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 2024-11-04.

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% 4 5% 4 5% 7% 32%	101135
	Night	19% 11% 4 8% 5% 4 4 3 5% 6% 30%	97796
Transparency	Day	28% 47% 8% 11% 5% 1	104596
	Night	30% 47% 7% 10% 5%	102412
Seeing	Day	23% 11% 28% 24% 11% 3	14568
	Night	25% 8% 28% 29% 9% 1	23579

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% 10% 5% 4 5% 3 4 5% 24%	2517
	11th to 20th	Day	12% 16% 6% 12% 6% 5% 4 3 4 4 28%	2520
	21st to end	Day	11% 14% 6% 12% 5% 5% 5% 3 6% 7% 26%	2772
February	1st to 10th	Day	13% 17% 5% 11% 6% 6% 4 3 4 5% 26%	1567
	11th to 20th	Day	15% 15% 5% 10% 6% 4 5% 4 5% 5% 25%	1804
	21st to end	Day	15% 13% 4 11% 7% 5% 3 4 4 6% 28%	1570
March	1st to 10th	Day	19% 12% 4 8% 5% 5% 4 3 5% 5% 30%	3116
	11th to 20th	Day	17% 16% 5% 9% 5% 4 3 3 5% 5% 27%	3251
	21st to end	Day	15% 13% 4 8% 4 4 4 3 5% 5% 36%	4154
April	1st to 10th	Day	23% 11% 3 7% 5% 4 4 4 4 5% 30%	2280
	11th to 20th	Day	20% 7% 3 7% 4 4 4 4 5% 6% 38%	2296
	21st to end	Day	24% 8% 3 7% 4 4 4 4 4 6% 31%	2470
May	1st to 10th	Day	22% 8% 3 6% 4 4 4 4 5% 6% 35%	4288
	11th to 20th	Day	17% 6% 2 8% 5% 6% 6% 4 6% 9% 33%	4398
	21st to end	Day	17% 7% 3 7% 5% 5% 5% 5% 6% 7% 34%	4837
June	1st to 10th	Day	20% 7% 3 7% 6% 4 6% 5% 6% 6% 30%	2660
	11th to 20th	Day	17% 6% 2 6% 5% 5% 5% 4 6% 8% 36%	2660
	21st to end	Day	21% 9% 3 7% 6% 5% 5% 4 5% 6% 28%	2660
July	1st to 10th	Day	14% 7% 3 7% 5% 5% 6% 5% 6% 8% 34%	4440
	11th to 20th	Day	16% 6% 2 7% 5% 5% 6% 5% 7% 9% 32%	4440
	21st to end	Day	14% 6% 2 6% 4 5% 5% 4 7% 7% 42%	4814
August	1st to 10th	Day	16% 5% 2 7% 4 6% 6% 5% 8% 10% 30%	4423
	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	19% 11% 3 7% 5% 4 4 3 4 6% 33%	1698
	11th to 20th	Day	22% 12% 4 8% 6% 4 3 3 5% 6% 26%	1672
	21st to end	Day	25% 13% 4 7% 5% 4 5% 3 6% 6% 23%	1520
December	1st to 10th	Day	27% 14% 4 9% 5% 3 4 3 4 3 23%	1335
	11th to 20th	Day	23% 15% 4 9% 6% 4 4 3 3 5% 25%	1682
	21st to end	Day	25% 16% 4 10% 5% 3 3 3 4 5% 22%	2772
January	1st to 10th	Night	18% 17% 5% 11% 5% 4 4 3 4 5% 23%	4429
	11th to 20th	Night	13% 16% 4 13% 8% 6% 5% 3 4 5% 24%	4440
	21st to end	Night	15% 14% 5% 12% 6% 5% 4 3 5% 6% 24%	4884
February	1st to 10th	Night	14% 14% 6% 12% 6% 5% 5% 4 5% 5% 26%	2608
	11th to 20th	Night	14% 14% 6% 11% 8% 5% 5% 4 4 5% 25%	2261
	21st to end	Night	16% 14% 4 8% 5% 5% 4 4 4 4 32%	1884
March	1st to 10th	Night	25% 12% 3 7% 5% 3 4 3 4 5% 29%	3724
	11th to 20th	Night	19% 18% 6% 9% 5% 5% 3 3 4 4 24%	3708
	21st to end	Night	16% 13% 4 9% 6% 4 4 3 4 5% 32%	3476
April	1st to 10th	Night	24% 13% 3 6% 5% 3 4 3 4 6% 29%	1900
	11th to 20th	Night	23% 8% 2 7% 5% 3 3 3 4 6% 35%	1832
	21st to end	Night	23% 9% 4 6% 3 3 4 2 4 7% 34%	1710
May	1st to 10th	Night	23% 9% 3 8% 5% 4 4 3 5% 6% 31%	2682
	11th to 20th	Night	22% 8% 2 6% 4 3 5% 4 5% 6% 35%	2495
	21st to end	Night	19% 6% 2 5% 4 5% 5% 4 7% 8% 33%	2738
June	1st to 10th	Night	20% 8% 3 6% 4 4 4 5% 6% 8% 32%	1520
	11th to 20th	Night	19% 6% 3 6% 5% 4 5% 3 5% 9% 35%	1436
	21st to end	Night	20% 8% 3 6% 6% 5% 5% 4 7% 7% 30%	1520
July	1st to 10th	Night	14% 6% 3 7% 6% 6% 6% 5% 6% 9% 32%	2520
	11th to 20th	Night	19% 5% 2 7% 5% 4 5% 4 6% 8% 37%	2520
	21st to end	Night	13% 5% 2 6% 5% 4 4 4 6% 7% 44%	2739
August	1st to 10th	Night	17% 7% 3 8% 5% 4 5% 5% 7% 7% 32%	2506
	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 4 6% 32%	2453
	11th to 20th	Night	21% 12% 4 8% 5% 4 4 3 4 4 29%	2506
	21st to end	Night	25% 14% 3 8% 5% 4 4 3 3 5% 26%	2660
December	1st to 10th	Night	24% 14% 5% 10% 6% 5% 4 4 4 4 21%	2839
	11th to 20th	Night	23% 15% 5% 10% 5% 4 4 3 4 5% 23%	3499
	21st to end	Night	26% 20% 4 8% 4 3 3 3 4 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	39% 39% 9% 10% 2	2518
	11th to 20th	Day	36% 39% 7% 14% 4	2520
	21st to end	Day	34% 41% 9% 14% 2	2772
February	1st to 10th	Day	22% 65% 4 5% 3 1	1567
	11th to 20th	Day	21% 64% 3 7% 4	1813
	21st to end	Day	22% 64% 4 4 4 2	1570
March	1st to 10th	Day	35% 42% 7% 11% 5% 1	3119
	11th to 20th	Day	36% 42% 6% 9% 6% 1	3251
	21st to end	Day	30% 41% 5% 12% 9% 3	4154
April	1st to 10th	Day	19% 65% 4 6% 5% 1	2280
	11th to 20th	Day	19% 65% 3 9% 3 1	2296
	21st to end	Day	22% 65% 4 5% 5%	2470
May	1st to 10th	Day	31% 42% 8% 11% 8%	4302
	11th to 20th	Day	28% 44% 15% 11% 3	4402
	21st to end	Day	28% 42% 7% 11% 11% 1	4837
June	1st to 10th	Day	18% 65% 4 8% 5% 1	2660
	11th to 20th	Day	16% 65% 5% 7% 6% 1	2660
	21st to end	Day	20% 64% 3 9% 5%	2660
July	1st to 10th	Day	32% 36% 10% 16% 6%	4370
	11th to 20th	Day	32% 37% 15% 14% 2	4365
	21st to end	Day	25% 36% 11% 21% 6%	4661
August	1st to 10th	Day	30% 38% 13% 14% 4	4409
	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	26% 58% 6% 7% 4	1698
	11th to 20th	Day	22% 60% 5% 10% 3	1672
	21st to end	Day	26% 60% 5% 5% 3 1	1520
December	1st to 10th	Day	27% 59% 4 7% 3	1335
	11th to 20th	Day	33% 48% 4 10% 4	1682
	21st to end	Day	41% 39% 6% 7% 5% 1	2772
January	1st to 10th	Night	38% 40% 11% 7% 4	4429
	11th to 20th	Night	40% 38% 7% 13% 2	4440
	21st to end	Night	39% 40% 8% 9% 3	4884
February	1st to 10th	Night	22% 65% 3 7% 3	2608
	11th to 20th	Night	22% 63% 3 7% 4	2263
	21st to end	Night	18% 64% 3 6% 7% 1	1884
March	1st to 10th	Night	35% 42% 9% 8% 5% 2	3734
	11th to 20th	Night	41% 41% 4 8% 5% 1	3709
	21st to end	Night	35% 40% 4 13% 6% 1	3476
April	1st to 10th	Night	19% 65% 3 5% 7% 1	1900
	11th to 20th	Night	22% 65% 2 7% 4 1	1832
	21st to end	Night	18% 66% 4 7% 5% 1	1710
May	1st to 10th	Night	34% 43% 7% 13% 3	2688
	11th to 20th	Night	29% 43% 10% 12% 5%	2496
	21st to end	Night	29% 42% 8% 10% 11% 1	2739
June	1st to 10th	Night	17% 65% 3 9% 6%	1520
	11th to 20th	Night	16% 65% 4 8% 6% 2	1436
	21st to end	Night	18% 65% 4 7% 6%	1520
July	1st to 10th	Night	34% 37% 12% 12% 5%	2480
	11th to 20th	Night	31% 37% 15% 15% 3	2472
	21st to end	Night	23% 36% 15% 19% 7%	2651
August	1st to 10th	Night	34% 39% 10% 12% 4	2496
	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	24% 58% 5% 8% 4 1	2453
	11th to 20th	Night	25% 59% 5% 8% 3	2506
	21st to end	Night	26% 60% 5% 5% 4	2660
December	1st to 10th	Night	27% 59% 4 6% 3	2839
	11th to 20th	Night	35% 49% 4 7% 5%	3500
	21st to end	Night	43% 36% 4 12% 3 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% 29% 21% 6% 2	460
	21st to end	Day	25% 15% 31% 18% 9% 2	506
April	1st to 10th	Day	29% 11% 27% 26% 7%	460
	11th to 20th	Day	26% 16% 27% 21% 8% 3	452
	21st to end	Day	27% 15% 32% 17% 8% 2	460
May	1st to 10th	Day	26% 14% 32% 19% 7% 2	463
	11th to 20th	Day	18% 10% 32% 23% 13% 3	487
	21st to end	Day	21% 14% 34% 19% 10% 2	529
June	1st to 10th	Day	19% 13% 32% 23% 9% 4	490
	11th to 20th	Day	19% 10% 30% 23% 16% 3	490
	21st to end	Day	24% 9% 26% 26% 11% 3	490
July	1st to 10th	Day	16% 7% 27% 32% 15% 3	485
	11th to 20th	Day	17% 6% 29% 32% 13% 3	484
	21st to end	Day	16% 7% 24% 33% 16% 4	532
August	1st to 10th	Day	16% 7% 23% 31% 17% 5%	486
	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% 11% 26% 26% 6% 1	374
	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% 32% 26% 8% 1	836
April	1st to 10th	Night	30% 8% 28% 28% 6%	760
	11th to 20th	Night	27% 10% 29% 27% 6% 1	708
	21st to end	Night	28% 14% 28% 24% 6%	570
May	1st to 10th	Night	26% 10% 28% 30% 6% 1	483
	11th to 20th	Night	24% 8% 29% 33% 6% 1	374
	21st to end	Night	25% 6% 32% 29% 8%	411
June	1st to 10th	Night	25% 6% 27% 34% 9%	380
	11th to 20th	Night	22% 5% 24% 36% 14%	380
	21st to end	Night	24% 6% 22% 34% 15% 1	380
July	1st to 10th	Night	17% 3 25% 37% 17% 1	370
	11th to 20th	Night	17% 3 23% 42% 15% 1	368
	21st to end	Night	15% 4 21% 45% 15%	416
August	1st to 10th	Night	15% 3 16% 43% 21% 1	378
	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% 28% 7% 1	755
	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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