Lac Lasalle
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lac Lasalle clear sky chart from 2005-11-06 to 2026-07-16.

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% 11% 4 9% 5% 5% 5% 4 5% 6% 29%	138341
	Night	14% 11% 4 10% 6% 5% 5% 4 5% 6% 30%	134350
Transparency	Day	52% 7% 11% 19% 10% 1	141775
	Night	52% 7% 12% 18% 10% 1	139005
Seeing	Day	24% 19% 32% 17% 6% 2	16599
	Night	21% 16% 31% 23% 8% 1	25550

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% 14% 6% 4 5% 3 5% 5% 21%	4661
	11th to 20th	Day	8% 18% 9% 19% 9% 5% 3 3 3 4 19%	4650
	21st to end	Day	6% 11% 8% 17% 8% 6% 6% 4 5% 6% 24%	5124
February	1st to 10th	Day	9% 18% 6% 11% 8% 5% 4 4 4 7% 25%	1850
	11th to 20th	Day	10% 17% 7% 11% 6% 5% 4 3 5% 6% 26%	1919
	21st to end	Day	13% 18% 6% 11% 7% 4 4 3 4 5% 24%	1730
March	1st to 10th	Day	16% 18% 5% 12% 8% 4 3 2 4 4 23%	4576
	11th to 20th	Day	10% 15% 5% 11% 6% 4 4 4 5% 7% 29%	4850
	21st to end	Day	16% 13% 4 9% 5% 4 4 3 4 5% 33%	6055
April	1st to 10th	Day	18% 15% 3 9% 5% 4 4 3 4 5% 30%	2520
	11th to 20th	Day	22% 11% 3 7% 5% 3 4 3 5% 5% 32%	2494
	21st to end	Day	19% 12% 4 9% 5% 4 4 4 4 5% 30%	2685
May	1st to 10th	Day	22% 11% 4 9% 5% 5% 5% 4 6% 6% 23%	8237
	11th to 20th	Day	19% 9% 3 8% 5% 5% 5% 5% 6% 8% 28%	8221
	21st to end	Day	22% 9% 3 7% 5% 5% 5% 4 5% 7% 30%	9060
June	1st to 10th	Day	21% 9% 3 7% 6% 4 5% 4 6% 7% 27%	2940
	11th to 20th	Day	15% 7% 3 8% 6% 5% 5% 5% 6% 7% 31%	2940
	21st to end	Day	21% 9% 3 8% 5% 5% 5% 4 7% 6% 27%	2940
July	1st to 10th	Day	15% 7% 3 9% 6% 6% 6% 4 7% 8% 29%	6500
	11th to 20th	Day	13% 5% 2 6% 5% 5% 5% 5% 7% 9% 38%	6430
	21st to end	Day	10% 5% 2 6% 5% 4 5% 4 7% 10% 43%	6926
August	1st to 10th	Day	14% 6% 2 7% 6% 6% 6% 5% 7% 8% 31%	4563
	11th to 20th	Day	15% 7% 3 7% 5% 5% 5% 5% 7% 8% 34%	4158
	21st to end	Day	15% 6% 2 7% 5% 5% 5% 4 6% 8% 36%	4312
September	1st to 10th	Day	15% 6% 2 6% 4 4 4 4 6% 7% 41%	2400
	11th to 20th	Day	14% 5% 2 6% 4 4 4 3 5% 7% 46%	2335
	21st to end	Day	19% 8% 3 6% 4 4 4 3 5% 7% 39%	2200
October	1st to 10th	Day	21% 7% 3 7% 4 4 4 3 6% 7% 35%	2033
	11th to 20th	Day	21% 11% 3 8% 4 4 6% 4 5% 4 29%	1968
	21st to end	Day	24% 11% 3 9% 5% 4 5% 3 5% 5% 26%	1980
November	1st to 10th	Day	15% 13% 5% 8% 5% 6% 4 3 5% 7% 30%	1851
	11th to 20th	Day	17% 14% 5% 10% 5% 5% 4 4 6% 6% 24%	1759
	21st to end	Day	19% 17% 6% 10% 6% 5% 4 4 5% 5% 20%	1680
December	1st to 10th	Day	16% 17% 11% 13% 5% 4 4 4 5% 5% 16%	2680
	11th to 20th	Day	15% 17% 7% 12% 5% 4 4 3 4 5% 23%	3066
	21st to end	Day	18% 16% 6% 10% 5% 4 3 3 4 5% 25%	4048
January	1st to 10th	Night	9% 18% 8% 14% 6% 5% 5% 3 5% 5% 21%	8234
	11th to 20th	Night	7% 16% 8% 20% 9% 7% 4 3 4 4 18%	8235
	21st to end	Night	6% 11% 6% 16% 8% 7% 6% 4 5% 6% 25%	9057
February	1st to 10th	Night	10% 14% 5% 12% 8% 5% 4 4 6% 5% 27%	2767
	11th to 20th	Night	9% 14% 6% 11% 7% 5% 5% 4 5% 6% 28%	2586
	21st to end	Night	11% 14% 5% 11% 5% 5% 4 4 6% 6% 28%	2076
March	1st to 10th	Night	18% 15% 5% 11% 5% 4 3 3 4 5% 27%	5484
	11th to 20th	Night	10% 14% 5% 10% 5% 5% 5% 4 6% 8% 29%	5325
	21st to end	Night	14% 11% 4 9% 6% 5% 5% 4 5% 6% 31%	5119
April	1st to 10th	Night	20% 12% 3 7% 6% 4 3 3 5% 6% 30%	2100
	11th to 20th	Night	17% 8% 3 7% 5% 5% 4 4 6% 6% 36%	2075
	21st to end	Night	20% 9% 4 7% 4 4 4 4 5% 5% 35%	1939
May	1st to 10th	Night	18% 11% 4 9% 6% 6% 5% 4 5% 7% 26%	4684
	11th to 20th	Night	20% 8% 3 6% 4 4 4 3 6% 7% 34%	4639
	21st to end	Night	21% 10% 3 7% 4 4 4 4 6% 6% 30%	5114
June	1st to 10th	Night	18% 7% 3 6% 5% 5% 5% 4 6% 8% 33%	1680
	11th to 20th	Night	18% 8% 2 5% 4 5% 4 4 5% 7% 38%	1680
	21st to end	Night	20% 6% 3 6% 4 5% 5% 4 5% 7% 35%	1680
July	1st to 10th	Night	14% 6% 3 8% 5% 6% 6% 4 7% 8% 34%	3680
	11th to 20th	Night	13% 6% 2 6% 4 4 5% 4 6% 7% 42%	3640
	21st to end	Night	8% 5% 2 5% 4 5% 5% 4 6% 8% 48%	3926
August	1st to 10th	Night	12% 5% 3 8% 4 5% 5% 5% 6% 8% 40%	2586
	11th to 20th	Night	15% 7% 2 7% 4 4 4 3 6% 6% 43%	2853
	21st to end	Night	17% 5% 2 7% 4 5% 4 3 5% 6% 42%	3586
September	1st to 10th	Night	11% 6% 2 6% 4 4 4 4 6% 7% 48%	2000
	11th to 20th	Night	13% 5% 2 5% 4 3 3 3 5% 8% 49%	2065
	21st to end	Night	17% 6% 2 6% 4 4 4 3 5% 7% 44%	2200
October	1st to 10th	Night	16% 7% 3 7% 5% 4 5% 3 4 6% 41%	2364
	11th to 20th	Night	19% 9% 2 7% 5% 5% 5% 4 5% 6% 34%	2431
	21st to end	Night	22% 9% 3 7% 6% 4 5% 3 5% 7% 30%	2860
November	1st to 10th	Night	17% 10% 4 8% 6% 5% 5% 4 6% 7% 29%	2667
	11th to 20th	Night	15% 11% 4 10% 6% 6% 5% 4 5% 7% 28%	2860
	21st to end	Night	17% 16% 5% 11% 5% 4 4 3 5% 5% 24%	2940
December	1st to 10th	Night	15% 13% 6% 13% 6% 5% 6% 4 6% 7% 19%	4720
	11th to 20th	Night	20% 14% 5% 11% 7% 5% 4 3 3 4 25%	5348
	21st to end	Night	19% 20% 5% 9% 5% 3 3 2 3 5% 27%	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	64% 5% 9% 16% 6%	4662
	11th to 20th	Day	67% 7% 3 11% 9% 2	4680
	21st to end	Day	60% 6% 8% 13% 13% 1	5124
February	1st to 10th	Day	60% 5% 8% 17% 8% 2	1850
	11th to 20th	Day	58% 6% 10% 15% 11% 1	1928
	21st to end	Day	61% 5% 8% 14% 10% 3	1730
March	1st to 10th	Day	64% 6% 6% 10% 11% 3	4579
	11th to 20th	Day	52% 8% 14% 12% 11% 3	4850
	21st to end	Day	52% 6% 8% 15% 17% 3	6055
April	1st to 10th	Day	55% 6% 9% 16% 11% 2	2520
	11th to 20th	Day	52% 7% 9% 20% 12% 2	2494
	21st to end	Day	54% 6% 8% 17% 12% 3	2685
May	1st to 10th	Day	58% 7% 8% 18% 9% 1	8249
	11th to 20th	Day	50% 9% 14% 18% 7% 2	8225
	21st to end	Day	51% 7% 10% 19% 11% 1	9061
June	1st to 10th	Day	53% 8% 10% 17% 11% 1	2940
	11th to 20th	Day	47% 8% 12% 19% 10% 3	2940
	21st to end	Day	55% 8% 11% 17% 8% 1	2940
July	1st to 10th	Day	50% 7% 13% 22% 7%	6430
	11th to 20th	Day	39% 7% 16% 30% 8%	6355
	21st to end	Day	35% 7% 17% 31% 9%	6728
August	1st to 10th	Day	45% 9% 18% 21% 6%	4549
	11th to 20th	Day	44% 9% 16% 25% 6%	4200
	21st to end	Day	44% 7% 15% 21% 12% 1	4312
September	1st to 10th	Day	40% 8% 14% 26% 12%	2400
	11th to 20th	Day	36% 7% 15% 29% 12% 1	2335
	21st to end	Day	45% 8% 12% 24% 12%	2200
October	1st to 10th	Day	44% 7% 13% 27% 9%	3306
	11th to 20th	Day	47% 8% 13% 24% 8% 1	3184
	21st to end	Day	48% 6% 21% 16% 9% 1	3180
November	1st to 10th	Day	52% 8% 13% 18% 9% 1	1851
	11th to 20th	Day	56% 9% 12% 13% 10% 1	1759
	21st to end	Day	63% 9% 10% 12% 5% 1	1680
December	1st to 10th	Day	69% 5% 9% 12% 4	2680
	11th to 20th	Day	61% 6% 8% 15% 9%	3066
	21st to end	Day	61% 6% 8% 15% 10%	4048
January	1st to 10th	Night	63% 7% 9% 15% 6% 1	8234
	11th to 20th	Night	66% 8% 9% 11% 6% 1	8280
	21st to end	Night	57% 8% 9% 12% 14% 1	9057
February	1st to 10th	Night	57% 6% 10% 18% 8% 1	2767
	11th to 20th	Night	54% 8% 10% 18% 9% 1	2588
	21st to end	Night	54% 6% 10% 17% 10% 2	2076
March	1st to 10th	Night	60% 6% 7% 11% 12% 3	5494
	11th to 20th	Night	49% 9% 13% 15% 11% 3	5326
	21st to end	Night	51% 6% 8% 20% 12% 3	5119
April	1st to 10th	Night	54% 5% 9% 18% 13% 2	2100
	11th to 20th	Night	46% 7% 11% 20% 14% 2	2075
	21st to end	Night	49% 7% 10% 19% 14% 2	1939
May	1st to 10th	Night	53% 9% 12% 17% 8% 1	4690
	11th to 20th	Night	47% 8% 14% 20% 9% 1	4640
	21st to end	Night	52% 7% 10% 19% 12% 1	5115
June	1st to 10th	Night	46% 8% 12% 21% 12%	1680
	11th to 20th	Night	45% 7% 11% 22% 13% 2	1680
	21st to end	Night	47% 8% 13% 19% 12% 1	1680
July	1st to 10th	Night	45% 7% 19% 20% 8%	3640
	11th to 20th	Night	38% 8% 19% 30% 6%	3592
	21st to end	Night	33% 7% 18% 31% 11%	3809
August	1st to 10th	Night	40% 8% 17% 27% 8%	2576
	11th to 20th	Night	41% 7% 19% 25% 8%	2877
	21st to end	Night	42% 7% 16% 23% 11% 2	3586
September	1st to 10th	Night	34% 9% 16% 27% 14% 1	2000
	11th to 20th	Night	33% 7% 17% 32% 11% 1	2065
	21st to end	Night	39% 8% 13% 28% 13%	2200
October	1st to 10th	Night	43% 6% 13% 25% 12% 1	3871
	11th to 20th	Night	43% 7% 12% 27% 10%	3954
	21st to end	Night	46% 7% 18% 17% 11% 2	4610
November	1st to 10th	Night	52% 8% 14% 19% 6% 1	2667
	11th to 20th	Night	52% 9% 13% 16% 8% 2	2860
	21st to end	Night	59% 9% 11% 15% 6% 1	2940
December	1st to 10th	Night	62% 7% 13% 14% 4	4720
	11th to 20th	Night	62% 6% 6% 14% 10% 1	5348
	21st to end	Night	61% 5% 6% 12% 14% 1	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	16% 27% 39% 16% 2	220
	11th to 20th	Day	28% 23% 33% 12% 4	220
	21st to end	Day	20% 22% 40% 14% 4 1	242
February	1st to 10th	Day	30% 30% 32% 7% 1	310
	11th to 20th	Day	25% 27% 38% 9% 1	406
	21st to end	Day	27% 24% 34% 13% 2	446
March	1st to 10th	Day	27% 24% 33% 13% 3	540
	11th to 20th	Day	27% 25% 33% 12% 3	540
	21st to end	Day	30% 25% 26% 13% 5% 1	594
April	1st to 10th	Day	33% 20% 32% 11% 4 1	540
	11th to 20th	Day	37% 20% 23% 13% 7% 1	532
	21st to end	Day	31% 21% 33% 11% 4 1	540
May	1st to 10th	Day	28% 22% 31% 14% 3 1	543
	11th to 20th	Day	26% 20% 30% 17% 5% 1	567
	21st to end	Day	27% 21% 29% 18% 4	617
June	1st to 10th	Day	26% 16% 36% 15% 6% 1	570
	11th to 20th	Day	19% 22% 34% 16% 9% 1	570
	21st to end	Day	24% 16% 33% 19% 7% 1	570
July	1st to 10th	Day	15% 13% 39% 23% 7% 2	565
	11th to 20th	Day	16% 15% 38% 26% 6% 1	544
	21st to end	Day	14% 13% 37% 26% 9% 1	576
August	1st to 10th	Day	16% 10% 30% 32% 10% 2	526
	11th to 20th	Day	14% 11% 30% 27% 13% 5%	519
	21st to end	Day	17% 17% 29% 21% 11% 5%	583
September	1st to 10th	Day	18% 13% 34% 20% 10% 5%	530
	11th to 20th	Day	12% 14% 27% 25% 16% 7%	530
	21st to end	Day	22% 15% 25% 21% 12% 4	530
October	1st to 10th	Day	25% 17% 27% 19% 10% 2	530
	11th to 20th	Day	26% 22% 29% 17% 6% 1	511
	21st to end	Day	31% 17% 32% 16% 3	462
November	1st to 10th	Day	31% 20% 28% 16% 3 1	425
	11th to 20th	Day	26% 24% 31% 14% 5%	299
	21st to end	Day	30% 27% 29% 11% 2	220
December	1st to 10th	Day	27% 23% 30% 15% 5%	220
	11th to 20th	Day	25% 28% 36% 8% 2	220
	21st to end	Day	32% 23% 28% 11% 5% 1	242
January	1st to 10th	Night	22% 20% 36% 17% 4	840
	11th to 20th	Night	22% 23% 30% 21% 4	840
	21st to end	Night	15% 17% 40% 22% 5% 1	924
February	1st to 10th	Night	17% 22% 37% 19% 4	840
	11th to 20th	Night	21% 21% 40% 15% 3	823
	21st to end	Night	21% 18% 37% 22% 2	692
March	1st to 10th	Night	25% 19% 34% 18% 3	840
	11th to 20th	Night	23% 21% 33% 17% 4 1	840
	21st to end	Night	23% 19% 32% 22% 4 1	924
April	1st to 10th	Night	28% 19% 30% 20% 4	840
	11th to 20th	Night	24% 18% 31% 22% 5% 1	831
	21st to end	Night	26% 17% 32% 19% 7%	679
May	1st to 10th	Night	23% 13% 35% 22% 6% 1	431
	11th to 20th	Night	21% 14% 29% 28% 6%	414
	21st to end	Night	21% 12% 39% 21% 7%	455
June	1st to 10th	Night	22% 8% 37% 26% 8%	420
	11th to 20th	Night	22% 9% 27% 31% 10% 1	420
	21st to end	Night	20% 8% 27% 31% 12%	420
July	1st to 10th	Night	13% 8% 32% 35% 12%	410
	11th to 20th	Night	12% 7% 26% 42% 13% 1	398
	21st to end	Night	12% 7% 27% 41% 12% 1	438
August	1st to 10th	Night	13% 5% 22% 44% 16% 1	398
	11th to 20th	Night	12% 6% 25% 33% 22% 1	569
	21st to end	Night	16% 9% 29% 29% 15% 2	880
September	1st to 10th	Night	14% 7% 32% 33% 12% 1	800
	11th to 20th	Night	14% 10% 25% 31% 19% 2	800
	21st to end	Night	20% 11% 26% 26% 15% 2	800
October	1st to 10th	Night	20% 14% 28% 25% 12% 1	800
	11th to 20th	Night	25% 15% 30% 22% 8% 1	800
	21st to end	Night	27% 14% 32% 22% 5%	880
November	1st to 10th	Night	24% 19% 30% 21% 5% 1	820
	11th to 20th	Night	24% 18% 31% 19% 8% 1	840
	21st to end	Night	27% 24% 27% 17% 4 1	840
December	1st to 10th	Night	26% 19% 31% 18% 5%	840
	11th to 20th	Night	27% 22% 30% 17% 4 1	840
	21st to end	Night	31% 20% 30% 16% 4	924

Page generated at 2026-07-13 03:14:48. Version ac07

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