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 2024-11-11.

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	14% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	101627
	Night	14% 10% 4 8% 5% 5% 5% 4 5% 6% 36%	97570
Transparency	Day	49% 6% 14% 20% 9% 1	105081
	Night	48% 6% 13% 21% 10% 1	102207
Seeing	Day	22% 14% 31% 22% 9% 2	15516
	Night	20% 10% 28% 31% 10% 1	23764

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	10% 15% 5% 9% 5% 4 4 3 5% 8% 31%	2402
	11th to 20th	Day	8% 10% 4 12% 6% 6% 5% 4 6% 5% 34%	2520
	21st to end	Day	7% 7% 4 12% 7% 5% 6% 4 6% 7% 36%	2772
February	1st to 10th	Day	5% 11% 4 10% 8% 6% 7% 4 7% 5% 31%	1537
	11th to 20th	Day	8% 12% 4 13% 8% 6% 5% 3 4 6% 31%	1781
	21st to end	Day	10% 11% 3 9% 6% 5% 5% 5% 7% 5% 35%	1570
March	1st to 10th	Day	13% 12% 4 9% 5% 4 5% 4 5% 6% 31%	3116
	11th to 20th	Day	11% 18% 5% 9% 5% 5% 4 4 5% 6% 28%	3370
	21st to end	Day	11% 15% 5% 9% 5% 4 3 3 4 5% 35%	3992
April	1st to 10th	Day	18% 15% 4 7% 5% 4 4 3 5% 6% 29%	2280
	11th to 20th	Day	17% 8% 3 8% 5% 5% 5% 3 5% 6% 36%	2390
	21st to end	Day	20% 11% 3 7% 5% 4 4 4 4 6% 33%	2470
May	1st to 10th	Day	16% 9% 3 8% 5% 5% 5% 4 6% 6% 33%	4186
	11th to 20th	Day	17% 8% 2 6% 5% 6% 5% 4 6% 8% 33%	4398
	21st to end	Day	15% 7% 3 7% 5% 5% 5% 5% 7% 8% 32%	5113
June	1st to 10th	Day	20% 8% 3 6% 6% 5% 5% 5% 6% 7% 29%	2850
	11th to 20th	Day	17% 8% 2 6% 5% 5% 5% 5% 6% 6% 35%	2850
	21st to end	Day	23% 8% 3 7% 5% 5% 5% 4 7% 6% 28%	2850
July	1st to 10th	Day	14% 7% 3 7% 6% 6% 7% 5% 8% 8% 30%	4746
	11th to 20th	Day	12% 6% 2 7% 6% 6% 7% 5% 7% 8% 32%	4440
	21st to end	Day	11% 5% 2 6% 5% 6% 6% 5% 8% 9% 38%	4814
August	1st to 10th	Day	12% 5% 2 7% 6% 7% 7% 5% 9% 9% 31%	4371
	11th to 20th	Day	14% 7% 3 9% 5% 6% 6% 5% 7% 9% 28%	4045
	21st to end	Day	16% 5% 2 6% 4 5% 5% 4 5% 8% 40%	4441
September	1st to 10th	Day	12% 6% 2 6% 6% 5% 5% 3 6% 8% 40%	2275
	11th to 20th	Day	14% 6% 2 5% 3 4 5% 4 5% 7% 46%	2090
	21st to end	Day	18% 6% 2 6% 4 4 4 3 5% 6% 40%	2090
October	1st to 10th	Day	17% 8% 2 7% 5% 5% 4 3 5% 7% 37%	2081
	11th to 20th	Day	19% 8% 3 8% 6% 5% 4 5% 6% 6% 29%	1739
	21st to end	Day	21% 11% 3 7% 4 3 5% 3 5% 7% 31%	1881
November	1st to 10th	Day	13% 11% 4 9% 5% 4 3 4 5% 5% 36%	1761
	11th to 20th	Day	15% 10% 4 9% 6% 5% 4 4 6% 6% 31%	1634
	21st to end	Day	15% 15% 3 8% 5% 5% 5% 3 5% 6% 30%	1343
December	1st to 10th	Day	15% 14% 5% 9% 6% 5% 4 4 4 5% 28%	1330
	11th to 20th	Day	16% 12% 4 9% 6% 4 4 3 4 4 33%	1668
	21st to end	Day	16% 14% 4 7% 5% 4 3 2 3 5% 37%	2431
January	1st to 10th	Night	9% 14% 6% 11% 6% 6% 5% 5% 6% 6% 28%	4542
	11th to 20th	Night	7% 12% 5% 11% 7% 5% 4 4 5% 6% 33%	4440
	21st to end	Night	6% 11% 6% 13% 6% 6% 5% 3 6% 7% 30%	4884
February	1st to 10th	Night	6% 10% 4 11% 6% 5% 5% 4 5% 7% 37%	2642
	11th to 20th	Night	7% 13% 6% 11% 6% 6% 5% 3 5% 6% 34%	2283
	21st to end	Night	10% 12% 3 8% 7% 5% 3 4 5% 7% 36%	1884
March	1st to 10th	Night	15% 15% 5% 8% 5% 4 6% 4 5% 6% 29%	3724
	11th to 20th	Night	10% 14% 5% 12% 6% 6% 6% 4 5% 6% 26%	3588
	21st to end	Night	13% 14% 4 9% 5% 4 5% 4 4 5% 34%	3636
April	1st to 10th	Night	17% 16% 3 8% 5% 4 3 3 5% 5% 33%	1900
	11th to 20th	Night	17% 9% 3 7% 4 5% 5% 3 5% 7% 35%	1739
	21st to end	Night	20% 11% 3 6% 4 4 4 3 5% 4 36%	1710
May	1st to 10th	Night	18% 8% 3 7% 4 4 4 3 5% 6% 37%	2784
	11th to 20th	Night	18% 8% 3 7% 4 4 4 4 5% 7% 35%	2495
	21st to end	Night	17% 6% 2 4 4 4 5% 5% 5% 9% 38%	2466
June	1st to 10th	Night	18% 8% 3 7% 5% 4 5% 4 5% 6% 34%	1330
	11th to 20th	Night	15% 6% 2 5% 5% 4 4 3 6% 8% 42%	1330
	21st to end	Night	19% 8% 3 7% 5% 5% 5% 5% 5% 5% 32%	1330
July	1st to 10th	Night	14% 6% 2 6% 3 4 5% 4 7% 8% 40%	2210
	11th to 20th	Night	13% 6% 2 5% 4 4 5% 5% 7% 7% 41%	2516
	21st to end	Night	11% 4 1 4 4 4 4 4 6% 9% 49%	2739
August	1st to 10th	Night	14% 6% 3 6% 4 5% 5% 4 7% 7% 39%	2526
	11th to 20th	Night	13% 4 2 9% 6% 6% 6% 5% 6% 8% 34%	2782
	21st to end	Night	15% 6% 3 7% 4 4 4 3 5% 7% 43%	3210
September	1st to 10th	Night	14% 5% 2 5% 4 4 4 3 6% 6% 48%	1904
	11th to 20th	Night	16% 6% 2 6% 4 4 3 3 5% 6% 45%	2090
	21st to end	Night	17% 7% 2 6% 4 3 4 3 4 6% 44%	2090
October	1st to 10th	Night	15% 8% 3 6% 4 4 4 2 5% 6% 43%	2099
	11th to 20th	Night	21% 9% 3 7% 4 3 4 3 5% 6% 36%	2439
	21st to end	Night	19% 9% 2 7% 4 5% 3 3 5% 7% 36%	2717
November	1st to 10th	Night	13% 10% 3 8% 4 5% 5% 3 5% 7% 37%	2537
	11th to 20th	Night	16% 10% 3 7% 4 4 5% 4 5% 6% 36%	2552
	21st to end	Night	14% 14% 4 7% 6% 3 4 3 5% 6% 33%	2835
December	1st to 10th	Night	14% 15% 5% 10% 6% 4 4 3 4 5% 31%	2850
	11th to 20th	Night	16% 11% 4 8% 5% 4 5% 4 5% 6% 32%	3531
	21st to end	Night	16% 16% 5% 8% 4 4 4 3 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	52% 5% 14% 22% 7%	2403
	11th to 20th	Day	52% 5% 8% 25% 9% 1	2520
	21st to end	Day	47% 6% 11% 19% 16% 1	2772
February	1st to 10th	Day	53% 5% 10% 18% 12% 3	1537
	11th to 20th	Day	56% 4 11% 16% 12% 2	1789
	21st to end	Day	50% 5% 8% 21% 12% 4	1570
March	1st to 10th	Day	52% 6% 13% 15% 9% 4	3119
	11th to 20th	Day	56% 6% 14% 15% 8% 2	3370
	21st to end	Day	52% 4 7% 19% 12% 6%	3992
April	1st to 10th	Day	57% 4 10% 14% 11% 3	2280
	11th to 20th	Day	49% 4 10% 23% 11% 3	2390
	21st to end	Day	54% 4 10% 17% 13% 2	2470
May	1st to 10th	Day	49% 6% 13% 18% 12% 1	4200
	11th to 20th	Day	49% 6% 16% 21% 7% 1	4402
	21st to end	Day	48% 7% 12% 21% 12% 1	5113
June	1st to 10th	Day	53% 7% 12% 20% 7% 1	2850
	11th to 20th	Day	48% 6% 15% 20% 9% 2	2850
	21st to end	Day	55% 6% 14% 17% 8% 1	2850
July	1st to 10th	Day	46% 8% 17% 21% 7%	4671
	11th to 20th	Day	46% 8% 18% 23% 5%	4365
	21st to end	Day	40% 8% 19% 23% 9%	4661
August	1st to 10th	Day	46% 8% 20% 19% 7%	4357
	11th to 20th	Day	50% 8% 22% 16% 4	4084
	21st to end	Day	42% 7% 19% 19% 12% 1	4441
September	1st to 10th	Day	42% 5% 17% 23% 12%	2275
	11th to 20th	Day	38% 5% 19% 28% 10% 1	2090
	21st to end	Day	45% 5% 15% 24% 10%	2090
October	1st to 10th	Day	53% 6% 11% 24% 6%	3458
	11th to 20th	Day	45% 7% 17% 25% 6%	2864
	21st to end	Day	43% 7% 21% 19% 10% 1	3081
November	1st to 10th	Day	51% 6% 13% 21% 8% 1	1761
	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% 12% 16% 9% 1	4542
	11th to 20th	Night	51% 6% 9% 22% 9% 1	4440
	21st to end	Night	51% 7% 9% 20% 11% 1	4884
February	1st to 10th	Night	45% 6% 11% 22% 14% 2	2642
	11th to 20th	Night	53% 5% 10% 17% 14% 1	2286
	21st to end	Night	49% 4 10% 22% 13% 3	1884
March	1st to 10th	Night	55% 6% 11% 18% 8% 3	3734
	11th to 20th	Night	59% 6% 12% 15% 7% 1	3589
	21st to end	Night	53% 4 9% 21% 11% 2	3636
April	1st to 10th	Night	55% 4 7% 17% 14% 3	1900
	11th to 20th	Night	49% 6% 9% 22% 13% 1	1739
	21st to end	Night	52% 3 9% 20% 13% 2	1710
May	1st to 10th	Night	47% 5% 13% 21% 13% 2	2790
	11th to 20th	Night	47% 6% 14% 21% 10% 1	2496
	21st to end	Night	41% 6% 14% 24% 13% 1	2467
June	1st to 10th	Night	49% 6% 13% 23% 8% 1	1330
	11th to 20th	Night	41% 5% 15% 24% 13% 3	1330
	21st to end	Night	52% 6% 14% 17% 10%	1330
July	1st to 10th	Night	40% 8% 22% 26% 4	2175
	11th to 20th	Night	39% 7% 22% 26% 5%	2469
	21st to end	Night	32% 8% 25% 23% 11%	2651
August	1st to 10th	Night	43% 8% 20% 23% 7%	2516
	11th to 20th	Night	45% 12% 21% 14% 8%	2809
	21st to end	Night	41% 6% 15% 28% 11%	3210
September	1st to 10th	Night	37% 7% 16% 27% 12% 1	1904
	11th to 20th	Night	41% 6% 17% 27% 8% 1	2090
	21st to end	Night	43% 6% 13% 27% 11% 1	2090
October	1st to 10th	Night	45% 5% 13% 28% 8%	3502
	11th to 20th	Night	45% 6% 15% 26% 8%	4053
	21st to end	Night	42% 7% 20% 19% 13%	4467
November	1st to 10th	Night	46% 6% 14% 24% 9% 1	2537
	11th to 20th	Night	49% 6% 11% 22% 10% 2	2552
	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% 14% 34% 21% 8% 1	180
	21st to end	Day	13% 18% 38% 20% 9% 3	198
February	1st to 10th	Day	18% 19% 40% 16% 6% 1	197
	11th to 20th	Day	17% 19% 38% 20% 6%	424
	21st to end	Day	18% 19% 36% 21% 5% 1	382
March	1st to 10th	Day	24% 18% 30% 21% 7%	460
	11th to 20th	Day	22% 18% 32% 20% 8% 1	460
	21st to end	Day	25% 19% 29% 18% 8% 1	506
April	1st to 10th	Day	31% 17% 27% 19% 6% 1	460
	11th to 20th	Day	25% 14% 34% 18% 7% 2	452
	21st to end	Day	30% 14% 35% 14% 5% 2	460
May	1st to 10th	Day	31% 11% 29% 20% 8% 1	463
	11th to 20th	Day	23% 18% 29% 20% 9% 2	487
	21st to end	Day	22% 17% 33% 20% 6% 1	688
June	1st to 10th	Day	27% 13% 25% 25% 9% 1	680
	11th to 20th	Day	23% 14% 25% 23% 13% 2	680
	21st to end	Day	26% 11% 27% 25% 9% 2	680
July	1st to 10th	Day	18% 11% 30% 29% 11% 1	669
	11th to 20th	Day	15% 10% 37% 27% 9% 2	484
	21st to end	Day	14% 9% 35% 28% 11% 2	532
August	1st to 10th	Day	16% 11% 35% 24% 11% 3	486
	11th to 20th	Day	16% 6% 32% 29% 13% 4	479
	21st to end	Day	18% 13% 31% 19% 17% 3	539
September	1st to 10th	Day	17% 14% 31% 25% 9% 5%	490
	11th to 20th	Day	21% 8% 32% 23% 11% 4	490
	21st to end	Day	23% 12% 26% 22% 12% 5%	490
October	1st to 10th	Day	22% 15% 26% 25% 10% 2	485
	11th to 20th	Day	28% 13% 28% 18% 11% 2	390
	21st to end	Day	30% 14% 28% 21% 7%	429
November	1st to 10th	Day	26% 14% 32% 21% 6% 1	395
	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% 10% 35% 31% 6%	760
	21st to end	Night	12% 9% 30% 40% 8% 1	836
February	1st to 10th	Night	12% 9% 39% 31% 8% 1	760
	11th to 20th	Night	16% 12% 38% 25% 8% 1	743
	21st to end	Night	19% 10% 33% 32% 7% 1	628
March	1st to 10th	Night	21% 12% 31% 29% 6% 1	760
	11th to 20th	Night	18% 14% 33% 27% 8% 1	760
	21st to end	Night	22% 14% 30% 26% 8% 1	836
April	1st to 10th	Night	26% 12% 31% 24% 7% 1	760
	11th to 20th	Night	24% 11% 29% 27% 8%	615
	21st to end	Night	29% 8% 28% 27% 8%	570
May	1st to 10th	Night	26% 8% 28% 29% 8%	546
	11th to 20th	Night	24% 9% 22% 32% 12%	374
	21st to end	Night	26% 11% 27% 28% 7% 1	411
June	1st to 10th	Night	21% 7% 21% 36% 13% 1	380
	11th to 20th	Night	18% 5% 22% 37% 16% 2	380
	21st to end	Night	22% 5% 21% 39% 11% 1	380
July	1st to 10th	Night	20% 4 26% 39% 10% 1	370
	11th to 20th	Night	15% 4 18% 44% 17% 1	368
	21st to end	Night	15% 4 20% 47% 13% 1	416
August	1st to 10th	Night	13% 5% 17% 44% 19% 1	385
	11th to 20th	Night	16% 4 19% 38% 21% 2	562
	21st to end	Night	15% 5% 25% 36% 16% 1	674
September	1st to 10th	Night	16% 7% 24% 37% 14% 1	760
	11th to 20th	Night	20% 5% 23% 35% 15% 2	760
	21st to end	Night	19% 7% 24% 35% 15% 1	760
October	1st to 10th	Night	20% 10% 25% 33% 10% 2	760
	11th to 20th	Night	27% 8% 23% 30% 11% 1	760
	21st to end	Night	26% 9% 27% 28% 9%	836
November	1st to 10th	Night	22% 12% 28% 28% 8% 1	780
	11th to 20th	Night	24% 11% 29% 26% 9% 1	799
	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

Page generated at 2024-11-08 06:44:45. Version ac07

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