Chapleau
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chapleau clear sky chart from 2005-11-06 to 2026-07-01.

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	15% 13% 5% 10% 5% 5% 4 3 5% 6% 29%	137886
	Night	14% 14% 5% 12% 6% 5% 5% 3 5% 5% 25%	134698
Transparency	Day	57% 3 10% 20% 9% 1	141329
	Night	60% 3 10% 18% 8% 1	139330
Seeing	Day	23% 16% 31% 20% 7% 2	17664
	Night	23% 13% 32% 24% 8% 1	26922

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	8% 21% 10% 17% 8% 6% 5% 3 3 4 15%	4094
	11th to 20th	Day	7% 17% 7% 20% 9% 7% 6% 3 3 4 18%	4597
	21st to end	Day	5% 15% 9% 17% 7% 9% 7% 4 7% 6% 14%	5156
February	1st to 10th	Day	7% 15% 5% 12% 10% 9% 6% 4 5% 6% 20%	1807
	11th to 20th	Day	8% 18% 7% 12% 8% 7% 4 4 4 6% 22%	1859
	21st to end	Day	7% 18% 8% 15% 8% 7% 5% 4 5% 6% 18%	1730
March	1st to 10th	Day	14% 16% 5% 9% 7% 4 5% 4 6% 6% 26%	4614
	11th to 20th	Day	14% 17% 5% 11% 8% 6% 4 3 5% 5% 22%	5090
	21st to end	Day	16% 16% 8% 13% 4 3 5% 3 4 5% 24%	5586
April	1st to 10th	Day	17% 18% 6% 11% 6% 4 4 3 4 5% 23%	2548
	11th to 20th	Day	19% 16% 4 9% 4 4 3 3 5% 5% 29%	2702
	21st to end	Day	18% 15% 4 8% 4 4 5% 4 4 5% 31%	2730
May	1st to 10th	Day	15% 13% 4 8% 5% 5% 4 3 4 6% 32%	7642
	11th to 20th	Day	17% 9% 3 8% 5% 5% 4 3 4 6% 35%	8317
	21st to end	Day	16% 8% 2 6% 4 4 4 3 4 7% 41%	9716
June	1st to 10th	Day	19% 9% 2 6% 5% 4 5% 3 5% 7% 34%	3150
	11th to 20th	Day	19% 7% 3 6% 5% 4 4 4 6% 7% 34%	3150
	21st to end	Day	20% 8% 3 7% 5% 5% 5% 4 5% 7% 31%	3150
July	1st to 10th	Day	15% 7% 3 7% 5% 5% 5% 4 6% 8% 35%	6820
	11th to 20th	Day	15% 6% 2 6% 5% 5% 5% 4 6% 8% 38%	6784
	21st to end	Day	16% 6% 2 5% 4 4 5% 4 6% 9% 38%	6926
August	1st to 10th	Day	12% 7% 3 8% 5% 5% 6% 4 7% 9% 34%	4378
	11th to 20th	Day	19% 7% 2 5% 4 4 4 3 5% 8% 39%	4174
	21st to end	Day	19% 7% 2 7% 4 3 4 3 5% 6% 40%	4675
September	1st to 10th	Day	21% 8% 2 7% 4 4 4 4 4 7% 35%	2391
	11th to 20th	Day	20% 10% 2 7% 4 4 3 3 6% 7% 36%	2200
	21st to end	Day	23% 12% 2 7% 4 3 4 2 4 5% 34%	2200
October	1st to 10th	Day	21% 16% 4 6% 4 4 4 3 4 5% 29%	2100
	11th to 20th	Day	24% 22% 4 7% 3 4 4 3 5% 5% 19%	1939
	21st to end	Day	23% 24% 7% 9% 5% 3 3 2 4 5% 15%	1980
November	1st to 10th	Day	21% 20% 6% 10% 5% 4 4 2 4 6% 19%	1816
	11th to 20th	Day	18% 22% 7% 12% 6% 5% 4 3 3 4 15%	1680
	21st to end	Day	19% 26% 8% 14% 6% 4 3 3 3 5% 9%	1591
December	1st to 10th	Day	13% 22% 9% 20% 11% 5% 3 2 3 3 8%	2350
	11th to 20th	Day	11% 20% 8% 15% 8% 5% 4 3 5% 6% 17%	2691
	21st to end	Day	19% 23% 9% 15% 7% 3 3 2 3 5% 12%	3553
January	1st to 10th	Night	9% 17% 7% 19% 9% 9% 6% 3 4 5% 13%	8831
	11th to 20th	Night	7% 20% 9% 19% 9% 7% 5% 4 4 3 13%	8314
	21st to end	Night	6% 12% 8% 17% 9% 8% 8% 6% 6% 5% 16%	9058
February	1st to 10th	Night	8% 15% 5% 12% 9% 8% 7% 5% 6% 6% 18%	2812
	11th to 20th	Night	8% 16% 7% 14% 9% 7% 5% 4 5% 5% 19%	2645
	21st to end	Night	8% 18% 7% 13% 8% 6% 7% 4 5% 5% 20%	2076
March	1st to 10th	Night	15% 14% 4 10% 7% 5% 5% 3 5% 6% 26%	5446
	11th to 20th	Night	14% 16% 6% 14% 6% 4 4 3 5% 5% 24%	5089
	21st to end	Night	15% 14% 6% 12% 5% 6% 5% 3 4 5% 23%	5588
April	1st to 10th	Night	17% 16% 4 9% 5% 5% 4 3 5% 6% 26%	2089
	11th to 20th	Night	18% 14% 4 9% 5% 3 4 3 4 5% 29%	1867
	21st to end	Night	18% 13% 4 8% 4 3 3 3 5% 6% 34%	1890
May	1st to 10th	Night	13% 11% 3 7% 4 4 4 3 4 5% 41%	5257
	11th to 20th	Night	14% 10% 3 7% 4 5% 5% 3 6% 6% 38%	4531
	21st to end	Night	15% 9% 2 5% 4 4 4 3 6% 6% 41%	4492
June	1st to 10th	Night	19% 8% 3 5% 4 3 4 4 6% 7% 37%	1470
	11th to 20th	Night	17% 8% 3 8% 5% 4 4 4 6% 6% 34%	1470
	21st to end	Night	16% 7% 2 7% 6% 4 4 4 5% 7% 39%	1470
July	1st to 10th	Night	15% 6% 2 4 3 3 4 3 5% 8% 46%	3160
	11th to 20th	Night	15% 7% 2 6% 3 3 4 4 5% 8% 43%	3193
	21st to end	Night	14% 6% 2 5% 4 4 3 3 6% 8% 44%	3948
August	1st to 10th	Night	11% 7% 3 8% 4 5% 5% 4 5% 8% 38%	2773
	11th to 20th	Night	17% 8% 3 5% 3 3 4 3 4 7% 43%	2875
	21st to end	Night	14% 6% 3 6% 3 3 3 3 4 6% 49%	3223
September	1st to 10th	Night	17% 9% 2 7% 4 4 4 3 5% 6% 38%	1985
	11th to 20th	Night	17% 9% 2 6% 4 4 4 4 5% 7% 41%	2200
	21st to end	Night	21% 11% 3 6% 4 4 4 2 3 7% 34%	2200
October	1st to 10th	Night	20% 13% 3 7% 5% 4 4 4 4 4 32%	2300
	11th to 20th	Night	22% 18% 4 9% 4 4 3 3 3 5% 24%	2459
	21st to end	Night	22% 21% 6% 9% 5% 3 4 3 4 4 20%	2860
November	1st to 10th	Night	18% 18% 5% 10% 5% 4 4 4 4 5% 22%	2700
	11th to 20th	Night	18% 20% 6% 12% 7% 5% 5% 3 4 5% 16%	2940
	21st to end	Night	19% 21% 8% 14% 7% 5% 4 3 3 4 12%	3024
December	1st to 10th	Night	11% 23% 9% 21% 9% 6% 4 3 3 3 8%	5060
	11th to 20th	Night	10% 21% 8% 15% 9% 6% 4 4 4 5% 15%	5736
	21st to end	Night	20% 22% 7% 15% 8% 5% 4 2 5% 4 9%	7667

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	75% 2 5% 11% 4 3	4095
	11th to 20th	Day	74% 1 5% 13% 7%	4628
	21st to end	Day	70% 3 5% 16% 6%	5156
February	1st to 10th	Day	65% 4 8% 14% 9%	1807
	11th to 20th	Day	64% 3 9% 15% 9% 1	1868
	21st to end	Day	67% 2 5% 14% 10% 1	1730
March	1st to 10th	Day	60% 2 9% 14% 12% 4	4616
	11th to 20th	Day	65% 3 8% 14% 9% 1	5090
	21st to end	Day	65% 2 7% 15% 10% 1	5586
April	1st to 10th	Day	66% 2 6% 16% 9% 1	2548
	11th to 20th	Day	58% 2 7% 22% 9% 1	2702
	21st to end	Day	56% 3 8% 16% 14% 2	2730
May	1st to 10th	Day	54% 3 6% 20% 15% 2	7651
	11th to 20th	Day	51% 3 8% 19% 16% 3	8321
	21st to end	Day	44% 3 9% 26% 14% 4	9717
June	1st to 10th	Day	50% 3 10% 21% 14% 2	3150
	11th to 20th	Day	48% 4 10% 24% 13% 1	3150
	21st to end	Day	52% 5% 11% 21% 11% 1	3150
July	1st to 10th	Day	46% 5% 12% 27% 9%	6747
	11th to 20th	Day	42% 5% 17% 26% 8% 1	6703
	21st to end	Day	42% 5% 12% 33% 8%	6728
August	1st to 10th	Day	44% 6% 14% 28% 8%	4363
	11th to 20th	Day	44% 5% 17% 27% 7%	4213
	21st to end	Day	45% 4 14% 26% 9% 1	4674
September	1st to 10th	Day	50% 3 13% 23% 10%	2391
	11th to 20th	Day	49% 4 16% 24% 6%	2200
	21st to end	Day	53% 3 12% 23% 9%	2200
October	1st to 10th	Day	50% 3 15% 22% 9%	3425
	11th to 20th	Day	60% 3 11% 20% 6%	3129
	21st to end	Day	72% 3 11% 9% 5%	3180
November	1st to 10th	Day	69% 2 10% 14% 4	1816
	11th to 20th	Day	75% 2 9% 10% 3	1680
	21st to end	Day	81% 3 8% 7% 1	1591
December	1st to 10th	Day	85% 2 4 5% 3	2350
	11th to 20th	Day	69% 3 11% 12% 5%	2691
	21st to end	Day	78% 1 4 13% 3	3553
January	1st to 10th	Night	76% 2 6% 10% 4 2	8831
	11th to 20th	Night	76% 2 5% 11% 5%	8358
	21st to end	Night	68% 3 7% 15% 7%	9058
February	1st to 10th	Night	65% 5% 8% 13% 8% 1	2812
	11th to 20th	Night	66% 3 9% 16% 6%	2647
	21st to end	Night	65% 4 8% 16% 7% 1	2076
March	1st to 10th	Night	59% 4 10% 15% 10% 2	5457
	11th to 20th	Night	63% 4 10% 16% 7%	5090
	21st to end	Night	65% 2 6% 15% 10% 2	5588
April	1st to 10th	Night	59% 4 8% 17% 12% 1	2089
	11th to 20th	Night	58% 2 7% 20% 12% 1	1867
	21st to end	Night	52% 4 9% 20% 12% 2	1890
May	1st to 10th	Night	46% 3 7% 25% 16% 3	5264
	11th to 20th	Night	47% 4 9% 29% 8% 2	4532
	21st to end	Night	43% 3 10% 24% 17% 2	4493
June	1st to 10th	Night	46% 3 11% 23% 15% 1	1470
	11th to 20th	Night	48% 4 11% 22% 14% 1	1470
	21st to end	Night	44% 5% 16% 25% 11% 1	1470
July	1st to 10th	Night	38% 4 13% 38% 6%	3125
	11th to 20th	Night	41% 5% 18% 29% 7%	3151
	21st to end	Night	38% 5% 16% 31% 9%	3832
August	1st to 10th	Night	43% 5% 15% 32% 5%	2764
	11th to 20th	Night	43% 5% 19% 29% 5%	2902
	21st to end	Night	37% 3 13% 33% 13% 1	3223
September	1st to 10th	Night	48% 4 14% 24% 9% 1	1985
	11th to 20th	Night	44% 4 18% 26% 7%	2200
	21st to end	Night	52% 4 14% 23% 7%	2200
October	1st to 10th	Night	48% 4 12% 27% 9%	3755
	11th to 20th	Night	55% 3 12% 22% 7%	3995
	21st to end	Night	65% 5% 15% 12% 3	4610
November	1st to 10th	Night	65% 4 11% 15% 6%	2700
	11th to 20th	Night	72% 3 10% 11% 4	2940
	21st to end	Night	78% 4 8% 6% 3	3024
December	1st to 10th	Night	82% 3 6% 6% 2	5060
	11th to 20th	Night	72% 4 6% 13% 5% 1	5735
	21st to end	Night	79% 2 5% 10% 5%	7667

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	21% 19% 36% 14% 9% 1	220
	11th to 20th	Day	18% 16% 33% 28% 5%	315
	21st to end	Day	17% 15% 35% 27% 6%	363
February	1st to 10th	Day	18% 26% 35% 15% 5% 2	330
	11th to 20th	Day	21% 20% 39% 15% 2 2	330
	21st to end	Day	20% 33% 34% 11% 2	273
March	1st to 10th	Day	24% 23% 38% 14% 2	340
	11th to 20th	Day	24% 21% 36% 14% 5% 1	540
	21st to end	Day	28% 18% 34% 14% 5%	594
April	1st to 10th	Day	26% 17% 36% 16% 4 1	540
	11th to 20th	Day	28% 19% 28% 15% 6% 3	532
	21st to end	Day	28% 18% 26% 17% 9% 2	540
May	1st to 10th	Day	23% 15% 33% 19% 8% 2	543
	11th to 20th	Day	23% 16% 34% 17% 8% 2	680
	21st to end	Day	22% 16% 34% 20% 6% 2	844
June	1st to 10th	Day	21% 18% 35% 18% 6% 2	780
	11th to 20th	Day	24% 18% 30% 20% 7% 2	780
	21st to end	Day	23% 12% 31% 22% 10% 3	780
July	1st to 10th	Day	16% 14% 35% 25% 7% 3	722
	11th to 20th	Day	18% 14% 30% 26% 9% 3	718
	21st to end	Day	17% 11% 31% 27% 10% 4	794
August	1st to 10th	Day	16% 12% 28% 29% 11% 4	619
	11th to 20th	Day	21% 8% 22% 26% 16% 7%	519
	21st to end	Day	23% 10% 27% 21% 14% 4	583
September	1st to 10th	Day	24% 13% 31% 18% 12% 3	530
	11th to 20th	Day	24% 9% 29% 23% 12% 4	530
	21st to end	Day	28% 12% 26% 23% 10% 2	530
October	1st to 10th	Day	29% 17% 26% 19% 7% 1	530
	11th to 20th	Day	32% 18% 31% 15% 3 1	469
	21st to end	Day	32% 22% 26% 16% 4	363
November	1st to 10th	Day	33% 20% 31% 14% 2	311
	11th to 20th	Day	35% 18% 30% 12% 3	220
	21st to end	Day	33% 23% 32% 12% 1	220
December	1st to 10th	Day	19% 17% 39% 17% 6% 2	220
	11th to 20th	Day	24% 20% 36% 17% 2 1	220
	21st to end	Day	32% 16% 29% 17% 6% 1	242
January	1st to 10th	Night	21% 15% 39% 20% 5%	1050
	11th to 20th	Night	22% 14% 33% 23% 7% 1	1050
	21st to end	Night	19% 12% 32% 27% 8% 1	1155
February	1st to 10th	Night	17% 14% 39% 24% 6% 1	922
	11th to 20th	Night	18% 17% 36% 23% 6% 1	823
	21st to end	Night	18% 16% 39% 21% 5%	692
March	1st to 10th	Night	18% 18% 38% 21% 5%	840
	11th to 20th	Night	20% 20% 38% 16% 6% 1	840
	21st to end	Night	17% 15% 38% 22% 8% 1	924
April	1st to 10th	Night	26% 13% 33% 21% 6% 1	656
	11th to 20th	Night	27% 15% 25% 25% 7% 1	623
	21st to end	Night	23% 13% 28% 24% 10% 1	630
May	1st to 10th	Night	20% 9% 34% 30% 7%	630
	11th to 20th	Night	20% 12% 31% 29% 7% 1	495
	21st to end	Night	21% 9% 36% 28% 5%	455
June	1st to 10th	Night	23% 10% 28% 33% 5%	420
	11th to 20th	Night	22% 10% 31% 29% 8%	420
	21st to end	Night	16% 10% 29% 31% 13% 1	420
July	1st to 10th	Night	15% 7% 36% 32% 9% 1	390
	11th to 20th	Night	18% 7% 31% 32% 11% 1	395
	21st to end	Night	14% 8% 29% 31% 16% 2	657
August	1st to 10th	Night	17% 7% 25% 35% 15% 1	597
	11th to 20th	Night	18% 5% 23% 34% 17% 2	594
	21st to end	Night	22% 7% 27% 27% 15% 2	660
September	1st to 10th	Night	22% 10% 28% 26% 12% 2	665
	11th to 20th	Night	22% 10% 25% 28% 13% 2	800
	21st to end	Night	27% 9% 26% 25% 11% 2	800
October	1st to 10th	Night	29% 10% 28% 24% 8%	800
	11th to 20th	Night	31% 13% 31% 20% 4 1	800
	21st to end	Night	34% 14% 26% 21% 5%	880
November	1st to 10th	Night	29% 15% 33% 18% 4 1	820
	11th to 20th	Night	30% 17% 29% 19% 5%	840
	21st to end	Night	29% 16% 31% 19% 5% 1	924
December	1st to 10th	Night	23% 15% 34% 22% 6% 1	1050
	11th to 20th	Night	23% 17% 35% 18% 7% 1	1050
	21st to end	Night	27% 17% 27% 20% 7% 1	1155

Page generated at 2026-06-28 02:10:45. Version ac07

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