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 2024-07-03.

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	17% 12% 4 9% 5% 5% 4 4 5% 6% 29%	89583
	Night	16% 13% 5% 9% 5% 4 4 3 5% 6% 29%	89616
Transparency	Day	55% 5% 11% 19% 9% 1	89302
	Night	56% 4 11% 18% 9% 1	89451
Seeing	Day	26% 17% 30% 18% 7% 2	13964
	Night	24% 14% 28% 24% 9% 1	23063

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	15% 19% 7% 16% 8% 4 4 3 3 3 17%	2517
	11th to 20th	Day	14% 15% 7% 17% 8% 5% 4 3 4 5% 19%	2520
	21st to end	Day	12% 16% 7% 16% 8% 6% 5% 4 4 4 17%	2818
February	1st to 10th	Day	11% 19% 6% 13% 8% 5% 4 4 5% 6% 20%	1710
	11th to 20th	Day	12% 19% 6% 13% 6% 4 4 3 3 5% 26%	1672
	21st to end	Day	17% 16% 6% 8% 7% 5% 4 3 4 4 25%	1570
March	1st to 10th	Day	17% 18% 5% 11% 5% 4 4 3 4 5% 24%	3116
	11th to 20th	Day	11% 19% 7% 12% 7% 5% 4 3 4 5% 24%	3441
	21st to end	Day	12% 10% 2 7% 6% 5% 5% 4 6% 7% 37%	4056
April	1st to 10th	Day	21% 15% 4 8% 4 4 3 3 4 5% 29%	2280
	11th to 20th	Day	22% 11% 4 8% 5% 3 3 3 4 6% 33%	2254
	21st to end	Day	21% 12% 4 8% 5% 4 4 3 4 5% 29%	2441
May	1st to 10th	Day	20% 11% 4 8% 5% 5% 4 4 5% 6% 28%	4426
	11th to 20th	Day	18% 9% 3 8% 5% 5% 4 4 5% 7% 31%	4398
	21st to end	Day	18% 7% 3 8% 5% 4 5% 4 6% 7% 34%	4837
June	1st to 10th	Day	22% 9% 3 8% 5% 5% 4 4 5% 7% 28%	2660
	11th to 20th	Day	16% 6% 2 6% 5% 4 5% 4 7% 9% 35%	2660
	21st to end	Day	21% 7% 3 7% 6% 4 5% 4 7% 7% 28%	2660
July	1st to 10th	Day	13% 7% 3 6% 5% 4 6% 4 7% 9% 37%	2548
	11th to 20th	Day	13% 7% 3 7% 4 5% 5% 5% 7% 8% 34%	2520
	21st to end	Day	13% 7% 2 7% 6% 4 5% 5% 7% 8% 36%	2744
August	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 4 7% 8% 34%	2506
	11th to 20th	Day	14% 8% 3 7% 4 5% 4 4 6% 8% 36%	2280
	21st to end	Day	16% 7% 3 7% 4 5% 4 4 5% 8% 38%	2376
September	1st to 10th	Day	15% 7% 3 6% 4 4 4 3 5% 7% 41%	2160
	11th to 20th	Day	15% 6% 2 6% 4 4 5% 3 6% 8% 41%	2150
	21st to end	Day	20% 8% 3 6% 3 3 3 3 5% 8% 38%	1939
October	1st to 10th	Day	20% 10% 3 7% 4 4 4 4 5% 6% 32%	1800
	11th to 20th	Day	26% 13% 4 8% 5% 5% 4 3 5% 6% 23%	1800
	21st to end	Day	27% 14% 3 8% 4 4 4 3 4 5% 23%	1810
November	1st to 10th	Day	17% 13% 3 8% 5% 3 3 4 5% 7% 33%	1671
	11th to 20th	Day	19% 17% 5% 10% 7% 4 5% 4 4 5% 21%	1525
	21st to end	Day	21% 17% 6% 12% 6% 4 4 4 4 5% 17%	1520
December	1st to 10th	Day	21% 22% 6% 12% 5% 6% 4 3 3 5% 13%	1520
	11th to 20th	Day	19% 15% 8% 14% 6% 3 4 3 4 5% 19%	1906
	21st to end	Day	22% 22% 7% 12% 5% 3 3 2 3 3 18%	2772
January	1st to 10th	Night	14% 20% 8% 11% 6% 4 4 3 4 5% 20%	4429
	11th to 20th	Night	11% 15% 6% 14% 8% 6% 5% 4 4 5% 21%	4440
	21st to end	Night	12% 18% 9% 14% 7% 7% 5% 3 4 4 18%	4821
February	1st to 10th	Night	12% 16% 5% 12% 9% 6% 5% 4 4 5% 22%	2470
	11th to 20th	Night	12% 15% 7% 12% 6% 6% 4 3 4 5% 26%	2392
	21st to end	Night	12% 17% 5% 10% 5% 5% 4 4 5% 6% 26%	1884
March	1st to 10th	Night	19% 14% 4 9% 5% 4 4 3 4 5% 30%	3724
	11th to 20th	Night	15% 19% 6% 10% 4 4 3 3 4 5% 26%	3516
	21st to end	Night	13% 11% 4 9% 5% 4 4 3 5% 5% 36%	3576
April	1st to 10th	Night	21% 13% 2 7% 4 5% 4 3 4 6% 30%	1900
	11th to 20th	Night	19% 10% 3 7% 4 4 4 3 5% 5% 36%	1875
	21st to end	Night	20% 11% 4 8% 3 4 4 3 4 6% 33%	1755
May	1st to 10th	Night	19% 12% 4 8% 5% 4 5% 3 6% 6% 28%	2514
	11th to 20th	Night	18% 8% 3 7% 4 5% 4 3 5% 6% 36%	2495
	21st to end	Night	18% 7% 3 7% 4 5% 5% 4 6% 7% 35%	2738
June	1st to 10th	Night	18% 8% 2 6% 5% 4 5% 4 6% 10% 31%	1520
	11th to 20th	Night	15% 7% 2 7% 5% 4 4 4 4 8% 40%	1520
	21st to end	Night	19% 7% 3 6% 5% 4 6% 4 5% 8% 34%	1520
July	1st to 10th	Night	12% 7% 2 5% 4 4 5% 4 5% 7% 46%	1456
	11th to 20th	Night	13% 6% 2 7% 4 3 4 3 6% 9% 42%	1440
	21st to end	Night	8% 7% 2 6% 5% 5% 5% 4 6% 9% 43%	1574
August	1st to 10th	Night	10% 6% 3 8% 5% 5% 5% 4 6% 7% 42%	1432
	11th to 20th	Night	11% 6% 3 6% 4 3 6% 4 6% 7% 44%	1599
	21st to end	Night	14% 7% 2 6% 3 4 4 4 5% 8% 43%	1980
September	1st to 10th	Night	14% 7% 3 7% 4 4 4 3 5% 6% 44%	1800
	11th to 20th	Night	15% 7% 2 5% 4 4 3 2 5% 7% 47%	1809
	21st to end	Night	17% 8% 3 5% 4 3 3 3 5% 6% 42%	2020
October	1st to 10th	Night	21% 9% 2 6% 4 4 4 3 5% 5% 36%	2160
	11th to 20th	Night	21% 12% 3 8% 6% 4 4 3 4 5% 29%	2160
	21st to end	Night	23% 13% 4 9% 5% 4 3 3 5% 6% 25%	2546
November	1st to 10th	Night	18% 13% 4 8% 5% 4 4 3 4 6% 30%	2407
	11th to 20th	Night	19% 13% 5% 10% 6% 5% 5% 3 4 5% 25%	2652
	21st to end	Night	20% 16% 5% 11% 6% 6% 4 3 4 5% 20%	2660
December	1st to 10th	Night	19% 20% 7% 11% 6% 4 4 3 4 4 16%	2660
	11th to 20th	Night	21% 17% 6% 11% 5% 3 4 3 3 4 23%	3288
	21st to end	Night	23% 23% 6% 11% 5% 3 3 2 3 3 17%	4884

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	73% 3 9% 11% 4	2518
	11th to 20th	Day	68% 3 9% 13% 6%	2520
	21st to end	Day	70% 4 9% 11% 6% 1	2818
February	1st to 10th	Day	65% 4 7% 16% 7% 1	1710
	11th to 20th	Day	63% 3 10% 13% 10% 1	1681
	21st to end	Day	63% 3 9% 14% 10% 1	1570
March	1st to 10th	Day	63% 3 8% 14% 10% 1	3119
	11th to 20th	Day	63% 3 10% 14% 8% 2	3441
	21st to end	Day	46% 4 7% 24% 16% 2	4056
April	1st to 10th	Day	58% 3 7% 18% 11% 3	2280
	11th to 20th	Day	54% 3 6% 21% 13% 2	2254
	21st to end	Day	58% 4 7% 15% 13% 3	2441
May	1st to 10th	Day	55% 5% 8% 21% 9% 2	4440
	11th to 20th	Day	50% 6% 14% 20% 9% 1	4402
	21st to end	Day	48% 5% 12% 19% 14% 1	4837
June	1st to 10th	Day	55% 5% 10% 18% 11% 1	2660
	11th to 20th	Day	43% 6% 13% 25% 11% 2	2660
	21st to end	Day	52% 6% 14% 19% 10%	2660
July	1st to 10th	Day	42% 5% 14% 27% 11%	2478
	11th to 20th	Day	43% 7% 14% 25% 11%	2445
	21st to end	Day	44% 6% 16% 25% 9%	2591
August	1st to 10th	Day	47% 7% 16% 24% 7%	2492
	11th to 20th	Day	44% 6% 15% 25% 8% 1	2280
	21st to end	Day	44% 5% 13% 26% 11% 1	2376
September	1st to 10th	Day	42% 5% 13% 27% 13%	2160
	11th to 20th	Day	41% 5% 13% 29% 11% 1	2150
	21st to end	Day	45% 6% 15% 26% 8%	1939
October	1st to 10th	Day	53% 4 11% 22% 10% 1	1800
	11th to 20th	Day	63% 4 12% 15% 5% 1	1800
	21st to end	Day	63% 4 11% 14% 6% 1	1810
November	1st to 10th	Day	51% 4 14% 23% 6% 1	1671
	11th to 20th	Day	66% 4 11% 12% 7% 1	1525
	21st to end	Day	69% 5% 11% 9% 5% 1	1520
December	1st to 10th	Day	73% 5% 9% 9% 3	1520
	11th to 20th	Day	67% 4 10% 12% 5%	1906
	21st to end	Day	73% 3 5% 14% 4	2772
January	1st to 10th	Night	68% 3 16% 11% 3	4429
	11th to 20th	Night	66% 4 13% 12% 5%	4440
	21st to end	Night	70% 4 9% 10% 7%	4821
February	1st to 10th	Night	64% 4 9% 16% 7% 1	2470
	11th to 20th	Night	61% 3 9% 19% 8% 1	2394
	21st to end	Night	58% 4 10% 17% 10% 1	1884
March	1st to 10th	Night	58% 3 10% 16% 10% 2	3734
	11th to 20th	Night	61% 3 11% 16% 8% 1	3517
	21st to end	Night	49% 4 8% 21% 15% 3	3576
April	1st to 10th	Night	55% 4 9% 17% 13% 2	1900
	11th to 20th	Night	50% 4 7% 23% 15% 1	1875
	21st to end	Night	53% 4 9% 17% 14% 3	1755
May	1st to 10th	Night	55% 6% 10% 19% 9% 2	2520
	11th to 20th	Night	48% 6% 12% 22% 11% 2	2496
	21st to end	Night	48% 5% 11% 20% 15% 2	2739
June	1st to 10th	Night	46% 6% 14% 23% 10% 1	1520
	11th to 20th	Night	43% 5% 12% 25% 13% 2	1520
	21st to end	Night	46% 8% 13% 21% 12% 1	1520
July	1st to 10th	Night	36% 6% 15% 28% 15% 1	1416
	11th to 20th	Night	38% 5% 13% 30% 13%	1392
	21st to end	Night	36% 7% 18% 27% 12%	1486
August	1st to 10th	Night	38% 7% 19% 24% 11%	1422
	11th to 20th	Night	37% 6% 18% 29% 10%	1599
	21st to end	Night	39% 5% 17% 28% 10%	1980
September	1st to 10th	Night	40% 5% 12% 28% 14% 1	1800
	11th to 20th	Night	38% 4 14% 33% 9% 1	1809
	21st to end	Night	42% 4 13% 31% 10%	2020
October	1st to 10th	Night	49% 5% 9% 24% 13% 1	2160
	11th to 20th	Night	56% 5% 12% 18% 7%	2160
	21st to end	Night	61% 4 12% 16% 7% 1	2546
November	1st to 10th	Night	54% 5% 14% 19% 7%	2407
	11th to 20th	Night	62% 4 11% 14% 8% 1	2652
	21st to end	Night	67% 5% 11% 13% 4	2660
December	1st to 10th	Night	71% 4 10% 11% 5%	2660
	11th to 20th	Night	66% 3 9% 15% 7% 1	3288
	21st to end	Night	73% 3 6% 13% 5%	4884

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	21% 23% 32% 20% 3	180
	11th to 20th	Day	29% 18% 33% 15% 4 1	180
	21st to end	Day	24% 21% 34% 17% 4	213
February	1st to 10th	Day	30% 31% 28% 8% 3	270
	11th to 20th	Day	29% 30% 33% 8%	279
	21st to end	Day	34% 22% 30% 13% 2	382
March	1st to 10th	Day	28% 18% 35% 13% 5% 1	460
	11th to 20th	Day	27% 23% 33% 13% 4 1	460
	21st to end	Day	31% 23% 25% 15% 6% 1	506
April	1st to 10th	Day	32% 19% 28% 14% 5% 1	460
	11th to 20th	Day	35% 20% 22% 12% 9% 1	452
	21st to end	Day	32% 21% 29% 13% 5% 1	460
May	1st to 10th	Day	30% 17% 32% 15% 5% 2	463
	11th to 20th	Day	23% 18% 30% 19% 7% 2	487
	21st to end	Day	24% 18% 32% 19% 7% 1	529
June	1st to 10th	Day	26% 15% 33% 20% 6% 1	490
	11th to 20th	Day	20% 17% 32% 19% 10% 2	490
	21st to end	Day	25% 14% 31% 21% 8% 2	490
July	1st to 10th	Day	15% 8% 35% 29% 9% 3	453
	11th to 20th	Day	14% 13% 36% 25% 9% 2	444
	21st to end	Day	15% 10% 36% 27% 10% 2	488
August	1st to 10th	Day	18% 9% 26% 34% 11% 2	446
	11th to 20th	Day	17% 8% 26% 28% 13% 8%	439
	21st to end	Day	20% 13% 31% 20% 11% 6%	495
September	1st to 10th	Day	16% 12% 32% 21% 12% 7%	450
	11th to 20th	Day	17% 13% 27% 20% 15% 8%	450
	21st to end	Day	22% 14% 24% 21% 11% 7%	450
October	1st to 10th	Day	26% 18% 23% 19% 11% 3	450
	11th to 20th	Day	34% 22% 25% 13% 5% 2	450
	21st to end	Day	36% 13% 28% 17% 5%	410
November	1st to 10th	Day	33% 14% 29% 19% 5%	365
	11th to 20th	Day	30% 23% 32% 10% 4 2	185
	21st to end	Day	34% 22% 27% 16% 1 1	180
December	1st to 10th	Day	36% 13% 34% 14% 3	180
	11th to 20th	Day	31% 25% 34% 8% 1 1	180
	21st to end	Day	32% 22% 30% 12% 2 1	198
January	1st to 10th	Night	27% 16% 35% 17% 4	760
	11th to 20th	Night	29% 15% 28% 22% 6%	760
	21st to end	Night	19% 16% 34% 23% 8% 1	836
February	1st to 10th	Night	20% 19% 33% 22% 5%	760
	11th to 20th	Night	20% 21% 35% 19% 4	743
	21st to end	Night	24% 21% 27% 25% 3	628
March	1st to 10th	Night	25% 17% 32% 21% 6%	760
	11th to 20th	Night	24% 21% 30% 19% 5%	760
	21st to end	Night	25% 16% 29% 23% 7%	836
April	1st to 10th	Night	28% 15% 27% 24% 6%	760
	11th to 20th	Night	26% 17% 29% 21% 7% 1	751
	21st to end	Night	26% 17% 25% 24% 8%	615
May	1st to 10th	Night	26% 12% 26% 25% 9% 2	380
	11th to 20th	Night	22% 8% 32% 29% 9%	374
	21st to end	Night	18% 12% 36% 25% 9% 1	411
June	1st to 10th	Night	20% 7% 32% 32% 8% 1	380
	11th to 20th	Night	19% 9% 27% 31% 13% 1	380
	21st to end	Night	20% 8% 23% 35% 14%	380
July	1st to 10th	Night	11% 4 30% 38% 16% 1	354
	11th to 20th	Night	15% 4 24% 39% 17% 1	348
	21st to end	Night	11% 5% 27% 40% 16% 2	394
August	1st to 10th	Night	10% 6% 23% 38% 21% 1	358
	11th to 20th	Night	14% 3 17% 38% 23% 4	535
	21st to end	Night	18% 6% 25% 31% 17% 3	792
September	1st to 10th	Night	18% 7% 28% 28% 18% 1	720
	11th to 20th	Night	19% 8% 24% 28% 18% 3	720
	21st to end	Night	21% 10% 25% 25% 17% 3	720
October	1st to 10th	Night	24% 12% 26% 23% 12% 1	720
	11th to 20th	Night	29% 14% 27% 22% 7% 1	720
	21st to end	Night	30% 15% 27% 22% 5%	792
November	1st to 10th	Night	28% 13% 29% 22% 7% 1	740
	11th to 20th	Night	26% 19% 30% 14% 10% 1	760
	21st to end	Night	31% 19% 25% 19% 6% 1	760
December	1st to 10th	Night	29% 19% 27% 20% 5%	760
	11th to 20th	Night	28% 19% 29% 18% 5% 1	760
	21st to end	Night	34% 15% 28% 18% 5%	836

Page generated at 2024-06-29 22:08:49. Version ac07

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