Lac des Piles
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lac des Piles clear sky chart from 2005-11-06 to 2026-09-14.

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% 10% 3 8% 5% 5% 5% 4 5% 7% 31%	149194
	Night	16% 11% 4 9% 5% 4 5% 3 5% 6% 31%	141864
Transparency	Day	51% 5% 13% 20% 10% 1	152628
	Night	53% 5% 12% 20% 10% 1	146520
Seeing	Day	23% 14% 31% 21% 9% 2	16855
	Night	24% 10% 29% 28% 9% 1	25778

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	13% 16% 5% 12% 5% 6% 5% 3 4 5% 25%	4661
	11th to 20th	Day	11% 17% 7% 16% 7% 6% 4 3 4 5% 21%	4650
	21st to end	Day	7% 11% 6% 12% 6% 5% 5% 4 5% 7% 30%	5124
February	1st to 10th	Day	12% 16% 5% 12% 7% 6% 4 2 3 5% 27%	1754
	11th to 20th	Day	12% 16% 6% 11% 5% 5% 4 3 5% 6% 27%	1972
	21st to end	Day	14% 16% 5% 10% 7% 5% 5% 3 3 5% 28%	1730
March	1st to 10th	Day	21% 16% 4 10% 6% 4 4 3 4 4 25%	4576
	11th to 20th	Day	12% 15% 4 10% 5% 5% 5% 3 5% 6% 31%	4751
	21st to end	Day	16% 14% 4 8% 5% 4 4 3 3 4 33%	6102
April	1st to 10th	Day	22% 13% 4 8% 4 4 4 3 4 5% 30%	2520
	11th to 20th	Day	22% 8% 2 8% 4 4 4 3 5% 5% 35%	2524
	21st to end	Day	21% 11% 3 7% 4 5% 4 4 5% 6% 30%	2730
May	1st to 10th	Day	25% 10% 3 8% 5% 5% 5% 4 5% 6% 26%	8075
	11th to 20th	Day	21% 7% 3 7% 5% 4 4 4 5% 8% 32%	8221
	21st to end	Day	21% 8% 3 8% 5% 5% 5% 4 6% 6% 29%	9060
June	1st to 10th	Day	20% 8% 2 7% 6% 5% 6% 4 6% 7% 28%	2940
	11th to 20th	Day	17% 7% 2 7% 5% 5% 5% 4 6% 7% 33%	2940
	21st to end	Day	22% 9% 3 8% 6% 5% 4 4 5% 7% 27%	2940
July	1st to 10th	Day	14% 6% 2 8% 5% 5% 5% 5% 6% 8% 36%	8280
	11th to 20th	Day	13% 5% 2 7% 5% 5% 5% 5% 8% 10% 36%	8280
	21st to end	Day	12% 5% 2 7% 5% 5% 6% 5% 8% 8% 37%	8993
August	1st to 10th	Day	15% 6% 3 7% 6% 6% 6% 5% 8% 9% 31%	6483
	11th to 20th	Day	17% 7% 3 6% 4 5% 6% 5% 7% 9% 32%	6074
	21st to end	Day	16% 6% 2 6% 4 5% 5% 4 6% 9% 35%	6081
September	1st to 10th	Day	15% 5% 2 6% 4 4 5% 3 7% 7% 41%	2520
	11th to 20th	Day	15% 6% 2 5% 3 4 4 3 5% 7% 46%	2317
	21st to end	Day	21% 7% 3 6% 3 4 3 3 4 7% 40%	2200
October	1st to 10th	Day	20% 8% 2 6% 4 4 5% 3 4 7% 36%	2110
	11th to 20th	Day	21% 10% 2 8% 6% 6% 4 5% 5% 6% 27%	1896
	21st to end	Day	26% 11% 3 7% 4 4 4 3 4 6% 27%	1980
November	1st to 10th	Day	18% 11% 4 8% 6% 5% 5% 3 4 5% 32%	1851
	11th to 20th	Day	21% 13% 4 8% 6% 4 4 4 4 6% 27%	1811
	21st to end	Day	21% 16% 5% 7% 6% 4 4 3 4 5% 24%	1680
December	1st to 10th	Day	19% 17% 6% 11% 6% 5% 4 3 4 4 22%	2460
	11th to 20th	Day	18% 13% 5% 10% 4 5% 4 3 5% 5% 28%	2860
	21st to end	Day	19% 15% 5% 10% 6% 4 4 3 4 4 26%	4048
January	1st to 10th	Night	12% 17% 7% 14% 6% 5% 5% 3 4 5% 21%	8234
	11th to 20th	Night	10% 20% 7% 15% 7% 5% 5% 3 4 5% 19%	8235
	21st to end	Night	7% 11% 5% 14% 8% 7% 6% 4 6% 6% 27%	9057
February	1st to 10th	Night	11% 14% 4 11% 6% 5% 5% 4 5% 5% 30%	2863
	11th to 20th	Night	12% 15% 5% 11% 7% 5% 5% 3 4 6% 28%	2533
	21st to end	Night	14% 12% 5% 9% 6% 5% 5% 4 5% 5% 31%	2076
March	1st to 10th	Night	22% 14% 4 11% 6% 4 4 3 4 4 23%	5484
	11th to 20th	Night	14% 14% 4 8% 5% 5% 5% 4 6% 7% 28%	5424
	21st to end	Night	16% 11% 4 9% 5% 5% 5% 4 5% 5% 31%	5072
April	1st to 10th	Night	22% 11% 3 7% 4 4 4 4 5% 6% 31%	2100
	11th to 20th	Night	20% 9% 3 7% 4 4 4 3 5% 6% 36%	2044
	21st to end	Night	22% 9% 3 7% 4 3 4 3 4 6% 36%	1890
May	1st to 10th	Night	23% 9% 2 8% 5% 4 5% 4 5% 7% 29%	4866
	11th to 20th	Night	22% 6% 2 6% 4 4 5% 4 5% 8% 33%	4639
	21st to end	Night	20% 8% 3 8% 5% 5% 4 3 5% 7% 31%	5114
June	1st to 10th	Night	20% 6% 2 6% 4 4 5% 4 6% 7% 35%	1680
	11th to 20th	Night	19% 7% 2 6% 5% 4 4 4 6% 8% 35%	1680
	21st to end	Night	19% 7% 3 7% 5% 4 5% 4 5% 7% 33%	1680
July	1st to 10th	Night	13% 6% 2 6% 5% 5% 5% 4 7% 9% 37%	4680
	11th to 20th	Night	13% 5% 2 6% 4 4 5% 4 7% 8% 42%	4680
	21st to end	Night	13% 5% 2 6% 5% 5% 5% 4 6% 8% 41%	5084
August	1st to 10th	Night	16% 6% 3 8% 5% 4 5% 4 6% 8% 35%	3666
	11th to 20th	Night	16% 6% 2 6% 4 4 4 3 6% 7% 40%	3924
	21st to end	Night	17% 8% 2 8% 4 4 4 3 4 6% 40%	5040
September	1st to 10th	Night	13% 6% 2 6% 4 4 4 5% 5% 7% 45%	2100
	11th to 20th	Night	14% 5% 2 4 4 3 3 3 5% 7% 50%	2149
	21st to end	Night	18% 6% 2 5% 4 3 4 3 5% 6% 45%	2200
October	1st to 10th	Night	18% 8% 3 6% 5% 3 4 3 5% 5% 42%	2287
	11th to 20th	Night	21% 8% 3 6% 5% 4 4 3 5% 6% 35%	2503
	21st to end	Night	24% 9% 3 7% 4 4 4 3 4 7% 30%	2860
November	1st to 10th	Night	19% 10% 3 8% 5% 4 4 3 5% 6% 32%	2667
	11th to 20th	Night	19% 10% 3 8% 5% 4 5% 3 6% 6% 30%	2805
	21st to end	Night	22% 15% 4 7% 5% 4 4 3 5% 5% 26%	2940
December	1st to 10th	Night	15% 14% 5% 10% 6% 5% 5% 4 5% 6% 23%	4924
	11th to 20th	Night	23% 12% 4 9% 6% 4 5% 3 4 4 26%	5534
	21st to end	Night	20% 17% 6% 9% 4 3 3 2 3 4 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	61% 4 13% 17% 6%	4662
	11th to 20th	Day	66% 3 8% 14% 8% 1	4680
	21st to end	Day	53% 4 9% 19% 14% 1	5124
February	1st to 10th	Day	61% 2 9% 18% 9% 2	1754
	11th to 20th	Day	57% 3 12% 15% 11% 1	1981
	21st to end	Day	60% 3 8% 17% 10% 3	1730
March	1st to 10th	Day	63% 3 9% 12% 11% 3	4579
	11th to 20th	Day	53% 5% 16% 14% 11% 1	4751
	21st to end	Day	54% 4 6% 17% 16% 3	6102
April	1st to 10th	Day	57% 3 10% 15% 12% 2	2520
	11th to 20th	Day	51% 3 10% 22% 12% 3	2524
	21st to end	Day	54% 4 10% 18% 13% 3	2730
May	1st to 10th	Day	57% 5% 10% 17% 10% 1	8087
	11th to 20th	Day	49% 5% 17% 20% 7% 2	8225
	21st to end	Day	53% 5% 11% 16% 13% 2	9061
June	1st to 10th	Day	53% 5% 11% 20% 9% 2	2940
	11th to 20th	Day	46% 5% 14% 22% 11% 2	2940
	21st to end	Day	56% 6% 12% 16% 9% 1	2940
July	1st to 10th	Day	43% 7% 14% 24% 12%	8210
	11th to 20th	Day	39% 8% 17% 26% 9%	8205
	21st to end	Day	40% 8% 19% 26% 7%	8795
August	1st to 10th	Day	46% 8% 17% 19% 8% 1	6469
	11th to 20th	Day	44% 8% 21% 21% 6%	6115
	21st to end	Day	42% 8% 18% 21% 11% 1	6081
September	1st to 10th	Day	40% 5% 18% 26% 11% 1	2520
	11th to 20th	Day	37% 4 17% 31% 10% 1	2317
	21st to end	Day	45% 4 13% 27% 10%	2200
October	1st to 10th	Day	46% 7% 13% 27% 7%	3435
	11th to 20th	Day	48% 7% 17% 24% 4	3060
	21st to end	Day	48% 6% 20% 20% 7% 1	3180
November	1st to 10th	Day	54% 4 13% 20% 9% 1	1851
	11th to 20th	Day	57% 4 11% 19% 9%	1811
	21st to end	Day	63% 5% 11% 15% 6%	1680
December	1st to 10th	Day	66% 4 9% 17% 5%	2460
	11th to 20th	Day	58% 4 9% 17% 12%	2861
	21st to end	Day	62% 4 9% 15% 10%	4048
January	1st to 10th	Night	65% 4 10% 14% 5%	8234
	11th to 20th	Night	68% 5% 8% 13% 5%	8280
	21st to end	Night	56% 4 10% 16% 14%	9057
February	1st to 10th	Night	56% 3 10% 19% 10% 1	2863
	11th to 20th	Night	59% 4 9% 18% 10% 1	2535
	21st to end	Night	54% 4 8% 19% 13% 2	2076
March	1st to 10th	Night	65% 3 8% 11% 10% 3	5494
	11th to 20th	Night	54% 5% 13% 15% 10% 2	5425
	21st to end	Night	54% 5% 6% 22% 11% 2	5072
April	1st to 10th	Night	54% 3 9% 17% 15% 2	2100
	11th to 20th	Night	48% 5% 9% 22% 13% 2	2044
	21st to end	Night	50% 4 8% 20% 15% 3	1890
May	1st to 10th	Night	55% 4 11% 20% 9% 1	4872
	11th to 20th	Night	49% 5% 13% 22% 10% 1	4640
	21st to end	Night	51% 4 11% 17% 15% 1	5115
June	1st to 10th	Night	46% 5% 13% 22% 13% 1	1680
	11th to 20th	Night	46% 5% 12% 20% 12% 4	1680
	21st to end	Night	49% 5% 13% 19% 13% 1	1680
July	1st to 10th	Night	40% 7% 19% 21% 11%	4640
	11th to 20th	Night	37% 8% 19% 27% 9%	4632
	21st to end	Night	40% 6% 17% 28% 8%	4967
August	1st to 10th	Night	46% 7% 16% 21% 9% 1	3656
	11th to 20th	Night	42% 7% 19% 26% 6%	3949
	21st to end	Night	44% 6% 15% 24% 11%	5040
September	1st to 10th	Night	37% 6% 17% 27% 12% 1	2100
	11th to 20th	Night	35% 3 18% 33% 10% 1	2149
	21st to end	Night	41% 4 11% 30% 13%	2200
October	1st to 10th	Night	48% 6% 12% 24% 9%	3742
	11th to 20th	Night	44% 6% 16% 28% 6%	4078
	21st to end	Night	45% 5% 18% 20% 11% 1	4610
November	1st to 10th	Night	52% 5% 13% 21% 8% 1	2667
	11th to 20th	Night	54% 5% 12% 20% 9% 1	2805
	21st to end	Night	61% 4 11% 16% 8%	2940
December	1st to 10th	Night	61% 5% 14% 16% 4	4924
	11th to 20th	Night	61% 4 8% 18% 8%	5534
	21st to end	Night	63% 3 7% 16% 11% 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	26% 13% 37% 18% 5%	220
	11th to 20th	Day	28% 13% 37% 17% 5%	220
	21st to end	Day	16% 15% 37% 22% 9%	242
February	1st to 10th	Day	25% 22% 38% 11% 4	259
	11th to 20th	Day	23% 21% 36% 18% 2	460
	21st to end	Day	24% 17% 37% 17% 4	446
March	1st to 10th	Day	25% 18% 32% 20% 5%	540
	11th to 20th	Day	26% 18% 34% 16% 5% 1	540
	21st to end	Day	26% 22% 28% 16% 6% 2	594
April	1st to 10th	Day	32% 14% 28% 20% 6% 1	540
	11th to 20th	Day	30% 17% 29% 18% 5% 2	532
	21st to end	Day	30% 14% 37% 12% 4 2	540
May	1st to 10th	Day	29% 14% 33% 17% 6% 1	543
	11th to 20th	Day	23% 15% 30% 24% 7% 1	567
	21st to end	Day	25% 16% 35% 16% 7% 1	617
June	1st to 10th	Day	22% 12% 35% 21% 7% 2	570
	11th to 20th	Day	22% 13% 33% 20% 10% 1	570
	21st to end	Day	25% 12% 30% 22% 10% 1	570
July	1st to 10th	Day	16% 11% 32% 27% 11% 2	565
	11th to 20th	Day	17% 10% 33% 30% 8% 2	564
	21st to end	Day	15% 10% 31% 27% 15% 3	620
August	1st to 10th	Day	15% 7% 30% 30% 16% 3	566
	11th to 20th	Day	16% 5% 27% 32% 16% 5%	559
	21st to end	Day	17% 12% 26% 23% 17% 6%	627
September	1st to 10th	Day	18% 11% 34% 22% 12% 5%	570
	11th to 20th	Day	17% 9% 25% 25% 16% 7%	542
	21st to end	Day	23% 12% 26% 21% 12% 6%	530
October	1st to 10th	Day	23% 13% 29% 20% 12% 2	530
	11th to 20th	Day	26% 12% 32% 19% 10% 1	472
	21st to end	Day	33% 11% 29% 20% 6%	462
November	1st to 10th	Day	29% 14% 31% 20% 6% 1	425
	11th to 20th	Day	27% 13% 30% 23% 6% 1	351
	21st to end	Day	29% 18% 31% 18% 3 1	220
December	1st to 10th	Day	31% 13% 31% 16% 7% 1	220
	11th to 20th	Day	29% 15% 37% 16% 2 1	220
	21st to end	Day	32% 15% 32% 15% 5% 2	242
January	1st to 10th	Night	28% 10% 33% 25% 4	840
	11th to 20th	Night	27% 13% 31% 22% 7%	840
	21st to end	Night	17% 9% 35% 32% 6% 1	924
February	1st to 10th	Night	19% 10% 38% 27% 7%	840
	11th to 20th	Night	21% 14% 38% 22% 5%	823
	21st to end	Night	22% 11% 32% 28% 6%	692
March	1st to 10th	Night	25% 12% 32% 27% 4	840
	11th to 20th	Night	24% 14% 34% 23% 5% 1	840
	21st to end	Night	23% 13% 32% 23% 7% 1	924
April	1st to 10th	Night	30% 12% 29% 23% 6%	840
	11th to 20th	Night	27% 11% 31% 26% 4	800
	21st to end	Night	28% 14% 31% 21% 5%	630
May	1st to 10th	Night	27% 12% 27% 29% 5% 1	496
	11th to 20th	Night	24% 8% 30% 31% 7%	414
	21st to end	Night	22% 7% 37% 26% 9%	455
June	1st to 10th	Night	23% 5% 26% 38% 8%	420
	11th to 20th	Night	23% 5% 23% 38% 10% 1	420
	21st to end	Night	22% 5% 24% 35% 13%	420
July	1st to 10th	Night	14% 4 28% 38% 16%	410
	11th to 20th	Night	14% 4 24% 42% 15% 1	408
	21st to end	Night	16% 6% 22% 40% 15% 1	460
August	1st to 10th	Night	12% 4 18% 46% 19%	418
	11th to 20th	Night	16% 4 21% 38% 20% 1	542
	21st to end	Night	19% 6% 24% 32% 19% 1	919
September	1st to 10th	Night	16% 5% 27% 37% 13% 1	840
	11th to 20th	Night	16% 6% 24% 31% 20% 2	813
	21st to end	Night	21% 7% 27% 29% 15% 2	800
October	1st to 10th	Night	21% 9% 29% 30% 10%	800
	11th to 20th	Night	25% 9% 28% 27% 10% 1	800
	21st to end	Night	31% 8% 31% 23% 6%	880
November	1st to 10th	Night	26% 10% 30% 26% 7% 1	820
	11th to 20th	Night	26% 12% 29% 23% 10% 1	840
	21st to end	Night	31% 14% 24% 25% 5%	840
December	1st to 10th	Night	28% 9% 29% 25% 8%	906
	11th to 20th	Night	28% 12% 32% 21% 6% 1	900
	21st to end	Night	33% 11% 28% 22% 5% 1	924

Page generated at 2026-09-11 04:11:54. Version ac07

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