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 2026-08-15.

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	16% 9% 3 8% 5% 5% 5% 4 5% 7% 32%	144226
	Night	16% 10% 4 9% 5% 4 4 4 5% 6% 33%	137693
Transparency	Day	49% 7% 13% 20% 10% 1	147660
	Night	51% 6% 11% 19% 11% 1	142348
Seeing	Day	22% 16% 31% 21% 8% 2	16739
	Night	22% 11% 30% 28% 9% 1	25592

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% 5% 12% 5% 4 4 3 4 5% 28%	4661
	11th to 20th	Day	11% 16% 7% 14% 6% 6% 5% 3 4 5% 23%	4650
	21st to end	Day	7% 11% 6% 14% 7% 6% 5% 4 5% 6% 29%	5124
February	1st to 10th	Day	11% 16% 6% 10% 6% 6% 5% 3 4 5% 29%	1807
	11th to 20th	Day	12% 14% 5% 11% 5% 5% 4 3 5% 6% 29%	1948
	21st to end	Day	15% 17% 4 8% 7% 5% 4 3 3 5% 29%	1730
March	1st to 10th	Day	20% 12% 5% 10% 7% 6% 4 3 4 4 24%	4576
	11th to 20th	Day	11% 15% 4 10% 5% 5% 4 3 5% 7% 32%	4790
	21st to end	Day	17% 12% 3 8% 5% 4 4 4 4 6% 33%	6102
April	1st to 10th	Day	20% 11% 3 8% 6% 4 4 3 4 5% 31%	2520
	11th to 20th	Day	22% 8% 2 7% 4 5% 4 3 5% 6% 35%	2494
	21st to end	Day	21% 9% 4 7% 4 4 4 4 5% 5% 33%	2715
May	1st to 10th	Day	24% 9% 3 9% 5% 5% 5% 4 5% 6% 25%	8167
	11th to 20th	Day	19% 9% 3 8% 4 5% 5% 4 6% 7% 31%	8221
	21st to end	Day	21% 8% 3 7% 5% 4 5% 4 5% 6% 31%	9060
June	1st to 10th	Day	21% 7% 3 7% 5% 5% 5% 4 6% 7% 30%	2940
	11th to 20th	Day	14% 6% 3 7% 5% 5% 6% 4 6% 8% 35%	2940
	21st to end	Day	19% 9% 3 8% 6% 5% 6% 4 6% 8% 28%	2940
July	1st to 10th	Day	13% 6% 2 7% 5% 5% 5% 4 6% 8% 38%	8280
	11th to 20th	Day	11% 4 2 5% 4 5% 6% 5% 8% 10% 40%	8280
	21st to end	Day	11% 5% 2 6% 5% 5% 6% 4 7% 10% 39%	8993
August	1st to 10th	Day	13% 6% 2 7% 6% 6% 7% 5% 7% 9% 32%	4703
	11th to 20th	Day	15% 5% 2 6% 5% 5% 5% 4 8% 9% 35%	4261
	21st to end	Day	16% 6% 2 6% 4 5% 5% 4 6% 8% 38%	4312
September	1st to 10th	Day	13% 5% 2 6% 4 4 5% 3 6% 8% 44%	2400
	11th to 20th	Day	13% 5% 2 5% 4 3 4 3 5% 7% 49%	2310
	21st to end	Day	20% 6% 3 5% 3 3 4 4 5% 6% 42%	2200
October	1st to 10th	Day	20% 7% 2 6% 4 4 5% 3 5% 7% 39%	2072
	11th to 20th	Day	21% 8% 3 7% 6% 5% 4 4 5% 7% 30%	1935
	21st to end	Day	24% 10% 3 7% 4 3 4 3 4 5% 32%	1980
November	1st to 10th	Day	15% 10% 3 7% 5% 5% 5% 4 5% 6% 35%	1851
	11th to 20th	Day	17% 11% 4 9% 5% 4 4 4 5% 6% 31%	1790
	21st to end	Day	21% 14% 4 8% 4 4 5% 3 4 6% 26%	1680
December	1st to 10th	Day	19% 17% 7% 11% 5% 5% 3 3 4 4 22%	2680
	11th to 20th	Day	18% 15% 4 10% 5% 4 3 3 4 4 29%	3066
	21st to end	Day	22% 13% 5% 10% 5% 4 4 3 4 4 27%	4048
January	1st to 10th	Night	13% 17% 6% 13% 6% 4 4 3 4 4 26%	8234
	11th to 20th	Night	10% 17% 7% 16% 7% 5% 5% 3 4 4 22%	8235
	21st to end	Night	7% 12% 5% 13% 8% 7% 6% 4 6% 5% 27%	9057
February	1st to 10th	Night	11% 14% 5% 11% 6% 5% 5% 4 5% 5% 29%	2809
	11th to 20th	Night	12% 13% 4 11% 7% 5% 5% 4 4 4 32%	2557
	21st to end	Night	14% 13% 3 9% 5% 5% 5% 4 5% 6% 32%	2076
March	1st to 10th	Night	22% 13% 4 10% 5% 4 4 3 4 5% 27%	5484
	11th to 20th	Night	13% 14% 4 8% 5% 5% 5% 4 5% 6% 31%	5384
	21st to end	Night	15% 11% 4 10% 5% 5% 5% 3 5% 5% 32%	5072
April	1st to 10th	Night	22% 11% 4 6% 5% 4 4 3 4 7% 31%	2100
	11th to 20th	Night	20% 7% 3 6% 4 4 5% 3 4 5% 37%	2075
	21st to end	Night	20% 10% 2 5% 4 3 4 4 5% 6% 37%	1903
May	1st to 10th	Night	23% 9% 3 8% 5% 5% 5% 4 6% 7% 27%	4786
	11th to 20th	Night	20% 7% 3 7% 4 5% 5% 4 5% 7% 34%	4639
	21st to end	Night	22% 8% 3 7% 5% 4 4 3 6% 7% 31%	5114
June	1st to 10th	Night	19% 7% 2 5% 4 5% 4 4 7% 7% 36%	1680
	11th to 20th	Night	18% 6% 3 7% 4 5% 4 4 6% 6% 36%	1680
	21st to end	Night	18% 6% 4 6% 5% 5% 5% 4 5% 7% 35%	1680
July	1st to 10th	Night	13% 5% 2 6% 4 5% 6% 5% 7% 9% 38%	4680
	11th to 20th	Night	11% 4 2 6% 4 4 4 4 6% 8% 46%	4680
	21st to end	Night	12% 4 2 5% 5% 5% 5% 5% 6% 7% 43%	5084
August	1st to 10th	Night	12% 6% 3 7% 5% 5% 5% 4 5% 8% 40%	2666
	11th to 20th	Night	16% 5% 2 6% 4 4 4 3 5% 7% 42%	2840
	21st to end	Night	19% 6% 2 5% 4 4 4 3 6% 6% 41%	3586
September	1st to 10th	Night	11% 5% 2 5% 4 4 4 4 5% 7% 50%	2000
	11th to 20th	Night	13% 4 2 5% 3 3 4 3 5% 6% 52%	2090
	21st to end	Night	18% 5% 2 5% 3 3 3 3 5% 6% 46%	2200
October	1st to 10th	Night	17% 7% 2 6% 5% 4 4 3 5% 5% 43%	2325
	11th to 20th	Night	20% 8% 2 6% 4 4 4 4 5% 6% 38%	2465
	21st to end	Night	22% 8% 3 8% 5% 4 4 3 5% 6% 32%	2860
November	1st to 10th	Night	17% 9% 4 8% 4 4 4 4 5% 6% 34%	2667
	11th to 20th	Night	18% 10% 3 7% 5% 4 4 3 5% 6% 35%	2827
	21st to end	Night	20% 14% 4 9% 5% 4 4 3 4 5% 29%	2940
December	1st to 10th	Night	16% 14% 5% 10% 6% 5% 5% 4 5% 6% 23%	4720
	11th to 20th	Night	23% 12% 4 9% 5% 4 4 2 4 4 29%	5348
	21st to end	Night	22% 17% 4 10% 4 3 3 2 3 4 29%	7150

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	56% 7% 12% 19% 6%	4662
	11th to 20th	Day	61% 6% 10% 13% 8% 2	4680
	21st to end	Day	54% 6% 9% 16% 13% 1	5124
February	1st to 10th	Day	58% 6% 8% 18% 8% 2	1807
	11th to 20th	Day	55% 6% 11% 14% 11% 1	1957
	21st to end	Day	58% 5% 8% 16% 11% 2	1730
March	1st to 10th	Day	60% 7% 8% 11% 11% 3	4579
	11th to 20th	Day	51% 7% 17% 11% 11% 3	4790
	21st to end	Day	52% 4 8% 15% 17% 3	6102
April	1st to 10th	Day	54% 5% 10% 17% 12% 2	2520
	11th to 20th	Day	51% 5% 9% 21% 13% 2	2494
	21st to end	Day	53% 6% 9% 17% 13% 3	2715
May	1st to 10th	Day	57% 7% 9% 18% 9% 1	8179
	11th to 20th	Day	48% 9% 15% 19% 8% 2	8225
	21st to end	Day	50% 7% 11% 19% 11% 1	9061
June	1st to 10th	Day	52% 7% 10% 19% 11% 2	2940
	11th to 20th	Day	44% 8% 13% 22% 12% 2	2940
	21st to end	Day	52% 9% 11% 17% 9% 1	2940
July	1st to 10th	Day	41% 8% 14% 25% 12%	8210
	11th to 20th	Day	35% 9% 17% 28% 12%	8205
	21st to end	Day	38% 9% 17% 27% 8%	8795
August	1st to 10th	Day	44% 10% 17% 21% 8%	4689
	11th to 20th	Day	42% 10% 18% 23% 6%	4303
	21st to end	Day	41% 9% 15% 21% 13% 1	4312
September	1st to 10th	Day	37% 8% 17% 26% 12% 1	2400
	11th to 20th	Day	35% 7% 14% 31% 13% 1	2310
	21st to end	Day	43% 7% 13% 25% 12%	2200
October	1st to 10th	Day	43% 7% 15% 25% 9%	3371
	11th to 20th	Day	45% 6% 17% 25% 7% 1	3125
	21st to end	Day	43% 5% 22% 21% 9% 1	3180
November	1st to 10th	Day	48% 7% 14% 20% 10% 1	1851
	11th to 20th	Day	53% 6% 14% 16% 11% 1	1790
	21st to end	Day	58% 6% 13% 15% 6% 1	1680
December	1st to 10th	Day	65% 5% 10% 15% 5%	2680
	11th to 20th	Day	57% 5% 9% 17% 12%	3066
	21st to end	Day	61% 5% 11% 13% 10%	4048
January	1st to 10th	Night	61% 7% 9% 16% 7% 1	8234
	11th to 20th	Night	64% 6% 9% 14% 6% 1	8280
	21st to end	Night	56% 7% 9% 13% 14%	9057
February	1st to 10th	Night	56% 6% 10% 17% 10% 1	2809
	11th to 20th	Night	55% 5% 9% 18% 12% 1	2559
	21st to end	Night	52% 6% 8% 19% 12% 2	2076
March	1st to 10th	Night	60% 5% 8% 13% 11% 4	5494
	11th to 20th	Night	52% 6% 13% 13% 13% 3	5385
	21st to end	Night	52% 4 8% 21% 12% 2	5072
April	1st to 10th	Night	54% 5% 9% 16% 15% 2	2100
	11th to 20th	Night	48% 6% 9% 20% 14% 2	2075
	21st to end	Night	48% 6% 8% 19% 16% 3	1903
May	1st to 10th	Night	54% 7% 12% 17% 8% 1	4792
	11th to 20th	Night	48% 8% 12% 20% 10% 1	4640
	21st to end	Night	50% 6% 12% 17% 15% 1	5115
June	1st to 10th	Night	45% 7% 11% 20% 15% 1	1680
	11th to 20th	Night	45% 8% 11% 19% 13% 3	1680
	21st to end	Night	47% 7% 12% 20% 13% 1	1680
July	1st to 10th	Night	39% 9% 18% 22% 12% 1	4640
	11th to 20th	Night	34% 7% 17% 32% 10%	4632
	21st to end	Night	37% 8% 17% 29% 9%	4967
August	1st to 10th	Night	43% 8% 14% 26% 9%	2656
	11th to 20th	Night	42% 7% 17% 25% 9%	2864
	21st to end	Night	44% 8% 12% 23% 13% 1	3586
September	1st to 10th	Night	34% 8% 15% 28% 14% 1	2000
	11th to 20th	Night	33% 7% 15% 33% 11% 1	2090
	21st to end	Night	40% 7% 10% 30% 14%	2200
October	1st to 10th	Night	44% 7% 13% 24% 12% 1	3806
	11th to 20th	Night	40% 6% 13% 31% 10%	4014
	21st to end	Night	45% 5% 17% 19% 12% 2	4610
November	1st to 10th	Night	50% 6% 14% 22% 8% 1	2667
	11th to 20th	Night	51% 6% 12% 18% 12% 1	2827
	21st to end	Night	58% 6% 11% 16% 8%	2940
December	1st to 10th	Night	61% 7% 13% 14% 5%	4720
	11th to 20th	Night	59% 5% 8% 15% 11% 1	5348
	21st to end	Night	61% 4 7% 15% 12% 1	7150

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% 20% 31% 25% 3	220
	11th to 20th	Day	25% 14% 37% 19% 4 1	220
	21st to end	Day	15% 21% 37% 19% 7%	242
February	1st to 10th	Day	24% 22% 40% 11% 3	287
	11th to 20th	Day	20% 21% 42% 15% 3	435
	21st to end	Day	25% 18% 36% 18% 4	446
March	1st to 10th	Day	25% 19% 34% 18% 3 1	540
	11th to 20th	Day	24% 19% 34% 19% 3 1	540
	21st to end	Day	28% 21% 29% 15% 5% 2	594
April	1st to 10th	Day	30% 20% 27% 16% 6% 1	540
	11th to 20th	Day	32% 19% 25% 15% 8% 1	532
	21st to end	Day	29% 18% 32% 14% 6% 1	540
May	1st to 10th	Day	29% 18% 32% 15% 3 1	543
	11th to 20th	Day	21% 19% 33% 19% 7% 2	567
	21st to end	Day	23% 21% 32% 17% 6% 2	617
June	1st to 10th	Day	23% 14% 34% 21% 8% 1	570
	11th to 20th	Day	18% 18% 33% 20% 9% 2	570
	21st to end	Day	23% 13% 30% 24% 9% 1	570
July	1st to 10th	Day	15% 10% 34% 28% 9% 3	565
	11th to 20th	Day	14% 11% 36% 29% 9% 1	564
	21st to end	Day	12% 9% 31% 32% 11% 4	620
August	1st to 10th	Day	14% 9% 28% 32% 15% 2	566
	11th to 20th	Day	14% 8% 27% 30% 15% 7%	535
	21st to end	Day	17% 14% 26% 24% 14% 5%	583
September	1st to 10th	Day	15% 12% 31% 24% 12% 5%	530
	11th to 20th	Day	12% 10% 27% 28% 16% 8%	530
	21st to end	Day	21% 12% 27% 22% 13% 5%	530
October	1st to 10th	Day	23% 13% 26% 24% 11% 3	530
	11th to 20th	Day	23% 16% 31% 19% 9% 1	494
	21st to end	Day	30% 16% 27% 22% 5%	462
November	1st to 10th	Day	26% 17% 29% 21% 7%	425
	11th to 20th	Day	23% 18% 33% 17% 8% 1	330
	21st to end	Day	30% 21% 29% 16% 4	220
December	1st to 10th	Day	29% 13% 33% 16% 8% 2	220
	11th to 20th	Day	26% 22% 33% 16% 3	220
	21st to end	Day	30% 16% 29% 18% 5% 2	242
January	1st to 10th	Night	25% 12% 34% 26% 4	840
	11th to 20th	Night	24% 14% 32% 23% 7%	840
	21st to end	Night	15% 11% 36% 30% 7%	924
February	1st to 10th	Night	18% 11% 40% 25% 6% 1	840
	11th to 20th	Night	19% 15% 38% 23% 4 1	823
	21st to end	Night	20% 14% 35% 27% 4	692
March	1st to 10th	Night	25% 14% 34% 23% 4	840
	11th to 20th	Night	24% 15% 33% 22% 5% 1	840
	21st to end	Night	21% 14% 34% 25% 6% 1	924
April	1st to 10th	Night	29% 13% 30% 24% 4	840
	11th to 20th	Night	24% 13% 34% 23% 5%	831
	21st to end	Night	26% 14% 33% 22% 5% 1	643
May	1st to 10th	Night	28% 12% 29% 24% 6% 1	468
	11th to 20th	Night	22% 10% 31% 30% 7%	414
	21st to end	Night	24% 7% 37% 24% 8%	455
June	1st to 10th	Night	23% 6% 29% 34% 8%	420
	11th to 20th	Night	21% 7% 26% 34% 12%	420
	21st to end	Night	20% 5% 25% 37% 12%	420
July	1st to 10th	Night	12% 6% 27% 43% 12%	410
	11th to 20th	Night	13% 3 26% 45% 13% 1	408
	21st to end	Night	15% 5% 22% 42% 14% 2	460
August	1st to 10th	Night	12% 3 18% 48% 17% 1	418
	11th to 20th	Night	14% 3 23% 36% 21% 2	558
	21st to end	Night	18% 5% 25% 32% 18% 2	880
September	1st to 10th	Night	13% 6% 28% 37% 15% 1	800
	11th to 20th	Night	16% 6% 23% 33% 21% 2	800
	21st to end	Night	20% 7% 26% 31% 15% 2	800
October	1st to 10th	Night	21% 8% 29% 28% 12% 1	800
	11th to 20th	Night	26% 10% 27% 27% 10% 1	800
	21st to end	Night	27% 10% 31% 26% 6%	880
November	1st to 10th	Night	25% 10% 29% 27% 8% 1	820
	11th to 20th	Night	24% 13% 31% 22% 9% 1	840
	21st to end	Night	27% 16% 26% 24% 6% 1	840
December	1st to 10th	Night	26% 10% 31% 26% 6%	840
	11th to 20th	Night	26% 14% 31% 23% 5% 1	840
	21st to end	Night	29% 14% 30% 22% 4	924

Page generated at 2026-08-12 03:37:13. Version ac07

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