Observatoire du Mont-Cosmos
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire du Mont-Cosmos clear sky chart from 2005-11-06 to 2024-11-04.

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	18% 12% 4 9% 6% 5% 4 4 5% 6% 28%	101302
	Night	17% 13% 4 10% 6% 5% 4 3 5% 5% 29%	97713
Transparency	Day	55% 7% 12% 18% 8% 1	104775
	Night	56% 6% 12% 18% 8% 1	102330
Seeing	Day	24% 20% 30% 18% 8% 2	15225
	Night	23% 16% 28% 24% 8% 1	23732

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	13% 17% 9% 14% 10% 7% 5% 3 3 4 14%	2517
	11th to 20th	Day	9% 15% 7% 19% 11% 7% 3 2 3 3 21%	2520
	21st to end	Day	9% 12% 7% 15% 7% 7% 5% 4 5% 6% 23%	2772
February	1st to 10th	Day	12% 18% 7% 14% 9% 5% 4 3 3 5% 20%	1540
	11th to 20th	Day	11% 21% 8% 12% 6% 5% 5% 2 4 4 20%	1838
	21st to end	Day	12% 17% 5% 12% 8% 5% 4 3 5% 5% 24%	1570
March	1st to 10th	Day	18% 16% 3 9% 6% 5% 3 4 4 6% 27%	3116
	11th to 20th	Day	14% 24% 6% 13% 5% 4 3 3 3 3 23%	3338
	21st to end	Day	16% 14% 5% 10% 5% 4 3 3 3 4 32%	4033
April	1st to 10th	Day	22% 16% 3 9% 5% 3 4 3 4 5% 25%	2280
	11th to 20th	Day	19% 13% 3 8% 4 3 3 3 3 5% 35%	2347
	21st to end	Day	23% 14% 3 8% 4 3 4 3 4 5% 28%	2470
May	1st to 10th	Day	22% 10% 3 8% 5% 5% 4 4 4 6% 29%	4156
	11th to 20th	Day	20% 9% 4 7% 5% 5% 5% 4 6% 8% 27%	4398
	21st to end	Day	16% 8% 3 9% 6% 6% 6% 4 7% 7% 29%	4837
June	1st to 10th	Day	22% 9% 2 7% 5% 5% 5% 4 7% 7% 26%	2850
	11th to 20th	Day	19% 6% 2 6% 5% 5% 5% 4 7% 8% 33%	2850
	21st to end	Day	23% 10% 3 8% 6% 5% 4 3 5% 6% 24%	2850
July	1st to 10th	Day	15% 7% 3 9% 7% 5% 5% 5% 6% 8% 29%	4444
	11th to 20th	Day	15% 6% 3 8% 6% 5% 6% 5% 7% 8% 31%	4440
	21st to end	Day	14% 6% 2 6% 4 4 5% 4 6% 7% 41%	4814
August	1st to 10th	Day	17% 7% 2 7% 6% 5% 6% 5% 7% 9% 28%	4364
	11th to 20th	Day	17% 7% 3 8% 5% 6% 6% 5% 7% 7% 27%	4045
	21st to end	Day	21% 7% 3 6% 4 5% 4 3 5% 7% 36%	4341
September	1st to 10th	Day	16% 7% 3 8% 4 5% 4 4 5% 7% 38%	2280
	11th to 20th	Day	18% 8% 3 5% 3 3 3 3 5% 6% 43%	2100
	21st to end	Day	19% 8% 3 5% 4 4 4 4 6% 8% 36%	2090
October	1st to 10th	Day	19% 11% 3 7% 4 4 5% 4 6% 7% 30%	2090
	11th to 20th	Day	19% 14% 3 9% 6% 6% 5% 4 3 4 26%	1749
	21st to end	Day	25% 15% 4 8% 6% 5% 4 2 4 5% 22%	1881
November	1st to 10th	Day	19% 15% 4 8% 5% 4 4 2 5% 5% 29%	1698
	11th to 20th	Day	19% 17% 6% 10% 6% 4 3 4 4 5% 22%	1710
	21st to end	Day	17% 21% 6% 12% 6% 3 4 3 3 4 21%	1417
December	1st to 10th	Day	20% 21% 6% 15% 6% 4 2 3 4 3 17%	1330
	11th to 20th	Day	18% 18% 6% 12% 6% 5% 4 3 4 3 22%	1668
	21st to end	Day	22% 19% 6% 12% 6% 5% 4 2 3 3 17%	2559
January	1st to 10th	Night	13% 17% 8% 15% 7% 5% 4 3 4 4 19%	4429
	11th to 20th	Night	10% 16% 6% 18% 11% 6% 4 3 3 3 20%	4440
	21st to end	Night	9% 16% 7% 13% 8% 5% 5% 4 5% 6% 22%	4884
February	1st to 10th	Night	10% 16% 5% 12% 9% 6% 5% 4 5% 4 22%	2638
	11th to 20th	Night	11% 17% 6% 14% 8% 7% 5% 3 4 4 21%	2227
	21st to end	Night	13% 15% 6% 11% 7% 5% 4 3 5% 5% 27%	1884
March	1st to 10th	Night	20% 14% 4 7% 5% 4 6% 3 3 5% 29%	3724
	11th to 20th	Night	14% 19% 6% 12% 6% 5% 4 3 4 4 23%	3620
	21st to end	Night	16% 16% 5% 11% 6% 4 3 3 3 4 30%	3598
April	1st to 10th	Night	21% 16% 4 8% 4 4 3 4 5% 5% 28%	1900
	11th to 20th	Night	19% 11% 3 7% 5% 5% 4 3 5% 6% 32%	1782
	21st to end	Night	20% 12% 4 9% 5% 4 3 3 3 5% 32%	1710
May	1st to 10th	Night	23% 9% 3 8% 5% 4 4 3 6% 6% 29%	2812
	11th to 20th	Night	21% 9% 3 7% 4 4 4 4 4 5% 34%	2495
	21st to end	Night	17% 7% 3 7% 5% 3 5% 4 6% 8% 36%	2721
June	1st to 10th	Night	22% 10% 3 7% 5% 5% 4 4 5% 7% 29%	1330
	11th to 20th	Night	17% 7% 2 8% 5% 4 5% 5% 6% 6% 35%	1330
	21st to end	Night	19% 8% 3 8% 7% 6% 4 4 7% 5% 31%	1330
July	1st to 10th	Night	12% 8% 3 9% 6% 6% 6% 4 6% 9% 32%	2510
	11th to 20th	Night	17% 6% 2 7% 6% 5% 5% 4 5% 7% 36%	2520
	21st to end	Night	13% 6% 3 6% 5% 4 4 4 5% 7% 43%	2739
August	1st to 10th	Night	19% 9% 3 7% 5% 5% 4 3 5% 8% 33%	2533
	11th to 20th	Night	16% 7% 3 9% 6% 6% 7% 4 6% 7% 29%	2782
	21st to end	Night	19% 6% 3 8% 4 4 4 3 5% 6% 38%	3311
September	1st to 10th	Night	16% 6% 3 7% 4 4 4 4 6% 6% 40%	1900
	11th to 20th	Night	17% 6% 2 5% 3 4 3 4 4 5% 46%	2079
	21st to end	Night	17% 8% 3 6% 4 4 3 3 4 7% 41%	2090
October	1st to 10th	Night	19% 8% 2 7% 4 4 5% 3 5% 5% 38%	2090
	11th to 20th	Night	21% 11% 3 7% 5% 5% 5% 3 5% 5% 31%	2427
	21st to end	Night	23% 14% 4 8% 5% 4 4 4 4 5% 27%	2717
November	1st to 10th	Night	19% 14% 4 7% 6% 5% 4 4 4 5% 28%	2453
	11th to 20th	Night	17% 13% 5% 11% 7% 4 4 3 4 4 28%	2470
	21st to end	Night	16% 18% 6% 11% 6% 4 4 3 4 4 24%	2758
December	1st to 10th	Night	20% 19% 7% 12% 7% 4 4 3 4 4 17%	2850
	11th to 20th	Night	16% 18% 6% 15% 6% 6% 4 2 4 4 20%	3531
	21st to end	Night	21% 21% 5% 11% 4 3 3 2 3 3 23%	5099

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	73% 6% 8% 10% 3	2518
	11th to 20th	Day	69% 4 6% 15% 5% 1	2520
	21st to end	Day	60% 9% 8% 13% 9% 1	2772
February	1st to 10th	Day	68% 4 6% 11% 8% 2	1540
	11th to 20th	Day	68% 4 9% 10% 7% 1	1847
	21st to end	Day	62% 5% 8% 16% 7% 3	1570
March	1st to 10th	Day	59% 6% 8% 15% 10% 2	3119
	11th to 20th	Day	66% 5% 9% 13% 7% 1	3338
	21st to end	Day	56% 4 7% 17% 13% 3	4033
April	1st to 10th	Day	61% 4 10% 14% 9% 3	2280
	11th to 20th	Day	53% 4 8% 21% 12% 2	2347
	21st to end	Day	58% 4 9% 15% 11% 2	2470
May	1st to 10th	Day	52% 8% 11% 17% 11% 1	4170
	11th to 20th	Day	51% 10% 15% 16% 7% 1	4402
	21st to end	Day	49% 9% 11% 18% 12% 1	4837
June	1st to 10th	Day	54% 8% 10% 20% 7% 1	2850
	11th to 20th	Day	47% 7% 14% 20% 10% 1	2850
	21st to end	Day	59% 8% 9% 16% 8%	2850
July	1st to 10th	Day	50% 8% 14% 21% 6%	4374
	11th to 20th	Day	47% 8% 17% 24% 4	4365
	21st to end	Day	41% 8% 15% 28% 7%	4661
August	1st to 10th	Day	49% 9% 18% 20% 4	4350
	11th to 20th	Day	51% 11% 18% 15% 5%	4084
	21st to end	Day	47% 8% 14% 19% 11% 1	4341
September	1st to 10th	Day	43% 9% 14% 22% 10% 1	2280
	11th to 20th	Day	42% 5% 13% 27% 12%	2100
	21st to end	Day	45% 8% 13% 25% 9%	2090
October	1st to 10th	Day	52% 7% 12% 24% 5%	3480
	11th to 20th	Day	52% 6% 16% 23% 3	2874
	21st to end	Day	55% 5% 15% 18% 7%	3081
November	1st to 10th	Day	57% 6% 12% 18% 7%	1698
	11th to 20th	Day	64% 6% 9% 14% 6% 1	1710
	21st to end	Day	67% 5% 12% 12% 4	1417
December	1st to 10th	Day	74% 4 8% 11% 4	1330
	11th to 20th	Day	66% 5% 7% 15% 7%	1668
	21st to end	Day	72% 6% 6% 9% 5% 2	2559
January	1st to 10th	Night	68% 7% 10% 10% 4	4429
	11th to 20th	Night	68% 5% 9% 13% 4 1	4440
	21st to end	Night	62% 6% 11% 12% 8% 1	4884
February	1st to 10th	Night	64% 6% 8% 13% 8% 1	2638
	11th to 20th	Night	65% 6% 8% 12% 8% 1	2229
	21st to end	Night	58% 4 9% 16% 12% 2	1884
March	1st to 10th	Night	59% 6% 10% 15% 9% 2	3734
	11th to 20th	Night	63% 5% 11% 13% 7% 1	3621
	21st to end	Night	59% 4 7% 19% 9% 2	3598
April	1st to 10th	Night	57% 4 10% 15% 11% 3	1900
	11th to 20th	Night	51% 5% 10% 21% 12% 2	1782
	21st to end	Night	55% 6% 9% 16% 12% 2	1710
May	1st to 10th	Night	53% 6% 14% 17% 9% 1	2818
	11th to 20th	Night	49% 9% 13% 18% 10% 1	2496
	21st to end	Night	43% 8% 15% 19% 14% 1	2722
June	1st to 10th	Night	53% 7% 11% 21% 8%	1330
	11th to 20th	Night	47% 6% 12% 21% 12% 2	1330
	21st to end	Night	52% 8% 14% 17% 9%	1330
July	1st to 10th	Night	45% 10% 19% 20% 6%	2470
	11th to 20th	Night	45% 8% 20% 22% 5%	2472
	21st to end	Night	38% 9% 20% 26% 7%	2651
August	1st to 10th	Night	49% 7% 17% 24% 4	2523
	11th to 20th	Night	50% 10% 17% 17% 6%	2809
	21st to end	Night	45% 8% 14% 19% 13%	3311
September	1st to 10th	Night	43% 7% 14% 25% 10% 1	1900
	11th to 20th	Night	39% 7% 16% 28% 9% 1	2079
	21st to end	Night	43% 8% 12% 24% 13%	2090
October	1st to 10th	Night	46% 7% 12% 28% 8%	3480
	11th to 20th	Night	49% 8% 13% 25% 4	4041
	21st to end	Night	50% 5% 18% 16% 9%	4467
November	1st to 10th	Night	56% 6% 13% 19% 6%	2453
	11th to 20th	Night	58% 6% 12% 15% 9% 1	2470
	21st to end	Night	64% 6% 11% 14% 5%	2758
December	1st to 10th	Night	71% 5% 10% 11% 3	2850
	11th to 20th	Night	68% 5% 8% 13% 6%	3532
	21st to end	Night	67% 4 8% 15% 6%	5099

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	27% 19% 34% 17% 2 1	180
	11th to 20th	Day	28% 28% 31% 11% 2	180
	21st to end	Day	18% 27% 34% 15% 6% 1	198
February	1st to 10th	Day	24% 33% 33% 7% 3 1	200
	11th to 20th	Day	23% 29% 34% 12% 2	451
	21st to end	Day	22% 29% 30% 17% 3	382
March	1st to 10th	Day	28% 23% 29% 14% 4	460
	11th to 20th	Day	27% 26% 28% 15% 3 1	460
	21st to end	Day	26% 26% 26% 13% 7% 1	506
April	1st to 10th	Day	35% 19% 27% 13% 6%	460
	11th to 20th	Day	29% 26% 23% 14% 6% 1	452
	21st to end	Day	29% 21% 34% 10% 5% 2	460
May	1st to 10th	Day	29% 20% 32% 14% 5% 1	463
	11th to 20th	Day	22% 17% 31% 21% 8% 1	487
	21st to end	Day	21% 23% 34% 15% 7% 1	529
June	1st to 10th	Day	24% 16% 31% 20% 7% 1	680
	11th to 20th	Day	21% 16% 26% 25% 11% 1	680
	21st to end	Day	27% 14% 27% 21% 9% 1	680
July	1st to 10th	Day	15% 17% 34% 24% 9% 1	489
	11th to 20th	Day	17% 14% 37% 22% 9% 1	484
	21st to end	Day	18% 12% 36% 24% 9% 1	532
August	1st to 10th	Day	19% 14% 31% 22% 11% 3	486
	11th to 20th	Day	17% 11% 29% 26% 15% 2	479
	21st to end	Day	20% 16% 26% 19% 14% 5%	539
September	1st to 10th	Day	17% 16% 30% 23% 10% 4	490
	11th to 20th	Day	20% 12% 27% 22% 14% 5%	490
	21st to end	Day	16% 19% 28% 22% 9% 6%	490
October	1st to 10th	Day	21% 20% 28% 17% 13% 3	490
	11th to 20th	Day	29% 19% 29% 14% 8% 1	403
	21st to end	Day	33% 21% 25% 16% 4	429
November	1st to 10th	Day	30% 19% 27% 19% 5%	374
	11th to 20th	Day	27% 22% 26% 15% 9% 1	370
	21st to end	Day	31% 24% 29% 15% 1	214
December	1st to 10th	Day	32% 19% 26% 18% 4 2	180
	11th to 20th	Day	29% 28% 27% 12% 3 1	180
	21st to end	Day	32% 27% 26% 12% 3 1	198
January	1st to 10th	Night	24% 24% 30% 18% 3	760
	11th to 20th	Night	24% 23% 32% 17% 4	760
	21st to end	Night	16% 20% 34% 25% 5% 1	836
February	1st to 10th	Night	19% 22% 35% 18% 6%	760
	11th to 20th	Night	22% 25% 34% 16% 3	743
	21st to end	Night	24% 20% 32% 21% 4	628
March	1st to 10th	Night	23% 19% 34% 21% 3	760
	11th to 20th	Night	25% 20% 32% 18% 4 1	760
	21st to end	Night	23% 19% 28% 24% 6%	836
April	1st to 10th	Night	29% 17% 30% 19% 5%	760
	11th to 20th	Night	26% 15% 29% 23% 6%	658
	21st to end	Night	26% 19% 26% 22% 6%	570
May	1st to 10th	Night	26% 12% 29% 25% 7%	561
	11th to 20th	Night	24% 10% 28% 29% 8% 1	374
	21st to end	Night	21% 9% 33% 29% 8%	411
June	1st to 10th	Night	26% 8% 27% 30% 9%	380
	11th to 20th	Night	19% 9% 25% 35% 12%	380
	21st to end	Night	21% 9% 26% 34% 9% 1	380
July	1st to 10th	Night	16% 7% 32% 34% 10% 1	370
	11th to 20th	Night	15% 5% 25% 43% 11%	368
	21st to end	Night	14% 6% 23% 45% 11%	416
August	1st to 10th	Night	17% 5% 22% 37% 18% 1	392
	11th to 20th	Night	19% 6% 26% 32% 15% 1	562
	21st to end	Night	16% 9% 25% 32% 16% 2	736
September	1st to 10th	Night	18% 8% 31% 28% 13% 1	760
	11th to 20th	Night	20% 9% 21% 31% 17% 2	760
	21st to end	Night	20% 11% 27% 25% 15% 1	760
October	1st to 10th	Night	20% 13% 27% 29% 11% 1	760
	11th to 20th	Night	26% 16% 25% 23% 9% 1	760
	21st to end	Night	30% 18% 26% 20% 6%	836
November	1st to 10th	Night	28% 16% 28% 22% 6%	755
	11th to 20th	Night	24% 20% 27% 19% 9% 1	760
	21st to end	Night	28% 20% 29% 17% 5% 1	825
December	1st to 10th	Night	31% 19% 27% 18% 6%	850
	11th to 20th	Night	24% 25% 25% 19% 7% 1	850
	21st to end	Night	31% 22% 26% 17% 3	895

Page generated at 2024-11-01 22:47:52. Version ac07

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