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 2025-06-10.

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% 4 9% 6% 5% 5% 4 6% 8% 33%	123693
	Night	8% 10% 4 10% 6% 6% 6% 4 6% 8% 32%	123221
Transparency	Day	47% 6% 17% 22% 7%	123429
	Night	49% 6% 16% 21% 8% 1	123131
Seeing	Day	14% 7% 26% 30% 19% 6%	16848
	Night	13% 5% 27% 37% 17% 2	25392

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	4 15% 6% 15% 10% 6% 5% 6% 6% 6% 22%	2967
	11th to 20th	Day	4 9% 3 11% 8% 6% 5% 7% 7% 11% 28%	3159
	21st to end	Day	6% 13% 7% 11% 5% 5% 4 3 6% 8% 32%	3617
February	1st to 10th	Day	6% 13% 4 10% 8% 7% 7% 5% 7% 8% 24%	1600
	11th to 20th	Day	6% 11% 5% 13% 8% 6% 6% 5% 6% 8% 27%	1678
	21st to end	Day	4 11% 6% 11% 8% 7% 7% 6% 8% 8% 24%	1509
March	1st to 10th	Day	4 10% 4 11% 9% 7% 8% 5% 7% 8% 27%	4518
	11th to 20th	Day	5% 12% 6% 12% 7% 5% 5% 4 5% 9% 31%	4954
	21st to end	Day	10% 16% 6% 14% 6% 4 4 3 5% 7% 23%	5566
April	1st to 10th	Day	7% 12% 4 9% 7% 6% 5% 5% 7% 7% 30%	2520
	11th to 20th	Day	10% 11% 3 8% 6% 6% 5% 4 6% 8% 31%	2570
	21st to end	Day	12% 11% 4 9% 7% 5% 6% 5% 7% 8% 26%	2612
May	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 4 6% 7% 39%	6780
	11th to 20th	Day	15% 12% 4 9% 6% 5% 5% 4 5% 7% 28%	6734
	21st to end	Day	10% 7% 3 7% 6% 5% 6% 5% 7% 8% 36%	7405
June	1st to 10th	Day	15% 7% 3 8% 6% 6% 6% 5% 6% 8% 31%	3045
	11th to 20th	Day	20% 10% 3 8% 6% 5% 7% 5% 7% 8% 23%	3040
	21st to end	Day	10% 6% 2 7% 6% 6% 7% 5% 7% 8% 35%	3040
July	1st to 10th	Day	9% 5% 2 6% 4 5% 5% 5% 7% 9% 43%	5060
	11th to 20th	Day	9% 4 2 5% 4 5% 5% 5% 7% 9% 46%	4780
	21st to end	Day	14% 5% 2 5% 3 4 5% 4 6% 9% 42%	5138
August	1st to 10th	Day	13% 7% 2 6% 4 4 5% 4 6% 7% 42%	4626
	11th to 20th	Day	10% 5% 2 6% 5% 4 5% 4 7% 9% 42%	4188
	21st to end	Day	11% 5% 2 7% 5% 5% 5% 4 6% 10% 41%	4521
September	1st to 10th	Day	12% 7% 3 7% 5% 4 5% 3 6% 8% 41%	2442
	11th to 20th	Day	14% 8% 2 6% 4 5% 5% 4 6% 8% 38%	2090
	21st to end	Day	9% 7% 2 7% 5% 5% 4 4 7% 8% 42%	2090
October	1st to 10th	Day	10% 9% 3 8% 5% 5% 5% 5% 7% 8% 34%	3271
	11th to 20th	Day	14% 11% 3 7% 5% 5% 5% 4 5% 8% 34%	2873
	21st to end	Day	9% 14% 5% 10% 5% 5% 5% 4 5% 7% 30%	2987
November	1st to 10th	Day	10% 16% 5% 10% 5% 5% 5% 4 6% 8% 27%	1566
	11th to 20th	Day	6% 13% 6% 14% 6% 7% 5% 3 6% 8% 28%	1400
	21st to end	Day	5% 14% 5% 14% 9% 5% 5% 4 5% 7% 29%	1400
December	1st to 10th	Day	9% 12% 4 12% 7% 6% 7% 5% 7% 8% 21%	2290
	11th to 20th	Day	10% 15% 5% 10% 5% 6% 6% 4 6% 7% 27%	2642
	21st to end	Day	4 8% 3 12% 8% 7% 7% 5% 7% 7% 33%	3015
January	1st to 10th	Night	4 11% 6% 16% 8% 8% 6% 5% 6% 6% 23%	6974
	11th to 20th	Night	4 11% 4 8% 7% 6% 7% 5% 5% 7% 36%	6739
	21st to end	Night	6% 12% 5% 11% 7% 6% 5% 4 5% 7% 33%	7384
February	1st to 10th	Night	7% 11% 5% 11% 7% 6% 7% 5% 7% 8% 26%	2800
	11th to 20th	Night	7% 10% 4 11% 8% 7% 7% 5% 6% 7% 29%	2609
	21st to end	Night	3 10% 4 9% 7% 6% 6% 7% 8% 8% 31%	2120
March	1st to 10th	Night	4 9% 5% 10% 6% 7% 7% 5% 7% 9% 32%	5376
	11th to 20th	Night	5% 10% 4 11% 7% 6% 5% 4 7% 9% 33%	5045
	21st to end	Night	11% 18% 7% 13% 5% 4 4 3 4 6% 24%	5407
April	1st to 10th	Night	9% 9% 3 8% 6% 7% 5% 4 6% 9% 35%	1879
	11th to 20th	Night	9% 11% 3 8% 7% 7% 7% 5% 6% 7% 31%	1781
	21st to end	Night	11% 13% 3 8% 5% 5% 5% 4 5% 7% 33%	1785
May	1st to 10th	Night	15% 6% 2 6% 5% 4 4 4 6% 7% 41%	3180
	11th to 20th	Night	15% 10% 4 9% 6% 7% 6% 4 6% 6% 28%	3159
	21st to end	Night	12% 7% 3 7% 6% 5% 5% 5% 7% 8% 35%	3470
June	1st to 10th	Night	15% 7% 3 8% 6% 6% 5% 4 6% 8% 32%	1335
	11th to 20th	Night	17% 9% 3 7% 5% 6% 6% 5% 7% 8% 28%	1140
	21st to end	Night	11% 6% 2 7% 5% 5% 5% 5% 7% 9% 38%	1140
July	1st to 10th	Night	8% 5% 2 6% 4 5% 5% 4 7% 9% 45%	1900
	11th to 20th	Night	7% 4 2 6% 4 4 6% 4 6% 11% 46%	2178
	21st to end	Night	15% 4 2 4 4 4 4 4 6% 10% 45%	2414
August	1st to 10th	Night	10% 5% 2 8% 5% 5% 5% 3 6% 8% 44%	2301
	11th to 20th	Night	14% 6% 2 6% 4 4 4 4 5% 9% 41%	2645
	21st to end	Night	13% 5% 2 5% 5% 5% 6% 5% 6% 7% 42%	3146
September	1st to 10th	Night	12% 7% 3 5% 4 5% 5% 4 5% 8% 43%	1735
	11th to 20th	Night	12% 7% 2 6% 4 4 4 4 6% 8% 43%	2090
	21st to end	Night	10% 6% 2 6% 4 4 4 4 5% 9% 44%	2090
October	1st to 10th	Night	8% 7% 3 8% 5% 6% 5% 5% 7% 10% 35%	3702
	11th to 20th	Night	9% 9% 3 8% 5% 5% 6% 4 7% 9% 35%	4051
	21st to end	Night	10% 10% 4 9% 4 5% 5% 5% 8% 8% 31%	4540
November	1st to 10th	Night	12% 14% 6% 10% 7% 5% 5% 4 5% 5% 27%	2730
	11th to 20th	Night	9% 13% 5% 12% 7% 6% 6% 5% 6% 7% 25%	3000
	21st to end	Night	6% 13% 6% 13% 8% 6% 5% 4 6% 8% 26%	3000
December	1st to 10th	Night	10% 14% 6% 13% 7% 6% 5% 4 6% 6% 22%	4890
	11th to 20th	Night	8% 16% 6% 14% 7% 6% 6% 5% 7% 7% 19%	5550
	21st to end	Night	3 8% 4 11% 6% 7% 6% 5% 7% 8% 36%	7936

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	61% 5% 12% 13% 9%	2967
	11th to 20th	Day	49% 5% 15% 15% 15% 1	3180
	21st to end	Day	50% 5% 23% 16% 6%	3617
February	1st to 10th	Day	55% 7% 12% 16% 10%	1600
	11th to 20th	Day	53% 7% 15% 17% 8%	1686
	21st to end	Day	53% 8% 18% 15% 7%	1509
March	1st to 10th	Day	53% 4 16% 20% 7%	4518
	11th to 20th	Day	50% 5% 17% 23% 6%	4955
	21st to end	Day	60% 5% 10% 19% 6%	5566
April	1st to 10th	Day	49% 8% 16% 18% 8% 1	2520
	11th to 20th	Day	49% 6% 14% 21% 9% 1	2570
	21st to end	Day	52% 7% 13% 20% 7% 1	2612
May	1st to 10th	Day	44% 5% 9% 26% 15% 1	6780
	11th to 20th	Day	54% 5% 10% 24% 7%	6738
	21st to end	Day	43% 7% 18% 22% 9% 1	7406
June	1st to 10th	Day	49% 7% 15% 22% 7% 1	3045
	11th to 20th	Day	56% 8% 15% 16% 5%	3040
	21st to end	Day	43% 9% 20% 20% 7%	3040
July	1st to 10th	Day	36% 6% 22% 26% 9% 1	4981
	11th to 20th	Day	34% 7% 17% 31% 12%	4697
	21st to end	Day	39% 6% 22% 28% 5%	4976
August	1st to 10th	Day	41% 6% 20% 30% 2	4608
	11th to 20th	Day	38% 6% 24% 25% 8%	4230
	21st to end	Day	39% 5% 30% 22% 3	4520
September	1st to 10th	Day	41% 8% 20% 24% 7% 1	2442
	11th to 20th	Day	42% 8% 22% 22% 5%	2090
	21st to end	Day	38% 8% 20% 24% 9% 1	2090
October	1st to 10th	Day	46% 4 23% 23% 4	3271
	11th to 20th	Day	50% 4 18% 24% 5%	2873
	21st to end	Day	54% 4 18% 21% 3	2987
November	1st to 10th	Day	55% 8% 15% 17% 4	1566
	11th to 20th	Day	54% 7% 20% 15% 5%	1400
	21st to end	Day	54% 8% 15% 18% 4 1	1400
December	1st to 10th	Day	59% 6% 18% 12% 5%	2290
	11th to 20th	Day	56% 6% 20% 14% 4	2644
	21st to end	Day	48% 5% 13% 26% 8% 1	3015
January	1st to 10th	Night	60% 5% 13% 13% 8% 1	6974
	11th to 20th	Night	46% 5% 14% 18% 16% 1	6780
	21st to end	Night	51% 5% 22% 17% 5%	7384
February	1st to 10th	Night	54% 7% 13% 16% 10% 1	2800
	11th to 20th	Night	54% 6% 12% 19% 9%	2611
	21st to end	Night	46% 9% 15% 21% 9%	2120
March	1st to 10th	Night	46% 5% 18% 23% 8%	5376
	11th to 20th	Night	46% 5% 17% 24% 8%	5045
	21st to end	Night	60% 6% 9% 15% 10%	5407
April	1st to 10th	Night	45% 6% 13% 21% 13% 1	1879
	11th to 20th	Night	50% 7% 10% 18% 13% 2	1781
	21st to end	Night	49% 6% 11% 22% 12% 1	1785
May	1st to 10th	Night	42% 5% 10% 22% 18% 3	3180
	11th to 20th	Night	55% 6% 11% 21% 8% 1	3159
	21st to end	Night	43% 7% 20% 22% 8% 1	3470
June	1st to 10th	Night	49% 6% 15% 19% 9% 2	1335
	11th to 20th	Night	52% 8% 14% 21% 6%	1140
	21st to end	Night	39% 9% 21% 24% 6% 1	1140
July	1st to 10th	Night	34% 7% 21% 25% 11% 1	1870
	11th to 20th	Night	33% 7% 16% 35% 10%	2138
	21st to end	Night	36% 5% 23% 29% 7%	2337
August	1st to 10th	Night	39% 6% 19% 34% 1	2294
	11th to 20th	Night	41% 5% 20% 23% 9%	2669
	21st to end	Night	40% 4 27% 24% 4	3146
September	1st to 10th	Night	38% 7% 21% 26% 6% 2	1735
	11th to 20th	Night	38% 6% 20% 28% 9%	2090
	21st to end	Night	36% 8% 17% 26% 11% 2	2090
October	1st to 10th	Night	43% 4 22% 24% 7%	3702
	11th to 20th	Night	45% 4 17% 30% 4	4051
	21st to end	Night	48% 4 22% 21% 5%	4540
November	1st to 10th	Night	58% 6% 12% 20% 5%	2730
	11th to 20th	Night	57% 8% 15% 15% 5%	3000
	21st to end	Night	56% 7% 17% 16% 4 1	3000
December	1st to 10th	Night	62% 6% 13% 14% 5%	4890
	11th to 20th	Night	63% 6% 16% 11% 3	5547
	21st to end	Night	46% 4 15% 23% 11% 1	7936

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% 5% 27% 37% 19% 4	200
	11th to 20th	Day	11% 7% 33% 30% 16% 5%	200
	21st to end	Day	10% 9% 39% 25% 13% 4	220
February	1st to 10th	Day	12% 8% 37% 29% 13% 4	200
	11th to 20th	Day	11% 7% 31% 32% 16% 4	260
	21st to end	Day	7% 7% 35% 33% 13% 5%	273
March	1st to 10th	Day	8% 9% 32% 32% 16% 3	500
	11th to 20th	Day	8% 9% 33% 30% 16% 4	500
	21st to end	Day	18% 5% 29% 28% 15% 4	550
April	1st to 10th	Day	9% 11% 34% 30% 11% 4	500
	11th to 20th	Day	15% 9% 28% 28% 15% 5%	492
	21st to end	Day	17% 9% 31% 29% 12% 2	508
May	1st to 10th	Day	13% 11% 24% 30% 18% 5%	703
	11th to 20th	Day	14% 7% 23% 31% 19% 6%	725
	21st to end	Day	16% 7% 19% 31% 20% 7%	789
June	1st to 10th	Day	19% 8% 25% 30% 14% 4	783
	11th to 20th	Day	20% 6% 18% 26% 23% 6%	870
	21st to end	Day	12% 3 18% 32% 26% 10%	870
July	1st to 10th	Day	12% 3 17% 33% 25% 9%	856
	11th to 20th	Day	14% 4 19% 30% 25% 8%	693
	21st to end	Day	11% 5% 19% 29% 26% 10%	739
August	1st to 10th	Day	14% 4 16% 28% 24% 14%	621
	11th to 20th	Day	10% 4 27% 30% 23% 6%	477
	21st to end	Day	11% 6% 22% 31% 23% 6%	539
September	1st to 10th	Day	17% 11% 25% 24% 17% 6%	490
	11th to 20th	Day	20% 7% 24% 30% 15% 4	490
	21st to end	Day	12% 11% 30% 28% 16% 4	490
October	1st to 10th	Day	14% 10% 30% 27% 15% 4	362
	11th to 20th	Day	16% 4 33% 31% 14% 2	300
	21st to end	Day	18% 12% 31% 24% 12% 4	330
November	1st to 10th	Day	19% 5% 29% 32% 14% 1	298
	11th to 20th	Day	11% 6% 41% 26% 14% 3	200
	21st to end	Day	9% 7% 40% 29% 12% 4	200
December	1st to 10th	Day	8% 8% 33% 32% 16% 5%	200
	11th to 20th	Day	13% 8% 32% 35% 10% 3	200
	21st to end	Day	9% 3 23% 36% 23% 6%	220
January	1st to 10th	Night	12% 6% 29% 38% 14% 1	1045
	11th to 20th	Night	11% 6% 33% 37% 12% 2	1000
	21st to end	Night	14% 7% 35% 32% 10% 2	1065
February	1st to 10th	Night	12% 7% 26% 34% 19% 2	800
	11th to 20th	Night	11% 3 27% 39% 18% 1	784
	21st to end	Night	6% 4 30% 38% 19% 4	660
March	1st to 10th	Night	9% 5% 27% 41% 15% 2	800
	11th to 20th	Night	12% 5% 27% 40% 15% 1	800
	21st to end	Night	15% 4 27% 35% 17% 2	880
April	1st to 10th	Night	11% 5% 25% 38% 18% 3	679
	11th to 20th	Night	12% 5% 27% 38% 16% 2	593
	21st to end	Night	15% 7% 21% 39% 17% 1	594
May	1st to 10th	Night	12% 7% 21% 39% 19% 3	400
	11th to 20th	Night	13% 5% 19% 40% 21% 3	394
	21st to end	Night	19% 4 18% 34% 23% 2	433
June	1st to 10th	Night	19% 5% 19% 39% 17% 2	399
	11th to 20th	Night	19% 5% 14% 37% 22% 3	380
	21st to end	Night	11% 4 13% 43% 26% 4	380
July	1st to 10th	Night	13% 2 16% 39% 29%	370
	11th to 20th	Night	12% 4 18% 41% 23% 2	368
	21st to end	Night	10% 3 14% 40% 30% 4	416
August	1st to 10th	Night	9% 3 15% 37% 31% 6%	378
	11th to 20th	Night	12% 2 19% 40% 26% 1	459
	21st to end	Night	14% 3 17% 43% 22% 1	627
September	1st to 10th	Night	16% 3 20% 36% 23% 2	587
	11th to 20th	Night	15% 3 17% 43% 20% 1	760
	21st to end	Night	12% 4 29% 37% 16% 1	760
October	1st to 10th	Night	16% 4 26% 37% 17% 1	760
	11th to 20th	Night	14% 4 30% 37% 12% 3	760
	21st to end	Night	16% 7% 30% 34% 11% 1	883
November	1st to 10th	Night	17% 5% 30% 35% 11% 2	975
	11th to 20th	Night	14% 7% 34% 32% 11% 3	1000
	21st to end	Night	12% 5% 36% 33% 12% 2	1000
December	1st to 10th	Night	13% 6% 33% 32% 12% 3	1000
	11th to 20th	Night	12% 7% 30% 36% 14% 2	1000
	21st to end	Night	9% 3 30% 36% 18% 3	1203

Page generated at 2025-06-07 08:28:12. Version ac07

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