Observatoire de la Découverte de Val-Bélair
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire de la Découverte de Val-Bélair clear sky chart from 2005-11-06 to 2026-08-30.

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% 10% 3 8% 5% 4 5% 4 5% 7% 31%	143711
	Night	18% 12% 4 9% 5% 5% 4 3 5% 6% 29%	138512
Transparency	Day	52% 5% 13% 20% 9% 1	147155
	Night	55% 4 11% 19% 9% 1	143158
Seeing	Day	26% 13% 30% 21% 9% 2	17514
	Night	25% 10% 28% 28% 9% 1	25953

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	15% 17% 6% 12% 5% 4 3 3 5% 5% 26%	4661
	11th to 20th	Day	10% 18% 8% 17% 7% 5% 4 3 4 4 20%	4650
	21st to end	Day	6% 12% 5% 11% 6% 4 5% 5% 7% 8% 32%	5124
February	1st to 10th	Day	10% 15% 5% 11% 8% 6% 4 5% 4 5% 27%	1680
	11th to 20th	Day	13% 16% 6% 12% 5% 4 4 3 5% 5% 27%	2032
	21st to end	Day	12% 14% 5% 11% 7% 5% 5% 3 4 6% 27%	1730
March	1st to 10th	Day	22% 14% 5% 10% 6% 4 4 2 4 4 26%	4576
	11th to 20th	Day	15% 15% 5% 8% 5% 5% 5% 4 5% 6% 29%	4844
	21st to end	Day	18% 14% 4 8% 4 4 4 3 4 4 33%	5959
April	1st to 10th	Day	22% 13% 3 8% 6% 4 4 3 4 5% 29%	2520
	11th to 20th	Day	22% 7% 3 7% 5% 4 3 3 5% 6% 35%	2587
	21st to end	Day	24% 8% 3 7% 6% 4 4 3 4 6% 31%	2730
May	1st to 10th	Day	26% 10% 3 7% 4 4 4 3 5% 6% 28%	7853
	11th to 20th	Day	20% 7% 2 8% 5% 5% 5% 4 6% 7% 32%	8221
	21st to end	Day	20% 8% 3 8% 5% 5% 5% 4 6% 6% 29%	9096
June	1st to 10th	Day	19% 7% 3 7% 6% 5% 6% 5% 7% 8% 27%	3150
	11th to 20th	Day	19% 7% 3 7% 4 5% 5% 4 6% 7% 33%	3150
	21st to end	Day	23% 9% 3 8% 5% 5% 5% 4 6% 7% 26%	3150
July	1st to 10th	Day	15% 7% 3 7% 5% 5% 6% 4 6% 9% 33%	8325
	11th to 20th	Day	15% 6% 3 7% 4 4 5% 4 7% 9% 35%	8280
	21st to end	Day	12% 5% 3 7% 5% 5% 6% 4 7% 9% 37%	8993
August	1st to 10th	Day	15% 5% 2 7% 5% 5% 6% 5% 8% 10% 32%	4687
	11th to 20th	Day	20% 6% 2 7% 5% 5% 5% 5% 7% 9% 29%	4305
	21st to end	Day	21% 6% 2 6% 4 4 4 4 5% 7% 37%	4567
September	1st to 10th	Day	17% 7% 3 6% 4 3 4 4 7% 8% 37%	2400
	11th to 20th	Day	18% 5% 2 5% 3 4 3 3 5% 7% 47%	2230
	21st to end	Day	21% 7% 3 6% 4 3 4 3 5% 7% 38%	2200
October	1st to 10th	Day	21% 7% 3 6% 4 5% 5% 4 5% 6% 35%	2185
	11th to 20th	Day	24% 8% 3 8% 6% 5% 5% 4 6% 6% 25%	1836
	21st to end	Day	28% 11% 2 7% 5% 4 4 3 5% 5% 25%	1980
November	1st to 10th	Day	20% 12% 3 7% 6% 5% 5% 2 5% 5% 30%	1851
	11th to 20th	Day	21% 14% 4 10% 5% 4 4 3 4 4 26%	1881
	21st to end	Day	22% 17% 5% 9% 5% 4 4 4 4 4 21%	1524
December	1st to 10th	Day	18% 16% 5% 9% 6% 5% 5% 3 5% 6% 22%	2350
	11th to 20th	Day	20% 14% 5% 11% 5% 4 3 3 3 4 28%	2688
	21st to end	Day	20% 17% 4 8% 4 4 4 4 5% 5% 26%	3716
January	1st to 10th	Night	14% 18% 6% 14% 6% 5% 4 3 4 4 22%	8234
	11th to 20th	Night	11% 22% 9% 16% 6% 5% 4 3 4 4 17%	8235
	21st to end	Night	6% 11% 5% 13% 8% 6% 5% 4 7% 7% 27%	9057
February	1st to 10th	Night	11% 13% 5% 11% 7% 5% 4 4 4 5% 29%	2940
	11th to 20th	Night	13% 17% 5% 11% 6% 5% 4 3 5% 5% 27%	2469
	21st to end	Night	14% 15% 5% 10% 5% 4 3 4 4 6% 30%	2076
March	1st to 10th	Night	22% 13% 4 10% 5% 4 6% 3 4 5% 25%	5484
	11th to 20th	Night	16% 14% 3 10% 6% 6% 6% 4 5% 6% 24%	5335
	21st to end	Night	18% 15% 4 8% 5% 4 4 3 4 5% 30%	5213
April	1st to 10th	Night	22% 14% 4 7% 5% 4 3 3 5% 4 29%	2100
	11th to 20th	Night	20% 9% 3 7% 5% 4 4 4 5% 6% 32%	1981
	21st to end	Night	23% 9% 3 8% 3 3 3 2 4 6% 35%	1890
May	1st to 10th	Night	25% 8% 3 7% 4 5% 4 3 5% 5% 30%	5087
	11th to 20th	Night	24% 7% 3 7% 5% 5% 4 4 5% 6% 32%	4639
	21st to end	Night	20% 7% 3 7% 5% 4 5% 3 5% 7% 34%	5065
June	1st to 10th	Night	21% 7% 3 7% 6% 4 4 4 7% 7% 30%	1470
	11th to 20th	Night	21% 5% 3 6% 4 4 4 4 7% 7% 35%	1470
	21st to end	Night	22% 7% 3 8% 5% 4 4 4 5% 8% 30%	1470
July	1st to 10th	Night	15% 7% 3 7% 5% 5% 5% 4 6% 7% 35%	4619
	11th to 20th	Night	17% 6% 2 6% 4 4 5% 4 6% 8% 38%	4680
	21st to end	Night	13% 6% 2 8% 5% 5% 5% 4 6% 8% 40%	5084
August	1st to 10th	Night	18% 7% 3 7% 5% 5% 4 3 6% 7% 35%	2666
	11th to 20th	Night	18% 7% 3 7% 5% 5% 6% 4 6% 6% 33%	2944
	21st to end	Night	21% 8% 2 7% 5% 4 4 4 4 6% 34%	3527
September	1st to 10th	Night	18% 6% 2 6% 4 4 3 3 5% 7% 42%	2000
	11th to 20th	Night	18% 5% 2 6% 4 4 3 3 5% 6% 45%	2170
	21st to end	Night	20% 7% 2 6% 3 4 3 3 4 6% 41%	2200
October	1st to 10th	Night	19% 7% 2 6% 4 4 4 3 6% 5% 39%	2210
	11th to 20th	Night	23% 9% 2 7% 5% 4 4 4 5% 5% 31%	2563
	21st to end	Night	26% 10% 3 6% 4 5% 4 3 5% 5% 30%	2860
November	1st to 10th	Night	21% 11% 3 8% 4 5% 4 3 4 6% 30%	2667
	11th to 20th	Night	20% 11% 4 8% 5% 4 4 3 4 6% 31%	2735
	21st to end	Night	22% 16% 5% 9% 6% 4 4 2 4 4 23%	3092
December	1st to 10th	Night	17% 15% 6% 11% 8% 6% 5% 3 4 4 21%	5060
	11th to 20th	Night	22% 14% 4 9% 5% 4 4 3 4 5% 24%	5741
	21st to end	Night	20% 18% 5% 10% 4 4 3 3 3 3 27%	7479

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	60% 2 9% 17% 10%	4662
	11th to 20th	Day	67% 4 8% 14% 6% 1	4680
	21st to end	Day	47% 4 10% 23% 14%	5124
February	1st to 10th	Day	57% 4 10% 17% 10% 2	1680
	11th to 20th	Day	59% 3 11% 16% 10% 1	2041
	21st to end	Day	58% 3 8% 20% 9% 2	1730
March	1st to 10th	Day	62% 3 10% 13% 10% 3	4579
	11th to 20th	Day	55% 4 14% 18% 8% 1	4844
	21st to end	Day	54% 2 8% 17% 15% 4	5959
April	1st to 10th	Day	58% 2 11% 16% 10% 3	2520
	11th to 20th	Day	50% 2 10% 24% 11% 2	2587
	21st to end	Day	54% 4 11% 18% 12% 2	2730
May	1st to 10th	Day	55% 4 10% 18% 12% 1	7865
	11th to 20th	Day	50% 5% 15% 21% 6% 2	8225
	21st to end	Day	53% 6% 11% 18% 12% 2	9097
June	1st to 10th	Day	52% 5% 12% 21% 8% 1	3150
	11th to 20th	Day	48% 5% 14% 21% 11% 1	3150
	21st to end	Day	56% 5% 13% 17% 8% 1	3150
July	1st to 10th	Day	46% 6% 15% 23% 10%	8255
	11th to 20th	Day	42% 7% 18% 26% 7%	8205
	21st to end	Day	41% 8% 21% 23% 7%	8795
August	1st to 10th	Day	45% 8% 21% 20% 7%	4673
	11th to 20th	Day	49% 8% 20% 19% 4	4344
	21st to end	Day	46% 5% 16% 20% 13%	4567
September	1st to 10th	Day	44% 3 17% 26% 10%	2400
	11th to 20th	Day	38% 3 18% 31% 10%	2230
	21st to end	Day	47% 3 14% 25% 10%	2200
October	1st to 10th	Day	52% 7% 12% 23% 6%	3562
	11th to 20th	Day	52% 6% 18% 23% 2	2961
	21st to end	Day	53% 7% 17% 16% 7%	3180
November	1st to 10th	Day	56% 4 12% 21% 7%	1851
	11th to 20th	Day	61% 4 9% 19% 7% 1	1881
	21st to end	Day	65% 5% 10% 13% 6% 1	1524
December	1st to 10th	Day	63% 5% 11% 13% 8%	2350
	11th to 20th	Day	61% 3 7% 17% 11%	2688
	21st to end	Day	60% 3 11% 15% 10% 2	3716
January	1st to 10th	Night	66% 3 9% 14% 8%	8234
	11th to 20th	Night	72% 3 6% 15% 4	8280
	21st to end	Night	53% 4 11% 18% 13%	9057
February	1st to 10th	Night	57% 3 8% 21% 10% 1	2940
	11th to 20th	Night	60% 3 9% 16% 11% 1	2471
	21st to end	Night	57% 2 7% 19% 13% 2	2076
March	1st to 10th	Night	63% 3 9% 12% 12% 1	5494
	11th to 20th	Night	60% 5% 12% 14% 8% 2	5336
	21st to end	Night	58% 3 5% 21% 11% 2	5213
April	1st to 10th	Night	58% 3 8% 15% 14% 3	2100
	11th to 20th	Night	51% 4 7% 23% 13% 2	1981
	21st to end	Night	52% 3 8% 20% 14% 2	1890
May	1st to 10th	Night	54% 4 10% 18% 13% 1	5093
	11th to 20th	Night	53% 5% 11% 21% 10% 1	4640
	21st to end	Night	49% 4 11% 17% 16% 3	5066
June	1st to 10th	Night	51% 4 12% 22% 10% 1	1470
	11th to 20th	Night	47% 5% 12% 21% 11% 3	1470
	21st to end	Night	54% 4 14% 17% 11%	1470
July	1st to 10th	Night	46% 6% 18% 20% 11%	4579
	11th to 20th	Night	42% 7% 19% 26% 6%	4632
	21st to end	Night	42% 7% 19% 24% 8%	4967
August	1st to 10th	Night	48% 5% 16% 23% 7%	2656
	11th to 20th	Night	48% 8% 20% 17% 6% 1	2971
	21st to end	Night	49% 6% 13% 22% 10%	3527
September	1st to 10th	Night	43% 4 14% 27% 12% 1	2000
	11th to 20th	Night	41% 3 18% 29% 8% 1	2170
	21st to end	Night	45% 4 11% 26% 13%	2200
October	1st to 10th	Night	48% 5% 12% 26% 8% 1	3613
	11th to 20th	Night	52% 4 15% 26% 4	4177
	21st to end	Night	50% 5% 18% 17% 10%	4610
November	1st to 10th	Night	55% 4 12% 21% 7% 1	2667
	11th to 20th	Night	55% 5% 12% 19% 10% 1	2735
	21st to end	Night	65% 4 9% 15% 7% 1	3092
December	1st to 10th	Night	66% 4 12% 14% 4	5060
	11th to 20th	Night	62% 4 6% 20% 7%	5742
	21st to end	Night	63% 2 8% 16% 10% 1	7479

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% 15% 33% 19% 4 1	220
	11th to 20th	Day	28% 21% 31% 13% 5%	220
	21st to end	Day	20% 21% 33% 21% 4 1	242
February	1st to 10th	Day	25% 20% 35% 15% 3 1	220
	11th to 20th	Day	24% 21% 35% 16% 3 1	522
	21st to end	Day	22% 20% 31% 20% 5%	446
March	1st to 10th	Day	27% 19% 31% 16% 6% 1	540
	11th to 20th	Day	27% 16% 33% 17% 6% 1	540
	21st to end	Day	26% 18% 24% 21% 9% 1	594
April	1st to 10th	Day	31% 14% 30% 17% 8%	540
	11th to 20th	Day	29% 13% 28% 20% 8% 1	532
	21st to end	Day	31% 13% 31% 18% 6% 1	540
May	1st to 10th	Day	30% 17% 33% 15% 5% 1	543
	11th to 20th	Day	23% 14% 32% 21% 8% 1	567
	21st to end	Day	27% 19% 31% 17% 6% 1	627
June	1st to 10th	Day	23% 12% 31% 25% 9% 1	780
	11th to 20th	Day	24% 12% 28% 24% 11% 1	780
	21st to end	Day	29% 9% 27% 22% 10% 2	780
July	1st to 10th	Day	20% 14% 32% 23% 11% 2	584
	11th to 20th	Day	20% 13% 32% 25% 9% 2	564
	21st to end	Day	18% 11% 32% 26% 11% 2	620
August	1st to 10th	Day	20% 6% 33% 24% 13% 4	566
	11th to 20th	Day	18% 5% 27% 30% 17% 3	559
	21st to end	Day	23% 10% 24% 22% 14% 7%	619
September	1st to 10th	Day	21% 10% 27% 25% 14% 3	530
	11th to 20th	Day	19% 10% 27% 22% 16% 5%	530
	21st to end	Day	24% 11% 25% 23% 12% 5%	530
October	1st to 10th	Day	23% 12% 29% 23% 11% 3	530
	11th to 20th	Day	33% 9% 27% 20% 10% 1	439
	21st to end	Day	37% 13% 27% 18% 5%	462
November	1st to 10th	Day	34% 13% 24% 21% 7%	425
	11th to 20th	Day	31% 13% 28% 19% 8% 1	421
	21st to end	Day	32% 19% 30% 15% 5%	220
December	1st to 10th	Day	30% 11% 29% 22% 5% 2	220
	11th to 20th	Day	32% 20% 28% 16% 3 1	220
	21st to end	Day	30% 19% 30% 15% 5%	242
January	1st to 10th	Night	26% 15% 30% 24% 5%	840
	11th to 20th	Night	27% 14% 27% 25% 7% 1	840
	21st to end	Night	16% 14% 32% 30% 7% 1	924
February	1st to 10th	Night	18% 13% 33% 28% 7% 1	840
	11th to 20th	Night	23% 15% 35% 22% 4 1	823
	21st to end	Night	25% 11% 31% 28% 5%	692
March	1st to 10th	Night	23% 12% 34% 25% 6%	840
	11th to 20th	Night	26% 14% 31% 22% 6% 1	840
	21st to end	Night	24% 10% 29% 29% 7% 1	924
April	1st to 10th	Night	30% 12% 27% 25% 6%	840
	11th to 20th	Night	28% 8% 34% 25% 6%	737
	21st to end	Night	29% 10% 32% 23% 6%	630
May	1st to 10th	Night	27% 9% 33% 26% 6%	574
	11th to 20th	Night	24% 8% 28% 33% 7%	414
	21st to end	Night	26% 5% 31% 29% 9%	455
June	1st to 10th	Night	25% 5% 28% 36% 6%	420
	11th to 20th	Night	21% 5% 24% 37% 13%	420
	21st to end	Night	25% 4 22% 38% 10% 1	420
July	1st to 10th	Night	19% 4 27% 40% 10% 1	410
	11th to 20th	Night	19% 6% 20% 41% 14%	408
	21st to end	Night	18% 3 17% 45% 15% 1	460
August	1st to 10th	Night	18% 4 15% 46% 17%	418
	11th to 20th	Night	18% 3 21% 41% 15% 1	604
	21st to end	Night	20% 5% 21% 34% 18% 2	819
September	1st to 10th	Night	22% 3 25% 34% 15% 1	800
	11th to 20th	Night	20% 5% 22% 32% 19% 2	800
	21st to end	Night	24% 6% 26% 30% 14% 2	800
October	1st to 10th	Night	24% 7% 26% 33% 9% 1	800
	11th to 20th	Night	29% 7% 25% 28% 10% 1	800
	21st to end	Night	32% 10% 28% 25% 5%	880
November	1st to 10th	Night	30% 12% 24% 26% 8%	820
	11th to 20th	Night	26% 13% 25% 27% 8% 1	840
	21st to end	Night	30% 14% 28% 20% 7% 1	920
December	1st to 10th	Night	30% 11% 27% 23% 8% 1	950
	11th to 20th	Night	27% 17% 27% 22% 6% 1	950
	21st to end	Night	31% 14% 29% 20% 5% 1	1001

Page generated at 2026-08-27 04:07:11. Version ac07

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