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 2024-04-25.

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	18% 12% 5% 9% 7% 3 5% 4 5% 6% 28%	83106
	Night	17% 12% 5% 9% 7% 3 5% 4 5% 6% 28%	85998
Transparency	Day	58% 4 10% 18% 9% 1	82811
	Night	58% 4 11% 17% 8% 1	85827
Seeing	Day	26% 16% 29% 19% 8% 2	13678
	Night	25% 12% 27% 25% 10% 1	22875

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% 9% 16% 9% 4 5% 3 2 4 13%	2517
	11th to 20th	Day	13% 15% 9% 19% 10% 3 3 3 3 4 19%	2520
	21st to end	Day	11% 16% 9% 14% 8% 4 7% 4 5% 4 18%	2772
February	1st to 10th	Day	10% 17% 8% 12% 12% 4 5% 3 5% 5% 19%	1705
	11th to 20th	Day	12% 18% 7% 12% 7% 4 5% 3 4 6% 23%	1685
	21st to end	Day	17% 16% 6% 8% 10% 4 4 3 4 4 24%	1570
March	1st to 10th	Day	15% 18% 5% 9% 7% 3 4 3 3 5% 25%	3116
	11th to 20th	Day	13% 18% 8% 11% 7% 4 4 3 4 4 23%	3402
	21st to end	Day	13% 8% 4 8% 7% 4 4 5% 6% 7% 35%	4088
April	1st to 10th	Day	22% 14% 4 7% 5% 2 4 3 4 4 29%	2280
	11th to 20th	Day	22% 10% 4 7% 5% 3 4 4 4 5% 32%	2254
	21st to end	Day	20% 12% 4 8% 5% 3 5% 4 4 5% 30%	2381
May	1st to 10th	Day	23% 10% 3 7% 6% 3 4 4 4 6% 31%	2520
	11th to 20th	Day	21% 9% 3 6% 6% 3 4 5% 4 6% 33%	2478
	21st to end	Day	18% 8% 3 7% 6% 4 5% 4 5% 7% 34%	2725
June	1st to 10th	Day	23% 9% 3 7% 6% 3 5% 5% 5% 6% 28%	2520
	11th to 20th	Day	16% 6% 3 6% 6% 4 5% 5% 7% 8% 34%	2520
	21st to end	Day	21% 7% 3 7% 6% 4 7% 5% 5% 8% 28%	2520
July	1st to 10th	Day	15% 6% 3 6% 6% 4 6% 5% 6% 9% 35%	2520
	11th to 20th	Day	15% 6% 3 6% 6% 4 6% 6% 7% 9% 33%	2520
	21st to end	Day	14% 7% 3 8% 6% 3 5% 5% 6% 8% 34%	2744
August	1st to 10th	Day	16% 8% 3 7% 7% 4 6% 6% 6% 8% 29%	2506
	11th to 20th	Day	15% 7% 3 6% 5% 4 5% 6% 6% 8% 35%	2308
	21st to end	Day	15% 7% 3 7% 6% 3 4 6% 6% 8% 35%	2376
September	1st to 10th	Day	17% 6% 2 5% 6% 3 4 4 5% 7% 39%	2160
	11th to 20th	Day	15% 8% 3 6% 5% 3 4 4 5% 7% 39%	2134
	21st to end	Day	21% 7% 3 5% 5% 2 4 4 5% 6% 37%	1961
October	1st to 10th	Day	22% 9% 3 6% 6% 4 5% 5% 5% 6% 31%	1800
	11th to 20th	Day	27% 14% 3 8% 6% 2 4 4 4 6% 23%	1800
	21st to end	Day	26% 15% 3 8% 6% 3 4 3 4 5% 22%	1782
November	1st to 10th	Day	16% 13% 4 8% 6% 3 4 4 5% 7% 30%	1671
	11th to 20th	Day	21% 15% 8% 9% 7% 3 5% 4 4 4 20%	1533
	21st to end	Day	23% 16% 7% 10% 8% 3 4 3 3 4 18%	1520
December	1st to 10th	Day	22% 20% 7% 10% 8% 3 4 4 4 4 14%	1520
	11th to 20th	Day	21% 15% 7% 12% 8% 4 4 3 4 5% 17%	1906
	21st to end	Day	21% 20% 6% 11% 7% 3 4 3 3 4 17%	2772
January	1st to 10th	Night	15% 19% 8% 12% 8% 3 4 4 4 5% 19%	4429
	11th to 20th	Night	13% 13% 6% 14% 13% 5% 4 4 4 6% 18%	4440
	21st to end	Night	11% 15% 8% 15% 8% 5% 6% 4 4 5% 17%	4884
February	1st to 10th	Night	11% 15% 7% 12% 9% 4 6% 5% 4 5% 22%	2470
	11th to 20th	Night	12% 14% 7% 12% 10% 4 5% 5% 5% 5% 23%	2380
	21st to end	Night	14% 14% 7% 9% 7% 4 5% 4 5% 6% 26%	1884
March	1st to 10th	Night	18% 15% 4 8% 6% 4 4 4 4 5% 27%	3724
	11th to 20th	Night	16% 17% 6% 10% 7% 3 4 4 4 5% 25%	3555
	21st to end	Night	13% 8% 4 8% 8% 4 5% 4 5% 6% 35%	3544
April	1st to 10th	Night	23% 11% 5% 6% 5% 3 3 4 5% 6% 30%	1900
	11th to 20th	Night	19% 9% 3 5% 6% 3 5% 4 5% 6% 35%	1875
	21st to end	Night	21% 10% 4 7% 5% 3 3 4 4 5% 34%	1693
May	1st to 10th	Night	21% 10% 4 5% 4 2 4 4 5% 7% 35%	1440
	11th to 20th	Night	19% 7% 3 5% 5% 3 4 4 6% 7% 37%	1415
	21st to end	Night	16% 7% 4 6% 5% 3 4 5% 5% 7% 38%	1550
June	1st to 10th	Night	19% 8% 2 7% 5% 4 5% 4 7% 9% 31%	1440
	11th to 20th	Night	15% 6% 3 6% 6% 4 4 6% 5% 8% 38%	1440
	21st to end	Night	17% 8% 2 6% 5% 4 5% 4 6% 8% 35%	1440
July	1st to 10th	Night	12% 6% 3 5% 5% 4 4 6% 6% 9% 40%	1440
	11th to 20th	Night	13% 5% 3 5% 5% 3 5% 6% 6% 7% 41%	1440
	21st to end	Night	10% 6% 2 6% 6% 3 5% 5% 8% 8% 40%	1574
August	1st to 10th	Night	13% 5% 2 6% 6% 5% 5% 5% 6% 8% 38%	1432
	11th to 20th	Night	13% 5% 3 6% 5% 3 5% 4 6% 8% 43%	1569
	21st to end	Night	16% 5% 3 5% 5% 3 4 4 6% 8% 40%	1980
September	1st to 10th	Night	16% 5% 2 5% 5% 2 4 4 6% 7% 43%	1800
	11th to 20th	Night	16% 6% 2 4 4 3 3 4 5% 7% 44%	1826
	21st to end	Night	18% 8% 2 5% 4 3 4 5% 5% 7% 39%	1997
October	1st to 10th	Night	21% 8% 3 5% 5% 3 4 4 5% 6% 36%	2160
	11th to 20th	Night	24% 12% 4 7% 6% 3 4 5% 5% 5% 26%	2160
	21st to end	Night	24% 12% 4 8% 6% 3 5% 4 4 5% 24%	2573
November	1st to 10th	Night	20% 12% 5% 7% 5% 3 4 4 5% 5% 28%	2407
	11th to 20th	Night	20% 13% 6% 9% 7% 4 5% 4 4 5% 23%	2645
	21st to end	Night	23% 17% 6% 11% 7% 3 5% 4 4 5% 17%	2660
December	1st to 10th	Night	20% 19% 8% 11% 7% 3 4 4 4 4 15%	2660
	11th to 20th	Night	22% 15% 7% 10% 7% 3 4 3 3 4 22%	3288
	21st to end	Night	23% 22% 6% 9% 7% 3 4 3 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	78% 2 8% 9% 3	2518
	11th to 20th	Day	72% 2 6% 14% 6%	2520
	21st to end	Day	70% 4 9% 10% 6% 1	2772
February	1st to 10th	Day	68% 3 6% 15% 7% 1	1705
	11th to 20th	Day	65% 3 11% 11% 10% 1	1694
	21st to end	Day	65% 2 8% 14% 10% 1	1570
March	1st to 10th	Day	64% 3 8% 14% 11% 1	3119
	11th to 20th	Day	65% 3 9% 13% 9% 2	3402
	21st to end	Day	48% 4 8% 23% 16% 2	4088
April	1st to 10th	Day	59% 3 8% 17% 10% 3	2280
	11th to 20th	Day	55% 4 7% 20% 12% 2	2254
	21st to end	Day	57% 4 8% 15% 12% 3	2381
May	1st to 10th	Day	54% 4 7% 20% 12% 3	2520
	11th to 20th	Day	53% 4 7% 18% 15% 2	2482
	21st to end	Day	50% 5% 11% 18% 14% 2	2725
June	1st to 10th	Day	56% 6% 9% 17% 10% 1	2520
	11th to 20th	Day	46% 6% 12% 23% 11% 2	2520
	21st to end	Day	54% 6% 13% 18% 9%	2520
July	1st to 10th	Day	45% 6% 13% 25% 10%	2450
	11th to 20th	Day	44% 7% 14% 25% 10%	2445
	21st to end	Day	48% 7% 15% 23% 7%	2591
August	1st to 10th	Day	51% 8% 14% 21% 5%	2492
	11th to 20th	Day	45% 7% 18% 22% 7%	2308
	21st to end	Day	45% 6% 14% 23% 11% 1	2376
September	1st to 10th	Day	45% 4 13% 24% 13%	2160
	11th to 20th	Day	44% 4 14% 26% 10% 1	2134
	21st to end	Day	47% 6% 14% 24% 8%	1961
October	1st to 10th	Day	55% 4 12% 19% 8% 1	1800
	11th to 20th	Day	64% 5% 10% 17% 4 1	1800
	21st to end	Day	66% 4 10% 14% 5% 1	1782
November	1st to 10th	Day	55% 4 14% 20% 6% 1	1671
	11th to 20th	Day	68% 4 11% 11% 6%	1533
	21st to end	Day	73% 4 9% 9% 5%	1520
December	1st to 10th	Day	74% 4 9% 10% 3	1520
	11th to 20th	Day	71% 4 8% 11% 5%	1906
	21st to end	Day	74% 3 7% 13% 4	2772
January	1st to 10th	Night	70% 3 14% 10% 3	4429
	11th to 20th	Night	69% 3 13% 10% 4 1	4440
	21st to end	Night	70% 4 10% 9% 7% 1	4884
February	1st to 10th	Night	65% 3 9% 15% 6% 1	2470
	11th to 20th	Night	64% 3 9% 15% 7% 1	2382
	21st to end	Night	61% 3 10% 16% 10% 1	1884
March	1st to 10th	Night	60% 3 11% 13% 10% 2	3734
	11th to 20th	Night	61% 4 9% 16% 9% 1	3556
	21st to end	Night	50% 4 8% 22% 13% 3	3544
April	1st to 10th	Night	56% 3 9% 16% 12% 3	1900
	11th to 20th	Night	49% 4 9% 22% 13% 2	1875
	21st to end	Night	54% 4 8% 18% 14% 3	1693
May	1st to 10th	Night	50% 4 8% 20% 15% 3	1440
	11th to 20th	Night	47% 4 9% 20% 16% 3	1416
	21st to end	Night	45% 4 12% 22% 14% 2	1551
June	1st to 10th	Night	49% 5% 13% 22% 10%	1440
	11th to 20th	Night	44% 6% 12% 22% 12% 3	1440
	21st to end	Night	47% 8% 13% 21% 11% 1	1440
July	1st to 10th	Night	38% 7% 18% 24% 12% 1	1400
	11th to 20th	Night	40% 7% 15% 28% 9% 1	1392
	21st to end	Night	39% 8% 19% 24% 9%	1486
August	1st to 10th	Night	43% 7% 17% 26% 6%	1422
	11th to 20th	Night	39% 7% 19% 25% 9%	1569
	21st to end	Night	42% 6% 16% 27% 8%	1980
September	1st to 10th	Night	41% 5% 15% 26% 13% 1	1800
	11th to 20th	Night	39% 4 16% 31% 8%	1826
	21st to end	Night	44% 6% 13% 29% 9%	1997
October	1st to 10th	Night	49% 6% 10% 24% 11%	2160
	11th to 20th	Night	60% 5% 12% 17% 6% 1	2160
	21st to end	Night	63% 5% 10% 15% 6% 1	2573
November	1st to 10th	Night	57% 5% 14% 18% 6%	2407
	11th to 20th	Night	64% 4 11% 14% 6% 2	2645
	21st to end	Night	71% 4 10% 11% 3	2660
December	1st to 10th	Night	73% 4 9% 10% 3	2660
	11th to 20th	Night	68% 3 9% 14% 6% 1	3288
	21st to end	Night	74% 3 6% 12% 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% 19% 38% 18% 4	180
	11th to 20th	Day	28% 17% 32% 16% 6% 1	180
	21st to end	Day	24% 15% 35% 21% 5% 1	198
February	1st to 10th	Day	30% 24% 33% 10% 2 1	267
	11th to 20th	Day	25% 27% 36% 11%	292
	21st to end	Day	31% 23% 29% 14% 3	382
March	1st to 10th	Day	27% 18% 31% 17% 7%	460
	11th to 20th	Day	27% 20% 32% 17% 3 1	460
	21st to end	Day	30% 20% 27% 15% 7% 2	506
April	1st to 10th	Day	32% 16% 28% 15% 7% 2	460
	11th to 20th	Day	34% 17% 24% 13% 9% 2	452
	21st to end	Day	29% 21% 29% 16% 5% 1	437
May	1st to 10th	Day	30% 17% 29% 16% 5% 2	423
	11th to 20th	Day	26% 16% 29% 19% 8% 2	447
	21st to end	Day	23% 16% 33% 19% 6% 1	485
June	1st to 10th	Day	28% 14% 32% 19% 6% 1	450
	11th to 20th	Day	21% 17% 31% 18% 11% 2	450
	21st to end	Day	24% 12% 30% 21% 11% 3	450
July	1st to 10th	Day	16% 9% 34% 28% 10% 2	445
	11th to 20th	Day	17% 12% 31% 29% 10% 2	444
	21st to end	Day	14% 10% 35% 28% 13% 2	488
August	1st to 10th	Day	19% 9% 24% 32% 12% 3	446
	11th to 20th	Day	18% 7% 26% 28% 13% 8%	439
	21st to end	Day	20% 16% 27% 17% 14% 7%	495
September	1st to 10th	Day	20% 10% 28% 21% 12% 8%	450
	11th to 20th	Day	17% 13% 24% 23% 16% 6%	450
	21st to end	Day	22% 14% 27% 18% 11% 8%	450
October	1st to 10th	Day	28% 15% 22% 18% 13% 3	450
	11th to 20th	Day	35% 18% 24% 14% 6% 3	450
	21st to end	Day	38% 12% 26% 18% 6%	396
November	1st to 10th	Day	30% 16% 28% 21% 4 1	365
	11th to 20th	Day	28% 21% 36% 8% 5% 2	193
	21st to end	Day	33% 21% 29% 13% 3 1	180
December	1st to 10th	Day	34% 18% 26% 16% 6%	180
	11th to 20th	Day	33% 23% 29% 11% 3 1	180
	21st to end	Day	32% 17% 32% 12% 5% 2	198
January	1st to 10th	Night	29% 14% 35% 17% 6%	760
	11th to 20th	Night	30% 13% 29% 21% 7%	760
	21st to end	Night	19% 12% 34% 27% 8% 1	836
February	1st to 10th	Night	20% 17% 33% 23% 6% 1	760
	11th to 20th	Night	21% 18% 34% 22% 4 1	743
	21st to end	Night	24% 17% 28% 26% 4	628
March	1st to 10th	Night	23% 17% 30% 24% 5%	760
	11th to 20th	Night	26% 15% 31% 20% 6% 1	760
	21st to end	Night	24% 14% 31% 24% 7%	836
April	1st to 10th	Night	30% 13% 25% 25% 8%	760
	11th to 20th	Night	25% 14% 30% 22% 9% 1	751
	21st to end	Night	28% 14% 25% 22% 10% 1	583
May	1st to 10th	Night	26% 10% 27% 26% 11% 1	360
	11th to 20th	Night	23% 9% 28% 31% 9%	354
	21st to end	Night	20% 8% 33% 30% 9% 1	389
June	1st to 10th	Night	22% 7% 32% 29% 10% 1	360
	11th to 20th	Night	17% 7% 27% 35% 13% 1	360
	21st to end	Night	20% 5% 21% 35% 18% 1	360
July	1st to 10th	Night	13% 4 25% 45% 13%	350
	11th to 20th	Night	15% 3 22% 40% 19%	348
	21st to end	Night	13% 4 25% 40% 16% 2	394
August	1st to 10th	Night	14% 4 21% 38% 23% 1	358
	11th to 20th	Night	14% 4 20% 35% 26% 2	505
	21st to end	Night	21% 6% 22% 31% 18% 2	792
September	1st to 10th	Night	20% 5% 23% 33% 18% 1	720
	11th to 20th	Night	20% 7% 20% 31% 20% 2	720
	21st to end	Night	24% 8% 24% 25% 16% 2	720
October	1st to 10th	Night	25% 10% 26% 24% 14% 1	720
	11th to 20th	Night	32% 12% 25% 22% 8% 2	720
	21st to end	Night	31% 13% 25% 25% 5%	792
November	1st to 10th	Night	29% 14% 27% 22% 7% 1	740
	11th to 20th	Night	28% 16% 29% 18% 9% 1	760
	21st to end	Night	34% 17% 23% 20% 6% 1	760
December	1st to 10th	Night	32% 15% 27% 20% 6%	760
	11th to 20th	Night	29% 15% 32% 18% 6% 1	760
	21st to end	Night	35% 14% 26% 20% 4 1	836

Page generated at 2024-04-22 09:25:41. Version ac07

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