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 2025-03-12.

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% 30%	108821
	Night	15% 12% 4 10% 6% 5% 4 3 5% 6% 31%	110177
Transparency	Day	51% 8% 12% 18% 9% 1	112301
	Night	51% 8% 12% 18% 10% 1	114861
Seeing	Day	24% 19% 32% 18% 6% 2	14836
	Night	21% 16% 31% 23% 8% 1	23971

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% 22% 7% 13% 6% 4 6% 3 4 4 19%	3597
	11th to 20th	Day	10% 16% 6% 17% 10% 5% 4 3 3 4 21%	3570
	21st to end	Day	7% 13% 8% 17% 6% 5% 5% 4 5% 5% 25%	3960
February	1st to 10th	Day	10% 19% 6% 11% 8% 5% 4 4 4 7% 23%	1762
	11th to 20th	Day	11% 17% 7% 12% 6% 6% 5% 3 5% 5% 25%	1825
	21st to end	Day	14% 18% 6% 10% 7% 4 4 3 4 5% 25%	1650
March	1st to 10th	Day	16% 18% 5% 11% 7% 5% 4 3 4 5% 24%	3216
	11th to 20th	Day	11% 18% 6% 13% 6% 4 4 3 5% 5% 25%	3325
	21st to end	Day	13% 11% 3 8% 4 5% 5% 3 5% 6% 37%	4134
April	1st to 10th	Day	18% 15% 3 9% 5% 4 4 3 5% 5% 30%	2280
	11th to 20th	Day	21% 10% 3 7% 5% 3 4 3 5% 5% 33%	2254
	21st to end	Day	20% 12% 4 9% 5% 4 4 4 4 5% 30%	2428
May	1st to 10th	Day	21% 11% 3 8% 4 5% 4 4 5% 6% 29%	4426
	11th to 20th	Day	19% 8% 3 8% 5% 5% 4 4 7% 8% 30%	4398
	21st to end	Day	17% 7% 3 7% 5% 5% 5% 4 6% 7% 34%	4837
June	1st to 10th	Day	22% 9% 3 7% 6% 4 5% 4 6% 7% 27%	2660
	11th to 20th	Day	15% 7% 3 8% 6% 5% 5% 5% 6% 7% 32%	2660
	21st to end	Day	22% 9% 3 8% 5% 5% 5% 4 6% 6% 26%	2660
July	1st to 10th	Day	13% 7% 2 8% 6% 6% 6% 5% 7% 8% 31%	4440
	11th to 20th	Day	15% 6% 2 6% 5% 5% 6% 5% 7% 8% 34%	4440
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 3 6% 7% 43%	4814
August	1st to 10th	Day	15% 6% 2 8% 6% 6% 6% 6% 7% 8% 30%	4423
	11th to 20th	Day	15% 7% 3 7% 5% 5% 5% 5% 7% 8% 34%	4029
	21st to end	Day	15% 6% 2 7% 5% 5% 5% 3 6% 8% 37%	4180
September	1st to 10th	Day	15% 6% 3 7% 4 4 4 4 6% 7% 40%	2280
	11th to 20th	Day	14% 5% 3 6% 4 4 4 3 5% 7% 44%	2218
	21st to end	Day	19% 8% 3 6% 4 4 4 3 5% 7% 38%	2090
October	1st to 10th	Day	21% 8% 3 8% 4 4 4 3 6% 7% 33%	1932
	11th to 20th	Day	21% 11% 4 9% 4 4 6% 4 5% 4 27%	1870
	21st to end	Day	24% 11% 3 9% 5% 4 4 3 5% 5% 26%	1881
November	1st to 10th	Day	15% 11% 4 8% 5% 6% 4 3 5% 7% 31%	1761
	11th to 20th	Day	17% 13% 5% 10% 5% 5% 4 4 6% 6% 25%	1675
	21st to end	Day	19% 16% 6% 10% 6% 5% 4 4 6% 5% 21%	1600
December	1st to 10th	Day	16% 17% 11% 13% 5% 4 4 4 5% 5% 16%	2600
	11th to 20th	Day	15% 17% 7% 12% 5% 4 4 3 4 5% 24%	2986
	21st to end	Day	18% 17% 6% 9% 4 4 3 3 4 5% 25%	3960
January	1st to 10th	Night	10% 21% 9% 14% 6% 5% 4 3 4 5% 20%	6349
	11th to 20th	Night	7% 13% 7% 19% 9% 7% 5% 3 4 5% 21%	6315
	21st to end	Night	7% 12% 7% 17% 8% 7% 6% 3 4 6% 24%	6996
February	1st to 10th	Night	10% 15% 5% 12% 8% 6% 5% 4 6% 5% 26%	2635
	11th to 20th	Night	9% 14% 6% 11% 7% 5% 5% 4 5% 6% 27%	2460
	21st to end	Night	11% 14% 6% 11% 5% 5% 4 4 6% 6% 28%	1980
March	1st to 10th	Night	17% 14% 5% 9% 5% 4 4 3 4 5% 30%	3844
	11th to 20th	Night	12% 18% 6% 11% 5% 4 5% 3 4 6% 27%	3659
	21st to end	Night	12% 10% 4 9% 6% 5% 5% 3 4 5% 36%	3498
April	1st to 10th	Night	20% 12% 3 7% 7% 4 3 3 5% 6% 30%	1900
	11th to 20th	Night	18% 8% 3 7% 5% 5% 4 4 6% 6% 36%	1875
	21st to end	Night	19% 9% 4 7% 4 4 4 4 5% 5% 35%	1755
May	1st to 10th	Night	17% 11% 3 8% 6% 5% 4 4 4 7% 30%	2524
	11th to 20th	Night	21% 7% 3 5% 5% 4 3 2 5% 7% 38%	2495
	21st to end	Night	17% 8% 3 8% 5% 4 5% 4 6% 7% 33%	2738
June	1st to 10th	Night	19% 7% 4 6% 5% 4 5% 4 6% 8% 31%	1520
	11th to 20th	Night	18% 8% 2 5% 5% 5% 4 4 5% 6% 38%	1520
	21st to end	Night	20% 7% 3 6% 4 5% 4 4 5% 7% 35%	1520
July	1st to 10th	Night	13% 6% 3 8% 6% 6% 5% 5% 6% 7% 35%	2520
	11th to 20th	Night	15% 6% 2 6% 4 4 5% 4 6% 7% 42%	2520
	21st to end	Night	10% 6% 2 5% 4 4 5% 4 6% 8% 47%	2739
August	1st to 10th	Night	12% 5% 3 8% 4 5% 5% 5% 6% 8% 40%	2506
	11th to 20th	Night	15% 7% 2 7% 4 4 4 3 6% 6% 42%	2764
	21st to end	Night	17% 5% 2 7% 4 4 4 3 5% 6% 42%	3476
September	1st to 10th	Night	11% 6% 2 6% 4 4 4 4 6% 7% 47%	1900
	11th to 20th	Night	13% 5% 2 5% 4 3 3 3 5% 8% 48%	1962
	21st to end	Night	18% 6% 2 5% 4 4 4 3 5% 7% 43%	2090
October	1st to 10th	Night	17% 7% 3 8% 5% 4 5% 3 4 6% 39%	2246
	11th to 20th	Night	20% 9% 3 7% 5% 5% 5% 4 5% 5% 33%	2309
	21st to end	Night	22% 9% 4 8% 6% 4 5% 3 5% 7% 29%	2717
November	1st to 10th	Night	16% 10% 4 9% 6% 5% 5% 4 7% 6% 29%	2537
	11th to 20th	Night	15% 11% 4 10% 5% 5% 5% 3 6% 7% 29%	2724
	21st to end	Night	17% 16% 5% 11% 5% 4 4 3 5% 5% 25%	2800
December	1st to 10th	Night	15% 13% 6% 12% 6% 5% 6% 4 6% 7% 19%	4580
	11th to 20th	Night	21% 14% 5% 11% 6% 5% 4 3 3 4 25%	5208
	21st to end	Night	19% 20% 4 9% 5% 3 3 2 3 5% 27%	6996

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	67% 6% 8% 14% 4	3598
	11th to 20th	Day	64% 9% 4 13% 8% 2	3600
	21st to end	Day	59% 7% 7% 13% 12% 2	3960
February	1st to 10th	Day	61% 5% 8% 15% 8% 2	1762
	11th to 20th	Day	59% 6% 10% 14% 10% 1	1834
	21st to end	Day	61% 5% 8% 14% 9% 3	1650
March	1st to 10th	Day	61% 7% 6% 13% 11% 2	3219
	11th to 20th	Day	57% 10% 10% 11% 10% 3	3325
	21st to end	Day	44% 7% 10% 19% 17% 3	4134
April	1st to 10th	Day	55% 6% 9% 16% 11% 3	2280
	11th to 20th	Day	51% 7% 9% 20% 11% 2	2254
	21st to end	Day	55% 7% 8% 16% 11% 4	2428
May	1st to 10th	Day	52% 9% 10% 19% 9% 1	4440
	11th to 20th	Day	46% 12% 19% 14% 8% 1	4402
	21st to end	Day	45% 10% 12% 18% 14% 1	4837
June	1st to 10th	Day	54% 8% 11% 16% 10% 1	2660
	11th to 20th	Day	47% 8% 13% 18% 11% 3	2660
	21st to end	Day	57% 8% 10% 16% 9%	2660
July	1st to 10th	Day	47% 9% 14% 23% 8%	4370
	11th to 20th	Day	43% 8% 18% 25% 6%	4365
	21st to end	Day	39% 7% 15% 29% 10%	4661
August	1st to 10th	Day	47% 9% 17% 21% 6%	4409
	11th to 20th	Day	44% 9% 16% 25% 5%	4071
	21st to end	Day	44% 7% 15% 21% 13% 1	4180
September	1st to 10th	Day	41% 8% 14% 25% 13%	2280
	11th to 20th	Day	38% 8% 15% 28% 11% 1	2218
	21st to end	Day	45% 7% 12% 25% 11%	2090
October	1st to 10th	Day	46% 7% 13% 26% 8%	3205
	11th to 20th	Day	47% 8% 13% 24% 7%	3086
	21st to end	Day	48% 6% 21% 15% 9% 1	3081
November	1st to 10th	Day	51% 8% 14% 18% 9% 1	1761
	11th to 20th	Day	56% 9% 11% 13% 10% 1	1675
	21st to end	Day	62% 10% 11% 13% 4 1	1600
December	1st to 10th	Day	69% 6% 9% 12% 4	2600
	11th to 20th	Day	61% 6% 8% 15% 9%	2986
	21st to end	Day	61% 6% 8% 14% 10%	3960
January	1st to 10th	Night	65% 8% 10% 13% 4	6349
	11th to 20th	Night	61% 10% 10% 12% 5% 1	6360
	21st to end	Night	59% 8% 8% 10% 14% 1	6996
February	1st to 10th	Night	57% 6% 10% 17% 8% 1	2635
	11th to 20th	Night	54% 8% 11% 18% 8% 1	2462
	21st to end	Night	54% 7% 10% 17% 11% 2	1980
March	1st to 10th	Night	55% 8% 9% 13% 11% 3	3854
	11th to 20th	Night	55% 9% 10% 13% 12% 1	3660
	21st to end	Night	47% 7% 10% 19% 13% 4	3498
April	1st to 10th	Night	53% 5% 10% 18% 13% 2	1900
	11th to 20th	Night	46% 7% 11% 20% 14% 2	1875
	21st to end	Night	49% 7% 10% 19% 12% 3	1755
May	1st to 10th	Night	48% 12% 12% 17% 8% 2	2530
	11th to 20th	Night	42% 10% 19% 15% 12% 2	2496
	21st to end	Night	46% 10% 11% 18% 13% 2	2739
June	1st to 10th	Night	47% 9% 13% 20% 11%	1520
	11th to 20th	Night	45% 7% 11% 22% 13% 2	1520
	21st to end	Night	48% 9% 12% 19% 12% 1	1520
July	1st to 10th	Night	45% 8% 18% 19% 10%	2480
	11th to 20th	Night	39% 8% 20% 28% 6%	2472
	21st to end	Night	33% 8% 20% 27% 12%	2651
August	1st to 10th	Night	41% 8% 16% 27% 7%	2496
	11th to 20th	Night	41% 7% 19% 25% 7%	2788
	21st to end	Night	42% 7% 16% 23% 11% 2	3476
September	1st to 10th	Night	34% 9% 16% 26% 14% 1	1900
	11th to 20th	Night	33% 7% 17% 31% 10% 1	1962
	21st to end	Night	39% 8% 13% 28% 12%	2090
October	1st to 10th	Night	44% 6% 13% 25% 12% 1	3753
	11th to 20th	Night	44% 7% 12% 27% 10%	3832
	21st to end	Night	46% 7% 18% 16% 11% 2	4467
November	1st to 10th	Night	51% 9% 14% 19% 6% 1	2537
	11th to 20th	Night	52% 9% 12% 16% 9% 2	2724
	21st to end	Night	58% 9% 12% 15% 6% 1	2800
December	1st to 10th	Night	62% 7% 13% 14% 4	4580
	11th to 20th	Night	62% 6% 6% 14% 10% 1	5208
	21st to end	Night	61% 6% 6% 12% 14% 1	6996

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	17% 27% 40% 15% 2	200
	11th to 20th	Day	27% 22% 34% 13% 5% 1	200
	21st to end	Day	19% 23% 40% 13% 4 1	220
February	1st to 10th	Day	32% 32% 29% 6% 1	282
	11th to 20th	Day	26% 28% 38% 8% 1	372
	21st to end	Day	28% 25% 31% 14% 2	414
March	1st to 10th	Day	28% 22% 33% 14% 3	500
	11th to 20th	Day	25% 25% 33% 13% 3	464
	21st to end	Day	30% 24% 26% 14% 5% 1	506
April	1st to 10th	Day	30% 19% 33% 13% 4 1	460
	11th to 20th	Day	34% 21% 24% 13% 7% 1	452
	21st to end	Day	30% 20% 34% 12% 3 1	460
May	1st to 10th	Day	26% 23% 33% 14% 3 1	463
	11th to 20th	Day	24% 20% 31% 19% 6% 1	487
	21st to end	Day	24% 20% 32% 19% 5%	529
June	1st to 10th	Day	25% 17% 36% 16% 6% 1	490
	11th to 20th	Day	18% 21% 33% 17% 10% 1	490
	21st to end	Day	25% 17% 32% 19% 6% 1	490
July	1st to 10th	Day	14% 12% 39% 25% 8% 2	485
	11th to 20th	Day	16% 13% 37% 27% 6% 1	484
	21st to end	Day	15% 12% 36% 27% 9% 1	532
August	1st to 10th	Day	17% 11% 31% 29% 10% 1	486
	11th to 20th	Day	14% 11% 30% 27% 12% 5%	479
	21st to end	Day	16% 17% 30% 20% 10% 6%	539
September	1st to 10th	Day	18% 12% 34% 21% 10% 5%	490
	11th to 20th	Day	13% 14% 27% 25% 14% 7%	490
	21st to end	Day	22% 16% 25% 22% 12% 4	490
October	1st to 10th	Day	26% 18% 26% 18% 10% 2	490
	11th to 20th	Day	27% 22% 27% 16% 6% 1	473
	21st to end	Day	31% 17% 33% 16% 3	429
November	1st to 10th	Day	31% 20% 29% 16% 4 1	395
	11th to 20th	Day	25% 25% 31% 13% 5%	275
	21st to end	Day	30% 28% 30% 11% 2	200
December	1st to 10th	Day	30% 21% 29% 16% 6%	200
	11th to 20th	Day	26% 29% 35% 9% 2	200
	21st to end	Day	33% 24% 26% 11% 5% 1	220
January	1st to 10th	Night	23% 21% 36% 17% 4	800
	11th to 20th	Night	21% 23% 31% 21% 4	800
	21st to end	Night	15% 16% 41% 23% 5% 1	880
February	1st to 10th	Night	18% 23% 37% 19% 4	800
	11th to 20th	Night	21% 21% 40% 15% 3	783
	21st to end	Night	21% 19% 36% 22% 2	660
March	1st to 10th	Night	25% 19% 34% 19% 3	800
	11th to 20th	Night	23% 22% 34% 17% 4 1	767
	21st to end	Night	21% 18% 33% 22% 5% 1	836
April	1st to 10th	Night	27% 19% 29% 21% 5%	760
	11th to 20th	Night	24% 18% 30% 22% 5% 1	751
	21st to end	Night	26% 17% 32% 19% 7%	615
May	1st to 10th	Night	22% 13% 36% 22% 6% 2	390
	11th to 20th	Night	21% 15% 29% 29% 6% 1	374
	21st to end	Night	19% 12% 41% 21% 7%	411
June	1st to 10th	Night	22% 8% 36% 26% 7%	380
	11th to 20th	Night	22% 9% 26% 32% 11% 1	380
	21st to end	Night	21% 7% 28% 30% 13% 1	380
July	1st to 10th	Night	14% 7% 31% 35% 13% 1	370
	11th to 20th	Night	11% 7% 27% 40% 14% 1	368
	21st to end	Night	13% 6% 27% 41% 13% 1	416
August	1st to 10th	Night	13% 5% 22% 44% 15%	378
	11th to 20th	Night	12% 6% 25% 33% 22% 1	540
	21st to end	Night	15% 9% 30% 29% 16% 2	836
September	1st to 10th	Night	15% 7% 33% 33% 11% 1	760
	11th to 20th	Night	14% 10% 25% 31% 18% 2	760
	21st to end	Night	20% 12% 26% 26% 15% 2	760
October	1st to 10th	Night	21% 14% 28% 25% 12% 1	760
	11th to 20th	Night	25% 16% 29% 22% 8% 1	760
	21st to end	Night	28% 15% 31% 21% 5%	836
November	1st to 10th	Night	23% 19% 30% 21% 6% 1	780
	11th to 20th	Night	23% 19% 31% 19% 8% 1	800
	21st to end	Night	27% 24% 27% 17% 4 1	800
December	1st to 10th	Night	26% 19% 31% 17% 5% 1	800
	11th to 20th	Night	27% 21% 29% 18% 4 1	800
	21st to end	Night	30% 20% 30% 16% 4	880

Page generated at 2025-03-09 08:08:45. Version ac07

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