Athabasca
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Athabasca clear sky chart from 2005-11-06 to 2026-10-14.

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	10% 9% 3 8% 6% 5% 5% 5% 7% 8% 34%	155261
	Night	8% 10% 4 10% 6% 6% 6% 4 6% 8% 33%	145173
Transparency	Day	46% 5% 18% 24% 7%	154953
	Night	49% 5% 17% 21% 8% 1	145067
Seeing	Day	14% 7% 25% 30% 19% 6%	18781
	Night	13% 5% 26% 37% 17% 2	27037

By Month

Percentage Cloud Cover NW (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	7% 16% 5% 13% 8% 6% 5% 6% 6% 7% 21%	3845
	11th to 20th	Day	3 8% 3 11% 8% 6% 5% 7% 7% 10% 32%	4119
	21st to end	Day	5% 12% 6% 12% 7% 6% 5% 4 6% 8% 29%	4691
February	1st to 10th	Day	6% 13% 4 10% 8% 7% 6% 5% 7% 9% 25%	1680
	11th to 20th	Day	6% 11% 5% 13% 7% 6% 6% 4 6% 8% 28%	1764
	21st to end	Day	4 11% 6% 11% 8% 7% 7% 6% 8% 8% 24%	1582
March	1st to 10th	Day	4 10% 4 11% 9% 7% 8% 5% 7% 8% 27%	4618
	11th to 20th	Day	5% 12% 6% 12% 7% 5% 5% 4 5% 9% 31%	5063
	21st to end	Day	10% 16% 6% 14% 6% 4 4 3 5% 8% 23%	5689
April	1st to 10th	Day	8% 12% 4 9% 7% 6% 5% 5% 7% 8% 29%	2646
	11th to 20th	Day	10% 12% 3 8% 6% 6% 5% 4 6% 7% 31%	2700
	21st to end	Day	12% 12% 4 9% 6% 5% 6% 5% 7% 8% 27%	2742
May	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 4 6% 8% 41%	8793
	11th to 20th	Day	16% 11% 3 9% 6% 5% 5% 5% 6% 7% 27%	8755
	21st to end	Day	11% 7% 2 7% 6% 6% 6% 5% 7% 9% 34%	9649
June	1st to 10th	Day	16% 7% 3 8% 6% 6% 6% 5% 6% 8% 30%	3210
	11th to 20th	Day	20% 9% 3 8% 6% 5% 7% 5% 6% 8% 23%	3360
	21st to end	Day	11% 6% 2 7% 6% 6% 7% 5% 7% 8% 35%	3360
July	1st to 10th	Day	8% 5% 2 6% 5% 6% 6% 5% 8% 11% 39%	9420
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 9% 43%	8888
	21st to end	Day	10% 4 2 5% 3 4 5% 5% 7% 10% 45%	9569
August	1st to 10th	Day	13% 6% 2 6% 4 5% 5% 4 7% 8% 40%	6771
	11th to 20th	Day	9% 6% 2 7% 5% 4 5% 5% 7% 10% 40%	6168
	21st to end	Day	8% 4 2 6% 4 4 5% 4 7% 11% 45%	6570
September	1st to 10th	Day	12% 7% 3 7% 5% 5% 5% 3 6% 7% 41%	2699
	11th to 20th	Day	13% 7% 2 6% 4 4 5% 4 6% 8% 40%	2310
	21st to end	Day	8% 7% 2 7% 5% 5% 4 4 7% 8% 44%	2310
October	1st to 10th	Day	10% 9% 3 8% 5% 5% 5% 5% 7% 9% 35%	3477
	11th to 20th	Day	13% 11% 3 7% 5% 5% 5% 4 5% 7% 35%	2992
	21st to end	Day	9% 14% 5% 9% 5% 5% 5% 4 5% 7% 30%	3082
November	1st to 10th	Day	11% 15% 5% 9% 5% 5% 5% 4 6% 8% 27%	1646
	11th to 20th	Day	5% 13% 5% 13% 6% 7% 5% 3 6% 8% 28%	1470
	21st to end	Day	5% 13% 5% 14% 9% 5% 5% 4 5% 7% 29%	1470
December	1st to 10th	Day	9% 13% 5% 13% 7% 6% 7% 5% 7% 8% 20%	2360
	11th to 20th	Day	10% 15% 5% 9% 5% 6% 6% 4 6% 7% 26%	2712
	21st to end	Day	4 8% 3 12% 8% 7% 7% 5% 7% 7% 32%	3081
January	1st to 10th	Night	7% 14% 6% 15% 7% 7% 6% 4 5% 6% 22%	9030
	11th to 20th	Night	3 9% 4 8% 7% 6% 6% 5% 6% 8% 39%	8779
	21st to end	Night	6% 12% 5% 11% 8% 7% 6% 4 5% 7% 30%	9548
February	1st to 10th	Night	7% 11% 5% 11% 7% 6% 7% 5% 7% 8% 26%	2940
	11th to 20th	Night	7% 10% 4 11% 8% 7% 6% 5% 6% 6% 29%	2743
	21st to end	Night	3 10% 4 10% 7% 6% 6% 7% 8% 8% 30%	2223
March	1st to 10th	Night	4 9% 5% 11% 6% 7% 7% 5% 7% 9% 31%	5496
	11th to 20th	Night	5% 9% 4 11% 7% 6% 5% 4 7% 10% 32%	5156
	21st to end	Night	11% 18% 7% 13% 5% 4 4 3 4 6% 24%	5526
April	1st to 10th	Night	9% 9% 3 8% 6% 7% 5% 4 6% 9% 34%	1973
	11th to 20th	Night	8% 11% 3 8% 7% 7% 7% 5% 6% 7% 31%	1871
	21st to end	Night	11% 13% 3 8% 5% 4 5% 4 5% 7% 33%	1875
May	1st to 10th	Night	12% 5% 2 6% 4 4 4 4 6% 8% 43%	4126
	11th to 20th	Night	16% 10% 4 9% 5% 6% 5% 5% 6% 6% 27%	4105
	21st to end	Night	11% 7% 2 7% 6% 5% 6% 4 8% 9% 35%	4522
June	1st to 10th	Night	16% 7% 3 8% 6% 6% 6% 4 6% 8% 31%	1406
	11th to 20th	Night	18% 9% 3 8% 5% 6% 5% 5% 7% 8% 28%	1260
	21st to end	Night	11% 7% 2 7% 5% 5% 4 5% 7% 9% 38%	1260
July	1st to 10th	Night	7% 4 2 6% 4 5% 5% 5% 7% 10% 46%	3540
	11th to 20th	Night	8% 6% 3 7% 5% 5% 6% 4 6% 9% 41%	4056
	21st to end	Night	10% 4 2 5% 4 4 4 4 6% 9% 47%	4499
August	1st to 10th	Night	12% 5% 2 8% 5% 5% 5% 4 6% 8% 38%	3376
	11th to 20th	Night	13% 7% 3 7% 4 5% 4 4 5% 9% 39%	3886
	21st to end	Night	10% 4 2 5% 5% 4 5% 4 7% 8% 46%	4578
September	1st to 10th	Night	12% 6% 3 5% 4 5% 5% 4 5% 9% 43%	1918
	11th to 20th	Night	11% 7% 2 5% 4 4 4 4 7% 8% 44%	2310
	21st to end	Night	10% 6% 2 6% 4 4 5% 4 5% 9% 44%	2310
October	1st to 10th	Night	8% 7% 3 7% 5% 5% 6% 5% 7% 10% 35%	3936
	11th to 20th	Night	9% 9% 3 7% 5% 5% 5% 4 7% 9% 36%	4218
	21st to end	Night	10% 10% 4 9% 4 5% 5% 5% 8% 8% 31%	4686
November	1st to 10th	Night	12% 15% 6% 10% 6% 5% 5% 3 5% 5% 27%	2870
	11th to 20th	Night	8% 13% 5% 11% 7% 6% 6% 5% 6% 7% 26%	3150
	21st to end	Night	6% 12% 5% 13% 8% 6% 5% 4 6% 7% 26%	3150
December	1st to 10th	Night	10% 15% 6% 13% 7% 6% 5% 4 6% 6% 21%	5040
	11th to 20th	Night	8% 16% 6% 14% 7% 6% 6% 5% 7% 7% 19%	5700
	21st to end	Night	3 8% 4 11% 6% 7% 6% 5% 6% 8% 35%	8111

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	62% 4 11% 13% 10%	3845
	11th to 20th	Day	46% 4 17% 17% 15% 1	4140
	21st to end	Day	54% 5% 21% 14% 6%	4692
February	1st to 10th	Day	54% 7% 13% 16% 10%	1680
	11th to 20th	Day	52% 7% 15% 17% 9%	1772
	21st to end	Day	53% 7% 18% 15% 7%	1582
March	1st to 10th	Day	53% 4 16% 20% 7%	4618
	11th to 20th	Day	50% 5% 16% 23% 6%	5064
	21st to end	Day	60% 5% 10% 19% 6%	5689
April	1st to 10th	Day	49% 8% 17% 17% 8% 1	2646
	11th to 20th	Day	49% 6% 14% 21% 9% 1	2700
	21st to end	Day	52% 7% 12% 20% 8% 1	2742
May	1st to 10th	Day	40% 4 11% 31% 12% 1	8793
	11th to 20th	Day	55% 4 9% 27% 6%	8759
	21st to end	Day	45% 5% 19% 22% 8% 1	9650
June	1st to 10th	Day	50% 6% 15% 21% 8%	3210
	11th to 20th	Day	57% 7% 14% 17% 5%	3360
	21st to end	Day	44% 9% 20% 21% 7%	3360
July	1st to 10th	Day	39% 4 26% 25% 6%	9341
	11th to 20th	Day	38% 4 14% 32% 12%	8805
	21st to end	Day	35% 4 24% 34% 4	9362
August	1st to 10th	Day	42% 4 23% 28% 2	6753
	11th to 20th	Day	40% 4 24% 27% 5%	6210
	21st to end	Day	34% 4 29% 30% 3	6569
September	1st to 10th	Day	42% 7% 20% 25% 6% 1	2699
	11th to 20th	Day	39% 7% 23% 24% 6%	2310
	21st to end	Day	37% 7% 20% 26% 9% 1	2310
October	1st to 10th	Day	46% 4 22% 23% 4	3477
	11th to 20th	Day	50% 4 17% 24% 5%	2992
	21st to end	Day	54% 4 18% 21% 3	3082
November	1st to 10th	Day	54% 8% 15% 17% 6%	1646
	11th to 20th	Day	54% 6% 19% 15% 6%	1470
	21st to end	Day	54% 8% 15% 18% 5% 1	1470
December	1st to 10th	Day	60% 6% 17% 11% 5%	2360
	11th to 20th	Day	56% 6% 20% 14% 4	2714
	21st to end	Day	48% 4 12% 26% 8% 1	3081
January	1st to 10th	Night	62% 4 11% 13% 9%	9031
	11th to 20th	Night	43% 4 17% 20% 15% 1	8820
	21st to end	Night	54% 5% 20% 16% 5%	9548
February	1st to 10th	Night	53% 6% 14% 16% 10% 1	2940
	11th to 20th	Night	54% 6% 12% 18% 10%	2745
	21st to end	Night	47% 8% 14% 21% 9%	2223
March	1st to 10th	Night	47% 5% 18% 23% 8%	5496
	11th to 20th	Night	47% 5% 17% 24% 8%	5156
	21st to end	Night	60% 6% 9% 15% 10%	5526
April	1st to 10th	Night	46% 6% 14% 21% 13% 1	1973
	11th to 20th	Night	49% 7% 11% 18% 12% 2	1871
	21st to end	Night	49% 6% 10% 22% 12% 1	1875
May	1st to 10th	Night	38% 4 11% 29% 15% 3	4126
	11th to 20th	Night	55% 4 9% 25% 6%	4105
	21st to end	Night	43% 5% 21% 24% 6%	4526
June	1st to 10th	Night	50% 5% 15% 19% 9% 1	1406
	11th to 20th	Night	53% 7% 14% 21% 6%	1260
	21st to end	Night	40% 8% 21% 24% 7% 1	1260
July	1st to 10th	Night	34% 5% 26% 25% 10% 1	3510
	11th to 20th	Night	41% 4 15% 30% 10%	4016
	21st to end	Night	36% 3 23% 33% 6%	4401
August	1st to 10th	Night	45% 5% 21% 28% 1	3369
	11th to 20th	Night	44% 4 23% 23% 6%	3910
	21st to end	Night	36% 3 25% 31% 5%	4578
September	1st to 10th	Night	38% 6% 22% 27% 6% 2	1918
	11th to 20th	Night	36% 5% 20% 29% 9%	2310
	21st to end	Night	37% 7% 16% 27% 11% 2	2310
October	1st to 10th	Night	43% 3 22% 24% 7%	3936
	11th to 20th	Night	45% 4 16% 30% 5%	4218
	21st to end	Night	48% 4 22% 21% 5%	4686
November	1st to 10th	Night	59% 5% 12% 19% 5%	2870
	11th to 20th	Night	55% 8% 15% 16% 5%	3150
	21st to end	Night	55% 7% 16% 16% 5% 1	3150
December	1st to 10th	Night	62% 6% 13% 13% 5%	5040
	11th to 20th	Night	63% 6% 16% 11% 3	5697
	21st to end	Night	46% 4 15% 23% 10% 1	8111

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	10% 4 27% 35% 19% 4	220
	11th to 20th	Day	11% 7% 34% 29% 15% 4	220
	21st to end	Day	10% 10% 36% 27% 13% 4	242
February	1st to 10th	Day	11% 7% 35% 30% 12% 4	220
	11th to 20th	Day	11% 6% 32% 31% 16% 3	286
	21st to end	Day	8% 6% 36% 32% 14% 5%	298
March	1st to 10th	Day	9% 9% 33% 31% 15% 3	540
	11th to 20th	Day	9% 8% 33% 30% 16% 4	540
	21st to end	Day	18% 5% 30% 28% 15% 4	594
April	1st to 10th	Day	10% 11% 33% 30% 11% 4	540
	11th to 20th	Day	16% 8% 27% 28% 16% 6%	532
	21st to end	Day	17% 9% 30% 29% 12% 3	548
May	1st to 10th	Day	12% 11% 24% 31% 18% 4	753
	11th to 20th	Day	15% 7% 23% 30% 19% 7%	775
	21st to end	Day	16% 7% 19% 31% 20% 7%	844
June	1st to 10th	Day	20% 8% 25% 29% 14% 4	840
	11th to 20th	Day	21% 6% 18% 26% 23% 6%	990
	21st to end	Day	13% 3 17% 32% 25% 10%	990
July	1st to 10th	Day	12% 4 17% 34% 24% 9%	976
	11th to 20th	Day	13% 4 20% 31% 24% 8%	795
	21st to end	Day	10% 5% 18% 29% 28% 11%	849
August	1st to 10th	Day	14% 4 16% 27% 25% 14%	715
	11th to 20th	Day	11% 4 27% 29% 22% 6%	557
	21st to end	Day	10% 6% 20% 32% 23% 9%	627
September	1st to 10th	Day	17% 9% 25% 24% 18% 7%	570
	11th to 20th	Day	18% 6% 22% 31% 18% 6%	570
	21st to end	Day	12% 10% 33% 27% 15% 3	570
October	1st to 10th	Day	14% 10% 30% 28% 15% 4	428
	11th to 20th	Day	16% 5% 33% 30% 15% 2	339
	21st to end	Day	19% 11% 31% 25% 11% 3	363
November	1st to 10th	Day	19% 5% 30% 31% 13% 1	328
	11th to 20th	Day	11% 6% 41% 26% 13% 3	220
	21st to end	Day	9% 6% 39% 29% 12% 6%	220
December	1st to 10th	Day	10% 7% 33% 31% 15% 5%	220
	11th to 20th	Day	13% 7% 33% 35% 10% 2	220
	21st to end	Day	11% 4 23% 36% 21% 6%	242
January	1st to 10th	Night	12% 5% 30% 38% 14% 1	1099
	11th to 20th	Night	11% 7% 34% 36% 12% 1	1050
	21st to end	Night	14% 7% 34% 32% 10% 2	1118
February	1st to 10th	Night	12% 6% 27% 34% 18% 2	840
	11th to 20th	Night	11% 4 27% 39% 18% 1	824
	21st to end	Night	7% 4 30% 38% 19% 4	692
March	1st to 10th	Night	9% 5% 27% 41% 15% 2	840
	11th to 20th	Night	12% 4 28% 40% 15% 1	840
	21st to end	Night	15% 4 27% 36% 17% 2	924
April	1st to 10th	Night	11% 5% 24% 39% 18% 3	713
	11th to 20th	Night	13% 4 27% 39% 15% 2	623
	21st to end	Night	15% 7% 21% 39% 18% 1	624
May	1st to 10th	Night	11% 7% 21% 40% 18% 3	420
	11th to 20th	Night	14% 5% 18% 40% 20% 3	414
	21st to end	Night	18% 4 18% 35% 23% 2	455
June	1st to 10th	Night	20% 5% 18% 39% 17% 2	420
	11th to 20th	Night	21% 5% 14% 36% 22% 3	420
	21st to end	Night	12% 4 12% 42% 26% 4	420
July	1st to 10th	Night	12% 2 17% 40% 29%	410
	11th to 20th	Night	12% 3 17% 42% 23% 2	408
	21st to end	Night	9% 2 13% 40% 31% 4	460
August	1st to 10th	Night	10% 3 14% 36% 32% 6%	418
	11th to 20th	Night	12% 2 19% 40% 26% 1	508
	21st to end	Night	12% 3 17% 43% 24% 2	693
September	1st to 10th	Night	16% 3 20% 35% 23% 2	649
	11th to 20th	Night	14% 3 16% 45% 20% 1	840
	21st to end	Night	12% 3 30% 38% 16% 1	840
October	1st to 10th	Night	15% 4 26% 38% 16% 1	840
	11th to 20th	Night	15% 4 30% 37% 12% 3	812
	21st to end	Night	17% 7% 30% 35% 11% 1	930
November	1st to 10th	Night	17% 5% 30% 34% 11% 2	1025
	11th to 20th	Night	14% 6% 34% 33% 11% 2	1050
	21st to end	Night	11% 5% 35% 33% 13% 2	1050
December	1st to 10th	Night	13% 6% 33% 32% 12% 3	1050
	11th to 20th	Night	12% 7% 30% 36% 13% 2	1050
	21st to end	Night	10% 3 30% 37% 17% 3	1268

Page generated at 2026-10-11 03:06:28. Version ac07

Copyright © 2026 Attilla Danko.