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 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	19% 10% 3 8% 5% 4 4 4 5% 7% 31%	101248
	Night	19% 12% 4 8% 5% 4 4 3 5% 5% 30%	97547
Transparency	Day	53% 4 14% 20% 9% 1	101006
	Night	56% 4 12% 19% 9% 1	97410
Seeing	Day	26% 13% 29% 22% 9% 2	15154
	Night	25% 10% 27% 28% 9% 1	23646

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% 7% 12% 6% 5% 4 3 5% 6% 21%	2517
	11th to 20th	Day	10% 16% 8% 15% 7% 4 4 3 4 4 26%	2520
	21st to end	Day	10% 13% 5% 10% 5% 4 4 4 5% 6% 33%	2772
February	1st to 10th	Day	11% 16% 5% 11% 8% 6% 3 5% 4 5% 25%	1520
	11th to 20th	Day	13% 16% 6% 12% 5% 4 5% 4 5% 5% 26%	1832
	21st to end	Day	13% 15% 5% 11% 7% 5% 5% 3 4 6% 27%	1570
March	1st to 10th	Day	21% 11% 4 8% 5% 4 4 2 5% 5% 29%	3116
	11th to 20th	Day	16% 18% 5% 8% 5% 4 4 4 4 5% 26%	3310
	21st to end	Day	15% 13% 4 8% 5% 4 4 4 3 5% 36%	4068
April	1st to 10th	Day	22% 13% 3 8% 6% 4 3 3 4 5% 29%	2280
	11th to 20th	Day	21% 7% 3 7% 5% 4 3 3 5% 6% 36%	2337
	21st to end	Day	24% 9% 3 7% 6% 4 3 3 4 6% 31%	2470
May	1st to 10th	Day	22% 8% 2 7% 5% 4 4 3 5% 6% 35%	4224
	11th to 20th	Day	18% 7% 2 7% 5% 5% 5% 4 6% 8% 32%	4398
	21st to end	Day	19% 6% 3 7% 5% 5% 6% 4 6% 7% 32%	4859
June	1st to 10th	Day	20% 7% 3 7% 6% 5% 6% 5% 7% 8% 26%	2850
	11th to 20th	Day	19% 7% 3 6% 4 5% 5% 5% 6% 7% 34%	2850
	21st to end	Day	23% 9% 3 8% 6% 5% 5% 4 5% 7% 26%	2850
July	1st to 10th	Day	15% 7% 3 9% 6% 5% 6% 4 6% 8% 30%	4457
	11th to 20th	Day	17% 6% 3 8% 5% 5% 5% 5% 7% 9% 30%	4440
	21st to end	Day	14% 6% 2 6% 4 4 5% 4 7% 8% 39%	4814
August	1st to 10th	Day	16% 5% 2 8% 6% 5% 6% 5% 8% 10% 30%	4407
	11th to 20th	Day	21% 6% 3 7% 5% 5% 5% 5% 7% 9% 28%	4045
	21st to end	Day	21% 6% 2 7% 4 4 4 4 4 7% 37%	4318
September	1st to 10th	Day	17% 7% 3 6% 4 4 4 4 6% 8% 37%	2280
	11th to 20th	Day	18% 5% 2 5% 3 4 3 3 5% 7% 46%	2119
	21st to end	Day	22% 7% 2 6% 3 3 4 3 5% 7% 37%	2090
October	1st to 10th	Day	22% 7% 3 7% 5% 5% 5% 4 5% 6% 33%	2076
	11th to 20th	Day	25% 8% 3 8% 6% 5% 4 4 6% 6% 24%	1744
	21st to end	Day	28% 11% 2 7% 5% 4 4 3 5% 5% 25%	1825
November	1st to 10th	Day	21% 11% 3 7% 6% 5% 5% 2 5% 5% 31%	1671
	11th to 20th	Day	22% 14% 4 9% 5% 5% 4 3 4 5% 25%	1703
	21st to end	Day	23% 16% 5% 8% 5% 4 4 4 4 5% 22%	1380
December	1st to 10th	Day	24% 18% 4 8% 6% 4 3 3 4 4 22%	1330
	11th to 20th	Day	22% 14% 4 10% 5% 4 3 2 3 4 27%	1668
	21st to end	Day	22% 18% 4 8% 5% 3 3 3 4 4 26%	2538
January	1st to 10th	Night	15% 20% 6% 13% 6% 4 4 2 3 4 22%	4429
	11th to 20th	Night	12% 16% 6% 13% 6% 5% 5% 3 4 4 25%	4440
	21st to end	Night	10% 14% 5% 10% 7% 6% 5% 4 6% 6% 26%	4884
February	1st to 10th	Night	12% 14% 5% 11% 7% 5% 4 4 4 5% 27%	2660
	11th to 20th	Night	13% 17% 5% 11% 6% 5% 4 3 4 5% 26%	2229
	21st to end	Night	15% 14% 5% 10% 5% 4 3 4 4 6% 29%	1884
March	1st to 10th	Night	24% 12% 3 7% 4 4 6% 2 4 5% 28%	3724
	11th to 20th	Night	18% 18% 4 9% 5% 5% 5% 3 4 5% 24%	3649
	21st to end	Night	18% 14% 4 8% 5% 4 4 3 4 5% 33%	3562
April	1st to 10th	Night	22% 14% 4 7% 5% 4 3 3 5% 4 29%	1900
	11th to 20th	Night	21% 9% 3 7% 5% 4 4 4 5% 6% 33%	1791
	21st to end	Night	23% 9% 3 8% 4 4 3 3 3 6% 35%	1710
May	1st to 10th	Night	23% 7% 3 6% 4 5% 5% 4 5% 5% 34%	2745
	11th to 20th	Night	23% 7% 3 7% 5% 4 4 3 5% 6% 34%	2495
	21st to end	Night	20% 5% 2 6% 5% 5% 5% 4 6% 8% 35%	2715
June	1st to 10th	Night	21% 7% 3 7% 6% 4 4 5% 6% 7% 29%	1330
	11th to 20th	Night	21% 5% 3 6% 4 4 4 4 6% 7% 36%	1330
	21st to end	Night	23% 8% 3 8% 5% 4 4 4 5% 7% 29%	1330
July	1st to 10th	Night	15% 7% 3 8% 6% 6% 5% 5% 6% 7% 32%	2485
	11th to 20th	Night	20% 7% 2 7% 5% 4 5% 4 5% 7% 34%	2520
	21st to end	Night	14% 5% 2 7% 4 4 5% 4 5% 7% 43%	2739
August	1st to 10th	Night	18% 7% 3 7% 5% 5% 5% 3 6% 7% 35%	2506
	11th to 20th	Night	19% 7% 3 8% 5% 5% 6% 3 6% 6% 32%	2766
	21st to end	Night	21% 7% 3 7% 5% 4 4 4 5% 6% 34%	3335
September	1st to 10th	Night	19% 6% 2 6% 4 4 3 3 5% 7% 41%	1900
	11th to 20th	Night	19% 5% 2 6% 4 4 3 3 5% 6% 44%	2061
	21st to end	Night	20% 7% 2 6% 3 4 3 3 4 6% 41%	2090
October	1st to 10th	Night	20% 7% 2 7% 5% 4 5% 3 6% 5% 37%	2099
	11th to 20th	Night	24% 9% 3 7% 5% 4 3 4 5% 5% 31%	2435
	21st to end	Night	26% 10% 3 6% 4 4 4 3 5% 5% 30%	2637
November	1st to 10th	Night	20% 11% 3 8% 4 5% 4 3 4 7% 31%	2407
	11th to 20th	Night	21% 11% 4 8% 5% 3 4 3 4 6% 31%	2474
	21st to end	Night	23% 14% 5% 8% 6% 4 4 2 4 4 25%	2797
December	1st to 10th	Night	24% 17% 4 9% 7% 4 4 3 4 4 20%	2850
	11th to 20th	Night	21% 15% 4 10% 6% 4 4 3 4 4 25%	3531
	21st to end	Night	23% 20% 4 9% 4 3 3 3 4 3 25%	5108

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	64% 2 12% 16% 5% 1	2518
	11th to 20th	Day	63% 2 10% 19% 6% 1	2520
	21st to end	Day	51% 2 12% 25% 9% 1	2772
February	1st to 10th	Day	59% 4 10% 16% 9% 2	1520
	11th to 20th	Day	60% 3 12% 15% 10% 1	1841
	21st to end	Day	58% 2 9% 19% 9% 2	1570
March	1st to 10th	Day	57% 2 13% 17% 9% 2	3119
	11th to 20th	Day	59% 3 11% 20% 7% 1	3310
	21st to end	Day	52% 2 9% 19% 14% 4	4068
April	1st to 10th	Day	58% 2 12% 15% 10% 4	2280
	11th to 20th	Day	49% 2 10% 25% 11% 3	2337
	21st to end	Day	55% 3 10% 17% 12% 2	2470
May	1st to 10th	Day	49% 3 13% 19% 14% 1	4238
	11th to 20th	Day	50% 3 18% 21% 7% 1	4402
	21st to end	Day	51% 4 10% 21% 14% 1	4859
June	1st to 10th	Day	53% 5% 13% 20% 8% 2	2850
	11th to 20th	Day	48% 5% 15% 20% 11% 1	2850
	21st to end	Day	57% 4 12% 17% 9%	2850
July	1st to 10th	Day	49% 7% 16% 21% 7%	4387
	11th to 20th	Day	47% 7% 21% 21% 4	4365
	21st to end	Day	42% 5% 21% 24% 8%	4661
August	1st to 10th	Day	46% 8% 21% 20% 6%	4393
	11th to 20th	Day	50% 8% 20% 18% 4	4084
	21st to end	Day	46% 5% 16% 19% 13%	4318
September	1st to 10th	Day	45% 3 16% 26% 10%	2280
	11th to 20th	Day	39% 3 18% 30% 10%	2119
	21st to end	Day	48% 3 15% 25% 9%	2090
October	1st to 10th	Day	51% 3 13% 24% 9%	2076
	11th to 20th	Day	59% 4 16% 18% 3	1744
	21st to end	Day	61% 4 12% 18% 5% 1	1825
November	1st to 10th	Day	56% 4 12% 20% 8%	1671
	11th to 20th	Day	61% 3 10% 19% 6% 1	1703
	21st to end	Day	64% 4 11% 14% 6% 1	1380
December	1st to 10th	Day	66% 3 10% 15% 6%	1330
	11th to 20th	Day	62% 3 6% 20% 9%	1668
	21st to end	Day	63% 3 12% 14% 7% 2	2538
January	1st to 10th	Night	68% 3 9% 13% 6% 1	4429
	11th to 20th	Night	64% 2 9% 20% 5% 1	4440
	21st to end	Night	58% 3 11% 18% 9% 1	4884
February	1st to 10th	Night	58% 3 8% 20% 10% 1	2660
	11th to 20th	Night	61% 3 10% 16% 10% 1	2231
	21st to end	Night	57% 2 8% 18% 12% 2	1884
March	1st to 10th	Night	60% 2 12% 15% 8% 2	3734
	11th to 20th	Night	63% 3 8% 16% 7% 2	3650
	21st to end	Night	56% 3 7% 21% 10% 3	3562
April	1st to 10th	Night	58% 2 8% 15% 14% 3	1900
	11th to 20th	Night	50% 4 8% 24% 13% 2	1791
	21st to end	Night	53% 4 8% 19% 15% 3	1710
May	1st to 10th	Night	51% 3 11% 21% 12% 1	2751
	11th to 20th	Night	52% 4 12% 20% 11% 1	2496
	21st to end	Night	46% 4 13% 19% 17% 1	2716
June	1st to 10th	Night	53% 4 13% 20% 9% 1	1330
	11th to 20th	Night	46% 5% 12% 22% 12% 3	1330
	21st to end	Night	56% 4 12% 17% 11%	1330
July	1st to 10th	Night	49% 5% 20% 20% 7%	2445
	11th to 20th	Night	48% 6% 19% 22% 4	2472
	21st to end	Night	39% 6% 23% 22% 9%	2651
August	1st to 10th	Night	48% 5% 16% 23% 7%	2496
	11th to 20th	Night	50% 8% 20% 16% 5%	2793
	21st to end	Night	49% 6% 13% 22% 10%	3335
September	1st to 10th	Night	44% 4 14% 26% 12% 1	1900
	11th to 20th	Night	42% 3 18% 29% 8% 1	2061
	21st to end	Night	46% 4 11% 26% 12%	2090
October	1st to 10th	Night	48% 5% 10% 25% 11% 1	2099
	11th to 20th	Night	56% 4 13% 21% 6%	2435
	21st to end	Night	56% 3 14% 18% 8%	2637
November	1st to 10th	Night	54% 4 13% 21% 7% 1	2407
	11th to 20th	Night	55% 4 12% 18% 10%	2474
	21st to end	Night	63% 3 10% 17% 7% 1	2797
December	1st to 10th	Night	69% 3 10% 14% 5%	2850
	11th to 20th	Night	63% 3 7% 18% 9%	3532
	21st to end	Night	66% 2 8% 16% 7% 2	5108

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% 14% 32% 22% 4 2	180
	11th to 20th	Day	27% 22% 32% 14% 4	180
	21st to end	Day	20% 20% 32% 22% 5% 1	198
February	1st to 10th	Day	28% 21% 35% 15% 1 1	180
	11th to 20th	Day	23% 21% 37% 16% 3 1	442
	21st to end	Day	24% 20% 29% 21% 6%	382
March	1st to 10th	Day	25% 18% 31% 18% 7% 1	460
	11th to 20th	Day	27% 15% 32% 18% 7% 2	460
	21st to end	Day	25% 16% 23% 24% 10% 2	506
April	1st to 10th	Day	30% 13% 30% 18% 9%	460
	11th to 20th	Day	27% 13% 28% 22% 9% 1	452
	21st to end	Day	32% 12% 31% 18% 5% 1	460
May	1st to 10th	Day	28% 16% 34% 16% 6% 1	463
	11th to 20th	Day	22% 12% 33% 23% 9% 1	487
	21st to end	Day	27% 18% 31% 17% 6% 1	538
June	1st to 10th	Day	24% 12% 30% 24% 9% 1	680
	11th to 20th	Day	23% 11% 28% 25% 12% 1	680
	21st to end	Day	30% 8% 26% 22% 11% 2	680
July	1st to 10th	Day	20% 11% 32% 24% 12% 1	502
	11th to 20th	Day	20% 9% 33% 26% 10% 2	484
	21st to end	Day	19% 9% 32% 28% 11% 2	532
August	1st to 10th	Day	21% 6% 32% 24% 13% 3	486
	11th to 20th	Day	20% 5% 25% 30% 17% 3	479
	21st to end	Day	23% 9% 24% 22% 13% 8%	539
September	1st to 10th	Day	22% 10% 26% 26% 13% 3	490
	11th to 20th	Day	21% 9% 28% 23% 15% 4	490
	21st to end	Day	24% 11% 23% 23% 12% 6%	490
October	1st to 10th	Day	24% 11% 27% 23% 11% 3	490
	11th to 20th	Day	35% 9% 25% 20% 11% 1	407
	21st to end	Day	37% 12% 27% 18% 5%	411
November	1st to 10th	Day	32% 12% 24% 23% 8% 1	365
	11th to 20th	Day	31% 13% 27% 20% 9% 1	363
	21st to end	Day	33% 16% 29% 17% 6%	180
December	1st to 10th	Day	34% 8% 27% 22% 7% 3	180
	11th to 20th	Day	32% 18% 29% 16% 3 2	180
	21st to end	Day	32% 18% 30% 15% 5%	198
January	1st to 10th	Night	26% 16% 30% 24% 5%	760
	11th to 20th	Night	27% 14% 29% 24% 6% 1	760
	21st to end	Night	17% 13% 32% 30% 7% 1	836
February	1st to 10th	Night	20% 13% 33% 28% 6%	760
	11th to 20th	Night	23% 15% 36% 21% 5% 1	743
	21st to end	Night	25% 11% 31% 27% 5%	628
March	1st to 10th	Night	23% 11% 34% 27% 6%	760
	11th to 20th	Night	26% 14% 30% 23% 7% 1	760
	21st to end	Night	24% 10% 28% 30% 7% 1	836
April	1st to 10th	Night	30% 11% 25% 26% 6% 1	760
	11th to 20th	Night	28% 7% 33% 25% 6%	667
	21st to end	Night	29% 10% 31% 23% 7%	570
May	1st to 10th	Night	26% 9% 32% 27% 6%	520
	11th to 20th	Night	24% 8% 27% 33% 7%	374
	21st to end	Night	26% 5% 31% 29% 9%	411
June	1st to 10th	Night	25% 6% 28% 34% 7% 1	380
	11th to 20th	Night	20% 4 25% 37% 13%	380
	21st to end	Night	26% 4 22% 37% 10% 1	380
July	1st to 10th	Night	19% 3 26% 39% 11% 1	370
	11th to 20th	Night	19% 5% 20% 41% 15%	368
	21st to end	Night	18% 3 17% 45% 16% 1	416
August	1st to 10th	Night	19% 4 14% 46% 17%	378
	11th to 20th	Night	19% 3 21% 40% 16% 2	546
	21st to end	Night	20% 4 22% 33% 19% 2	747
September	1st to 10th	Night	22% 3 25% 33% 15% 1	760
	11th to 20th	Night	21% 5% 22% 31% 19% 2	760
	21st to end	Night	24% 6% 25% 29% 14% 2	760
October	1st to 10th	Night	24% 8% 26% 33% 9% 1	760
	11th to 20th	Night	30% 7% 24% 28% 10% 1	760
	21st to end	Night	33% 10% 28% 24% 5%	812
November	1st to 10th	Night	29% 11% 24% 28% 9% 1	740
	11th to 20th	Night	27% 13% 24% 26% 8% 1	760
	21st to end	Night	31% 12% 29% 21% 6% 1	825
December	1st to 10th	Night	32% 11% 26% 22% 8% 1	850
	11th to 20th	Night	27% 17% 27% 23% 6% 1	850
	21st to end	Night	33% 14% 28% 19% 5% 1	899

Page generated at 2024-10-22 20:21:00. Version ac07

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