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 2025-02-06.

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% 28%	108409
	Night	19% 15% 5% 10% 5% 4 4 3 4 5% 26%	109839
Transparency	Day	58% 5% 11% 18% 8% 1	111912
	Night	62% 4 9% 16% 8% 1	114500
Seeing	Day	29% 15% 28% 18% 8% 2	14861
	Night	29% 13% 25% 23% 9% 1	23932

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	16% 26% 8% 19% 5% 6% 2 2 2 3 12%	3597
	11th to 20th	Day	10% 17% 9% 25% 9% 5% 5% 3 4 3 10%	3570
	21st to end	Day	13% 19% 8% 12% 6% 9% 5% 3 4 5% 17%	3960
February	1st to 10th	Day	15% 18% 6% 14% 8% 6% 5% 3 3 3 19%	1670
	11th to 20th	Day	15% 19% 7% 13% 7% 4 5% 3 4 5% 19%	1814
	21st to end	Day	14% 20% 5% 9% 8% 5% 4 4 5% 5% 21%	1570
March	1st to 10th	Day	22% 14% 4 10% 6% 5% 4 3 4 5% 23%	3116
	11th to 20th	Day	15% 23% 5% 11% 5% 4 3 3 3 4 23%	3246
	21st to end	Day	18% 14% 5% 10% 4 3 3 2 4 4 33%	4166
April	1st to 10th	Day	23% 16% 3 8% 4 4 4 3 4 5% 26%	2280
	11th to 20th	Day	21% 13% 4 7% 3 4 4 3 4 5% 34%	2254
	21st to end	Day	26% 11% 3 6% 4 4 4 3 4 5% 29%	2470
May	1st to 10th	Day	25% 10% 3 7% 5% 5% 4 4 5% 6% 27%	4250
	11th to 20th	Day	20% 7% 3 8% 5% 5% 6% 4 6% 7% 27%	4398
	21st to end	Day	16% 7% 3 7% 5% 4 5% 4 7% 8% 34%	4837
June	1st to 10th	Day	27% 7% 2 5% 5% 4 4 4 6% 7% 29%	2660
	11th to 20th	Day	18% 6% 2 5% 5% 3 5% 4 6% 7% 36%	2660
	21st to end	Day	25% 8% 2 6% 5% 5% 5% 4 5% 6% 29%	2660
July	1st to 10th	Day	15% 6% 2 6% 5% 5% 6% 5% 7% 10% 34%	4440
	11th to 20th	Day	16% 6% 2 6% 5% 5% 5% 5% 7% 9% 33%	4440
	21st to end	Day	15% 7% 2 5% 4 4 4 4 5% 8% 40%	4814
August	1st to 10th	Day	19% 7% 3 8% 5% 5% 6% 4 7% 8% 29%	4423
	11th to 20th	Day	19% 6% 2 7% 5% 5% 5% 4 6% 8% 33%	3980
	21st to end	Day	19% 6% 2 5% 3 4 4 3 6% 8% 39%	4180
September	1st to 10th	Day	17% 7% 2 5% 4 4 5% 4 5% 6% 41%	2280
	11th to 20th	Day	18% 5% 2 5% 3 3 4 3 4 7% 45%	2161
	21st to end	Day	19% 6% 2 6% 4 4 3 4 6% 8% 37%	2090
October	1st to 10th	Day	25% 10% 2 6% 4 4 4 4 5% 6% 29%	2024
	11th to 20th	Day	23% 10% 3 7% 4 4 5% 4 6% 6% 29%	1819
	21st to end	Day	28% 16% 3 6% 4 4 3 3 3 5% 25%	1881
November	1st to 10th	Day	21% 16% 3 6% 5% 4 4 4 5% 4 29%	1761
	11th to 20th	Day	19% 18% 5% 9% 6% 4 3 3 4 4 25%	1792
	21st to end	Day	22% 19% 6% 11% 5% 3 3 3 6% 4 18%	1600
December	1st to 10th	Day	19% 25% 8% 15% 6% 4 3 2 3 4 12%	2600
	11th to 20th	Day	20% 18% 7% 13% 5% 3 4 3 4 4 20%	2986
	21st to end	Day	20% 19% 5% 12% 5% 5% 4 3 4 5% 18%	3960
January	1st to 10th	Night	15% 25% 10% 17% 5% 4 3 2 3 3 14%	6349
	11th to 20th	Night	11% 22% 9% 21% 8% 5% 5% 3 3 3 12%	6315
	21st to end	Night	13% 18% 6% 14% 8% 6% 4 3 3 4 20%	6996
February	1st to 10th	Night	16% 19% 5% 14% 7% 5% 4 3 4 4 18%	2620
	11th to 20th	Night	15% 17% 6% 14% 7% 5% 3 3 4 5% 20%	2252
	21st to end	Night	15% 18% 5% 11% 6% 5% 4 2 3 5% 26%	1884
March	1st to 10th	Night	22% 13% 4 8% 5% 4 3 2 4 4 30%	3724
	11th to 20th	Night	18% 23% 5% 10% 5% 4 3 2 3 4 24%	3708
	21st to end	Night	16% 18% 5% 10% 4 3 3 3 3 3 31%	3466
April	1st to 10th	Night	24% 13% 4 8% 5% 4 3 3 5% 5% 27%	1900
	11th to 20th	Night	25% 11% 2 6% 5% 3 3 3 4 5% 33%	1874
	21st to end	Night	23% 12% 3 7% 4 4 3 2 4 6% 32%	1710
May	1st to 10th	Night	25% 10% 3 8% 5% 4 4 4 5% 6% 27%	2720
	11th to 20th	Night	24% 8% 3 7% 4 4 4 3 5% 6% 32%	2495
	21st to end	Night	18% 7% 2 6% 4 5% 5% 4 5% 7% 36%	2738
June	1st to 10th	Night	27% 7% 3 5% 4 3 5% 3 6% 8% 30%	1520
	11th to 20th	Night	21% 6% 2 6% 4 3 4 3 5% 8% 37%	1520
	21st to end	Night	20% 9% 2 6% 5% 4 5% 3 7% 7% 31%	1520
July	1st to 10th	Night	16% 8% 3 8% 6% 5% 5% 4 6% 7% 33%	2520
	11th to 20th	Night	17% 7% 2 6% 4 4 5% 3 6% 7% 37%	2520
	21st to end	Night	17% 8% 2 6% 4 4 5% 4 5% 6% 38%	2739
August	1st to 10th	Night	24% 7% 3 7% 4 4 4 3 5% 7% 32%	2506
	11th to 20th	Night	17% 7% 3 8% 5% 6% 5% 4 6% 7% 32%	2801
	21st to end	Night	19% 6% 2 5% 4 4 4 4 5% 6% 42%	3476
September	1st to 10th	Night	18% 6% 2 6% 4 4 4 3 5% 6% 42%	1900
	11th to 20th	Night	15% 5% 2 6% 3 4 4 4 5% 6% 46%	2019
	21st to end	Night	21% 6% 2 5% 4 4 3 2 5% 6% 42%	2090
October	1st to 10th	Night	22% 8% 3 7% 4 3 4 4 4 6% 34%	2154
	11th to 20th	Night	24% 11% 3 8% 4 4 4 3 4 5% 30%	2360
	21st to end	Night	28% 12% 3 7% 4 4 4 3 4 5% 26%	2717
November	1st to 10th	Night	22% 13% 4 7% 4 4 5% 3 5% 6% 27%	2537
	11th to 20th	Night	21% 15% 4 9% 5% 4 4 3 4 5% 27%	2605
	21st to end	Night	22% 19% 5% 10% 4 3 4 3 4 4 22%	2800
December	1st to 10th	Night	19% 27% 10% 14% 5% 3 3 2 3 3 11%	4580
	11th to 20th	Night	23% 20% 6% 13% 5% 4 3 2 3 3 18%	5208
	21st to end	Night	22% 19% 5% 10% 5% 4 3 2 3 6% 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	81% 2 8% 8% 1	3598
	11th to 20th	Day	79% 5% 7% 6% 3	3600
	21st to end	Day	73% 3 9% 10% 5% 1	3960
February	1st to 10th	Day	73% 3 6% 13% 4 1	1670
	11th to 20th	Day	72% 2 9% 11% 5% 1	1823
	21st to end	Day	67% 3 9% 13% 7% 1	1570
March	1st to 10th	Day	66% 4 8% 15% 7% 1	3119
	11th to 20th	Day	67% 4 9% 10% 9% 1	3246
	21st to end	Day	58% 3 6% 16% 16% 1	4166
April	1st to 10th	Day	63% 3 8% 17% 8% 1	2280
	11th to 20th	Day	56% 4 7% 19% 13% 1	2254
	21st to end	Day	60% 4 8% 17% 10% 2	2470
May	1st to 10th	Day	58% 5% 9% 19% 8% 1	4264
	11th to 20th	Day	55% 6% 15% 16% 7% 1	4402
	21st to end	Day	46% 6% 12% 24% 11% 1	4837
June	1st to 10th	Day	55% 5% 11% 19% 9% 1	2660
	11th to 20th	Day	46% 6% 12% 23% 11% 2	2660
	21st to end	Day	56% 5% 11% 19% 8% 1	2660
July	1st to 10th	Day	45% 6% 14% 27% 8%	4370
	11th to 20th	Day	46% 7% 15% 28% 4	4365
	21st to end	Day	44% 6% 13% 30% 7%	4661
August	1st to 10th	Day	53% 6% 15% 20% 6%	4409
	11th to 20th	Day	50% 6% 18% 20% 6%	4019
	21st to end	Day	44% 5% 17% 19% 13% 1	4180
September	1st to 10th	Day	43% 5% 13% 27% 11% 1	2280
	11th to 20th	Day	40% 4 11% 32% 13%	2161
	21st to end	Day	45% 5% 14% 26% 10% 1	2090
October	1st to 10th	Day	48% 4 14% 26% 7%	3362
	11th to 20th	Day	53% 5% 14% 22% 6%	2996
	21st to end	Day	54% 3 16% 21% 6% 1	3081
November	1st to 10th	Day	59% 5% 10% 18% 8% 1	1761
	11th to 20th	Day	65% 3 10% 12% 8% 1	1792
	21st to end	Day	70% 5% 12% 9% 4	1600
December	1st to 10th	Day	80% 3 8% 7% 1	2600
	11th to 20th	Day	70% 3 7% 15% 5%	2986
	21st to end	Day	70% 4 7% 10% 8%	3960
January	1st to 10th	Night	80% 3 8% 7% 2	6349
	11th to 20th	Night	80% 4 7% 7% 2	6360
	21st to end	Night	71% 3 9% 8% 9% 1	6996
February	1st to 10th	Night	72% 4 6% 12% 5%	2620
	11th to 20th	Night	69% 4 8% 14% 6%	2254
	21st to end	Night	65% 3 8% 13% 10% 1	1884
March	1st to 10th	Night	59% 4 8% 18% 8% 2	3734
	11th to 20th	Night	67% 3 7% 14% 9% 1	3709
	21st to end	Night	61% 3 5% 19% 11% 2	3466
April	1st to 10th	Night	61% 3 7% 16% 11% 1	1900
	11th to 20th	Night	57% 4 7% 19% 13%	1874
	21st to end	Night	55% 5% 8% 18% 12% 3	1710
May	1st to 10th	Night	58% 5% 9% 17% 8% 2	2726
	11th to 20th	Night	52% 5% 12% 20% 9% 1	2496
	21st to end	Night	47% 5% 10% 21% 16% 1	2739
June	1st to 10th	Night	54% 4 10% 22% 9% 1	1520
	11th to 20th	Night	46% 6% 11% 22% 12% 3	1520
	21st to end	Night	51% 7% 13% 19% 10% 1	1520
July	1st to 10th	Night	50% 5% 12% 22% 11%	2480
	11th to 20th	Night	46% 7% 13% 27% 7%	2472
	21st to end	Night	47% 6% 13% 24% 11%	2651
August	1st to 10th	Night	52% 5% 13% 22% 7%	2496
	11th to 20th	Night	51% 7% 17% 19% 7%	2828
	21st to end	Night	43% 5% 12% 24% 14% 1	3476
September	1st to 10th	Night	44% 5% 11% 27% 12% 1	1900
	11th to 20th	Night	39% 4 15% 31% 12%	2019
	21st to end	Night	45% 5% 11% 25% 13% 1	2090
October	1st to 10th	Night	53% 4 10% 24% 9%	3596
	11th to 20th	Night	53% 4 11% 24% 9%	3922
	21st to end	Night	55% 4 13% 18% 10% 1	4467
November	1st to 10th	Night	60% 4 10% 17% 7% 1	2537
	11th to 20th	Night	62% 4 9% 15% 9% 2	2605
	21st to end	Night	68% 4 10% 14% 4	2800
December	1st to 10th	Night	82% 3 7% 6% 2	4580
	11th to 20th	Night	75% 3 5% 11% 6%	5208
	21st to end	Night	69% 4 7% 12% 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	33% 19% 31% 11% 7%	200
	11th to 20th	Day	32% 25% 29% 11% 3 1	200
	21st to end	Day	27% 23% 30% 15% 5%	220
February	1st to 10th	Day	40% 27% 23% 8% 2	242
	11th to 20th	Day	35% 25% 29% 9% 2	422
	21st to end	Day	35% 17% 29% 17% 1	382
March	1st to 10th	Day	34% 19% 26% 17% 3	460
	11th to 20th	Day	35% 19% 28% 13% 4 1	460
	21st to end	Day	37% 19% 23% 14% 7% 1	506
April	1st to 10th	Day	38% 17% 25% 14% 6% 1	460
	11th to 20th	Day	38% 19% 22% 14% 6% 2	452
	21st to end	Day	34% 18% 29% 12% 6% 2	460
May	1st to 10th	Day	32% 18% 27% 14% 7% 2	463
	11th to 20th	Day	25% 15% 30% 18% 9% 2	487
	21st to end	Day	22% 16% 33% 22% 6% 1	529
June	1st to 10th	Day	32% 12% 32% 15% 8% 1	490
	11th to 20th	Day	22% 12% 33% 23% 8% 1	490
	21st to end	Day	29% 12% 34% 16% 7% 2	490
July	1st to 10th	Day	18% 10% 32% 28% 10% 2	485
	11th to 20th	Day	18% 11% 35% 25% 9% 3	484
	21st to end	Day	20% 8% 32% 29% 8% 2	532
August	1st to 10th	Day	21% 8% 28% 28% 14% 1	486
	11th to 20th	Day	20% 8% 29% 25% 14% 4	479
	21st to end	Day	22% 12% 24% 25% 13% 5%	539
September	1st to 10th	Day	20% 11% 29% 22% 13% 5%	490
	11th to 20th	Day	20% 11% 21% 23% 18% 9%	490
	21st to end	Day	21% 11% 25% 26% 12% 5%	490
October	1st to 10th	Day	29% 15% 23% 19% 11% 4	490
	11th to 20th	Day	34% 17% 22% 18% 9% 1	447
	21st to end	Day	42% 14% 23% 17% 4	429
November	1st to 10th	Day	36% 17% 28% 14% 4 1	395
	11th to 20th	Day	36% 19% 22% 15% 6% 1	392
	21st to end	Day	36% 22% 28% 13% 2	200
December	1st to 10th	Day	37% 16% 31% 12% 4 1	200
	11th to 20th	Day	35% 23% 31% 9% 2 1	200
	21st to end	Day	40% 19% 25% 11% 5% 1	220
January	1st to 10th	Night	33% 19% 28% 16% 3	800
	11th to 20th	Night	29% 21% 27% 18% 5%	800
	21st to end	Night	23% 18% 32% 22% 6%	880
February	1st to 10th	Night	29% 18% 31% 18% 4	781
	11th to 20th	Night	25% 22% 31% 18% 3	743
	21st to end	Night	30% 16% 30% 21% 2	628
March	1st to 10th	Night	32% 14% 28% 22% 4	760
	11th to 20th	Night	32% 17% 24% 20% 6%	760
	21st to end	Night	29% 17% 25% 20% 8% 1	836
April	1st to 10th	Night	32% 15% 28% 21% 4	760
	11th to 20th	Night	33% 15% 23% 20% 8% 1	750
	21st to end	Night	33% 14% 27% 19% 6%	570
May	1st to 10th	Night	27% 12% 28% 24% 8% 1	508
	11th to 20th	Night	26% 9% 29% 27% 8% 1	374
	21st to end	Night	22% 8% 30% 32% 7% 1	411
June	1st to 10th	Night	32% 7% 23% 29% 8% 1	380
	11th to 20th	Night	23% 7% 25% 32% 13% 1	380
	21st to end	Night	23% 7% 23% 37% 10% 1	380
July	1st to 10th	Night	16% 5% 29% 36% 13% 1	370
	11th to 20th	Night	14% 5% 22% 40% 18% 1	368
	21st to end	Night	18% 5% 22% 41% 14%	416
August	1st to 10th	Night	21% 4 17% 37% 21% 1	378
	11th to 20th	Night	18% 6% 19% 36% 20% 2	567
	21st to end	Night	19% 6% 22% 32% 19% 1	836
September	1st to 10th	Night	21% 7% 24% 31% 15% 2	760
	11th to 20th	Night	20% 6% 18% 30% 23% 2	760
	21st to end	Night	24% 9% 24% 24% 17% 2	760
October	1st to 10th	Night	27% 11% 24% 26% 11% 2	760
	11th to 20th	Night	31% 13% 23% 23% 9% 1	760
	21st to end	Night	38% 12% 25% 19% 5%	836
November	1st to 10th	Night	34% 15% 26% 18% 6% 1	780
	11th to 20th	Night	32% 17% 24% 17% 9% 1	800
	21st to end	Night	34% 21% 23% 16% 6% 1	800
December	1st to 10th	Night	38% 18% 24% 15% 4	800
	11th to 20th	Night	35% 17% 26% 17% 5% 1	800
	21st to end	Night	38% 16% 24% 18% 3	880

Page generated at 2025-02-03 03:05:53. Version ac07

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