Observatoire astronomique de Charlevoix
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire astronomique de Charlevoix 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	14% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	144095
	Night	15% 11% 4 9% 5% 5% 5% 4 5% 6% 32%	137933
Transparency	Day	32% 36% 11% 13% 6% 1	147531
	Night	34% 37% 9% 13% 7% 1	142587
Seeing	Day	22% 17% 30% 21% 8% 2	17882
	Night	21% 12% 28% 29% 9% 1	26007

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% 18% 4 9% 5% 4 4 3 5% 8% 25%	4378
	11th to 20th	Day	8% 13% 5% 12% 7% 6% 6% 5% 7% 7% 24%	4650
	21st to end	Day	4 6% 4 10% 7% 6% 7% 7% 8% 9% 33%	5124
February	1st to 10th	Day	7% 10% 4 8% 9% 8% 7% 5% 6% 7% 29%	1715
	11th to 20th	Day	10% 13% 5% 12% 7% 5% 5% 4 6% 5% 28%	1957
	21st to end	Day	11% 10% 3 8% 7% 6% 7% 4 7% 6% 32%	1730
March	1st to 10th	Day	18% 12% 4 10% 5% 4 4 4 5% 5% 28%	4576
	11th to 20th	Day	12% 13% 4 9% 6% 6% 6% 4 6% 7% 28%	4949
	21st to end	Day	14% 15% 5% 9% 5% 4 3 3 5% 5% 32%	5808
April	1st to 10th	Day	19% 12% 4 7% 5% 5% 5% 4 5% 6% 28%	2520
	11th to 20th	Day	16% 8% 3 8% 5% 5% 4 3 5% 6% 37%	2660
	21st to end	Day	21% 9% 3 6% 4 4 4 3 5% 6% 33%	2730
May	1st to 10th	Day	18% 10% 3 8% 5% 4 5% 4 5% 6% 31%	7730
	11th to 20th	Day	20% 7% 3 8% 4 4 4 4 5% 7% 34%	8221
	21st to end	Day	17% 7% 3 8% 5% 5% 5% 4 6% 8% 32%	9675
June	1st to 10th	Day	18% 8% 2 7% 5% 5% 5% 4 6% 8% 32%	3150
	11th to 20th	Day	17% 6% 3 6% 4 6% 5% 4 6% 7% 36%	3150
	21st to end	Day	19% 8% 3 7% 6% 5% 5% 5% 6% 7% 29%	3150
July	1st to 10th	Day	10% 5% 3 7% 5% 5% 6% 5% 8% 10% 36%	8880
	11th to 20th	Day	11% 6% 2 7% 5% 6% 6% 5% 7% 9% 35%	8382
	21st to end	Day	9% 6% 2 6% 5% 5% 6% 5% 7% 9% 40%	8993
August	1st to 10th	Day	11% 5% 2 7% 5% 6% 6% 5% 8% 9% 35%	4621
	11th to 20th	Day	13% 6% 3 7% 6% 4 6% 4 8% 9% 34%	4227
	21st to end	Day	16% 5% 2 6% 4 4 4 4 5% 8% 43%	4617
September	1st to 10th	Day	12% 6% 2 6% 4 4 5% 4 6% 8% 42%	2384
	11th to 20th	Day	13% 5% 2 5% 3 3 4 3 5% 7% 49%	2200
	21st to end	Day	16% 6% 2 6% 3 4 4 3 5% 9% 42%	2200
October	1st to 10th	Day	15% 5% 2 8% 5% 4 5% 3 6% 7% 39%	2175
	11th to 20th	Day	19% 7% 3 8% 4 4 5% 4 6% 7% 32%	1847
	21st to end	Day	23% 10% 3 8% 4 5% 4 3 5% 6% 29%	1980
November	1st to 10th	Day	15% 10% 3 9% 8% 4 5% 4 6% 5% 32%	1851
	11th to 20th	Day	16% 10% 4 9% 6% 5% 5% 4 5% 7% 27%	1775
	21st to end	Day	18% 14% 4 9% 6% 5% 4 3 4 5% 26%	1499
December	1st to 10th	Day	14% 13% 5% 11% 6% 4 5% 3 4 5% 29%	2350
	11th to 20th	Day	17% 9% 4 8% 5% 5% 5% 4 6% 6% 33%	2688
	21st to end	Day	16% 11% 4 9% 5% 5% 5% 3 8% 4 29%	3553
January	1st to 10th	Night	14% 16% 5% 12% 6% 5% 4 3 5% 6% 24%	8513
	11th to 20th	Night	8% 15% 7% 15% 7% 6% 5% 4 5% 6% 21%	8235
	21st to end	Night	3 8% 5% 11% 7% 7% 6% 4 8% 8% 33%	9057
February	1st to 10th	Night	7% 12% 4 11% 6% 6% 5% 4 7% 6% 33%	2904
	11th to 20th	Night	9% 15% 5% 13% 7% 5% 5% 4 5% 5% 28%	2548
	21st to end	Night	12% 11% 4 9% 5% 4 5% 4 5% 7% 33%	2076
March	1st to 10th	Night	19% 12% 4 9% 5% 4 5% 4 5% 6% 27%	5484
	11th to 20th	Night	12% 13% 4 11% 7% 6% 5% 4 5% 6% 25%	5230
	21st to end	Night	18% 16% 4 8% 4 4 4 3 4 5% 31%	5364
April	1st to 10th	Night	20% 13% 4 8% 5% 3 4 4 4 4 32%	2100
	11th to 20th	Night	18% 9% 3 8% 6% 5% 4 3 5% 6% 33%	1909
	21st to end	Night	23% 9% 3 6% 4 4 4 4 4 5% 34%	1890
May	1st to 10th	Night	20% 9% 3 8% 4 4 5% 4 5% 7% 32%	5223
	11th to 20th	Night	23% 9% 3 7% 4 4 4 3 5% 6% 31%	4639
	21st to end	Night	16% 7% 2 7% 4 4 5% 4 6% 8% 36%	4530
June	1st to 10th	Night	18% 8% 3 7% 6% 5% 4 4 5% 6% 34%	1470
	11th to 20th	Night	16% 6% 3 5% 5% 4 5% 3 7% 8% 39%	1470
	21st to end	Night	20% 8% 3 8% 5% 4 5% 5% 6% 6% 30%	1470
July	1st to 10th	Night	11% 7% 3 7% 5% 5% 5% 4 7% 9% 38%	4110
	11th to 20th	Night	14% 6% 2 6% 4 5% 5% 4 7% 9% 39%	4579
	21st to end	Night	9% 6% 3 7% 5% 4 4 3 6% 8% 44%	5084
August	1st to 10th	Night	15% 6% 2 7% 5% 5% 5% 4 6% 8% 37%	2714
	11th to 20th	Night	13% 5% 3 9% 6% 6% 6% 5% 7% 8% 31%	2909
	21st to end	Night	17% 6% 3 6% 4 4 4 4 4 6% 42%	3279
September	1st to 10th	Night	13% 5% 2 5% 5% 4 4 4 6% 8% 44%	2015
	11th to 20th	Night	16% 6% 2 6% 4 5% 4 3 5% 6% 43%	2200
	21st to end	Night	15% 7% 2 6% 4 4 4 4 4 5% 45%	2200
October	1st to 10th	Night	16% 7% 3 6% 4 3 5% 4 4 5% 42%	2225
	11th to 20th	Night	22% 8% 2 6% 4 4 5% 4 5% 6% 35%	2550
	21st to end	Night	21% 9% 3 7% 5% 4 4 3 5% 6% 33%	2860
November	1st to 10th	Night	17% 9% 4 7% 5% 4 4 4 5% 7% 33%	2667
	11th to 20th	Night	19% 10% 3 6% 4 5% 4 4 5% 7% 31%	2842
	21st to end	Night	17% 14% 4 9% 6% 5% 5% 4 5% 5% 27%	3119
December	1st to 10th	Night	11% 14% 6% 12% 6% 5% 5% 4 5% 6% 26%	5060
	11th to 20th	Night	19% 11% 3 8% 5% 5% 5% 4 5% 6% 28%	5741
	21st to end	Night	16% 15% 4 9% 5% 5% 5% 5% 6% 5% 25%	7667

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	44% 24% 9% 17% 6%	4379
	11th to 20th	Day	44% 27% 8% 15% 6%	4680
	21st to end	Day	33% 28% 10% 14% 15%	5124
February	1st to 10th	Day	19% 60% 5% 10% 5% 2	1715
	11th to 20th	Day	23% 59% 5% 7% 5%	1965
	21st to end	Day	19% 60% 4 11% 4 2	1730
March	1st to 10th	Day	41% 31% 8% 7% 8% 4	4579
	11th to 20th	Day	39% 33% 13% 9% 4 1	4949
	21st to end	Day	40% 30% 5% 11% 10% 4	5808
April	1st to 10th	Day	22% 59% 4 8% 6% 2	2520
	11th to 20th	Day	22% 60% 5% 9% 2 1	2660
	21st to end	Day	23% 60% 4 8% 5% 1	2730
May	1st to 10th	Day	43% 26% 11% 12% 7%	7742
	11th to 20th	Day	40% 25% 11% 18% 4 2	8225
	21st to end	Day	39% 26% 12% 12% 10% 1	9676
June	1st to 10th	Day	19% 60% 5% 11% 4	3150
	11th to 20th	Day	19% 61% 7% 8% 5%	3150
	21st to end	Day	21% 59% 6% 9% 4 1	3150
July	1st to 10th	Day	34% 23% 15% 19% 10%	8805
	11th to 20th	Day	34% 25% 18% 18% 5%	8305
	21st to end	Day	31% 24% 17% 22% 6%	8795
August	1st to 10th	Day	26% 40% 16% 14% 5%	4607
	11th to 20th	Day	32% 39% 15% 12% 2	4266
	21st to end	Day	27% 38% 15% 11% 9%	4617
September	1st to 10th	Day	15% 59% 11% 12% 4	2384
	11th to 20th	Day	15% 58% 9% 13% 4 1	2200
	21st to end	Day	16% 57% 7% 14% 6%	2200
October	1st to 10th	Day	34% 39% 10% 14% 3	3539
	11th to 20th	Day	26% 39% 13% 20% 3	2985
	21st to end	Day	29% 37% 16% 12% 6%	3180
November	1st to 10th	Day	25% 55% 8% 8% 3	1851
	11th to 20th	Day	25% 57% 5% 9% 3	1775
	21st to end	Day	30% 56% 5% 6% 3	1499
December	1st to 10th	Day	35% 36% 8% 12% 9%	2350
	11th to 20th	Day	36% 35% 7% 13% 9% 1	2688
	21st to end	Day	38% 28% 10% 14% 8% 2	3553
January	1st to 10th	Night	46% 25% 11% 11% 7%	8513
	11th to 20th	Night	50% 26% 7% 10% 6%	8280
	21st to end	Night	34% 27% 9% 15% 14% 1	9057
February	1st to 10th	Night	19% 60% 4 10% 6% 1	2904
	11th to 20th	Night	24% 59% 3 9% 5%	2551
	21st to end	Night	20% 60% 2 9% 8% 1	2076
March	1st to 10th	Night	43% 32% 6% 7% 11% 1	5494
	11th to 20th	Night	41% 32% 11% 9% 3 2	5231
	21st to end	Night	43% 30% 4 13% 10% 1	5364
April	1st to 10th	Night	22% 59% 2 8% 8% 2	2100
	11th to 20th	Night	24% 60% 4 8% 4	1909
	21st to end	Night	26% 60% 3 7% 5% 1	1890
May	1st to 10th	Night	40% 26% 9% 15% 9%	5229
	11th to 20th	Night	42% 26% 9% 15% 8%	4640
	21st to end	Night	33% 26% 10% 17% 12% 2	4531
June	1st to 10th	Night	21% 60% 3 12% 4	1470
	11th to 20th	Night	18% 61% 6% 8% 6% 1	1470
	21st to end	Night	22% 59% 6% 9% 4	1470
July	1st to 10th	Night	34% 23% 15% 21% 7%	4075
	11th to 20th	Night	32% 24% 19% 21% 4	4533
	21st to end	Night	29% 23% 19% 22% 7%	4967
August	1st to 10th	Night	31% 37% 13% 14% 5%	2704
	11th to 20th	Night	33% 41% 14% 7% 5%	2936
	21st to end	Night	27% 38% 8% 18% 8%	3279
September	1st to 10th	Night	16% 59% 7% 13% 5%	2015
	11th to 20th	Night	19% 59% 7% 11% 4	2200
	21st to end	Night	15% 58% 5% 14% 7% 1	2200
October	1st to 10th	Night	32% 37% 7% 19% 4	3641
	11th to 20th	Night	26% 37% 12% 21% 5%	4151
	21st to end	Night	28% 38% 13% 12% 8%	4610
November	1st to 10th	Night	28% 55% 6% 8% 3	2667
	11th to 20th	Night	26% 58% 4 9% 4	2842
	21st to end	Night	31% 56% 5% 5% 4	3119
December	1st to 10th	Night	37% 37% 7% 15% 5%	5060
	11th to 20th	Night	40% 34% 4 14% 6% 1	5742
	21st to end	Night	40% 29% 9% 13% 8% 1	7667

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	20% 15% 37% 21% 5% 1	220
	11th to 20th	Day	26% 14% 35% 17% 6% 2	220
	21st to end	Day	14% 20% 40% 15% 10% 2	242
February	1st to 10th	Day	15% 23% 35% 19% 7% 2	255
	11th to 20th	Day	16% 21% 37% 19% 6%	487
	21st to end	Day	19% 21% 35% 19% 4 1	446
March	1st to 10th	Day	26% 21% 29% 19% 6%	540
	11th to 20th	Day	23% 20% 30% 19% 6% 1	540
	21st to end	Day	24% 25% 29% 14% 6% 1	594
April	1st to 10th	Day	29% 23% 29% 15% 4 1	540
	11th to 20th	Day	28% 18% 30% 16% 6% 1	532
	21st to end	Day	28% 16% 35% 14% 5% 2	540
May	1st to 10th	Day	27% 20% 30% 16% 6% 2	543
	11th to 20th	Day	23% 21% 27% 23% 5% 1	567
	21st to end	Day	23% 20% 32% 20% 5% 1	829
June	1st to 10th	Day	25% 16% 29% 21% 8% 1	780
	11th to 20th	Day	23% 17% 25% 24% 9% 1	780
	21st to end	Day	23% 10% 31% 24% 9% 2	780
July	1st to 10th	Day	19% 13% 32% 24% 9% 2	770
	11th to 20th	Day	17% 14% 34% 25% 8% 1	599
	21st to end	Day	16% 11% 35% 28% 8% 2	620
August	1st to 10th	Day	16% 12% 28% 26% 14% 3	566
	11th to 20th	Day	16% 13% 30% 27% 12% 3	535
	21st to end	Day	17% 16% 30% 20% 14% 3	583
September	1st to 10th	Day	17% 15% 33% 24% 8% 4	530
	11th to 20th	Day	19% 13% 30% 23% 11% 5%	530
	21st to end	Day	20% 15% 28% 21% 12% 4	530
October	1st to 10th	Day	19% 21% 26% 22% 9% 2	516
	11th to 20th	Day	25% 16% 29% 19% 10% 1	420
	21st to end	Day	34% 15% 28% 17% 6%	462
November	1st to 10th	Day	28% 17% 28% 21% 5% 1	425
	11th to 20th	Day	25% 14% 26% 23% 10% 1	430
	21st to end	Day	32% 22% 30% 14% 1	249
December	1st to 10th	Day	22% 20% 30% 16% 10% 2	220
	11th to 20th	Day	27% 20% 33% 15% 4 1	220
	21st to end	Day	27% 18% 25% 24% 5% 1	242
January	1st to 10th	Night	20% 12% 29% 33% 6% 1	892
	11th to 20th	Night	19% 12% 33% 29% 7% 1	840
	21st to end	Night	12% 10% 32% 37% 9% 1	924
February	1st to 10th	Night	13% 13% 35% 30% 9% 1	840
	11th to 20th	Night	17% 14% 35% 27% 6% 1	823
	21st to end	Night	18% 13% 31% 32% 6% 1	692
March	1st to 10th	Night	18% 16% 33% 27% 5% 1	840
	11th to 20th	Night	21% 15% 34% 22% 7% 1	840
	21st to end	Night	20% 18% 28% 26% 6% 1	924
April	1st to 10th	Night	29% 13% 31% 22% 4 1	840
	11th to 20th	Night	23% 14% 34% 22% 7%	665
	21st to end	Night	28% 14% 26% 24% 7%	630
May	1st to 10th	Night	25% 12% 29% 28% 5%	620
	11th to 20th	Night	25% 10% 27% 26% 11%	414
	21st to end	Night	24% 14% 30% 23% 9%	455
June	1st to 10th	Night	20% 9% 24% 37% 10% 1	420
	11th to 20th	Night	19% 8% 22% 34% 16% 2	420
	21st to end	Night	22% 8% 24% 34% 12%	420
July	1st to 10th	Night	17% 6% 26% 40% 10%	410
	11th to 20th	Night	14% 4 26% 42% 13% 1	408
	21st to end	Night	15% 5% 23% 44% 13% 1	460
August	1st to 10th	Night	16% 3 19% 44% 17% 1	440
	11th to 20th	Night	16% 5% 20% 38% 20% 2	605
	21st to end	Night	14% 9% 24% 34% 17% 1	690
September	1st to 10th	Night	17% 8% 25% 36% 14% 1	800
	11th to 20th	Night	21% 8% 21% 31% 16% 3	800
	21st to end	Night	19% 9% 25% 32% 14% 1	800
October	1st to 10th	Night	21% 12% 23% 32% 10% 1	800
	11th to 20th	Night	25% 9% 26% 28% 11% 1	800
	21st to end	Night	24% 13% 27% 26% 9%	880
November	1st to 10th	Night	24% 15% 26% 27% 7% 1	820
	11th to 20th	Night	24% 15% 27% 26% 7% 1	900
	21st to end	Night	24% 16% 25% 27% 7% 1	950
December	1st to 10th	Night	22% 13% 30% 26% 7% 1	950
	11th to 20th	Night	23% 16% 28% 25% 7%	950
	21st to end	Night	24% 14% 28% 25% 8% 1	1045

Page generated at 2026-08-12 03:37:19. Version ac07

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