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 2025-04-11.

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	15% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	112929
	Night	15% 11% 4 9% 5% 5% 5% 4 5% 6% 31%	115418
Transparency	Day	29% 44% 9% 11% 6% 1	116411
	Night	32% 42% 8% 12% 6%	120101
Seeing	Day	22% 17% 30% 21% 8% 2	16021
	Night	21% 12% 27% 30% 9% 1	24439

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	18% 20% 4 9% 5% 4 4 3 5% 5% 23%	3377
	11th to 20th	Day	8% 12% 6% 14% 8% 6% 6% 5% 7% 7% 23%	3570
	21st to end	Day	5% 6% 3 9% 7% 6% 7% 6% 7% 9% 34%	3960
February	1st to 10th	Day	7% 11% 4 8% 9% 8% 7% 5% 6% 6% 27%	1633
	11th to 20th	Day	10% 13% 5% 12% 7% 5% 5% 4 6% 5% 28%	1861
	21st to end	Day	11% 10% 3 8% 7% 6% 6% 4 6% 6% 32%	1650
March	1st to 10th	Day	19% 12% 4 10% 5% 4 4 4 4 5% 28%	4476
	11th to 20th	Day	12% 12% 4 9% 6% 6% 6% 4 6% 7% 28%	4842
	21st to end	Day	14% 15% 4 9% 5% 4 3 3 5% 5% 32%	5683
April	1st to 10th	Day	19% 12% 4 7% 5% 5% 5% 4 5% 6% 28%	2400
	11th to 20th	Day	16% 8% 2 7% 5% 5% 4 3 5% 6% 38%	2404
	21st to end	Day	21% 10% 3 6% 4 4 4 3 5% 7% 33%	2470
May	1st to 10th	Day	15% 9% 3 8% 6% 5% 5% 4 5% 6% 35%	4156
	11th to 20th	Day	18% 7% 2 6% 4 4 5% 4 6% 8% 35%	4398
	21st to end	Day	16% 6% 3 8% 5% 5% 5% 4 6% 8% 33%	5172
June	1st to 10th	Day	19% 8% 2 7% 5% 5% 5% 4 6% 7% 31%	2850
	11th to 20th	Day	16% 5% 3 7% 4 6% 5% 4 6% 7% 37%	2850
	21st to end	Day	20% 8% 3 7% 6% 5% 5% 5% 6% 7% 30%	2850
July	1st to 10th	Day	12% 5% 3 7% 5% 5% 6% 5% 8% 9% 35%	4760
	11th to 20th	Day	11% 6% 2 7% 5% 6% 6% 5% 7% 9% 36%	4486
	21st to end	Day	11% 6% 2 5% 5% 5% 5% 4 7% 9% 41%	4814
August	1st to 10th	Day	11% 5% 2 7% 6% 6% 6% 5% 8% 9% 33%	4345
	11th to 20th	Day	14% 6% 3 7% 6% 4 6% 4 8% 9% 33%	4045
	21st to end	Day	17% 5% 2 6% 4 4 4 4 5% 7% 43%	4476
September	1st to 10th	Day	13% 6% 2 6% 5% 5% 5% 3 6% 8% 42%	2265
	11th to 20th	Day	13% 5% 2 6% 4 3 4 3 5% 7% 48%	2090
	21st to end	Day	16% 6% 2 6% 3 4 4 3 5% 9% 41%	2090
October	1st to 10th	Day	16% 5% 2 8% 5% 4 5% 3 6% 7% 37%	2066
	11th to 20th	Day	20% 7% 3 8% 4 4 5% 4 6% 6% 31%	1755
	21st to end	Day	23% 10% 3 8% 4 5% 4 3 5% 6% 29%	1881
November	1st to 10th	Day	15% 10% 3 9% 7% 4 5% 4 6% 5% 32%	1761
	11th to 20th	Day	17% 9% 4 9% 6% 5% 5% 4 5% 7% 27%	1691
	21st to end	Day	19% 14% 5% 9% 6% 5% 4 3 4 5% 26%	1428
December	1st to 10th	Day	15% 13% 5% 11% 6% 4 5% 3 4 5% 29%	2280
	11th to 20th	Day	17% 9% 4 7% 5% 4 5% 4 6% 6% 33%	2618
	21st to end	Day	17% 11% 4 9% 5% 5% 5% 4 8% 4 29%	3476
January	1st to 10th	Night	17% 19% 5% 11% 7% 5% 4 3 4 5% 21%	6560
	11th to 20th	Night	8% 15% 8% 17% 7% 6% 5% 3 5% 6% 22%	6315
	21st to end	Night	4 9% 4 10% 7% 7% 6% 4 7% 8% 33%	6996
February	1st to 10th	Night	7% 12% 4 10% 6% 6% 5% 4 7% 6% 33%	2766
	11th to 20th	Night	9% 14% 5% 13% 7% 5% 5% 4 5% 5% 27%	2424
	21st to end	Night	12% 11% 4 10% 5% 4 5% 4 5% 7% 32%	1980
March	1st to 10th	Night	19% 12% 4 9% 5% 4 5% 4 5% 6% 26%	5364
	11th to 20th	Night	12% 13% 4 11% 7% 6% 5% 4 6% 6% 25%	5117
	21st to end	Night	18% 16% 4 8% 4 4 4 3 4 5% 31%	5248
April	1st to 10th	Night	20% 13% 4 8% 5% 3 4 4 4 4 32%	2000
	11th to 20th	Night	18% 8% 3 8% 5% 4 4 3 5% 6% 34%	1732
	21st to end	Night	24% 9% 3 6% 3 3 4 4 5% 4 35%	1710
May	1st to 10th	Night	18% 8% 2 7% 4 4 4 4 5% 6% 36%	2812
	11th to 20th	Night	19% 10% 3 7% 5% 5% 5% 3 6% 6% 32%	2495
	21st to end	Night	17% 6% 2 6% 4 4 5% 5% 7% 9% 35%	2414
June	1st to 10th	Night	19% 8% 3 7% 6% 4 4 4 5% 6% 33%	1330
	11th to 20th	Night	15% 6% 2 5% 5% 4 5% 3 6% 8% 40%	1330
	21st to end	Night	21% 8% 3 8% 5% 4 5% 5% 5% 6% 31%	1330
July	1st to 10th	Night	11% 7% 3 8% 4 5% 5% 5% 7% 9% 37%	2210
	11th to 20th	Night	14% 6% 2 7% 5% 5% 5% 4 7% 8% 38%	2471
	21st to end	Night	10% 5% 2 6% 4 4 4 4 7% 10% 45%	2739
August	1st to 10th	Night	15% 6% 2 7% 5% 5% 5% 4 6% 8% 36%	2552
	11th to 20th	Night	14% 5% 3 9% 6% 7% 6% 6% 7% 8% 29%	2782
	21st to end	Night	17% 6% 3 6% 4 4 4 4 4 6% 42%	3178
September	1st to 10th	Night	14% 5% 2 5% 5% 4 4 4 5% 8% 43%	1914
	11th to 20th	Night	17% 6% 2 6% 4 5% 4 3 5% 5% 43%	2090
	21st to end	Night	16% 7% 2 7% 4 4 4 4 4 5% 44%	2090
October	1st to 10th	Night	16% 8% 3 7% 5% 3 5% 4 4 5% 41%	2114
	11th to 20th	Night	22% 8% 2 6% 4 4 4 4 5% 5% 35%	2422
	21st to end	Night	20% 9% 3 7% 5% 4 4 3 5% 6% 33%	2717
November	1st to 10th	Night	16% 9% 4 7% 5% 4 4 4 5% 7% 34%	2537
	11th to 20th	Night	19% 10% 3 7% 4 5% 4 4 5% 7% 31%	2706
	21st to end	Night	17% 14% 4 9% 6% 5% 5% 4 5% 5% 27%	2970
December	1st to 10th	Night	12% 14% 7% 12% 6% 5% 5% 4 5% 6% 26%	4910
	11th to 20th	Night	20% 11% 3 8% 5% 5% 5% 4 5% 6% 28%	5591
	21st to end	Night	16% 15% 4 8% 5% 5% 5% 5% 6% 5% 25%	7502

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	46% 30% 8% 13% 3	3378
	11th to 20th	Day	41% 32% 7% 14% 5% 1	3600
	21st to end	Day	30% 34% 8% 12% 16%	3960
February	1st to 10th	Day	19% 63% 4 8% 4 2	1633
	11th to 20th	Day	22% 62% 5% 7% 4	1869
	21st to end	Day	18% 63% 4 9% 4 2	1650
March	1st to 10th	Day	42% 32% 8% 7% 9% 4	4479
	11th to 20th	Day	39% 33% 13% 9% 4 1	4842
	21st to end	Day	40% 30% 5% 12% 10% 4	5683
April	1st to 10th	Day	20% 62% 3 7% 6% 2	2400
	11th to 20th	Day	18% 67% 5% 8% 2 1	2404
	21st to end	Day	20% 66% 3 6% 4 1	2470
May	1st to 10th	Day	29% 44% 10% 10% 7%	4170
	11th to 20th	Day	28% 43% 12% 14% 3	4402
	21st to end	Day	29% 45% 7% 12% 7%	5172
June	1st to 10th	Day	16% 66% 4 9% 4	2850
	11th to 20th	Day	15% 66% 7% 7% 4	2850
	21st to end	Day	17% 64% 5% 9% 3	2850
July	1st to 10th	Day	28% 39% 13% 15% 6%	4685
	11th to 20th	Day	26% 39% 19% 14% 2	4409
	21st to end	Day	24% 39% 13% 18% 6%	4661
August	1st to 10th	Day	26% 42% 15% 13% 4	4331
	11th to 20th	Day	32% 41% 15% 11% 2	4084
	21st to end	Day	26% 39% 15% 11% 9%	4476
September	1st to 10th	Day	15% 61% 10% 11% 4	2265
	11th to 20th	Day	15% 61% 9% 11% 4 1	2090
	21st to end	Day	16% 60% 6% 13% 5%	2090
October	1st to 10th	Day	35% 40% 10% 13% 3	3430
	11th to 20th	Day	26% 40% 12% 19% 3	2893
	21st to end	Day	28% 38% 16% 12% 6%	3081
November	1st to 10th	Day	24% 58% 8% 7% 3	1761
	11th to 20th	Day	24% 59% 5% 9% 3	1691
	21st to end	Day	28% 58% 5% 6% 2	1428
December	1st to 10th	Day	35% 37% 8% 12% 8%	2280
	11th to 20th	Day	35% 36% 7% 13% 9%	2618
	21st to end	Day	38% 29% 10% 14% 8% 2	3476
January	1st to 10th	Night	46% 31% 9% 9% 4	6560
	11th to 20th	Night	47% 32% 7% 9% 4	6360
	21st to end	Night	30% 34% 7% 15% 14% 1	6996
February	1st to 10th	Night	19% 62% 4 8% 6% 1	2766
	11th to 20th	Night	23% 61% 3 8% 5%	2427
	21st to end	Night	20% 62% 2 8% 7% 1	1980
March	1st to 10th	Night	44% 32% 5% 7% 11% 1	5374
	11th to 20th	Night	40% 33% 12% 9% 3 2	5118
	21st to end	Night	42% 30% 4 13% 10% 1	5248
April	1st to 10th	Night	20% 62% 2 7% 7% 2	2000
	11th to 20th	Night	20% 65% 3 8% 4	1732
	21st to end	Night	23% 65% 2 5% 4 1	1710
May	1st to 10th	Night	27% 44% 9% 12% 7%	2818
	11th to 20th	Night	30% 44% 9% 11% 5%	2496
	21st to end	Night	24% 44% 8% 16% 7%	2415
June	1st to 10th	Night	19% 66% 3 10% 2	1330
	11th to 20th	Night	15% 66% 6% 7% 5% 1	1330
	21st to end	Night	19% 64% 5% 8% 4	1330
July	1st to 10th	Night	29% 38% 14% 17% 2	2175
	11th to 20th	Night	27% 38% 17% 16% 2	2425
	21st to end	Night	20% 38% 19% 15% 8%	2651
August	1st to 10th	Night	31% 40% 12% 13% 4	2542
	11th to 20th	Night	34% 43% 13% 6% 4	2809
	21st to end	Night	26% 39% 8% 18% 8%	3178
September	1st to 10th	Night	15% 62% 6% 11% 5%	1914
	11th to 20th	Night	19% 61% 7% 9% 3	2090
	21st to end	Night	15% 61% 5% 13% 6% 1	2090
October	1st to 10th	Night	32% 38% 7% 18% 4	3530
	11th to 20th	Night	26% 38% 11% 20% 4	4023
	21st to end	Night	27% 39% 13% 12% 8%	4467
November	1st to 10th	Night	26% 57% 6% 8% 4	2537
	11th to 20th	Night	24% 60% 4 8% 4	2706
	21st to end	Night	29% 59% 4 4 3	2970
December	1st to 10th	Night	36% 38% 7% 14% 5%	4910
	11th to 20th	Night	39% 35% 4 14% 6% 1	5592
	21st to end	Night	40% 30% 9% 13% 8% 1	7502

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	22% 16% 35% 21% 6% 1	200
	11th to 20th	Day	26% 14% 35% 18% 7% 2	200
	21st to end	Day	15% 20% 39% 15% 9% 1	220
February	1st to 10th	Day	16% 25% 36% 16% 6%	233
	11th to 20th	Day	17% 21% 37% 19% 5%	451
	21st to end	Day	20% 21% 34% 19% 4 1	414
March	1st to 10th	Day	25% 20% 29% 20% 6%	500
	11th to 20th	Day	22% 21% 30% 20% 7% 1	500
	21st to end	Day	25% 24% 28% 15% 7% 1	550
April	1st to 10th	Day	28% 23% 29% 16% 4 1	500
	11th to 20th	Day	27% 19% 30% 16% 7% 1	452
	21st to end	Day	28% 17% 36% 14% 4 2	460
May	1st to 10th	Day	26% 19% 30% 17% 6% 2	463
	11th to 20th	Day	22% 22% 27% 22% 5% 1	487
	21st to end	Day	23% 19% 32% 19% 5% 1	721
June	1st to 10th	Day	26% 17% 27% 21% 8% 1	680
	11th to 20th	Day	23% 17% 24% 24% 10% 1	680
	21st to end	Day	24% 11% 30% 24% 9% 2	680
July	1st to 10th	Day	19% 13% 32% 25% 10% 2	670
	11th to 20th	Day	17% 12% 35% 27% 8% 2	515
	21st to end	Day	16% 10% 34% 30% 9% 2	532
August	1st to 10th	Day	17% 14% 28% 26% 13% 3	486
	11th to 20th	Day	16% 13% 29% 27% 12% 3	479
	21st to end	Day	17% 16% 30% 19% 14% 4	539
September	1st to 10th	Day	17% 15% 32% 24% 8% 4	490
	11th to 20th	Day	19% 12% 31% 22% 11% 4	490
	21st to end	Day	21% 14% 29% 20% 12% 4	490
October	1st to 10th	Day	20% 20% 25% 22% 10% 2	477
	11th to 20th	Day	26% 17% 29% 17% 10% 1	390
	21st to end	Day	34% 15% 28% 16% 7%	429
November	1st to 10th	Day	27% 17% 27% 22% 5% 1	395
	11th to 20th	Day	25% 14% 27% 23% 10% 1	400
	21st to end	Day	32% 21% 29% 15% 1	228
December	1st to 10th	Day	23% 20% 28% 17% 11% 3	200
	11th to 20th	Day	27% 21% 32% 15% 5% 2	200
	21st to end	Day	29% 18% 22% 25% 5% 1	220
January	1st to 10th	Night	21% 12% 28% 32% 6% 1	847
	11th to 20th	Night	19% 12% 33% 29% 7% 1	800
	21st to end	Night	12% 10% 31% 38% 9% 1	880
February	1st to 10th	Night	13% 14% 36% 29% 8% 1	800
	11th to 20th	Night	18% 15% 35% 26% 6% 1	783
	21st to end	Night	19% 13% 30% 32% 6% 1	660
March	1st to 10th	Night	18% 15% 32% 28% 5% 1	800
	11th to 20th	Night	21% 15% 35% 22% 7% 1	800
	21st to end	Night	21% 18% 27% 26% 6%	880
April	1st to 10th	Night	29% 13% 31% 23% 5% 1	800
	11th to 20th	Night	23% 14% 32% 22% 8%	604
	21st to end	Night	29% 14% 27% 23% 7% 1	570
May	1st to 10th	Night	25% 11% 29% 28% 6% 1	561
	11th to 20th	Night	26% 9% 25% 27% 12% 1	374
	21st to end	Night	25% 14% 28% 23% 9%	411
June	1st to 10th	Night	21% 9% 23% 36% 10% 1	380
	11th to 20th	Night	18% 7% 21% 34% 17% 2	380
	21st to end	Night	23% 8% 23% 33% 12% 1	380
July	1st to 10th	Night	17% 6% 26% 40% 11% 1	370
	11th to 20th	Night	15% 3 23% 44% 13% 1	368
	21st to end	Night	15% 5% 21% 45% 14% 1	416
August	1st to 10th	Night	16% 4 19% 44% 17% 1	398
	11th to 20th	Night	17% 5% 20% 36% 20% 2	562
	21st to end	Night	14% 9% 23% 35% 17% 1	655
September	1st to 10th	Night	17% 8% 24% 35% 14% 1	760
	11th to 20th	Night	22% 8% 21% 31% 16% 3	760
	21st to end	Night	20% 9% 23% 32% 15% 1	760
October	1st to 10th	Night	22% 13% 22% 32% 11% 1	760
	11th to 20th	Night	26% 9% 26% 27% 11% 1	760
	21st to end	Night	24% 14% 28% 26% 9%	836
November	1st to 10th	Night	23% 15% 27% 27% 7% 1	780
	11th to 20th	Night	24% 15% 27% 26% 7% 1	854
	21st to end	Night	25% 16% 25% 28% 7% 1	900
December	1st to 10th	Night	23% 13% 29% 27% 7% 1	900
	11th to 20th	Night	23% 16% 27% 26% 8%	900
	21st to end	Night	24% 14% 28% 25% 8% 1	990

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