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 2024-03-28.

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% 5% 8% 7% 4 5% 4 5% 6% 27%	78358
	Night	17% 12% 5% 9% 7% 3 5% 4 4 5% 28%	81627
Transparency	Day	57% 6% 11% 17% 8% 1	78063
	Night	57% 6% 11% 17% 8% 1	81457
Seeing	Day	24% 20% 30% 18% 8% 2	14334
	Night	23% 16% 29% 24% 8% 1	23070

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% 16% 10% 13% 11% 5% 6% 4 3 4 14%	2517
	11th to 20th	Day	10% 14% 7% 17% 13% 6% 4 3 3 3 21%	2520
	21st to end	Day	9% 12% 7% 13% 9% 6% 5% 5% 5% 6% 23%	2772
February	1st to 10th	Day	12% 17% 7% 13% 10% 4 5% 4 3 5% 20%	1540
	11th to 20th	Day	12% 20% 9% 11% 8% 4 5% 3 4 4 20%	1838
	21st to end	Day	12% 16% 6% 11% 8% 4 5% 4 5% 5% 24%	1570
March	1st to 10th	Day	16% 14% 6% 10% 8% 3 4 4 3 6% 27%	1897
	11th to 20th	Day	15% 18% 6% 8% 6% 4 4 4 4 4 28%	2000
	21st to end	Day	16% 12% 6% 10% 7% 3 4 4 4 5% 29%	2379
April	1st to 10th	Day	23% 14% 5% 8% 6% 3 4 4 4 5% 25%	2160
	11th to 20th	Day	20% 12% 3 7% 5% 2 4 3 3 5% 35%	2222
	21st to end	Day	24% 14% 3 7% 5% 3 4 4 4 5% 27%	2340
May	1st to 10th	Day	22% 11% 4 7% 5% 3 4 5% 3 6% 31%	2362
	11th to 20th	Day	20% 9% 4 6% 5% 3 4 5% 6% 7% 31%	2478
	21st to end	Day	20% 8% 4 7% 5% 4 5% 5% 6% 7% 29%	2725
June	1st to 10th	Day	23% 8% 3 6% 5% 3 6% 5% 6% 7% 26%	2700
	11th to 20th	Day	20% 6% 3 5% 6% 3 5% 5% 6% 8% 33%	2700
	21st to end	Day	23% 9% 4 7% 7% 4 5% 4 5% 7% 25%	2700
July	1st to 10th	Day	17% 7% 3 6% 6% 3 6% 5% 6% 9% 30%	2524
	11th to 20th	Day	15% 6% 3 7% 8% 4 6% 6% 7% 9% 30%	2520
	21st to end	Day	18% 7% 3 6% 6% 3 6% 6% 6% 8% 31%	2744
August	1st to 10th	Day	20% 8% 3 6% 7% 3 5% 5% 6% 9% 27%	2474
	11th to 20th	Day	15% 8% 3 6% 6% 4 5% 5% 5% 8% 34%	2304
	21st to end	Day	17% 7% 3 6% 6% 4 5% 5% 5% 7% 36%	2467
September	1st to 10th	Day	17% 7% 3 6% 6% 3 5% 4 6% 7% 36%	2160
	11th to 20th	Day	19% 8% 3 4 3 2 3 4 5% 6% 42%	1990
	21st to end	Day	19% 7% 3 5% 4 3 4 5% 5% 8% 37%	1980
October	1st to 10th	Day	20% 10% 3 6% 5% 3 5% 5% 5% 7% 31%	1980
	11th to 20th	Day	20% 14% 3 8% 7% 5% 6% 5% 4 4 25%	1658
	21st to end	Day	26% 15% 4 8% 7% 4 4 3 4 5% 21%	1782
November	1st to 10th	Day	19% 14% 4 7% 6% 3 4 4 4 5% 29%	1671
	11th to 20th	Day	21% 15% 7% 9% 7% 3 4 4 4 5% 22%	1710
	21st to end	Day	18% 20% 6% 11% 7% 2 4 4 3 5% 21%	1417
December	1st to 10th	Day	21% 19% 8% 12% 8% 3 3 3 4 3 17%	1330
	11th to 20th	Day	18% 15% 8% 11% 6% 4 4 4 4 3 22%	1668
	21st to end	Day	22% 18% 7% 10% 8% 4 4 3 3 3 17%	2559
January	1st to 10th	Night	14% 16% 9% 13% 10% 4 5% 4 3 4 19%	4429
	11th to 20th	Night	10% 15% 7% 15% 14% 4 5% 4 3 3 20%	4440
	21st to end	Night	9% 15% 8% 12% 9% 3 6% 5% 5% 6% 22%	4884
February	1st to 10th	Night	11% 15% 5% 11% 11% 5% 6% 5% 5% 4 22%	2638
	11th to 20th	Night	11% 15% 7% 12% 9% 6% 6% 4 4 4 21%	2227
	21st to end	Night	13% 14% 6% 9% 7% 4 5% 4 5% 5% 28%	1884
March	1st to 10th	Night	15% 15% 6% 8% 7% 4 4 4 4 5% 29%	2270
	11th to 20th	Night	16% 14% 5% 8% 7% 4 5% 4 4 5% 28%	2178
	21st to end	Night	17% 13% 5% 8% 6% 3 4 4 4 4 32%	2131
April	1st to 10th	Night	22% 15% 4 7% 6% 3 3 5% 5% 5% 26%	1800
	11th to 20th	Night	19% 10% 3 6% 6% 3 5% 4 5% 6% 33%	1687
	21st to end	Night	21% 11% 4 8% 6% 3 3 4 3 5% 31%	1620
May	1st to 10th	Night	23% 9% 4 7% 5% 3 4 4 5% 5% 31%	1612
	11th to 20th	Night	21% 9% 4 6% 5% 3 5% 5% 4 6% 34%	1415
	21st to end	Night	22% 6% 3 6% 5% 2 4 4 5% 6% 36%	1546
June	1st to 10th	Night	23% 9% 3 5% 6% 3 5% 5% 5% 7% 29%	1260
	11th to 20th	Night	18% 7% 2 7% 6% 3 6% 5% 6% 7% 34%	1260
	21st to end	Night	18% 7% 3 7% 7% 4 6% 5% 7% 5% 32%	1260
July	1st to 10th	Night	15% 6% 3 6% 6% 4 5% 4 6% 9% 35%	1430
	11th to 20th	Night	14% 5% 3 6% 7% 4 5% 5% 6% 9% 36%	1440
	21st to end	Night	14% 6% 4 6% 6% 4 6% 6% 6% 7% 37%	1574
August	1st to 10th	Night	15% 6% 3 4 5% 3 5% 5% 6% 11% 39%	1445
	11th to 20th	Night	17% 7% 3 6% 6% 4 5% 5% 6% 8% 34%	1596
	21st to end	Night	15% 6% 2 6% 5% 3 5% 5% 5% 8% 41%	1885
September	1st to 10th	Night	16% 6% 3 6% 5% 3 4 6% 6% 7% 39%	1800
	11th to 20th	Night	18% 7% 2 4 3 3 4 4 4 5% 45%	1969
	21st to end	Night	18% 7% 3 6% 4 3 3 4 4 7% 42%	1980
October	1st to 10th	Night	19% 8% 3 5% 5% 3 5% 4 5% 5% 38%	1980
	11th to 20th	Night	22% 10% 3 6% 6% 4 5% 4 5% 5% 30%	2298
	21st to end	Night	24% 14% 4 7% 5% 3 4 4 4 5% 26%	2574
November	1st to 10th	Night	20% 13% 4 7% 6% 3 5% 4 4 5% 28%	2407
	11th to 20th	Night	17% 11% 6% 9% 8% 3 4 4 4 5% 28%	2470
	21st to end	Night	17% 17% 7% 9% 7% 3 4 4 4 4 24%	2758
December	1st to 10th	Night	20% 17% 7% 11% 8% 4 4 4 4 4 17%	2850
	11th to 20th	Night	16% 17% 7% 13% 7% 4 5% 3 3 4 20%	3531
	21st to end	Night	22% 21% 5% 10% 5% 2 3 3 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	60% 4 8% 15% 11% 2	1900
	11th to 20th	Day	60% 5% 9% 15% 11% 1	2000
	21st to end	Day	57% 5% 8% 16% 10% 3	2379
April	1st to 10th	Day	62% 4 10% 13% 9% 3	2160
	11th to 20th	Day	52% 4 9% 21% 12% 2	2222
	21st to end	Day	59% 5% 8% 15% 11% 3	2340
May	1st to 10th	Day	54% 6% 9% 16% 13% 2	2362
	11th to 20th	Day	51% 6% 10% 20% 11% 1	2482
	21st to end	Day	53% 8% 10% 17% 11% 1	2725
June	1st to 10th	Day	55% 8% 10% 20% 7% 1	2700
	11th to 20th	Day	47% 7% 13% 21% 11% 1	2700
	21st to end	Day	59% 8% 9% 16% 8%	2700
July	1st to 10th	Day	48% 9% 15% 22% 7%	2454
	11th to 20th	Day	48% 8% 15% 22% 7%	2445
	21st to end	Day	50% 9% 14% 21% 6%	2591
August	1st to 10th	Day	52% 9% 17% 19% 3	2460
	11th to 20th	Day	47% 9% 16% 19% 9%	2304
	21st to end	Day	46% 9% 13% 23% 9%	2467
September	1st to 10th	Day	45% 10% 14% 21% 10% 1	2160
	11th to 20th	Day	43% 5% 13% 26% 12%	1990
	21st to end	Day	44% 8% 13% 25% 9%	1980
October	1st to 10th	Day	51% 7% 11% 24% 7%	1980
	11th to 20th	Day	61% 6% 14% 17% 3	1658
	21st to end	Day	66% 5% 8% 16% 4 1	1782
November	1st to 10th	Day	57% 6% 12% 17% 7%	1671
	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	58% 5% 9% 17% 10% 2	2280
	11th to 20th	Night	58% 5% 11% 13% 11% 2	2179
	21st to end	Night	55% 5% 8% 19% 10% 3	2131
April	1st to 10th	Night	59% 4 9% 14% 11% 3	1800
	11th to 20th	Night	50% 5% 10% 21% 12% 2	1687
	21st to end	Night	56% 6% 9% 15% 12% 2	1620
May	1st to 10th	Night	54% 5% 11% 15% 14% 2	1612
	11th to 20th	Night	50% 6% 10% 19% 15% 1	1416
	21st to end	Night	48% 7% 11% 20% 13% 1	1547
June	1st to 10th	Night	54% 7% 11% 19% 9%	1260
	11th to 20th	Night	47% 6% 12% 22% 11% 2	1260
	21st to end	Night	50% 8% 14% 18% 9%	1260
July	1st to 10th	Night	43% 10% 17% 22% 8%	1390
	11th to 20th	Night	43% 9% 17% 23% 8%	1392
	21st to end	Night	45% 10% 16% 20% 8%	1486
August	1st to 10th	Night	40% 9% 20% 28% 4	1435
	11th to 20th	Night	45% 10% 18% 21% 6%	1596
	21st to end	Night	41% 8% 15% 26% 10%	1885
September	1st to 10th	Night	43% 8% 15% 24% 10% 1	1800
	11th to 20th	Night	40% 7% 16% 27% 9% 1	1969
	21st to end	Night	42% 8% 12% 24% 13%	1980
October	1st to 10th	Night	47% 7% 11% 24% 11%	1980
	11th to 20th	Night	55% 7% 13% 20% 5%	2298
	21st to end	Night	60% 6% 11% 15% 8%	2574
November	1st to 10th	Night	56% 6% 13% 18% 6%	2407
	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% 25% 27% 13% 7% 1	490
April	1st to 10th	Day	34% 19% 27% 13% 6%	420
	11th to 20th	Day	29% 25% 24% 14% 6% 1	412
	21st to end	Day	30% 20% 34% 10% 5% 2	420
May	1st to 10th	Day	29% 20% 32% 13% 5% 1	423
	11th to 20th	Day	23% 18% 32% 19% 7% 1	447
	21st to end	Day	21% 23% 34% 15% 7% 1	485
June	1st to 10th	Day	25% 16% 31% 20% 7% 1	630
	11th to 20th	Day	22% 15% 26% 24% 11% 1	630
	21st to end	Day	25% 14% 28% 22% 10% 1	630
July	1st to 10th	Day	15% 17% 33% 25% 10% 1	449
	11th to 20th	Day	16% 14% 37% 23% 9% 1	444
	21st to end	Day	19% 12% 36% 24% 8% 1	488
August	1st to 10th	Day	19% 13% 32% 22% 11% 3	446
	11th to 20th	Day	17% 11% 29% 26% 15% 3	439
	21st to end	Day	20% 17% 25% 18% 14% 6%	495
September	1st to 10th	Day	17% 15% 29% 24% 10% 4	450
	11th to 20th	Day	22% 13% 26% 21% 14% 5%	450
	21st to end	Day	16% 19% 28% 21% 9% 6%	450
October	1st to 10th	Day	21% 20% 27% 17% 13% 3	450
	11th to 20th	Day	28% 19% 29% 14% 8% 2	372
	21st to end	Day	34% 20% 25% 16% 4	396
November	1st to 10th	Day	30% 19% 27% 19% 5%	365
	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	24% 18% 28% 24% 6%	821
April	1st to 10th	Night	29% 18% 30% 18% 5%	720
	11th to 20th	Night	25% 15% 30% 24% 7%	623
	21st to end	Night	27% 18% 26% 22% 7%	540
May	1st to 10th	Night	26% 13% 28% 25% 8%	532
	11th to 20th	Night	25% 10% 28% 29% 7% 1	354
	21st to end	Night	21% 10% 32% 29% 8%	389
June	1st to 10th	Night	26% 8% 27% 29% 9%	360
	11th to 20th	Night	19% 8% 26% 36% 12%	360
	21st to end	Night	20% 9% 27% 34% 9% 1	360
July	1st to 10th	Night	17% 6% 32% 34% 10% 1	350
	11th to 20th	Night	15% 5% 26% 43% 12%	348
	21st to end	Night	15% 6% 24% 45% 10%	394
August	1st to 10th	Night	16% 5% 23% 37% 19% 1	371
	11th to 20th	Night	19% 5% 26% 33% 16% 1	532
	21st to end	Night	16% 9% 25% 32% 15% 2	697
September	1st to 10th	Night	18% 8% 32% 28% 14% 1	720
	11th to 20th	Night	21% 9% 22% 31% 15% 2	720
	21st to end	Night	21% 11% 28% 25% 14% 1	720
October	1st to 10th	Night	21% 13% 27% 29% 11% 1	720
	11th to 20th	Night	26% 16% 26% 22% 9% 1	720
	21st to end	Night	31% 18% 26% 20% 6%	792
November	1st to 10th	Night	28% 16% 28% 22% 6%	740
	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 2024-03-24 23:37:03. Version ac07

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