Observatoire St Marc des Carrières
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire St Marc des Carrières clear sky chart from 2005-11-06 to 2026-02-16.

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	19% 10% 3 8% 5% 5% 5% 4 5% 6% 30%	130375
	Night	19% 12% 4 9% 5% 5% 4 3 5% 6% 28%	130482
Transparency	Day	35% 38% 9% 12% 6% 1	133818
	Night	38% 37% 7% 12% 5%	135127
Seeing	Day	24% 15% 29% 21% 9% 2	16444
	Night	24% 11% 29% 27% 8% 1	25323

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	18% 16% 5% 12% 5% 4 4 3 5% 5% 23%	4661
	11th to 20th	Day	12% 18% 7% 17% 7% 5% 4 2 3 4 20%	4650
	21st to end	Day	7% 13% 6% 11% 5% 5% 6% 6% 7% 8% 26%	5124
February	1st to 10th	Day	12% 16% 5% 11% 8% 5% 5% 3 5% 4 26%	1712
	11th to 20th	Day	14% 16% 6% 10% 6% 5% 5% 3 4 5% 25%	1961
	21st to end	Day	14% 15% 4 10% 6% 4 4 3 5% 6% 27%	1650
March	1st to 10th	Day	23% 16% 4 9% 6% 4 4 3 4 3 26%	4476
	11th to 20th	Day	15% 15% 4 9% 5% 4 4 3 5% 6% 29%	4691
	21st to end	Day	20% 13% 4 7% 4 4 4 3 4 4 33%	5914
April	1st to 10th	Day	23% 12% 4 7% 6% 5% 4 3 3 4 30%	2400
	11th to 20th	Day	21% 9% 3 7% 4 3 4 3 5% 5% 37%	2435
	21st to end	Day	24% 9% 3 7% 4 5% 4 3 5% 7% 30%	2600
May	1st to 10th	Day	28% 8% 3 7% 4 4 4 4 5% 6% 28%	6114
	11th to 20th	Day	21% 7% 3 7% 4 4 4 4 5% 8% 32%	6318
	21st to end	Day	20% 9% 3 8% 5% 5% 5% 4 5% 6% 30%	6949
June	1st to 10th	Day	21% 6% 3 8% 5% 5% 5% 4 7% 8% 28%	2890
	11th to 20th	Day	17% 7% 2 6% 5% 4 4 5% 6% 8% 34%	3000
	21st to end	Day	23% 8% 3 7% 5% 4 6% 4 5% 6% 29%	2893
July	1st to 10th	Day	16% 7% 3 7% 6% 6% 6% 5% 7% 9% 29%	6360
	11th to 20th	Day	15% 7% 2 7% 5% 5% 6% 4 7% 9% 32%	6360
	21st to end	Day	11% 5% 2 5% 4 5% 5% 5% 7% 9% 41%	6926
August	1st to 10th	Day	16% 5% 2 7% 5% 5% 6% 5% 8% 10% 30%	4563
	11th to 20th	Day	19% 7% 3 7% 4 5% 5% 4 5% 9% 33%	4206
	21st to end	Day	21% 7% 2 6% 4 4 4 4 5% 6% 38%	4388
September	1st to 10th	Day	17% 6% 2 6% 4 5% 4 4 6% 7% 40%	2400
	11th to 20th	Day	16% 5% 2 6% 4 4 4 3 5% 7% 45%	2250
	21st to end	Day	24% 7% 1 6% 4 3 3 3 4 6% 39%	2200
October	1st to 10th	Day	22% 7% 3 7% 4 4 5% 4 5% 7% 33%	2155
	11th to 20th	Day	23% 8% 3 9% 5% 5% 5% 4 4 7% 27%	1864
	21st to end	Day	27% 11% 3 7% 5% 4 4 3 4 6% 25%	1980
November	1st to 10th	Day	20% 11% 4 7% 5% 4 4 3 4 6% 31%	1851
	11th to 20th	Day	22% 14% 4 8% 6% 5% 4 3 4 5% 26%	1857
	21st to end	Day	23% 16% 5% 7% 5% 5% 4 3 4 5% 21%	1612
December	1st to 10th	Day	21% 15% 5% 10% 6% 6% 4 3 4 4 22%	2350
	11th to 20th	Day	21% 14% 5% 9% 5% 4 4 3 3 5% 26%	2688
	21st to end	Day	21% 16% 4 9% 5% 5% 5% 4 6% 4 22%	3927
January	1st to 10th	Night	16% 17% 7% 14% 5% 5% 5% 3 4 5% 20%	8234
	11th to 20th	Night	13% 24% 8% 15% 7% 5% 4 2 3 3 16%	8235
	21st to end	Night	8% 13% 5% 14% 7% 6% 5% 4 6% 7% 24%	9057
February	1st to 10th	Night	12% 14% 6% 12% 7% 4 4 3 5% 5% 28%	2904
	11th to 20th	Night	13% 16% 5% 12% 6% 6% 5% 3 5% 5% 25%	2436
	21st to end	Night	17% 15% 4 9% 6% 5% 4 3 5% 6% 29%	1980
March	1st to 10th	Night	24% 13% 4 11% 5% 4 5% 3 4 5% 23%	5364
	11th to 20th	Night	16% 13% 5% 10% 5% 6% 5% 4 6% 6% 25%	5267
	21st to end	Night	19% 15% 4 8% 5% 4 3 3 4 4 30%	5014
April	1st to 10th	Night	23% 13% 4 7% 3 4 4 3 5% 5% 30%	2000
	11th to 20th	Night	23% 9% 3 7% 4 4 4 3 5% 6% 34%	1913
	21st to end	Night	24% 9% 3 6% 4 4 3 3 5% 5% 35%	1800
May	1st to 10th	Night	27% 8% 3 8% 4 4 4 3 5% 5% 28%	3856
	11th to 20th	Night	25% 7% 2 7% 4 4 4 3 5% 6% 32%	3575
	21st to end	Night	19% 8% 3 7% 5% 5% 5% 4 5% 8% 31%	3926
June	1st to 10th	Night	22% 7% 2 6% 4 4 4 4 6% 7% 32%	1505
	11th to 20th	Night	20% 7% 2 7% 4 4 4 4 6% 7% 36%	1400
	21st to end	Night	22% 8% 3 7% 4 4 5% 4 6% 7% 30%	1498
July	1st to 10th	Night	14% 7% 3 8% 6% 5% 6% 5% 8% 10% 29%	3600
	11th to 20th	Night	20% 6% 2 7% 5% 4 4 3 5% 7% 37%	3600
	21st to end	Night	12% 5% 2 6% 5% 5% 5% 4 6% 8% 42%	3926
August	1st to 10th	Night	16% 7% 3 8% 5% 5% 5% 4 5% 9% 33%	2586
	11th to 20th	Night	18% 7% 3 8% 5% 5% 5% 4 5% 7% 32%	2810
	21st to end	Night	18% 8% 3 9% 5% 5% 4 3 5% 6% 34%	3508
September	1st to 10th	Night	17% 6% 3 6% 4 3 4 3 5% 6% 42%	2000
	11th to 20th	Night	16% 5% 2 5% 4 4 5% 3 4 7% 46%	2149
	21st to end	Night	21% 6% 1 6% 4 4 3 3 5% 7% 40%	2200
October	1st to 10th	Night	19% 7% 2 7% 4 4 5% 3 5% 6% 38%	2242
	11th to 20th	Night	22% 9% 3 8% 5% 4 4 4 3 5% 33%	2535
	21st to end	Night	27% 9% 3 6% 5% 4 4 3 4 6% 28%	2860
November	1st to 10th	Night	21% 11% 3 9% 5% 4 3 3 5% 6% 30%	2667
	11th to 20th	Night	22% 11% 4 8% 5% 4 4 3 5% 5% 28%	2762
	21st to end	Night	24% 15% 4 9% 5% 4 4 3 4 5% 24%	3003
December	1st to 10th	Night	18% 17% 6% 11% 7% 6% 4 4 4 4 20%	5060
	11th to 20th	Night	25% 14% 4 9% 6% 4 4 3 5% 5% 20%	5741
	21st to end	Night	23% 17% 5% 9% 4 4 3 3 4 5% 23%	7269

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	50% 23% 8% 13% 5%	4662
	11th to 20th	Day	56% 22% 5% 11% 5% 1	4680
	21st to end	Day	41% 25% 8% 17% 9%	5124
February	1st to 10th	Day	24% 60% 4 7% 4 1	1712
	11th to 20th	Day	24% 59% 4 8% 4	1970
	21st to end	Day	23% 62% 3 6% 4 2	1650
March	1st to 10th	Day	47% 31% 4 8% 7% 3	4479
	11th to 20th	Day	40% 31% 12% 9% 8%	4691
	21st to end	Day	41% 28% 5% 13% 11% 2	5914
April	1st to 10th	Day	21% 62% 4 6% 5% 1	2400
	11th to 20th	Day	21% 63% 4 8% 3 1	2435
	21st to end	Day	24% 62% 4 5% 5%	2600
May	1st to 10th	Day	43% 30% 8% 12% 7%	6125
	11th to 20th	Day	36% 33% 14% 12% 4 2	6322
	21st to end	Day	39% 31% 9% 10% 8% 2	6949
June	1st to 10th	Day	20% 62% 5% 9% 4 1	2890
	11th to 20th	Day	17% 62% 6% 8% 7%	3000
	21st to end	Day	20% 61% 5% 8% 5%	2893
July	1st to 10th	Day	39% 27% 11% 17% 5%	6290
	11th to 20th	Day	35% 28% 16% 19% 3	6285
	21st to end	Day	27% 27% 14% 25% 7%	6728
August	1st to 10th	Day	29% 39% 14% 14% 5%	4549
	11th to 20th	Day	35% 39% 13% 12% 2	4246
	21st to end	Day	31% 38% 10% 11% 9% 1	4388
September	1st to 10th	Day	17% 59% 8% 12% 4 1	2400
	11th to 20th	Day	17% 57% 9% 12% 4	2250
	21st to end	Day	18% 57% 5% 15% 5%	2200
October	1st to 10th	Day	34% 38% 9% 16% 3	3506
	11th to 20th	Day	34% 39% 12% 13% 1	3015
	21st to end	Day	33% 37% 15% 11% 4	3180
November	1st to 10th	Day	30% 54% 6% 7% 3	1851
	11th to 20th	Day	27% 54% 5% 10% 2	1857
	21st to end	Day	32% 56% 4 5% 2	1612
December	1st to 10th	Day	44% 35% 7% 10% 4	2350
	11th to 20th	Day	43% 31% 6% 10% 9%	2688
	21st to end	Day	46% 29% 7% 10% 8% 1	3927
January	1st to 10th	Night	55% 23% 7% 10% 4	8234
	11th to 20th	Night	62% 22% 5% 9% 2	8280
	21st to end	Night	46% 25% 8% 12% 9%	9057
February	1st to 10th	Night	24% 59% 3 10% 3	2904
	11th to 20th	Night	25% 60% 3 8% 4	2438
	21st to end	Night	20% 62% 3 7% 7% 1	1980
March	1st to 10th	Night	47% 30% 7% 7% 8% 1	5374
	11th to 20th	Night	43% 31% 9% 10% 6% 1	5268
	21st to end	Night	44% 29% 4 16% 6% 1	5014
April	1st to 10th	Night	21% 61% 2 7% 7% 1	2000
	11th to 20th	Night	23% 62% 3 7% 4 1	1913
	21st to end	Night	20% 63% 4 8% 6% 1	1800
May	1st to 10th	Night	43% 31% 8% 12% 6%	3862
	11th to 20th	Night	38% 32% 11% 14% 5%	3576
	21st to end	Night	38% 31% 10% 10% 11% 1	3927
June	1st to 10th	Night	18% 62% 5% 9% 6%	1505
	11th to 20th	Night	17% 62% 4 9% 7% 1	1400
	21st to end	Night	21% 61% 4 8% 6%	1498
July	1st to 10th	Night	37% 28% 16% 14% 3	3560
	11th to 20th	Night	37% 26% 17% 18% 3	3552
	21st to end	Night	28% 28% 13% 24% 7%	3809
August	1st to 10th	Night	34% 38% 11% 12% 5%	2576
	11th to 20th	Night	36% 39% 11% 10% 3	2836
	21st to end	Night	36% 37% 7% 12% 8%	3508
September	1st to 10th	Night	16% 58% 7% 12% 6% 1	2000
	11th to 20th	Night	15% 58% 10% 13% 3	2149
	21st to end	Night	16% 57% 5% 14% 8%	2200
October	1st to 10th	Night	36% 37% 9% 14% 4	3671
	11th to 20th	Night	31% 39% 10% 18% 2	4123
	21st to end	Night	32% 37% 13% 11% 8%	4610
November	1st to 10th	Night	28% 54% 6% 8% 4	2667
	11th to 20th	Night	27% 55% 4 10% 4	2762
	21st to end	Night	31% 55% 5% 5% 4	3003
December	1st to 10th	Night	46% 35% 8% 9% 2	5060
	11th to 20th	Night	47% 32% 4 12% 4	5742
	21st to end	Night	48% 27% 5% 14% 6%	7269

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	31% 17% 30% 20% 2	220
	11th to 20th	Day	30% 19% 29% 16% 6%	220
	21st to end	Day	17% 20% 36% 19% 8% 1	242
February	1st to 10th	Day	22% 24% 31% 16% 5% 1	237
	11th to 20th	Day	23% 23% 35% 17% 3	479
	21st to end	Day	24% 24% 31% 17% 4	414
March	1st to 10th	Day	27% 19% 30% 19% 5%	500
	11th to 20th	Day	25% 21% 32% 16% 4 2	500
	21st to end	Day	26% 21% 29% 15% 7% 1	550
April	1st to 10th	Day	27% 19% 29% 20% 5%	500
	11th to 20th	Day	30% 17% 27% 20% 5% 2	492
	21st to end	Day	30% 20% 29% 16% 5% 1	500
May	1st to 10th	Day	28% 17% 33% 17% 5% 1	503
	11th to 20th	Day	20% 14% 31% 24% 9% 2	527
	21st to end	Day	23% 19% 31% 16% 10%	573
June	1st to 10th	Day	23% 12% 33% 24% 8% 1	620
	11th to 20th	Day	21% 12% 27% 27% 12% 1	730
	21st to end	Day	24% 11% 29% 24% 11% 1	623
July	1st to 10th	Day	17% 11% 31% 26% 14% 1	525
	11th to 20th	Day	15% 10% 34% 29% 10% 2	524
	21st to end	Day	16% 10% 29% 31% 11% 2	576
August	1st to 10th	Day	16% 8% 27% 30% 16% 3	526
	11th to 20th	Day	18% 7% 21% 31% 19% 4	519
	21st to end	Day	21% 12% 26% 17% 18% 6%	583
September	1st to 10th	Day	17% 10% 30% 24% 14% 5%	530
	11th to 20th	Day	17% 11% 24% 24% 18% 6%	530
	21st to end	Day	22% 12% 26% 23% 12% 5%	530
October	1st to 10th	Day	24% 10% 28% 25% 12% 2	530
	11th to 20th	Day	25% 13% 31% 19% 9% 2	455
	21st to end	Day	32% 12% 30% 19% 6%	462
November	1st to 10th	Day	32% 14% 27% 21% 5%	425
	11th to 20th	Day	31% 16% 28% 18% 7% 1	397
	21st to end	Day	29% 23% 30% 14% 4	220
December	1st to 10th	Day	32% 10% 32% 19% 5% 1	220
	11th to 20th	Day	30% 20% 31% 14% 5% 1	220
	21st to end	Day	34% 17% 32% 11% 5% 2	242
January	1st to 10th	Night	28% 13% 35% 20% 4	840
	11th to 20th	Night	29% 15% 30% 21% 6%	840
	21st to end	Night	17% 12% 34% 30% 7% 1	924
February	1st to 10th	Night	18% 12% 39% 25% 6%	840
	11th to 20th	Night	21% 17% 38% 19% 6%	804
	21st to end	Night	25% 14% 31% 26% 4	660
March	1st to 10th	Night	24% 13% 33% 26% 4	800
	11th to 20th	Night	24% 13% 37% 20% 5% 1	800
	21st to end	Night	23% 13% 32% 25% 6% 1	880
April	1st to 10th	Night	30% 13% 30% 23% 5%	800
	11th to 20th	Night	28% 12% 30% 25% 5%	729
	21st to end	Night	28% 16% 30% 22% 5%	600
May	1st to 10th	Night	26% 12% 32% 25% 5% 1	519
	11th to 20th	Night	24% 8% 31% 29% 7%	394
	21st to end	Night	23% 9% 33% 27% 9%	433
June	1st to 10th	Night	25% 6% 29% 33% 7%	400
	11th to 20th	Night	21% 8% 24% 33% 13%	400
	21st to end	Night	25% 5% 23% 34% 13% 1	400
July	1st to 10th	Night	15% 4 30% 37% 13% 1	390
	11th to 20th	Night	18% 4 24% 38% 14% 1	388
	21st to end	Night	14% 5% 24% 44% 13%	438
August	1st to 10th	Night	14% 4 18% 43% 21% 1	398
	11th to 20th	Night	17% 5% 21% 38% 19% 1	554
	21st to end	Night	18% 8% 24% 32% 17% 1	828
September	1st to 10th	Night	20% 5% 27% 34% 14% 1	800
	11th to 20th	Night	18% 6% 22% 32% 21% 2	800
	21st to end	Night	21% 9% 25% 30% 14% 1	800
October	1st to 10th	Night	23% 9% 26% 33% 9%	800
	11th to 20th	Night	27% 10% 26% 27% 9% 1	800
	21st to end	Night	31% 11% 30% 24% 5%	880
November	1st to 10th	Night	28% 12% 29% 25% 6% 1	820
	11th to 20th	Night	28% 13% 29% 20% 9% 1	840
	21st to end	Night	32% 15% 25% 21% 7%	873
December	1st to 10th	Night	32% 12% 26% 23% 7%	950
	11th to 20th	Night	28% 17% 29% 20% 6%	950
	21st to end	Night	34% 13% 29% 19% 4 1	951

Page generated at 2026-02-13 01:42:16. Version ac07

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