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 2024-03-08.

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	18% 9% 4 7% 6% 4 5% 5% 5% 7% 31%	78134
	Night	19% 11% 4 7% 6% 3 5% 4 5% 6% 30%	81426
Transparency	Day	52% 8% 13% 18% 8% 1	77839
	Night	56% 6% 12% 17% 9% 1	81256
Seeing	Day	23% 14% 29% 22% 10% 2	14297
	Night	24% 11% 29% 27% 8% 1	22976

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% 6% 12% 6% 4 4 4 4 6% 22%	2517
	11th to 20th	Day	10% 14% 8% 12% 9% 4 5% 4 4 4 27%	2520
	21st to end	Day	10% 12% 5% 9% 6% 3 5% 5% 5% 7% 33%	2772
February	1st to 10th	Day	11% 14% 6% 11% 7% 5% 5% 6% 5% 6% 26%	1524
	11th to 20th	Day	14% 13% 6% 10% 6% 3 5% 4 5% 6% 28%	1829
	21st to end	Day	13% 14% 6% 8% 7% 4 4 5% 5% 6% 28%	1570
March	1st to 10th	Day	15% 11% 4 8% 6% 3 4 4 5% 6% 33%	1867
	11th to 20th	Day	16% 11% 5% 7% 6% 4 4 4 5% 5% 33%	1891
	21st to end	Day	15% 10% 3 7% 6% 3 5% 6% 5% 6% 33%	2304
April	1st to 10th	Day	22% 10% 3 7% 6% 4 5% 4 5% 6% 29%	2160
	11th to 20th	Day	20% 6% 2 6% 5% 4 4 3 4 6% 40%	2226
	21st to end	Day	24% 8% 3 6% 6% 3 4 4 4 6% 32%	2340
May	1st to 10th	Day	22% 7% 2 5% 6% 3 5% 4 5% 7% 34%	2384
	11th to 20th	Day	19% 7% 3 6% 6% 4 6% 6% 5% 7% 33%	2478
	21st to end	Day	20% 6% 3 6% 6% 4 5% 5% 5% 7% 33%	2765
June	1st to 10th	Day	20% 6% 3 6% 6% 4 6% 7% 7% 8% 28%	2700
	11th to 20th	Day	19% 6% 2 6% 5% 4 5% 5% 6% 8% 34%	2700
	21st to end	Day	22% 7% 4 7% 6% 4 5% 5% 6% 7% 27%	2700
July	1st to 10th	Day	14% 6% 3 6% 6% 3 6% 6% 7% 10% 32%	2571
	11th to 20th	Day	15% 6% 3 6% 6% 4 6% 6% 8% 9% 32%	2520
	21st to end	Day	14% 7% 3 6% 5% 4 6% 6% 6% 9% 33%	2744
August	1st to 10th	Day	17% 5% 2 5% 7% 4 7% 7% 6% 9% 29%	2489
	11th to 20th	Day	15% 6% 2 5% 6% 4 5% 4 6% 9% 37%	2304
	21st to end	Day	17% 6% 2 6% 5% 4 5% 5% 6% 8% 38%	2475
September	1st to 10th	Day	17% 7% 3 6% 5% 3 4 5% 6% 9% 37%	2160
	11th to 20th	Day	18% 5% 2 4 4 2 4 4 4 7% 46%	1996
	21st to end	Day	21% 6% 2 5% 4 3 4 4 5% 6% 39%	1980
October	1st to 10th	Day	20% 7% 3 6% 6% 3 5% 5% 5% 8% 33%	1980
	11th to 20th	Day	24% 7% 3 7% 7% 4 5% 5% 7% 7% 24%	1648
	21st to end	Day	28% 10% 4 7% 4 3 4 5% 5% 6% 24%	1782
November	1st to 10th	Day	19% 9% 5% 7% 6% 3 4 5% 4 6% 31%	1671
	11th to 20th	Day	23% 12% 3 8% 6% 3 5% 4 5% 5% 25%	1710
	21st to end	Day	23% 15% 5% 7% 6% 3 4 5% 5% 5% 23%	1362
December	1st to 10th	Day	23% 18% 4 7% 6% 4 5% 4 6% 4 20%	1330
	11th to 20th	Day	21% 14% 4 7% 8% 3 4 3 5% 4 26%	1668
	21st to end	Day	22% 17% 4 7% 6% 3 4 3 4 4 25%	2497
January	1st to 10th	Night	15% 19% 6% 12% 8% 3 4 4 3 4 22%	4429
	11th to 20th	Night	12% 15% 5% 11% 8% 4 5% 4 5% 5% 24%	4440
	21st to end	Night	11% 13% 5% 9% 8% 4 6% 5% 6% 6% 25%	4884
February	1st to 10th	Night	12% 12% 5% 10% 9% 4 5% 4 5% 5% 26%	2656
	11th to 20th	Night	13% 16% 6% 10% 7% 4 4 4 4 6% 26%	2235
	21st to end	Night	15% 13% 4 9% 6% 3 5% 4 5% 5% 30%	1884
March	1st to 10th	Night	16% 12% 5% 8% 6% 3 5% 5% 4 6% 30%	2241
	11th to 20th	Night	18% 12% 4 7% 6% 4 5% 4 5% 5% 30%	2066
	21st to end	Night	18% 11% 4 6% 5% 3 5% 4 3 6% 35%	2050
April	1st to 10th	Night	23% 12% 4 7% 5% 3 4 4 5% 5% 27%	1800
	11th to 20th	Night	20% 7% 3 5% 6% 3 4 5% 5% 8% 35%	1683
	21st to end	Night	24% 9% 4 6% 5% 2 3 3 4 5% 34%	1620
May	1st to 10th	Night	24% 8% 3 5% 5% 3 6% 4 5% 5% 32%	1590
	11th to 20th	Night	23% 6% 3 5% 6% 3 4 5% 4 6% 36%	1415
	21st to end	Night	22% 6% 3 5% 5% 3 4 4 5% 6% 37%	1509
June	1st to 10th	Night	22% 7% 3 5% 6% 4 6% 5% 6% 8% 28%	1260
	11th to 20th	Night	19% 6% 3 6% 5% 3 5% 5% 5% 7% 36%	1260
	21st to end	Night	22% 9% 4 6% 5% 3 5% 4 4 7% 31%	1260
July	1st to 10th	Night	17% 7% 3 4 5% 3 4 6% 6% 9% 36%	1385
	11th to 20th	Night	17% 6% 3 6% 5% 3 6% 5% 6% 8% 35%	1440
	21st to end	Night	15% 7% 3 6% 5% 4 5% 6% 7% 9% 34%	1574
August	1st to 10th	Night	16% 4 2 5% 5% 3 6% 5% 6% 9% 38%	1432
	11th to 20th	Night	16% 7% 4 7% 5% 4 5% 6% 6% 7% 34%	1594
	21st to end	Night	16% 5% 2 6% 5% 3 6% 5% 5% 7% 40%	1879
September	1st to 10th	Night	18% 5% 3 5% 6% 3 5% 4 5% 7% 39%	1800
	11th to 20th	Night	18% 6% 2 4 5% 3 3 4 4 6% 44%	1963
	21st to end	Night	20% 6% 3 5% 4 3 4 4 5% 5% 41%	1980
October	1st to 10th	Night	19% 7% 3 5% 5% 4 4 5% 5% 7% 36%	1980
	11th to 20th	Night	26% 8% 3 6% 5% 4 4 5% 5% 4 30%	2310
	21st to end	Night	25% 10% 3 7% 5% 3 4 4 5% 6% 28%	2574
November	1st to 10th	Night	19% 10% 4 7% 6% 4 4 4 5% 6% 32%	2407
	11th to 20th	Night	20% 10% 4 8% 6% 3 5% 4 4 6% 32%	2470
	21st to end	Night	22% 14% 5% 7% 6% 3 5% 4 5% 5% 25%	2812
December	1st to 10th	Night	24% 15% 5% 9% 7% 4 5% 5% 4 4 19%	2850
	11th to 20th	Night	20% 14% 5% 9% 7% 4 4 4 4 5% 25%	3531
	21st to end	Night	24% 19% 4 8% 5% 2 3 3 3 4 24%	5163

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	63% 7% 13% 12% 4	2518
	11th to 20th	Day	62% 7% 10% 16% 5% 1	2520
	21st to end	Day	49% 9% 12% 21% 9%	2772
February	1st to 10th	Day	59% 6% 11% 14% 9% 2	1524
	11th to 20th	Day	59% 5% 11% 13% 10% 1	1838
	21st to end	Day	56% 5% 12% 17% 8% 2	1570
March	1st to 10th	Day	53% 6% 12% 16% 12% 2	1870
	11th to 20th	Day	53% 6% 10% 16% 13% 2	1891
	21st to end	Day	51% 6% 12% 18% 11% 3	2304
April	1st to 10th	Day	57% 5% 12% 13% 9% 3	2160
	11th to 20th	Day	47% 5% 11% 23% 12% 2	2226
	21st to end	Day	54% 6% 10% 16% 12% 2	2340
May	1st to 10th	Day	49% 8% 12% 16% 14% 2	2384
	11th to 20th	Day	49% 9% 10% 20% 11% 1	2482
	21st to end	Day	51% 9% 10% 18% 11% 1	2765
June	1st to 10th	Day	51% 10% 12% 18% 8% 1	2700
	11th to 20th	Day	47% 8% 14% 19% 10% 1	2700
	21st to end	Day	56% 9% 11% 16% 9%	2700
July	1st to 10th	Day	45% 11% 17% 21% 6%	2501
	11th to 20th	Day	44% 11% 16% 22% 7%	2445
	21st to end	Day	47% 11% 16% 19% 6%	2591
August	1st to 10th	Day	47% 12% 19% 19% 3	2475
	11th to 20th	Day	43% 9% 18% 21% 8%	2304
	21st to end	Day	43% 10% 14% 24% 9%	2475
September	1st to 10th	Day	43% 8% 17% 22% 10%	2160
	11th to 20th	Day	38% 6% 18% 27% 10%	1996
	21st to end	Day	44% 7% 14% 26% 8%	1980
October	1st to 10th	Day	49% 8% 12% 24% 8%	1980
	11th to 20th	Day	58% 7% 16% 15% 3	1648
	21st to end	Day	61% 8% 11% 15% 5% 1	1782
November	1st to 10th	Day	54% 7% 14% 18% 8%	1671
	11th to 20th	Day	60% 5% 11% 17% 6% 1	1710
	21st to end	Day	63% 6% 13% 12% 5% 1	1362
December	1st to 10th	Day	66% 7% 11% 12% 4	1330
	11th to 20th	Day	61% 5% 9% 18% 7%	1668
	21st to end	Day	63% 6% 12% 11% 6% 2	2497
January	1st to 10th	Night	68% 5% 11% 11% 5%	4429
	11th to 20th	Night	63% 5% 11% 16% 4	4440
	21st to end	Night	57% 7% 12% 16% 8% 1	4884
February	1st to 10th	Night	59% 5% 11% 16% 9% 1	2656
	11th to 20th	Night	60% 6% 11% 13% 9% 1	2237
	21st to end	Night	57% 4 9% 16% 12% 1	1884
March	1st to 10th	Night	56% 6% 10% 15% 11% 2	2251
	11th to 20th	Night	56% 5% 10% 15% 11% 3	2067
	21st to end	Night	52% 6% 10% 17% 11% 4	2050
April	1st to 10th	Night	59% 4 10% 13% 12% 3	1800
	11th to 20th	Night	48% 6% 11% 20% 13% 2	1683
	21st to end	Night	55% 5% 8% 15% 14% 2	1620
May	1st to 10th	Night	53% 7% 10% 14% 14% 2	1590
	11th to 20th	Night	50% 6% 10% 18% 15% 1	1416
	21st to end	Night	49% 7% 10% 18% 15% 1	1510
June	1st to 10th	Night	53% 8% 13% 17% 9% 1	1260
	11th to 20th	Night	48% 7% 11% 20% 11% 3	1260
	21st to end	Night	54% 7% 12% 17% 10%	1260
July	1st to 10th	Night	44% 10% 17% 20% 9%	1345
	11th to 20th	Night	45% 9% 16% 22% 7% 1	1392
	21st to end	Night	47% 10% 16% 19% 8%	1486
August	1st to 10th	Night	39% 11% 18% 27% 4	1422
	11th to 20th	Night	48% 10% 17% 18% 6%	1594
	21st to end	Night	42% 8% 14% 28% 9%	1879
September	1st to 10th	Night	45% 7% 14% 22% 11% 1	1800
	11th to 20th	Night	42% 8% 17% 26% 8%	1963
	21st to end	Night	44% 7% 11% 26% 12%	1980
October	1st to 10th	Night	46% 7% 11% 24% 11% 1	1980
	11th to 20th	Night	56% 7% 13% 19% 5%	2310
	21st to end	Night	57% 7% 13% 15% 8%	2574
November	1st to 10th	Night	53% 7% 14% 18% 6% 1	2407
	11th to 20th	Night	55% 7% 13% 16% 9%	2470
	21st to end	Night	63% 5% 12% 13% 6% 1	2812
December	1st to 10th	Night	68% 5% 11% 11% 4	2850
	11th to 20th	Night	62% 5% 10% 14% 8%	3532
	21st to end	Night	65% 4 9% 15% 6% 1	5163

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	26% 19% 31% 18% 4 2	180
	11th to 20th	Day	29% 21% 34% 12% 4	180
	21st to end	Day	15% 21% 37% 23% 3 1	198
February	1st to 10th	Day	24% 23% 34% 15% 3 1	184
	11th to 20th	Day	22% 19% 38% 18% 2	447
	21st to end	Day	21% 21% 30% 21% 5% 1	382
March	1st to 10th	Day	24% 18% 31% 20% 6% 1	448
	11th to 20th	Day	25% 17% 33% 17% 7% 2	420
	21st to end	Day	22% 16% 25% 23% 12% 2	462
April	1st to 10th	Day	29% 14% 28% 20% 9% 1	420
	11th to 20th	Day	26% 12% 29% 24% 8% 2	412
	21st to end	Day	28% 15% 31% 19% 6% 2	420
May	1st to 10th	Day	27% 14% 33% 20% 6% 1	423
	11th to 20th	Day	20% 14% 30% 26% 8% 2	447
	21st to end	Day	22% 19% 31% 18% 8% 1	525
June	1st to 10th	Day	23% 13% 28% 27% 9%	630
	11th to 20th	Day	23% 10% 27% 26% 13% 1	630
	21st to end	Day	25% 9% 27% 25% 13% 1	630
July	1st to 10th	Day	19% 11% 29% 27% 13% 1	496
	11th to 20th	Day	17% 10% 32% 27% 12% 2	444
	21st to end	Day	16% 9% 35% 25% 13% 2	488
August	1st to 10th	Day	18% 8% 28% 26% 15% 4	446
	11th to 20th	Day	17% 6% 28% 29% 16% 4	439
	21st to end	Day	22% 12% 24% 20% 16% 7%	495
September	1st to 10th	Day	20% 10% 26% 27% 13% 4	450
	11th to 20th	Day	20% 12% 26% 21% 16% 4	450
	21st to end	Day	21% 14% 23% 21% 15% 6%	450
October	1st to 10th	Day	22% 11% 29% 24% 10% 3	450
	11th to 20th	Day	27% 15% 27% 19% 10% 1	372
	21st to end	Day	36% 14% 29% 15% 7% 1	396
November	1st to 10th	Day	29% 15% 27% 22% 7% 1	365
	11th to 20th	Day	30% 16% 27% 19% 8% 1	370
	21st to end	Day	31% 17% 28% 20% 3 1	190
December	1st to 10th	Day	32% 14% 23% 22% 6% 3	180
	11th to 20th	Day	29% 18% 27% 20% 4 1	180
	21st to end	Day	33% 19% 30% 13% 5% 1	198
January	1st to 10th	Night	26% 17% 31% 22% 3	760
	11th to 20th	Night	25% 15% 32% 23% 4	760
	21st to end	Night	16% 14% 35% 28% 6% 1	836
February	1st to 10th	Night	21% 12% 33% 27% 6%	760
	11th to 20th	Night	22% 15% 39% 20% 4 1	743
	21st to end	Night	24% 13% 32% 27% 4	628
March	1st to 10th	Night	22% 13% 34% 26% 5%	751
	11th to 20th	Night	25% 13% 33% 23% 6% 1	720
	21st to end	Night	24% 9% 31% 28% 7% 1	792
April	1st to 10th	Night	30% 13% 25% 26% 6%	720
	11th to 20th	Night	25% 8% 36% 25% 6%	619
	21st to end	Night	29% 11% 29% 24% 7%	540
May	1st to 10th	Night	26% 9% 30% 28% 6%	510
	11th to 20th	Night	25% 8% 28% 31% 7%	354
	21st to end	Night	27% 6% 29% 30% 7%	389
June	1st to 10th	Night	25% 7% 27% 34% 6%	360
	11th to 20th	Night	21% 4 26% 37% 12%	360
	21st to end	Night	24% 7% 24% 35% 9% 1	360
July	1st to 10th	Night	19% 4 29% 36% 11% 1	350
	11th to 20th	Night	18% 2 23% 41% 15% 1	348
	21st to end	Night	16% 5% 19% 46% 13%	394
August	1st to 10th	Night	18% 4 15% 45% 17%	358
	11th to 20th	Night	17% 5% 22% 39% 15% 2	530
	21st to end	Night	18% 5% 26% 31% 18% 2	691
September	1st to 10th	Night	21% 5% 24% 33% 16% 1	720
	11th to 20th	Night	22% 7% 24% 31% 15% 1	720
	21st to end	Night	22% 8% 24% 29% 15% 1	720
October	1st to 10th	Night	22% 9% 28% 33% 8% 1	720
	11th to 20th	Night	29% 11% 25% 26% 9% 1	720
	21st to end	Night	30% 11% 32% 21% 5%	792
November	1st to 10th	Night	27% 13% 25% 25% 9%	740
	11th to 20th	Night	26% 15% 24% 26% 8% 1	760
	21st to end	Night	30% 14% 30% 19% 6% 1	838
December	1st to 10th	Night	32% 12% 29% 19% 7% 1	850
	11th to 20th	Night	26% 18% 29% 20% 6% 1	850
	21st to end	Night	33% 16% 28% 18% 4	913

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