 8% 3 6% 3 3 5% 3 5% 6% 41%	2891
	21st to end	Night	16% 7% 2 6% 4 4 4 4 5% 8% 40%	3586
September	1st to 10th	Night	13% 7% 3 7% 4 4 4 3 5% 6% 45%	2000
	11th to 20th	Night	14% 6% 2 5% 3 4 3 2 5% 7% 50%	2011
	21st to end	Night	16% 9% 3 5% 4 3 3 3 5% 5% 43%	2245
October	1st to 10th	Night	19% 9% 2 6% 4 4 4 3 5% 6% 39%	2400
	11th to 20th	Night	20% 11% 3 8% 6% 4 4 3 4 5% 31%	2400
	21st to end	Night	22% 13% 4 9% 5% 4 3 3 5% 6% 26%	2830
November	1st to 10th	Night	18% 14% 4 8% 5% 4 4 3 4 6% 29%	2667
	11th to 20th	Night	18% 14% 6% 11% 6% 5% 5% 3 4 5% 25%	2932
	21st to end	Night	20% 17% 6% 12% 6% 6% 4 3 4 5% 19%	2940
December	1st to 10th	Night	17% 20% 7% 13% 7% 5% 5% 4 5% 5% 14%	4720
	11th to 20th	Night	21% 17% 5% 12% 5% 3 3 2 3 4 23%	5348
	21st to end	Night	20% 22% 5% 10% 5% 3 3 3 4 4 20%	7150

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	72% 3 8% 13% 4	4662
	11th to 20th	Day	72% 3 5% 10% 9%	4680
	21st to end	Day	67% 4 8% 10% 9%	5226
February	1st to 10th	Day	64% 4 7% 16% 7% 1	1890
	11th to 20th	Day	64% 3 10% 14% 9% 1	1863
	21st to end	Day	64% 3 8% 14% 9% 1	1730
March	1st to 10th	Day	65% 3 7% 11% 12% 3	4499
	11th to 20th	Day	57% 4 14% 14% 9% 1	4927
	21st to end	Day	53% 4 5% 19% 17% 2	5804
April	1st to 10th	Day	57% 3 7% 18% 12% 3	2400
	11th to 20th	Day	54% 3 6% 21% 13% 2	2374
	21st to end	Day	57% 4 7% 15% 13% 3	2570
May	1st to 10th	Day	59% 5% 7% 19% 8% 2	6357
	11th to 20th	Day	52% 6% 13% 18% 10% 1	6322
	21st to end	Day	53% 5% 11% 17% 13% 1	6949
June	1st to 10th	Day	55% 5% 10% 18% 11% 1	2800
	11th to 20th	Day	43% 6% 13% 25% 11% 2	2800
	21st to end	Day	51% 6% 14% 19% 10%	2800
July	1st to 10th	Day	47% 7% 13% 25% 7%	6290
	11th to 20th	Day	39% 7% 14% 31% 9%	6285
	21st to end	Day	34% 6% 16% 35% 9%	6728
August	1st to 10th	Day	47% 7% 17% 23% 7%	4549
	11th to 20th	Day	44% 7% 15% 28% 6% 1	4160
	21st to end	Day	40% 6% 17% 24% 12% 1	4312
September	1st to 10th	Day	41% 5% 13% 28% 12%	2400
	11th to 20th	Day	38% 4 14% 31% 12% 1	2388
	21st to end	Day	45% 5% 15% 25% 11%	2153
October	1st to 10th	Day	50% 5% 11% 27% 7%	3260
	11th to 20th	Day	53% 6% 13% 20% 8% 1	3240
	21st to end	Day	55% 5% 19% 16% 5%	3222
November	1st to 10th	Day	53% 4 13% 22% 6% 1	1851
	11th to 20th	Day	66% 4 10% 12% 7%	1685
	21st to end	Day	71% 5% 10% 8% 5% 1	1680
December	1st to 10th	Day	75% 6% 8% 9% 2	2680
	11th to 20th	Day	69% 3 8% 14% 6%	3066
	21st to end	Day	68% 5% 7% 16% 4	4048
January	1st to 10th	Night	70% 4 11% 12% 3	8234
	11th to 20th	Night	72% 4 8% 11% 5%	8280
	21st to end	Night	67% 4 7% 11% 11%	8938
February	1st to 10th	Night	63% 4 8% 17% 7% 1	2730
	11th to 20th	Night	61% 3 8% 19% 8% 1	2652
	21st to end	Night	59% 3 9% 17% 10% 1	2076
March	1st to 10th	Night	63% 3 8% 12% 12% 3	5399
	11th to 20th	Night	54% 5% 13% 17% 7% 3	5031
	21st to end	Night	56% 4 7% 20% 11% 2	5114
April	1st to 10th	Night	55% 4 9% 17% 13% 2	2000
	11th to 20th	Night	50% 4 7% 22% 15% 1	1975
	21st to end	Night	53% 4 9% 17% 14% 3	1846
May	1st to 10th	Night	58% 5% 9% 18% 8% 2	3600
	11th to 20th	Night	46% 7% 12% 21% 11% 2	3576
	21st to end	Night	54% 5% 10% 17% 12% 1	3927
June	1st to 10th	Night	47% 6% 13% 22% 11% 1	1600
	11th to 20th	Night	43% 5% 12% 25% 13% 2	1600
	21st to end	Night	47% 8% 12% 21% 12% 1	1600
July	1st to 10th	Night	46% 7% 18% 21% 8%	3560
	11th to 20th	Night	38% 6% 16% 31% 9%	3552
	21st to end	Night	33% 7% 15% 33% 12%	3809
August	1st to 10th	Night	43% 7% 15% 26% 9%	2576
	11th to 20th	Night	42% 6% 17% 28% 7%	2918
	21st to end	Night	42% 5% 15% 24% 11% 2	3586
September	1st to 10th	Night	39% 5% 13% 30% 13% 1	2000
	11th to 20th	Night	35% 4 14% 35% 10% 1	2011
	21st to end	Night	42% 4 13% 29% 12%	2245
October	1st to 10th	Night	42% 5% 14% 27% 12%	3920
	11th to 20th	Night	49% 6% 14% 22% 9%	3899
	21st to end	Night	52% 5% 18% 16% 9%	4568
November	1st to 10th	Night	56% 5% 13% 19% 7%	2667
	11th to 20th	Night	62% 4 10% 14% 8% 1	2932
	21st to end	Night	68% 5% 11% 13% 3	2940
December	1st to 10th	Night	71% 6% 11% 10% 3	4720
	11th to 20th	Night	67% 2 6% 14% 10% 1	5348
	21st to end	Night	68% 3 5% 14% 9%	7150

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	20% 22% 37% 18% 3	220
	11th to 20th	Day	30% 22% 31% 13% 3 1	220
	21st to end	Day	24% 21% 35% 17% 3	261
February	1st to 10th	Day	29% 29% 30% 10% 2	330
	11th to 20th	Day	28% 29% 34% 9%	341
	21st to end	Day	31% 22% 33% 13% 1	446
March	1st to 10th	Day	29% 19% 34% 13% 5% 1	508
	11th to 20th	Day	28% 23% 32% 12% 3 1	500
	21st to end	Day	31% 23% 25% 14% 5% 1	550
April	1st to 10th	Day	34% 19% 26% 14% 5% 1	500
	11th to 20th	Day	36% 22% 21% 12% 9% 1	492
	21st to end	Day	33% 21% 29% 12% 4 1	500
May	1st to 10th	Day	30% 18% 31% 14% 5% 2	503
	11th to 20th	Day	24% 19% 31% 18% 7% 2	527
	21st to end	Day	25% 17% 30% 20% 7% 1	573
June	1st to 10th	Day	27% 16% 32% 19% 5% 1	530
	11th to 20th	Day	20% 17% 34% 18% 9% 2	530
	21st to end	Day	25% 15% 32% 20% 7% 2	530
July	1st to 10th	Day	16% 10% 36% 28% 8% 3	525
	11th to 20th	Day	15% 13% 36% 26% 8% 2	524
	21st to end	Day	14% 12% 35% 26% 10% 2	576
August	1st to 10th	Day	17% 9% 26% 35% 11% 2	526
	11th to 20th	Day	18% 8% 27% 29% 12% 7%	519
	21st to end	Day	19% 13% 33% 20% 11% 5%	583
September	1st to 10th	Day	18% 11% 32% 20% 12% 7%	530
	11th to 20th	Day	15% 11% 24% 23% 18% 9%	530
	21st to end	Day	23% 14% 25% 21% 11% 7%	530
October	1st to 10th	Day	25% 17% 24% 20% 11% 3	530
	11th to 20th	Day	32% 21% 26% 14% 5% 2	530
	21st to end	Day	34% 14% 29% 17% 5%	478
November	1st to 10th	Day	33% 16% 28% 18% 4	425
	11th to 20th	Day	28% 22% 32% 12% 4 1	225
	21st to end	Day	36% 25% 25% 13% 1	220
December	1st to 10th	Day	35% 14% 35% 14% 3	220
	11th to 20th	Day	30% 25% 36% 7% 1 1	220
	21st to end	Day	30% 24% 30% 13% 2 1	242
January	1st to 10th	Night	26% 16% 36% 18% 4	840
	11th to 20th	Night	30% 16% 27% 21% 6%	840
	21st to end	Night	19% 16% 33% 23% 8% 1	924
February	1st to 10th	Night	19% 20% 34% 23% 5%	840
	11th to 20th	Night	20% 21% 36% 19% 4	823
	21st to end	Night	24% 20% 29% 24% 4	692
March	1st to 10th	Night	25% 17% 32% 20% 6%	809
	11th to 20th	Night	24% 21% 30% 20% 5%	800
	21st to end	Night	25% 16% 29% 23% 7%	880
April	1st to 10th	Night	29% 15% 27% 24% 5%	800
	11th to 20th	Night	26% 16% 29% 21% 7% 1	791
	21st to end	Night	26% 17% 25% 24% 7%	646
May	1st to 10th	Night	26% 12% 26% 26% 9% 2	400
	11th to 20th	Night	22% 8% 32% 29% 9%	394
	21st to end	Night	18% 12% 35% 25% 9% 1	433
June	1st to 10th	Night	20% 8% 32% 32% 8% 1	400
	11th to 20th	Night	19% 10% 28% 30% 13% 1	400
	21st to end	Night	20% 8% 24% 35% 13%	400
July	1st to 10th	Night	12% 4 28% 40% 15% 1	390
	11th to 20th	Night	14% 4 23% 41% 16% 1	388
	21st to end	Night	11% 5% 27% 40% 16% 2	438
August	1st to 10th	Night	11% 6% 21% 40% 21% 1	398
	11th to 20th	Night	15% 3 17% 38% 23% 4	597
	21st to end	Night	18% 6% 24% 32% 17% 3	880
September	1st to 10th	Night	17% 6% 29% 29% 18% 1	800
	11th to 20th	Night	18% 7% 23% 28% 21% 3	800
	21st to end	Night	20% 9% 26% 26% 17% 2	800
October	1st to 10th	Night	23% 12% 28% 24% 13% 1	800
	11th to 20th	Night	27% 14% 28% 22% 7% 1	800
	21st to end	Night	29% 15% 28% 24% 5%	880
November	1st to 10th	Night	29% 13% 28% 22% 7% 1	820
	11th to 20th	Night	25% 19% 30% 15% 10% 1	840
	21st to end	Night	30% 20% 25% 20% 5%	840
December	1st to 10th	Night	28% 20% 27% 21% 5%	840
	11th to 20th	Night	29% 19% 29% 18% 4 1	840
	21st to end	Night	34% 15% 28% 18% 5%	924

Page generated at 2026-02-28 01:40:21. Version ac07

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