Observatoire de Labelle Etoile
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire de Labelle Etoile clear sky chart from 2005-11-06 to 2026-01-17.

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% 4 10% 6% 4 4 3 5% 6% 28%	127686
	Night	17% 14% 5% 11% 6% 4 4 3 4 5% 27%	123996
Transparency	Day	56% 5% 11% 18% 8% 1	131117
	Night	58% 5% 12% 16% 8% 1	128652
Seeing	Day	26% 17% 28% 18% 8% 2	15868
	Night	25% 13% 26% 25% 10% 1	24964

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% 19% 7% 23% 10% 6% 4 2 3 3 11%	3677
	11th to 20th	Day	11% 18% 7% 21% 10% 3 2 2 4 4 16%	3618
	21st to end	Day	8% 16% 9% 15% 6% 5% 6% 3 5% 5% 20%	3960
February	1st to 10th	Day	10% 19% 7% 14% 9% 5% 3 3 4 4 20%	1785
	11th to 20th	Day	12% 20% 6% 13% 7% 5% 4 3 3 5% 22%	1790
	21st to end	Day	15% 19% 5% 10% 8% 5% 4 4 4 4 22%	1650
March	1st to 10th	Day	17% 17% 7% 14% 7% 4 4 2 5% 4 20%	4476
	11th to 20th	Day	15% 16% 5% 11% 6% 4 4 3 4 6% 26%	4832
	21st to end	Day	17% 14% 4 9% 6% 4 3 3 4 5% 32%	5873
April	1st to 10th	Day	21% 16% 4 8% 5% 3 4 2 4 4 29%	2400
	11th to 20th	Day	21% 14% 4 7% 4 4 3 3 4 4 32%	2374
	21st to end	Day	20% 13% 3 8% 5% 4 4 3 4 4 30%	2581
May	1st to 10th	Day	23% 13% 4 9% 5% 5% 4 4 5% 5% 23%	6346
	11th to 20th	Day	19% 9% 3 8% 5% 5% 4 3 5% 7% 31%	6318
	21st to end	Day	23% 10% 3 8% 5% 4 4 3 4 5% 30%	6949
June	1st to 10th	Day	24% 9% 3 7% 5% 5% 4 4 6% 6% 27%	2800
	11th to 20th	Day	17% 6% 3 7% 5% 6% 6% 5% 6% 7% 32%	2800
	21st to end	Day	23% 8% 3 7% 5% 5% 5% 4 7% 6% 28%	2800
July	1st to 10th	Day	18% 8% 3 8% 6% 5% 6% 5% 7% 9% 28%	6360
	11th to 20th	Day	14% 7% 3 7% 5% 4 5% 4 6% 9% 36%	6360
	21st to end	Day	12% 6% 2 6% 4 4 5% 4 6% 10% 42%	6926
August	1st to 10th	Day	17% 7% 3 8% 6% 5% 6% 4 7% 8% 29%	4563
	11th to 20th	Day	16% 9% 3 7% 5% 5% 5% 4 6% 7% 33%	4175
	21st to end	Day	16% 6% 3 7% 4 5% 5% 4 7% 8% 35%	4312
September	1st to 10th	Day	18% 5% 2 6% 5% 4 4 4 5% 8% 39%	2400
	11th to 20th	Day	16% 7% 3 5% 4 4 4 4 6% 7% 41%	2360
	21st to end	Day	23% 7% 2 6% 4 3 3 4 4 7% 37%	2194
October	1st to 10th	Day	23% 9% 3 6% 5% 4 5% 3 4 7% 32%	2000
	11th to 20th	Day	25% 15% 4 7% 4 4 4 2 4 5% 26%	1991
	21st to end	Day	27% 17% 3 8% 4 4 4 3 4 5% 23%	1980
November	1st to 10th	Day	18% 18% 4 8% 4 3 4 3 4 6% 27%	1851
	11th to 20th	Day	21% 18% 7% 11% 6% 3 4 3 4 4 19%	1711
	21st to end	Day	22% 19% 7% 13% 6% 4 3 3 3 4 16%	1680
December	1st to 10th	Day	19% 23% 10% 12% 8% 4 3 3 3 4 11%	2680
	11th to 20th	Day	18% 20% 7% 14% 7% 4 4 3 4 3 17%	3066
	21st to end	Day	18% 18% 5% 13% 5% 6% 5% 3 4 4 19%	4048
January	1st to 10th	Night	12% 23% 10% 17% 8% 4 3 2 3 3 15%	6489
	11th to 20th	Night	11% 18% 7% 20% 12% 5% 4 3 4 4 13%	6400
	21st to end	Night	9% 16% 8% 16% 8% 7% 6% 4 4 5% 18%	6996
February	1st to 10th	Night	12% 17% 6% 14% 7% 6% 5% 4 4 4 22%	2610
	11th to 20th	Night	13% 16% 7% 15% 7% 5% 4 3 4 4 21%	2494
	21st to end	Night	15% 16% 6% 10% 7% 4 5% 3 4 5% 24%	1980
March	1st to 10th	Night	19% 16% 6% 12% 6% 4 4 2 3 4 24%	5364
	11th to 20th	Night	13% 15% 5% 10% 5% 5% 4 3 5% 7% 28%	5123
	21st to end	Night	16% 13% 4 11% 6% 5% 4 3 4 5% 27%	5059
April	1st to 10th	Night	23% 13% 4 7% 4 4 3 3 5% 4 30%	2000
	11th to 20th	Night	20% 11% 4 6% 4 3 3 3 6% 5% 34%	1975
	21st to end	Night	20% 12% 3 8% 4 4 3 3 4 5% 33%	1835
May	1st to 10th	Night	21% 13% 3 7% 4 5% 5% 4 5% 6% 27%	3594
	11th to 20th	Night	19% 10% 3 7% 5% 4 4 3 5% 7% 33%	3575
	21st to end	Night	22% 10% 3 8% 5% 5% 5% 4 5% 6% 28%	3926
June	1st to 10th	Night	20% 8% 4 6% 4 5% 4 4 6% 7% 31%	1600
	11th to 20th	Night	17% 8% 2 5% 5% 5% 4 4 6% 6% 39%	1600
	21st to end	Night	21% 7% 2 5% 6% 4 5% 4 5% 6% 34%	1600
July	1st to 10th	Night	16% 7% 3 8% 5% 5% 6% 5% 7% 8% 29%	3600
	11th to 20th	Night	17% 7% 3 6% 4 4 5% 3 6% 7% 39%	3600
	21st to end	Night	11% 5% 2 5% 4 5% 5% 4 6% 8% 45%	3926
August	1st to 10th	Night	14% 8% 3 8% 5% 5% 4 4 5% 7% 37%	2586
	11th to 20th	Night	18% 8% 2 6% 4 4 5% 3 6% 6% 38%	2836
	21st to end	Night	20% 6% 3 7% 4 4 4 3 5% 6% 37%	3586
September	1st to 10th	Night	18% 7% 2 5% 3 3 2 4 5% 6% 44%	2000
	11th to 20th	Night	17% 6% 2 4 3 3 3 3 5% 6% 47%	2040
	21st to end	Night	18% 8% 2 6% 3 3 3 3 5% 7% 41%	2204
October	1st to 10th	Night	20% 9% 2 6% 3 4 5% 3 4 6% 38%	2400
	11th to 20th	Night	23% 14% 3 7% 5% 4 4 3 4 5% 28%	2408
	21st to end	Night	26% 14% 4 8% 4 4 4 3 4 5% 24%	2860
November	1st to 10th	Night	22% 15% 5% 8% 4 4 4 3 4 5% 26%	2667
	11th to 20th	Night	19% 17% 6% 11% 6% 5% 4 3 4 5% 21%	2905
	21st to end	Night	22% 21% 6% 12% 5% 5% 3 3 4 3 16%	2940
December	1st to 10th	Night	18% 20% 8% 17% 8% 5% 4 3 4 4 11%	4720
	11th to 20th	Night	22% 18% 6% 13% 6% 4 3 2 3 3 20%	5348
	21st to end	Night	21% 21% 5% 11% 6% 4 4 2 3 4 20%	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	79% 3 6% 9% 3	3678
	11th to 20th	Day	74% 2 4 12% 7%	3648
	21st to end	Day	65% 4 9% 12% 9% 1	3960
February	1st to 10th	Day	68% 2 6% 15% 7% 2	1785
	11th to 20th	Day	66% 3 10% 11% 9% 1	1799
	21st to end	Day	66% 2 8% 13% 10% 1	1650
March	1st to 10th	Day	68% 3 6% 10% 10% 2	4479
	11th to 20th	Day	60% 4 13% 12% 10% 1	4832
	21st to end	Day	56% 3 7% 17% 16% 2	5873
April	1st to 10th	Day	59% 3 8% 17% 10% 3	2400
	11th to 20th	Day	56% 3 8% 19% 12% 2	2374
	21st to end	Day	58% 4 8% 15% 12% 3	2581
May	1st to 10th	Day	61% 5% 8% 18% 8% 1	6357
	11th to 20th	Day	52% 6% 14% 18% 9% 1	6322
	21st to end	Day	56% 4 10% 16% 13% 1	6949
June	1st to 10th	Day	55% 6% 10% 17% 11% 1	2800
	11th to 20th	Day	49% 6% 13% 21% 10% 2	2800
	21st to end	Day	55% 6% 12% 17% 9% 1	2800
July	1st to 10th	Day	50% 8% 14% 22% 6%	6290
	11th to 20th	Day	42% 8% 17% 27% 6%	6285
	21st to end	Day	36% 8% 17% 32% 8%	6728
August	1st to 10th	Day	50% 7% 17% 21% 5%	4549
	11th to 20th	Day	46% 8% 17% 24% 5%	4217
	21st to end	Day	44% 7% 15% 20% 12% 1	4312
September	1st to 10th	Day	44% 4 15% 25% 12%	2400
	11th to 20th	Day	41% 5% 14% 30% 10% 1	2360
	21st to end	Day	47% 5% 13% 24% 11%	2194
October	1st to 10th	Day	52% 5% 12% 25% 6%	3260
	11th to 20th	Day	56% 6% 11% 20% 6% 1	3219
	21st to end	Day	58% 6% 18% 13% 5% 1	3180
November	1st to 10th	Day	58% 5% 12% 19% 6% 1	1851
	11th to 20th	Day	69% 4 9% 10% 7% 1	1711
	21st to end	Day	73% 5% 8% 9% 4 1	1680
December	1st to 10th	Day	78% 3 7% 9% 3	2680
	11th to 20th	Day	71% 4 7% 13% 5%	3066
	21st to end	Day	68% 4 7% 15% 6%	4048
January	1st to 10th	Night	75% 3 10% 10% 2	6489
	11th to 20th	Night	74% 3 10% 8% 4	6445
	21st to end	Night	69% 4 8% 8% 11% 1	6996
February	1st to 10th	Night	65% 3 9% 15% 6% 1	2610
	11th to 20th	Night	66% 3 9% 14% 7% 1	2496
	21st to end	Night	61% 3 11% 15% 9% 1	1980
March	1st to 10th	Night	65% 2 9% 11% 11% 2	5374
	11th to 20th	Night	57% 5% 12% 15% 8% 2	5124
	21st to end	Night	58% 4 7% 20% 9% 2	5059
April	1st to 10th	Night	57% 3 10% 16% 12% 3	2000
	11th to 20th	Night	50% 4 10% 21% 14% 2	1975
	21st to end	Night	54% 3 10% 18% 13% 2	1835
May	1st to 10th	Night	55% 7% 10% 18% 8% 2	3600
	11th to 20th	Night	50% 7% 14% 17% 10% 2	3576
	21st to end	Night	56% 5% 11% 16% 11% 1	3927
June	1st to 10th	Night	50% 7% 12% 20% 11%	1600
	11th to 20th	Night	44% 6% 14% 22% 12% 3	1600
	21st to end	Night	50% 7% 12% 20% 12% 1	1600
July	1st to 10th	Night	48% 10% 18% 18% 6%	3560
	11th to 20th	Night	42% 8% 19% 26% 5%	3552
	21st to end	Night	35% 8% 17% 30% 10%	3809
August	1st to 10th	Night	44% 8% 16% 25% 7%	2576
	11th to 20th	Night	45% 7% 19% 23% 7%	2860
	21st to end	Night	47% 6% 15% 22% 10% 2	3586
September	1st to 10th	Night	40% 5% 16% 26% 13% 1	2000
	11th to 20th	Night	38% 4 16% 32% 9% 1	2040
	21st to end	Night	43% 5% 14% 28% 11%	2204
October	1st to 10th	Night	45% 7% 16% 22% 11%	3920
	11th to 20th	Night	52% 5% 15% 20% 8%	3919
	21st to end	Night	56% 5% 16% 14% 8% 1	4610
November	1st to 10th	Night	59% 4 15% 16% 5%	2667
	11th to 20th	Night	65% 4 11% 13% 7% 1	2905
	21st to end	Night	73% 4 9% 11% 3	2940
December	1st to 10th	Night	77% 5% 9% 7% 2	4720
	11th to 20th	Night	71% 3 6% 13% 7%	5348
	21st to end	Night	69% 3 5% 12% 11%	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	19% 22% 40% 15% 4	220
	11th to 20th	Day	28% 21% 32% 12% 6% 1	212
	21st to end	Day	22% 21% 35% 18% 4 1	220
February	1st to 10th	Day	32% 30% 29% 6% 2	293
	11th to 20th	Day	29% 28% 31% 12%	337
	21st to end	Day	30% 25% 30% 13% 2	414
March	1st to 10th	Day	27% 20% 33% 15% 4 1	500
	11th to 20th	Day	30% 22% 28% 16% 3 1	500
	21st to end	Day	32% 23% 25% 14% 5% 2	550
April	1st to 10th	Day	33% 19% 25% 15% 6% 1	500
	11th to 20th	Day	36% 17% 24% 11% 10% 2	492
	21st to end	Day	30% 22% 28% 14% 5% 1	500
May	1st to 10th	Day	32% 19% 30% 12% 5% 2	503
	11th to 20th	Day	25% 18% 29% 18% 8% 2	527
	21st to end	Day	27% 18% 29% 17% 7% 1	573
June	1st to 10th	Day	30% 15% 32% 17% 6% 1	530
	11th to 20th	Day	22% 17% 32% 19% 9% 1	530
	21st to end	Day	27% 16% 31% 17% 8% 2	530
July	1st to 10th	Day	16% 13% 34% 26% 8% 2	525
	11th to 20th	Day	16% 14% 33% 27% 8% 2	524
	21st to end	Day	15% 13% 33% 26% 10% 2	576
August	1st to 10th	Day	18% 10% 25% 32% 12% 2	526
	11th to 20th	Day	17% 8% 28% 25% 14% 7%	519
	21st to end	Day	21% 14% 28% 17% 13% 7%	583
September	1st to 10th	Day	21% 14% 27% 18% 14% 6%	530
	11th to 20th	Day	16% 10% 25% 22% 18% 9%	530
	21st to end	Day	24% 15% 24% 19% 12% 7%	530
October	1st to 10th	Day	28% 16% 22% 18% 13% 3	530
	11th to 20th	Day	34% 19% 24% 15% 6% 2	524
	21st to end	Day	38% 14% 24% 18% 6%	462
November	1st to 10th	Day	34% 16% 25% 18% 5% 1	425
	11th to 20th	Day	29% 25% 27% 11% 8% 1	251
	21st to end	Day	35% 24% 25% 13% 3	220
December	1st to 10th	Day	35% 16% 30% 15% 5%	220
	11th to 20th	Day	31% 25% 26% 15% 1 1	220
	21st to end	Day	31% 20% 29% 13% 5% 2	242
January	1st to 10th	Night	27% 18% 33% 17% 5%	840
	11th to 20th	Night	31% 17% 26% 20% 6%	825
	21st to end	Night	18% 15% 34% 25% 7% 1	880
February	1st to 10th	Night	21% 18% 34% 21% 5% 1	800
	11th to 20th	Night	22% 23% 33% 19% 3	783
	21st to end	Night	25% 18% 28% 25% 4	660
March	1st to 10th	Night	25% 18% 30% 22% 5%	800
	11th to 20th	Night	27% 19% 27% 21% 5% 1	800
	21st to end	Night	25% 15% 28% 23% 8% 1	880
April	1st to 10th	Night	32% 15% 24% 24% 6%	800
	11th to 20th	Night	27% 16% 27% 22% 8% 1	791
	21st to end	Night	26% 17% 27% 21% 8% 1	635
May	1st to 10th	Night	26% 12% 24% 27% 10% 2	400
	11th to 20th	Night	23% 10% 27% 29% 11%	394
	21st to end	Night	21% 8% 33% 28% 9%	433
June	1st to 10th	Night	21% 8% 31% 31% 9% 1	400
	11th to 20th	Night	21% 8% 25% 31% 15% 1	400
	21st to end	Night	22% 6% 19% 36% 17% 1	400
July	1st to 10th	Night	15% 5% 23% 44% 13%	390
	11th to 20th	Night	15% 5% 19% 41% 20% 1	388
	21st to end	Night	13% 5% 23% 39% 18% 2	438
August	1st to 10th	Night	15% 4 16% 42% 23% 1	398
	11th to 20th	Night	15% 5% 18% 34% 26% 2	565
	21st to end	Night	19% 9% 22% 30% 18% 2	880
September	1st to 10th	Night	22% 6% 23% 32% 17% 1	800
	11th to 20th	Night	20% 6% 17% 31% 24% 2	800
	21st to end	Night	22% 9% 21% 28% 18% 2	800
October	1st to 10th	Night	25% 10% 23% 25% 16% 1	800
	11th to 20th	Night	32% 12% 24% 23% 9% 1	800
	21st to end	Night	33% 13% 24% 24% 6%	880
November	1st to 10th	Night	30% 14% 25% 23% 8% 1	820
	11th to 20th	Night	28% 17% 27% 18% 9% 1	840
	21st to end	Night	35% 17% 24% 19% 5% 1	840
December	1st to 10th	Night	30% 18% 27% 18% 6%	840
	11th to 20th	Night	30% 18% 27% 18% 6% 1	840
	21st to end	Night	35% 16% 25% 18% 6%	924

Page generated at 2026-01-14 01:14:28. Version ac07

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