Observatoire du Cégep de Trois-Rivières à Champlain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire du Cégep de Trois-Rivières à Champlain clear sky chart from 2005-11-06 to 2025-08-05.

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	19% 10% 3 8% 5% 4 5% 4 5% 7% 31%	125309
	Night	19% 12% 4 9% 5% 4 4 3 5% 6% 29%	122672
Transparency	Day	34% 38% 9% 13% 6% 1	128752
	Night	37% 38% 7% 12% 6%	127304
Seeing	Day	23% 11% 28% 24% 11% 3	15482
	Night	25% 8% 28% 29% 9% 1	24490

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	20% 19% 6% 12% 5% 4 5% 3 4 4 19%	3597
	11th to 20th	Day	10% 16% 7% 16% 6% 5% 4 3 4 4 23%	3570
	21st to end	Day	9% 13% 6% 12% 5% 5% 4 3 6% 8% 28%	3960
February	1st to 10th	Day	13% 16% 5% 10% 6% 6% 5% 3 4 5% 26%	1650
	11th to 20th	Day	15% 16% 6% 10% 6% 4 5% 4 5% 5% 25%	1902
	21st to end	Day	15% 14% 4 11% 6% 5% 3 4 4 6% 28%	1650
March	1st to 10th	Day	22% 14% 5% 9% 5% 4 4 3 4 4 26%	4476
	11th to 20th	Day	15% 14% 4 9% 5% 4 4 4 5% 6% 32%	4653
	21st to end	Day	19% 13% 4 8% 4 4 4 3 4 5% 33%	5958
April	1st to 10th	Day	23% 11% 3 7% 5% 4 4 4 4 5% 30%	2400
	11th to 20th	Day	21% 7% 3 7% 4 4 4 4 5% 6% 37%	2419
	21st to end	Day	24% 8% 3 7% 4 4 4 4 4 6% 30%	2600
May	1st to 10th	Day	28% 8% 3 7% 4 4 5% 4 5% 6% 28%	6152
	11th to 20th	Day	21% 7% 2 7% 5% 5% 5% 3 5% 7% 32%	6318
	21st to end	Day	20% 9% 3 7% 5% 5% 5% 4 5% 6% 31%	6949
June	1st to 10th	Day	21% 7% 3 7% 5% 4 6% 5% 6% 6% 30%	2800
	11th to 20th	Day	17% 6% 2 6% 5% 5% 5% 4 6% 8% 36%	2800
	21st to end	Day	21% 9% 3 7% 6% 5% 5% 4 5% 6% 29%	2800
July	1st to 10th	Day	16% 7% 3 7% 5% 5% 6% 5% 7% 9% 31%	6360
	11th to 20th	Day	14% 6% 2 7% 5% 5% 6% 5% 7% 9% 35%	6360
	21st to end	Day	12% 5% 2 5% 4 4 5% 4 7% 9% 43%	6926
August	1st to 10th	Day	16% 5% 2 7% 4 5% 6% 5% 8% 10% 30%	4479
	11th to 20th	Day	19% 6% 3 7% 4 5% 5% 4 6% 8% 34%	4084
	21st to end	Day	19% 6% 2 6% 4 4 4 3 5% 6% 40%	4217
September	1st to 10th	Day	16% 5% 2 6% 4 4 5% 4 6% 8% 40%	2280
	11th to 20th	Day	16% 5% 1 5% 4 3 4 2 5% 7% 46%	2149
	21st to end	Day	21% 6% 2 6% 4 5% 3 3 5% 6% 39%	2090
October	1st to 10th	Day	21% 7% 2 6% 4 4 5% 3 6% 8% 33%	2033
	11th to 20th	Day	21% 8% 4 8% 7% 5% 5% 4 5% 7% 26%	1785
	21st to end	Day	26% 11% 3 7% 5% 4 4 2 4 6% 27%	1881
November	1st to 10th	Day	20% 11% 3 7% 5% 4 4 3 4 6% 33%	1761
	11th to 20th	Day	21% 12% 4 9% 5% 4 3 2 5% 6% 27%	1760
	21st to end	Day	25% 14% 4 7% 5% 4 5% 3 5% 6% 22%	1600
December	1st to 10th	Day	21% 16% 5% 10% 5% 4 5% 3 4 3 23%	2285
	11th to 20th	Day	21% 15% 5% 9% 5% 4 4 3 5% 5% 26%	2645
	21st to end	Day	23% 13% 4 9% 5% 4 5% 4 5% 6% 23%	3960
January	1st to 10th	Night	18% 20% 6% 13% 6% 4 3 3 4 4 19%	6349
	11th to 20th	Night	11% 20% 7% 16% 7% 5% 5% 3 3 4 18%	6315
	21st to end	Night	12% 13% 5% 13% 6% 5% 4 4 6% 7% 26%	6996
February	1st to 10th	Night	14% 13% 6% 12% 7% 5% 5% 4 5% 5% 26%	2745
	11th to 20th	Night	14% 15% 5% 11% 8% 5% 5% 3 4 4 25%	2383
	21st to end	Night	17% 15% 4 8% 6% 5% 4 4 4 4 31%	1980
March	1st to 10th	Night	24% 14% 3 10% 5% 4 4 3 4 5% 25%	5364
	11th to 20th	Night	16% 14% 5% 9% 6% 5% 4 4 5% 7% 25%	5306
	21st to end	Night	19% 14% 4 9% 5% 4 4 3 4 5% 29%	4972
April	1st to 10th	Night	23% 13% 3 6% 5% 3 4 3 4 6% 29%	2000
	11th to 20th	Night	22% 9% 2 8% 5% 3 3 3 4 6% 34%	1929
	21st to end	Night	24% 9% 4 6% 3 3 4 2 4 7% 35%	1800
May	1st to 10th	Night	27% 9% 4 7% 4 4 4 3 5% 6% 26%	3832
	11th to 20th	Night	24% 9% 3 7% 4 4 4 3 5% 6% 32%	3575
	21st to end	Night	20% 8% 3 7% 5% 5% 5% 4 6% 7% 30%	3926
June	1st to 10th	Night	20% 8% 3 6% 4 4 4 5% 6% 8% 32%	1600
	11th to 20th	Night	20% 5% 3 6% 5% 4 5% 4 6% 9% 35%	1512
	21st to end	Night	20% 8% 3 6% 6% 5% 5% 4 7% 7% 31%	1600
July	1st to 10th	Night	14% 6% 3 7% 6% 5% 6% 5% 7% 9% 31%	3600
	11th to 20th	Night	19% 5% 2 6% 4 4 5% 3 5% 7% 38%	3600
	21st to end	Night	11% 5% 2 7% 5% 4 5% 4 6% 7% 43%	3926
August	1st to 10th	Night	16% 7% 3 8% 5% 4 5% 5% 7% 7% 33%	2538
	11th to 20th	Night	18% 7% 3 7% 5% 5% 5% 3 5% 7% 34%	2713
	21st to end	Night	19% 6% 2 8% 5% 5% 4 3 4 6% 37%	3435
September	1st to 10th	Night	16% 5% 2 6% 4 3 4 3 5% 8% 42%	1900
	11th to 20th	Night	16% 5% 2 5% 3 4 3 3 4 7% 48%	2030
	21st to end	Night	20% 7% 2 6% 4 4 4 2 4 6% 42%	2090
October	1st to 10th	Night	18% 7% 3 7% 5% 5% 5% 3 5% 6% 37%	2144
	11th to 20th	Night	22% 9% 3 8% 5% 4 4 3 4 5% 32%	2394
	21st to end	Night	26% 9% 3 8% 4 5% 4 3 4 6% 29%	2717
November	1st to 10th	Night	20% 11% 3 8% 6% 4 4 3 5% 5% 31%	2537
	11th to 20th	Night	21% 12% 4 8% 5% 4 4 3 4 5% 30%	2638
	21st to end	Night	25% 15% 3 8% 5% 4 4 3 3 5% 25%	2800
December	1st to 10th	Night	19% 15% 6% 11% 7% 6% 4 4 4 5% 19%	4899
	11th to 20th	Night	25% 13% 4 9% 5% 4 4 4 5% 5% 22%	5531
	21st to end	Night	24% 17% 5% 8% 4 4 3 3 5% 5% 21%	6996

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	52% 28% 7% 10% 2	3598
	11th to 20th	Day	48% 28% 6% 13% 4 1	3600
	21st to end	Day	39% 29% 6% 14% 11%	3960
February	1st to 10th	Day	24% 61% 4 5% 4 1	1650
	11th to 20th	Day	24% 61% 4 7% 5%	1911
	21st to end	Day	23% 61% 4 5% 5% 2	1650
March	1st to 10th	Day	48% 29% 5% 8% 7% 2	4479
	11th to 20th	Day	38% 30% 12% 9% 9% 1	4653
	21st to end	Day	40% 29% 4 13% 11% 3	5958
April	1st to 10th	Day	20% 62% 4 7% 6% 1	2400
	11th to 20th	Day	21% 62% 3 9% 4 1	2419
	21st to end	Day	23% 62% 4 5% 5%	2600
May	1st to 10th	Day	44% 30% 7% 11% 7%	6163
	11th to 20th	Day	37% 31% 14% 12% 4 1	6322
	21st to end	Day	40% 30% 8% 10% 9% 2	6949
June	1st to 10th	Day	19% 62% 4 8% 5% 1	2800
	11th to 20th	Day	17% 62% 5% 8% 6% 1	2800
	21st to end	Day	21% 60% 4 10% 5%	2800
July	1st to 10th	Day	39% 26% 11% 18% 5%	6290
	11th to 20th	Day	34% 26% 15% 21% 3	6285
	21st to end	Day	27% 26% 13% 27% 7%	6728
August	1st to 10th	Day	30% 38% 14% 14% 4	4465
	11th to 20th	Day	34% 38% 13% 12% 2	4124
	21st to end	Day	31% 37% 10% 11% 9% 1	4217
September	1st to 10th	Day	16% 61% 8% 10% 5% 1	2280
	11th to 20th	Day	16% 60% 7% 13% 4 1	2149
	21st to end	Day	16% 60% 4 14% 6%	2090
October	1st to 10th	Day	33% 38% 8% 18% 3	3384
	11th to 20th	Day	34% 38% 11% 14% 2	2936
	21st to end	Day	30% 38% 16% 13% 4	3081
November	1st to 10th	Day	27% 57% 6% 8% 3	1761
	11th to 20th	Day	23% 57% 5% 11% 4	1760
	21st to end	Day	30% 57% 5% 6% 3 1	1600
December	1st to 10th	Day	44% 35% 6% 11% 4	2285
	11th to 20th	Day	42% 32% 7% 11% 9%	2645
	21st to end	Day	46% 28% 6% 12% 8%	3960
January	1st to 10th	Night	52% 28% 8% 8% 4	6349
	11th to 20th	Night	55% 27% 6% 10% 2	6360
	21st to end	Night	43% 28% 7% 13% 9%	6996
February	1st to 10th	Night	24% 62% 3 7% 4 1	2745
	11th to 20th	Night	24% 60% 3 8% 5%	2385
	21st to end	Night	21% 61% 3 7% 7% 1	1980
March	1st to 10th	Night	46% 30% 7% 7% 9% 2	5374
	11th to 20th	Night	44% 30% 10% 10% 6% 1	5307
	21st to end	Night	45% 28% 4 16% 6% 1	4972
April	1st to 10th	Night	21% 61% 3 6% 8% 1	2000
	11th to 20th	Night	24% 62% 2 7% 5% 1	1929
	21st to end	Night	20% 62% 4 8% 5% 1	1800
May	1st to 10th	Night	45% 30% 6% 13% 5%	3838
	11th to 20th	Night	40% 31% 10% 15% 5%	3576
	21st to end	Night	39% 30% 9% 9% 11% 1	3927
June	1st to 10th	Night	18% 62% 4 10% 7%	1600
	11th to 20th	Night	17% 62% 4 9% 6% 2	1512
	21st to end	Night	19% 61% 4 8% 7% 1	1600
July	1st to 10th	Night	37% 26% 16% 16% 4	3560
	11th to 20th	Night	36% 26% 15% 20% 4	3552
	21st to end	Night	28% 26% 13% 24% 8%	3809
August	1st to 10th	Night	34% 39% 11% 12% 5%	2528
	11th to 20th	Night	35% 40% 11% 11% 3	2739
	21st to end	Night	33% 37% 6% 14% 9%	3435
September	1st to 10th	Night	15% 61% 6% 11% 6% 1	1900
	11th to 20th	Night	15% 60% 9% 13% 3	2030
	21st to end	Night	16% 60% 3 13% 8%	2090
October	1st to 10th	Night	37% 37% 9% 13% 4	3573
	11th to 20th	Night	32% 37% 10% 17% 2	3969
	21st to end	Night	30% 37% 13% 12% 8% 1	4467
November	1st to 10th	Night	26% 56% 6% 8% 4 1	2537
	11th to 20th	Night	26% 56% 5% 9% 4	2638
	21st to end	Night	29% 57% 5% 5% 4	2800
December	1st to 10th	Night	45% 35% 9% 9% 2	4899
	11th to 20th	Night	46% 32% 5% 11% 6%	5532
	21st to end	Night	48% 26% 5% 14% 6%	6996

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	31% 9% 33% 24% 4 1	200
	11th to 20th	Day	25% 13% 33% 20% 9% 1	200
	21st to end	Day	20% 13% 34% 23% 10% 1	220
February	1st to 10th	Day	25% 19% 34% 18% 4	225
	11th to 20th	Day	24% 15% 38% 20% 3	450
	21st to end	Day	23% 17% 34% 20% 6%	414
March	1st to 10th	Day	27% 13% 27% 25% 7%	500
	11th to 20th	Day	25% 16% 31% 21% 6% 2	500
	21st to end	Day	26% 14% 31% 18% 9% 2	550
April	1st to 10th	Day	29% 12% 26% 26% 6%	500
	11th to 20th	Day	27% 16% 26% 21% 7% 2	492
	21st to end	Day	27% 15% 32% 17% 8% 2	500
May	1st to 10th	Day	27% 14% 31% 20% 7% 2	503
	11th to 20th	Day	20% 10% 31% 23% 13% 3	527
	21st to end	Day	22% 14% 32% 20% 10% 2	573
June	1st to 10th	Day	20% 12% 32% 24% 9% 4	530
	11th to 20th	Day	18% 10% 30% 23% 15% 3	530
	21st to end	Day	24% 9% 26% 26% 11% 3	530
July	1st to 10th	Day	17% 7% 27% 31% 15% 3	525
	11th to 20th	Day	17% 6% 31% 31% 13% 3	524
	21st to end	Day	15% 8% 26% 32% 15% 3	576
August	1st to 10th	Day	16% 7% 23% 32% 17% 5%	502
	11th to 20th	Day	17% 6% 18% 31% 22% 6%	479
	21st to end	Day	19% 11% 25% 19% 17% 9%	539
September	1st to 10th	Day	17% 8% 28% 26% 13% 7%	490
	11th to 20th	Day	17% 9% 22% 27% 19% 7%	490
	21st to end	Day	23% 7% 26% 22% 16% 7%	490
October	1st to 10th	Day	23% 9% 27% 25% 13% 3	490
	11th to 20th	Day	27% 11% 28% 22% 9% 3	429
	21st to end	Day	33% 10% 28% 21% 8%	429
November	1st to 10th	Day	29% 12% 27% 25% 6% 1	395
	11th to 20th	Day	28% 14% 26% 25% 8%	360
	21st to end	Day	35% 15% 32% 12% 7% 2	200
December	1st to 10th	Day	34% 11% 24% 26% 5% 2	200
	11th to 20th	Day	29% 18% 30% 17% 6% 2	200
	21st to end	Day	35% 11% 27% 18% 5% 2	220
January	1st to 10th	Night	30% 8% 33% 24% 5%	800
	11th to 20th	Night	28% 10% 31% 23% 8%	800
	21st to end	Night	19% 7% 32% 35% 7% 1	880
February	1st to 10th	Night	20% 8% 38% 28% 6%	800
	11th to 20th	Night	23% 12% 35% 23% 7%	783
	21st to end	Night	27% 10% 29% 29% 5%	660
March	1st to 10th	Night	24% 10% 32% 29% 5%	800
	11th to 20th	Night	25% 10% 33% 26% 5% 1	800
	21st to end	Night	22% 11% 32% 26% 8% 1	880
April	1st to 10th	Night	30% 8% 29% 27% 6%	800
	11th to 20th	Night	27% 10% 29% 28% 6% 1	745
	21st to end	Night	28% 13% 28% 24% 6%	600
May	1st to 10th	Night	26% 10% 28% 30% 5% 1	508
	11th to 20th	Night	23% 8% 29% 32% 6% 1	394
	21st to end	Night	24% 5% 31% 30% 9%	433
June	1st to 10th	Night	25% 6% 26% 34% 9%	400
	11th to 20th	Night	21% 5% 25% 35% 14%	400
	21st to end	Night	24% 5% 22% 34% 14% 1	400
July	1st to 10th	Night	17% 3 25% 37% 17% 1	390
	11th to 20th	Night	16% 3 23% 42% 15% 1	388
	21st to end	Night	15% 4 21% 45% 14%	438
August	1st to 10th	Night	15% 3 16% 44% 21% 1	386
	11th to 20th	Night	15% 5% 21% 34% 22% 1	517
	21st to end	Night	19% 4 22% 32% 20% 2	808
September	1st to 10th	Night	19% 4 24% 37% 13% 2	760
	11th to 20th	Night	20% 5% 23% 29% 22% 1	760
	21st to end	Night	23% 5% 24% 30% 16% 2	760
October	1st to 10th	Night	24% 8% 27% 31% 11% 1	760
	11th to 20th	Night	26% 9% 26% 29% 9% 1	760
	21st to end	Night	30% 8% 32% 24% 5%	836
November	1st to 10th	Night	26% 11% 27% 27% 7% 1	780
	11th to 20th	Night	27% 11% 30% 22% 9% 1	800
	21st to end	Night	34% 12% 24% 24% 6% 1	800
December	1st to 10th	Night	31% 11% 26% 24% 7% 1	895
	11th to 20th	Night	29% 13% 26% 24% 6% 1	889
	21st to end	Night	36% 10% 25% 21% 7% 1	880

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