La Butte à Mounette
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the La Butte à Mounette clear sky chart from 2005-11-06 to 2026-06-01.

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	17% 13% 5% 12% 6% 5% 4 3 4 5% 26%	133271
	Night	19% 14% 6% 15% 7% 4 4 3 4 5% 21%	130082
Transparency	Day	61% 5% 12% 16% 6%	136752
	Night	67% 4 9% 14% 5%	134696
Seeing	Day	24% 9% 24% 27% 14% 2	19830
	Night	27% 10% 25% 26% 11% 2	26788

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	14% 22% 10% 29% 11% 3 2 1 1 2 4	4690
	11th to 20th	Day	18% 17% 11% 27% 7% 5% 3 2 3 2 5%	4681
	21st to end	Day	7% 13% 7% 30% 18% 10% 3 1 2 2 6%	5306
February	1st to 10th	Day	17% 16% 6% 20% 11% 6% 4 2 2 3 12%	1890
	11th to 20th	Day	17% 16% 4 17% 11% 6% 4 2 3 4 16%	1843
	21st to end	Day	12% 13% 5% 12% 8% 8% 5% 3 5% 6% 25%	1649
March	1st to 10th	Day	16% 15% 5% 13% 10% 7% 4 3 3 4 21%	4668
	11th to 20th	Day	15% 13% 6% 17% 7% 5% 4 3 5% 5% 20%	5090
	21st to end	Day	23% 14% 7% 16% 6% 4 4 3 4 4 15%	5816
April	1st to 10th	Day	22% 12% 4 10% 4 4 3 3 4 5% 28%	2520
	11th to 20th	Day	18% 11% 4 8% 3 4 4 3 5% 7% 32%	2503
	21st to end	Day	20% 12% 3 7% 4 3 3 3 5% 6% 34%	2792
May	1st to 10th	Day	21% 15% 5% 9% 4 4 3 2 3 4 28%	6485
	11th to 20th	Day	20% 8% 3 7% 4 4 4 3 5% 6% 36%	6458
	21st to end	Day	16% 10% 4 7% 4 4 4 3 5% 7% 36%	7102
June	1st to 10th	Day	24% 11% 4 8% 4 4 3 3 5% 6% 28%	2800
	11th to 20th	Day	16% 9% 3 7% 5% 4 5% 3 5% 6% 37%	2972
	21st to end	Day	23% 11% 4 8% 5% 4 3 3 5% 6% 30%	3000
July	1st to 10th	Day	14% 9% 4 10% 6% 5% 5% 4 6% 8% 29%	6738
	11th to 20th	Day	14% 7% 2 7% 4 4 4 4 5% 7% 40%	6360
	21st to end	Day	13% 8% 3 7% 5% 5% 4 4 5% 7% 39%	6927
August	1st to 10th	Day	16% 8% 3 7% 5% 4 4 4 6% 8% 34%	4517
	11th to 20th	Day	15% 8% 3 7% 4 4 4 3 5% 7% 39%	4175
	21st to end	Day	17% 7% 2 6% 4 4 4 3 5% 7% 40%	4411
September	1st to 10th	Day	18% 7% 3 6% 4 4 4 4 6% 8% 37%	2400
	11th to 20th	Day	18% 9% 3 7% 5% 4 3 3 5% 7% 36%	2400
	21st to end	Day	19% 9% 3 7% 5% 3 4 2 5% 6% 36%	2112
October	1st to 10th	Day	19% 8% 3 8% 4 5% 5% 4 7% 7% 32%	2000
	11th to 20th	Day	22% 14% 3 9% 5% 4 5% 4 5% 6% 23%	2000
	21st to end	Day	22% 18% 3 9% 4 5% 4 3 4 6% 22%	2045
November	1st to 10th	Day	24% 22% 5% 8% 5% 3 4 3 4 5% 17%	1725
	11th to 20th	Day	25% 26% 6% 10% 6% 4 4 3 3 4 9%	1680
	21st to end	Day	21% 25% 12% 11% 6% 3 3 2 5% 4 9%	1680
December	1st to 10th	Day	16% 23% 12% 22% 7% 4 4 2 2 3 5%	2690
	11th to 20th	Day	24% 19% 11% 20% 5% 3 2 1 2 2 10%	3076
	21st to end	Day	21% 18% 9% 21% 6% 4 3 2 2 2 11%	4070
January	1st to 10th	Night	17% 20% 11% 28% 9% 3 2 1 2 2 5%	8234
	11th to 20th	Night	19% 18% 10% 29% 7% 4 3 2 2 2 6%	8234
	21st to end	Night	7% 15% 8% 28% 19% 9% 3 1 2 2 6%	8894
February	1st to 10th	Night	16% 15% 5% 20% 12% 5% 4 3 3 3 14%	2730
	11th to 20th	Night	17% 16% 6% 15% 10% 5% 3 3 4 5% 16%	2663
	21st to end	Night	12% 14% 5% 14% 8% 5% 4 4 5% 6% 25%	2156
March	1st to 10th	Night	18% 13% 4 14% 11% 4 3 2 3 4 21%	5378
	11th to 20th	Night	18% 16% 5% 15% 6% 5% 3 3 4 5% 20%	5089
	21st to end	Night	23% 17% 6% 13% 5% 4 3 3 4 5% 17%	5358
April	1st to 10th	Night	22% 13% 4 9% 6% 4 3 2 4 5% 26%	2100
	11th to 20th	Night	20% 11% 4 7% 4 4 3 3 5% 6% 32%	2064
	21st to end	Night	21% 11% 3 8% 4 4 4 3 4 5% 32%	1827
May	1st to 10th	Night	25% 16% 4 8% 4 4 3 3 4 5% 24%	3695
	11th to 20th	Night	20% 9% 3 5% 3 4 4 3 5% 7% 36%	3676
	21st to end	Night	14% 9% 3 7% 5% 4 5% 4 5% 6% 38%	4036
June	1st to 10th	Night	26% 11% 3 7% 4 4 5% 2 5% 6% 25%	1601
	11th to 20th	Night	21% 6% 2 7% 4 4 4 3 5% 7% 36%	1442
	21st to end	Night	21% 12% 4 7% 5% 5% 4 4 6% 6% 28%	1400
July	1st to 10th	Night	18% 11% 6% 11% 6% 5% 5% 4 5% 6% 22%	3178
	11th to 20th	Night	12% 6% 3 8% 5% 6% 5% 4 7% 7% 38%	3620
	21st to end	Night	17% 7% 2 7% 5% 4 5% 3 5% 6% 40%	3948
August	1st to 10th	Night	18% 8% 2 6% 5% 5% 6% 5% 7% 8% 30%	2626
	11th to 20th	Night	15% 8% 3 7% 5% 3 4 3 6% 7% 38%	2872
	21st to end	Night	14% 7% 2 5% 3 4 4 3 6% 8% 43%	3487
September	1st to 10th	Night	17% 7% 2 7% 5% 4 4 3 5% 8% 39%	2000
	11th to 20th	Night	23% 7% 3 6% 4 4 3 2 4 6% 39%	2000
	21st to end	Night	20% 8% 3 7% 4 4 4 3 5% 6% 36%	2285
October	1st to 10th	Night	21% 8% 3 7% 5% 4 4 4 5% 6% 32%	2400
	11th to 20th	Night	24% 14% 4 7% 5% 4 3 3 4 5% 27%	2400
	21st to end	Night	25% 15% 4 9% 5% 5% 4 2 5% 5% 20%	2795
November	1st to 10th	Night	22% 19% 4 8% 5% 4 4 3 4 4 21%	2791
	11th to 20th	Night	26% 23% 6% 9% 5% 4 4 3 5% 4 11%	2940
	21st to end	Night	25% 25% 9% 11% 5% 4 4 2 3 4 8%	2940
December	1st to 10th	Night	18% 20% 11% 20% 7% 5% 4 3 3 3 7%	4720
	11th to 20th	Night	24% 17% 8% 20% 6% 3 2 1 2 3 13%	5353
	21st to end	Night	22% 19% 8% 22% 4 2 2 2 2 4 12%	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	91% 2 4 2 1	4691
	11th to 20th	Day	86% 5% 5% 2 2	4710
	21st to end	Day	87% 4 3 4 2	5306
February	1st to 10th	Day	80% 3 6% 8% 4	1890
	11th to 20th	Day	74% 4 9% 9% 3 1	1851
	21st to end	Day	60% 6% 10% 15% 8% 1	1649
March	1st to 10th	Day	68% 3 8% 15% 5%	4672
	11th to 20th	Day	66% 7% 12% 11% 4 1	5090
	21st to end	Day	73% 3 6% 13% 4 1	5816
April	1st to 10th	Day	58% 5% 10% 15% 10% 1	2520
	11th to 20th	Day	52% 4 12% 21% 11% 1	2503
	21st to end	Day	51% 4 12% 18% 12% 2	2792
May	1st to 10th	Day	61% 5% 10% 16% 8%	6497
	11th to 20th	Day	49% 4 14% 24% 8%	6462
	21st to end	Day	48% 7% 13% 23% 10%	7102
June	1st to 10th	Day	58% 7% 11% 17% 7%	2800
	11th to 20th	Day	48% 6% 14% 22% 9% 1	2972
	21st to end	Day	56% 6% 12% 17% 9% 1	3000
July	1st to 10th	Day	54% 4 16% 18% 8%	6664
	11th to 20th	Day	44% 4 21% 26% 6%	6284
	21st to end	Day	45% 4 21% 24% 6%	6730
August	1st to 10th	Day	48% 7% 18% 22% 5%	4503
	11th to 20th	Day	46% 5% 16% 26% 7% 1	4214
	21st to end	Day	45% 4 15% 28% 8%	4411
September	1st to 10th	Day	43% 8% 16% 24% 9%	2400
	11th to 20th	Day	49% 5% 16% 22% 8%	2400
	21st to end	Day	50% 5% 12% 25% 8%	2112
October	1st to 10th	Day	54% 4 15% 22% 5%	3260
	11th to 20th	Day	62% 3 13% 17% 5%	3240
	21st to end	Day	59% 4 15% 18% 5%	3291
November	1st to 10th	Day	70% 6% 11% 10% 3	1725
	11th to 20th	Day	81% 5% 8% 5% 1	1680
	21st to end	Day	80% 4 10% 4 2	1680
December	1st to 10th	Day	87% 2 4 6% 1	2690
	11th to 20th	Day	85% 1 7% 6% 1	3075
	21st to end	Day	81% 4 7% 7% 1	4070
January	1st to 10th	Night	89% 3 3 4 1	8234
	11th to 20th	Night	88% 2 4 4 1	8280
	21st to end	Night	88% 3 3 4 2	8894
February	1st to 10th	Night	75% 5% 8% 8% 4	2730
	11th to 20th	Night	71% 5% 9% 12% 3 1	2666
	21st to end	Night	60% 5% 10% 15% 9% 1	2156
March	1st to 10th	Night	68% 3 7% 13% 7% 1	5387
	11th to 20th	Night	66% 5% 11% 12% 4 1	5090
	21st to end	Night	70% 3 6% 15% 5% 1	5358
April	1st to 10th	Night	61% 4 9% 14% 11% 1	2100
	11th to 20th	Night	52% 4 10% 22% 11% 1	2064
	21st to end	Night	54% 5% 10% 16% 13% 2	1827
May	1st to 10th	Night	63% 5% 8% 16% 8%	3700
	11th to 20th	Night	48% 5% 12% 26% 9% 1	3677
	21st to end	Night	46% 7% 14% 24% 10% 1	4037
June	1st to 10th	Night	60% 6% 9% 18% 7%	1601
	11th to 20th	Night	47% 6% 12% 24% 11%	1442
	21st to end	Night	56% 6% 12% 17% 9% 1	1400
July	1st to 10th	Night	63% 3 10% 17% 6% 1	3143
	11th to 20th	Night	46% 4 17% 25% 8%	3572
	21st to end	Night	46% 4 19% 25% 7%	3831
August	1st to 10th	Night	50% 7% 18% 21% 5%	2615
	11th to 20th	Night	46% 5% 17% 25% 7% 1	2899
	21st to end	Night	40% 4 14% 33% 8%	3486
September	1st to 10th	Night	44% 6% 14% 28% 9%	2000
	11th to 20th	Night	48% 4 13% 24% 10% 1	2000
	21st to end	Night	49% 6% 13% 24% 8%	2285
October	1st to 10th	Night	56% 4 12% 21% 7%	3920
	11th to 20th	Night	59% 3 11% 22% 5%	3899
	21st to end	Night	63% 3 10% 17% 7%	4507
November	1st to 10th	Night	66% 7% 11% 12% 4	2791
	11th to 20th	Night	77% 5% 8% 7% 2	2940
	21st to end	Night	82% 5% 8% 5% 1	2940
December	1st to 10th	Night	84% 2 5% 8% 1	4720
	11th to 20th	Night	81% 2 6% 9% 2	5355
	21st to end	Night	79% 3 7% 10% 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	29% 16% 32% 17% 5%	430
	11th to 20th	Day	27% 18% 26% 22% 7% 1	430
	21st to end	Day	18% 15% 32% 27% 7% 1	473
February	1st to 10th	Day	27% 15% 33% 17% 7% 2	430
	11th to 20th	Day	27% 15% 29% 22% 6% 1	426
	21st to end	Day	19% 12% 31% 27% 9% 2	355
March	1st to 10th	Day	20% 13% 33% 25% 7% 1	452
	11th to 20th	Day	19% 14% 28% 24% 12% 3	540
	21st to end	Day	23% 13% 30% 25% 7% 2	594
April	1st to 10th	Day	28% 14% 29% 21% 6% 1	540
	11th to 20th	Day	21% 11% 29% 25% 12% 2	532
	21st to end	Day	25% 8% 22% 27% 16% 2	602
May	1st to 10th	Day	30% 6% 20% 28% 12% 4	753
	11th to 20th	Day	25% 5% 20% 26% 21% 4	774
	21st to end	Day	24% 4 24% 34% 12% 2	845
June	1st to 10th	Day	28% 5% 17% 30% 18% 2	730
	11th to 20th	Day	19% 5% 20% 35% 20% 2	730
	21st to end	Day	28% 3 18% 29% 20% 3	730
July	1st to 10th	Day	21% 1 18% 39% 18% 3	720
	11th to 20th	Day	18% 2 18% 34% 25% 4	718
	21st to end	Day	24% 2 16% 33% 22% 3	795
August	1st to 10th	Day	15% 3 15% 35% 27% 5%	704
	11th to 20th	Day	20% 3 15% 30% 27% 5%	519
	21st to end	Day	19% 5% 19% 30% 25% 3	583
September	1st to 10th	Day	18% 5% 26% 32% 16% 3	530
	11th to 20th	Day	23% 8% 22% 30% 15% 1	530
	21st to end	Day	22% 7% 31% 25% 14% 1	445
October	1st to 10th	Day	21% 8% 24% 31% 15% 1	420
	11th to 20th	Day	28% 11% 23% 23% 13% 2	420
	21st to end	Day	28% 14% 31% 20% 7% 1	462
November	1st to 10th	Day	32% 18% 29% 16% 4 1	425
	11th to 20th	Day	38% 13% 23% 18% 6% 2	430
	21st to end	Day	35% 17% 27% 19% 3	430
December	1st to 10th	Day	33% 14% 30% 19% 4	430
	11th to 20th	Day	31% 22% 25% 20% 1	430
	21st to end	Day	28% 17% 28% 18% 8% 1	473
January	1st to 10th	Night	31% 16% 28% 18% 7%	950
	11th to 20th	Night	31% 15% 27% 21% 6% 1	950
	21st to end	Night	22% 17% 33% 20% 8% 1	1015
February	1st to 10th	Night	24% 13% 32% 21% 8% 1	840
	11th to 20th	Night	26% 12% 33% 22% 6% 1	823
	21st to end	Night	20% 11% 31% 25% 12% 2	692
March	1st to 10th	Night	20% 11% 34% 25% 8% 1	840
	11th to 20th	Night	25% 10% 28% 26% 9% 2	840
	21st to end	Night	25% 11% 28% 27% 8% 2	824
April	1st to 10th	Night	27% 10% 26% 29% 8%	630
	11th to 20th	Night	25% 8% 25% 28% 12% 1	624
	21st to end	Night	24% 6% 24% 29% 15% 2	630
May	1st to 10th	Night	31% 4 23% 25% 12% 5%	630
	11th to 20th	Night	27% 4 17% 31% 18% 4	622
	21st to end	Night	22% 5% 25% 32% 14% 2	682
June	1st to 10th	Night	29% 5% 17% 34% 13% 2	601
	11th to 20th	Night	23% 3 18% 36% 19% 2	442
	21st to end	Night	25% 3 17% 37% 17% 2	400
July	1st to 10th	Night	23% 3 14% 37% 20% 3	395
	11th to 20th	Night	15% 3 16% 40% 24% 1	582
	21st to end	Night	21% 5% 15% 37% 20% 2	656
August	1st to 10th	Night	18% 1 15% 40% 22% 4	598
	11th to 20th	Night	19% 4 14% 36% 24% 3	592
	21st to end	Night	18% 4 18% 35% 22% 4	660
September	1st to 10th	Night	19% 4 26% 34% 15% 2	600
	11th to 20th	Night	25% 8% 19% 29% 17% 2	600
	21st to end	Night	22% 8% 28% 28% 11% 2	730
October	1st to 10th	Night	26% 7% 24% 29% 12% 1	800
	11th to 20th	Night	32% 10% 22% 23% 12% 2	800
	21st to end	Night	34% 14% 24% 21% 6% 1	965
November	1st to 10th	Night	34% 17% 23% 20% 6% 1	930
	11th to 20th	Night	37% 15% 26% 16% 6% 1	950
	21st to end	Night	37% 15% 24% 19% 4	950
December	1st to 10th	Night	34% 17% 29% 15% 6%	950
	11th to 20th	Night	34% 22% 26% 14% 3	950
	21st to end	Night	32% 15% 27% 20% 5% 1	1045

Page generated at 2026-05-29 01:53:25. Version ac07

Copyright © 2026 Attilla Danko.