Jasper Athabasca Glacier
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Jasper Athabasca Glacier clear sky chart from 2005-11-06 to 2025-05-11.

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	5% 13% 6% 17% 9% 7% 6% 4 6% 6% 22%	117294
	Night	3 12% 7% 19% 10% 7% 6% 4 6% 6% 18%	120352
Transparency	Day	32% 45% 8% 9% 5% 1	117040
	Night	35% 43% 8% 8% 4 1	120252
Seeing	Day	15% 19% 28% 23% 12% 3	16457
	Night	12% 18% 34% 24% 11% 1	25059

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	6% 6% 26% 13% 13% 9% 6% 7% 4 9%	2786
	11th to 20th	Day	1 7% 3 20% 13% 8% 7% 5% 6% 5% 26%	3454
	21st to end	Day	12% 7% 30% 12% 6% 4 3 3 4 21%	4004
February	1st to 10th	Day	1 12% 7% 27% 10% 7% 6% 5% 5% 5% 15%	1600
	11th to 20th	Day	1 11% 7% 21% 13% 9% 6% 5% 6% 7% 14%	1660
	21st to end	Day	1 9% 6% 21% 16% 11% 8% 5% 6% 5% 13%	1650
March	1st to 10th	Day	8% 7% 22% 14% 9% 7% 4 6% 8% 14%	4518
	11th to 20th	Day	1 9% 7% 24% 11% 7% 6% 5% 5% 5% 20%	4687
	21st to end	Day	1 13% 10% 25% 11% 7% 6% 4 5% 5% 13%	5920
April	1st to 10th	Day	2 16% 9% 21% 12% 8% 7% 5% 6% 4 9%	2400
	11th to 20th	Day	2 18% 9% 18% 10% 8% 7% 4 4 5% 14%	2523
	21st to end	Day	3 20% 7% 18% 8% 7% 5% 4 6% 6% 15%	2695
May	1st to 10th	Day	5% 21% 7% 13% 7% 6% 5% 4 5% 7% 21%	4560
	11th to 20th	Day	6% 19% 7% 12% 6% 6% 6% 5% 6% 7% 20%	4593
	21st to end	Day	8% 22% 9% 15% 9% 6% 5% 4 5% 6% 12%	5161
June	1st to 10th	Day	14% 19% 6% 11% 7% 5% 6% 4 5% 6% 16%	2930
	11th to 20th	Day	14% 22% 6% 12% 6% 5% 5% 4 5% 7% 13%	3040
	21st to end	Day	11% 15% 5% 11% 7% 6% 5% 4 6% 6% 23%	3040
July	1st to 10th	Day	7% 9% 3 9% 6% 5% 4 4 5% 6% 42%	5060
	11th to 20th	Day	5% 5% 2 6% 4 4 4 4 6% 7% 51%	4848
	21st to end	Day	5% 10% 5% 11% 6% 5% 5% 3 6% 7% 37%	4832
August	1st to 10th	Day	7% 8% 3 8% 4 5% 5% 5% 7% 9% 39%	4401
	11th to 20th	Day	8% 8% 4 8% 6% 5% 5% 5% 7% 9% 34%	4313
	21st to end	Day	10% 12% 5% 11% 7% 6% 5% 4 5% 7% 28%	4441
September	1st to 10th	Day	8% 14% 4 11% 6% 6% 5% 4 5% 6% 30%	2280
	11th to 20th	Day	8% 17% 5% 11% 5% 4 4 4 6% 8% 29%	2190
	21st to end	Day	10% 22% 6% 11% 6% 5% 4 4 5% 6% 21%	2090
October	1st to 10th	Day	5% 15% 7% 17% 8% 6% 7% 5% 7% 7% 18%	3304
	11th to 20th	Day	6% 19% 9% 14% 7% 5% 5% 6% 6% 8% 15%	2874
	21st to end	Day	3 16% 7% 21% 10% 6% 5% 3 5% 6% 18%	3101
November	1st to 10th	Day	3 21% 11% 20% 11% 6% 5% 4 4 4 11%	1679
	11th to 20th	Day	2 15% 8% 23% 12% 8% 6% 4 5% 4 15%	1400
	21st to end	Day	1 14% 8% 23% 12% 8% 6% 4 4 5% 16%	1400
December	1st to 10th	Day	1 9% 6% 20% 10% 6% 6% 5% 7% 8% 21%	2290
	11th to 20th	Day	9% 7% 30% 15% 10% 6% 5% 6% 4 9%	2578
	21st to end	Day	6% 6% 25% 17% 10% 6% 4 5% 5% 15%	2992
January	1st to 10th	Night	7% 6% 27% 18% 9% 8% 5% 6% 5% 9%	7155
	11th to 20th	Night	6% 4 17% 12% 9% 8% 5% 8% 7% 24%	6489
	21st to end	Night	10% 10% 26% 11% 6% 5% 3 4 5% 19%	6952
February	1st to 10th	Night	1 10% 8% 24% 11% 8% 6% 5% 6% 6% 15%	2800
	11th to 20th	Night	1 10% 8% 23% 13% 8% 6% 4 6% 5% 16%	2623
	21st to end	Night	9% 7% 19% 14% 9% 7% 5% 6% 7% 16%	1980
March	1st to 10th	Night	7% 6% 24% 11% 10% 8% 7% 7% 6% 13%	5376
	11th to 20th	Night	1 9% 7% 23% 11% 8% 8% 5% 6% 7% 16%	5312
	21st to end	Night	1 14% 10% 24% 12% 7% 5% 4 5% 5% 12%	5054
April	1st to 10th	Night	2 13% 10% 24% 11% 6% 6% 4 5% 6% 12%	2000
	11th to 20th	Night	1 18% 8% 17% 10% 7% 6% 5% 7% 6% 16%	1828
	21st to end	Night	4 17% 7% 15% 8% 6% 5% 5% 6% 7% 20%	1702
May	1st to 10th	Night	4 21% 7% 13% 6% 6% 5% 4 6% 7% 21%	2620
	11th to 20th	Night	6% 17% 7% 15% 6% 6% 5% 5% 6% 8% 20%	2304
	21st to end	Night	8% 24% 10% 14% 7% 6% 5% 3 5% 5% 13%	2414
June	1st to 10th	Night	15% 19% 4 10% 5% 5% 6% 3 7% 8% 20%	1247
	11th to 20th	Night	16% 22% 6% 14% 6% 5% 5% 4 6% 6% 10%	1140
	21st to end	Night	12% 14% 5% 11% 7% 5% 5% 4 5% 7% 24%	1140
July	1st to 10th	Night	9% 12% 4 9% 5% 4 5% 3 5% 6% 39%	1900
	11th to 20th	Night	6% 6% 2 5% 5% 5% 4 3 5% 7% 53%	2110
	21st to end	Night	9% 13% 4 7% 5% 4 4 3 6% 8% 36%	2718
August	1st to 10th	Night	9% 9% 2 10% 6% 6% 6% 4 7% 9% 32%	2529
	11th to 20th	Night	8% 6% 3 7% 5% 5% 7% 6% 9% 12% 32%	2515
	21st to end	Night	9% 12% 5% 14% 6% 5% 5% 4 5% 6% 29%	3228
September	1st to 10th	Night	10% 15% 6% 9% 4 4 4 3 6% 7% 32%	1900
	11th to 20th	Night	9% 17% 5% 10% 5% 5% 3 3 4 7% 30%	1990
	21st to end	Night	9% 18% 7% 11% 5% 5% 6% 3 5% 7% 24%	2090
October	1st to 10th	Night	3 14% 7% 15% 7% 6% 6% 5% 7% 8% 21%	3675
	11th to 20th	Night	5% 18% 8% 14% 6% 5% 5% 5% 7% 9% 18%	4055
	21st to end	Night	2 15% 8% 19% 9% 6% 5% 4 5% 8% 18%	4457
November	1st to 10th	Night	4 21% 10% 22% 11% 5% 4 3 4 6% 10%	2604
	11th to 20th	Night	1 15% 7% 25% 14% 8% 5% 4 4 4 13%	2995
	21st to end	Night	1 13% 8% 22% 13% 8% 7% 4 5% 5% 13%	3000
December	1st to 10th	Night	1 11% 7% 22% 12% 9% 7% 4 6% 7% 14%	4890
	11th to 20th	Night	6% 8% 30% 15% 11% 8% 5% 6% 4 8%	5596
	21st to end	Night	1 8% 6% 24% 15% 10% 6% 5% 7% 7% 11%	7964

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	48% 34% 8% 6% 3 1	2786
	11th to 20th	Day	34% 30% 9% 10% 11% 6%	3478
	21st to end	Day	42% 34% 10% 9% 6%	4004
February	1st to 10th	Day	23% 63% 3 3 6% 2	1600
	11th to 20th	Day	21% 63% 7% 5% 4 1	1668
	21st to end	Day	24% 62% 3 5% 4 2	1650
March	1st to 10th	Day	41% 34% 9% 7% 9% 1	4518
	11th to 20th	Day	42% 33% 10% 12% 3	4687
	21st to end	Day	50% 32% 8% 6% 4 1	5920
April	1st to 10th	Day	28% 63% 5% 3 1	2400
	11th to 20th	Day	25% 64% 7% 3 1	2523
	21st to end	Day	26% 62% 5% 6% 1	2695
May	1st to 10th	Day	36% 41% 9% 10% 3	4560
	11th to 20th	Day	37% 41% 11% 8% 3	4597
	21st to end	Day	45% 41% 8% 5% 1	5162
June	1st to 10th	Day	19% 66% 6% 7% 2	2930
	11th to 20th	Day	22% 66% 4 6% 2	3040
	21st to end	Day	18% 66% 4 9% 3	3040
July	1st to 10th	Day	19% 38% 6% 14% 21% 2	4981
	11th to 20th	Day	12% 37% 7% 23% 20% 1	4763
	21st to end	Day	24% 41% 10% 15% 9% 1	4679
August	1st to 10th	Day	23% 42% 8% 23% 4	4384
	11th to 20th	Day	23% 43% 14% 17% 3	4355
	21st to end	Day	30% 43% 12% 11% 3	4440
September	1st to 10th	Day	20% 61% 7% 8% 2 1	2280
	11th to 20th	Day	25% 60% 5% 7% 3	2190
	21st to end	Day	26% 62% 4 5% 3 1	2090
October	1st to 10th	Day	36% 44% 13% 6% 2	3304
	11th to 20th	Day	39% 41% 11% 9% 1	2874
	21st to end	Day	36% 42% 11% 8% 2	3101
November	1st to 10th	Day	29% 59% 5% 5% 2	1679
	11th to 20th	Day	25% 59% 8% 4 3 1	1400
	21st to end	Day	24% 59% 8% 3 3 3	1400
December	1st to 10th	Day	38% 42% 13% 4 2 1	2290
	11th to 20th	Day	50% 38% 6% 5% 2	2580
	21st to end	Day	40% 35% 9% 9% 6% 1	2992
January	1st to 10th	Night	53% 31% 7% 5% 3 2	7155
	11th to 20th	Night	32% 32% 8% 9% 14% 5%	6527
	21st to end	Night	41% 33% 12% 9% 5%	6952
February	1st to 10th	Night	23% 63% 4 4 5% 3	2800
	11th to 20th	Night	19% 64% 9% 4 4 1	2625
	21st to end	Night	21% 62% 5% 7% 3 2	1980
March	1st to 10th	Night	41% 35% 12% 6% 5% 1	5376
	11th to 20th	Night	41% 35% 9% 12% 2	5313
	21st to end	Night	52% 32% 6% 6% 3 1	5054
April	1st to 10th	Night	20% 66% 5% 7% 2	2000
	11th to 20th	Night	20% 64% 8% 6% 2	1828
	21st to end	Night	20% 64% 6% 7% 4	1702
May	1st to 10th	Night	36% 39% 10% 12% 2	2620
	11th to 20th	Night	41% 41% 7% 9% 3	2304
	21st to end	Night	42% 42% 8% 6% 2	2414
June	1st to 10th	Night	17% 66% 9% 6% 2	1247
	11th to 20th	Night	22% 66% 5% 4 3	1140
	21st to end	Night	15% 64% 7% 10% 3	1140
July	1st to 10th	Night	24% 37% 6% 14% 19% 1	1870
	11th to 20th	Night	11% 36% 7% 23% 22% 1	2072
	21st to end	Night	27% 38% 8% 18% 9% 1	2632
August	1st to 10th	Night	27% 41% 10% 19% 3	2521
	11th to 20th	Night	21% 41% 17% 19% 2	2539
	21st to end	Night	31% 40% 14% 12% 2	3228
September	1st to 10th	Night	20% 62% 7% 8% 4 1	1900
	11th to 20th	Night	23% 60% 5% 8% 4	1990
	21st to end	Night	24% 62% 6% 5% 3	2090
October	1st to 10th	Night	39% 46% 9% 5% 2	3675
	11th to 20th	Night	36% 42% 9% 11% 3	4055
	21st to end	Night	32% 44% 12% 8% 2 1	4457
November	1st to 10th	Night	32% 58% 3 5% 2 1	2604
	11th to 20th	Night	26% 61% 6% 3 4 1	2995
	21st to end	Night	25% 59% 8% 4 2 3	3000
December	1st to 10th	Night	45% 41% 7% 4 3	4890
	11th to 20th	Night	50% 38% 5% 6% 2	5593
	21st to end	Night	47% 32% 9% 7% 4 1	7964

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	9% 23% 32% 24% 11% 3	200
	11th to 20th	Day	10% 27% 34% 19% 9% 2	200
	21st to end	Day	16% 25% 37% 14% 4 3	220
February	1st to 10th	Day	16% 29% 30% 15% 8% 3	200
	11th to 20th	Day	11% 21% 36% 22% 9% 3	287
	21st to end	Day	15% 24% 33% 21% 7% 1	414
March	1st to 10th	Day	15% 25% 31% 17% 10% 2	500
	11th to 20th	Day	10% 28% 34% 20% 6% 2	500
	21st to end	Day	11% 29% 29% 20% 8% 3	550
April	1st to 10th	Day	17% 23% 34% 19% 6% 1	500
	11th to 20th	Day	12% 27% 29% 20% 9% 2	492
	21st to end	Day	13% 22% 33% 20% 9% 3	500
May	1st to 10th	Day	19% 18% 28% 22% 11% 2	503
	11th to 20th	Day	14% 10% 22% 31% 18% 5%	611
	21st to end	Day	17% 14% 20% 25% 20% 4	734
June	1st to 10th	Day	21% 14% 28% 24% 12% 1	760
	11th to 20th	Day	20% 15% 26% 26% 12% 2	870
	21st to end	Day	16% 9% 22% 28% 20% 5%	870
July	1st to 10th	Day	13% 9% 23% 32% 18% 5%	856
	11th to 20th	Day	12% 10% 26% 29% 18% 5%	733
	21st to end	Day	8% 12% 25% 29% 18% 7%	560
August	1st to 10th	Day	9% 10% 20% 36% 19% 6%	487
	11th to 20th	Day	12% 12% 29% 32% 12% 4	477
	21st to end	Day	14% 17% 31% 24% 11% 2	539
September	1st to 10th	Day	18% 21% 28% 22% 10% 1	490
	11th to 20th	Day	19% 18% 30% 23% 9% 1	490
	21st to end	Day	25% 26% 27% 15% 6% 1	490
October	1st to 10th	Day	21% 22% 28% 17% 9% 3	490
	11th to 20th	Day	20% 28% 25% 16% 9% 1	319
	21st to end	Day	17% 28% 28% 18% 6% 2	330
November	1st to 10th	Day	17% 33% 28% 14% 6% 2	265
	11th to 20th	Day	17% 26% 35% 17% 5% 2	200
	21st to end	Day	17% 26% 29% 16% 8% 5%	200
December	1st to 10th	Day	12% 24% 31% 18% 11% 6%	200
	11th to 20th	Day	10% 30% 34% 20% 5% 2	200
	21st to end	Day	10% 16% 40% 21% 11% 2	220
January	1st to 10th	Night	8% 26% 40% 20% 5% 1	1083
	11th to 20th	Night	8% 24% 43% 18% 5% 1	890
	21st to end	Night	6% 26% 44% 19% 6% 1	880
February	1st to 10th	Night	8% 23% 36% 23% 8% 2	800
	11th to 20th	Night	6% 18% 43% 23% 8% 1	784
	21st to end	Night	10% 14% 36% 26% 12% 2	660
March	1st to 10th	Night	6% 22% 38% 24% 10% 1	800
	11th to 20th	Night	5% 20% 43% 25% 7% 1	800
	21st to end	Night	8% 16% 40% 23% 12% 2	880
April	1st to 10th	Night	9% 16% 36% 27% 11% 1	800
	11th to 20th	Night	8% 15% 40% 27% 11%	640
	21st to end	Night	12% 15% 32% 27% 13% 1	502
May	1st to 10th	Night	14% 12% 27% 32% 14% 2	400
	11th to 20th	Night	12% 7% 24% 35% 21% 1	375
	21st to end	Night	20% 11% 21% 25% 19% 4	411
June	1st to 10th	Night	23% 10% 28% 26% 11% 3	380
	11th to 20th	Night	24% 14% 22% 23% 13% 3	380
	21st to end	Night	17% 8% 19% 28% 24% 4	380
July	1st to 10th	Night	18% 3 21% 29% 24% 5%	370
	11th to 20th	Night	15% 9% 20% 30% 24% 3	368
	21st to end	Night	10% 9% 17% 37% 25% 2	416
August	1st to 10th	Night	13% 6% 13% 38% 26% 4	378
	11th to 20th	Night	13% 6% 18% 34% 26% 3	381
	21st to end	Night	16% 10% 26% 34% 13% 1	670
September	1st to 10th	Night	18% 10% 27% 27% 15% 2	760
	11th to 20th	Night	17% 11% 21% 30% 16% 4	760
	21st to end	Night	21% 19% 27% 21% 10% 2	760
October	1st to 10th	Night	18% 14% 31% 24% 10% 1	760
	11th to 20th	Night	17% 21% 32% 24% 6% 1	760
	21st to end	Night	15% 23% 38% 18% 6% 1	836
November	1st to 10th	Night	13% 29% 35% 17% 6%	780
	11th to 20th	Night	12% 26% 41% 17% 4	995
	21st to end	Night	10% 24% 41% 18% 5% 2	1000
December	1st to 10th	Night	9% 23% 42% 17% 9% 1	1000
	11th to 20th	Night	7% 24% 42% 19% 7%	1010
	21st to end	Night	6% 23% 43% 20% 8% 1	1210

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