Observatoire de la Montagne Coupée
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire de la Montagne Coupée clear sky chart from 2005-11-06 to 2024-03-01.

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	17% 9% 4 7% 6% 3 5% 5% 5% 7% 33%	78280
	Night	17% 10% 4 7% 6% 3 4 4 5% 6% 34%	81121
Transparency	Day	50% 7% 12% 19% 10% 1	77985
	Night	51% 7% 11% 19% 10% 1	80950
Seeing	Day	22% 15% 31% 22% 8% 2	13554
	Night	22% 10% 30% 28% 9% 1	22674

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	16% 14% 4 9% 6% 3 5% 5% 4 4 29%	2517
	11th to 20th	Day	14% 13% 6% 9% 7% 4 5% 4 4 5% 29%	2520
	21st to end	Day	11% 13% 7% 11% 8% 5% 5% 4 5% 6% 25%	2772
February	1st to 10th	Day	13% 16% 7% 8% 7% 3 6% 4 4 5% 27%	1634
	11th to 20th	Day	12% 14% 5% 10% 6% 4 5% 4 5% 6% 29%	1757
	21st to end	Day	16% 15% 6% 7% 8% 3 4 4 4 5% 29%	1570
March	1st to 10th	Day	15% 10% 5% 8% 7% 4 6% 5% 4 6% 30%	1797
	11th to 20th	Day	14% 13% 4 7% 7% 4 5% 3 5% 6% 32%	1855
	21st to end	Day	17% 9% 4 7% 6% 3 4 5% 5% 6% 35%	2376
April	1st to 10th	Day	21% 10% 5% 7% 6% 3 4 4 4 5% 31%	2160
	11th to 20th	Day	21% 7% 2 5% 5% 3 4 4 5% 6% 37%	2134
	21st to end	Day	22% 9% 4 6% 5% 3 5% 4 4 5% 33%	2326
May	1st to 10th	Day	21% 8% 3 5% 6% 3 4 4 4 6% 36%	2492
	11th to 20th	Day	19% 8% 3 6% 5% 4 4 4 5% 7% 36%	2478
	21st to end	Day	18% 6% 3 6% 6% 3 5% 5% 5% 7% 35%	2725
June	1st to 10th	Day	21% 7% 3 6% 6% 4 5% 5% 6% 7% 29%	2520
	11th to 20th	Day	15% 5% 3 6% 6% 3 6% 6% 6% 9% 35%	2520
	21st to end	Day	20% 9% 3 7% 6% 4 6% 5% 6% 8% 27%	2520
July	1st to 10th	Day	13% 4 2 5% 7% 4 6% 6% 6% 8% 37%	2520
	11th to 20th	Day	14% 5% 3 6% 6% 4 7% 6% 7% 9% 35%	2520
	21st to end	Day	13% 6% 3 6% 6% 4 6% 6% 8% 10% 33%	2744
August	1st to 10th	Day	13% 6% 3 7% 7% 4 7% 6% 6% 10% 32%	2506
	11th to 20th	Day	12% 4 2 6% 6% 4 5% 6% 8% 9% 37%	2322
	21st to end	Day	13% 5% 2 5% 5% 3 5% 5% 6% 9% 42%	2376
September	1st to 10th	Day	14% 5% 2 5% 5% 3 5% 5% 6% 8% 43%	2160
	11th to 20th	Day	15% 5% 2 4 4 3 4 4 5% 7% 47%	2080
	21st to end	Day	20% 6% 3 4 4 3 4 4 5% 6% 42%	1980
October	1st to 10th	Day	22% 6% 2 5% 4 3 4 4 5% 6% 37%	1866
	11th to 20th	Day	22% 8% 4 7% 7% 4 4 5% 5% 7% 27%	1742
	21st to end	Day	25% 10% 4 6% 5% 3 4 4 4 5% 30%	1782
November	1st to 10th	Day	15% 9% 4 6% 5% 3 5% 5% 5% 6% 36%	1671
	11th to 20th	Day	19% 10% 4 8% 6% 3 4 5% 5% 6% 30%	1620
	21st to end	Day	20% 12% 4 7% 5% 3 6% 4 4 6% 28%	1520
December	1st to 10th	Day	24% 14% 5% 7% 7% 3 4 5% 4 4 24%	1520
	11th to 20th	Day	21% 14% 5% 8% 5% 3 3 4 4 5% 29%	1906
	21st to end	Day	26% 15% 6% 8% 5% 2 4 3 3 4 24%	2772
January	1st to 10th	Night	16% 15% 5% 8% 6% 4 4 5% 5% 5% 28%	4429
	11th to 20th	Night	11% 11% 5% 11% 9% 4 6% 5% 5% 5% 29%	4440
	21st to end	Night	11% 14% 5% 11% 8% 5% 6% 5% 5% 5% 26%	4884
February	1st to 10th	Night	12% 13% 6% 9% 7% 4 5% 5% 4 5% 28%	2542
	11th to 20th	Night	13% 11% 5% 9% 8% 4 5% 5% 4 4 32%	2308
	21st to end	Night	15% 12% 4 8% 6% 3 5% 4 5% 6% 33%	1884
March	1st to 10th	Night	16% 13% 5% 8% 6% 3 5% 4 4 6% 30%	2157
	11th to 20th	Night	16% 13% 5% 7% 5% 3 4 5% 5% 4 32%	2099
	21st to end	Night	16% 9% 3 7% 5% 4 5% 4 4 6% 38%	1980
April	1st to 10th	Night	22% 10% 4 6% 6% 3 4 3 4 7% 31%	1800
	11th to 20th	Night	20% 6% 3 5% 5% 3 6% 4 4 5% 40%	1775
	21st to end	Night	20% 10% 3 5% 4 3 4 4 5% 6% 35%	1632
May	1st to 10th	Night	22% 8% 3 6% 5% 2 3 3 5% 6% 36%	1482
	11th to 20th	Night	19% 7% 2 5% 5% 3 4 4 4 7% 38%	1415
	21st to end	Night	18% 5% 2 6% 6% 3 4 5% 5% 6% 40%	1550
June	1st to 10th	Night	20% 7% 3 5% 5% 3 5% 5% 7% 7% 35%	1440
	11th to 20th	Night	19% 6% 3 6% 4 3 5% 5% 6% 7% 36%	1440
	21st to end	Night	18% 6% 4 5% 6% 3 6% 5% 6% 7% 35%	1440
July	1st to 10th	Night	12% 4 3 5% 5% 3 4 5% 7% 8% 44%	1440
	11th to 20th	Night	12% 4 3 6% 6% 4 6% 5% 6% 8% 43%	1440
	21st to end	Night	12% 5% 2 5% 5% 3 4 5% 7% 9% 43%	1574
August	1st to 10th	Night	11% 6% 3 5% 6% 2 5% 5% 5% 9% 43%	1432
	11th to 20th	Night	14% 4 2 5% 6% 3 4 4 6% 8% 43%	1558
	21st to end	Night	16% 5% 2 4 4 3 4 4 5% 6% 46%	1980
September	1st to 10th	Night	11% 5% 2 5% 5% 3 4 5% 5% 7% 48%	1800
	11th to 20th	Night	14% 5% 2 4 4 2 3 4 5% 6% 51%	1880
	21st to end	Night	19% 5% 2 4 3 3 3 3 5% 7% 46%	1980
October	1st to 10th	Night	18% 7% 3 6% 5% 3 5% 3 4 5% 42%	2092
	11th to 20th	Night	22% 8% 2 5% 5% 3 4 5% 5% 6% 36%	2218
	21st to end	Night	23% 9% 3 7% 5% 3 4 5% 5% 5% 31%	2574
November	1st to 10th	Night	17% 8% 4 7% 5% 3 4 5% 5% 6% 35%	2407
	11th to 20th	Night	19% 9% 3 6% 6% 3 4 4 5% 6% 35%	2557
	21st to end	Night	21% 12% 5% 7% 5% 3 4 4 4 5% 30%	2660
December	1st to 10th	Night	20% 13% 5% 10% 6% 4 5% 4 4 6% 24%	2660
	11th to 20th	Night	22% 13% 5% 8% 5% 3 3 3 4 4 29%	3288
	21st to end	Night	24% 18% 5% 8% 5% 2 3 3 3 4 25%	4884

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% 10% 13% 16% 5% 1	2518
	11th to 20th	Day	55% 7% 13% 18% 7%	2520
	21st to end	Day	57% 8% 11% 15% 7% 1	2772
February	1st to 10th	Day	59% 6% 8% 18% 8% 2	1634
	11th to 20th	Day	56% 7% 12% 13% 11% 1	1766
	21st to end	Day	59% 5% 9% 15% 9% 3	1570
March	1st to 10th	Day	55% 6% 10% 16% 12% 2	1800
	11th to 20th	Day	53% 5% 12% 13% 14% 3	1855
	21st to end	Day	50% 6% 10% 18% 14% 3	2376
April	1st to 10th	Day	55% 5% 10% 16% 11% 3	2160
	11th to 20th	Day	49% 5% 9% 21% 13% 3	2134
	21st to end	Day	54% 6% 8% 16% 13% 3	2326
May	1st to 10th	Day	50% 5% 9% 20% 14% 3	2492
	11th to 20th	Day	47% 6% 10% 17% 16% 3	2482
	21st to end	Day	48% 7% 11% 19% 13% 2	2725
June	1st to 10th	Day	52% 8% 11% 18% 10% 2	2520
	11th to 20th	Day	45% 7% 12% 21% 13% 2	2520
	21st to end	Day	54% 9% 10% 16% 10% 1	2520
July	1st to 10th	Day	40% 11% 14% 23% 12% 1	2450
	11th to 20th	Day	42% 10% 15% 23% 10%	2445
	21st to end	Day	44% 11% 15% 21% 8%	2591
August	1st to 10th	Day	45% 12% 16% 21% 6%	2492
	11th to 20th	Day	40% 12% 16% 22% 10%	2322
	21st to end	Day	37% 10% 15% 25% 13%	2376
September	1st to 10th	Day	38% 8% 16% 24% 13% 1	2160
	11th to 20th	Day	37% 7% 14% 29% 12% 1	2080
	21st to end	Day	43% 7% 13% 25% 12%	1980
October	1st to 10th	Day	47% 6% 12% 23% 11% 1	1866
	11th to 20th	Day	56% 7% 13% 18% 5%	1742
	21st to end	Day	57% 4 13% 16% 9% 1	1782
November	1st to 10th	Day	47% 7% 14% 20% 10% 1	1671
	11th to 20th	Day	54% 6% 14% 15% 11% 1	1620
	21st to end	Day	57% 7% 14% 15% 6% 1	1520
December	1st to 10th	Day	63% 6% 10% 15% 6%	1520
	11th to 20th	Day	59% 5% 10% 18% 8%	1906
	21st to end	Day	65% 5% 12% 10% 7%	2772
January	1st to 10th	Night	57% 10% 13% 14% 6%	4429
	11th to 20th	Night	55% 8% 13% 18% 5% 1	4440
	21st to end	Night	58% 8% 12% 13% 8% 1	4884
February	1st to 10th	Night	58% 6% 9% 17% 9% 1	2542
	11th to 20th	Night	55% 6% 9% 18% 12% 1	2310
	21st to end	Night	53% 6% 8% 18% 13% 2	1884
March	1st to 10th	Night	55% 6% 9% 17% 12% 2	2167
	11th to 20th	Night	54% 5% 9% 15% 13% 3	2100
	21st to end	Night	48% 6% 8% 20% 15% 4	1980
April	1st to 10th	Night	54% 5% 9% 16% 15% 2	1800
	11th to 20th	Night	46% 6% 9% 21% 15% 3	1775
	21st to end	Night	50% 6% 7% 19% 15% 3	1632
May	1st to 10th	Night	50% 5% 9% 16% 15% 5%	1482
	11th to 20th	Night	46% 7% 9% 17% 16% 4	1416
	21st to end	Night	45% 6% 12% 20% 16% 2	1551
June	1st to 10th	Night	46% 8% 12% 20% 13% 1	1440
	11th to 20th	Night	45% 8% 10% 20% 13% 4	1440
	21st to end	Night	48% 8% 11% 20% 13%	1440
July	1st to 10th	Night	36% 10% 15% 24% 13% 1	1400
	11th to 20th	Night	39% 10% 12% 28% 10% 1	1392
	21st to end	Night	37% 9% 17% 25% 11%	1486
August	1st to 10th	Night	37% 11% 16% 26% 9%	1422
	11th to 20th	Night	38% 9% 15% 24% 13%	1558
	21st to end	Night	39% 8% 13% 28% 13%	1980
September	1st to 10th	Night	35% 9% 15% 27% 14% 1	1800
	11th to 20th	Night	34% 7% 14% 32% 11% 1	1880
	21st to end	Night	39% 7% 10% 30% 14%	1980
October	1st to 10th	Night	46% 6% 9% 24% 15% 1	2092
	11th to 20th	Night	48% 7% 14% 22% 8%	2218
	21st to end	Night	55% 6% 12% 17% 10%	2574
November	1st to 10th	Night	50% 6% 14% 21% 8% 1	2407
	11th to 20th	Night	51% 6% 12% 18% 11% 1	2557
	21st to end	Night	57% 6% 11% 17% 8% 1	2660
December	1st to 10th	Night	62% 6% 11% 15% 5%	2660
	11th to 20th	Night	59% 5% 9% 17% 9% 1	3288
	21st to end	Night	64% 5% 8% 16% 6% 1	4884

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	21% 17% 32% 26% 4	180
	11th to 20th	Day	25% 13% 36% 21% 4 1	180
	21st to end	Day	16% 19% 39% 18% 7% 1	198
February	1st to 10th	Day	27% 22% 40% 9% 3	234
	11th to 20th	Day	19% 20% 44% 15% 2	364
	21st to end	Day	26% 19% 33% 18% 4	382
March	1st to 10th	Day	24% 17% 36% 19% 3 1	420
	11th to 20th	Day	23% 20% 34% 19% 4 1	420
	21st to end	Day	28% 18% 28% 17% 6% 2	462
April	1st to 10th	Day	27% 18% 29% 18% 7% 1	420
	11th to 20th	Day	28% 20% 27% 16% 8% 1	412
	21st to end	Day	29% 16% 33% 15% 6% 1	420
May	1st to 10th	Day	27% 17% 35% 16% 3 2	423
	11th to 20th	Day	21% 19% 33% 18% 8% 2	447
	21st to end	Day	20% 20% 34% 19% 6% 2	485
June	1st to 10th	Day	23% 14% 34% 20% 7% 1	450
	11th to 20th	Day	18% 18% 31% 21% 10% 2	450
	21st to end	Day	23% 12% 28% 24% 10% 2	450
July	1st to 10th	Day	14% 8% 33% 31% 11% 3	445
	11th to 20th	Day	14% 9% 34% 31% 11% 2	444
	21st to end	Day	12% 7% 29% 35% 12% 4	488
August	1st to 10th	Day	14% 9% 26% 32% 17% 2	446
	11th to 20th	Day	14% 7% 25% 32% 15% 7%	439
	21st to end	Day	16% 13% 27% 24% 15% 5%	495
September	1st to 10th	Day	15% 10% 32% 25% 12% 6%	450
	11th to 20th	Day	14% 11% 29% 26% 12% 7%	450
	21st to end	Day	21% 12% 26% 21% 14% 5%	450
October	1st to 10th	Day	25% 13% 25% 23% 11% 3	450
	11th to 20th	Day	24% 17% 29% 19% 9% 2	421
	21st to end	Day	32% 16% 26% 21% 5%	396
November	1st to 10th	Day	23% 17% 29% 22% 8% 1	365
	11th to 20th	Day	24% 19% 33% 16% 9%	280
	21st to end	Day	26% 22% 32% 17% 4	180
December	1st to 10th	Day	31% 13% 29% 17% 8% 2	180
	11th to 20th	Day	26% 22% 32% 16% 4 1	180
	21st to end	Day	33% 18% 25% 18% 5% 1	198
January	1st to 10th	Night	26% 12% 32% 25% 4	760
	11th to 20th	Night	24% 13% 34% 23% 7%	760
	21st to end	Night	16% 10% 36% 30% 7%	836
February	1st to 10th	Night	19% 11% 40% 25% 5% 1	760
	11th to 20th	Night	19% 15% 38% 23% 4 1	743
	21st to end	Night	21% 15% 35% 26% 4	628
March	1st to 10th	Night	24% 14% 35% 23% 4	723
	11th to 20th	Night	24% 15% 32% 23% 6% 1	720
	21st to end	Night	20% 14% 33% 25% 7% 1	792
April	1st to 10th	Night	28% 13% 29% 25% 5%	720
	11th to 20th	Night	23% 13% 33% 25% 6% 1	711
	21st to end	Night	26% 14% 32% 22% 5% 1	552
May	1st to 10th	Night	26% 12% 29% 24% 7% 1	402
	11th to 20th	Night	23% 9% 32% 28% 7%	354
	21st to end	Night	23% 6% 38% 24% 9%	389
June	1st to 10th	Night	24% 6% 30% 31% 9%	360
	11th to 20th	Night	22% 6% 26% 33% 13% 1	360
	21st to end	Night	20% 5% 25% 36% 13%	360
July	1st to 10th	Night	12% 7% 27% 41% 13%	350
	11th to 20th	Night	12% 3 25% 46% 13% 1	348
	21st to end	Night	14% 5% 22% 43% 14% 2	394
August	1st to 10th	Night	13% 4 17% 47% 17% 2	358
	11th to 20th	Night	15% 2 24% 36% 20% 3	494
	21st to end	Night	16% 5% 26% 31% 19% 2	792
September	1st to 10th	Night	13% 6% 29% 37% 15% 1	720
	11th to 20th	Night	18% 6% 24% 32% 19% 1	720
	21st to end	Night	20% 8% 27% 29% 15% 2	720
October	1st to 10th	Night	22% 9% 29% 28% 12% 1	720
	11th to 20th	Night	28% 9% 27% 26% 10% 1	720
	21st to end	Night	27% 10% 31% 25% 6%	792
November	1st to 10th	Night	25% 10% 29% 27% 8% 1	740
	11th to 20th	Night	24% 12% 31% 21% 10% 1	760
	21st to end	Night	27% 16% 26% 25% 6% 1	760
December	1st to 10th	Night	28% 10% 31% 26% 6%	760
	11th to 20th	Night	26% 14% 30% 23% 6% 1	760
	21st to end	Night	29% 13% 31% 22% 4	836

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