Trois-Rivières
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Trois-Rivières clear sky chart from 2005-11-06 to 2025-09-04.

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% 10% 3 8% 5% 4 5% 4 5% 7% 32%	125974
	Night	19% 11% 4 9% 5% 4 4 3 5% 6% 29%	122714
Transparency	Day	52% 5% 13% 20% 9% 1	129418
	Night	56% 5% 11% 19% 9% 1	127358
Seeing	Day	22% 12% 29% 24% 11% 3	15601
	Night	24% 9% 29% 29% 9% 1	24515

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% 20% 5% 11% 5% 4 4 3 5% 5% 20%	3597
	11th to 20th	Day	10% 16% 7% 14% 8% 5% 5% 3 4 5% 23%	3570
	21st to end	Day	10% 13% 7% 10% 6% 5% 5% 4 5% 8% 28%	3960
February	1st to 10th	Day	14% 17% 4 8% 7% 6% 5% 3 4 5% 27%	1666
	11th to 20th	Day	15% 14% 5% 11% 6% 5% 5% 3 6% 5% 25%	1894
	21st to end	Day	15% 14% 4 10% 6% 5% 4 2 5% 5% 29%	1650
March	1st to 10th	Day	21% 13% 4 9% 6% 4 5% 3 4 5% 26%	4476
	11th to 20th	Day	13% 14% 4 9% 5% 4 4 3 5% 6% 33%	4644
	21st to end	Day	19% 12% 4 9% 4 4 4 3 4 4 33%	5970
April	1st to 10th	Day	23% 10% 3 7% 4 4 4 4 5% 5% 32%	2400
	11th to 20th	Day	21% 7% 2 6% 3 4 4 4 5% 6% 37%	2407
	21st to end	Day	23% 10% 3 7% 5% 4 4 3 5% 6% 31%	2600
May	1st to 10th	Day	27% 9% 3 7% 5% 4 5% 3 5% 6% 27%	6160
	11th to 20th	Day	20% 8% 3 8% 5% 4 4 4 6% 7% 32%	6318
	21st to end	Day	20% 9% 3 8% 4 5% 5% 4 5% 6% 32%	6949
June	1st to 10th	Day	20% 8% 2 7% 5% 5% 5% 4 6% 6% 31%	2800
	11th to 20th	Day	16% 7% 3 6% 4 5% 5% 3 6% 8% 37%	2800
	21st to end	Day	21% 8% 2 8% 5% 4 5% 4 6% 6% 30%	2800
July	1st to 10th	Day	15% 6% 3 7% 6% 5% 6% 4 7% 9% 31%	6360
	11th to 20th	Day	13% 6% 2 7% 5% 5% 5% 5% 7% 10% 36%	6360
	21st to end	Day	11% 5% 2 5% 4 4 5% 4 6% 10% 43%	6926
August	1st to 10th	Day	15% 5% 2 7% 5% 5% 6% 6% 8% 11% 30%	4563
	11th to 20th	Day	17% 6% 3 6% 5% 4 5% 4 6% 9% 35%	4222
	21st to end	Day	18% 6% 2 6% 4 4 4 3 5% 7% 39%	4320
September	1st to 10th	Day	15% 5% 2 6% 5% 4 4 4 6% 8% 41%	2316
	11th to 20th	Day	16% 5% 2 5% 4 3 4 3 5% 7% 48%	2157
	21st to end	Day	20% 6% 2 5% 4 4 4 3 5% 6% 40%	2090
October	1st to 10th	Day	21% 7% 3 7% 4 4 5% 3 5% 8% 34%	2022
	11th to 20th	Day	21% 8% 3 9% 5% 5% 4 4 6% 7% 28%	1796
	21st to end	Day	26% 10% 3 8% 3 3 4 3 5% 6% 29%	1881
November	1st to 10th	Day	19% 11% 3 7% 5% 4 5% 3 4 5% 34%	1761
	11th to 20th	Day	20% 13% 4 9% 5% 4 3 3 5% 6% 29%	1752
	21st to end	Day	24% 14% 3 7% 6% 4 4 4 5% 6% 25%	1600
December	1st to 10th	Day	22% 17% 5% 9% 6% 5% 4 3 3 3 23%	2411
	11th to 20th	Day	20% 15% 5% 9% 5% 4 4 3 4 5% 26%	2816
	21st to end	Day	22% 13% 4 11% 5% 5% 4 4 5% 5% 23%	3960
January	1st to 10th	Night	17% 20% 7% 13% 6% 4 3 3 4 4 20%	6349
	11th to 20th	Night	11% 19% 7% 17% 7% 5% 4 3 4 4 19%	6315
	21st to end	Night	12% 12% 4 13% 7% 5% 5% 4 5% 6% 26%	6996
February	1st to 10th	Night	13% 14% 5% 11% 7% 5% 4 4 5% 5% 26%	2730
	11th to 20th	Night	14% 16% 5% 12% 7% 5% 4 3 4 4 26%	2391
	21st to end	Night	16% 14% 4 9% 5% 4 4 4 4 4 32%	1980
March	1st to 10th	Night	25% 13% 3 10% 5% 4 5% 3 4 4 25%	5364
	11th to 20th	Night	16% 14% 4 9% 5% 5% 5% 4 5% 7% 26%	5297
	21st to end	Night	18% 13% 5% 9% 5% 4 5% 3 4 5% 30%	4962
April	1st to 10th	Night	23% 11% 3 8% 4 4 4 3 5% 6% 30%	2000
	11th to 20th	Night	22% 9% 2 6% 5% 3 4 4 4 6% 34%	1941
	21st to end	Night	23% 10% 3 6% 3 3 3 3 4 6% 35%	1800
May	1st to 10th	Night	26% 10% 3 9% 4 5% 5% 3 5% 6% 25%	3810
	11th to 20th	Night	23% 9% 3 7% 5% 4 4 3 5% 6% 31%	3575
	21st to end	Night	19% 8% 3 7% 5% 5% 5% 4 5% 8% 30%	3926
June	1st to 10th	Night	21% 7% 3 5% 4 5% 4 4 6% 8% 33%	1600
	11th to 20th	Night	18% 7% 2 6% 4 4 5% 5% 6% 8% 36%	1600
	21st to end	Night	20% 8% 2 6% 4 4 5% 4 7% 7% 32%	1600
July	1st to 10th	Night	13% 6% 3 7% 6% 5% 6% 5% 8% 10% 30%	3600
	11th to 20th	Night	17% 6% 2 7% 4 4 4 4 5% 7% 38%	3600
	21st to end	Night	11% 5% 2 7% 5% 5% 4 4 6% 7% 43%	3926
August	1st to 10th	Night	16% 7% 2 8% 5% 5% 5% 4 6% 8% 34%	2586
	11th to 20th	Night	17% 8% 2 7% 4 4 5% 4 6% 7% 36%	2792
	21st to end	Night	19% 6% 3 7% 5% 4 4 3 4 7% 38%	3576
September	1st to 10th	Night	15% 5% 2 6% 4 3 4 4 5% 7% 44%	1931
	11th to 20th	Night	17% 4 2 4 3 3 3 3 4 7% 49%	2023
	21st to end	Night	18% 6% 2 6% 5% 5% 4 3 4 6% 41%	2090
October	1st to 10th	Night	19% 6% 2 7% 5% 5% 4 3 5% 5% 39%	2156
	11th to 20th	Night	22% 8% 3 7% 4 4 4 3 5% 5% 34%	2384
	21st to end	Night	26% 8% 3 7% 5% 4 4 3 5% 6% 29%	2717
November	1st to 10th	Night	20% 10% 3 8% 5% 5% 5% 3 5% 5% 32%	2537
	11th to 20th	Night	21% 11% 3 9% 4 4 4 3 4 5% 30%	2645
	21st to end	Night	25% 15% 3 8% 4 4 3 2 4 5% 26%	2800
December	1st to 10th	Night	18% 15% 6% 10% 7% 6% 5% 4 5% 5% 19%	4763
	11th to 20th	Night	24% 13% 4 9% 5% 4 4 3 5% 5% 23%	5356
	21st to end	Night	24% 17% 4 8% 4 3 3 3 5% 6% 22%	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	67% 4 10% 16% 3	3598
	11th to 20th	Day	64% 5% 8% 16% 6% 1	3600
	21st to end	Day	55% 5% 8% 18% 13% 1	3960
February	1st to 10th	Day	61% 3 8% 17% 8% 2	1666
	11th to 20th	Day	60% 5% 11% 14% 9% 1	1903
	21st to end	Day	58% 3 9% 18% 10% 2	1650
March	1st to 10th	Day	61% 5% 8% 14% 9% 3	4479
	11th to 20th	Day	52% 5% 17% 14% 12% 1	4644
	21st to end	Day	54% 4 6% 19% 15% 3	5970
April	1st to 10th	Day	55% 4 9% 18% 13% 2	2400
	11th to 20th	Day	49% 4 9% 22% 13% 2	2407
	21st to end	Day	55% 4 10% 16% 13% 3	2600
May	1st to 10th	Day	57% 5% 9% 18% 10% 1	6171
	11th to 20th	Day	50% 7% 16% 17% 8% 2	6322
	21st to end	Day	52% 6% 11% 17% 13% 2	6949
June	1st to 10th	Day	51% 6% 11% 21% 10% 2	2800
	11th to 20th	Day	44% 5% 13% 24% 12% 2	2800
	21st to end	Day	54% 5% 12% 18% 10% 1	2800
July	1st to 10th	Day	48% 6% 15% 25% 7%	6290
	11th to 20th	Day	42% 5% 18% 27% 7%	6285
	21st to end	Day	36% 5% 17% 33% 9%	6728
August	1st to 10th	Day	45% 7% 20% 22% 7%	4549
	11th to 20th	Day	45% 6% 21% 22% 6%	4262
	21st to end	Day	45% 4 15% 21% 13% 1	4320
September	1st to 10th	Day	40% 5% 16% 26% 11% 1	2316
	11th to 20th	Day	37% 5% 15% 31% 12% 1	2157
	21st to end	Day	45% 5% 13% 27% 11%	2090
October	1st to 10th	Day	47% 4 14% 28% 7%	3360
	11th to 20th	Day	51% 6% 18% 22% 3	2960
	21st to end	Day	47% 4 19% 21% 7% 1	3081
November	1st to 10th	Day	54% 4 12% 21% 8% 1	1761
	11th to 20th	Day	57% 3 11% 18% 10%	1752
	21st to end	Day	61% 5% 12% 17% 4 1	1600
December	1st to 10th	Day	67% 3 9% 15% 5%	2411
	11th to 20th	Day	61% 4 8% 17% 10%	2817
	21st to end	Day	63% 5% 9% 14% 9%	3960
January	1st to 10th	Night	69% 4 10% 12% 4	6349
	11th to 20th	Night	69% 5% 8% 13% 4 1	6360
	21st to end	Night	59% 4 10% 15% 12%	6996
February	1st to 10th	Night	61% 4 8% 17% 9% 1	2730
	11th to 20th	Night	62% 4 8% 15% 10% 1	2393
	21st to end	Night	57% 3 9% 17% 13% 2	1980
March	1st to 10th	Night	63% 4 8% 13% 10% 3	5374
	11th to 20th	Night	57% 5% 13% 14% 9% 1	5298
	21st to end	Night	57% 4 5% 22% 9% 2	4962
April	1st to 10th	Night	56% 4 8% 16% 14% 2	2000
	11th to 20th	Night	51% 5% 7% 20% 15% 2	1941
	21st to end	Night	51% 4 8% 20% 15% 3	1800
May	1st to 10th	Night	60% 5% 9% 16% 9% 1	3816
	11th to 20th	Night	53% 6% 11% 19% 9% 2	3576
	21st to end	Night	52% 5% 11% 15% 15% 1	3927
June	1st to 10th	Night	48% 6% 11% 21% 13% 1	1600
	11th to 20th	Night	45% 6% 10% 22% 14% 3	1600
	21st to end	Night	49% 6% 11% 20% 13% 1	1600
July	1st to 10th	Night	47% 5% 20% 21% 7%	3560
	11th to 20th	Night	44% 5% 18% 25% 7%	3552
	21st to end	Night	39% 5% 18% 28% 11%	3809
August	1st to 10th	Night	47% 6% 15% 24% 7%	2576
	11th to 20th	Night	47% 6% 18% 22% 7%	2818
	21st to end	Night	47% 4 12% 24% 13% 1	3576
September	1st to 10th	Night	39% 5% 15% 27% 12% 2	1931
	11th to 20th	Night	37% 4 15% 32% 11% 1	2023
	21st to end	Night	45% 5% 9% 27% 14%	2090
October	1st to 10th	Night	51% 4 13% 24% 8%	3598
	11th to 20th	Night	48% 5% 15% 26% 6%	3959
	21st to end	Night	48% 4 16% 20% 10% 2	4467
November	1st to 10th	Night	55% 4 11% 21% 7% 1	2537
	11th to 20th	Night	56% 5% 10% 18% 10% 1	2645
	21st to end	Night	62% 5% 11% 15% 7%	2800
December	1st to 10th	Night	67% 4 12% 13% 4	4763
	11th to 20th	Night	63% 4 7% 17% 8%	5356
	21st to end	Night	64% 3 7% 17% 8%	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	29% 9% 36% 22% 4 1	200
	11th to 20th	Day	25% 15% 32% 20% 8% 1	200
	21st to end	Day	18% 10% 38% 23% 10% 1	220
February	1st to 10th	Day	26% 16% 37% 18% 2	234
	11th to 20th	Day	24% 13% 37% 23% 3	442
	21st to end	Day	23% 14% 35% 24% 4	414
March	1st to 10th	Day	26% 12% 29% 26% 7%	500
	11th to 20th	Day	24% 15% 33% 21% 5% 1	500
	21st to end	Day	25% 14% 32% 19% 8% 2	550
April	1st to 10th	Day	30% 10% 28% 24% 7% 1	500
	11th to 20th	Day	27% 16% 28% 20% 7% 2	492
	21st to end	Day	29% 12% 34% 16% 8% 1	500
May	1st to 10th	Day	26% 13% 33% 18% 8% 1	503
	11th to 20th	Day	19% 10% 34% 23% 12% 2	527
	21st to end	Day	21% 14% 34% 19% 10% 2	573
June	1st to 10th	Day	21% 12% 31% 25% 9% 2	530
	11th to 20th	Day	18% 12% 30% 25% 13% 2	530
	21st to end	Day	23% 8% 29% 25% 14% 2	530
July	1st to 10th	Day	15% 10% 28% 30% 15% 2	525
	11th to 20th	Day	16% 8% 30% 30% 13% 3	524
	21st to end	Day	15% 8% 28% 30% 16% 3	576
August	1st to 10th	Day	15% 7% 24% 32% 18% 5%	526
	11th to 20th	Day	14% 7% 21% 33% 19% 6%	519
	21st to end	Day	16% 10% 27% 20% 19% 9%	583
September	1st to 10th	Day	16% 8% 29% 27% 13% 7%	502
	11th to 20th	Day	14% 8% 23% 29% 18% 8%	490
	21st to end	Day	20% 9% 26% 23% 15% 6%	490
October	1st to 10th	Day	22% 13% 24% 26% 12% 3	490
	11th to 20th	Day	25% 10% 29% 23% 11% 2	435
	21st to end	Day	30% 12% 28% 23% 7%	429
November	1st to 10th	Day	28% 14% 28% 24% 6% 1	395
	11th to 20th	Day	26% 14% 28% 24% 6%	352
	21st to end	Day	32% 21% 23% 18% 6% 2	200
December	1st to 10th	Day	35% 11% 25% 22% 6% 2	200
	11th to 20th	Day	27% 20% 33% 16% 5% 1	200
	21st to end	Day	31% 15% 28% 17% 7% 3	220
January	1st to 10th	Night	30% 10% 32% 24% 5%	800
	11th to 20th	Night	27% 10% 31% 26% 6%	800
	21st to end	Night	19% 7% 31% 35% 7%	880
February	1st to 10th	Night	19% 10% 38% 27% 5% 1	800
	11th to 20th	Night	22% 11% 38% 24% 5% 1	783
	21st to end	Night	25% 10% 31% 29% 5%	660
March	1st to 10th	Night	24% 10% 32% 30% 4	800
	11th to 20th	Night	23% 12% 33% 26% 6%	800
	21st to end	Night	23% 12% 32% 26% 7%	880
April	1st to 10th	Night	29% 10% 28% 27% 6%	800
	11th to 20th	Night	26% 13% 30% 27% 4	757
	21st to end	Night	29% 10% 31% 23% 7%	600
May	1st to 10th	Night	28% 9% 29% 27% 6%	499
	11th to 20th	Night	24% 6% 32% 31% 6% 1	394
	21st to end	Night	22% 7% 33% 28% 9%	433
June	1st to 10th	Night	23% 6% 27% 35% 9% 1	400
	11th to 20th	Night	21% 5% 25% 39% 11%	400
	21st to end	Night	21% 5% 27% 34% 13%	400
July	1st to 10th	Night	14% 5% 28% 37% 15% 1	390
	11th to 20th	Night	15% 5% 22% 42% 15% 1	388
	21st to end	Night	14% 4 26% 41% 14% 1	438
August	1st to 10th	Night	14% 3 14% 45% 22% 1	398
	11th to 20th	Night	14% 3 23% 38% 20% 1	536
	21st to end	Night	18% 5% 23% 35% 18% 2	870
September	1st to 10th	Night	17% 5% 25% 38% 13% 2	773
	11th to 20th	Night	18% 6% 23% 31% 21% 1	760
	21st to end	Night	21% 6% 26% 30% 15% 2	760
October	1st to 10th	Night	21% 7% 30% 30% 11%	760
	11th to 20th	Night	25% 10% 27% 29% 9% 1	760
	21st to end	Night	29% 10% 32% 24% 5%	836
November	1st to 10th	Night	26% 11% 27% 28% 7% 1	780
	11th to 20th	Night	26% 9% 32% 23% 10% 1	800
	21st to end	Night	33% 13% 25% 23% 7%	800
December	1st to 10th	Night	30% 10% 28% 24% 7%	853
	11th to 20th	Night	29% 10% 30% 23% 7%	847
	21st to end	Night	34% 11% 25% 23% 6% 1	880

Page generated at 2025-09-01 01:51:08. Version ac07

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