L'acceuil du Petit Lac
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the L'acceuil du Petit Lac clear sky chart from 2005-11-06 to 2025-10-04.

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 10% 6% 5% 4 3 5% 6% 28%	126775
	Night	16% 13% 4 10% 6% 5% 4 3 5% 6% 27%	122586
Transparency	Day	56% 5% 11% 19% 9% 1	130217
	Night	58% 5% 11% 17% 8% 1	127231
Seeing	Day	25% 16% 29% 19% 8% 3	15582
	Night	24% 12% 27% 26% 10% 1	24534

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	12% 19% 9% 22% 8% 6% 5% 2 3 4 11%	3597
	11th to 20th	Day	10% 17% 8% 21% 10% 4 3 2 4 4 17%	3570
	21st to end	Day	8% 15% 9% 17% 6% 5% 5% 4 5% 6% 20%	3960
February	1st to 10th	Day	10% 18% 7% 14% 11% 5% 4 3 5% 5% 19%	1795
	11th to 20th	Day	11% 20% 6% 13% 7% 6% 4 2 4 5% 22%	1777
	21st to end	Day	16% 17% 5% 10% 10% 4 4 2 4 4 23%	1650
March	1st to 10th	Day	16% 18% 5% 13% 7% 4 4 2 4 5% 21%	4476
	11th to 20th	Day	13% 15% 6% 11% 6% 5% 4 3 5% 6% 26%	4860
	21st to end	Day	17% 13% 4 9% 5% 4 3 3 5% 5% 32%	5850
April	1st to 10th	Day	21% 16% 4 9% 4 4 3 2 4 5% 29%	2400
	11th to 20th	Day	22% 11% 4 8% 4 4 3 3 4 5% 32%	2374
	21st to end	Day	20% 13% 3 9% 5% 4 4 4 4 4 30%	2590
May	1st to 10th	Day	23% 12% 4 8% 5% 5% 5% 4 5% 6% 24%	6346
	11th to 20th	Day	19% 10% 3 8% 5% 4 5% 4 5% 7% 31%	6318
	21st to end	Day	22% 10% 3 8% 5% 5% 4 3 4 6% 30%	6949
June	1st to 10th	Day	23% 9% 3 8% 5% 4 5% 3 5% 6% 28%	2800
	11th to 20th	Day	16% 6% 2 7% 5% 6% 6% 4 7% 8% 33%	2800
	21st to end	Day	21% 7% 3 8% 6% 5% 6% 4 6% 7% 28%	2800
July	1st to 10th	Day	16% 7% 3 8% 5% 6% 6% 5% 8% 8% 28%	6360
	11th to 20th	Day	13% 6% 2 7% 5% 5% 5% 5% 7% 9% 37%	6360
	21st to end	Day	10% 5% 2 6% 4 4 5% 4 7% 10% 42%	6926
August	1st to 10th	Day	15% 7% 3 8% 6% 6% 6% 4 7% 9% 30%	4563
	11th to 20th	Day	16% 7% 3 7% 4 5% 5% 5% 6% 9% 33%	4163
	21st to end	Day	14% 6% 3 7% 5% 4 5% 5% 7% 9% 35%	4312
September	1st to 10th	Day	16% 6% 2 6% 5% 4 4 4 6% 8% 39%	2400
	11th to 20th	Day	14% 8% 2 6% 4 4 4 3 5% 7% 42%	2370
	21st to end	Day	21% 7% 2 6% 4 3 4 3 5% 6% 38%	2178
October	1st to 10th	Day	21% 9% 3 7% 4 4 5% 3 5% 6% 31%	1930
	11th to 20th	Day	26% 15% 3 8% 5% 3 4 3 4 6% 24%	1900
	21st to end	Day	25% 15% 3 9% 5% 4 4 3 4 6% 23%	1881
November	1st to 10th	Day	17% 14% 4 9% 5% 4 4 3 4 7% 29%	1761
	11th to 20th	Day	19% 17% 6% 10% 6% 4 5% 3 4 4 20%	1613
	21st to end	Day	22% 18% 6% 13% 6% 5% 4 2 3 4 17%	1600
December	1st to 10th	Day	18% 22% 9% 13% 8% 5% 3 3 4 4 10%	2600
	11th to 20th	Day	18% 17% 6% 15% 8% 5% 3 3 3 4 18%	2986
	21st to end	Day	18% 18% 6% 12% 6% 5% 5% 3 3 4 19%	3960
January	1st to 10th	Night	11% 22% 10% 17% 7% 5% 4 2 3 4 15%	6349
	11th to 20th	Night	11% 15% 7% 18% 11% 6% 4 3 4 5% 15%	6315
	21st to end	Night	8% 15% 8% 17% 7% 7% 6% 3 5% 5% 19%	6996
February	1st to 10th	Night	10% 16% 6% 14% 7% 5% 6% 4 5% 4 23%	2600
	11th to 20th	Night	12% 15% 5% 14% 8% 5% 5% 3 5% 4 22%	2508
	21st to end	Night	13% 16% 6% 11% 6% 5% 5% 3 5% 6% 25%	1980
March	1st to 10th	Night	19% 17% 4 11% 5% 4 4 3 4 4 24%	5364
	11th to 20th	Night	12% 14% 4 12% 7% 5% 4 4 5% 6% 27%	5083
	21st to end	Night	16% 12% 4 10% 6% 5% 4 3 5% 5% 29%	5082
April	1st to 10th	Night	22% 12% 4 7% 5% 4 3 3 5% 6% 30%	2000
	11th to 20th	Night	18% 10% 4 6% 5% 4 4 3 5% 6% 35%	1975
	21st to end	Night	22% 10% 3 8% 4 4 3 3 5% 5% 34%	1826
May	1st to 10th	Night	20% 12% 4 8% 5% 4 5% 3 6% 6% 26%	3594
	11th to 20th	Night	18% 10% 3 8% 5% 5% 4 4 5% 7% 32%	3575
	21st to end	Night	20% 10% 3 8% 5% 5% 5% 4 5% 7% 29%	3926
June	1st to 10th	Night	19% 9% 2 7% 4 5% 4 3 7% 9% 31%	1600
	11th to 20th	Night	15% 7% 3 7% 5% 4 5% 4 5% 8% 38%	1600
	21st to end	Night	18% 8% 2 7% 5% 5% 5% 4 6% 8% 34%	1600
July	1st to 10th	Night	15% 7% 3 8% 6% 6% 6% 5% 8% 9% 29%	3600
	11th to 20th	Night	13% 7% 3 6% 4 4 5% 4 6% 8% 40%	3600
	21st to end	Night	10% 5% 2 6% 4 5% 5% 4 6% 7% 47%	3926
August	1st to 10th	Night	13% 6% 3 7% 6% 6% 5% 4 5% 8% 37%	2586
	11th to 20th	Night	18% 6% 2 6% 4 4 5% 3 6% 6% 39%	2847
	21st to end	Night	20% 7% 3 7% 4 4 4 3 5% 7% 36%	3586
September	1st to 10th	Night	15% 6% 2 6% 4 3 4 4 6% 7% 43%	2000
	11th to 20th	Night	15% 6% 2 5% 3 4 3 3 6% 7% 47%	2030
	21st to end	Night	18% 9% 2 5% 3 4 4 4 5% 7% 40%	2219
October	1st to 10th	Night	20% 8% 3 6% 4 4 5% 3 5% 6% 37%	2317
	11th to 20th	Night	23% 12% 4 8% 5% 4 4 3 5% 5% 27%	2280
	21st to end	Night	23% 13% 3 9% 5% 4 5% 3 4 5% 25%	2716
November	1st to 10th	Night	19% 14% 5% 8% 4 5% 4 3 5% 5% 28%	2537
	11th to 20th	Night	19% 14% 5% 11% 6% 5% 5% 4 4 5% 23%	2785
	21st to end	Night	21% 18% 5% 13% 6% 4 4 3 4 5% 16%	2800
December	1st to 10th	Night	17% 18% 7% 13% 9% 6% 5% 4 5% 5% 11%	4580
	11th to 20th	Night	23% 14% 5% 12% 7% 4 4 3 3 5% 21%	5208
	21st to end	Night	21% 21% 5% 10% 6% 4 4 3 4 5% 18%	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	80% 2 6% 9% 3	3598
	11th to 20th	Day	72% 2 5% 12% 7%	3600
	21st to end	Day	65% 4 9% 12% 10% 1	3960
February	1st to 10th	Day	68% 3 6% 14% 7% 1	1795
	11th to 20th	Day	66% 3 10% 11% 9% 1	1786
	21st to end	Day	65% 2 8% 14% 10% 1	1650
March	1st to 10th	Day	67% 3 6% 10% 12% 2	4479
	11th to 20th	Day	60% 4 14% 12% 10% 1	4860
	21st to end	Day	55% 3 6% 19% 16% 2	5850
April	1st to 10th	Day	59% 3 8% 17% 10% 3	2400
	11th to 20th	Day	55% 4 7% 20% 12% 2	2374
	21st to end	Day	58% 4 8% 15% 12% 3	2590
May	1st to 10th	Day	59% 5% 7% 19% 8% 1	6357
	11th to 20th	Day	52% 5% 13% 20% 9% 1	6322
	21st to end	Day	55% 5% 9% 16% 13% 1	6949
June	1st to 10th	Day	56% 6% 9% 17% 11% 1	2800
	11th to 20th	Day	46% 6% 12% 23% 11% 2	2800
	21st to end	Day	53% 6% 13% 18% 9%	2800
July	1st to 10th	Day	48% 8% 13% 25% 6%	6290
	11th to 20th	Day	41% 7% 17% 29% 7%	6285
	21st to end	Day	37% 7% 17% 31% 8%	6728
August	1st to 10th	Day	50% 8% 15% 22% 6%	4549
	11th to 20th	Day	46% 8% 17% 24% 5%	4204
	21st to end	Day	43% 8% 15% 21% 12% 1	4312
September	1st to 10th	Day	43% 5% 14% 25% 12%	2400
	11th to 20th	Day	41% 4 15% 28% 11% 1	2370
	21st to end	Day	47% 6% 13% 24% 10%	2178
October	1st to 10th	Day	53% 4 11% 26% 5%	3190
	11th to 20th	Day	57% 6% 11% 21% 5%	3140
	21st to end	Day	58% 5% 17% 13% 5% 1	3081
November	1st to 10th	Day	56% 4 13% 20% 6% 1	1761
	11th to 20th	Day	68% 4 10% 11% 7%	1613
	21st to end	Day	74% 4 9% 8% 5%	1600
December	1st to 10th	Day	79% 4 7% 9% 2	2600
	11th to 20th	Day	71% 4 6% 13% 6%	2986
	21st to end	Day	70% 3 7% 16% 4	3960
January	1st to 10th	Night	75% 3 10% 10% 2	6349
	11th to 20th	Night	73% 3 11% 9% 4	6360
	21st to end	Night	67% 4 8% 10% 11%	6996
February	1st to 10th	Night	64% 3 9% 15% 7% 1	2600
	11th to 20th	Night	65% 3 9% 15% 7% 1	2510
	21st to end	Night	61% 3 10% 16% 9% 1	1980
March	1st to 10th	Night	65% 3 8% 10% 12% 2	5374
	11th to 20th	Night	56% 6% 12% 16% 8% 2	5084
	21st to end	Night	56% 4 7% 22% 10% 2	5082
April	1st to 10th	Night	56% 3 9% 16% 12% 3	2000
	11th to 20th	Night	50% 4 9% 22% 14% 2	1975
	21st to end	Night	54% 4 8% 18% 14% 3	1826
May	1st to 10th	Night	56% 6% 10% 18% 9% 2	3600
	11th to 20th	Night	50% 7% 13% 18% 10% 2	3576
	21st to end	Night	55% 5% 10% 17% 12% 1	3927
June	1st to 10th	Night	50% 5% 12% 22% 11%	1600
	11th to 20th	Night	44% 6% 13% 23% 12% 3	1600
	21st to end	Night	48% 7% 13% 20% 11% 1	1600
July	1st to 10th	Night	48% 9% 18% 19% 6%	3560
	11th to 20th	Night	40% 7% 18% 29% 5%	3552
	21st to end	Night	35% 7% 17% 31% 10%	3809
August	1st to 10th	Night	44% 7% 16% 25% 7%	2576
	11th to 20th	Night	44% 8% 18% 24% 6%	2872
	21st to end	Night	47% 6% 14% 22% 10% 1	3586
September	1st to 10th	Night	39% 5% 16% 27% 12% 1	2000
	11th to 20th	Night	37% 4 17% 32% 9%	2030
	21st to end	Night	43% 6% 13% 27% 10%	2219
October	1st to 10th	Night	45% 7% 14% 24% 10%	3837
	11th to 20th	Night	51% 7% 14% 20% 7%	3779
	21st to end	Night	56% 6% 16% 12% 9% 1	4466
November	1st to 10th	Night	58% 5% 13% 18% 6%	2537
	11th to 20th	Night	63% 4 11% 13% 7% 1	2785
	21st to end	Night	72% 4 10% 11% 3	2800
December	1st to 10th	Night	75% 6% 9% 7% 2	4580
	11th to 20th	Night	69% 3 7% 13% 8% 1	5208
	21st to end	Night	70% 3 6% 12% 9%	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	20% 19% 42% 16% 4	200
	11th to 20th	Day	28% 17% 35% 15% 6% 1	200
	21st to end	Day	22% 18% 35% 20% 5%	220
February	1st to 10th	Day	29% 25% 33% 10% 2 1	297
	11th to 20th	Day	27% 26% 37% 11%	324
	21st to end	Day	30% 22% 31% 14% 3	414
March	1st to 10th	Day	27% 19% 31% 16% 6%	500
	11th to 20th	Day	27% 22% 31% 17% 3 1	500
	21st to end	Day	30% 20% 27% 15% 6% 2	550
April	1st to 10th	Day	33% 17% 27% 15% 7% 2	500
	11th to 20th	Day	35% 17% 23% 13% 9% 2	492
	21st to end	Day	30% 20% 30% 14% 5% 1	500
May	1st to 10th	Day	29% 18% 30% 16% 5% 2	503
	11th to 20th	Day	24% 17% 29% 19% 8% 2	527
	21st to end	Day	26% 16% 32% 19% 6% 1	573
June	1st to 10th	Day	27% 15% 32% 20% 6% 1	530
	11th to 20th	Day	20% 18% 31% 18% 10% 2	530
	21st to end	Day	24% 14% 32% 19% 9% 2	530
July	1st to 10th	Day	17% 10% 34% 27% 10% 2	525
	11th to 20th	Day	16% 12% 32% 29% 10% 2	524
	21st to end	Day	13% 11% 34% 28% 12% 2	576
August	1st to 10th	Day	18% 9% 25% 32% 13% 3	526
	11th to 20th	Day	17% 7% 26% 28% 14% 8%	519
	21st to end	Day	19% 15% 27% 18% 14% 7%	583
September	1st to 10th	Day	20% 11% 29% 20% 12% 7%	530
	11th to 20th	Day	15% 11% 22% 24% 19% 10%	530
	21st to end	Day	21% 15% 25% 18% 12% 8%	530
October	1st to 10th	Day	26% 15% 23% 19% 14% 3	502
	11th to 20th	Day	34% 18% 24% 15% 6% 3	490
	21st to end	Day	37% 13% 26% 18% 6%	429
November	1st to 10th	Day	31% 15% 28% 20% 4 1	395
	11th to 20th	Day	28% 21% 34% 10% 6% 1	213
	21st to end	Day	34% 21% 31% 12% 3 1	200
December	1st to 10th	Day	35% 18% 24% 18% 5%	200
	11th to 20th	Day	33% 23% 28% 12% 4 1	200
	21st to end	Day	30% 17% 32% 12% 6% 2	220
January	1st to 10th	Night	27% 14% 36% 17% 5%	800
	11th to 20th	Night	30% 14% 28% 22% 7%	800
	21st to end	Night	18% 12% 34% 27% 8% 1	880
February	1st to 10th	Night	19% 18% 33% 23% 6% 1	800
	11th to 20th	Night	21% 18% 35% 21% 4 1	783
	21st to end	Night	24% 17% 28% 27% 4	660
March	1st to 10th	Night	24% 17% 29% 24% 5%	800
	11th to 20th	Night	26% 15% 32% 21% 6% 1	800
	21st to end	Night	24% 15% 30% 23% 7%	880
April	1st to 10th	Night	30% 13% 25% 24% 7%	800
	11th to 20th	Night	25% 14% 30% 22% 9% 1	791
	21st to end	Night	29% 14% 25% 22% 10% 1	626
May	1st to 10th	Night	26% 10% 27% 27% 10% 1	400
	11th to 20th	Night	23% 10% 27% 30% 10%	394
	21st to end	Night	21% 8% 31% 30% 9%	433
June	1st to 10th	Night	23% 6% 31% 31% 10% 1	400
	11th to 20th	Night	17% 7% 27% 35% 13% 1	400
	21st to end	Night	22% 5% 21% 35% 16% 1	400
July	1st to 10th	Night	13% 5% 24% 46% 12%	390
	11th to 20th	Night	15% 5% 21% 41% 19%	388
	21st to end	Night	12% 4 26% 40% 16% 2	438
August	1st to 10th	Night	13% 4 19% 40% 22% 1	398
	11th to 20th	Night	14% 4 20% 34% 26% 2	564
	21st to end	Night	21% 6% 21% 31% 18% 2	880
September	1st to 10th	Night	20% 5% 24% 33% 18% 1	800
	11th to 20th	Night	18% 7% 19% 31% 23% 3	800
	21st to end	Night	23% 8% 24% 25% 17% 2	800
October	1st to 10th	Night	24% 10% 26% 25% 14% 1	773
	11th to 20th	Night	31% 12% 25% 22% 8% 2	760
	21st to end	Night	31% 13% 25% 25% 5%	836
November	1st to 10th	Night	29% 14% 28% 22% 6% 1	780
	11th to 20th	Night	27% 15% 28% 18% 10% 1	800
	21st to end	Night	34% 17% 23% 20% 6% 1	800
December	1st to 10th	Night	32% 15% 27% 20% 6%	800
	11th to 20th	Night	29% 14% 32% 18% 6% 1	800
	21st to end	Night	35% 14% 26% 20% 6% 1	880

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