Coaticook
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Coaticook clear sky chart from 2005-11-06 to 2026-05-02.

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	17% 12% 4 10% 6% 5% 5% 4 5% 6% 25%	131579
	Night	16% 14% 5% 12% 7% 5% 4 3 4 5% 24%	130939
Transparency	Day	59% 6% 10% 17% 7% 1	135047
	Night	63% 5% 9% 14% 7% 1	135558
Seeing	Day	28% 19% 28% 16% 7% 2	16532
	Night	27% 17% 27% 21% 7% 1	25513

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	11% 17% 10% 20% 10% 9% 4 3 3 3 11%	4661
	11th to 20th	Day	7% 17% 8% 23% 14% 7% 5% 3 3 4 9%	4650
	21st to end	Day	7% 15% 8% 14% 10% 13% 7% 3 5% 4 14%	5124
February	1st to 10th	Day	13% 17% 7% 16% 10% 7% 5% 3 3 3 17%	1769
	11th to 20th	Day	11% 18% 9% 18% 9% 5% 4 3 4 4 15%	2048
	21st to end	Day	11% 18% 6% 12% 9% 7% 5% 3 4 4 20%	1730
March	1st to 10th	Day	17% 16% 6% 14% 7% 5% 5% 3 3 4 19%	4576
	11th to 20th	Day	13% 18% 6% 11% 5% 4 4 3 5% 5% 26%	4808
	21st to end	Day	19% 15% 6% 11% 6% 4 3 2 3 5% 25%	6001
April	1st to 10th	Day	20% 19% 5% 9% 4 3 4 3 3 5% 25%	2520
	11th to 20th	Day	19% 16% 4 6% 4 4 3 3 4 5% 31%	2540
	21st to end	Day	22% 15% 4 7% 4 4 4 4 4 6% 27%	2730
May	1st to 10th	Day	30% 12% 3 8% 5% 5% 4 3 4 5% 20%	5941
	11th to 20th	Day	21% 9% 3 8% 5% 5% 5% 3 6% 7% 27%	6318
	21st to end	Day	21% 9% 3 7% 5% 5% 5% 4 6% 8% 28%	6949
June	1st to 10th	Day	27% 10% 3 6% 4 5% 4 4 6% 6% 26%	2800
	11th to 20th	Day	18% 7% 3 7% 5% 4 5% 4 6% 8% 34%	2800
	21st to end	Day	23% 8% 2 7% 5% 4 5% 4 7% 7% 27%	2800
July	1st to 10th	Day	16% 7% 3 8% 5% 6% 6% 6% 8% 9% 26%	6360
	11th to 20th	Day	14% 6% 2 7% 5% 6% 5% 5% 8% 10% 33%	6360
	21st to end	Day	16% 7% 2 6% 4 4 5% 4 6% 8% 38%	6926
August	1st to 10th	Day	18% 8% 3 7% 6% 6% 5% 4 6% 8% 28%	4499
	11th to 20th	Day	18% 7% 3 8% 5% 6% 5% 5% 7% 9% 26%	4175
	21st to end	Day	20% 6% 2 5% 3 4 5% 4 6% 8% 36%	4345
September	1st to 10th	Day	17% 7% 2 6% 4 4 5% 4 4 7% 41%	2400
	11th to 20th	Day	18% 7% 2 5% 3 3 4 3 4 8% 43%	2234
	21st to end	Day	19% 8% 2 6% 3 4 5% 4 6% 8% 34%	2200
October	1st to 10th	Day	22% 11% 4 7% 3 3 4 4 6% 6% 31%	2190
	11th to 20th	Day	20% 14% 3 8% 4 3 4 4 5% 6% 28%	1874
	21st to end	Day	24% 21% 4 6% 4 4 4 3 3 4 24%	1980
November	1st to 10th	Day	19% 19% 4 7% 6% 4 4 3 4 5% 26%	1851
	11th to 20th	Day	17% 19% 6% 11% 6% 4 3 3 4 5% 22%	1890
	21st to end	Day	17% 19% 7% 12% 6% 5% 4 3 5% 5% 17%	1736
December	1st to 10th	Day	12% 20% 8% 22% 11% 4 3 2 3 3 11%	2680
	11th to 20th	Day	15% 18% 7% 15% 5% 4 5% 3 4 4 20%	3066
	21st to end	Day	17% 18% 5% 14% 6% 4 5% 3 4 5% 18%	4048
January	1st to 10th	Night	9% 20% 9% 21% 12% 7% 5% 2 3 3 11%	8234
	11th to 20th	Night	9% 19% 10% 21% 13% 6% 5% 3 3 3 9%	8235
	21st to end	Night	8% 13% 6% 15% 12% 12% 6% 4 4 4 15%	9057
February	1st to 10th	Night	12% 16% 7% 16% 10% 7% 5% 3 4 4 16%	2850
	11th to 20th	Night	10% 18% 7% 17% 10% 7% 4 2 3 3 18%	2458
	21st to end	Night	13% 16% 6% 12% 9% 7% 5% 3 3 4 24%	2076
March	1st to 10th	Night	18% 18% 6% 14% 6% 5% 5% 2 3 4 20%	5484
	11th to 20th	Night	14% 18% 6% 11% 6% 5% 4 4 5% 6% 23%	5371
	21st to end	Night	15% 19% 6% 13% 6% 4 4 2 3 3 24%	5171
April	1st to 10th	Night	21% 17% 5% 9% 5% 3 3 3 4 5% 25%	2100
	11th to 20th	Night	22% 15% 4 7% 5% 3 3 3 4 5% 30%	2029
	21st to end	Night	22% 13% 3 6% 5% 4 3 3 4 6% 30%	1890
May	1st to 10th	Night	28% 13% 3 8% 5% 4 3 3 4 6% 23%	4064
	11th to 20th	Night	24% 9% 3 7% 6% 4 4 4 5% 6% 29%	3575
	21st to end	Night	20% 9% 3 8% 5% 5% 4 3 5% 7% 32%	3926
June	1st to 10th	Night	27% 9% 3 6% 4 3 5% 4 6% 6% 29%	1600
	11th to 20th	Night	20% 6% 3 5% 4 4 5% 5% 6% 7% 35%	1600
	21st to end	Night	21% 7% 3 7% 6% 4 5% 4 6% 7% 31%	1600
July	1st to 10th	Night	16% 7% 3 8% 6% 6% 6% 4 6% 8% 30%	3600
	11th to 20th	Night	18% 7% 3 7% 4 4 4 4 5% 7% 37%	3600
	21st to end	Night	14% 6% 3 6% 5% 5% 5% 4 7% 8% 38%	3926
August	1st to 10th	Night	24% 8% 3 6% 4 4 3 4 5% 6% 32%	2617
	11th to 20th	Night	17% 7% 3 8% 5% 5% 5% 5% 7% 8% 30%	2872
	21st to end	Night	19% 7% 2 6% 4 4 4 4 5% 6% 40%	3549
September	1st to 10th	Night	16% 8% 2 6% 3 4 4 4 5% 6% 41%	2000
	11th to 20th	Night	17% 5% 2 5% 3 3 4 3 4 6% 47%	2165
	21st to end	Night	21% 7% 2 5% 3 3 4 3 5% 7% 41%	2200
October	1st to 10th	Night	21% 9% 3 7% 4 4 4 3 5% 6% 35%	2208
	11th to 20th	Night	22% 14% 3 8% 5% 4 4 3 4 5% 28%	2525
	21st to end	Night	26% 16% 3 6% 4 4 4 4 4 6% 24%	2860
November	1st to 10th	Night	20% 18% 4 8% 5% 4 4 2 5% 5% 25%	2667
	11th to 20th	Night	17% 18% 6% 12% 5% 3 3 3 4 5% 25%	2730
	21st to end	Night	17% 20% 7% 14% 5% 4 3 3 4 5% 19%	2882
December	1st to 10th	Night	13% 21% 12% 23% 8% 4 4 3 3 3 8%	4720
	11th to 20th	Night	15% 22% 6% 19% 7% 4 3 2 3 3 15%	5348
	21st to end	Night	17% 17% 6% 13% 7% 5% 5% 3 3 4 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	81% 3 8% 7% 1	4662
	11th to 20th	Day	79% 5% 5% 7% 3 1	4680
	21st to end	Day	73% 5% 6% 9% 7% 1	5124
February	1st to 10th	Day	73% 4 5% 11% 6% 1	1769
	11th to 20th	Day	74% 3 8% 9% 5% 1	2057
	21st to end	Day	68% 5% 7% 12% 7% 2	1730
March	1st to 10th	Day	70% 6% 6% 8% 8% 3	4579
	11th to 20th	Day	60% 5% 12% 12% 10% 2	4808
	21st to end	Day	64% 3 7% 12% 13% 1	6001
April	1st to 10th	Day	63% 4 7% 16% 8% 2	2520
	11th to 20th	Day	57% 4 8% 18% 12% 1	2540
	21st to end	Day	59% 5% 9% 16% 9% 2	2730
May	1st to 10th	Day	67% 6% 7% 15% 5%	5952
	11th to 20th	Day	55% 8% 13% 15% 7% 1	6322
	21st to end	Day	52% 8% 11% 20% 8%	6949
June	1st to 10th	Day	59% 6% 11% 18% 7% 1	2800
	11th to 20th	Day	48% 7% 11% 23% 10% 1	2800
	21st to end	Day	55% 8% 10% 19% 7%	2800
July	1st to 10th	Day	50% 9% 15% 19% 7%	6290
	11th to 20th	Day	43% 10% 13% 27% 7%	6285
	21st to end	Day	43% 8% 12% 30% 7%	6728
August	1st to 10th	Day	53% 8% 14% 19% 5%	4485
	11th to 20th	Day	52% 10% 16% 18% 5%	4214
	21st to end	Day	44% 7% 16% 19% 12% 2	4345
September	1st to 10th	Day	43% 6% 12% 28% 10%	2400
	11th to 20th	Day	42% 5% 10% 27% 14% 1	2234
	21st to end	Day	46% 8% 12% 22% 11% 1	2200
October	1st to 10th	Day	49% 6% 13% 22% 10%	3567
	11th to 20th	Day	53% 5% 11% 21% 8%	3025
	21st to end	Day	54% 4 13% 20% 8% 1	3180
November	1st to 10th	Day	62% 4 10% 16% 8% 1	1851
	11th to 20th	Day	66% 5% 8% 9% 9% 2	1890
	21st to end	Day	70% 6% 10% 11% 3	1736
December	1st to 10th	Day	80% 4 7% 6% 3	2680
	11th to 20th	Day	69% 4 7% 13% 7%	3066
	21st to end	Day	70% 5% 5% 10% 8% 2	4048
January	1st to 10th	Night	81% 4 7% 6% 2	8234
	11th to 20th	Night	82% 4 5% 6% 3	8280
	21st to end	Night	72% 5% 6% 9% 8% 1	9057
February	1st to 10th	Night	73% 4 6% 11% 6%	2850
	11th to 20th	Night	74% 4 6% 11% 5%	2460
	21st to end	Night	66% 4 6% 13% 9% 1	2076
March	1st to 10th	Night	70% 4 7% 11% 6% 2	5494
	11th to 20th	Night	63% 5% 13% 11% 7% 1	5372
	21st to end	Night	67% 4 4 13% 12% 1	5171
April	1st to 10th	Night	62% 4 8% 15% 10% 1	2100
	11th to 20th	Night	57% 5% 8% 18% 11%	2029
	21st to end	Night	56% 6% 9% 15% 12% 2	1890
May	1st to 10th	Night	64% 7% 11% 12% 6% 1	4070
	11th to 20th	Night	54% 9% 12% 19% 6% 1	3576
	21st to end	Night	52% 7% 12% 18% 10%	3927
June	1st to 10th	Night	55% 7% 9% 20% 9%	1600
	11th to 20th	Night	47% 8% 12% 21% 10% 2	1600
	21st to end	Night	53% 8% 13% 19% 7% 1	1600
July	1st to 10th	Night	49% 9% 15% 20% 6%	3560
	11th to 20th	Night	45% 8% 13% 27% 7%	3552
	21st to end	Night	43% 8% 15% 25% 9%	3809
August	1st to 10th	Night	52% 7% 13% 23% 5%	2607
	11th to 20th	Night	49% 11% 16% 16% 7%	2899
	21st to end	Night	45% 6% 13% 22% 13% 1	3549
September	1st to 10th	Night	44% 6% 13% 26% 11%	2000
	11th to 20th	Night	39% 5% 14% 30% 12% 1	2165
	21st to end	Night	43% 7% 13% 25% 12% 2	2200
October	1st to 10th	Night	50% 6% 11% 24% 9%	3611
	11th to 20th	Night	55% 5% 9% 20% 10%	4113
	21st to end	Night	55% 5% 14% 17% 8% 1	4610
November	1st to 10th	Night	63% 5% 10% 15% 7% 1	2667
	11th to 20th	Night	64% 4 8% 14% 8% 2	2730
	21st to end	Night	70% 5% 9% 11% 4	2882
December	1st to 10th	Night	83% 5% 5% 6% 1	4720
	11th to 20th	Night	77% 3 5% 8% 7%	5348
	21st to end	Night	70% 5% 6% 10% 7% 2	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	29% 23% 35% 12% 1	220
	11th to 20th	Day	31% 30% 29% 7% 3	220
	21st to end	Day	29% 25% 32% 10% 3	242
February	1st to 10th	Day	34% 29% 26% 9% 1	277
	11th to 20th	Day	31% 29% 28% 10% 2	536
	21st to end	Day	29% 29% 28% 13% 1	446
March	1st to 10th	Day	31% 24% 29% 12% 3	540
	11th to 20th	Day	33% 27% 25% 12% 3	540
	21st to end	Day	38% 22% 22% 12% 5% 1	594
April	1st to 10th	Day	39% 21% 24% 12% 4 1	540
	11th to 20th	Day	37% 22% 24% 10% 5% 2	532
	21st to end	Day	34% 24% 24% 12% 5% 1	540
May	1st to 10th	Day	41% 17% 23% 13% 5% 1	507
	11th to 20th	Day	26% 19% 31% 18% 5% 2	527
	21st to end	Day	24% 20% 32% 18% 5% 1	573
June	1st to 10th	Day	32% 14% 32% 15% 6%	530
	11th to 20th	Day	23% 18% 30% 20% 8% 1	530
	21st to end	Day	26% 17% 33% 15% 8% 2	530
July	1st to 10th	Day	20% 15% 33% 23% 8% 1	525
	11th to 20th	Day	17% 12% 38% 23% 7% 2	524
	21st to end	Day	19% 11% 37% 24% 7% 1	576
August	1st to 10th	Day	18% 12% 29% 27% 12% 2	526
	11th to 20th	Day	18% 9% 31% 22% 16% 4	519
	21st to end	Day	24% 15% 24% 23% 11% 4	583
September	1st to 10th	Day	21% 14% 28% 20% 13% 4	530
	11th to 20th	Day	20% 12% 21% 23% 17% 8%	530
	21st to end	Day	20% 16% 23% 24% 12% 4	530
October	1st to 10th	Day	25% 17% 25% 18% 11% 3	530
	11th to 20th	Day	30% 20% 25% 16% 8% 1	460
	21st to end	Day	34% 23% 24% 14% 5%	462
November	1st to 10th	Day	37% 19% 27% 13% 4	425
	11th to 20th	Day	31% 23% 26% 13% 5% 1	430
	21st to end	Day	34% 22% 29% 12% 2	276
December	1st to 10th	Day	30% 24% 29% 12% 5%	220
	11th to 20th	Day	36% 28% 27% 8% 1	220
	21st to end	Day	38% 21% 29% 9% 2	242
January	1st to 10th	Night	27% 27% 30% 14% 2	840
	11th to 20th	Night	25% 27% 29% 15% 3	840
	21st to end	Night	22% 24% 31% 18% 5%	924
February	1st to 10th	Night	24% 25% 30% 19% 3	840
	11th to 20th	Night	24% 25% 33% 15% 2	823
	21st to end	Night	25% 20% 34% 18% 2	692
March	1st to 10th	Night	29% 22% 30% 17% 2	840
	11th to 20th	Night	31% 21% 27% 16% 5%	840
	21st to end	Night	32% 19% 25% 18% 6% 1	924
April	1st to 10th	Night	35% 20% 24% 17% 4	840
	11th to 20th	Night	32% 19% 25% 18% 6%	785
	21st to end	Night	31% 17% 28% 18% 5%	630
May	1st to 10th	Night	31% 13% 28% 21% 6% 1	604
	11th to 20th	Night	23% 12% 32% 25% 7% 1	394
	21st to end	Night	23% 10% 27% 32% 7% 1	433
June	1st to 10th	Night	31% 8% 25% 27% 8% 1	400
	11th to 20th	Night	20% 9% 26% 33% 12%	400
	21st to end	Night	20% 8% 29% 34% 9%	400
July	1st to 10th	Night	17% 6% 29% 35% 13% 1	390
	11th to 20th	Night	15% 6% 27% 35% 15% 1	388
	21st to end	Night	15% 7% 25% 38% 14%	438
August	1st to 10th	Night	20% 4 16% 41% 18%	416
	11th to 20th	Night	18% 7% 23% 32% 19% 1	592
	21st to end	Night	20% 6% 24% 32% 16% 2	856
September	1st to 10th	Night	19% 8% 26% 32% 14% 1	800
	11th to 20th	Night	21% 8% 19% 30% 21% 2	800
	21st to end	Night	23% 11% 26% 25% 13% 2	800
October	1st to 10th	Night	27% 12% 22% 25% 13% 1	800
	11th to 20th	Night	31% 15% 24% 21% 8% 1	800
	21st to end	Night	34% 17% 27% 19% 4	880
November	1st to 10th	Night	34% 16% 28% 17% 5%	820
	11th to 20th	Night	28% 21% 28% 15% 7% 1	840
	21st to end	Night	30% 24% 25% 15% 5% 1	840
December	1st to 10th	Night	31% 25% 27% 13% 3	840
	11th to 20th	Night	32% 24% 27% 13% 4	840
	21st to end	Night	33% 23% 26% 16% 2	924

Page generated at 2026-04-29 02:21:45. Version ac07

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