Cowansville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cowansville clear sky chart from 2005-11-06 to 2026-06-01.

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% 12% 4 9% 5% 5% 4 3 5% 6% 27%	132065
	Night	19% 15% 5% 10% 6% 4 4 3 4 5% 26%	131083
Transparency	Day	58% 4 11% 18% 8% 1	135520
	Night	62% 4 9% 16% 8% 1	135715
Seeing	Day	29% 16% 28% 18% 7% 2	16579
	Night	29% 14% 26% 23% 8% 1	25568

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	15% 23% 7% 18% 6% 6% 3 2 3 3 13%	4661
	11th to 20th	Day	9% 18% 9% 24% 9% 6% 5% 3 4 3 10%	4650
	21st to end	Day	11% 16% 7% 13% 11% 10% 5% 3 5% 5% 15%	5124
February	1st to 10th	Day	14% 17% 6% 15% 9% 6% 5% 3 3 3 19%	1801
	11th to 20th	Day	15% 18% 7% 13% 7% 4 5% 3 4 6% 18%	2011
	21st to end	Day	14% 20% 5% 10% 8% 5% 3 4 4 5% 21%	1730
March	1st to 10th	Day	20% 16% 7% 12% 5% 5% 5% 2 3 4 20%	4576
	11th to 20th	Day	14% 17% 4 9% 5% 4 4 3 5% 5% 28%	4751
	21st to end	Day	21% 15% 5% 10% 4 4 3 3 4 4 27%	6102
April	1st to 10th	Day	23% 17% 4 8% 4 4 4 3 4 5% 26%	2520
	11th to 20th	Day	21% 13% 4 7% 3 4 4 3 4 4 33%	2494
	21st to end	Day	25% 11% 3 6% 4 4 5% 3 4 5% 29%	2730
May	1st to 10th	Day	30% 12% 3 8% 5% 5% 4 4 5% 6% 21%	6220
	11th to 20th	Day	22% 7% 3 8% 5% 5% 6% 4 6% 7% 28%	6458
	21st to end	Day	22% 9% 3 7% 4 4 4 4 6% 6% 30%	7103
June	1st to 10th	Day	27% 7% 2 5% 5% 4 5% 4 6% 7% 29%	2800
	11th to 20th	Day	18% 6% 2 6% 5% 3 5% 4 6% 7% 36%	2800
	21st to end	Day	25% 8% 2 6% 5% 5% 5% 4 5% 6% 29%	2800
July	1st to 10th	Day	16% 7% 3 7% 5% 6% 6% 5% 7% 10% 29%	6360
	11th to 20th	Day	15% 5% 2 6% 4 5% 5% 5% 7% 9% 37%	6360
	21st to end	Day	14% 7% 2 5% 4 4 4 4 6% 9% 42%	6926
August	1st to 10th	Day	18% 7% 3 8% 5% 5% 6% 4 7% 8% 30%	4563
	11th to 20th	Day	19% 6% 2 7% 5% 5% 5% 4 6% 8% 34%	4108
	21st to end	Day	19% 6% 2 5% 4 4 4 3 6% 8% 39%	4312
September	1st to 10th	Day	16% 7% 2 5% 4 4 5% 4 5% 6% 43%	2400
	11th to 20th	Day	17% 5% 2 5% 3 3 4 3 4 7% 46%	2274
	21st to end	Day	19% 6% 2 5% 4 4 4 4 6% 8% 38%	2200
October	1st to 10th	Day	24% 9% 2 6% 4 4 4 4 5% 6% 32%	2130
	11th to 20th	Day	22% 10% 3 7% 4 5% 5% 4 5% 6% 29%	1915
	21st to end	Day	28% 16% 3 7% 4 4 3 3 3 5% 25%	1980
November	1st to 10th	Day	21% 18% 4 6% 5% 4 4 4 4 4 28%	1851
	11th to 20th	Day	19% 19% 6% 9% 6% 4 3 3 4 4 24%	1881
	21st to end	Day	22% 19% 6% 11% 5% 3 3 3 6% 4 17%	1680
December	1st to 10th	Day	18% 24% 8% 15% 6% 4 3 2 3 4 12%	2680
	11th to 20th	Day	20% 18% 7% 13% 5% 3 4 3 4 4 20%	3066
	21st to end	Day	20% 19% 5% 12% 5% 5% 4 3 4 5% 18%	4048
January	1st to 10th	Night	14% 24% 9% 15% 6% 5% 3 2 3 3 15%	8234
	11th to 20th	Night	11% 22% 9% 20% 8% 5% 5% 3 3 3 11%	8235
	21st to end	Night	11% 16% 6% 15% 11% 7% 5% 3 4 4 19%	9057
February	1st to 10th	Night	15% 18% 6% 15% 7% 5% 4 3 4 5% 18%	2818
	11th to 20th	Night	14% 17% 6% 15% 7% 5% 4 3 4 5% 20%	2494
	21st to end	Night	15% 19% 6% 11% 6% 5% 4 2 3 4 26%	2076
March	1st to 10th	Night	20% 16% 5% 9% 6% 4 4 2 4 4 27%	5484
	11th to 20th	Night	16% 17% 4 10% 5% 4 4 3 5% 6% 25%	5423
	21st to end	Night	17% 19% 5% 11% 5% 3 3 3 3 4 26%	5072
April	1st to 10th	Night	24% 13% 4 8% 5% 4 3 3 5% 5% 27%	2100
	11th to 20th	Night	26% 12% 2 6% 5% 4 3 3 4 5% 32%	2074
	21st to end	Night	22% 11% 3 7% 3 4 3 2 4 6% 33%	1890
May	1st to 10th	Night	28% 11% 3 9% 5% 4 4 3 4 5% 23%	3971
	11th to 20th	Night	25% 8% 3 7% 5% 4 4 3 5% 6% 29%	3655
	21st to end	Night	21% 9% 3 8% 5% 5% 4 3 4 6% 32%	4014
June	1st to 10th	Night	27% 7% 3 5% 4 4 4 3 6% 7% 30%	1600
	11th to 20th	Night	21% 6% 2 6% 4 4 4 3 6% 8% 37%	1600
	21st to end	Night	20% 9% 2 6% 5% 4 5% 4 7% 7% 32%	1600
July	1st to 10th	Night	16% 7% 3 8% 6% 6% 6% 5% 6% 8% 31%	3600
	11th to 20th	Night	19% 7% 2 6% 4 4 4 3 6% 7% 38%	3600
	21st to end	Night	14% 7% 2 7% 5% 4 5% 4 6% 8% 39%	3926
August	1st to 10th	Night	24% 7% 3 7% 4 4 4 3 5% 7% 34%	2586
	11th to 20th	Night	17% 7% 3 8% 5% 5% 5% 4 6% 7% 33%	2891
	21st to end	Night	19% 6% 2 5% 4 4 4 4 5% 6% 42%	3586
September	1st to 10th	Night	18% 6% 2 6% 4 4 4 3 5% 6% 43%	2000
	11th to 20th	Night	15% 5% 2 6% 3 4 4 4 5% 6% 46%	2125
	21st to end	Night	21% 6% 2 5% 4 4 3 2 4 6% 42%	2200
October	1st to 10th	Night	22% 7% 3 6% 4 3 4 4 4 6% 36%	2268
	11th to 20th	Night	23% 10% 3 8% 4 4 4 3 4 5% 31%	2484
	21st to end	Night	28% 12% 3 7% 4 4 4 3 4 5% 26%	2860
November	1st to 10th	Night	23% 13% 4 7% 4 4 5% 3 4 6% 27%	2667
	11th to 20th	Night	21% 17% 4 9% 5% 4 4 3 4 5% 27%	2735
	21st to end	Night	21% 19% 6% 9% 5% 4 4 3 4 4 22%	2940
December	1st to 10th	Night	18% 27% 10% 14% 5% 3 3 2 3 3 11%	4720
	11th to 20th	Night	22% 20% 6% 13% 5% 4 3 2 3 3 18%	5348
	21st to end	Night	22% 19% 6% 10% 5% 4 3 2 3 6% 20%	7150

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	79% 3 9% 8% 1	4662
	11th to 20th	Day	80% 4 6% 6% 3	4680
	21st to end	Day	74% 3 8% 9% 6%	5124
February	1st to 10th	Day	72% 3 6% 13% 5% 1	1801
	11th to 20th	Day	71% 3 9% 12% 5% 1	2020
	21st to end	Day	68% 3 9% 13% 7% 1	1730
March	1st to 10th	Day	71% 3 6% 10% 7% 2	4579
	11th to 20th	Day	60% 4 13% 13% 10% 1	4751
	21st to end	Day	63% 3 6% 13% 14% 1	6102
April	1st to 10th	Day	64% 3 7% 17% 8% 1	2520
	11th to 20th	Day	57% 4 7% 18% 13% 1	2494
	21st to end	Day	59% 4 8% 18% 10% 2	2730
May	1st to 10th	Day	65% 5% 8% 16% 6% 1	6231
	11th to 20th	Day	55% 6% 13% 16% 8% 1	6462
	21st to end	Day	53% 5% 11% 21% 9% 1	7103
June	1st to 10th	Day	55% 4 11% 19% 9% 1	2800
	11th to 20th	Day	46% 6% 12% 24% 11% 2	2800
	21st to end	Day	55% 5% 11% 20% 8% 1	2800
July	1st to 10th	Day	50% 6% 15% 23% 7%	6290
	11th to 20th	Day	43% 7% 14% 28% 8%	6285
	21st to end	Day	41% 5% 14% 33% 7%	6728
August	1st to 10th	Day	52% 6% 15% 21% 6%	4549
	11th to 20th	Day	49% 6% 18% 21% 6%	4147
	21st to end	Day	44% 5% 17% 20% 13% 1	4312
September	1st to 10th	Day	42% 5% 13% 29% 11% 1	2400
	11th to 20th	Day	39% 4 11% 32% 13%	2274
	21st to end	Day	45% 5% 13% 25% 11% 1	2200
October	1st to 10th	Day	47% 4 14% 27% 8%	3468
	11th to 20th	Day	53% 4 14% 22% 6%	3092
	21st to end	Day	54% 3 15% 20% 6% 1	3180
November	1st to 10th	Day	61% 5% 10% 17% 7%	1851
	11th to 20th	Day	66% 3 10% 12% 8% 1	1881
	21st to end	Day	71% 5% 12% 9% 4	1680
December	1st to 10th	Day	80% 3 8% 7% 2	2680
	11th to 20th	Day	70% 3 7% 15% 5%	3066
	21st to end	Day	70% 4 7% 10% 8%	4048
January	1st to 10th	Night	77% 3 9% 9% 2	8234
	11th to 20th	Night	80% 3 6% 7% 3	8280
	21st to end	Night	71% 3 8% 9% 8%	9057
February	1st to 10th	Night	71% 4 6% 13% 5%	2818
	11th to 20th	Night	69% 4 8% 14% 5%	2496
	21st to end	Night	65% 3 8% 13% 10% 1	2076
March	1st to 10th	Night	64% 4 7% 14% 10% 2	5494
	11th to 20th	Night	62% 4 12% 14% 8% 1	5424
	21st to end	Night	65% 3 5% 17% 10% 1	5072
April	1st to 10th	Night	62% 3 7% 16% 11% 1	2100
	11th to 20th	Night	58% 4 7% 18% 13%	2074
	21st to end	Night	54% 5% 8% 18% 13% 2	1890
May	1st to 10th	Night	64% 5% 9% 15% 6% 1	3977
	11th to 20th	Night	54% 6% 10% 21% 8% 1	3656
	21st to end	Night	54% 5% 9% 19% 12% 1	4015
June	1st to 10th	Night	54% 4 10% 22% 10% 1	1600
	11th to 20th	Night	47% 6% 11% 22% 12% 3	1600
	21st to end	Night	50% 7% 13% 19% 10% 1	1600
July	1st to 10th	Night	50% 6% 15% 20% 8%	3560
	11th to 20th	Night	46% 6% 12% 28% 9%	3552
	21st to end	Night	44% 6% 14% 27% 10%	3809
August	1st to 10th	Night	51% 5% 14% 23% 7%	2576
	11th to 20th	Night	50% 6% 17% 19% 7%	2918
	21st to end	Night	44% 5% 12% 24% 14% 1	3586
September	1st to 10th	Night	43% 5% 11% 28% 12% 1	2000
	11th to 20th	Night	38% 4 14% 31% 12%	2125
	21st to end	Night	45% 5% 10% 25% 14% 1	2200
October	1st to 10th	Night	52% 4 10% 24% 10%	3710
	11th to 20th	Night	52% 3 11% 24% 9%	4046
	21st to end	Night	55% 4 12% 18% 10% 1	4610
November	1st to 10th	Night	60% 4 10% 18% 7% 1	2667
	11th to 20th	Night	63% 4 9% 14% 9% 2	2735
	21st to end	Night	69% 4 10% 13% 4	2940
December	1st to 10th	Night	82% 3 6% 7% 2	4720
	11th to 20th	Night	75% 3 5% 10% 6%	5348
	21st to end	Night	70% 4 7% 12% 8%	7150

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	32% 19% 31% 12% 6%	220
	11th to 20th	Day	32% 28% 27% 10% 3	220
	21st to end	Day	29% 21% 31% 14% 4	242
February	1st to 10th	Day	35% 26% 27% 10% 2	283
	11th to 20th	Day	33% 25% 29% 10% 2	499
	21st to end	Day	33% 20% 30% 16% 1	446
March	1st to 10th	Day	34% 21% 27% 15% 3	540
	11th to 20th	Day	36% 20% 27% 12% 4 1	540
	21st to end	Day	38% 20% 23% 12% 6% 1	594
April	1st to 10th	Day	39% 16% 26% 13% 5% 1	540
	11th to 20th	Day	40% 17% 22% 14% 5% 2	532
	21st to end	Day	33% 19% 29% 12% 6% 2	540
May	1st to 10th	Day	35% 18% 26% 13% 6% 1	543
	11th to 20th	Day	27% 16% 29% 19% 8% 2	567
	21st to end	Day	24% 17% 33% 20% 5% 1	617
June	1st to 10th	Day	32% 12% 33% 15% 8% 1	530
	11th to 20th	Day	22% 12% 34% 23% 8% 1	530
	21st to end	Day	28% 12% 35% 16% 6% 2	530
July	1st to 10th	Day	18% 11% 33% 27% 10% 2	525
	11th to 20th	Day	17% 11% 36% 26% 9% 2	524
	21st to end	Day	20% 9% 33% 28% 8% 2	576
August	1st to 10th	Day	19% 8% 28% 30% 14% 1	526
	11th to 20th	Day	19% 8% 30% 25% 14% 4	519
	21st to end	Day	22% 12% 25% 25% 12% 5%	583
September	1st to 10th	Day	19% 11% 28% 23% 13% 5%	530
	11th to 20th	Day	19% 10% 22% 22% 18% 8%	530
	21st to end	Day	22% 12% 25% 25% 12% 5%	530
October	1st to 10th	Day	27% 15% 24% 19% 12% 3	530
	11th to 20th	Day	33% 17% 22% 18% 8% 1	483
	21st to end	Day	42% 13% 23% 17% 4	462
November	1st to 10th	Day	38% 17% 27% 13% 4	425
	11th to 20th	Day	36% 19% 23% 15% 6% 1	421
	21st to end	Day	36% 22% 28% 12% 2	220
December	1st to 10th	Day	35% 17% 31% 12% 4	220
	11th to 20th	Day	35% 24% 31% 8% 2	220
	21st to end	Day	39% 19% 24% 13% 4 1	242
January	1st to 10th	Night	33% 19% 29% 16% 3	840
	11th to 20th	Night	30% 22% 26% 17% 5%	840
	21st to end	Night	23% 18% 31% 21% 6%	924
February	1st to 10th	Night	28% 18% 31% 19% 4	840
	11th to 20th	Night	26% 22% 31% 18% 3	823
	21st to end	Night	30% 16% 30% 21% 2	692
March	1st to 10th	Night	32% 16% 27% 20% 4	840
	11th to 20th	Night	33% 18% 24% 19% 6%	840
	21st to end	Night	30% 18% 25% 19% 7% 1	924
April	1st to 10th	Night	33% 16% 27% 20% 4	840
	11th to 20th	Night	35% 15% 23% 20% 7%	830
	21st to end	Night	32% 15% 28% 19% 6%	630
May	1st to 10th	Night	28% 13% 29% 22% 8% 1	561
	11th to 20th	Night	26% 10% 29% 26% 8% 1	414
	21st to end	Night	23% 8% 31% 31% 7% 1	455
June	1st to 10th	Night	32% 7% 24% 29% 8% 1	400
	11th to 20th	Night	23% 7% 26% 31% 13% 1	400
	21st to end	Night	23% 7% 24% 36% 10% 1	400
July	1st to 10th	Night	16% 5% 29% 37% 12% 1	390
	11th to 20th	Night	14% 5% 22% 41% 17% 1	388
	21st to end	Night	17% 5% 23% 41% 13%	438
August	1st to 10th	Night	20% 4 16% 38% 21% 1	398
	11th to 20th	Night	17% 6% 18% 37% 20% 2	597
	21st to end	Night	20% 6% 23% 32% 19% 1	880
September	1st to 10th	Night	21% 7% 25% 31% 15% 2	800
	11th to 20th	Night	20% 6% 17% 31% 24% 2	800
	21st to end	Night	24% 9% 24% 25% 17% 2	800
October	1st to 10th	Night	26% 11% 24% 26% 11% 2	800
	11th to 20th	Night	30% 13% 25% 23% 9% 1	800
	21st to end	Night	38% 12% 26% 19% 5%	880
November	1st to 10th	Night	34% 15% 26% 18% 6% 1	820
	11th to 20th	Night	33% 16% 24% 17% 9% 1	840
	21st to end	Night	34% 21% 24% 16% 5% 1	840
December	1st to 10th	Night	38% 18% 25% 15% 4	840
	11th to 20th	Night	35% 18% 26% 16% 4 1	840
	21st to end	Night	38% 17% 24% 18% 3	924

Page generated at 2026-05-29 01:53:26. Version ac07

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