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 2025-02-25.

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	16% 13% 5% 10% 6% 5% 4 3 5% 6% 28%	108225
	Night	14% 15% 5% 12% 6% 5% 5% 3 5% 5% 25%	110595
Transparency	Day	57% 3 10% 19% 9% 1	111715
	Night	61% 3 10% 18% 7% 1	115255
Seeing	Day	23% 16% 31% 20% 8% 2	15792
	Night	23% 13% 32% 24% 8% 1	25253

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% 20% 9% 19% 9% 7% 6% 3 4 4 13%	3158
	11th to 20th	Day	7% 15% 7% 20% 8% 7% 6% 3 3 4 19%	3521
	21st to end	Day	7% 20% 10% 19% 7% 8% 6% 4 5% 5% 10%	3982
February	1st to 10th	Day	6% 15% 5% 12% 11% 9% 6% 4 5% 7% 20%	1721
	11th to 20th	Day	9% 17% 7% 12% 8% 7% 4 4 4 6% 23%	1768
	21st to end	Day	8% 18% 8% 14% 8% 7% 5% 4 5% 6% 18%	1610
March	1st to 10th	Day	11% 14% 4 10% 7% 5% 5% 4 5% 6% 28%	3140
	11th to 20th	Day	9% 18% 6% 12% 9% 5% 4 3 4 5% 25%	3480
	21st to end	Day	15% 15% 9% 12% 4 3 5% 3 4 5% 23%	3815
April	1st to 10th	Day	17% 18% 6% 11% 6% 4 4 3 4 5% 22%	2304
	11th to 20th	Day	19% 15% 4 8% 4 4 4 4 5% 5% 28%	2442
	21st to end	Day	18% 14% 4 8% 4 4 4 4 4 5% 31%	2470
May	1st to 10th	Day	18% 11% 3 7% 5% 5% 4 3 4 7% 32%	4108
	11th to 20th	Day	14% 9% 3 8% 5% 5% 5% 4 6% 7% 34%	4450
	21st to end	Day	18% 8% 3 6% 5% 4 4 3 5% 7% 38%	5185
June	1st to 10th	Day	20% 9% 2 7% 5% 4 5% 3 6% 7% 32%	2850
	11th to 20th	Day	19% 7% 2 6% 5% 4 4 4 6% 7% 35%	2850
	21st to end	Day	20% 8% 3 7% 5% 5% 4 4 5% 7% 32%	2850
July	1st to 10th	Day	17% 8% 3 8% 5% 5% 5% 4 6% 7% 32%	4760
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 4 6% 8% 41%	4738
	21st to end	Day	16% 6% 3 5% 4 4 5% 4 6% 8% 39%	4814
August	1st to 10th	Day	12% 7% 2 8% 6% 5% 6% 4 7% 9% 34%	4244
	11th to 20th	Day	19% 7% 2 5% 4 4 4 3 5% 8% 40%	4044
	21st to end	Day	19% 6% 2 7% 4 3 4 3 5% 6% 40%	4532
September	1st to 10th	Day	21% 8% 3 7% 3 4 4 4 4 7% 36%	2271
	11th to 20th	Day	21% 9% 2 7% 4 4 3 3 6% 7% 35%	2090
	21st to end	Day	23% 12% 2 7% 4 3 4 2 4 5% 33%	2090
October	1st to 10th	Day	22% 17% 4 6% 4 4 4 3 4 5% 28%	1995
	11th to 20th	Day	24% 23% 5% 7% 3 3 4 3 5% 5% 18%	1842
	21st to end	Day	23% 24% 7% 9% 5% 4 3 2 4 5% 14%	1881
November	1st to 10th	Day	21% 20% 6% 9% 5% 4 4 2 4 6% 19%	1728
	11th to 20th	Day	18% 23% 7% 12% 6% 5% 4 3 3 3 15%	1600
	21st to end	Day	18% 27% 8% 14% 6% 4 3 3 3 5% 9%	1515
December	1st to 10th	Day	13% 23% 9% 20% 11% 5% 4 2 3 3 7%	2280
	11th to 20th	Day	11% 20% 7% 15% 8% 5% 4 3 5% 6% 17%	2621
	21st to end	Day	19% 23% 9% 15% 7% 3 3 2 3 5% 11%	3476
January	1st to 10th	Night	8% 18% 7% 18% 9% 10% 6% 4 5% 5% 11%	6808
	11th to 20th	Night	7% 18% 8% 18% 9% 8% 6% 3 4 3 16%	6380
	21st to end	Night	8% 15% 10% 18% 8% 7% 7% 4 5% 4 15%	6996
February	1st to 10th	Night	8% 15% 5% 12% 9% 9% 6% 6% 6% 6% 18%	2678
	11th to 20th	Night	8% 16% 7% 14% 9% 7% 6% 4 5% 5% 19%	2516
	21st to end	Night	8% 19% 7% 12% 8% 6% 7% 4 4 4 20%	1939
March	1st to 10th	Night	15% 15% 3 9% 6% 4 4 3 5% 7% 30%	3700
	11th to 20th	Night	9% 16% 7% 15% 6% 4 4 3 4 5% 28%	3479
	21st to end	Night	12% 12% 7% 12% 6% 8% 5% 3 4 5% 26%	3817
April	1st to 10th	Night	17% 16% 3 9% 5% 4 4 4 6% 6% 26%	1891
	11th to 20th	Night	17% 14% 4 9% 5% 3 4 3 5% 6% 30%	1687
	21st to end	Night	17% 13% 4 7% 4 3 3 3 5% 6% 35%	1710
May	1st to 10th	Night	18% 12% 3 6% 4 4 3 3 4 4 39%	2833
	11th to 20th	Night	13% 10% 3 9% 5% 5% 5% 3 6% 5% 35%	2433
	21st to end	Night	19% 9% 2 5% 4 4 5% 4 6% 6% 37%	2402
June	1st to 10th	Night	19% 8% 3 5% 4 4 4 4 6% 7% 36%	1330
	11th to 20th	Night	18% 8% 3 8% 5% 4 4 4 6% 6% 35%	1330
	21st to end	Night	16% 6% 2 7% 6% 4 4 4 5% 7% 39%	1330
July	1st to 10th	Night	15% 7% 3 4 4 4 4 3 5% 8% 44%	2210
	11th to 20th	Night	12% 7% 3 7% 4 4 4 4 5% 7% 43%	2229
	21st to end	Night	14% 6% 2 5% 3 4 3 3 5% 8% 46%	2750
August	1st to 10th	Night	11% 8% 3 8% 4 5% 5% 4 6% 8% 38%	2688
	11th to 20th	Night	17% 8% 3 5% 3 3 4 3 4 7% 43%	2785
	21st to end	Night	14% 6% 3 6% 3 3 3 3 4 6% 50%	3124
September	1st to 10th	Night	17% 9% 2 7% 4 3 4 3 5% 6% 39%	1886
	11th to 20th	Night	18% 8% 2 6% 4 4 4 4 5% 7% 39%	2090
	21st to end	Night	21% 11% 3 6% 4 4 4 2 3 7% 34%	2090
October	1st to 10th	Night	21% 14% 3 7% 5% 4 4 4 4 5% 31%	2185
	11th to 20th	Night	22% 18% 4 9% 4 4 3 3 4 5% 24%	2336
	21st to end	Night	23% 21% 6% 9% 5% 4 3 3 4 4 19%	2717
November	1st to 10th	Night	18% 18% 5% 10% 5% 4 4 4 4 5% 22%	2568
	11th to 20th	Night	19% 19% 5% 12% 7% 5% 5% 3 4 5% 16%	2800
	21st to end	Night	19% 21% 8% 14% 7% 5% 4 3 3 4 12%	2880
December	1st to 10th	Night	11% 23% 9% 21% 9% 6% 4 3 3 3 8%	4910
	11th to 20th	Night	10% 21% 8% 15% 9% 6% 4 4 4 5% 15%	5586
	21st to end	Night	20% 22% 7% 15% 8% 5% 4 3 5% 4 9%	7502

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	77% 2 5% 10% 4 1	3159
	11th to 20th	Day	72% 1 6% 13% 7% 1	3552
	21st to end	Day	77% 2 5% 10% 5%	3982
February	1st to 10th	Day	64% 4 8% 14% 9%	1721
	11th to 20th	Day	63% 3 9% 15% 10% 1	1777
	21st to end	Day	67% 3 6% 13% 11% 1	1610
March	1st to 10th	Day	57% 2 12% 17% 10% 1	3142
	11th to 20th	Day	62% 2 9% 18% 8% 1	3480
	21st to end	Day	64% 2 6% 15% 12% 1	3815
April	1st to 10th	Day	66% 2 6% 15% 10% 1	2304
	11th to 20th	Day	58% 2 7% 23% 9% 1	2442
	21st to end	Day	56% 3 8% 16% 15% 2	2470
May	1st to 10th	Day	52% 3 7% 24% 12% 1	4120
	11th to 20th	Day	49% 3 10% 22% 14% 1	4454
	21st to end	Day	47% 3 10% 22% 14% 4	5185
June	1st to 10th	Day	52% 3 10% 21% 13% 1	2850
	11th to 20th	Day	47% 4 10% 24% 13% 1	2850
	21st to end	Day	52% 4 11% 20% 11% 1	2850
July	1st to 10th	Day	50% 5% 13% 23% 9%	4686
	11th to 20th	Day	40% 5% 17% 27% 10% 1	4657
	21st to end	Day	43% 4 11% 32% 10%	4662
August	1st to 10th	Day	44% 6% 14% 27% 8%	4229
	11th to 20th	Day	44% 5% 17% 28% 7%	4083
	21st to end	Day	45% 4 14% 26% 9% 2	4531
September	1st to 10th	Day	49% 3 13% 24% 11%	2271
	11th to 20th	Day	50% 4 17% 23% 6%	2090
	21st to end	Day	54% 3 12% 22% 9%	2090
October	1st to 10th	Day	51% 3 14% 22% 9%	3320
	11th to 20th	Day	60% 3 11% 20% 6%	3032
	21st to end	Day	73% 3 11% 8% 5%	3081
November	1st to 10th	Day	69% 2 10% 14% 4	1728
	11th to 20th	Day	75% 2 9% 10% 3 1	1600
	21st to end	Day	81% 3 8% 7% 1	1515
December	1st to 10th	Day	86% 2 4 5% 3	2280
	11th to 20th	Day	69% 3 11% 12% 5%	2621
	21st to end	Day	78% 1 4 13% 3	3476
January	1st to 10th	Night	78% 2 6% 9% 3 2	6808
	11th to 20th	Night	74% 2 6% 12% 6%	6424
	21st to end	Night	72% 3 6% 13% 7%	6996
February	1st to 10th	Night	64% 6% 8% 13% 8% 1	2678
	11th to 20th	Night	66% 3 9% 15% 6%	2518
	21st to end	Night	66% 4 7% 15% 6% 1	1939
March	1st to 10th	Night	55% 4 12% 19% 9% 1	3711
	11th to 20th	Night	61% 3 9% 19% 8% 1	3480
	21st to end	Night	63% 3 7% 15% 10% 2	3817
April	1st to 10th	Night	59% 4 8% 17% 12%	1891
	11th to 20th	Night	57% 2 7% 20% 13% 1	1687
	21st to end	Night	51% 3 9% 21% 13% 3	1710
May	1st to 10th	Night	48% 3 7% 24% 16% 1	2840
	11th to 20th	Night	50% 3 9% 30% 8% 1	2434
	21st to end	Night	48% 4 12% 19% 14% 3	2403
June	1st to 10th	Night	47% 3 12% 23% 13% 1	1330
	11th to 20th	Night	49% 4 11% 21% 14% 1	1330
	21st to end	Night	44% 5% 16% 24% 11% 1	1330
July	1st to 10th	Night	40% 4 15% 33% 8% 1	2175
	11th to 20th	Night	40% 4 17% 29% 9% 1	2187
	21st to end	Night	38% 4 14% 30% 13% 1	2662
August	1st to 10th	Night	43% 5% 15% 32% 5%	2679
	11th to 20th	Night	42% 5% 19% 29% 5%	2812
	21st to end	Night	37% 3 13% 33% 14% 1	3124
September	1st to 10th	Night	48% 4 14% 24% 10% 1	1886
	11th to 20th	Night	45% 4 19% 25% 7%	2090
	21st to end	Night	52% 4 15% 22% 7%	2090
October	1st to 10th	Night	49% 4 12% 26% 9%	3640
	11th to 20th	Night	55% 3 12% 22% 7%	3872
	21st to end	Night	65% 5% 16% 11% 3	4467
November	1st to 10th	Night	65% 4 11% 15% 5%	2568
	11th to 20th	Night	72% 3 10% 12% 4	2800
	21st to end	Night	78% 4 9% 6% 2	2880
December	1st to 10th	Night	82% 3 6% 6% 2	4910
	11th to 20th	Night	71% 4 6% 13% 5% 1	5585
	21st to end	Night	79% 2 5% 10% 5%	7502

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% 37% 13% 9% 2	200
	11th to 20th	Day	18% 16% 33% 27% 5%	286
	21st to end	Day	19% 16% 33% 26% 6%	330
February	1st to 10th	Day	18% 26% 36% 14% 5% 2	300
	11th to 20th	Day	22% 20% 38% 15% 2 2	300
	21st to end	Day	19% 35% 35% 9% 1	237
March	1st to 10th	Day	20% 22% 39% 16% 3	279
	11th to 20th	Day	22% 20% 37% 15% 6% 2	460
	21st to end	Day	28% 15% 35% 16% 6%	506
April	1st to 10th	Day	25% 16% 37% 17% 4	460
	11th to 20th	Day	29% 20% 27% 14% 7% 3	452
	21st to end	Day	28% 19% 24% 18% 10% 2	460
May	1st to 10th	Day	24% 15% 33% 17% 8% 2	463
	11th to 20th	Day	22% 15% 34% 18% 9% 3	589
	21st to end	Day	22% 17% 34% 19% 6% 2	734
June	1st to 10th	Day	22% 18% 35% 18% 5% 1	680
	11th to 20th	Day	24% 18% 30% 20% 7% 2	680
	21st to end	Day	23% 12% 31% 22% 10% 3	680
July	1st to 10th	Day	15% 14% 35% 25% 8% 3	671
	11th to 20th	Day	18% 13% 29% 27% 9% 4	668
	21st to end	Day	17% 11% 30% 27% 11% 4	739
August	1st to 10th	Day	17% 13% 27% 29% 11% 4	575
	11th to 20th	Day	20% 7% 23% 27% 16% 7%	479
	21st to end	Day	24% 9% 27% 21% 14% 4	539
September	1st to 10th	Day	24% 12% 31% 18% 12% 3	490
	11th to 20th	Day	25% 9% 30% 23% 10% 2	490
	21st to end	Day	28% 12% 26% 23% 10% 2	490
October	1st to 10th	Day	30% 18% 25% 19% 8% 1	490
	11th to 20th	Day	32% 18% 31% 14% 3 1	432
	21st to end	Day	33% 23% 28% 14% 2	330
November	1st to 10th	Day	34% 20% 31% 13% 2	283
	11th to 20th	Day	38% 19% 28% 12% 4 1	200
	21st to end	Day	32% 23% 32% 13% 1	200
December	1st to 10th	Day	21% 16% 39% 16% 7% 2	200
	11th to 20th	Day	24% 19% 37% 18% 3 1	200
	21st to end	Day	31% 16% 29% 16% 6% 1	220
January	1st to 10th	Night	21% 14% 39% 20% 5% 1	1000
	11th to 20th	Night	22% 15% 32% 23% 7% 1	1000
	21st to end	Night	20% 13% 31% 27% 9% 1	1100
February	1st to 10th	Night	17% 14% 39% 23% 6% 1	878
	11th to 20th	Night	18% 16% 36% 23% 6% 1	783
	21st to end	Night	19% 17% 39% 21% 4	647
March	1st to 10th	Night	17% 18% 37% 22% 6%	760
	11th to 20th	Night	19% 20% 37% 17% 6% 1	760
	21st to end	Night	17% 15% 38% 22% 8% 1	836
April	1st to 10th	Night	26% 13% 33% 23% 6% 1	594
	11th to 20th	Night	26% 15% 26% 25% 7% 1	563
	21st to end	Night	22% 13% 30% 24% 11% 1	570
May	1st to 10th	Night	21% 9% 34% 30% 7%	570
	11th to 20th	Night	20% 12% 31% 28% 7% 1	447
	21st to end	Night	22% 8% 36% 29% 5%	411
June	1st to 10th	Night	23% 11% 28% 34% 4	380
	11th to 20th	Night	23% 10% 30% 28% 8%	380
	21st to end	Night	17% 10% 28% 32% 13% 1	380
July	1st to 10th	Night	15% 7% 36% 32% 8% 1	370
	11th to 20th	Night	17% 7% 30% 32% 11% 1	374
	21st to end	Night	14% 8% 29% 30% 17% 2	624
August	1st to 10th	Night	17% 7% 25% 35% 15% 1	567
	11th to 20th	Night	18% 5% 23% 34% 18% 2	564
	21st to end	Night	22% 7% 28% 26% 15% 2	627
September	1st to 10th	Night	22% 9% 28% 26% 12% 2	632
	11th to 20th	Night	23% 11% 26% 26% 13% 1	760
	21st to end	Night	27% 9% 26% 25% 11% 1	760
October	1st to 10th	Night	30% 11% 28% 24% 8%	760
	11th to 20th	Night	31% 13% 30% 20% 4 1	760
	21st to end	Night	36% 14% 26% 19% 4	836
November	1st to 10th	Night	29% 14% 34% 17% 4 1	780
	11th to 20th	Night	30% 17% 29% 19% 6%	800
	21st to end	Night	29% 16% 31% 19% 5% 1	880
December	1st to 10th	Night	23% 15% 34% 22% 6% 1	1000
	11th to 20th	Night	23% 17% 35% 18% 7% 1	1000
	21st to end	Night	27% 17% 28% 20% 7% 1	1100

Page generated at 2025-02-22 06:51:38. Version ac07

Copyright © 2025 Attilla Danko.