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 2024-11-30.

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% 31%	101556
	Night	20% 11% 4 8% 5% 4 4 3 5% 6% 30%	98033
Transparency	Day	28% 48% 8% 11% 4	105017
	Night	30% 48% 7% 10% 4	102662
Seeing	Day	24% 15% 29% 21% 9% 2	15004
	Night	25% 11% 29% 26% 8%	23731

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	19% 16% 5% 10% 6% 4 4 4 5% 5% 22%	2517
	11th to 20th	Day	12% 15% 6% 15% 7% 5% 5% 3 3 4 26%	2520
	21st to end	Day	12% 14% 6% 10% 6% 4 4 4 5% 7% 28%	2772
February	1st to 10th	Day	12% 17% 5% 11% 8% 5% 5% 3 4 4 25%	1548
	11th to 20th	Day	15% 16% 6% 11% 6% 5% 5% 3 4 5% 25%	1814
	21st to end	Day	15% 15% 4 10% 6% 4 4 3 5% 6% 27%	1570
March	1st to 10th	Day	21% 13% 4 8% 5% 4 4 3 4 4 30%	3116
	11th to 20th	Day	17% 18% 5% 10% 5% 4 3 3 4 5% 25%	3275
	21st to end	Day	16% 12% 4 7% 4 4 4 3 5% 4 36%	4124
April	1st to 10th	Day	23% 12% 4 7% 5% 5% 4 3 3 4 30%	2280
	11th to 20th	Day	21% 9% 2 7% 4 3 3 3 5% 5% 37%	2312
	21st to end	Day	24% 9% 3 7% 4 5% 4 3 4 7% 30%	2470
May	1st to 10th	Day	22% 8% 2 7% 3 4 4 4 5% 6% 35%	4264
	11th to 20th	Day	16% 7% 3 7% 5% 5% 5% 4 6% 9% 33%	4398
	21st to end	Day	17% 8% 3 8% 5% 5% 5% 4 5% 7% 33%	4837
June	1st to 10th	Day	21% 6% 3 8% 5% 6% 5% 4 7% 8% 28%	2745
	11th to 20th	Day	17% 7% 2 6% 5% 4 4 5% 6% 8% 35%	2850
	21st to end	Day	23% 8% 3 7% 5% 4 6% 4 5% 6% 28%	2749
July	1st to 10th	Day	14% 7% 3 8% 6% 6% 5% 5% 6% 8% 32%	4440
	11th to 20th	Day	16% 7% 2 7% 6% 6% 6% 5% 7% 8% 30%	4440
	21st to end	Day	14% 6% 2 6% 4 5% 5% 4 7% 8% 40%	4814
August	1st to 10th	Day	17% 5% 2 7% 5% 5% 6% 5% 8% 10% 29%	4423
	11th to 20th	Day	20% 7% 3 7% 4 5% 5% 4 5% 9% 31%	4075
	21st to end	Day	21% 7% 2 6% 4 4 4 3 5% 6% 38%	4254
September	1st to 10th	Day	17% 6% 2 6% 4 5% 4 4 6% 7% 39%	2280
	11th to 20th	Day	17% 5% 2 6% 4 4 3 3 5% 7% 44%	2138
	21st to end	Day	24% 7% 1 6% 4 3 3 3 4 6% 39%	2090
October	1st to 10th	Day	23% 8% 3 7% 4 4 5% 4 5% 6% 32%	2047
	11th to 20th	Day	24% 9% 3 9% 6% 5% 5% 4 4 6% 26%	1771
	21st to end	Day	27% 11% 3 7% 5% 4 4 3 4 6% 26%	1881
November	1st to 10th	Day	20% 11% 4 7% 5% 4 4 3 4 6% 32%	1761
	11th to 20th	Day	22% 13% 4 8% 5% 5% 4 3 4 5% 27%	1769
	21st to end	Day	24% 16% 5% 7% 4 5% 4 3 4 5% 22%	1534
December	1st to 10th	Day	27% 15% 4 10% 5% 4 3 3 4 4 22%	1330
	11th to 20th	Day	23% 14% 4 9% 6% 4 4 3 3 4 26%	1668
	21st to end	Day	23% 19% 4 9% 4 4 3 3 4 4 22%	2680
January	1st to 10th	Night	18% 17% 6% 11% 5% 4 4 3 4 6% 22%	4429
	11th to 20th	Night	13% 16% 6% 12% 7% 5% 5% 3 4 4 24%	4440
	21st to end	Night	13% 15% 5% 11% 7% 5% 5% 4 5% 6% 24%	4884
February	1st to 10th	Night	13% 14% 6% 12% 7% 4 4 4 5% 5% 26%	2628
	11th to 20th	Night	13% 16% 5% 12% 7% 6% 5% 3 5% 5% 25%	2252
	21st to end	Night	16% 14% 3 9% 6% 5% 3 3 4 6% 29%	1884
March	1st to 10th	Night	26% 11% 3 7% 5% 4 5% 3 4 5% 28%	3724
	11th to 20th	Night	19% 17% 6% 10% 5% 5% 4 3 4 5% 23%	3683
	21st to end	Night	17% 14% 4 8% 5% 4 4 3 4 4 33%	3504
April	1st to 10th	Night	23% 13% 4 7% 3 4 4 3 5% 5% 29%	1900
	11th to 20th	Night	24% 8% 3 7% 4 4 4 2 5% 6% 34%	1816
	21st to end	Night	23% 9% 3 6% 4 4 3 3 5% 5% 35%	1710
May	1st to 10th	Night	23% 8% 3 8% 4 4 5% 3 5% 5% 32%	2692
	11th to 20th	Night	22% 7% 2 6% 4 3 4 3 5% 7% 36%	2495
	21st to end	Night	20% 6% 2 6% 4 5% 4 5% 6% 9% 33%	2738
June	1st to 10th	Night	21% 7% 3 7% 4 5% 4 4 6% 7% 32%	1430
	11th to 20th	Night	20% 7% 2 7% 4 4 4 4 6% 7% 36%	1330
	21st to end	Night	22% 9% 3 7% 4 5% 5% 4 6% 6% 29%	1423
July	1st to 10th	Night	15% 7% 3 8% 6% 5% 6% 5% 7% 8% 31%	2520
	11th to 20th	Night	19% 6% 2 7% 5% 5% 5% 3 6% 7% 35%	2520
	21st to end	Night	13% 5% 2 6% 4 5% 5% 4 6% 8% 42%	2739
August	1st to 10th	Night	17% 8% 3 8% 5% 5% 5% 4 5% 9% 32%	2506
	11th to 20th	Night	19% 7% 3 8% 5% 5% 5% 4 5% 8% 32%	2722
	21st to end	Night	18% 8% 3 9% 5% 6% 4 3 5% 6% 34%	3400
September	1st to 10th	Night	18% 6% 3 6% 4 3 4 3 6% 6% 41%	1900
	11th to 20th	Night	17% 5% 2 4 3 4 5% 3 4 7% 46%	2041
	21st to end	Night	21% 6% 1 6% 4 4 3 3 5% 7% 40%	2090
October	1st to 10th	Night	19% 7% 2 8% 4 5% 5% 3 5% 6% 37%	2130
	11th to 20th	Night	23% 9% 3 8% 5% 4 4 3 3 4 32%	2408
	21st to end	Night	28% 9% 3 6% 4 4 4 3 4 6% 29%	2717
November	1st to 10th	Night	20% 11% 3 8% 5% 4 4 3 5% 6% 31%	2537
	11th to 20th	Night	22% 11% 4 7% 5% 4 4 3 5% 5% 29%	2630
	21st to end	Night	25% 14% 4 9% 5% 4 4 3 4 5% 25%	2857
December	1st to 10th	Night	24% 16% 5% 9% 6% 5% 3 4 4 4 21%	2850
	11th to 20th	Night	23% 15% 4 10% 6% 4 3 3 4 5% 23%	3531
	21st to end	Night	25% 20% 4 8% 4 3 3 2 3 3 23%	4973

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	39% 42% 8% 9% 2	2518
	11th to 20th	Day	38% 40% 7% 12% 3	2520
	21st to end	Day	32% 43% 8% 15% 2	2772
February	1st to 10th	Day	21% 66% 4 5% 3 1	1548
	11th to 20th	Day	22% 64% 4 7% 4	1823
	21st to end	Day	22% 65% 3 5% 3 2	1570
March	1st to 10th	Day	34% 44% 6% 10% 5% 1	3119
	11th to 20th	Day	37% 43% 6% 8% 5% 1	3275
	21st to end	Day	30% 40% 5% 13% 8% 3	4124
April	1st to 10th	Day	20% 65% 4 6% 4 1	2280
	11th to 20th	Day	19% 66% 3 8% 3 1	2312
	21st to end	Day	22% 65% 3 4 5%	2470
May	1st to 10th	Day	30% 42% 10% 11% 8%	4278
	11th to 20th	Day	26% 46% 14% 11% 3	4402
	21st to end	Day	29% 43% 7% 11% 9% 1	4837
June	1st to 10th	Day	18% 65% 4 8% 4 1	2745
	11th to 20th	Day	15% 65% 6% 7% 6%	2850
	21st to end	Day	19% 64% 4 8% 4	2749
July	1st to 10th	Day	33% 37% 10% 15% 5%	4370
	11th to 20th	Day	32% 38% 15% 13% 2	4365
	21st to end	Day	24% 38% 13% 19% 5%	4661
August	1st to 10th	Day	29% 40% 13% 13% 4	4409
	11th to 20th	Day	35% 40% 13% 10% 2	4115
	21st to end	Day	31% 39% 10% 10% 9% 1	4254
September	1st to 10th	Day	16% 62% 6% 10% 4 1	2280
	11th to 20th	Day	17% 60% 9% 11% 4	2138
	21st to end	Day	16% 59% 5% 15% 4	2090
October	1st to 10th	Day	35% 39% 8% 16% 2	3398
	11th to 20th	Day	34% 40% 12% 13% 1	2922
	21st to end	Day	32% 38% 15% 10% 4	3081
November	1st to 10th	Day	27% 57% 6% 7% 3	1761
	11th to 20th	Day	24% 57% 5% 10% 3 1	1769
	21st to end	Day	30% 58% 5% 5% 2 1	1534
December	1st to 10th	Day	26% 60% 4 7% 2	1330
	11th to 20th	Day	32% 49% 4 11% 4	1668
	21st to end	Day	41% 40% 7% 7% 5% 1	2680
January	1st to 10th	Night	39% 41% 9% 7% 3	4429
	11th to 20th	Night	39% 40% 6% 13% 2	4440
	21st to end	Night	36% 44% 7% 9% 3	4884
February	1st to 10th	Night	22% 65% 3 7% 2	2628
	11th to 20th	Night	21% 65% 3 7% 4	2254
	21st to end	Night	18% 65% 3 6% 7% 1	1884
March	1st to 10th	Night	35% 42% 9% 7% 4 2	3734
	11th to 20th	Night	40% 42% 4 9% 4 1	3684
	21st to end	Night	35% 41% 5% 13% 5% 1	3504
April	1st to 10th	Night	19% 64% 2 6% 6% 1	1900
	11th to 20th	Night	21% 65% 2 7% 4 1	1816
	21st to end	Night	18% 66% 4 6% 5% 1	1710
May	1st to 10th	Night	32% 43% 9% 13% 3	2698
	11th to 20th	Night	27% 45% 11% 12% 5%	2496
	21st to end	Night	27% 43% 8% 10% 10% 1	2739
June	1st to 10th	Night	17% 66% 5% 8% 5%	1430
	11th to 20th	Night	15% 66% 4 8% 7% 1	1330
	21st to end	Night	20% 64% 4 7% 5%	1423
July	1st to 10th	Night	33% 39% 12% 11% 4	2480
	11th to 20th	Night	33% 36% 16% 13% 2	2472
	21st to end	Night	22% 38% 15% 19% 6%	2651
August	1st to 10th	Night	35% 39% 10% 12% 4	2496
	11th to 20th	Night	37% 40% 11% 10% 2	2748
	21st to end	Night	35% 38% 6% 12% 9%	3400
September	1st to 10th	Night	16% 61% 7% 10% 6% 1	1900
	11th to 20th	Night	15% 61% 9% 12% 3	2041
	21st to end	Night	15% 60% 5% 13% 7%	2090
October	1st to 10th	Night	36% 38% 9% 13% 4	3559
	11th to 20th	Night	31% 40% 10% 17% 2	3996
	21st to end	Night	31% 38% 13% 10% 8%	4467
November	1st to 10th	Night	26% 56% 6% 8% 4	2537
	11th to 20th	Night	25% 58% 4 10% 4	2630
	21st to end	Night	29% 58% 5% 5% 3	2857
December	1st to 10th	Night	27% 60% 5% 7% 2	2850
	11th to 20th	Night	34% 49% 4 8% 4	3532
	21st to end	Night	42% 38% 5% 12% 4 1	4973

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% 19% 30% 19% 2	180
	11th to 20th	Day	30% 19% 30% 17% 4	180
	21st to end	Day	18% 20% 39% 15% 7% 1	198
February	1st to 10th	Day	24% 28% 31% 14% 3 1	193
	11th to 20th	Day	23% 23% 36% 16% 2	422
	21st to end	Day	24% 24% 30% 17% 4	382
March	1st to 10th	Day	26% 19% 30% 20% 5%	460
	11th to 20th	Day	25% 22% 31% 16% 4 2	460
	21st to end	Day	25% 21% 28% 16% 7% 2	506
April	1st to 10th	Day	27% 18% 30% 20% 5%	460
	11th to 20th	Day	29% 17% 27% 20% 4 2	452
	21st to end	Day	30% 20% 29% 15% 5% 1	460
May	1st to 10th	Day	27% 19% 33% 16% 5% 1	463
	11th to 20th	Day	18% 15% 31% 25% 9% 1	487
	21st to end	Day	22% 19% 33% 16% 9%	529
June	1st to 10th	Day	22% 13% 34% 22% 8% 1	575
	11th to 20th	Day	21% 11% 28% 26% 13% 1	680
	21st to end	Day	23% 11% 29% 25% 11% 1	579
July	1st to 10th	Day	16% 11% 31% 27% 14% 1	485
	11th to 20th	Day	16% 10% 33% 29% 10% 2	484
	21st to end	Day	17% 10% 28% 31% 12% 2	532
August	1st to 10th	Day	17% 8% 28% 29% 15% 3	486
	11th to 20th	Day	20% 7% 21% 31% 18% 4	479
	21st to end	Day	21% 13% 26% 16% 19% 6%	539
September	1st to 10th	Day	18% 11% 29% 24% 13% 4	490
	11th to 20th	Day	19% 11% 23% 25% 18% 5%	490
	21st to end	Day	22% 12% 26% 22% 13% 6%	490
October	1st to 10th	Day	25% 10% 28% 24% 11% 1	490
	11th to 20th	Day	27% 14% 31% 18% 9% 2	422
	21st to end	Day	33% 13% 31% 17% 7%	429
November	1st to 10th	Day	32% 13% 27% 22% 5% 1	395
	11th to 20th	Day	29% 17% 28% 19% 7%	369
	21st to end	Day	29% 24% 30% 14% 4 1	200
December	1st to 10th	Day	35% 11% 30% 20% 3 2	180
	11th to 20th	Day	29% 21% 29% 16% 4 1	180
	21st to end	Day	38% 18% 27% 11% 5% 1	198
January	1st to 10th	Night	28% 13% 35% 20% 4	760
	11th to 20th	Night	28% 15% 31% 21% 5%	760
	21st to end	Night	18% 12% 34% 30% 6%	836
February	1st to 10th	Night	19% 12% 39% 25% 5%	760
	11th to 20th	Night	21% 17% 38% 18% 6%	743
	21st to end	Night	25% 14% 32% 25% 4	628
March	1st to 10th	Night	24% 12% 34% 26% 4	760
	11th to 20th	Night	25% 14% 35% 20% 6% 1	760
	21st to end	Night	23% 13% 32% 25% 6% 1	836
April	1st to 10th	Night	30% 12% 29% 24% 5%	760
	11th to 20th	Night	28% 12% 30% 25% 5%	692
	21st to end	Night	28% 16% 30% 22% 5%	570
May	1st to 10th	Night	26% 12% 32% 25% 5% 1	493
	11th to 20th	Night	24% 9% 31% 29% 6%	374
	21st to end	Night	23% 9% 34% 26% 8%	411
June	1st to 10th	Night	24% 7% 30% 32% 7%	380
	11th to 20th	Night	21% 7% 25% 33% 13%	380
	21st to end	Night	25% 6% 23% 34% 13% 1	380
July	1st to 10th	Night	15% 4 31% 36% 13% 1	370
	11th to 20th	Night	18% 4 24% 38% 15% 1	368
	21st to end	Night	14% 5% 24% 43% 13%	416
August	1st to 10th	Night	15% 4 18% 43% 20% 1	378
	11th to 20th	Night	17% 5% 21% 37% 18% 1	526
	21st to end	Night	17% 8% 24% 32% 17% 1	786
September	1st to 10th	Night	20% 5% 27% 34% 12% 1	760
	11th to 20th	Night	19% 6% 23% 31% 19% 2	760
	21st to end	Night	21% 9% 25% 29% 14% 1	760
October	1st to 10th	Night	23% 9% 26% 32% 9%	760
	11th to 20th	Night	29% 10% 25% 26% 9% 1	760
	21st to end	Night	31% 12% 30% 23% 4	836
November	1st to 10th	Night	27% 11% 29% 26% 7% 1	780
	11th to 20th	Night	28% 13% 29% 20% 9% 1	800
	21st to end	Night	32% 15% 25% 22% 6%	829
December	1st to 10th	Night	34% 12% 25% 22% 7%	850
	11th to 20th	Night	27% 17% 29% 20% 6%	850
	21st to end	Night	35% 14% 29% 19% 3	859

Page generated at 2024-11-27 17:30:51. Version ac07

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