Observatoire du Cap Martin
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire du Cap Martin clear sky chart from 2005-11-06 to 2025-12-18.

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	15% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	127114
	Night	13% 10% 4 8% 5% 5% 5% 4 5% 6% 35%	123986
Transparency	Day	49% 6% 14% 20% 10% 1	130550
	Night	48% 6% 13% 21% 11% 1	128639
Seeing	Day	22% 14% 31% 22% 9% 2	16901
	Night	20% 10% 28% 31% 10% 1	25219

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	11% 21% 6% 9% 5% 4 4 3 4 6% 28%	3443
	11th to 20th	Day	6% 12% 4 13% 7% 6% 6% 4 6% 6% 30%	3570
	21st to end	Day	5% 6% 3 12% 7% 6% 5% 4 6% 7% 40%	3960
February	1st to 10th	Day	5% 11% 4 10% 8% 6% 8% 4 7% 6% 31%	1618
	11th to 20th	Day	8% 12% 5% 13% 8% 6% 5% 3 4 6% 31%	1878
	21st to end	Day	10% 11% 3 9% 6% 5% 5% 5% 7% 5% 35%	1650
March	1st to 10th	Day	15% 15% 4 10% 5% 4 5% 3 5% 5% 28%	4476
	11th to 20th	Day	9% 14% 4 9% 5% 5% 5% 4 6% 8% 31%	4828
	21st to end	Day	12% 16% 5% 10% 5% 4 4 3 4 5% 32%	5726
April	1st to 10th	Day	17% 14% 4 7% 5% 4 5% 3 5% 6% 29%	2400
	11th to 20th	Day	16% 8% 3 8% 5% 5% 5% 3 5% 6% 36%	2517
	21st to end	Day	20% 11% 3 7% 5% 5% 4 3 4 5% 33%	2600
May	1st to 10th	Day	21% 11% 3 7% 4 4 5% 4 5% 5% 31%	5994
	11th to 20th	Day	22% 9% 3 6% 5% 5% 5% 4 5% 6% 30%	6318
	21st to end	Day	17% 9% 3 8% 5% 5% 5% 4 6% 8% 30%	7351
June	1st to 10th	Day	21% 8% 3 6% 6% 5% 5% 4 6% 7% 29%	3000
	11th to 20th	Day	17% 8% 2 6% 5% 5% 5% 5% 7% 6% 34%	3000
	21st to end	Day	23% 8% 3 7% 5% 5% 5% 4 7% 6% 28%	3000
July	1st to 10th	Day	16% 7% 3 8% 6% 5% 6% 5% 7% 8% 29%	6806
	11th to 20th	Day	13% 6% 2 7% 6% 5% 7% 5% 8% 8% 32%	6360
	21st to end	Day	10% 4 2 5% 5% 5% 6% 5% 8% 9% 41%	6926
August	1st to 10th	Day	11% 5% 2 7% 6% 7% 7% 5% 8% 9% 32%	4509
	11th to 20th	Day	14% 7% 3 9% 5% 6% 6% 5% 7% 9% 29%	4175
	21st to end	Day	16% 5% 2 6% 4 5% 5% 4 6% 8% 39%	4581
September	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 3 6% 8% 41%	2395
	11th to 20th	Day	14% 6% 2 5% 3 4 4 4 5% 7% 47%	2200
	21st to end	Day	17% 6% 2 6% 4 4 4 4 6% 6% 41%	2200
October	1st to 10th	Day	17% 7% 2 7% 5% 5% 4 3 5% 7% 39%	2190
	11th to 20th	Day	18% 8% 3 8% 6% 5% 4 5% 6% 6% 30%	1830
	21st to end	Day	21% 11% 3 7% 4 3 5% 3 5% 7% 31%	1980
November	1st to 10th	Day	13% 11% 4 9% 5% 5% 4 4 5% 5% 35%	1851
	11th to 20th	Day	15% 10% 4 9% 6% 5% 4 4 6% 6% 32%	1806
	21st to end	Day	16% 15% 4 9% 5% 4 5% 3 5% 5% 29%	1483
December	1st to 10th	Day	11% 15% 6% 8% 5% 4 4 3 5% 6% 34%	2350
	11th to 20th	Day	14% 10% 4 9% 7% 5% 4 3 5% 5% 35%	2667
	21st to end	Day	14% 12% 4 9% 5% 4 4 3 5% 5% 35%	3476
January	1st to 10th	Night	10% 18% 6% 10% 5% 5% 4 4 5% 5% 27%	6504
	11th to 20th	Night	6% 13% 7% 15% 8% 6% 5% 4 4 6% 27%	6315
	21st to end	Night	4 8% 5% 13% 6% 6% 5% 4 6% 8% 37%	6996
February	1st to 10th	Night	6% 9% 4 11% 6% 5% 5% 4 5% 7% 38%	2781
	11th to 20th	Night	7% 13% 6% 11% 6% 5% 5% 3 5% 6% 33%	2406
	21st to end	Night	10% 13% 3 8% 6% 5% 3 4 5% 7% 36%	1980
March	1st to 10th	Night	16% 14% 4 9% 5% 4 6% 4 5% 5% 26%	5364
	11th to 20th	Night	9% 12% 4 10% 6% 6% 6% 4 6% 7% 28%	5130
	21st to end	Night	14% 16% 5% 9% 4 4 4 3 4 5% 34%	5202
April	1st to 10th	Night	17% 15% 4 8% 5% 4 3 3 5% 5% 33%	2000
	11th to 20th	Night	17% 8% 3 7% 5% 5% 6% 3 5% 7% 35%	1832
	21st to end	Night	21% 10% 3 6% 4 4 4 3 4 4 35%	1800
May	1st to 10th	Night	19% 10% 3 7% 4 4 3 3 5% 6% 35%	3976
	11th to 20th	Night	23% 8% 3 7% 4 3 4 3 5% 6% 33%	3575
	21st to end	Night	18% 8% 2 5% 4 3 5% 4 5% 8% 38%	3537
June	1st to 10th	Night	19% 8% 3 7% 5% 4 5% 4 5% 6% 35%	1400
	11th to 20th	Night	15% 6% 2 6% 5% 4 4 4 6% 8% 41%	1400
	21st to end	Night	20% 8% 3 7% 5% 5% 5% 5% 5% 6% 32%	1400
July	1st to 10th	Night	12% 6% 2 7% 4 5% 5% 4 7% 9% 40%	3160
	11th to 20th	Night	14% 7% 2 6% 4 4 4 4 7% 7% 40%	3596
	21st to end	Night	10% 4 2 4 4 4 4 4 6% 8% 50%	3926
August	1st to 10th	Night	14% 6% 3 6% 4 5% 4 4 6% 7% 40%	2607
	11th to 20th	Night	13% 4 2 9% 6% 6% 6% 5% 6% 8% 35%	2872
	21st to end	Night	15% 6% 3 7% 4 4 4 3 5% 7% 43%	3312
September	1st to 10th	Night	13% 5% 2 5% 4 4 4 3 6% 6% 49%	2004
	11th to 20th	Night	15% 5% 2 6% 4 4 4 3 5% 6% 45%	2200
	21st to end	Night	16% 7% 2 5% 4 3 4 3 4 6% 45%	2200
October	1st to 10th	Night	14% 8% 3 6% 4 4 3 3 5% 6% 45%	2210
	11th to 20th	Night	20% 8% 2 7% 4 3 5% 3 5% 6% 37%	2568
	21st to end	Night	19% 9% 2 7% 4 5% 4 3 5% 7% 35%	2860
November	1st to 10th	Night	14% 10% 3 8% 4 5% 5% 3 5% 7% 37%	2667
	11th to 20th	Night	16% 11% 3 7% 4 4 5% 3 5% 5% 35%	2813
	21st to end	Night	14% 14% 4 7% 6% 4 4 4 5% 6% 32%	3134
December	1st to 10th	Night	10% 11% 5% 12% 6% 5% 5% 3 4 6% 34%	5060
	11th to 20th	Night	16% 11% 4 8% 5% 4 5% 4 5% 5% 32%	5697
	21st to end	Night	15% 13% 5% 9% 5% 4 5% 3 5% 5% 32%	7502

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	58% 4 11% 19% 8%	3444
	11th to 20th	Day	53% 6% 10% 22% 8% 2	3600
	21st to end	Day	42% 6% 10% 18% 23% 1	3960
February	1st to 10th	Day	52% 5% 10% 17% 13% 3	1618
	11th to 20th	Day	56% 4 11% 16% 12% 2	1886
	21st to end	Day	49% 5% 8% 22% 12% 4	1650
March	1st to 10th	Day	57% 5% 10% 11% 11% 6%	4479
	11th to 20th	Day	51% 7% 17% 15% 9% 2	4828
	21st to end	Day	54% 4 6% 17% 13% 5%	5726
April	1st to 10th	Day	57% 5% 10% 14% 12% 3	2400
	11th to 20th	Day	49% 4 10% 22% 12% 3	2517
	21st to end	Day	54% 4 10% 17% 12% 2	2600
May	1st to 10th	Day	53% 6% 11% 17% 12% 1	6005
	11th to 20th	Day	54% 5% 13% 19% 6% 3	6322
	21st to end	Day	51% 6% 13% 18% 11%	7351
June	1st to 10th	Day	53% 7% 12% 21% 7% 1	3000
	11th to 20th	Day	48% 7% 15% 20% 9% 2	3000
	21st to end	Day	55% 6% 14% 17% 8% 1	3000
July	1st to 10th	Day	48% 8% 16% 21% 8%	6731
	11th to 20th	Day	45% 9% 18% 24% 5%	6285
	21st to end	Day	37% 8% 19% 27% 9%	6728
August	1st to 10th	Day	45% 8% 20% 19% 8%	4495
	11th to 20th	Day	49% 8% 21% 18% 4	4214
	21st to end	Day	42% 7% 19% 19% 11% 1	4581
September	1st to 10th	Day	41% 5% 18% 24% 11%	2395
	11th to 20th	Day	37% 5% 19% 28% 10% 1	2200
	21st to end	Day	44% 6% 15% 24% 11%	2200
October	1st to 10th	Day	51% 6% 12% 25% 6%	3567
	11th to 20th	Day	45% 7% 17% 25% 6%	2955
	21st to end	Day	44% 7% 21% 19% 9% 1	3180
November	1st to 10th	Day	51% 6% 13% 21% 8% 1	1851
	11th to 20th	Day	52% 6% 9% 22% 8% 1	1806
	21st to end	Day	56% 7% 12% 16% 9%	1483
December	1st to 10th	Day	51% 4 14% 19% 11%	2350
	11th to 20th	Day	50% 6% 10% 18% 15% 1	2667
	21st to end	Day	50% 5% 12% 18% 12% 3	3476
January	1st to 10th	Night	58% 5% 11% 17% 7% 1	6504
	11th to 20th	Night	57% 6% 11% 18% 7% 1	6360
	21st to end	Night	43% 7% 9% 22% 18% 1	6996
February	1st to 10th	Night	45% 6% 11% 21% 15% 2	2781
	11th to 20th	Night	53% 5% 11% 16% 14% 1	2409
	21st to end	Night	48% 4 10% 22% 13% 2	1980
March	1st to 10th	Night	58% 5% 9% 13% 12% 2	5374
	11th to 20th	Night	53% 7% 15% 14% 8% 3	5131
	21st to end	Night	54% 4 7% 20% 13% 2	5202
April	1st to 10th	Night	55% 4 6% 17% 15% 4	2000
	11th to 20th	Night	49% 5% 9% 22% 13% 1	1832
	21st to end	Night	52% 4 9% 20% 13% 2	1800
May	1st to 10th	Night	50% 5% 11% 19% 14% 1	3982
	11th to 20th	Night	52% 6% 11% 22% 9% 1	3576
	21st to end	Night	45% 6% 13% 21% 12% 2	3538
June	1st to 10th	Night	49% 6% 13% 24% 9% 1	1400
	11th to 20th	Night	42% 5% 15% 24% 13% 3	1400
	21st to end	Night	52% 6% 14% 17% 11%	1400
July	1st to 10th	Night	40% 7% 22% 27% 5%	3125
	11th to 20th	Night	40% 7% 22% 25% 5%	3549
	21st to end	Night	31% 8% 23% 28% 10%	3809
August	1st to 10th	Night	41% 8% 20% 23% 8%	2597
	11th to 20th	Night	44% 11% 20% 15% 9%	2899
	21st to end	Night	41% 6% 15% 28% 11%	3312
September	1st to 10th	Night	36% 6% 16% 28% 12% 1	2004
	11th to 20th	Night	40% 6% 17% 28% 9% 1	2200
	21st to end	Night	42% 6% 13% 27% 12% 1	2200
October	1st to 10th	Night	44% 5% 14% 29% 8% 1	3613
	11th to 20th	Night	45% 5% 15% 27% 8%	4182
	21st to end	Night	42% 7% 20% 19% 12%	4610
November	1st to 10th	Night	47% 5% 15% 24% 9%	2667
	11th to 20th	Night	50% 6% 11% 22% 10% 1	2813
	21st to end	Night	54% 6% 11% 18% 9% 1	3134
December	1st to 10th	Night	52% 6% 11% 23% 8%	5060
	11th to 20th	Night	51% 6% 10% 20% 12% 1	5698
	21st to end	Night	54% 6% 12% 16% 11% 1	7502

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	17% 12% 38% 26% 8% 1	200
	11th to 20th	Day	23% 14% 33% 20% 9% 1	200
	21st to end	Day	13% 18% 39% 20% 9% 2	220
February	1st to 10th	Day	17% 20% 42% 15% 6%	218
	11th to 20th	Day	18% 19% 38% 19% 6%	461
	21st to end	Day	17% 19% 38% 21% 4 1	414
March	1st to 10th	Day	24% 18% 31% 21% 6%	500
	11th to 20th	Day	21% 19% 32% 19% 8% 1	500
	21st to end	Day	25% 19% 30% 17% 8% 1	550
April	1st to 10th	Day	32% 18% 27% 17% 5% 1	500
	11th to 20th	Day	25% 14% 34% 18% 7% 1	492
	21st to end	Day	30% 15% 35% 14% 4 2	500
May	1st to 10th	Day	31% 12% 29% 20% 8% 1	503
	11th to 20th	Day	24% 17% 28% 20% 8% 2	527
	21st to end	Day	22% 17% 33% 21% 7% 1	741
June	1st to 10th	Day	27% 12% 26% 25% 9% 1	730
	11th to 20th	Day	23% 15% 25% 22% 12% 2	730
	21st to end	Day	26% 11% 29% 24% 9% 2	730
July	1st to 10th	Day	18% 12% 30% 29% 10% 1	719
	11th to 20th	Day	15% 11% 37% 26% 9% 2	524
	21st to end	Day	14% 11% 36% 27% 10% 2	576
August	1st to 10th	Day	15% 10% 35% 26% 11% 4	526
	11th to 20th	Day	15% 7% 32% 29% 12% 4	519
	21st to end	Day	18% 13% 30% 20% 16% 3	583
September	1st to 10th	Day	16% 13% 32% 24% 9% 5%	530
	11th to 20th	Day	20% 9% 31% 23% 12% 5%	530
	21st to end	Day	22% 13% 26% 22% 12% 4	530
October	1st to 10th	Day	21% 15% 27% 24% 10% 2	524
	11th to 20th	Day	27% 13% 29% 18% 11% 2	420
	21st to end	Day	30% 14% 29% 21% 6%	462
November	1st to 10th	Day	27% 14% 32% 20% 5% 1	425
	11th to 20th	Day	25% 12% 28% 24% 10% 1	430
	21st to end	Day	28% 19% 32% 16% 4	233
December	1st to 10th	Day	18% 16% 32% 20% 11% 2	220
	11th to 20th	Day	25% 20% 31% 16% 6% 2	214
	21st to end	Day	24% 19% 25% 21% 9% 2	220
January	1st to 10th	Night	18% 12% 32% 32% 6% 1	833
	11th to 20th	Night	17% 11% 34% 31% 8%	800
	21st to end	Night	12% 9% 31% 40% 8% 1	880
February	1st to 10th	Night	12% 10% 40% 31% 7% 1	800
	11th to 20th	Night	16% 12% 38% 25% 8% 1	783
	21st to end	Night	18% 10% 33% 32% 6% 1	660
March	1st to 10th	Night	21% 12% 31% 29% 5% 1	800
	11th to 20th	Night	18% 13% 34% 27% 7% 1	800
	21st to end	Night	22% 14% 30% 25% 8% 1	880
April	1st to 10th	Night	26% 13% 32% 23% 6% 1	800
	11th to 20th	Night	24% 11% 31% 26% 8%	648
	21st to end	Night	30% 8% 29% 26% 7%	600
May	1st to 10th	Night	26% 9% 28% 29% 7%	574
	11th to 20th	Night	25% 9% 23% 31% 12%	394
	21st to end	Night	25% 12% 27% 28% 7% 1	433
June	1st to 10th	Night	21% 7% 22% 37% 12% 1	400
	11th to 20th	Night	18% 6% 23% 37% 16% 2	400
	21st to end	Night	23% 6% 22% 39% 11% 1	400
July	1st to 10th	Night	20% 5% 25% 40% 9% 1	390
	11th to 20th	Night	15% 5% 19% 44% 16% 1	388
	21st to end	Night	15% 4 22% 46% 13% 1	438
August	1st to 10th	Night	13% 5% 16% 45% 19% 1	406
	11th to 20th	Night	16% 4 19% 39% 21% 2	592
	21st to end	Night	15% 6% 25% 37% 16% 1	710
September	1st to 10th	Night	16% 7% 25% 37% 15% 1	800
	11th to 20th	Night	19% 6% 23% 34% 16% 2	800
	21st to end	Night	18% 7% 25% 35% 15% 1	800
October	1st to 10th	Night	20% 10% 25% 34% 10% 2	800
	11th to 20th	Night	25% 8% 24% 31% 11% 1	800
	21st to end	Night	26% 9% 28% 28% 9%	880
November	1st to 10th	Night	23% 12% 28% 28% 8% 1	820
	11th to 20th	Night	24% 12% 29% 26% 9% 1	884
	21st to end	Night	24% 14% 27% 27% 7% 1	950
December	1st to 10th	Night	21% 12% 30% 27% 8% 1	950
	11th to 20th	Night	20% 14% 30% 27% 8% 1	936
	21st to end	Night	24% 12% 28% 26% 9% 1	990

Page generated at 2025-12-15 01:13:55. Version ac07

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