Tour d'observation Montagnes Noires
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tour d'observation Montagnes Noires clear sky chart from 2005-11-06 to 2026-03-03.

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	16% 11% 4 9% 5% 5% 5% 4 5% 7% 30%	131160
	Night	16% 12% 4 9% 5% 5% 4 3 5% 6% 30%	129977
Transparency	Day	53% 6% 11% 20% 10% 1	134612
	Night	54% 6% 11% 19% 10% 1	134611
Seeing	Day	24% 17% 30% 19% 8% 2	16024
	Night	23% 13% 30% 24% 9% 1	25203

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	12% 16% 7% 15% 7% 7% 5% 3 4 5% 19%	4661
	11th to 20th	Day	10% 21% 8% 17% 8% 4 3 3 4 4 18%	4650
	21st to end	Day	7% 14% 6% 15% 9% 8% 6% 4 5% 5% 21%	5202
February	1st to 10th	Day	11% 17% 5% 14% 8% 4 4 3 4 5% 24%	1890
	11th to 20th	Day	11% 18% 5% 12% 6% 5% 4 3 3 6% 26%	1872
	21st to end	Day	16% 17% 4 10% 7% 6% 3 3 5% 4 24%	1730
March	1st to 10th	Day	18% 16% 4 12% 7% 4 4 3 4 5% 24%	4496
	11th to 20th	Day	11% 14% 5% 10% 6% 5% 4 4 5% 7% 28%	4883
	21st to end	Day	17% 13% 3 7% 5% 4 4 3 4 5% 34%	5830
April	1st to 10th	Day	21% 14% 3 7% 4 3 3 3 4 5% 32%	2400
	11th to 20th	Day	22% 10% 3 7% 5% 4 3 3 5% 5% 34%	2374
	21st to end	Day	22% 10% 4 8% 4 5% 4 3 4 5% 31%	2557
May	1st to 10th	Day	23% 11% 3 9% 5% 5% 5% 4 5% 6% 24%	6346
	11th to 20th	Day	18% 8% 3 8% 5% 5% 5% 4 5% 7% 31%	6318
	21st to end	Day	23% 8% 3 7% 5% 4 5% 3 5% 7% 30%	6949
June	1st to 10th	Day	23% 8% 4 7% 5% 4 5% 3 6% 7% 29%	2800
	11th to 20th	Day	15% 6% 3 7% 5% 5% 5% 4 6% 9% 36%	2800
	21st to end	Day	21% 6% 2 7% 5% 5% 6% 4 6% 8% 29%	2800
July	1st to 10th	Day	15% 6% 3 7% 6% 6% 6% 4 7% 9% 31%	6360
	11th to 20th	Day	13% 5% 2 7% 5% 5% 5% 5% 7% 8% 39%	6360
	21st to end	Day	10% 5% 2 5% 4 4 5% 3 6% 10% 46%	6926
August	1st to 10th	Day	14% 6% 3 8% 5% 5% 5% 4 7% 9% 34%	4563
	11th to 20th	Day	15% 7% 2 6% 5% 4 5% 4 6% 9% 37%	4103
	21st to end	Day	15% 5% 2 6% 5% 5% 4 4 6% 9% 38%	4312
September	1st to 10th	Day	14% 6% 2 6% 5% 4 4 4 6% 7% 43%	2400
	11th to 20th	Day	13% 5% 2 5% 4 4 4 3 5% 8% 47%	2375
	21st to end	Day	20% 7% 2 6% 4 3 4 3 5% 7% 40%	2171
October	1st to 10th	Day	22% 8% 2 5% 4 4 4 3 5% 6% 36%	2000
	11th to 20th	Day	24% 9% 3 9% 4 5% 5% 4 4 6% 27%	2000
	21st to end	Day	25% 11% 3 8% 5% 4 4 3 5% 5% 27%	2000
November	1st to 10th	Day	16% 12% 4 7% 5% 5% 4 3 5% 7% 32%	1851
	11th to 20th	Day	19% 14% 4 10% 5% 5% 5% 3 5% 6% 24%	1707
	21st to end	Day	22% 16% 5% 10% 5% 4 4 4 4 5% 21%	1680
December	1st to 10th	Day	19% 21% 7% 13% 5% 4 4 4 5% 5% 14%	2680
	11th to 20th	Day	17% 16% 8% 11% 6% 5% 4 3 3 4 23%	3066
	21st to end	Day	21% 19% 5% 9% 5% 3 5% 3 4 4 22%	4048
January	1st to 10th	Night	12% 18% 7% 14% 6% 4 4 3 4 6% 21%	8234
	11th to 20th	Night	10% 19% 8% 17% 8% 5% 5% 3 4 4 18%	8235
	21st to end	Night	9% 14% 7% 13% 8% 7% 6% 4 5% 6% 22%	8963
February	1st to 10th	Night	11% 14% 6% 13% 7% 5% 5% 4 5% 6% 25%	2730
	11th to 20th	Night	11% 14% 5% 12% 8% 5% 5% 3 4 5% 28%	2632
	21st to end	Night	13% 14% 5% 11% 6% 5% 5% 4 5% 5% 28%	2076
March	1st to 10th	Night	21% 16% 4 10% 4 4 3 3 4 5% 28%	5389
	11th to 20th	Night	12% 14% 3 8% 5% 5% 6% 4 6% 8% 30%	5071
	21st to end	Night	17% 11% 3 9% 6% 4 5% 3 5% 5% 32%	5101
April	1st to 10th	Night	21% 12% 2 7% 5% 5% 4 3 5% 6% 32%	2000
	11th to 20th	Night	20% 9% 3 7% 4 3 4 4 4 6% 36%	1975
	21st to end	Night	20% 10% 4 7% 4 4 4 3 5% 6% 35%	1857
May	1st to 10th	Night	20% 11% 3 9% 5% 5% 5% 4 5% 6% 25%	3594
	11th to 20th	Night	17% 7% 3 7% 5% 5% 5% 4 5% 6% 37%	3575
	21st to end	Night	21% 9% 4 8% 5% 5% 4 4 5% 6% 30%	3926
June	1st to 10th	Night	15% 8% 3 8% 5% 4 5% 4 7% 9% 32%	1600
	11th to 20th	Night	15% 7% 3 7% 4 4 4 4 5% 7% 41%	1600
	21st to end	Night	19% 6% 3 7% 4 5% 4 4 5% 6% 37%	1600
July	1st to 10th	Night	14% 6% 2 7% 5% 5% 7% 5% 7% 8% 35%	3600
	11th to 20th	Night	14% 6% 2 6% 4 3 4 4 6% 8% 44%	3600
	21st to end	Night	9% 4 2 5% 4 4 4 4 6% 8% 50%	3926
August	1st to 10th	Night	12% 6% 3 7% 4 5% 5% 4 6% 8% 40%	2586
	11th to 20th	Night	15% 7% 2 5% 4 3 5% 3 5% 7% 43%	2897
	21st to end	Night	15% 6% 2 6% 4 4 5% 3 5% 7% 42%	3586
September	1st to 10th	Night	12% 6% 1 6% 4 4 5% 3 6% 6% 48%	2000
	11th to 20th	Night	14% 5% 2 4 3 4 3 3 5% 6% 51%	2025
	21st to end	Night	17% 6% 2 6% 4 4 3 4 5% 6% 44%	2225
October	1st to 10th	Night	18% 8% 2 5% 4 4 3 4 5% 6% 39%	2400
	11th to 20th	Night	20% 9% 3 7% 5% 5% 4 3 5% 7% 33%	2400
	21st to end	Night	22% 10% 4 7% 5% 4 4 3 4 6% 31%	2840
November	1st to 10th	Night	19% 11% 4 7% 5% 4 4 4 5% 6% 31%	2667
	11th to 20th	Night	18% 12% 4 8% 6% 6% 4 3 6% 5% 29%	2909
	21st to end	Night	19% 16% 5% 9% 6% 5% 5% 3 5% 5% 23%	2940
December	1st to 10th	Night	17% 17% 5% 11% 6% 6% 5% 4 5% 6% 19%	4720
	11th to 20th	Night	23% 13% 4 10% 5% 4 4 3 4 4 26%	5348
	21st to end	Night	22% 21% 4 9% 4 4 3 2 3 5% 23%	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	67% 6% 8% 15% 4	4662
	11th to 20th	Day	70% 4 6% 10% 10%	4680
	21st to end	Day	64% 6% 9% 10% 10% 1	5202
February	1st to 10th	Day	63% 4 7% 18% 7% 2	1890
	11th to 20th	Day	60% 5% 9% 15% 9% 1	1881
	21st to end	Day	62% 5% 8% 14% 10% 1	1730
March	1st to 10th	Day	63% 5% 6% 11% 12% 3	4499
	11th to 20th	Day	54% 6% 16% 12% 10% 1	4883
	21st to end	Day	52% 3 7% 17% 18% 2	5830
April	1st to 10th	Day	55% 4 8% 18% 13% 3	2400
	11th to 20th	Day	53% 4 7% 20% 14% 2	2374
	21st to end	Day	56% 5% 8% 15% 13% 4	2557
May	1st to 10th	Day	58% 7% 7% 18% 8% 2	6357
	11th to 20th	Day	50% 7% 14% 18% 10% 1	6322
	21st to end	Day	53% 6% 10% 17% 13% 1	6949
June	1st to 10th	Day	54% 6% 9% 18% 11% 1	2800
	11th to 20th	Day	44% 6% 12% 23% 12% 2	2800
	21st to end	Day	51% 8% 13% 18% 10% 1	2800
July	1st to 10th	Day	46% 7% 14% 25% 8%	6290
	11th to 20th	Day	39% 7% 14% 30% 10%	6285
	21st to end	Day	33% 7% 16% 35% 9%	6728
August	1st to 10th	Day	46% 7% 17% 23% 7%	4549
	11th to 20th	Day	42% 7% 15% 29% 7% 1	4142
	21st to end	Day	41% 7% 16% 23% 12% 1	4312
September	1st to 10th	Day	40% 6% 14% 28% 12%	2400
	11th to 20th	Day	36% 6% 13% 32% 12% 1	2375
	21st to end	Day	44% 6% 14% 25% 11%	2171
October	1st to 10th	Day	47% 7% 11% 27% 7%	3260
	11th to 20th	Day	49% 7% 13% 23% 7% 1	3240
	21st to end	Day	51% 6% 19% 17% 6%	3212
November	1st to 10th	Day	52% 6% 14% 21% 6% 1	1851
	11th to 20th	Day	62% 6% 11% 12% 9% 1	1707
	21st to end	Day	67% 5% 12% 10% 5% 1	1680
December	1st to 10th	Day	72% 5% 9% 11% 2	2680
	11th to 20th	Day	66% 6% 8% 14% 7%	3066
	21st to end	Day	66% 5% 7% 16% 6%	4048
January	1st to 10th	Night	65% 5% 12% 14% 5% 1	8234
	11th to 20th	Night	69% 6% 8% 11% 6%	8280
	21st to end	Night	62% 6% 8% 12% 12%	8963
February	1st to 10th	Night	60% 5% 9% 18% 8% 1	2730
	11th to 20th	Night	59% 4 9% 19% 8%	2634
	21st to end	Night	57% 6% 9% 17% 11% 1	2076
March	1st to 10th	Night	61% 3 8% 12% 13% 3	5399
	11th to 20th	Night	50% 7% 15% 17% 8% 3	5072
	21st to end	Night	54% 4 8% 21% 12% 2	5101
April	1st to 10th	Night	53% 5% 9% 17% 14% 2	2000
	11th to 20th	Night	49% 6% 8% 21% 15% 1	1975
	21st to end	Night	50% 4 10% 18% 14% 3	1857
May	1st to 10th	Night	56% 8% 8% 18% 8% 2	3600
	11th to 20th	Night	46% 8% 14% 19% 11% 2	3576
	21st to end	Night	54% 6% 9% 17% 12% 1	3927
June	1st to 10th	Night	46% 8% 12% 22% 12%	1600
	11th to 20th	Night	43% 5% 12% 25% 14% 2	1600
	21st to end	Night	46% 8% 11% 20% 14% 1	1600
July	1st to 10th	Night	44% 8% 18% 22% 8%	3560
	11th to 20th	Night	37% 7% 16% 31% 8%	3552
	21st to end	Night	32% 7% 16% 32% 14%	3809
August	1st to 10th	Night	40% 9% 15% 27% 9%	2576
	11th to 20th	Night	39% 7% 17% 30% 8%	2923
	21st to end	Night	41% 7% 15% 23% 12% 2	3586
September	1st to 10th	Night	36% 6% 13% 30% 14% 1	2000
	11th to 20th	Night	34% 6% 14% 35% 11% 1	2025
	21st to end	Night	40% 5% 13% 29% 12%	2225
October	1st to 10th	Night	40% 6% 14% 27% 12% 1	3920
	11th to 20th	Night	44% 7% 15% 25% 9%	3899
	21st to end	Night	48% 5% 18% 18% 10%	4578
November	1st to 10th	Night	53% 6% 14% 20% 8%	2667
	11th to 20th	Night	57% 6% 12% 15% 9% 1	2909
	21st to end	Night	63% 7% 11% 15% 4	2940
December	1st to 10th	Night	66% 6% 13% 12% 3	4720
	11th to 20th	Night	62% 5% 6% 15% 11% 1	5348
	21st to end	Night	66% 4 5% 14% 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	24% 20% 31% 19% 5%	220
	11th to 20th	Day	34% 17% 33% 11% 5%	220
	21st to end	Day	20% 20% 32% 23% 5%	256
February	1st to 10th	Day	29% 25% 32% 11% 2	330
	11th to 20th	Day	28% 28% 33% 11% 1	359
	21st to end	Day	27% 22% 33% 16% 1	446
March	1st to 10th	Day	29% 21% 31% 14% 5%	508
	11th to 20th	Day	27% 23% 32% 15% 3 1	500
	21st to end	Day	32% 22% 25% 14% 5% 1	550
April	1st to 10th	Day	32% 21% 27% 14% 6% 1	500
	11th to 20th	Day	35% 19% 22% 13% 9% 2	492
	21st to end	Day	32% 21% 31% 11% 6%	500
May	1st to 10th	Day	27% 19% 32% 15% 5% 2	503
	11th to 20th	Day	22% 18% 30% 20% 8% 2	527
	21st to end	Day	26% 15% 31% 18% 9% 2	573
June	1st to 10th	Day	27% 12% 32% 21% 8%	530
	11th to 20th	Day	18% 19% 33% 20% 9% 2	530
	21st to end	Day	24% 13% 31% 20% 10% 1	530
July	1st to 10th	Day	15% 13% 31% 28% 9% 4	525
	11th to 20th	Day	15% 12% 33% 27% 10% 2	524
	21st to end	Day	13% 11% 34% 30% 11% 2	576
August	1st to 10th	Day	14% 8% 28% 37% 11% 2	526
	11th to 20th	Day	14% 9% 27% 28% 15% 8%	519
	21st to end	Day	18% 12% 30% 21% 13% 7%	583
September	1st to 10th	Day	16% 11% 32% 22% 12% 6%	530
	11th to 20th	Day	12% 11% 24% 25% 20% 9%	530
	21st to end	Day	21% 15% 26% 20% 13% 5%	530
October	1st to 10th	Day	25% 16% 23% 18% 14% 3	530
	11th to 20th	Day	28% 22% 26% 15% 7% 1	530
	21st to end	Day	33% 15% 30% 17% 5%	473
November	1st to 10th	Day	32% 16% 28% 18% 5% 1	425
	11th to 20th	Day	28% 19% 34% 11% 6% 1	247
	21st to end	Day	33% 22% 28% 14% 3	220
December	1st to 10th	Day	30% 14% 37% 16% 3	220
	11th to 20th	Day	28% 21% 38% 11% 1 1	220
	21st to end	Day	30% 23% 29% 14% 4 1	242
January	1st to 10th	Night	26% 16% 37% 17% 4	840
	11th to 20th	Night	29% 17% 29% 20% 5%	840
	21st to end	Night	20% 15% 36% 23% 6% 1	924
February	1st to 10th	Night	18% 19% 35% 23% 6%	840
	11th to 20th	Night	20% 19% 38% 18% 4	823
	21st to end	Night	23% 17% 32% 24% 3 1	692
March	1st to 10th	Night	25% 17% 33% 20% 5%	809
	11th to 20th	Night	25% 18% 32% 21% 5% 1	800
	21st to end	Night	25% 16% 30% 22% 6%	880
April	1st to 10th	Night	28% 16% 29% 23% 4	800
	11th to 20th	Night	26% 16% 30% 21% 6%	791
	21st to end	Night	26% 14% 30% 22% 7%	657
May	1st to 10th	Night	25% 13% 26% 27% 7% 2	400
	11th to 20th	Night	21% 12% 29% 29% 9%	394
	21st to end	Night	17% 10% 36% 25% 11% 1	433
June	1st to 10th	Night	17% 9% 33% 33% 8%	400
	11th to 20th	Night	19% 8% 29% 32% 12% 1	400
	21st to end	Night	21% 7% 27% 31% 15% 1	400
July	1st to 10th	Night	9% 7% 32% 37% 15%	390
	11th to 20th	Night	15% 4 21% 43% 17% 1	388
	21st to end	Night	10% 6% 27% 39% 16% 2	438
August	1st to 10th	Night	13% 5% 20% 40% 21% 1	398
	11th to 20th	Night	13% 4 20% 36% 25% 3	602
	21st to end	Night	16% 7% 25% 31% 18% 2	880
September	1st to 10th	Night	15% 6% 30% 31% 17% 1	800
	11th to 20th	Night	16% 8% 22% 29% 23% 2	800
	21st to end	Night	20% 9% 25% 27% 18% 2	800
October	1st to 10th	Night	21% 11% 27% 25% 15% 1	800
	11th to 20th	Night	25% 14% 29% 24% 8% 1	800
	21st to end	Night	27% 13% 30% 25% 5%	880
November	1st to 10th	Night	27% 14% 28% 23% 7% 1	820
	11th to 20th	Night	25% 17% 31% 16% 10%	840
	21st to end	Night	29% 19% 26% 20% 6%	840
December	1st to 10th	Night	30% 16% 31% 19% 4	840
	11th to 20th	Night	30% 18% 31% 17% 4 1	840
	21st to end	Night	34% 16% 29% 17% 4	924

Page generated at 2026-02-28 01:40:26. Version ac07

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