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 2024-10-25.

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% 3 8% 5% 5% 5% 4 5% 7% 33%	101489
	Night	17% 10% 3 8% 5% 4 4 3 5% 6% 34%	97334
Transparency	Day	49% 8% 13% 19% 10% 1	101250
	Night	51% 7% 12% 19% 10% 1	97193
Seeing	Day	22% 15% 31% 22% 8% 2	14501
	Night	22% 10% 30% 28% 9% 1	23403

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 11% 5% 4 5% 4 4 4 28%	2517
	11th to 20th	Day	14% 14% 6% 11% 5% 5% 5% 3 4 4 29%	2520
	21st to end	Day	11% 13% 6% 12% 6% 6% 5% 4 5% 6% 25%	2772
February	1st to 10th	Day	12% 18% 6% 10% 6% 5% 4 3 4 5% 27%	1634
	11th to 20th	Day	12% 15% 5% 11% 5% 5% 4 4 5% 6% 29%	1757
	21st to end	Day	16% 17% 4 9% 7% 4 4 3 3 5% 28%	1570
March	1st to 10th	Day	20% 11% 5% 9% 6% 6% 5% 4 5% 4 26%	3116
	11th to 20th	Day	11% 18% 4 11% 6% 5% 4 3 5% 6% 27%	3271
	21st to end	Day	14% 10% 3 7% 4 4 4 4 5% 7% 38%	4166
April	1st to 10th	Day	20% 11% 3 8% 6% 4 4 3 4 5% 31%	2280
	11th to 20th	Day	22% 8% 2 6% 4 4 4 4 5% 6% 36%	2254
	21st to end	Day	21% 10% 4 7% 4 4 4 4 4 4 33%	2456
May	1st to 10th	Day	21% 8% 3 7% 5% 4 4 4 5% 5% 34%	4384
	11th to 20th	Day	17% 8% 3 7% 5% 5% 5% 4 6% 8% 33%	4398
	21st to end	Day	16% 6% 3 7% 5% 5% 5% 5% 6% 7% 35%	4837
June	1st to 10th	Day	21% 7% 3 7% 5% 5% 5% 4 6% 7% 29%	2660
	11th to 20th	Day	15% 6% 3 7% 5% 5% 6% 4 6% 8% 35%	2660
	21st to end	Day	20% 9% 3 8% 6% 5% 6% 4 5% 7% 27%	2660
July	1st to 10th	Day	12% 6% 2 7% 6% 5% 6% 5% 7% 8% 35%	4440
	11th to 20th	Day	14% 5% 2 6% 5% 5% 6% 5% 8% 9% 35%	4440
	21st to end	Day	11% 5% 2 6% 5% 4 5% 4 7% 8% 43%	4814
August	1st to 10th	Day	13% 6% 2 7% 6% 6% 7% 5% 7% 10% 31%	4423
	11th to 20th	Day	16% 6% 2 6% 5% 5% 5% 4 8% 9% 34%	4074
	21st to end	Day	16% 6% 2 6% 4 5% 5% 4 6% 8% 38%	4180
September	1st to 10th	Day	14% 5% 2 6% 4 4 5% 3 6% 8% 43%	2280
	11th to 20th	Day	14% 5% 2 5% 4 3 4 3 5% 7% 48%	2195
	21st to end	Day	20% 6% 3 5% 3 4 3 4 5% 6% 41%	2090
October	1st to 10th	Day	21% 7% 2 6% 4 4 5% 3 5% 6% 37%	1969
	11th to 20th	Day	21% 8% 4 8% 6% 5% 4 4 5% 7% 29%	1838
	21st to end	Day	24% 11% 3 7% 4 3 4 3 5% 6% 31%	1825
November	1st to 10th	Day	15% 10% 3 7% 5% 5% 5% 4 5% 6% 36%	1671
	11th to 20th	Day	18% 11% 4 9% 5% 4 4 4 5% 6% 30%	1620
	21st to end	Day	20% 13% 3 8% 4 5% 5% 3 5% 6% 27%	1520
December	1st to 10th	Day	23% 16% 4 8% 6% 4 3 4 4 4 24%	1520
	11th to 20th	Day	21% 15% 4 8% 4 3 4 3 4 4 29%	1906
	21st to end	Day	25% 16% 5% 9% 4 3 3 2 3 4 24%	2772
January	1st to 10th	Night	16% 15% 5% 9% 5% 4 4 4 5% 5% 28%	4429
	11th to 20th	Night	11% 12% 5% 12% 7% 5% 5% 4 5% 5% 29%	4440
	21st to end	Night	11% 14% 5% 12% 7% 6% 5% 4 5% 5% 26%	4884
February	1st to 10th	Night	12% 15% 5% 10% 6% 5% 5% 4 5% 5% 28%	2542
	11th to 20th	Night	12% 12% 4 11% 6% 5% 5% 4 4 4 32%	2308
	21st to end	Night	15% 13% 3 9% 5% 4 4 3 5% 6% 32%	1884
March	1st to 10th	Night	21% 13% 4 7% 5% 4 4 3 4 5% 31%	3724
	11th to 20th	Night	15% 18% 5% 9% 5% 4 4 3 4 4 29%	3683
	21st to end	Night	14% 9% 3 10% 5% 4 4 3 4 5% 37%	3466
April	1st to 10th	Night	22% 11% 3 6% 5% 4 4 3 5% 7% 31%	1900
	11th to 20th	Night	20% 7% 3 6% 4 4 5% 3 4 5% 38%	1875
	21st to end	Night	20% 10% 3 5% 4 3 3 4 5% 6% 36%	1722
May	1st to 10th	Night	20% 9% 4 8% 5% 4 4 4 6% 6% 31%	2584
	11th to 20th	Night	20% 7% 2 6% 4 4 5% 4 4 7% 38%	2495
	21st to end	Night	18% 6% 3 7% 5% 5% 5% 4 6% 8% 33%	2738
June	1st to 10th	Night	19% 7% 2 5% 5% 5% 4 4 7% 7% 35%	1520
	11th to 20th	Night	18% 7% 3 6% 4 5% 4 4 6% 7% 37%	1520
	21st to end	Night	18% 7% 4 7% 5% 4 5% 4 5% 7% 35%	1520
July	1st to 10th	Night	13% 6% 3 7% 5% 5% 6% 5% 7% 8% 35%	2520
	11th to 20th	Night	14% 5% 2 6% 4 4 5% 4 6% 7% 43%	2520
	21st to end	Night	11% 4 2 4 4 4 5% 5% 6% 8% 48%	2739
August	1st to 10th	Night	12% 6% 2 8% 5% 5% 5% 4 5% 8% 39%	2506
	11th to 20th	Night	17% 5% 2 6% 5% 4 4 3 5% 7% 41%	2720
	21st to end	Night	19% 6% 2 6% 4 4 4 3 5% 6% 41%	3476
September	1st to 10th	Night	11% 5% 2 5% 4 4 4 4 5% 7% 49%	1900
	11th to 20th	Night	14% 5% 2 5% 3 3 4 3 5% 6% 52%	1985
	21st to end	Night	19% 5% 2 5% 3 3 3 3 5% 7% 45%	2090
October	1st to 10th	Night	17% 7% 2 7% 5% 4 4 3 5% 4 42%	2209
	11th to 20th	Night	21% 8% 2 6% 4 4 4 4 5% 6% 37%	2342
	21st to end	Night	23% 9% 3 8% 5% 4 4 3 5% 6% 32%	2637
November	1st to 10th	Night	17% 9% 4 8% 4 4 4 4 5% 6% 35%	2407
	11th to 20th	Night	18% 10% 3 7% 5% 4 4 3 5% 6% 35%	2557
	21st to end	Night	20% 13% 4 8% 4 4 4 3 4 5% 30%	2660
December	1st to 10th	Night	20% 14% 4 10% 5% 5% 4 3 4 6% 24%	2660
	11th to 20th	Night	22% 14% 4 8% 5% 4 3 2 4 4 29%	3288
	21st to end	Night	24% 19% 4 9% 4 3 2 2 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	57% 7% 9% 15% 9% 1	3119
	11th to 20th	Day	56% 6% 13% 10% 11% 4	3271
	21st to end	Day	45% 5% 11% 19% 17% 3	4166
April	1st to 10th	Day	55% 6% 10% 16% 11% 2	2280
	11th to 20th	Day	49% 5% 9% 21% 13% 2	2254
	21st to end	Day	54% 6% 9% 16% 13% 3	2456
May	1st to 10th	Day	50% 6% 11% 20% 11% 2	4398
	11th to 20th	Day	44% 12% 17% 17% 9% 2	4402
	21st to end	Day	44% 8% 12% 20% 14% 2	4837
June	1st to 10th	Day	52% 7% 11% 17% 10% 2	2660
	11th to 20th	Day	44% 7% 13% 21% 13% 2	2660
	21st to end	Day	54% 9% 10% 16% 10% 1	2660
July	1st to 10th	Day	43% 10% 14% 23% 10%	4370
	11th to 20th	Day	41% 10% 18% 24% 7%	4365
	21st to end	Day	37% 9% 15% 29% 10%	4661
August	1st to 10th	Day	45% 10% 16% 21% 8%	4409
	11th to 20th	Day	43% 10% 18% 22% 6%	4116
	21st to end	Day	41% 9% 15% 20% 14% 1	4180
September	1st to 10th	Day	38% 8% 16% 25% 13% 1	2280
	11th to 20th	Day	36% 7% 14% 30% 12% 1	2195
	21st to end	Day	43% 7% 13% 25% 11%	2090
October	1st to 10th	Day	47% 6% 12% 23% 11% 1	1969
	11th to 20th	Day	54% 7% 13% 19% 5%	1838
	21st to end	Day	56% 5% 14% 17% 8% 1	1825
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	52% 6% 8% 18% 13% 2	1884
March	1st to 10th	Night	55% 6% 10% 16% 9% 4	3734
	11th to 20th	Night	58% 6% 9% 13% 13% 2	3684
	21st to end	Night	48% 5% 10% 21% 14% 3	3466
April	1st to 10th	Night	53% 5% 9% 16% 15% 2	1900
	11th to 20th	Night	47% 6% 9% 20% 15% 3	1875
	21st to end	Night	50% 6% 7% 19% 16% 2	1722
May	1st to 10th	Night	52% 8% 12% 17% 9% 3	2590
	11th to 20th	Night	44% 10% 13% 18% 11% 2	2496
	21st to end	Night	46% 6% 14% 17% 16% 1	2739
June	1st to 10th	Night	46% 8% 12% 20% 13% 1	1520
	11th to 20th	Night	45% 8% 11% 20% 13% 3	1520
	21st to end	Night	49% 8% 11% 19% 13% 1	1520
July	1st to 10th	Night	44% 9% 17% 19% 11% 1	2480
	11th to 20th	Night	39% 9% 18% 28% 7%	2472
	21st to end	Night	33% 8% 20% 27% 12%	2651
August	1st to 10th	Night	44% 8% 13% 26% 8%	2496
	11th to 20th	Night	43% 8% 17% 24% 8%	2744
	21st to end	Night	44% 8% 12% 22% 13% 1	3476
September	1st to 10th	Night	35% 9% 15% 27% 14% 1	1900
	11th to 20th	Night	33% 7% 15% 32% 11% 1	1985
	21st to end	Night	40% 7% 10% 30% 13%	2090
October	1st to 10th	Night	46% 6% 10% 24% 14% 1	2209
	11th to 20th	Night	47% 7% 14% 24% 8%	2342
	21st to end	Night	54% 6% 13% 17% 10%	2637
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% 34% 18% 4	382
March	1st to 10th	Day	24% 18% 34% 20% 3 1	460
	11th to 20th	Day	22% 20% 34% 20% 3 1	460
	21st to end	Day	27% 20% 29% 16% 6% 2	506
April	1st to 10th	Day	28% 19% 29% 17% 6% 1	460
	11th to 20th	Day	29% 20% 27% 15% 8% 1	452
	21st to end	Day	29% 17% 33% 14% 6% 1	460
May	1st to 10th	Day	27% 18% 35% 15% 4 2	463
	11th to 20th	Day	19% 18% 33% 20% 8% 2	487
	21st to end	Day	21% 19% 33% 19% 6% 2	529
June	1st to 10th	Day	23% 13% 34% 21% 8% 1	490
	11th to 20th	Day	17% 18% 32% 21% 10% 2	490
	21st to end	Day	25% 13% 29% 23% 9% 1	490
July	1st to 10th	Day	14% 9% 33% 30% 10% 3	485
	11th to 20th	Day	14% 10% 34% 30% 10% 2	484
	21st to end	Day	12% 8% 29% 35% 12% 4	532
August	1st to 10th	Day	14% 10% 27% 30% 17% 1	486
	11th to 20th	Day	15% 8% 24% 32% 15% 7%	479
	21st to end	Day	16% 13% 27% 24% 14% 5%	539
September	1st to 10th	Day	16% 11% 32% 24% 12% 6%	490
	11th to 20th	Day	13% 10% 27% 27% 15% 8%	490
	21st to end	Day	21% 12% 27% 21% 13% 5%	490
October	1st to 10th	Day	24% 13% 26% 23% 11% 3	490
	11th to 20th	Day	25% 16% 30% 19% 9% 2	457
	21st to end	Day	31% 15% 27% 21% 6%	411
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% 14% 35% 26% 4	628
March	1st to 10th	Night	25% 13% 34% 24% 4	760
	11th to 20th	Night	24% 15% 33% 22% 5% 1	760
	21st to end	Night	20% 14% 34% 24% 6% 1	836
April	1st to 10th	Night	28% 13% 29% 25% 5%	760
	11th to 20th	Night	23% 14% 33% 23% 6% 1	751
	21st to end	Night	26% 14% 32% 22% 5% 1	582
May	1st to 10th	Night	27% 12% 30% 24% 6% 1	424
	11th to 20th	Night	22% 10% 31% 29% 7%	374
	21st to end	Night	23% 6% 38% 25% 9%	411
June	1st to 10th	Night	23% 7% 29% 32% 9%	380
	11th to 20th	Night	21% 6% 26% 34% 12% 1	380
	21st to end	Night	21% 5% 25% 36% 13%	380
July	1st to 10th	Night	12% 7% 27% 42% 12%	370
	11th to 20th	Night	13% 2 26% 46% 13% 1	368
	21st to end	Night	14% 5% 22% 44% 14% 2	416
August	1st to 10th	Night	13% 4 18% 48% 16% 2	378
	11th to 20th	Night	15% 2 24% 36% 21% 2	522
	21st to end	Night	17% 5% 26% 31% 18% 2	836
September	1st to 10th	Night	13% 6% 29% 37% 14% 1	760
	11th to 20th	Night	17% 6% 23% 32% 20% 2	760
	21st to end	Night	20% 8% 26% 29% 16% 2	760
October	1st to 10th	Night	22% 9% 29% 28% 12% 1	760
	11th to 20th	Night	27% 10% 27% 26% 10% 1	760
	21st to end	Night	27% 10% 31% 26% 6%	812
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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