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 2024-11-02.

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% 3 8% 5% 5% 5% 4 6% 7% 31%	101375
	Night	19% 12% 4 8% 5% 4 4 3 5% 6% 30%	97590
Transparency	Day	51% 7% 14% 18% 8% 1	101133
	Night	56% 6% 12% 17% 8% 1	97453
Seeing	Day	23% 14% 29% 22% 10% 2	15267
	Night	24% 11% 29% 27% 8% 1	23703

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	14% 18% 6% 13% 5% 5% 4 3 5% 5% 22%	2517
	11th to 20th	Day	10% 14% 8% 14% 7% 5% 4 3 4 4 27%	2520
	21st to end	Day	10% 12% 5% 10% 5% 4 5% 4 5% 7% 33%	2772
February	1st to 10th	Day	11% 15% 5% 12% 6% 6% 5% 4 5% 6% 26%	1524
	11th to 20th	Day	14% 14% 5% 11% 5% 5% 5% 3 6% 6% 28%	1829
	21st to end	Day	12% 15% 5% 10% 6% 5% 4 4 5% 6% 28%	1570
March	1st to 10th	Day	19% 11% 4 9% 6% 4 4 3 4 5% 30%	3116
	11th to 20th	Day	15% 17% 4 9% 5% 4 4 3 6% 5% 27%	3335
	21st to end	Day	14% 13% 3 8% 5% 4 4 4 4 5% 37%	4038
April	1st to 10th	Day	21% 12% 3 8% 6% 4 4 3 5% 6% 29%	2280
	11th to 20th	Day	20% 7% 2 6% 4 5% 4 3 4 6% 38%	2352
	21st to end	Day	24% 8% 3 8% 5% 4 3 3 5% 6% 32%	2470
May	1st to 10th	Day	21% 7% 2 6% 5% 4 4 3 5% 6% 36%	4192
	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% 10% 4 8% 4 5% 4 4 5% 6% 24%	1881
November	1st to 10th	Day	19% 11% 3 8% 6% 4 5% 3 4 6% 31%	1680
	11th to 20th	Day	23% 13% 3 9% 5% 4 4 4 5% 5% 25%	1710
	21st to end	Day	23% 16% 4 9% 5% 4 4 4 5% 5% 23%	1362
December	1st to 10th	Day	22% 19% 4 8% 5% 6% 4 3 6% 4 20%	1330
	11th to 20th	Day	20% 15% 4 9% 7% 4 4 2 5% 4 26%	1668
	21st to end	Day	22% 17% 4 9% 5% 5% 3 3 4 4 25%	2497
January	1st to 10th	Night	15% 20% 6% 14% 6% 4 4 3 3 4 22%	4429
	11th to 20th	Night	12% 16% 5% 13% 7% 6% 4 4 5% 5% 23%	4440
	21st to end	Night	11% 14% 5% 11% 7% 6% 5% 4 6% 6% 25%	4884
February	1st to 10th	Night	12% 13% 5% 12% 8% 5% 4 4 5% 6% 26%	2656
	11th to 20th	Night	13% 18% 4 11% 6% 5% 4 3 5% 5% 26%	2235
	21st to end	Night	15% 14% 4 10% 5% 4 4 4 5% 5% 30%	1884
March	1st to 10th	Night	24% 12% 4 7% 4 3 5% 3 4 5% 28%	3724
	11th to 20th	Night	17% 17% 4 10% 6% 5% 4 3 5% 5% 23%	3622
	21st to end	Night	17% 15% 5% 8% 5% 4 3 3 3 4 32%	3578
April	1st to 10th	Night	22% 13% 3 8% 4 4 4 4 5% 5% 29%	1900
	11th to 20th	Night	21% 8% 3 6% 5% 4 4 3 5% 8% 33%	1777
	21st to end	Night	24% 9% 4 6% 4 3 3 3 4 5% 34%	1710
May	1st to 10th	Night	22% 7% 3 6% 5% 4 5% 4 5% 6% 33%	2776
	11th to 20th	Night	23% 8% 3 7% 5% 4 4 4 4 6% 32%	2495
	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% 6% 32%	2421
	11th to 20th	Night	20% 11% 3 8% 5% 4 5% 4 4 5% 31%	2470
	21st to end	Night	22% 15% 4 7% 5% 5% 4 3 5% 5% 25%	2812
December	1st to 10th	Night	23% 16% 4 10% 6% 5% 5% 4 4 4 19%	2850
	11th to 20th	Night	20% 15% 5% 10% 6% 4 4 3 4 5% 25%	3531
	21st to end	Night	24% 20% 4 9% 4 3 3 2 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	54% 8% 12% 15% 9% 2	3119
	11th to 20th	Day	57% 6% 11% 17% 7% 1	3335
	21st to end	Day	50% 5% 9% 18% 13% 4	4038
April	1st to 10th	Day	57% 5% 11% 14% 10% 3	2280
	11th to 20th	Day	48% 5% 11% 23% 12% 2	2352
	21st to end	Day	54% 6% 10% 16% 12% 2	2470
May	1st to 10th	Day	47% 6% 14% 16% 15% 1	4206
	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	50% 7% 11% 24% 8%	2090
	11th to 20th	Day	58% 7% 17% 16% 3	1739
	21st to end	Day	60% 7% 12% 16% 5% 1	1881
November	1st to 10th	Day	54% 7% 14% 18% 8%	1680
	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	59% 6% 11% 14% 8% 2	3734
	11th to 20th	Night	63% 5% 10% 14% 7% 1	3623
	21st to end	Night	56% 4 9% 19% 9% 2	3578
April	1st to 10th	Night	57% 4 10% 14% 13% 3	1900
	11th to 20th	Night	49% 6% 11% 20% 12% 2	1777
	21st to end	Night	54% 5% 8% 16% 15% 2	1710
May	1st to 10th	Night	50% 6% 14% 18% 11% 1	2782
	11th to 20th	Night	49% 9% 14% 16% 11% 1	2496
	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	47% 7% 11% 24% 11% 1	2090
	11th to 20th	Night	55% 7% 13% 20% 5%	2439
	21st to end	Night	56% 6% 14% 15% 8%	2717
November	1st to 10th	Night	53% 7% 14% 18% 6% 1	2421
	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	460
	11th to 20th	Day	24% 17% 33% 17% 7% 2	460
	21st to end	Day	23% 17% 26% 22% 11% 1	506
April	1st to 10th	Day	29% 14% 29% 19% 9% 1	460
	11th to 20th	Day	26% 13% 28% 23% 7% 2	452
	21st to end	Day	27% 17% 30% 18% 6% 2	460
May	1st to 10th	Day	27% 14% 33% 19% 6% 1	463
	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	29% 15% 27% 22% 7% 1	368
	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% 12% 34% 26% 5%	760
	11th to 20th	Night	25% 13% 33% 23% 6% 1	760
	21st to end	Night	24% 10% 31% 27% 7% 1	836
April	1st to 10th	Night	30% 13% 25% 26% 6%	760
	11th to 20th	Night	26% 8% 35% 24% 6%	653
	21st to end	Night	29% 11% 30% 24% 6%	570
May	1st to 10th	Night	26% 9% 32% 27% 6%	538
	11th to 20th	Night	25% 9% 27% 32% 7%	374
	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% 9%	745
	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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