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 2024-01-13.

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% 4 7% 6% 4 5% 5% 6% 7% 33%	74554
	Night	15% 10% 4 7% 6% 3 4 5% 5% 6% 36%	75180
Transparency	Day	50% 6% 13% 20% 10% 1	74253
	Night	49% 6% 12% 21% 11% 1	75017
Seeing	Day	22% 14% 31% 22% 9% 2	14349
	Night	20% 10% 28% 31% 10% 1	22784

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% 14% 5% 10% 8% 3 3 5% 4 7% 31%	1450
	11th to 20th	Day	9% 11% 5% 10% 7% 4 6% 4 5% 6% 32%	1456
	21st to end	Day	7% 7% 5% 9% 8% 4 6% 5% 6% 7% 36%	1584
February	1st to 10th	Day	5% 10% 5% 9% 9% 5% 8% 5% 8% 6% 31%	1456
	11th to 20th	Day	8% 12% 5% 12% 8% 4 5% 4 4 7% 31%	1685
	21st to end	Day	10% 11% 3 8% 7% 4 5% 6% 6% 5% 35%	1480
March	1st to 10th	Day	12% 13% 5% 9% 5% 3 6% 4 5% 6% 33%	1797
	11th to 20th	Day	11% 12% 4 8% 6% 3 5% 6% 5% 6% 34%	1912
	21st to end	Day	12% 14% 5% 8% 6% 3 4 4 4 6% 34%	2272
April	1st to 10th	Day	17% 14% 5% 7% 6% 4 5% 3 5% 6% 28%	2160
	11th to 20th	Day	16% 7% 3 6% 5% 3 5% 5% 5% 6% 37%	2262
	21st to end	Day	21% 11% 3 5% 6% 3 4 5% 4 6% 32%	2340
May	1st to 10th	Day	20% 8% 3 6% 5% 3 5% 5% 5% 6% 35%	2378
	11th to 20th	Day	18% 8% 3 5% 6% 5% 5% 5% 4 6% 35%	2478
	21st to end	Day	16% 7% 3 5% 6% 3 6% 6% 5% 8% 35%	2875
June	1st to 10th	Day	20% 7% 3 6% 6% 4 6% 6% 6% 7% 29%	2700
	11th to 20th	Day	18% 7% 3 6% 5% 4 5% 6% 6% 6% 34%	2700
	21st to end	Day	23% 7% 3 6% 6% 3 5% 5% 7% 6% 28%	2700
July	1st to 10th	Day	14% 7% 3 7% 6% 4 6% 6% 7% 9% 31%	2700
	11th to 20th	Day	12% 6% 3 7% 8% 4 7% 7% 7% 8% 31%	2520
	21st to end	Day	12% 5% 3 6% 7% 4 6% 6% 8% 10% 31%	2744
August	1st to 10th	Day	14% 5% 3 6% 9% 5% 7% 7% 8% 9% 27%	2481
	11th to 20th	Day	12% 6% 3 7% 6% 4 7% 6% 7% 10% 33%	2304
	21st to end	Day	12% 5% 2 6% 6% 3 6% 6% 7% 9% 38%	2525
September	1st to 10th	Day	13% 6% 3 5% 7% 3 5% 5% 6% 8% 40%	2156
	11th to 20th	Day	15% 6% 2 4 4 3 5% 5% 5% 7% 45%	1980
	21st to end	Day	18% 5% 2 6% 5% 3 5% 5% 5% 7% 41%	1980
October	1st to 10th	Day	17% 7% 2 6% 5% 3 5% 4 5% 7% 38%	1972
	11th to 20th	Day	20% 8% 4 7% 7% 4 5% 6% 6% 6% 29%	1648
	21st to end	Day	21% 11% 4 6% 5% 3 4 4 5% 7% 30%	1782
November	1st to 10th	Day	14% 10% 5% 7% 7% 3 4 5% 5% 5% 36%	1671
	11th to 20th	Day	16% 9% 4 8% 7% 3 5% 5% 6% 7% 31%	1634
	21st to end	Day	15% 13% 5% 7% 6% 3 6% 4 5% 6% 30%	1343
December	1st to 10th	Day	15% 13% 6% 9% 7% 4 4 4 4 5% 29%	1330
	11th to 20th	Day	16% 11% 5% 8% 7% 3 5% 4 3 5% 33%	1668
	21st to end	Day	16% 14% 4 6% 5% 3 4 3 3 5% 37%	2431
January	1st to 10th	Night	10% 13% 6% 10% 7% 4 5% 5% 5% 5% 29%	2710
	11th to 20th	Night	10% 12% 5% 9% 8% 4 5% 5% 5% 6% 32%	2560
	21st to end	Night	7% 9% 5% 11% 6% 4 5% 5% 5% 8% 36%	2772
February	1st to 10th	Night	6% 9% 4 9% 7% 5% 5% 5% 5% 8% 37%	2503
	11th to 20th	Night	7% 13% 6% 10% 7% 4 5% 4 4 6% 33%	2159
	21st to end	Night	10% 12% 4 6% 8% 3 4 5% 5% 7% 35%	1776
March	1st to 10th	Night	11% 14% 6% 7% 5% 3 4 4 5% 7% 34%	2150
	11th to 20th	Night	12% 12% 5% 9% 6% 3 5% 4 4 5% 35%	2046
	21st to end	Night	11% 13% 4 5% 5% 3 5% 5% 4 5% 39%	2080
April	1st to 10th	Night	17% 15% 4 7% 6% 3 3 4 5% 5% 31%	1800
	11th to 20th	Night	16% 8% 3 6% 5% 4 5% 4 5% 7% 36%	1647
	21st to end	Night	22% 10% 3 5% 5% 2 4 4 5% 4 35%	1620
May	1st to 10th	Night	23% 8% 3 6% 5% 3 4 3 4 5% 36%	1598
	11th to 20th	Night	21% 7% 3 4 5% 3 4 5% 4 6% 37%	1415
	21st to end	Night	20% 8% 3 4 5% 2 4 5% 4 6% 39%	1395
June	1st to 10th	Night	19% 7% 4 7% 5% 3 5% 5% 5% 7% 34%	1260
	11th to 20th	Night	15% 6% 2 5% 5% 2 5% 4 6% 7% 41%	1260
	21st to end	Night	19% 7% 3 6% 6% 4 5% 6% 5% 6% 33%	1260
July	1st to 10th	Night	17% 5% 3 5% 4 2 5% 4 7% 8% 41%	1260
	11th to 20th	Night	11% 6% 3 5% 5% 4 6% 6% 7% 8% 39%	1436
	21st to end	Night	13% 6% 2 5% 5% 4 6% 7% 7% 8% 40%	1574
August	1st to 10th	Night	12% 4 2 5% 5% 2 5% 6% 7% 8% 44%	1438
	11th to 20th	Night	16% 4 2 6% 6% 4 4 6% 5% 9% 38%	1596
	21st to end	Night	13% 5% 3 5% 4 3 4 4 5% 8% 46%	1826
September	1st to 10th	Night	14% 4 2 4 4 3 4 4 6% 6% 48%	1803
	11th to 20th	Night	17% 6% 3 5% 5% 3 3 5% 5% 5% 44%	1980
	21st to end	Night	17% 7% 2 4 4 2 4 4 4 6% 45%	1980
October	1st to 10th	Night	14% 7% 3 5% 5% 3 4 3 5% 6% 44%	1988
	11th to 20th	Night	21% 9% 3 5% 5% 2 4 4 5% 7% 35%	2310
	21st to end	Night	20% 9% 3 6% 5% 4 3 4 5% 7% 35%	2574
November	1st to 10th	Night	14% 9% 4 6% 5% 3 5% 5% 5% 7% 37%	2407
	11th to 20th	Night	16% 9% 4 7% 5% 3 5% 5% 5% 6% 36%	2545
	21st to end	Night	14% 12% 5% 7% 6% 3 4 4 5% 6% 34%	2835
December	1st to 10th	Night	15% 13% 6% 9% 7% 3 4 4 4 5% 31%	2850
	11th to 20th	Night	16% 11% 4 7% 6% 3 5% 5% 6% 6% 32%	3531
	21st to end	Night	16% 15% 5% 7% 5% 3 4 4 4 4 33%	5236

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	55% 5% 10% 19% 10%	1451
	11th to 20th	Day	54% 5% 9% 18% 11% 2	1456
	21st to end	Day	46% 6% 10% 19% 17% 2	1584
February	1st to 10th	Day	53% 5% 10% 17% 12% 3	1456
	11th to 20th	Day	56% 4 10% 16% 12% 2	1693
	21st to end	Day	52% 4 7% 21% 13% 3	1480
March	1st to 10th	Day	54% 4 9% 16% 14% 4	1800
	11th to 20th	Day	51% 6% 11% 17% 13% 3	1912
	21st to end	Day	53% 5% 9% 19% 10% 4	2272
April	1st to 10th	Day	58% 5% 10% 13% 11% 3	2160
	11th to 20th	Day	49% 4 10% 23% 12% 3	2262
	21st to end	Day	55% 4 10% 16% 12% 2	2340
May	1st to 10th	Day	50% 4 12% 18% 13% 2	2378
	11th to 20th	Day	51% 4 12% 21% 10% 1	2482
	21st to end	Day	47% 7% 13% 22% 11% 1	2875
June	1st to 10th	Day	53% 7% 12% 20% 7% 1	2700
	11th to 20th	Day	49% 6% 13% 21% 9% 2	2700
	21st to end	Day	55% 6% 14% 17% 8% 1	2700
July	1st to 10th	Day	47% 7% 18% 22% 6%	2625
	11th to 20th	Day	49% 7% 17% 20% 7%	2445
	21st to end	Day	47% 8% 18% 20% 7%	2591
August	1st to 10th	Day	51% 8% 19% 18% 4	2467
	11th to 20th	Day	45% 6% 21% 21% 6%	2304
	21st to end	Day	41% 7% 19% 24% 8%	2525
September	1st to 10th	Day	42% 5% 18% 23% 12%	2156
	11th to 20th	Day	39% 5% 19% 26% 10% 1	1980
	21st to end	Day	45% 5% 15% 24% 11%	1980
October	1st to 10th	Day	47% 4 13% 25% 10%	1972
	11th to 20th	Day	55% 6% 15% 19% 4	1648
	21st to end	Day	56% 6% 13% 19% 6% 1	1782
November	1st to 10th	Day	51% 6% 12% 21% 8% 1	1671
	11th to 20th	Day	53% 6% 10% 22% 8% 1	1634
	21st to end	Day	55% 7% 13% 16% 8%	1343
December	1st to 10th	Day	58% 5% 10% 19% 8%	1330
	11th to 20th	Day	56% 5% 6% 21% 12% 1	1668
	21st to end	Day	52% 4 12% 20% 8% 4	2431
January	1st to 10th	Night	56% 6% 9% 17% 9% 1	2710
	11th to 20th	Night	54% 7% 10% 17% 10% 2	2560
	21st to end	Night	47% 5% 8% 23% 16% 2	2772
February	1st to 10th	Night	46% 6% 11% 22% 14% 2	2503
	11th to 20th	Night	54% 4 11% 16% 14% 1	2162
	21st to end	Night	49% 4 10% 22% 14% 2	1776
March	1st to 10th	Night	51% 5% 9% 22% 12% 2	2160
	11th to 20th	Night	53% 5% 9% 19% 13% 2	2047
	21st to end	Night	48% 4 10% 21% 13% 4	2080
April	1st to 10th	Night	56% 4 7% 16% 14% 3	1800
	11th to 20th	Night	47% 6% 9% 23% 14% 2	1647
	21st to end	Night	53% 3 9% 20% 13% 2	1620
May	1st to 10th	Night	52% 3 11% 18% 13% 3	1598
	11th to 20th	Night	48% 4 11% 23% 11% 2	1416
	21st to end	Night	47% 6% 12% 20% 13% 1	1396
June	1st to 10th	Night	50% 6% 14% 22% 8% 1	1260
	11th to 20th	Night	43% 4 13% 25% 12% 3	1260
	21st to end	Night	52% 7% 14% 17% 10%	1260
July	1st to 10th	Night	41% 8% 19% 24% 7%	1225
	11th to 20th	Night	41% 8% 17% 26% 8%	1389
	21st to end	Night	41% 9% 18% 25% 8%	1486
August	1st to 10th	Night	36% 10% 22% 26% 5%	1428
	11th to 20th	Night	43% 8% 21% 19% 9%	1596
	21st to end	Night	38% 6% 17% 32% 7%	1826
September	1st to 10th	Night	37% 6% 17% 27% 12% 1	1803
	11th to 20th	Night	42% 6% 17% 26% 8% 1	1980
	21st to end	Night	42% 5% 13% 28% 11% 1	1980
October	1st to 10th	Night	43% 5% 13% 27% 12% 1	1988
	11th to 20th	Night	50% 5% 15% 22% 7%	2310
	21st to end	Night	50% 6% 15% 20% 9% 1	2574
November	1st to 10th	Night	46% 6% 14% 24% 9% 1	2407
	11th to 20th	Night	49% 6% 11% 22% 10% 2	2545
	21st to end	Night	52% 6% 11% 19% 10% 1	2835
December	1st to 10th	Night	58% 5% 9% 18% 9% 1	2850
	11th to 20th	Night	52% 6% 10% 19% 12% 1	3532
	21st to end	Night	56% 5% 12% 16% 9% 2	5236

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	15% 11% 38% 27% 9% 1	180
	11th to 20th	Day	23% 13% 31% 24% 9% 1	164
	21st to end	Day	14% 18% 38% 18% 10% 2	176
February	1st to 10th	Day	18% 20% 41% 15% 6% 1	176
	11th to 20th	Day	19% 19% 37% 20% 6%	388
	21st to end	Day	18% 19% 35% 22% 5% 1	346
March	1st to 10th	Day	24% 18% 30% 21% 7%	420
	11th to 20th	Day	21% 19% 32% 20% 8% 1	420
	21st to end	Day	24% 18% 29% 19% 9% 1	462
April	1st to 10th	Day	30% 18% 26% 19% 6% 1	420
	11th to 20th	Day	25% 13% 35% 18% 8% 2	412
	21st to end	Day	30% 13% 35% 15% 5% 2	420
May	1st to 10th	Day	31% 10% 29% 20% 8% 1	423
	11th to 20th	Day	23% 19% 30% 19% 8% 2	447
	21st to end	Day	22% 17% 33% 20% 7% 2	635
June	1st to 10th	Day	27% 13% 26% 24% 9% 1	630
	11th to 20th	Day	25% 12% 26% 23% 13% 2	630
	21st to end	Day	25% 9% 27% 26% 10% 2	630
July	1st to 10th	Day	18% 10% 30% 29% 11% 1	620
	11th to 20th	Day	16% 9% 37% 26% 10% 2	444
	21st to end	Day	15% 9% 35% 28% 11% 2	488
August	1st to 10th	Day	16% 10% 34% 24% 12% 4	446
	11th to 20th	Day	16% 7% 32% 29% 13% 3	439
	21st to end	Day	17% 13% 32% 18% 17% 2	495
September	1st to 10th	Day	17% 14% 31% 25% 9% 5%	450
	11th to 20th	Day	22% 9% 34% 22% 10% 5%	450
	21st to end	Day	23% 12% 27% 22% 12% 4	450
October	1st to 10th	Day	21% 15% 26% 26% 10% 3	446
	11th to 20th	Day	28% 13% 27% 18% 11% 3	360
	21st to end	Day	31% 12% 28% 21% 7% 1	396
November	1st to 10th	Day	25% 14% 32% 21% 6% 1	365
	11th to 20th	Day	25% 12% 26% 25% 11% 1	370
	21st to end	Day	26% 19% 33% 17% 5% 1	193
December	1st to 10th	Day	21% 14% 29% 21% 12% 3	180
	11th to 20th	Day	26% 18% 32% 17% 6% 2	180
	21st to end	Day	25% 20% 24% 22% 7% 2	198
January	1st to 10th	Night	18% 12% 32% 33% 6% 1	790
	11th to 20th	Night	17% 11% 34% 31% 7%	732
	21st to end	Night	13% 9% 31% 39% 8% 1	792
February	1st to 10th	Night	13% 10% 39% 31% 7% 1	720
	11th to 20th	Night	17% 12% 36% 26% 9% 1	703
	21st to end	Night	19% 10% 33% 31% 7% 1	592
March	1st to 10th	Night	21% 12% 32% 28% 6% 1	720
	11th to 20th	Night	19% 13% 33% 26% 8% 1	720
	21st to end	Night	21% 15% 29% 26% 9% 1	792
April	1st to 10th	Night	26% 12% 30% 24% 7% 1	720
	11th to 20th	Night	23% 11% 29% 27% 9%	583
	21st to end	Night	29% 8% 28% 27% 8%	540
May	1st to 10th	Night	27% 8% 27% 29% 8%	518
	11th to 20th	Night	25% 9% 23% 31% 12%	354
	21st to end	Night	26% 12% 27% 27% 8% 1	389
June	1st to 10th	Night	22% 7% 21% 37% 12% 1	360
	11th to 20th	Night	18% 5% 22% 38% 16% 2	360
	21st to end	Night	23% 5% 20% 41% 12% 1	360
July	1st to 10th	Night	21% 4 26% 38% 11% 1	350
	11th to 20th	Night	14% 4 19% 43% 18% 1	348
	21st to end	Night	15% 4 20% 46% 14% 1	394
August	1st to 10th	Night	13% 5% 16% 44% 21% 1	364
	11th to 20th	Night	16% 5% 18% 39% 20% 2	532
	21st to end	Night	16% 5% 25% 37% 16% 2	638
September	1st to 10th	Night	16% 6% 25% 36% 15% 1	720
	11th to 20th	Night	21% 5% 24% 34% 14% 2	720
	21st to end	Night	19% 7% 24% 35% 14% 1	720
October	1st to 10th	Night	19% 10% 26% 33% 10% 2	720
	11th to 20th	Night	26% 7% 24% 30% 12% 1	720
	21st to end	Night	27% 9% 26% 29% 9%	792
November	1st to 10th	Night	22% 12% 27% 29% 9% 1	740
	11th to 20th	Night	24% 11% 28% 26% 9% 1	796
	21st to end	Night	23% 14% 27% 28% 7% 1	850
December	1st to 10th	Night	23% 12% 28% 27% 8% 1	850
	11th to 20th	Night	20% 14% 28% 28% 8% 1	850
	21st to end	Night	24% 12% 29% 26% 8% 1	935

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