Observatoire du CEGEP de Lévis-Lauzon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire du CEGEP de Lévis-Lauzon clear sky chart from 2005-11-06 to 2025-05-11.

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	17% 10% 3 8% 5% 5% 5% 4 6% 7% 31%	113225
	Night	18% 12% 4 9% 5% 5% 4 3 5% 6% 28%	115732
Transparency	Day	53% 6% 14% 18% 9% 1	116728
	Night	57% 5% 12% 17% 8% 1	120394
Seeing	Day	24% 14% 29% 22% 10% 2	15844
	Night	25% 11% 29% 27% 8% 1	24474

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	17% 20% 6% 13% 5% 4 3 2 3 4 23%	3597
	11th to 20th	Day	9% 15% 8% 15% 7% 6% 4 3 4 4 24%	3570
	21st to end	Day	7% 12% 5% 12% 6% 5% 4 4 5% 7% 33%	3960
February	1st to 10th	Day	11% 14% 5% 12% 6% 6% 5% 4 5% 5% 26%	1605
	11th to 20th	Day	14% 15% 5% 11% 4 5% 5% 3 6% 6% 27%	1928
	21st to end	Day	12% 15% 5% 10% 6% 5% 4 4 5% 6% 28%	1650
March	1st to 10th	Day	21% 14% 5% 9% 6% 5% 4 3 4 4 26%	4476
	11th to 20th	Day	14% 13% 4 8% 5% 5% 5% 4 6% 6% 30%	4765
	21st to end	Day	17% 14% 4 8% 4 4 4 3 4 5% 34%	5786
April	1st to 10th	Day	21% 11% 3 8% 5% 4 4 3 5% 6% 30%	2400
	11th to 20th	Day	20% 7% 3 6% 4 5% 4 3 4 6% 38%	2477
	21st to end	Day	24% 8% 2 8% 5% 4 3 3 5% 6% 32%	2600
May	1st to 10th	Day	22% 7% 2 6% 5% 4 4 3 5% 6% 35%	4325
	11th to 20th	Day	17% 7% 2 7% 5% 5% 5% 5% 6% 9% 31%	4398
	21st to end	Day	17% 7% 3 8% 6% 5% 6% 5% 7% 7% 31%	4919
June	1st to 10th	Day	19% 7% 3 7% 5% 5% 6% 5% 8% 8% 28%	2850
	11th to 20th	Day	18% 6% 2 6% 4 5% 5% 4 6% 8% 34%	2850
	21st to end	Day	22% 8% 3 7% 6% 5% 5% 4 6% 7% 27%	2850
July	1st to 10th	Day	14% 8% 3 8% 5% 5% 5% 5% 7% 8% 31%	4519
	11th to 20th	Day	16% 6% 3 7% 5% 5% 5% 5% 8% 9% 32%	4440
	21st to end	Day	13% 6% 2 5% 4 4 5% 4 6% 8% 41%	4814
August	1st to 10th	Day	15% 5% 2 6% 6% 5% 7% 6% 7% 10% 31%	4393
	11th to 20th	Day	20% 6% 3 7% 5% 6% 5% 4 6% 9% 29%	4045
	21st to end	Day	20% 6% 2 6% 4 4 4 4 5% 7% 38%	4349
September	1st to 10th	Day	16% 7% 2 6% 4 4 4 4 6% 9% 38%	2280
	11th to 20th	Day	17% 6% 2 4 3 3 4 3 4 7% 47%	2106
	21st to end	Day	21% 6% 2 6% 4 4 4 3 5% 7% 38%	2090
October	1st to 10th	Day	20% 8% 3 8% 5% 4 4 4 6% 7% 32%	2090
	11th to 20th	Day	23% 8% 3 8% 6% 5% 6% 4 6% 7% 25%	1739
	21st to end	Day	27% 11% 4 8% 4 5% 4 4 5% 6% 25%	1881
November	1st to 10th	Day	19% 11% 4 8% 6% 4 5% 3 4 6% 31%	1761
	11th to 20th	Day	22% 13% 3 9% 5% 4 4 4 5% 5% 27%	1800
	21st to end	Day	23% 16% 4 9% 5% 4 4 4 5% 5% 22%	1433
December	1st to 10th	Day	18% 17% 4 9% 5% 6% 5% 4 6% 5% 20%	2280
	11th to 20th	Day	19% 14% 4 10% 6% 5% 4 3 5% 4 26%	2618
	21st to end	Day	20% 16% 4 9% 5% 5% 4 4 5% 4 24%	3581
January	1st to 10th	Night	16% 22% 6% 13% 6% 4 3 3 2 3 21%	6349
	11th to 20th	Night	11% 20% 7% 15% 7% 6% 4 3 4 4 19%	6315
	21st to end	Night	8% 12% 5% 13% 6% 6% 6% 4 6% 7% 27%	6996
February	1st to 10th	Night	12% 13% 5% 12% 8% 5% 4 4 5% 5% 27%	2795
	11th to 20th	Night	13% 18% 4 11% 6% 5% 4 3 5% 5% 26%	2355
	21st to end	Night	15% 15% 4 10% 5% 4 4 3 5% 5% 30%	1980
March	1st to 10th	Night	23% 14% 4 9% 5% 4 5% 3 4 5% 25%	5364
	11th to 20th	Night	15% 14% 3 9% 6% 6% 5% 4 6% 7% 24%	5192
	21st to end	Night	19% 15% 5% 8% 4 4 3 3 3 4 31%	5130
April	1st to 10th	Night	22% 13% 3 8% 4 4 4 3 5% 5% 29%	2000
	11th to 20th	Night	21% 8% 3 7% 5% 4 4 3 5% 8% 33%	1872
	21st to end	Night	24% 9% 4 6% 4 3 3 3 4 5% 35%	1800
May	1st to 10th	Night	22% 7% 3 6% 5% 4 5% 4 5% 6% 33%	2864
	11th to 20th	Night	23% 8% 3 7% 5% 4 4 4 4 6% 32%	2501
	21st to end	Night	18% 5% 3 6% 4 5% 5% 3 6% 8% 36%	2658
June	1st to 10th	Night	21% 8% 3 6% 5% 5% 5% 4 6% 8% 28%	1330
	11th to 20th	Night	18% 6% 3 7% 5% 4 5% 4 5% 7% 36%	1330
	21st to end	Night	22% 11% 3 7% 4 5% 5% 3 4 6% 29%	1330
July	1st to 10th	Night	15% 8% 3 6% 6% 5% 6% 5% 7% 8% 31%	2426
	11th to 20th	Night	21% 7% 2 7% 5% 4 5% 4 6% 7% 34%	2520
	21st to end	Night	14% 5% 2 7% 4 4 5% 4 6% 8% 41%	2739
August	1st to 10th	Night	19% 8% 3 7% 4 5% 4 4 5% 8% 34%	2506
	11th to 20th	Night	18% 8% 3 7% 5% 5% 6% 4 5% 8% 30%	2780
	21st to end	Night	20% 7% 2 8% 5% 5% 5% 4 5% 6% 34%	3305
September	1st to 10th	Night	18% 6% 3 6% 5% 4 4 3 5% 7% 39%	1900
	11th to 20th	Night	17% 6% 2 5% 4 3 4 3 4 6% 45%	2073
	21st to end	Night	20% 6% 3 6% 4 4 4 3 4 5% 40%	2090
October	1st to 10th	Night	19% 8% 3 7% 4 5% 4 4 5% 7% 36%	2090
	11th to 20th	Night	25% 9% 3 7% 4 5% 5% 3 5% 4 31%	2439
	21st to end	Night	24% 10% 3 8% 4 4 4 3 5% 6% 29%	2717
November	1st to 10th	Night	19% 11% 3 7% 5% 5% 4 3 5% 5% 32%	2537
	11th to 20th	Night	19% 10% 3 8% 5% 4 5% 4 4 5% 32%	2600
	21st to end	Night	22% 16% 4 8% 5% 5% 4 3 5% 4 24%	2961
December	1st to 10th	Night	18% 16% 6% 12% 8% 6% 5% 3 5% 5% 17%	4910
	11th to 20th	Night	22% 14% 4 10% 6% 5% 4 3 5% 5% 22%	5591
	21st to end	Night	21% 18% 4 9% 4 4 4 4 5% 4 23%	7387

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	66% 5% 9% 13% 7%	3598
	11th to 20th	Day	64% 5% 9% 16% 5% 1	3600
	21st to end	Day	50% 6% 9% 19% 16%	3960
February	1st to 10th	Day	59% 6% 11% 14% 10% 2	1605
	11th to 20th	Day	60% 5% 12% 13% 9% 1	1937
	21st to end	Day	56% 4 11% 18% 9% 2	1650
March	1st to 10th	Day	61% 5% 9% 11% 11% 3	4479
	11th to 20th	Day	54% 5% 16% 16% 9% 1	4765
	21st to end	Day	54% 4 8% 18% 14% 3	5786
April	1st to 10th	Day	56% 5% 11% 14% 11% 3	2400
	11th to 20th	Day	49% 5% 10% 23% 12% 2	2477
	21st to end	Day	54% 6% 10% 17% 12% 2	2600
May	1st to 10th	Day	48% 6% 14% 16% 14% 1	4339
	11th to 20th	Day	46% 10% 20% 17% 6% 1	4402
	21st to end	Day	48% 9% 12% 18% 13% 1	4919
June	1st to 10th	Day	50% 10% 12% 19% 7% 1	2850
	11th to 20th	Day	46% 8% 15% 19% 10% 1	2850
	21st to end	Day	56% 8% 11% 16% 9%	2850
July	1st to 10th	Day	49% 6% 15% 23% 6%	4449
	11th to 20th	Day	47% 6% 20% 22% 4	4365
	21st to end	Day	41% 8% 19% 25% 8%	4661
August	1st to 10th	Day	47% 7% 20% 20% 5%	4379
	11th to 20th	Day	52% 6% 20% 16% 5%	4084
	21st to end	Day	47% 6% 15% 19% 12% 1	4349
September	1st to 10th	Day	42% 8% 17% 23% 10%	2280
	11th to 20th	Day	37% 6% 18% 28% 10%	2106
	21st to end	Day	45% 7% 14% 26% 8%	2090
October	1st to 10th	Day	54% 5% 10% 25% 5%	3480
	11th to 20th	Day	54% 4 18% 22% 2	2864
	21st to end	Day	53% 5% 17% 17% 7%	3081
November	1st to 10th	Day	55% 6% 13% 18% 7%	1761
	11th to 20th	Day	60% 5% 11% 18% 7% 1	1800
	21st to end	Day	64% 6% 12% 12% 5%	1433
December	1st to 10th	Day	65% 4 13% 12% 7%	2280
	11th to 20th	Day	61% 4 10% 14% 11%	2618
	21st to end	Day	64% 5% 9% 13% 8% 2	3581
January	1st to 10th	Night	71% 3 9% 11% 6%	6349
	11th to 20th	Night	69% 4 9% 14% 3	6360
	21st to end	Night	56% 5% 9% 17% 12%	6996
February	1st to 10th	Night	59% 5% 10% 15% 9% 1	2795
	11th to 20th	Night	60% 6% 11% 13% 9% 1	2357
	21st to end	Night	57% 4 9% 16% 12% 1	1980
March	1st to 10th	Night	63% 4 8% 11% 12% 1	5374
	11th to 20th	Night	60% 5% 13% 13% 7% 2	5193
	21st to end	Night	59% 3 6% 20% 10% 2	5130
April	1st to 10th	Night	58% 4 9% 14% 13% 2	2000
	11th to 20th	Night	50% 6% 11% 19% 12% 2	1872
	21st to end	Night	54% 5% 8% 16% 14% 2	1800
May	1st to 10th	Night	51% 6% 13% 17% 11% 1	2870
	11th to 20th	Night	49% 9% 14% 16% 11% 1	2502
	21st to end	Night	45% 7% 14% 18% 16% 1	2659
June	1st to 10th	Night	53% 8% 13% 18% 9% 1	1330
	11th to 20th	Night	48% 7% 12% 19% 11% 3	1330
	21st to end	Night	56% 7% 11% 16% 10%	1330
July	1st to 10th	Night	49% 5% 19% 20% 6%	2386
	11th to 20th	Night	50% 5% 20% 21% 4	2472
	21st to end	Night	43% 6% 21% 23% 7%	2651
August	1st to 10th	Night	49% 7% 15% 24% 5%	2496
	11th to 20th	Night	53% 8% 17% 16% 5%	2807
	21st to end	Night	50% 5% 12% 21% 12%	3305
September	1st to 10th	Night	45% 7% 13% 23% 12% 1	1900
	11th to 20th	Night	41% 7% 16% 27% 8%	2073
	21st to end	Night	45% 6% 11% 25% 12%	2090
October	1st to 10th	Night	51% 4 11% 27% 7%	3480
	11th to 20th	Night	55% 4 14% 24% 3	4053
	21st to end	Night	53% 4 18% 16% 10%	4467
November	1st to 10th	Night	53% 7% 14% 19% 6% 1	2537
	11th to 20th	Night	55% 6% 13% 17% 9%	2600
	21st to end	Night	65% 5% 11% 13% 6% 1	2961
December	1st to 10th	Night	70% 3 11% 12% 3	4910
	11th to 20th	Night	65% 3 7% 17% 7%	5592
	21st to end	Night	65% 3 8% 16% 7% 1	7387

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	29% 20% 29% 18% 4 2	200
	11th to 20th	Day	28% 20% 34% 13% 5% 2	200
	21st to end	Day	15% 20% 37% 23% 4 1	220
February	1st to 10th	Day	24% 21% 36% 15% 3	205
	11th to 20th	Day	24% 19% 38% 17% 2	486
	21st to end	Day	21% 21% 31% 21% 5%	414
March	1st to 10th	Day	25% 17% 31% 19% 6% 1	500
	11th to 20th	Day	24% 17% 34% 17% 7% 2	500
	21st to end	Day	24% 16% 27% 21% 11% 1	550
April	1st to 10th	Day	30% 15% 29% 18% 8% 1	500
	11th to 20th	Day	28% 13% 29% 22% 7% 2	492
	21st to end	Day	28% 17% 30% 18% 6% 1	500
May	1st to 10th	Day	28% 14% 33% 19% 5% 1	503
	11th to 20th	Day	20% 13% 29% 26% 9% 2	487
	21st to end	Day	22% 19% 32% 18% 8% 1	572
June	1st to 10th	Day	23% 14% 28% 26% 9% 1	680
	11th to 20th	Day	23% 9% 28% 26% 14% 1	680
	21st to end	Day	26% 9% 28% 24% 12% 1	680
July	1st to 10th	Day	19% 11% 29% 27% 12% 1	538
	11th to 20th	Day	17% 10% 33% 26% 12% 2	484
	21st to end	Day	16% 8% 34% 26% 13% 3	532
August	1st to 10th	Day	18% 9% 29% 25% 15% 4	486
	11th to 20th	Day	18% 6% 27% 28% 16% 5%	479
	21st to end	Day	22% 11% 23% 21% 17% 7%	539
September	1st to 10th	Day	19% 11% 27% 27% 13% 3	490
	11th to 20th	Day	18% 11% 25% 24% 17% 4	490
	21st to end	Day	22% 13% 24% 21% 15% 6%	490
October	1st to 10th	Day	23% 11% 29% 24% 10% 3	490
	11th to 20th	Day	27% 15% 28% 18% 9% 2	403
	21st to end	Day	36% 13% 28% 16% 7%	429
November	1st to 10th	Day	30% 15% 26% 22% 7% 1	395
	11th to 20th	Day	30% 15% 28% 19% 7% 1	400
	21st to end	Day	32% 16% 30% 18% 3	210
December	1st to 10th	Day	32% 13% 25% 23% 6% 3	200
	11th to 20th	Day	29% 19% 27% 20% 5% 2	200
	21st to end	Day	32% 17% 30% 15% 4 1	220
January	1st to 10th	Night	26% 17% 31% 22% 3	800
	11th to 20th	Night	25% 15% 31% 24% 5%	800
	21st to end	Night	16% 14% 35% 29% 6% 1	880
February	1st to 10th	Night	20% 13% 34% 27% 6%	800
	11th to 20th	Night	23% 15% 39% 19% 3 1	783
	21st to end	Night	25% 12% 31% 27% 4	660
March	1st to 10th	Night	22% 12% 34% 27% 5%	800
	11th to 20th	Night	24% 13% 33% 23% 6% 1	800
	21st to end	Night	25% 9% 31% 27% 6% 1	880
April	1st to 10th	Night	29% 14% 27% 25% 6%	800
	11th to 20th	Night	26% 8% 35% 24% 6%	688
	21st to end	Night	30% 11% 29% 24% 6%	600
May	1st to 10th	Night	25% 9% 32% 28% 6%	566
	11th to 20th	Night	24% 9% 27% 32% 8%	376
	21st to end	Night	27% 6% 29% 31% 7%	411
June	1st to 10th	Night	24% 7% 27% 34% 6% 1	380
	11th to 20th	Night	20% 4 26% 37% 13%	380
	21st to end	Night	24% 7% 24% 35% 9% 1	380
July	1st to 10th	Night	18% 4 29% 37% 11% 1	370
	11th to 20th	Night	19% 2 22% 41% 14% 1	368
	21st to end	Night	16% 5% 19% 46% 14%	416
August	1st to 10th	Night	19% 4 16% 44% 17%	378
	11th to 20th	Night	17% 6% 22% 39% 15% 2	560
	21st to end	Night	19% 5% 25% 31% 18% 2	730
September	1st to 10th	Night	21% 5% 24% 33% 16% 1	760
	11th to 20th	Night	21% 6% 23% 32% 16% 2	760
	21st to end	Night	22% 8% 24% 29% 15% 1	760
October	1st to 10th	Night	23% 8% 27% 32% 9% 1	760
	11th to 20th	Night	29% 11% 25% 26% 9% 1	760
	21st to end	Night	29% 11% 32% 22% 5%	836
November	1st to 10th	Night	28% 13% 25% 25% 8%	780
	11th to 20th	Night	25% 14% 24% 27% 8% 1	800
	21st to end	Night	32% 14% 30% 19% 6% 1	887
December	1st to 10th	Night	31% 12% 29% 20% 7% 1	900
	11th to 20th	Night	27% 18% 28% 20% 6% 1	900
	21st to end	Night	32% 15% 28% 19% 4 1	965

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