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 2024-03-23.

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% 9% 4 7% 6% 3 5% 5% 5% 7% 32%	78108
	Night	19% 11% 4 7% 6% 3 5% 4 4 6% 30%	81674
Transparency	Day	53% 6% 12% 19% 9% 1	77813
	Night	55% 5% 11% 18% 9% 1	81504
Seeing	Day	23% 11% 28% 23% 11% 3	13685
	Night	25% 8% 28% 29% 9% 1	22898

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	19% 15% 5% 9% 6% 3 5% 4 4 5% 24%	2517
	11th to 20th	Day	12% 15% 7% 11% 7% 4 5% 4 4 4 28%	2520
	21st to end	Day	12% 14% 6% 10% 7% 4 5% 4 6% 7% 27%	2772
February	1st to 10th	Day	14% 16% 6% 10% 7% 4 5% 4 4 5% 26%	1567
	11th to 20th	Day	15% 15% 6% 9% 7% 3 5% 5% 5% 5% 25%	1804
	21st to end	Day	15% 13% 4 10% 8% 4 4 4 4 6% 28%	1570
March	1st to 10th	Day	16% 11% 5% 7% 6% 4 5% 4 5% 6% 32%	1897
	11th to 20th	Day	18% 12% 4 7% 6% 3 4 4 5% 6% 31%	1952
	21st to end	Day	17% 10% 4 7% 6% 3 5% 5% 5% 6% 32%	2388
April	1st to 10th	Day	24% 9% 4 7% 6% 3 5% 5% 4 5% 30%	2160
	11th to 20th	Day	21% 6% 3 6% 5% 3 4 5% 5% 6% 39%	2173
	21st to end	Day	25% 8% 3 6% 6% 3 5% 4 4 6% 30%	2340
May	1st to 10th	Day	22% 7% 3 5% 5% 3 5% 4 5% 6% 36%	2438
	11th to 20th	Day	19% 5% 2 7% 6% 4 5% 5% 5% 7% 37%	2478
	21st to end	Day	20% 6% 4 6% 6% 4 5% 5% 5% 7% 32%	2725
June	1st to 10th	Day	21% 6% 3 6% 6% 3 5% 6% 6% 7% 30%	2520
	11th to 20th	Day	17% 6% 3 5% 5% 3 6% 5% 5% 8% 36%	2520
	21st to end	Day	21% 8% 3 6% 7% 3 5% 6% 5% 6% 29%	2520
July	1st to 10th	Day	14% 5% 3 6% 5% 3 6% 6% 7% 10% 35%	2520
	11th to 20th	Day	14% 5% 3 6% 6% 4 6% 6% 7% 10% 34%	2520
	21st to end	Day	15% 6% 3 6% 5% 4 7% 6% 7% 8% 33%	2744
August	1st to 10th	Day	17% 6% 2 6% 5% 4 6% 6% 8% 10% 31%	2506
	11th to 20th	Day	14% 5% 3 6% 6% 3 6% 6% 6% 8% 38%	2330
	21st to end	Day	15% 6% 2 5% 5% 3 5% 5% 6% 7% 41%	2399
September	1st to 10th	Day	17% 5% 2 5% 5% 3 5% 5% 6% 8% 40%	2160
	11th to 20th	Day	17% 5% 2 4 4 3 4 3 5% 7% 46%	2036
	21st to end	Day	21% 5% 2 5% 4 3 4 4 5% 6% 40%	1980
October	1st to 10th	Day	22% 7% 2 5% 5% 3 4 5% 6% 8% 33%	1926
	11th to 20th	Day	22% 7% 4 8% 8% 4 6% 5% 4 7% 26%	1692
	21st to end	Day	28% 10% 3 5% 7% 3 4 3 4 6% 26%	1782
November	1st to 10th	Day	20% 10% 4 6% 6% 3 5% 4 4 5% 33%	1671
	11th to 20th	Day	23% 11% 5% 7% 6% 3 4 3 5% 6% 26%	1672
	21st to end	Day	25% 12% 4 6% 6% 3 5% 4 5% 6% 23%	1520
December	1st to 10th	Day	28% 13% 5% 8% 6% 2 4 4 4 3 23%	1335
	11th to 20th	Day	23% 13% 5% 8% 6% 3 4 3 3 6% 25%	1682
	21st to end	Day	25% 16% 4 9% 6% 3 3 4 3 5% 22%	2772
January	1st to 10th	Night	18% 16% 5% 10% 6% 3 4 4 4 5% 23%	4429
	11th to 20th	Night	14% 15% 5% 11% 9% 4 6% 4 4 5% 24%	4440
	21st to end	Night	15% 13% 5% 10% 8% 4 5% 4 5% 5% 25%	4884
February	1st to 10th	Night	14% 12% 6% 11% 7% 4 5% 5% 5% 5% 26%	2608
	11th to 20th	Night	14% 13% 7% 10% 8% 4 5% 4 4 5% 25%	2261
	21st to end	Night	17% 13% 4 8% 6% 3 5% 5% 4 4 32%	1884
March	1st to 10th	Night	17% 12% 5% 8% 7% 3 5% 4 4 5% 29%	2270
	11th to 20th	Night	18% 13% 5% 7% 7% 4 5% 4 4 5% 29%	2227
	21st to end	Night	18% 11% 4 7% 5% 2 5% 4 4 6% 34%	2011
April	1st to 10th	Night	24% 12% 4 6% 5% 3 3 4 4 6% 29%	1800
	11th to 20th	Night	22% 7% 2 6% 6% 3 3 3 4 7% 36%	1735
	21st to end	Night	24% 9% 4 5% 4 2 4 3 4 7% 34%	1620
May	1st to 10th	Night	23% 9% 3 6% 6% 2 4 4 4 5% 34%	1538
	11th to 20th	Night	20% 8% 3 5% 5% 2 5% 5% 4 6% 36%	1415
	21st to end	Night	21% 7% 2 5% 3 3 4 5% 5% 7% 37%	1550
June	1st to 10th	Night	21% 7% 3 5% 4 3 5% 6% 6% 8% 32%	1440
	11th to 20th	Night	20% 5% 3 5% 6% 3 5% 4 5% 9% 36%	1359
	21st to end	Night	18% 7% 4 6% 6% 4 5% 5% 6% 8% 31%	1440
July	1st to 10th	Night	15% 5% 3 5% 6% 3 5% 5% 7% 9% 36%	1440
	11th to 20th	Night	15% 5% 2 6% 5% 3 5% 6% 6% 8% 38%	1440
	21st to end	Night	14% 5% 2 6% 6% 3 5% 6% 6% 9% 37%	1574
August	1st to 10th	Night	13% 5% 2 6% 6% 3 5% 6% 8% 9% 38%	1432
	11th to 20th	Night	15% 6% 3 6% 6% 3 6% 5% 5% 7% 37%	1553
	21st to end	Night	16% 5% 2 6% 5% 3 5% 4 5% 7% 42%	1953
September	1st to 10th	Night	17% 5% 2 5% 5% 3 5% 4 6% 8% 42%	1800
	11th to 20th	Night	17% 5% 2 4 3 3 3 4 3 8% 47%	1923
	21st to end	Night	20% 6% 2 5% 4 2 4 3 4 6% 42%	1980
October	1st to 10th	Night	18% 7% 3 6% 6% 3 5% 4 5% 6% 38%	2031
	11th to 20th	Night	23% 8% 3 7% 7% 3 4 4 4 5% 32%	2268
	21st to end	Night	27% 8% 4 6% 6% 3 4 4 4 6% 28%	2574
November	1st to 10th	Night	20% 10% 4 7% 6% 3 4 4 4 6% 31%	2407
	11th to 20th	Night	22% 11% 5% 7% 6% 4 4 4 4 4 29%	2506
	21st to end	Night	25% 13% 4 7% 5% 3 4 4 3 5% 26%	2660
December	1st to 10th	Night	24% 13% 6% 9% 6% 4 5% 4 4 4 21%	2839
	11th to 20th	Night	23% 14% 5% 9% 7% 3 4 3 4 5% 23%	3499
	21st to end	Night	27% 19% 4 7% 5% 2 3 3 3 4 22%	4884

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% 6% 12% 16% 5%	2518
	11th to 20th	Day	60% 6% 9% 19% 6%	2520
	21st to end	Day	56% 5% 11% 20% 6% 1	2772
February	1st to 10th	Day	61% 5% 9% 15% 8% 2	1567
	11th to 20th	Day	61% 4 12% 13% 9% 1	1813
	21st to end	Day	58% 4 10% 18% 8% 2	1570
March	1st to 10th	Day	54% 5% 10% 18% 11% 2	1900
	11th to 20th	Day	54% 5% 12% 15% 12% 2	1952
	21st to end	Day	53% 5% 10% 18% 12% 3	2388
April	1st to 10th	Day	58% 4 10% 15% 10% 3	2160
	11th to 20th	Day	48% 5% 10% 23% 12% 3	2173
	21st to end	Day	56% 4 9% 15% 13% 3	2340
May	1st to 10th	Day	50% 4 9% 19% 15% 3	2438
	11th to 20th	Day	47% 5% 11% 21% 14% 2	2482
	21st to end	Day	52% 5% 11% 16% 14% 2	2725
June	1st to 10th	Day	52% 7% 11% 19% 9% 2	2520
	11th to 20th	Day	46% 6% 12% 22% 12% 2	2520
	21st to end	Day	55% 6% 11% 17% 10% 1	2520
July	1st to 10th	Day	42% 9% 15% 25% 8%	2450
	11th to 20th	Day	44% 7% 16% 24% 9%	2445
	21st to end	Day	47% 8% 16% 22% 7%	2591
August	1st to 10th	Day	47% 9% 19% 21% 4	2492
	11th to 20th	Day	43% 8% 16% 24% 9%	2330
	21st to end	Day	42% 7% 14% 26% 11%	2399
September	1st to 10th	Day	42% 7% 15% 23% 12% 1	2160
	11th to 20th	Day	39% 5% 15% 29% 12% 1	2036
	21st to end	Day	45% 6% 14% 26% 10%	1980
October	1st to 10th	Day	51% 6% 10% 24% 9%	1926
	11th to 20th	Day	59% 6% 13% 19% 3	1692
	21st to end	Day	61% 5% 10% 17% 7% 1	1782
November	1st to 10th	Day	54% 5% 13% 20% 9%	1671
	11th to 20th	Day	60% 5% 11% 17% 8%	1672
	21st to end	Day	62% 6% 12% 15% 4 1	1520
December	1st to 10th	Day	66% 4 9% 15% 5%	1335
	11th to 20th	Day	63% 4 8% 19% 7%	1682
	21st to end	Day	65% 6% 9% 11% 8% 1	2772
January	1st to 10th	Night	62% 7% 14% 12% 5%	4429
	11th to 20th	Night	63% 5% 10% 17% 4	4440
	21st to end	Night	61% 5% 12% 15% 7%	4884
February	1st to 10th	Night	61% 5% 9% 16% 9% 1	2608
	11th to 20th	Night	62% 6% 8% 14% 9% 1	2263
	21st to end	Night	57% 3 9% 17% 13% 2	1884
March	1st to 10th	Night	58% 5% 9% 16% 10% 2	2280
	11th to 20th	Night	59% 5% 9% 13% 13% 2	2228
	21st to end	Night	51% 4 9% 20% 12% 4	2011
April	1st to 10th	Night	57% 4 9% 16% 11% 2	1800
	11th to 20th	Night	49% 5% 9% 21% 14% 2	1735
	21st to end	Night	52% 5% 9% 17% 14% 3	1620
May	1st to 10th	Night	53% 4 9% 15% 15% 3	1538
	11th to 20th	Night	50% 4 11% 17% 15% 4	1416
	21st to end	Night	47% 5% 11% 18% 16% 2	1551
June	1st to 10th	Night	48% 6% 13% 21% 10% 1	1440
	11th to 20th	Night	47% 6% 10% 21% 13% 4	1359
	21st to end	Night	50% 8% 12% 18% 12% 1	1440
July	1st to 10th	Night	43% 7% 17% 21% 11% 1	1400
	11th to 20th	Night	43% 7% 14% 25% 10% 1	1392
	21st to end	Night	43% 9% 16% 23% 10%	1486
August	1st to 10th	Night	39% 10% 17% 26% 7%	1422
	11th to 20th	Night	46% 7% 16% 23% 8%	1553
	21st to end	Night	42% 7% 14% 27% 10%	1953
September	1st to 10th	Night	41% 7% 15% 25% 12% 1	1800
	11th to 20th	Night	38% 5% 17% 28% 10% 1	1923
	21st to end	Night	45% 5% 10% 27% 13%	1980
October	1st to 10th	Night	48% 5% 9% 24% 13%	2031
	11th to 20th	Night	56% 6% 12% 21% 6%	2268
	21st to end	Night	59% 5% 11% 16% 8%	2574
November	1st to 10th	Night	54% 6% 12% 19% 8% 1	2407
	11th to 20th	Night	58% 5% 12% 17% 8%	2506
	21st to end	Night	62% 5% 12% 15% 7%	2660
December	1st to 10th	Night	68% 4 11% 13% 5%	2839
	11th to 20th	Night	64% 5% 7% 16% 7%	3500
	21st to end	Night	67% 4 7% 16% 5% 1	4884

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	28% 10% 33% 24% 4 1	180
	11th to 20th	Day	27% 14% 32% 19% 7% 1	180
	21st to end	Day	21% 12% 34% 21% 11% 2	198
February	1st to 10th	Day	26% 19% 33% 18% 3	202
	11th to 20th	Day	23% 13% 39% 21% 3	412
	21st to end	Day	24% 18% 33% 19% 6%	382
March	1st to 10th	Day	26% 13% 27% 26% 7%	460
	11th to 20th	Day	26% 16% 30% 20% 6% 2	460
	21st to end	Day	26% 13% 30% 19% 9% 2	470
April	1st to 10th	Day	29% 11% 28% 25% 7%	420
	11th to 20th	Day	25% 16% 28% 20% 8% 3	412
	21st to end	Day	28% 14% 32% 17% 8% 2	420
May	1st to 10th	Day	25% 14% 33% 19% 7% 2	423
	11th to 20th	Day	19% 10% 33% 23% 12% 3	447
	21st to end	Day	20% 15% 34% 19% 11% 2	485
June	1st to 10th	Day	20% 12% 32% 23% 8% 4	450
	11th to 20th	Day	20% 10% 29% 22% 16% 3	450
	21st to end	Day	23% 8% 26% 27% 12% 4	450
July	1st to 10th	Day	16% 7% 26% 32% 16% 3	445
	11th to 20th	Day	17% 5% 29% 32% 14% 3	444
	21st to end	Day	16% 8% 23% 34% 15% 4	488
August	1st to 10th	Day	16% 7% 22% 32% 17% 5%	446
	11th to 20th	Day	16% 6% 18% 32% 21% 6%	439
	21st to end	Day	18% 11% 26% 19% 16% 10%	495
September	1st to 10th	Day	18% 7% 28% 26% 13% 8%	450
	11th to 20th	Day	18% 10% 24% 25% 17% 6%	450
	21st to end	Day	23% 7% 26% 21% 16% 7%	450
October	1st to 10th	Day	24% 9% 27% 24% 13% 3	450
	11th to 20th	Day	28% 10% 29% 22% 9% 2	396
	21st to end	Day	35% 10% 27% 19% 8%	396
November	1st to 10th	Day	29% 12% 27% 25% 6% 1	365
	11th to 20th	Day	28% 14% 25% 26% 7%	332
	21st to end	Day	34% 16% 29% 12% 7% 2	180
December	1st to 10th	Day	34% 12% 23% 24% 4 2	180
	11th to 20th	Day	28% 18% 29% 17% 6% 2	180
	21st to end	Day	37% 13% 27% 17% 5% 2	198
January	1st to 10th	Night	30% 9% 33% 24% 5%	760
	11th to 20th	Night	28% 9% 32% 23% 7%	760
	21st to end	Night	20% 7% 32% 33% 7% 1	836
February	1st to 10th	Night	21% 8% 37% 27% 7%	760
	11th to 20th	Night	22% 12% 35% 23% 7%	743
	21st to end	Night	26% 10% 30% 29% 5%	628
March	1st to 10th	Night	24% 10% 31% 30% 4	760
	11th to 20th	Night	26% 10% 32% 25% 6% 1	760
	21st to end	Night	22% 11% 31% 27% 8% 1	801
April	1st to 10th	Night	31% 8% 28% 27% 6%	720
	11th to 20th	Night	26% 10% 29% 28% 6% 1	671
	21st to end	Night	28% 13% 28% 25% 6%	540
May	1st to 10th	Night	26% 9% 27% 32% 6% 1	458
	11th to 20th	Night	25% 8% 29% 31% 6% 1	354
	21st to end	Night	26% 5% 32% 29% 8%	389
June	1st to 10th	Night	25% 6% 26% 33% 9%	360
	11th to 20th	Night	22% 5% 23% 36% 14%	360
	21st to end	Night	22% 6% 22% 35% 15% 1	360
July	1st to 10th	Night	17% 3 26% 37% 16% 1	350
	11th to 20th	Night	16% 3 24% 41% 15% 1	348
	21st to end	Night	15% 4 22% 44% 14% 1	394
August	1st to 10th	Night	15% 3 16% 44% 21% 1	358
	11th to 20th	Night	15% 5% 22% 35% 21% 1	489
	21st to end	Night	19% 5% 22% 33% 19% 2	765
September	1st to 10th	Night	19% 4 24% 37% 13% 2	720
	11th to 20th	Night	21% 5% 24% 29% 20% 1	720
	21st to end	Night	23% 6% 25% 29% 15% 2	720
October	1st to 10th	Night	23% 7% 27% 31% 11% 1	720
	11th to 20th	Night	26% 9% 26% 29% 9% 1	720
	21st to end	Night	31% 7% 32% 23% 5%	792
November	1st to 10th	Night	26% 11% 27% 27% 7% 1	740
	11th to 20th	Night	28% 11% 29% 21% 9% 1	760
	21st to end	Night	33% 12% 24% 25% 6% 1	760
December	1st to 10th	Night	32% 11% 26% 23% 7% 1	845
	11th to 20th	Night	29% 13% 27% 24% 6% 1	841
	21st to end	Night	36% 11% 25% 21% 6% 1	836

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