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 2025-02-06.

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% 13% 5% 12% 6% 4 4 3 4 5% 26%	109300
	Night	19% 14% 6% 14% 6% 4 4 3 4 5% 21%	109087
Transparency	Day	61% 5% 12% 16% 6%	112828
	Night	66% 5% 10% 14% 5%	113731
Seeing	Day	24% 8% 23% 27% 14% 2	17970
	Night	27% 10% 25% 26% 11% 2	25046

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% 25% 10% 27% 8% 4 2 1 1 2 4	3616
	11th to 20th	Day	13% 15% 13% 28% 7% 5% 4 3 3 3 7%	3591
	21st to end	Day	8% 11% 7% 33% 18% 7% 3 2 2 2 8%	4092
February	1st to 10th	Day	18% 15% 5% 19% 11% 7% 4 2 2 3 13%	1755
	11th to 20th	Day	18% 16% 4 14% 10% 7% 5% 2 3 4 17%	1663
	21st to end	Day	11% 13% 4 11% 9% 8% 5% 3 5% 6% 25%	1496
March	1st to 10th	Day	18% 14% 5% 9% 6% 7% 3 2 3 5% 28%	3178
	11th to 20th	Day	15% 15% 7% 16% 7% 5% 4 3 5% 4 18%	3480
	21st to end	Day	22% 15% 8% 12% 5% 4 3 3 4 5% 19%	3970
April	1st to 10th	Day	21% 13% 4 9% 4 4 3 3 4 6% 29%	2280
	11th to 20th	Day	18% 11% 4 7% 3 4 4 3 5% 7% 33%	2262
	21st to end	Day	20% 12% 4 7% 3 3 3 3 5% 6% 34%	2526
May	1st to 10th	Day	22% 16% 4 7% 4 4 3 2 4 5% 29%	4425
	11th to 20th	Day	18% 8% 3 6% 4 4 3 3 5% 7% 39%	4398
	21st to end	Day	17% 11% 3 8% 5% 5% 5% 4 5% 7% 30%	4836
June	1st to 10th	Day	25% 12% 4 8% 4 4 3 3 5% 6% 27%	2660
	11th to 20th	Day	17% 9% 3 7% 5% 4 4 3 5% 6% 36%	2823
	21st to end	Day	24% 11% 4 8% 5% 4 3 3 5% 6% 30%	2850
July	1st to 10th	Day	16% 9% 4 9% 5% 4 5% 4 5% 7% 32%	4706
	11th to 20th	Day	16% 9% 3 8% 5% 4 5% 4 6% 7% 35%	4440
	21st to end	Day	14% 8% 3 6% 4 5% 4 4 6% 7% 39%	4815
August	1st to 10th	Day	17% 9% 3 8% 5% 5% 5% 4 6% 8% 32%	4378
	11th to 20th	Day	16% 8% 3 7% 4 4 4 3 5% 7% 38%	4045
	21st to end	Day	17% 7% 2 6% 4 4 4 3 5% 7% 40%	4276
September	1st to 10th	Day	18% 7% 3 6% 4 4 4 4 6% 8% 36%	2280
	11th to 20th	Day	19% 9% 3 7% 5% 4 3 3 4 7% 35%	2280
	21st to end	Day	19% 9% 3 7% 5% 3 4 2 5% 6% 34%	2007
October	1st to 10th	Day	19% 9% 3 8% 4 5% 5% 4 6% 7% 31%	1900
	11th to 20th	Day	23% 13% 3 9% 5% 4 5% 4 4 6% 23%	1900
	21st to end	Day	23% 18% 3 9% 4 5% 4 3 4 5% 21%	1943
November	1st to 10th	Day	23% 22% 4 8% 5% 3 4 3 4 5% 18%	1641
	11th to 20th	Day	26% 24% 6% 11% 6% 4 4 3 3 4 10%	1600
	21st to end	Day	21% 25% 12% 11% 6% 3 3 2 5% 4 10%	1600
December	1st to 10th	Day	16% 22% 12% 21% 7% 5% 4 2 2 3 5%	2610
	11th to 20th	Day	24% 19% 11% 20% 5% 3 2 1 2 2 11%	2996
	21st to end	Day	21% 18% 9% 21% 6% 4 3 2 2 2 11%	3982
January	1st to 10th	Night	18% 22% 12% 27% 5% 3 2 1 2 2 5%	6349
	11th to 20th	Night	17% 17% 11% 31% 7% 4 3 2 2 2 5%	6314
	21st to end	Night	8% 14% 8% 26% 20% 7% 3 2 2 2 7%	6876
February	1st to 10th	Night	16% 14% 4 19% 13% 5% 4 3 4 4 15%	2536
	11th to 20th	Night	17% 16% 6% 15% 9% 5% 3 3 4 5% 18%	2403
	21st to end	Night	12% 14% 5% 13% 8% 5% 4 4 5% 6% 25%	1957
March	1st to 10th	Night	18% 12% 3 9% 8% 4 4 3 4 6% 30%	3648
	11th to 20th	Night	19% 18% 5% 13% 6% 5% 3 3 4 5% 19%	3479
	21st to end	Night	24% 14% 5% 12% 5% 3 3 3 5% 6% 19%	3662
April	1st to 10th	Night	22% 13% 4 9% 6% 4 3 2 4 5% 26%	1900
	11th to 20th	Night	19% 10% 4 7% 4 4 4 3 6% 7% 33%	1866
	21st to end	Night	21% 12% 3 9% 4 4 4 3 4 5% 31%	1653
May	1st to 10th	Night	25% 15% 4 8% 4 4 3 3 5% 6% 24%	2525
	11th to 20th	Night	15% 8% 3 5% 4 5% 4 4 5% 7% 40%	2506
	21st to end	Night	16% 9% 4 8% 6% 4 5% 5% 7% 7% 30%	2749
June	1st to 10th	Night	26% 12% 4 8% 4 5% 5% 2 5% 6% 23%	1520
	11th to 20th	Night	22% 6% 3 7% 4 4 4 3 5% 7% 36%	1370
	21st to end	Night	21% 12% 3 7% 5% 5% 4 4 6% 6% 27%	1330
July	1st to 10th	Night	19% 11% 6% 10% 6% 6% 5% 4 5% 6% 25%	2228
	11th to 20th	Night	15% 8% 2 7% 5% 6% 5% 5% 8% 7% 32%	2530
	21st to end	Night	15% 7% 2 6% 4 3 4 3 5% 6% 46%	2750
August	1st to 10th	Night	18% 8% 2 6% 5% 5% 6% 5% 8% 8% 28%	2545
	11th to 20th	Night	15% 8% 3 7% 5% 3 4 3 6% 7% 37%	2782
	21st to end	Night	14% 8% 2 5% 3 4 4 3 5% 8% 43%	3380
September	1st to 10th	Night	17% 7% 3 7% 5% 4 4 3 5% 8% 38%	1900
	11th to 20th	Night	24% 7% 3 5% 3 4 3 2 4 6% 39%	1900
	21st to end	Night	21% 8% 3 7% 4 4 4 3 5% 6% 36%	2170
October	1st to 10th	Night	22% 8% 3 8% 5% 4 4 4 5% 6% 31%	2280
	11th to 20th	Night	25% 13% 4 7% 5% 4 3 3 4 5% 26%	2280
	21st to end	Night	27% 16% 4 9% 5% 4 4 2 4 5% 19%	2655
November	1st to 10th	Night	22% 19% 5% 8% 5% 4 4 3 4 4 22%	2655
	11th to 20th	Night	26% 22% 6% 9% 5% 4 4 3 5% 5% 12%	2800
	21st to end	Night	26% 25% 9% 11% 5% 4 3 2 3 4 8%	2800
December	1st to 10th	Night	18% 20% 11% 19% 7% 5% 4 2 3 3 7%	4580
	11th to 20th	Night	24% 17% 8% 20% 6% 3 2 1 2 3 13%	5213
	21st to end	Night	22% 19% 9% 21% 4 2 2 2 2 4 12%	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	90% 3 4 2 1	3617
	11th to 20th	Day	83% 7% 6% 3 2	3620
	21st to end	Day	84% 5% 4 5% 2	4092
February	1st to 10th	Day	79% 3 6% 8% 4	1755
	11th to 20th	Day	72% 5% 9% 10% 4 1	1671
	21st to end	Day	59% 7% 10% 15% 8% 1	1496
March	1st to 10th	Day	60% 4 9% 20% 6%	3182
	11th to 20th	Day	66% 9% 8% 12% 4 1	3480
	21st to end	Day	67% 4 7% 14% 6% 1	3970
April	1st to 10th	Day	58% 5% 11% 16% 10% 1	2280
	11th to 20th	Day	50% 5% 12% 20% 11% 1	2262
	21st to end	Day	51% 5% 12% 18% 12% 2	2526
May	1st to 10th	Day	58% 6% 13% 15% 7% 1	4440
	11th to 20th	Day	44% 6% 16% 26% 8%	4402
	21st to end	Day	51% 9% 12% 18% 9%	4836
June	1st to 10th	Day	59% 7% 11% 16% 7%	2660
	11th to 20th	Day	48% 6% 14% 22% 9% 1	2823
	21st to end	Day	56% 6% 12% 16% 8% 1	2850
July	1st to 10th	Day	52% 5% 17% 16% 10%	4632
	11th to 20th	Day	49% 5% 17% 22% 6%	4364
	21st to end	Day	45% 6% 22% 20% 7%	4662
August	1st to 10th	Day	49% 7% 18% 21% 4	4364
	11th to 20th	Day	46% 5% 16% 25% 7%	4084
	21st to end	Day	45% 4 14% 28% 8%	4276
September	1st to 10th	Day	44% 8% 15% 22% 10%	2280
	11th to 20th	Day	49% 6% 16% 21% 8%	2280
	21st to end	Day	51% 6% 13% 24% 7%	2007
October	1st to 10th	Day	54% 4 15% 22% 5%	3160
	11th to 20th	Day	62% 4 13% 18% 4	3140
	21st to end	Day	59% 4 15% 18% 5%	3189
November	1st to 10th	Day	68% 6% 12% 10% 3	1641
	11th to 20th	Day	80% 5% 8% 5% 1	1600
	21st to end	Day	80% 5% 10% 4 2	1600
December	1st to 10th	Day	87% 2 4 6% 1	2610
	11th to 20th	Day	85% 2 7% 6% 1	2995
	21st to end	Day	81% 4 7% 7% 1	3982
January	1st to 10th	Night	89% 4 3 4	6349
	11th to 20th	Night	88% 3 4 3 1	6360
	21st to end	Night	86% 4 4 5% 2	6876
February	1st to 10th	Night	74% 5% 8% 8% 4	2536
	11th to 20th	Night	69% 5% 9% 13% 3 1	2406
	21st to end	Night	59% 6% 11% 14% 9% 1	1957
March	1st to 10th	Night	56% 5% 11% 19% 8% 1	3657
	11th to 20th	Night	66% 7% 10% 12% 4 1	3480
	21st to end	Night	65% 5% 8% 15% 6% 2	3662
April	1st to 10th	Night	61% 4 10% 13% 11% 1	1900
	11th to 20th	Night	50% 5% 10% 22% 11% 1	1866
	21st to end	Night	55% 5% 10% 16% 12% 2	1653
May	1st to 10th	Night	61% 7% 10% 15% 6%	2530
	11th to 20th	Night	41% 7% 15% 25% 11% 1	2507
	21st to end	Night	50% 10% 15% 17% 8% 1	2750
June	1st to 10th	Night	61% 6% 10% 16% 7%	1520
	11th to 20th	Night	47% 6% 12% 23% 11%	1370
	21st to end	Night	56% 6% 12% 17% 8%	1330
July	1st to 10th	Night	61% 5% 11% 15% 7% 2	2193
	11th to 20th	Night	49% 5% 17% 21% 7%	2482
	21st to end	Night	39% 6% 22% 24% 9%	2663
August	1st to 10th	Night	51% 7% 18% 20% 4	2534
	11th to 20th	Night	46% 5% 17% 24% 7% 1	2809
	21st to end	Night	40% 5% 14% 33% 8%	3379
September	1st to 10th	Night	44% 6% 14% 26% 9%	1900
	11th to 20th	Night	48% 4 13% 24% 10% 1	1900
	21st to end	Night	49% 6% 13% 23% 7%	2170
October	1st to 10th	Night	57% 4 12% 20% 7%	3800
	11th to 20th	Night	59% 3 11% 22% 5%	3779
	21st to end	Night	63% 3 10% 16% 7%	4367
November	1st to 10th	Night	66% 7% 10% 12% 4	2655
	11th to 20th	Night	76% 6% 9% 8% 2	2800
	21st to end	Night	82% 5% 7% 5% 1	2800
December	1st to 10th	Night	84% 2 5% 8% 1	4580
	11th to 20th	Night	80% 2 6% 9% 2	5215
	21st to end	Night	79% 3 7% 10% 1	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	30% 16% 31% 17% 6%	400
	11th to 20th	Day	25% 17% 27% 23% 8% 1	400
	21st to end	Day	17% 15% 33% 26% 8% 1	440
February	1st to 10th	Day	29% 15% 33% 16% 6% 2	385
	11th to 20th	Day	27% 14% 31% 23% 4 1	366
	21st to end	Day	18% 12% 30% 28% 10% 2	307
March	1st to 10th	Day	20% 10% 31% 29% 8% 2	388
	11th to 20th	Day	18% 12% 28% 25% 13% 4	460
	21st to end	Day	24% 11% 28% 27% 8% 2	506
April	1st to 10th	Day	27% 13% 28% 23% 8% 1	460
	11th to 20th	Day	21% 10% 27% 26% 14% 2	452
	21st to end	Day	26% 6% 23% 27% 17% 2	516
May	1st to 10th	Day	30% 5% 19% 28% 13% 4	653
	11th to 20th	Day	23% 4 19% 27% 23% 4	674
	21st to end	Day	24% 3 25% 34% 12% 2	735
June	1st to 10th	Day	29% 5% 16% 30% 18% 3	680
	11th to 20th	Day	20% 4 18% 35% 20% 2	680
	21st to end	Day	28% 2 17% 29% 21% 3	680
July	1st to 10th	Day	21% 1 18% 38% 18% 3	670
	11th to 20th	Day	18% 2 17% 34% 25% 4	668
	21st to end	Day	24% 2 15% 34% 23% 3	740
August	1st to 10th	Day	16% 3 15% 35% 27% 4	655
	11th to 20th	Day	21% 3 15% 30% 27% 5%	479
	21st to end	Day	20% 5% 18% 29% 26% 4	539
September	1st to 10th	Day	18% 5% 27% 32% 16% 3	490
	11th to 20th	Day	24% 8% 22% 29% 16% 1	490
	21st to end	Day	23% 6% 30% 26% 15% 1	413
October	1st to 10th	Day	22% 8% 23% 31% 16% 1	390
	11th to 20th	Day	27% 11% 25% 23% 13% 1	390
	21st to end	Day	29% 14% 30% 19% 7% 1	429
November	1st to 10th	Day	30% 18% 29% 17% 4 1	395
	11th to 20th	Day	37% 13% 24% 18% 6% 2	400
	21st to end	Day	36% 16% 27% 19% 3	400
December	1st to 10th	Day	32% 13% 30% 20% 5%	400
	11th to 20th	Day	31% 22% 26% 21% 2	400
	21st to end	Day	28% 16% 29% 18% 8% 1	440
January	1st to 10th	Night	32% 15% 27% 19% 7%	900
	11th to 20th	Night	30% 15% 26% 21% 6% 1	900
	21st to end	Night	21% 16% 34% 20% 8% 1	963
February	1st to 10th	Night	24% 13% 33% 21% 8% 1	781
	11th to 20th	Night	26% 12% 34% 22% 4 1	743
	21st to end	Night	19% 11% 30% 25% 12% 2	628
March	1st to 10th	Night	21% 9% 35% 27% 9% 1	760
	11th to 20th	Night	24% 9% 27% 27% 9% 2	760
	21st to end	Night	24% 10% 28% 27% 8% 3	746
April	1st to 10th	Night	26% 9% 26% 30% 9%	570
	11th to 20th	Night	23% 9% 25% 29% 13% 2	564
	21st to end	Night	24% 6% 25% 29% 13% 2	570
May	1st to 10th	Night	31% 4 21% 25% 13% 5%	570
	11th to 20th	Night	25% 4 16% 32% 19% 5%	562
	21st to end	Night	22% 6% 24% 33% 14% 2	616
June	1st to 10th	Night	29% 5% 17% 34% 14% 2	570
	11th to 20th	Night	23% 3 17% 36% 19% 2	420
	21st to end	Night	24% 2 17% 37% 18% 2	380
July	1st to 10th	Night	23% 3 14% 37% 19% 3	375
	11th to 20th	Night	16% 3 16% 40% 24% 1	552
	21st to end	Night	21% 5% 14% 38% 20% 2	623
August	1st to 10th	Night	19% 1 15% 39% 22% 3	568
	11th to 20th	Night	19% 4 15% 36% 23% 3	562
	21st to end	Night	18% 4 17% 35% 22% 4	627
September	1st to 10th	Night	19% 4 26% 34% 15% 2	570
	11th to 20th	Night	26% 7% 19% 28% 17% 2	570
	21st to end	Night	23% 8% 28% 28% 11% 2	693
October	1st to 10th	Night	27% 7% 24% 29% 12% 1	760
	11th to 20th	Night	32% 10% 22% 23% 11% 2	760
	21st to end	Night	36% 14% 24% 20% 5% 1	913
November	1st to 10th	Night	33% 17% 23% 20% 6% 1	880
	11th to 20th	Night	35% 16% 26% 16% 6% 1	900
	21st to end	Night	38% 15% 24% 19% 4	900
December	1st to 10th	Night	34% 16% 29% 14% 7%	900
	11th to 20th	Night	34% 22% 25% 15% 3	900
	21st to end	Night	33% 14% 27% 20% 5% 1	990

Page generated at 2025-02-03 03:05:50. Version ac07

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