Athabasca Falls
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Athabasca Falls clear sky chart from 2005-11-06 to 2026-03-03.

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	7% 13% 5% 13% 7% 7% 6% 5% 6% 7% 25%	134625
	Night	4 10% 5% 14% 9% 7% 7% 5% 7% 8% 24%	135224
Transparency	Day	57% 11% 13% 13% 6% 1	134327
	Night	57% 11% 14% 12% 5% 1	135101
Seeing	Day	19% 18% 31% 21% 9% 2	17674
	Night	11% 14% 39% 26% 9% 1	26194

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	1 8% 6% 19% 11% 10% 9% 7% 9% 7% 13%	3527
	11th to 20th	Day	1 6% 5% 16% 8% 8% 6% 5% 7% 7% 32%	4237
	21st to end	Day	1 11% 6% 15% 8% 8% 6% 6% 8% 9% 23%	5186
February	1st to 10th	Day	3 14% 5% 16% 8% 7% 8% 7% 6% 8% 19%	1680
	11th to 20th	Day	2 11% 6% 20% 8% 8% 7% 5% 7% 7% 19%	1732
	21st to end	Day	1 10% 7% 20% 11% 9% 7% 4 7% 6% 18%	1725
March	1st to 10th	Day	9% 6% 17% 11% 9% 8% 6% 8% 9% 18%	4539
	11th to 20th	Day	2 12% 8% 16% 11% 8% 7% 4 5% 5% 21%	4657
	21st to end	Day	2 16% 8% 22% 10% 7% 6% 4 5% 6% 15%	5969
April	1st to 10th	Day	4 20% 10% 18% 9% 6% 6% 4 5% 5% 12%	2400
	11th to 20th	Day	4 20% 8% 17% 9% 7% 5% 3 5% 6% 17%	2506
	21st to end	Day	7% 23% 6% 14% 6% 6% 4 3 6% 6% 19%	2740
May	1st to 10th	Day	7% 18% 5% 9% 5% 5% 5% 4 5% 7% 29%	6320
	11th to 20th	Day	8% 18% 5% 12% 7% 6% 6% 5% 7% 8% 17%	6566
	21st to end	Day	10% 20% 4 9% 5% 5% 4 3 4 6% 28%	7405
June	1st to 10th	Day	17% 14% 3 10% 6% 7% 6% 4 5% 6% 21%	3181
	11th to 20th	Day	21% 14% 5% 10% 7% 6% 6% 5% 5% 6% 14%	3200
	21st to end	Day	14% 11% 4 10% 7% 7% 7% 5% 6% 6% 23%	3200
July	1st to 10th	Day	10% 7% 3 8% 6% 6% 5% 4 6% 6% 37%	7240
	11th to 20th	Day	11% 8% 4 9% 6% 5% 5% 5% 7% 7% 33%	7151
	21st to end	Day	10% 9% 4 10% 7% 7% 7% 5% 7% 7% 29%	6922
August	1st to 10th	Day	13% 8% 3 8% 5% 6% 6% 5% 6% 7% 33%	4541
	11th to 20th	Day	11% 9% 3 10% 7% 7% 7% 5% 6% 7% 28%	4470
	21st to end	Day	14% 9% 4 8% 5% 6% 6% 5% 6% 6% 31%	4588
September	1st to 10th	Day	13% 10% 5% 9% 5% 5% 5% 4 5% 6% 34%	2400
	11th to 20th	Day	12% 12% 3 8% 6% 5% 5% 4 6% 7% 33%	2330
	21st to end	Day	12% 16% 5% 12% 5% 5% 4 4 5% 6% 26%	2200
October	1st to 10th	Day	6% 16% 5% 15% 7% 6% 6% 5% 6% 7% 22%	3349
	11th to 20th	Day	7% 15% 8% 15% 6% 5% 5% 4 5% 7% 22%	2983
	21st to end	Day	2 13% 7% 16% 7% 7% 5% 4 5% 5% 27%	3200
November	1st to 10th	Day	4 19% 6% 14% 10% 7% 7% 5% 6% 6% 17%	1728
	11th to 20th	Day	2 11% 7% 12% 8% 7% 6% 7% 7% 8% 24%	1470
	21st to end	Day	2 13% 3 13% 9% 10% 7% 6% 7% 9% 21%	1470
December	1st to 10th	Day	3 8% 5% 16% 10% 9% 7% 6% 7% 9% 21%	2360
	11th to 20th	Day	1 10% 7% 13% 8% 9% 9% 7% 8% 9% 18%	2395
	21st to end	Day	9% 6% 15% 9% 8% 8% 6% 7% 8% 24%	3058
January	1st to 10th	Night	1 7% 6% 21% 13% 11% 10% 6% 7% 7% 11%	9366
	11th to 20th	Night	1 7% 6% 13% 8% 7% 6% 6% 8% 8% 30%	8692
	21st to end	Night	1 9% 6% 15% 9% 10% 8% 5% 6% 7% 22%	8994
February	1st to 10th	Night	4 13% 7% 15% 11% 9% 8% 5% 6% 8% 15%	2940
	11th to 20th	Night	2 11% 6% 15% 10% 9% 8% 6% 7% 8% 19%	2772
	21st to end	Night	1 12% 5% 15% 12% 8% 7% 6% 8% 8% 17%	2081
March	1st to 10th	Night	1 9% 6% 15% 11% 9% 7% 5% 7% 8% 22%	5400
	11th to 20th	Night	1 10% 7% 16% 12% 9% 8% 5% 6% 7% 18%	5329
	21st to end	Night	3 17% 8% 19% 9% 7% 6% 4 6% 6% 16%	5006
April	1st to 10th	Night	2 15% 10% 15% 9% 8% 7% 5% 7% 6% 17%	2000
	11th to 20th	Night	3 13% 6% 15% 9% 6% 6% 4 6% 9% 24%	1844
	21st to end	Night	5% 16% 5% 12% 7% 7% 6% 4 6% 6% 27%	1658
May	1st to 10th	Night	4 15% 5% 9% 6% 5% 6% 4 7% 8% 32%	3640
	11th to 20th	Night	7% 18% 4 11% 7% 6% 5% 5% 6% 8% 22%	3325
	21st to end	Night	7% 15% 5% 9% 5% 4 6% 4 5% 7% 33%	3470
June	1st to 10th	Night	14% 11% 4 9% 6% 6% 6% 3 7% 7% 28%	1215
	11th to 20th	Night	17% 11% 4 10% 7% 7% 7% 4 7% 9% 19%	1200
	21st to end	Night	11% 6% 3 10% 7% 5% 6% 5% 7% 9% 30%	1200
July	1st to 10th	Night	11% 6% 2 5% 3 3 4 3 5% 8% 50%	2720
	11th to 20th	Night	10% 8% 3 7% 5% 4 5% 4 6% 6% 43%	2807
	21st to end	Night	11% 7% 3 7% 6% 5% 5% 4 6% 8% 39%	3918
August	1st to 10th	Night	11% 8% 3 7% 5% 4 6% 5% 7% 9% 34%	2609
	11th to 20th	Night	12% 6% 3 7% 6% 6% 6% 5% 8% 9% 33%	2577
	21st to end	Night	13% 9% 3 7% 5% 5% 5% 5% 6% 8% 35%	3319
September	1st to 10th	Night	13% 8% 3 7% 4 4 4 3 6% 7% 42%	2000
	11th to 20th	Night	10% 10% 3 8% 5% 4 6% 3 5% 7% 39%	2070
	21st to end	Night	9% 11% 4 10% 5% 5% 5% 4 6% 8% 31%	2200
October	1st to 10th	Night	4 13% 6% 15% 9% 7% 6% 5% 5% 8% 23%	3849
	11th to 20th	Night	5% 11% 5% 14% 8% 7% 6% 5% 7% 8% 24%	4165
	21st to end	Night	4 12% 6% 14% 8% 8% 6% 5% 6% 6% 25%	4600
November	1st to 10th	Night	5% 15% 7% 14% 10% 9% 6% 6% 7% 7% 14%	2783
	11th to 20th	Night	2 13% 6% 13% 9% 8% 8% 7% 8% 8% 19%	3133
	21st to end	Night	2 12% 5% 15% 10% 9% 8% 6% 8% 8% 19%	3150
December	1st to 10th	Night	2 8% 5% 16% 11% 8% 8% 6% 8% 8% 19%	5040
	11th to 20th	Night	1 8% 6% 15% 11% 9% 9% 7% 9% 9% 15%	6012
	21st to end	Night	1 8% 6% 18% 9% 9% 8% 6% 8% 9% 20%	8140

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	65% 14% 14% 5% 2 1	3527
	11th to 20th	Day	51% 8% 15% 14% 8% 4	4260
	21st to end	Day	58% 12% 18% 9% 3	5187
February	1st to 10th	Day	64% 9% 9% 7% 9% 2	1680
	11th to 20th	Day	65% 9% 9% 11% 5% 1	1740
	21st to end	Day	65% 9% 11% 10% 4 2	1725
March	1st to 10th	Day	62% 10% 10% 10% 8%	4539
	11th to 20th	Day	59% 13% 10% 14% 4	4657
	21st to end	Day	67% 9% 10% 8% 5% 1	5969
April	1st to 10th	Day	75% 9% 9% 6% 2	2400
	11th to 20th	Day	68% 9% 12% 9% 2	2506
	21st to end	Day	67% 10% 10% 11% 2	2740
May	1st to 10th	Day	54% 8% 16% 17% 5%	6320
	11th to 20th	Day	59% 13% 13% 12% 3	6570
	21st to end	Day	56% 10% 18% 13% 3	7406
June	1st to 10th	Day	64% 9% 11% 10% 5% 1	3181
	11th to 20th	Day	70% 10% 10% 7% 3	3200
	21st to end	Day	61% 10% 13% 11% 4 1	3200
July	1st to 10th	Day	43% 10% 11% 19% 13% 4	7161
	11th to 20th	Day	47% 10% 12% 19% 12% 1	7064
	21st to end	Day	48% 12% 14% 16% 9% 3	6727
August	1st to 10th	Day	45% 11% 12% 24% 8%	4524
	11th to 20th	Day	51% 12% 15% 17% 5%	4512
	21st to end	Day	52% 9% 13% 19% 6% 1	4587
September	1st to 10th	Day	53% 7% 14% 19% 5% 1	2400
	11th to 20th	Day	52% 8% 14% 16% 9%	2330
	21st to end	Day	58% 9% 14% 12% 6% 1	2200
October	1st to 10th	Day	58% 12% 16% 12% 3	3349
	11th to 20th	Day	61% 10% 15% 13% 1	2983
	21st to end	Day	58% 11% 17% 11% 3	3200
November	1st to 10th	Day	69% 11% 8% 8% 3 1	1728
	11th to 20th	Day	57% 14% 14% 8% 6% 1	1470
	21st to end	Day	61% 14% 13% 6% 4 4	1470
December	1st to 10th	Day	63% 19% 8% 7% 3 1	2360
	11th to 20th	Day	62% 13% 11% 9% 4 1	2397
	21st to end	Day	54% 13% 14% 11% 7%	3058
January	1st to 10th	Night	70% 12% 11% 5% 2 1	9367
	11th to 20th	Night	50% 10% 13% 11% 13% 3	8731
	21st to end	Night	62% 11% 13% 11% 2	8994
February	1st to 10th	Night	68% 8% 8% 7% 7% 2	2940
	11th to 20th	Night	64% 10% 10% 8% 7% 1	2774
	21st to end	Night	60% 10% 9% 13% 6% 2	2081
March	1st to 10th	Night	56% 12% 13% 10% 8% 1	5400
	11th to 20th	Night	61% 11% 12% 13% 3	5330
	21st to end	Night	62% 11% 11% 10% 6%	5006
April	1st to 10th	Night	66% 12% 12% 9% 1	2000
	11th to 20th	Night	58% 10% 15% 12% 5%	1844
	21st to end	Night	57% 12% 13% 15% 4	1658
May	1st to 10th	Night	48% 11% 20% 19% 3	3637
	11th to 20th	Night	57% 12% 13% 13% 5%	3325
	21st to end	Night	50% 10% 21% 15% 3	3470
June	1st to 10th	Night	54% 10% 17% 11% 6% 1	1215
	11th to 20th	Night	61% 13% 12% 10% 3	1200
	21st to end	Night	50% 14% 20% 13% 4 1	1200
July	1st to 10th	Night	35% 8% 16% 24% 16% 2	2690
	11th to 20th	Night	39% 10% 13% 21% 16%	2771
	21st to end	Night	41% 11% 18% 21% 7% 4	3808
August	1st to 10th	Night	40% 13% 17% 27% 3	2601
	11th to 20th	Night	43% 14% 21% 18% 4	2601
	21st to end	Night	47% 10% 22% 16% 6%	3319
September	1st to 10th	Night	44% 9% 18% 22% 6% 1	2000
	11th to 20th	Night	46% 9% 17% 19% 8%	2070
	21st to end	Night	51% 13% 16% 15% 6% 1	2200
October	1st to 10th	Night	58% 14% 15% 10% 2	3849
	11th to 20th	Night	57% 10% 18% 13% 3	4165
	21st to end	Night	58% 12% 19% 7% 3	4600
November	1st to 10th	Night	69% 12% 10% 6% 3 1	2783
	11th to 20th	Night	64% 13% 10% 7% 5% 1	3133
	21st to end	Night	63% 12% 10% 8% 4 3	3150
December	1st to 10th	Night	64% 17% 7% 6% 5%	5040
	11th to 20th	Night	67% 14% 10% 6% 3	6009
	21st to end	Night	59% 12% 13% 10% 5% 1	8140

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% 15% 37% 29% 6% 3	220
	11th to 20th	Day	12% 14% 41% 25% 5% 3	220
	21st to end	Day	14% 17% 39% 24% 5% 2	242
February	1st to 10th	Day	17% 20% 34% 20% 6% 3	220
	11th to 20th	Day	12% 17% 38% 22% 8% 2	312
	21st to end	Day	16% 23% 37% 15% 8% 1	443
March	1st to 10th	Day	16% 26% 31% 16% 10% 2	509
	11th to 20th	Day	14% 25% 35% 17% 7% 2	500
	21st to end	Day	17% 22% 31% 18% 8% 3	550
April	1st to 10th	Day	20% 24% 34% 17% 5% 1	500
	11th to 20th	Day	16% 21% 30% 22% 8% 3	492
	21st to end	Day	21% 21% 28% 19% 8% 3	500
May	1st to 10th	Day	23% 17% 29% 22% 8% 1	503
	11th to 20th	Day	18% 13% 25% 28% 13% 3	648
	21st to end	Day	20% 14% 23% 24% 16% 3	789
June	1st to 10th	Day	22% 18% 31% 21% 7% 1	911
	11th to 20th	Day	26% 15% 29% 20% 9% 1	930
	21st to end	Day	19% 13% 29% 25% 12% 2	930
July	1st to 10th	Day	20% 12% 28% 27% 12% 1	916
	11th to 20th	Day	17% 14% 33% 25% 9% 1	875
	21st to end	Day	15% 16% 29% 22% 14% 3	597
August	1st to 10th	Day	19% 10% 28% 27% 12% 4	527
	11th to 20th	Day	16% 20% 37% 16% 9% 2	517
	21st to end	Day	20% 15% 31% 21% 10% 3	583
September	1st to 10th	Day	22% 18% 27% 22% 10% 2	530
	11th to 20th	Day	16% 19% 30% 25% 8% 2	530
	21st to end	Day	33% 23% 24% 15% 4 1	530
October	1st to 10th	Day	26% 21% 27% 16% 8% 2	530
	11th to 20th	Day	24% 20% 29% 19% 7% 1	368
	21st to end	Day	20% 18% 38% 19% 4 1	363
November	1st to 10th	Day	24% 23% 36% 12% 4 2	267
	11th to 20th	Day	18% 22% 34% 20% 4 2	220
	21st to end	Day	15% 21% 30% 21% 10% 3	220
December	1st to 10th	Day	11% 19% 36% 22% 6% 5%	220
	11th to 20th	Day	11% 16% 43% 21% 7% 1	220
	21st to end	Day	9% 14% 38% 25% 11% 3	242
January	1st to 10th	Night	9% 17% 48% 21% 4 1	1160
	11th to 20th	Night	9% 18% 48% 18% 5% 1	978
	21st to end	Night	10% 19% 48% 17% 5% 1	924
February	1st to 10th	Night	12% 17% 38% 23% 8% 1	840
	11th to 20th	Night	8% 13% 45% 28% 7%	824
	21st to end	Night	9% 15% 40% 25% 10% 2	692
March	1st to 10th	Night	6% 16% 42% 25% 10% 1	808
	11th to 20th	Night	5% 16% 46% 25% 7% 1	800
	21st to end	Night	7% 13% 38% 30% 11% 2	880
April	1st to 10th	Night	8% 15% 35% 32% 10% 1	800
	11th to 20th	Night	8% 14% 38% 27% 14%	656
	21st to end	Night	14% 12% 31% 32% 10% 1	458
May	1st to 10th	Night	11% 11% 25% 40% 13%	400
	11th to 20th	Night	11% 6% 24% 39% 19% 1	394
	21st to end	Night	16% 9% 29% 24% 20% 1	433
June	1st to 10th	Night	17% 6% 35% 27% 14% 1	400
	11th to 20th	Night	18% 9% 28% 30% 14% 1	400
	21st to end	Night	12% 8% 27% 34% 19% 1	400
July	1st to 10th	Night	16% 5% 26% 37% 16% 1	390
	11th to 20th	Night	17% 9% 22% 35% 17%	388
	21st to end	Night	9% 8% 21% 40% 21%	438
August	1st to 10th	Night	13% 4 17% 41% 23% 2	398
	11th to 20th	Night	14% 5% 25% 36% 19% 1	396
	21st to end	Night	16% 8% 28% 35% 11% 1	695
September	1st to 10th	Night	17% 8% 29% 33% 13% 1	800
	11th to 20th	Night	16% 9% 27% 32% 16% 2	800
	21st to end	Night	19% 16% 33% 21% 10% 1	800
October	1st to 10th	Night	15% 14% 34% 27% 9% 1	800
	11th to 20th	Night	14% 17% 39% 25% 5% 1	800
	21st to end	Night	14% 16% 44% 21% 4	880
November	1st to 10th	Night	14% 19% 45% 17% 5%	820
	11th to 20th	Night	12% 20% 48% 17% 3	1033
	21st to end	Night	10% 16% 51% 17% 5% 1	1050
December	1st to 10th	Night	10% 19% 45% 20% 7%	1050
	11th to 20th	Night	9% 16% 49% 20% 6% 1	1133
	21st to end	Night	6% 16% 49% 22% 7%	1276

Page generated at 2026-02-27 23:40:22. Version ac07

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