Observatoire de Leclercville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire de Leclercville clear sky chart from 2005-11-06 to 2026-02-01.

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% 10% 4 8% 5% 4 5% 4 5% 7% 30%	127169
	Night	18% 12% 4 10% 5% 4 4 3 5% 6% 28%	124882
Transparency	Day	54% 5% 12% 19% 8% 1	130611
	Night	57% 5% 11% 18% 8% 1	129515
Seeing	Day	25% 16% 30% 20% 8% 2	16391
	Night	25% 12% 30% 25% 7% 1	25270

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	20% 19% 5% 13% 5% 5% 4 3 4 4 18%	3677
	11th to 20th	Day	10% 18% 8% 18% 6% 4 4 2 3 4 23%	3650
	21st to end	Day	9% 13% 6% 12% 6% 5% 5% 4 5% 7% 28%	4048
February	1st to 10th	Day	12% 16% 5% 13% 7% 5% 5% 3 4 5% 24%	1630
	11th to 20th	Day	14% 17% 6% 10% 6% 5% 5% 3 4 5% 23%	1917
	21st to end	Day	14% 15% 4 11% 6% 4 4 4 4 5% 28%	1650
March	1st to 10th	Day	20% 15% 5% 10% 6% 4 4 3 4 4 24%	4476
	11th to 20th	Day	16% 15% 5% 9% 5% 4 4 3 5% 6% 29%	4694
	21st to end	Day	19% 14% 4 8% 4 4 4 3 4 5% 32%	5913
April	1st to 10th	Day	22% 13% 4 8% 5% 4 4 3 4 5% 29%	2400
	11th to 20th	Day	20% 9% 3 7% 4 3 5% 3 4 5% 36%	2435
	21st to end	Day	24% 9% 3 8% 4 5% 5% 3 4 6% 30%	2600
May	1st to 10th	Day	28% 9% 3 7% 4 3 4 4 6% 6% 27%	6106
	11th to 20th	Day	20% 7% 3 8% 5% 5% 5% 4 6% 8% 30%	6318
	21st to end	Day	20% 9% 3 8% 5% 5% 5% 4 6% 6% 29%	6949
June	1st to 10th	Day	20% 8% 2 7% 6% 5% 5% 4 6% 8% 28%	2880
	11th to 20th	Day	16% 7% 3 6% 5% 4 5% 4 7% 8% 35%	3000
	21st to end	Day	22% 8% 3 8% 5% 4 5% 4 6% 6% 29%	2879
July	1st to 10th	Day	16% 7% 3 8% 6% 6% 6% 5% 7% 9% 28%	6360
	11th to 20th	Day	14% 6% 2 7% 5% 5% 6% 5% 7% 9% 34%	6360
	21st to end	Day	12% 5% 2 5% 4 5% 5% 5% 7% 9% 42%	6926
August	1st to 10th	Day	16% 6% 3 7% 5% 5% 6% 5% 8% 10% 31%	4563
	11th to 20th	Day	18% 7% 3 8% 5% 5% 5% 4 6% 8% 33%	4189
	21st to end	Day	20% 6% 3 6% 4 4 4 4 5% 6% 38%	4388
September	1st to 10th	Day	15% 6% 2 6% 5% 4 5% 3 6% 7% 40%	2400
	11th to 20th	Day	17% 5% 2 5% 4 3 4 3 4 7% 46%	2250
	21st to end	Day	21% 7% 2 5% 4 4 4 3 5% 5% 39%	2200
October	1st to 10th	Day	21% 8% 3 7% 4 4 5% 3 4 8% 33%	2159
	11th to 20th	Day	21% 10% 3 9% 5% 4 5% 4 5% 6% 27%	1864
	21st to end	Day	27% 11% 4 7% 5% 4 4 3 4 6% 25%	1980
November	1st to 10th	Day	19% 13% 4 9% 5% 4 4 3 4 5% 30%	1851
	11th to 20th	Day	21% 14% 5% 10% 5% 4 4 2 5% 4 25%	1864
	21st to end	Day	24% 18% 4 8% 5% 5% 5% 3 4 5% 20%	1619
December	1st to 10th	Day	20% 16% 6% 11% 7% 4 4 3 4 5% 21%	2350
	11th to 20th	Day	21% 15% 5% 10% 5% 4 3 3 3 6% 25%	2688
	21st to end	Day	22% 14% 4 9% 5% 5% 6% 4 5% 4 22%	3936
January	1st to 10th	Night	18% 18% 7% 15% 6% 5% 4 3 4 4 18%	6489
	11th to 20th	Night	11% 20% 8% 17% 7% 5% 4 3 4 4 16%	6455
	21st to end	Night	10% 14% 5% 13% 7% 6% 5% 4 5% 6% 26%	7150
February	1st to 10th	Night	13% 14% 6% 13% 7% 6% 4 4 4 4 25%	2766
	11th to 20th	Night	13% 16% 5% 13% 8% 6% 5% 4 4 3 23%	2368
	21st to end	Night	16% 15% 4 10% 5% 4 4 4 4 5% 29%	1980
March	1st to 10th	Night	23% 14% 4 10% 5% 4 4 3 4 5% 24%	5364
	11th to 20th	Night	15% 14% 5% 10% 6% 5% 5% 4 6% 6% 24%	5265
	21st to end	Night	17% 16% 4 9% 5% 3 3 3 4 4 30%	5018
April	1st to 10th	Night	23% 13% 4 7% 3 4 3 4 5% 5% 28%	2000
	11th to 20th	Night	23% 9% 2 8% 4 5% 3 3 4 6% 32%	1913
	21st to end	Night	24% 11% 3 7% 3 3 3 3 5% 6% 33%	1800
May	1st to 10th	Night	26% 10% 3 8% 5% 4 4 3 5% 6% 26%	3875
	11th to 20th	Night	24% 9% 3 6% 5% 4 5% 3 5% 7% 30%	3575
	21st to end	Night	19% 8% 3 7% 5% 5% 5% 4 6% 7% 32%	3926
June	1st to 10th	Night	21% 9% 3 5% 4 3 5% 3 7% 7% 32%	1515
	11th to 20th	Night	19% 7% 2 6% 4 4 5% 4 6% 8% 35%	1400
	21st to end	Night	21% 8% 3 8% 4 5% 5% 5% 5% 6% 30%	1511
July	1st to 10th	Night	14% 6% 3 8% 6% 6% 6% 6% 7% 9% 29%	3600
	11th to 20th	Night	20% 6% 2 7% 4 4 4 4 4 8% 37%	3600
	21st to end	Night	11% 5% 3 7% 5% 5% 5% 4 6% 8% 40%	3926
August	1st to 10th	Night	17% 8% 3 8% 5% 4 5% 4 6% 8% 32%	2586
	11th to 20th	Night	17% 8% 2 8% 5% 5% 5% 5% 6% 7% 31%	2827
	21st to end	Night	18% 7% 3 8% 5% 4 5% 4 5% 6% 36%	3509
September	1st to 10th	Night	17% 5% 3 6% 5% 4 3 3 5% 7% 43%	2000
	11th to 20th	Night	15% 6% 2 5% 4 3 4 3 4 8% 47%	2150
	21st to end	Night	19% 7% 2 6% 4 4 4 2 4 7% 41%	2200
October	1st to 10th	Night	18% 8% 3 6% 5% 4 5% 3 5% 6% 39%	2239
	11th to 20th	Night	22% 9% 3 7% 5% 5% 4 3 4 5% 32%	2535
	21st to end	Night	26% 10% 3 7% 4 4 4 3 5% 6% 28%	2860
November	1st to 10th	Night	20% 12% 3 8% 6% 4 4 2 5% 5% 31%	2667
	11th to 20th	Night	21% 13% 4 9% 4 4 4 3 4 6% 28%	2753
	21st to end	Night	22% 18% 4 9% 5% 4 4 3 4 5% 23%	2997
December	1st to 10th	Night	18% 17% 7% 12% 7% 4 5% 4 4 4 18%	5060
	11th to 20th	Night	23% 15% 4 11% 5% 4 4 3 4 5% 21%	5741
	21st to end	Night	22% 17% 5% 9% 5% 4 3 2 5% 5% 22%	7262

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	71% 3 8% 14% 4	3678
	11th to 20th	Day	68% 4 7% 15% 5% 1	3680
	21st to end	Day	56% 5% 8% 18% 13%	4048
February	1st to 10th	Day	64% 4 7% 15% 8% 2	1630
	11th to 20th	Day	64% 5% 10% 13% 7% 1	1926
	21st to end	Day	59% 5% 9% 18% 8% 2	1650
March	1st to 10th	Day	65% 4 7% 13% 9% 3	4479
	11th to 20th	Day	56% 6% 14% 14% 10% 1	4694
	21st to end	Day	56% 4 6% 17% 14% 2	5913
April	1st to 10th	Day	60% 4 9% 15% 10% 3	2400
	11th to 20th	Day	51% 4 8% 23% 11% 2	2435
	21st to end	Day	57% 4 8% 17% 12% 2	2600
May	1st to 10th	Day	57% 5% 10% 17% 11% 1	6117
	11th to 20th	Day	52% 7% 15% 16% 8% 2	6322
	21st to end	Day	54% 6% 9% 17% 12% 2	6949
June	1st to 10th	Day	52% 6% 11% 20% 8% 1	2880
	11th to 20th	Day	45% 6% 14% 22% 12% 1	3000
	21st to end	Day	56% 6% 11% 17% 9%	2879
July	1st to 10th	Day	50% 7% 15% 22% 6%	6290
	11th to 20th	Day	43% 7% 19% 26% 5%	6285
	21st to end	Day	38% 6% 17% 30% 9%	6728
August	1st to 10th	Day	46% 7% 21% 20% 6%	4549
	11th to 20th	Day	49% 8% 18% 20% 6%	4228
	21st to end	Day	46% 5% 15% 20% 12% 1	4388
September	1st to 10th	Day	42% 5% 16% 26% 10% 1	2400
	11th to 20th	Day	38% 5% 15% 30% 12%	2250
	21st to end	Day	46% 5% 13% 26% 9%	2200
October	1st to 10th	Day	50% 6% 14% 25% 5%	3510
	11th to 20th	Day	53% 6% 18% 22% 2	3015
	21st to end	Day	54% 5% 17% 18% 6%	3180
November	1st to 10th	Day	57% 4 12% 19% 7%	1851
	11th to 20th	Day	63% 4 10% 16% 7%	1864
	21st to end	Day	67% 6% 11% 13% 3	1619
December	1st to 10th	Day	67% 4 10% 14% 5%	2350
	11th to 20th	Day	63% 4 8% 16% 10%	2688
	21st to end	Day	65% 5% 9% 12% 9% 1	3936
January	1st to 10th	Night	72% 4 9% 11% 4	6489
	11th to 20th	Night	73% 4 7% 12% 3	6500
	21st to end	Night	59% 4 9% 16% 11%	7150
February	1st to 10th	Night	63% 4 8% 15% 8% 1	2766
	11th to 20th	Night	64% 5% 8% 14% 8% 1	2370
	21st to end	Night	58% 4 8% 17% 12% 1	1980
March	1st to 10th	Night	64% 3 9% 12% 11% 1	5374
	11th to 20th	Night	60% 4 12% 14% 8% 1	5266
	21st to end	Night	59% 3 5% 21% 10% 2	5018
April	1st to 10th	Night	58% 3 9% 17% 11% 2	2000
	11th to 20th	Night	53% 4 7% 21% 12% 2	1913
	21st to end	Night	53% 5% 8% 17% 14% 2	1800
May	1st to 10th	Night	59% 4 10% 16% 10% 1	3881
	11th to 20th	Night	54% 5% 10% 20% 9% 1	3576
	21st to end	Night	50% 5% 13% 15% 16% 1	3927
June	1st to 10th	Night	50% 4 12% 22% 11% 1	1515
	11th to 20th	Night	45% 6% 12% 21% 13% 3	1400
	21st to end	Night	53% 5% 13% 18% 11% 1	1511
July	1st to 10th	Night	48% 6% 20% 20% 6%	3560
	11th to 20th	Night	46% 6% 19% 23% 5%	3552
	21st to end	Night	40% 7% 16% 27% 9%	3809
August	1st to 10th	Night	48% 7% 16% 22% 6%	2576
	11th to 20th	Night	50% 7% 18% 19% 6%	2854
	21st to end	Night	48% 5% 12% 23% 12%	3509
September	1st to 10th	Night	42% 6% 14% 26% 11% 1	2000
	11th to 20th	Night	38% 4 18% 30% 9% 1	2150
	21st to end	Night	44% 5% 11% 27% 13%	2200
October	1st to 10th	Night	49% 5% 13% 25% 8%	3655
	11th to 20th	Night	51% 5% 15% 26% 3	4123
	21st to end	Night	50% 4 17% 18% 10%	4610
November	1st to 10th	Night	57% 5% 12% 19% 6% 1	2667
	11th to 20th	Night	59% 5% 11% 17% 8%	2753
	21st to end	Night	66% 4 10% 15% 5%	2997
December	1st to 10th	Night	70% 4 11% 12% 3	5060
	11th to 20th	Night	66% 5% 6% 17% 6%	5742
	21st to end	Night	65% 3 8% 16% 7%	7262

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	34% 18% 30% 15% 2	220
	11th to 20th	Day	29% 23% 34% 9% 5% 1	220
	21st to end	Day	26% 21% 34% 14% 5%	242
February	1st to 10th	Day	25% 26% 38% 9% 3	215
	11th to 20th	Day	26% 23% 37% 11% 2	465
	21st to end	Day	27% 24% 29% 17% 3	414
March	1st to 10th	Day	29% 20% 28% 18% 5%	500
	11th to 20th	Day	27% 22% 30% 15% 4 1	500
	21st to end	Day	29% 20% 26% 17% 7% 1	550
April	1st to 10th	Day	32% 18% 28% 16% 5% 1	500
	11th to 20th	Day	31% 18% 26% 19% 5% 1	492
	21st to end	Day	30% 20% 31% 13% 5% 1	500
May	1st to 10th	Day	29% 20% 30% 16% 5% 1	503
	11th to 20th	Day	22% 14% 31% 23% 9% 2	527
	21st to end	Day	22% 21% 32% 18% 7% 1	573
June	1st to 10th	Day	23% 14% 34% 20% 8% 1	610
	11th to 20th	Day	22% 11% 30% 25% 10% 1	730
	21st to end	Day	25% 12% 29% 24% 8% 2	609
July	1st to 10th	Day	17% 12% 32% 27% 10% 1	525
	11th to 20th	Day	16% 13% 36% 24% 9% 2	524
	21st to end	Day	17% 10% 32% 30% 10% 1	576
August	1st to 10th	Day	18% 9% 29% 28% 12% 4	526
	11th to 20th	Day	19% 7% 25% 30% 14% 4	519
	21st to end	Day	21% 14% 27% 19% 14% 6%	583
September	1st to 10th	Day	18% 11% 30% 26% 11% 4	530
	11th to 20th	Day	18% 10% 27% 24% 16% 6%	530
	21st to end	Day	20% 14% 26% 24% 12% 5%	530
October	1st to 10th	Day	22% 12% 30% 24% 9% 3	530
	11th to 20th	Day	27% 14% 31% 18% 9% 1	455
	21st to end	Day	33% 17% 27% 18% 5%	462
November	1st to 10th	Day	34% 14% 29% 18% 4	425
	11th to 20th	Day	30% 19% 27% 16% 7%	404
	21st to end	Day	35% 21% 28% 13% 2	220
December	1st to 10th	Day	32% 16% 28% 18% 5% 1	220
	11th to 20th	Day	33% 21% 31% 10% 3 1	220
	21st to end	Day	32% 20% 29% 14% 4 1	242
January	1st to 10th	Night	28% 15% 35% 18% 3	840
	11th to 20th	Night	29% 16% 31% 20% 4	840
	21st to end	Night	18% 13% 36% 27% 6%	924
February	1st to 10th	Night	20% 15% 35% 25% 4	801
	11th to 20th	Night	22% 20% 38% 16% 4	783
	21st to end	Night	26% 14% 33% 23% 4	660
March	1st to 10th	Night	25% 14% 36% 22% 3	800
	11th to 20th	Night	25% 15% 35% 19% 5% 1	800
	21st to end	Night	24% 15% 31% 24% 6% 1	880
April	1st to 10th	Night	31% 15% 30% 20% 4	800
	11th to 20th	Night	27% 15% 32% 21% 4	729
	21st to end	Night	30% 16% 28% 21% 6%	600
May	1st to 10th	Night	26% 12% 30% 26% 5%	525
	11th to 20th	Night	26% 8% 31% 28% 6%	394
	21st to end	Night	25% 10% 33% 26% 6%	433
June	1st to 10th	Night	26% 6% 31% 32% 5%	400
	11th to 20th	Night	21% 8% 28% 33% 10%	400
	21st to end	Night	22% 9% 27% 31% 11%	400
July	1st to 10th	Night	16% 6% 31% 36% 11%	390
	11th to 20th	Night	18% 5% 28% 36% 12% 1	388
	21st to end	Night	15% 6% 27% 43% 9%	438
August	1st to 10th	Night	16% 3 23% 40% 17% 1	398
	11th to 20th	Night	16% 7% 24% 37% 14% 1	559
	21st to end	Night	17% 8% 29% 29% 16% 1	829
September	1st to 10th	Night	19% 8% 27% 34% 11% 2	800
	11th to 20th	Night	18% 6% 26% 31% 18% 2	800
	21st to end	Night	20% 8% 30% 28% 13% 1	800
October	1st to 10th	Night	21% 9% 30% 31% 9% 1	800
	11th to 20th	Night	25% 12% 29% 26% 7% 1	800
	21st to end	Night	32% 12% 31% 21% 5%	880
November	1st to 10th	Night	30% 15% 28% 21% 6%	820
	11th to 20th	Night	28% 14% 30% 19% 9% 1	840
	21st to end	Night	32% 16% 26% 20% 6% 1	870
December	1st to 10th	Night	30% 16% 27% 20% 6%	950
	11th to 20th	Night	28% 20% 27% 18% 6%	950
	21st to end	Night	35% 14% 29% 17% 4 1	949

Page generated at 2026-01-29 01:21:40. Version ac07

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