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 2026-09-14.

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%	149117
	Night	18% 12% 4 9% 5% 5% 4 4 5% 6% 28%	141984
Transparency	Day	53% 5% 13% 20% 9% 1	152574
	Night	57% 4 12% 18% 9% 1	146617
Seeing	Day	24% 13% 29% 22% 9% 2	17673
	Night	24% 10% 29% 28% 8% 1	26048

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% 5% 12% 5% 4 3 3 4 5% 28%	4661
	11th to 20th	Day	11% 17% 8% 15% 7% 6% 5% 3 4 4 21%	4650
	21st to end	Day	6% 12% 5% 10% 5% 4 5% 5% 7% 8% 32%	5124
February	1st to 10th	Day	10% 14% 5% 12% 6% 6% 5% 4 5% 6% 27%	1685
	11th to 20th	Day	13% 14% 5% 11% 4 4 5% 3 6% 6% 28%	2027
	21st to end	Day	12% 14% 5% 10% 6% 5% 4 4 5% 6% 28%	1730
March	1st to 10th	Day	20% 14% 4 9% 6% 5% 4 3 4 4 26%	4576
	11th to 20th	Day	15% 13% 4 8% 5% 5% 5% 4 6% 6% 30%	4870
	21st to end	Day	17% 14% 4 8% 4 4 4 3 4 5% 33%	5914
April	1st to 10th	Day	21% 12% 3 8% 5% 4 4 3 5% 6% 29%	2520
	11th to 20th	Day	21% 7% 3 6% 4 5% 4 3 4 6% 37%	2602
	21st to end	Day	23% 8% 2 8% 5% 4 3 3 5% 6% 32%	2730
May	1st to 10th	Day	25% 9% 3 7% 5% 4 4 3 5% 6% 28%	7807
	11th to 20th	Day	20% 7% 2 7% 5% 5% 5% 4 6% 8% 31%	8221
	21st to end	Day	20% 8% 3 7% 5% 5% 6% 4 6% 7% 29%	9198
June	1st to 10th	Day	19% 6% 3 7% 5% 6% 6% 5% 8% 8% 28%	3150
	11th to 20th	Day	19% 6% 2 6% 5% 5% 5% 4 6% 8% 33%	3150
	21st to end	Day	22% 8% 3 7% 6% 5% 5% 4 6% 7% 27%	3150
July	1st to 10th	Day	15% 7% 3 7% 5% 5% 5% 4 7% 9% 33%	8443
	11th to 20th	Day	14% 6% 3 7% 4 4 5% 5% 7% 9% 35%	8280
	21st to end	Day	11% 6% 2 6% 5% 5% 6% 4 7% 9% 39%	8993
August	1st to 10th	Day	15% 6% 2 7% 5% 5% 6% 5% 7% 10% 33%	6438
	11th to 20th	Day	18% 7% 3 7% 5% 6% 5% 4 7% 9% 28%	5953
	21st to end	Day	18% 6% 2 6% 4 4 4 4 6% 8% 38%	6321
September	1st to 10th	Day	16% 7% 2 6% 4 4 4 4 6% 9% 37%	2520
	11th to 20th	Day	17% 5% 2 4 3 3 4 3 4 7% 48%	2251
	21st to end	Day	20% 7% 2 6% 4 4 4 3 5% 6% 38%	2200
October	1st to 10th	Day	19% 7% 3 7% 5% 4 4 4 6% 8% 34%	2200
	11th to 20th	Day	23% 7% 3 8% 6% 5% 6% 4 6% 7% 25%	1830
	21st to end	Day	26% 11% 4 8% 4 4 4 4 5% 6% 24%	1980
November	1st to 10th	Day	19% 12% 3 8% 6% 4 5% 3 4 6% 30%	1851
	11th to 20th	Day	22% 14% 3 9% 5% 4 3 4 5% 5% 26%	1890
	21st to end	Day	23% 15% 4 10% 5% 4 4 4 4 5% 22%	1504
December	1st to 10th	Day	18% 17% 4 9% 5% 6% 5% 4 6% 6% 20%	2350
	11th to 20th	Day	19% 14% 5% 10% 6% 5% 4 3 5% 4 26%	2688
	21st to end	Day	20% 16% 4 9% 5% 5% 4 4 4 4 24%	3660
January	1st to 10th	Night	14% 19% 6% 14% 6% 5% 4 3 3 4 22%	8234
	11th to 20th	Night	12% 23% 7% 15% 7% 5% 4 3 4 4 16%	8235
	21st to end	Night	6% 12% 6% 14% 7% 6% 5% 5% 7% 8% 25%	9057
February	1st to 10th	Night	11% 13% 5% 12% 8% 5% 4 4 5% 5% 28%	2934
	11th to 20th	Night	13% 18% 4 11% 6% 5% 4 3 5% 6% 27%	2476
	21st to end	Night	15% 14% 4 11% 5% 4 4 3 5% 5% 31%	2076
March	1st to 10th	Night	23% 14% 4 9% 5% 4 5% 3 4 5% 25%	5484
	11th to 20th	Night	16% 14% 4 9% 6% 6% 5% 4 6% 7% 24%	5307
	21st to end	Night	19% 16% 5% 9% 5% 4 3 3 3 4 30%	5244
April	1st to 10th	Night	23% 13% 3 8% 4 4 4 3 5% 4 28%	2100
	11th to 20th	Night	21% 8% 3 7% 5% 4 4 3 4 7% 33%	1967
	21st to end	Night	24% 9% 4 6% 4 3 3 3 4 5% 35%	1890
May	1st to 10th	Night	24% 8% 3 8% 5% 4 5% 4 5% 6% 29%	5146
	11th to 20th	Night	24% 7% 3 7% 5% 4 4 4 5% 6% 30%	4639
	21st to end	Night	20% 7% 3 7% 4 5% 5% 3 5% 6% 34%	4969
June	1st to 10th	Night	21% 8% 3 6% 5% 5% 5% 4 5% 8% 30%	1470
	11th to 20th	Night	19% 7% 3 7% 5% 4 5% 4 5% 7% 34%	1470
	21st to end	Night	21% 10% 3 7% 4 5% 5% 3 5% 7% 30%	1470
July	1st to 10th	Night	17% 8% 3 6% 5% 5% 5% 4 7% 8% 33%	4508
	11th to 20th	Night	19% 6% 2 6% 5% 4 5% 4 6% 7% 37%	4680
	21st to end	Night	12% 6% 2 8% 5% 5% 5% 4 6% 8% 38%	5084
August	1st to 10th	Night	20% 8% 3 7% 4 4 5% 4 5% 8% 32%	3666
	11th to 20th	Night	17% 8% 3 7% 4 5% 6% 4 6% 8% 33%	4090
	21st to end	Night	21% 7% 2 7% 5% 4 5% 4 5% 5% 35%	4788
September	1st to 10th	Night	18% 6% 3 6% 5% 4 4 3 5% 7% 39%	2100
	11th to 20th	Night	16% 6% 2 5% 4 3 4 4 5% 6% 45%	2215
	21st to end	Night	20% 6% 3 6% 4 4 4 3 5% 5% 41%	2200
October	1st to 10th	Night	18% 7% 3 6% 3 5% 4 4 5% 7% 37%	2200
	11th to 20th	Night	24% 8% 3 7% 4 5% 5% 3 5% 4 31%	2568
	21st to end	Night	24% 10% 3 8% 4 4 4 3 5% 6% 29%	2860
November	1st to 10th	Night	20% 11% 3 7% 5% 5% 3 3 5% 5% 31%	2667
	11th to 20th	Night	19% 11% 4 9% 5% 4 5% 4 4 5% 31%	2730
	21st to end	Night	22% 16% 4 8% 6% 5% 4 3 5% 4 23%	3110
December	1st to 10th	Night	17% 16% 6% 12% 7% 6% 5% 4 5% 5% 17%	5060
	11th to 20th	Night	22% 14% 4 10% 6% 5% 4 3 5% 5% 22%	5741
	21st to end	Night	21% 18% 5% 9% 4 4 4 4 5% 4 23%	7549

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	61% 4 10% 17% 9%	4662
	11th to 20th	Day	68% 4 7% 15% 6% 1	4680
	21st to end	Day	48% 5% 11% 21% 15%	5124
February	1st to 10th	Day	58% 5% 10% 15% 9% 2	1685
	11th to 20th	Day	59% 5% 11% 15% 10% 1	2036
	21st to end	Day	56% 4 11% 18% 9% 2	1730
March	1st to 10th	Day	61% 5% 9% 11% 11% 3	4579
	11th to 20th	Day	54% 5% 15% 16% 9% 1	4870
	21st to end	Day	55% 4 7% 17% 14% 3	5914
April	1st to 10th	Day	57% 5% 11% 15% 10% 3	2520
	11th to 20th	Day	49% 4 10% 22% 12% 2	2602
	21st to end	Day	53% 5% 10% 18% 12% 2	2730
May	1st to 10th	Day	56% 4 10% 17% 12% 1	7819
	11th to 20th	Day	51% 6% 15% 20% 6% 2	8225
	21st to end	Day	53% 5% 11% 18% 10% 2	9199
June	1st to 10th	Day	50% 9% 12% 20% 8% 1	3150
	11th to 20th	Day	47% 7% 14% 20% 10% 1	3150
	21st to end	Day	56% 7% 11% 16% 9%	3150
July	1st to 10th	Day	48% 4 14% 25% 9%	8373
	11th to 20th	Day	46% 4 16% 27% 7%	8205
	21st to end	Day	43% 5% 19% 26% 7%	8795
August	1st to 10th	Day	47% 6% 19% 20% 7% 1	6424
	11th to 20th	Day	52% 4 20% 19% 5%	5992
	21st to end	Day	46% 4 16% 24% 9%	6321
September	1st to 10th	Day	42% 7% 17% 24% 10%	2520
	11th to 20th	Day	36% 6% 18% 29% 10%	2251
	21st to end	Day	45% 7% 14% 26% 9%	2200
October	1st to 10th	Day	53% 5% 10% 26% 5%	3590
	11th to 20th	Day	54% 4 18% 22% 2	2955
	21st to end	Day	54% 5% 17% 17% 7%	3180
November	1st to 10th	Day	56% 6% 13% 18% 7%	1851
	11th to 20th	Day	61% 4 10% 17% 7% 1	1890
	21st to end	Day	65% 5% 12% 12% 5%	1504
December	1st to 10th	Day	65% 4 13% 12% 7%	2350
	11th to 20th	Day	61% 4 10% 14% 11%	2688
	21st to end	Day	64% 5% 9% 13% 8% 2	3660
January	1st to 10th	Night	68% 3 9% 13% 7%	8234
	11th to 20th	Night	73% 3 7% 12% 4	8280
	21st to end	Night	57% 4 10% 16% 12%	9057
February	1st to 10th	Night	57% 5% 10% 17% 9% 1	2934
	11th to 20th	Night	60% 6% 11% 14% 9% 1	2478
	21st to end	Night	57% 4 9% 17% 12% 1	2076
March	1st to 10th	Night	63% 4 8% 11% 12% 2	5494
	11th to 20th	Night	61% 5% 13% 13% 7% 2	5308
	21st to end	Night	60% 3 6% 20% 10% 2	5244
April	1st to 10th	Night	58% 4 9% 14% 13% 2	2100
	11th to 20th	Night	51% 5% 10% 19% 12% 2	1967
	21st to end	Night	54% 5% 8% 17% 15% 2	1890
May	1st to 10th	Night	56% 4 11% 16% 12% 1	5152
	11th to 20th	Night	54% 5% 11% 20% 10%	4640
	21st to end	Night	51% 4 11% 16% 16% 2	4970
June	1st to 10th	Night	52% 7% 12% 19% 10% 1	1470
	11th to 20th	Night	49% 7% 11% 20% 11% 3	1470
	21st to end	Night	55% 6% 12% 16% 10%	1470
July	1st to 10th	Night	49% 3 17% 20% 11%	4468
	11th to 20th	Night	48% 3 18% 25% 6%	4632
	21st to end	Night	47% 4 18% 25% 7%	4967
August	1st to 10th	Night	52% 5% 16% 21% 6%	3656
	11th to 20th	Night	50% 6% 19% 20% 4	4117
	21st to end	Night	50% 3 14% 22% 11%	4788
September	1st to 10th	Night	45% 6% 14% 23% 11% 1	2100
	11th to 20th	Night	40% 7% 16% 28% 8%	2215
	21st to end	Night	45% 6% 11% 25% 13%	2200
October	1st to 10th	Night	50% 4 11% 27% 7%	3590
	11th to 20th	Night	55% 4 14% 24% 3	4182
	21st to end	Night	53% 4 17% 16% 10%	4610
November	1st to 10th	Night	55% 7% 14% 19% 6% 1	2667
	11th to 20th	Night	56% 6% 12% 17% 9%	2730
	21st to end	Night	65% 5% 11% 12% 6% 1	3110
December	1st to 10th	Night	70% 3 11% 12% 4	5060
	11th to 20th	Night	66% 3 7% 17% 7%	5742
	21st to end	Night	65% 3 8% 16% 7% 1	7549

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% 19% 31% 18% 4 1	220
	11th to 20th	Day	30% 21% 31% 13% 4 1	220
	21st to end	Day	15% 21% 36% 23% 4 1	242
February	1st to 10th	Day	22% 21% 35% 17% 5%	225
	11th to 20th	Day	24% 18% 38% 18% 2	525
	21st to end	Day	20% 21% 33% 21% 5%	446
March	1st to 10th	Day	25% 19% 31% 18% 6% 1	540
	11th to 20th	Day	25% 17% 34% 16% 6% 1	540
	21st to end	Day	24% 17% 27% 20% 10% 1	594
April	1st to 10th	Day	30% 15% 29% 18% 8% 1	540
	11th to 20th	Day	28% 13% 29% 21% 7% 2	532
	21st to end	Day	27% 16% 30% 19% 6% 2	540
May	1st to 10th	Day	29% 14% 32% 18% 6% 1	543
	11th to 20th	Day	21% 14% 30% 24% 9% 2	567
	21st to end	Day	23% 19% 31% 19% 8% 1	664
June	1st to 10th	Day	22% 12% 28% 28% 9% 1	780
	11th to 20th	Day	24% 9% 28% 26% 13% 1	780
	21st to end	Day	26% 9% 28% 25% 12% 1	780
July	1st to 10th	Day	19% 11% 31% 26% 12% 1	624
	11th to 20th	Day	18% 10% 34% 25% 11% 2	564
	21st to end	Day	15% 9% 33% 26% 13% 4	620
August	1st to 10th	Day	17% 8% 29% 26% 15% 5%	566
	11th to 20th	Day	18% 5% 27% 28% 17% 5%	559
	21st to end	Day	22% 10% 23% 22% 16% 7%	627
September	1st to 10th	Day	19% 11% 27% 27% 13% 3	570
	11th to 20th	Day	17% 11% 25% 24% 17% 5%	542
	21st to end	Day	22% 13% 24% 22% 14% 6%	530
October	1st to 10th	Day	22% 11% 29% 24% 10% 3	530
	11th to 20th	Day	26% 15% 29% 20% 9% 2	434
	21st to end	Day	35% 12% 29% 16% 7% 1	462
November	1st to 10th	Day	30% 15% 27% 21% 6%	425
	11th to 20th	Day	30% 15% 28% 18% 7% 1	430
	21st to end	Day	32% 17% 30% 18% 3	230
December	1st to 10th	Day	30% 14% 27% 22% 6% 2	220
	11th to 20th	Day	30% 19% 26% 20% 4 1	220
	21st to end	Day	31% 18% 31% 16% 4 1	242
January	1st to 10th	Night	25% 16% 31% 23% 3	840
	11th to 20th	Night	25% 14% 32% 23% 5%	840
	21st to end	Night	15% 14% 34% 29% 6% 1	924
February	1st to 10th	Night	20% 12% 33% 28% 7%	840
	11th to 20th	Night	23% 14% 38% 20% 4 1	823
	21st to end	Night	24% 13% 31% 28% 5%	692
March	1st to 10th	Night	22% 13% 35% 26% 5%	840
	11th to 20th	Night	25% 13% 33% 23% 6% 1	840
	21st to end	Night	24% 10% 32% 27% 6% 1	924
April	1st to 10th	Night	30% 13% 27% 24% 5%	840
	11th to 20th	Night	26% 8% 36% 24% 5%	723
	21st to end	Night	29% 10% 30% 24% 7%	630
May	1st to 10th	Night	26% 9% 32% 28% 6%	594
	11th to 20th	Night	25% 8% 29% 31% 8%	414
	21st to end	Night	28% 5% 28% 31% 7%	455
June	1st to 10th	Night	24% 7% 26% 35% 7%	420
	11th to 20th	Night	21% 4 25% 37% 13%	420
	21st to end	Night	24% 6% 23% 37% 10%	420
July	1st to 10th	Night	19% 4 29% 37% 11% 1	410
	11th to 20th	Night	19% 2 23% 41% 14% 1	408
	21st to end	Night	16% 5% 19% 46% 14%	460
August	1st to 10th	Night	18% 4 16% 45% 16%	418
	11th to 20th	Night	16% 5% 22% 40% 16% 1	620
	21st to end	Night	19% 5% 25% 32% 18% 2	807
September	1st to 10th	Night	21% 5% 24% 34% 15% 1	840
	11th to 20th	Night	20% 6% 23% 32% 18% 1	813
	21st to end	Night	22% 7% 25% 30% 15% 1	800
October	1st to 10th	Night	22% 8% 27% 33% 9% 1	800
	11th to 20th	Night	27% 11% 25% 28% 9% 1	800
	21st to end	Night	30% 11% 31% 23% 6%	880
November	1st to 10th	Night	29% 13% 25% 24% 8%	820
	11th to 20th	Night	26% 14% 24% 27% 8% 1	840
	21st to end	Night	31% 14% 30% 19% 6% 1	936
December	1st to 10th	Night	30% 12% 28% 21% 7% 1	950
	11th to 20th	Night	27% 18% 29% 20% 6% 1	950
	21st to end	Night	32% 15% 29% 20% 4	1017

Page generated at 2026-09-11 04:11:54. Version ac07

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