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 2024-03-18.

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 7% 7% 4 6% 6% 6% 8% 32%	78095
	Night	8% 9% 4 8% 7% 4 6% 6% 6% 8% 33%	81642
Transparency	Day	48% 8% 18% 20% 6%	77789
	Night	48% 7% 16% 20% 8% 1	81528
Seeing	Day	13% 7% 25% 30% 19% 6%	15118
	Night	13% 5% 27% 37% 17% 2	23865

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	5% 15% 7% 13% 13% 5% 5% 7% 6% 7% 18%	2063
	11th to 20th	Day	5% 8% 4 7% 9% 5% 6% 10% 8% 12% 26%	2199
	21st to end	Day	6% 12% 5% 10% 7% 4 5% 5% 6% 8% 33%	2519
February	1st to 10th	Day	7% 13% 5% 9% 9% 6% 7% 6% 7% 8% 23%	1520
	11th to 20th	Day	7% 11% 5% 11% 9% 4 7% 6% 6% 8% 27%	1592
	21st to end	Day	5% 9% 8% 10% 10% 6% 6% 8% 7% 7% 24%	1436
March	1st to 10th	Day	5% 12% 6% 10% 11% 4 7% 6% 7% 8% 22%	1900
	11th to 20th	Day	8% 10% 6% 8% 7% 3 6% 6% 5% 8% 32%	2037
	21st to end	Day	10% 14% 6% 8% 8% 4 5% 6% 6% 8% 24%	2207
April	1st to 10th	Day	8% 11% 4 9% 8% 5% 5% 7% 6% 7% 29%	2268
	11th to 20th	Day	11% 11% 3 7% 7% 5% 6% 5% 6% 7% 30%	2310
	21st to end	Day	12% 11% 5% 8% 8% 4 5% 6% 7% 8% 26%	2349
May	1st to 10th	Day	11% 9% 4 7% 8% 5% 7% 7% 7% 7% 28%	2700
	11th to 20th	Day	12% 6% 3 6% 5% 3 5% 6% 6% 8% 40%	2654
	21st to end	Day	15% 8% 2 6% 6% 4 5% 6% 6% 7% 35%	2917
June	1st to 10th	Day	16% 7% 3 7% 7% 5% 6% 6% 6% 7% 31%	2751
	11th to 20th	Day	20% 9% 4 7% 6% 4 7% 6% 6% 8% 23%	2880
	21st to end	Day	10% 5% 3 6% 8% 4 7% 7% 7% 9% 34%	2880
July	1st to 10th	Day	12% 5% 2 5% 6% 4 6% 6% 7% 9% 38%	2880
	11th to 20th	Day	13% 5% 3 5% 7% 4 5% 7% 7% 10% 34%	2726
	21st to end	Day	10% 5% 3 5% 5% 3 6% 6% 7% 10% 41%	2938
August	1st to 10th	Day	12% 5% 2 6% 6% 4 6% 6% 7% 9% 37%	2634
	11th to 20th	Day	8% 5% 2 5% 7% 3 6% 6% 7% 9% 42%	2398
	21st to end	Day	10% 6% 3 6% 6% 4 5% 6% 6% 10% 38%	2574
September	1st to 10th	Day	13% 7% 3 7% 6% 3 4 5% 6% 8% 39%	2314
	11th to 20th	Day	14% 7% 2 5% 5% 3 6% 5% 6% 8% 37%	1980
	21st to end	Day	9% 6% 2 6% 6% 3 5% 4 7% 8% 43%	1980
October	1st to 10th	Day	11% 10% 4 8% 7% 3 4 5% 5% 7% 36%	1859
	11th to 20th	Day	12% 10% 3 5% 5% 3 6% 6% 5% 8% 37%	1638
	21st to end	Day	12% 13% 5% 9% 7% 4 6% 5% 4 6% 29%	1720
November	1st to 10th	Day	11% 14% 6% 8% 7% 4 5% 6% 5% 8% 26%	1487
	11th to 20th	Day	6% 13% 6% 12% 7% 5% 5% 5% 5% 8% 28%	1330
	21st to end	Day	5% 11% 7% 12% 10% 4 5% 6% 5% 7% 30%	1330
December	1st to 10th	Day	4 11% 6% 10% 9% 5% 8% 6% 7% 8% 27%	1330
	11th to 20th	Day	9% 11% 4 9% 7% 5% 7% 6% 7% 7% 27%	1682
	21st to end	Day	3 7% 4 8% 8% 4 7% 5% 7% 8% 39%	2113
January	1st to 10th	Night	5% 12% 7% 15% 11% 5% 6% 5% 6% 6% 22%	4878
	11th to 20th	Night	4 9% 4 7% 8% 6% 8% 8% 6% 7% 32%	4699
	21st to end	Night	6% 11% 5% 10% 9% 4 6% 5% 5% 8% 30%	5168
February	1st to 10th	Night	7% 10% 6% 10% 8% 4 8% 7% 6% 8% 26%	2660
	11th to 20th	Night	8% 10% 4 10% 9% 5% 7% 5% 6% 7% 29%	2475
	21st to end	Night	3 9% 5% 8% 8% 4 7% 7% 8% 8% 31%	2017
March	1st to 10th	Night	6% 10% 5% 9% 9% 5% 6% 6% 6% 8% 31%	2280
	11th to 20th	Night	9% 9% 4 7% 7% 5% 6% 5% 6% 9% 34%	2088
	21st to end	Night	9% 15% 4 9% 6% 4 5% 5% 6% 9% 29%	2147
April	1st to 10th	Night	9% 7% 5% 8% 6% 4 7% 5% 6% 10% 35%	1692
	11th to 20th	Night	9% 11% 3 7% 8% 5% 8% 6% 6% 7% 30%	1601
	21st to end	Night	11% 12% 4 8% 6% 3 6% 5% 5% 7% 32%	1609
May	1st to 10th	Night	10% 7% 4 7% 8% 4 5% 6% 8% 7% 34%	1260
	11th to 20th	Night	11% 6% 3 5% 6% 3 5% 4 5% 6% 44%	1239
	21st to end	Night	18% 7% 3 5% 6% 4 5% 6% 7% 7% 32%	1358
June	1st to 10th	Night	15% 7% 3 7% 8% 5% 6% 4 6% 8% 32%	1206
	11th to 20th	Night	17% 8% 3 7% 6% 4 6% 7% 8% 8% 28%	1080
	21st to end	Night	10% 5% 3 7% 6% 4 5% 6% 7% 9% 38%	1080
July	1st to 10th	Night	11% 6% 2 5% 5% 4 6% 6% 7% 10% 39%	1080
	11th to 20th	Night	11% 5% 3 5% 5% 4 6% 7% 6% 10% 39%	1232
	21st to end	Night	8% 3 3 5% 5% 4 5% 5% 7% 11% 44%	1379
August	1st to 10th	Night	8% 3 2 6% 6% 4 6% 6% 8% 11% 41%	1302
	11th to 20th	Night	9% 5% 2 5% 6% 3 5% 5% 6% 10% 45%	1502
	21st to end	Night	14% 5% 2 5% 7% 4 6% 6% 5% 6% 40%	1782
September	1st to 10th	Night	12% 7% 3 4 5% 4 5% 4 5% 8% 43%	1643
	11th to 20th	Night	12% 7% 3 4 5% 3 4 5% 6% 8% 43%	1980
	21st to end	Night	9% 5% 2 6% 5% 3 5% 5% 5% 9% 45%	1980
October	1st to 10th	Night	12% 8% 3 6% 6% 4 5% 5% 6% 9% 37%	2101
	11th to 20th	Night	10% 9% 4 7% 6% 3 5% 5% 6% 8% 37%	2318
	21st to end	Night	11% 11% 4 9% 6% 4 5% 5% 6% 6% 33%	2618
November	1st to 10th	Night	12% 13% 6% 9% 7% 4 6% 4 5% 6% 27%	2590
	11th to 20th	Night	9% 12% 6% 11% 9% 4 7% 6% 6% 7% 25%	2850
	21st to end	Night	6% 11% 6% 12% 10% 4 6% 5% 6% 8% 27%	2850
December	1st to 10th	Night	7% 11% 5% 9% 8% 5% 6% 6% 6% 8% 30%	2850
	11th to 20th	Night	8% 13% 5% 12% 9% 5% 6% 6% 6% 7% 22%	3510
	21st to end	Night	4 7% 4 6% 7% 4 6% 5% 7% 9% 41%	5538

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	63% 7% 13% 13% 4	2063
	11th to 20th	Day	48% 6% 14% 18% 13% 1	2220
	21st to end	Day	49% 6% 22% 16% 7%	2519
February	1st to 10th	Day	56% 7% 13% 16% 8%	1520
	11th to 20th	Day	54% 7% 16% 16% 7%	1600
	21st to end	Day	54% 8% 17% 15% 7%	1436
March	1st to 10th	Day	57% 8% 16% 15% 5%	1900
	11th to 20th	Day	50% 8% 15% 19% 9%	2038
	21st to end	Day	57% 9% 14% 16% 4	2207
April	1st to 10th	Day	50% 9% 17% 17% 7%	2268
	11th to 20th	Day	51% 7% 14% 21% 7% 1	2310
	21st to end	Day	53% 8% 13% 18% 7% 1	2349
May	1st to 10th	Day	50% 8% 12% 19% 9%	2700
	11th to 20th	Day	40% 7% 13% 27% 13% 1	2658
	21st to end	Day	46% 7% 13% 24% 10% 1	2918
June	1st to 10th	Day	50% 7% 15% 21% 6%	2751
	11th to 20th	Day	57% 8% 15% 15% 4	2880
	21st to end	Day	44% 10% 20% 20% 5%	2880
July	1st to 10th	Day	40% 10% 21% 23% 5% 1	2801
	11th to 20th	Day	43% 12% 25% 19% 2	2643
	21st to end	Day	37% 11% 24% 26% 3	2775
August	1st to 10th	Day	42% 11% 26% 19% 3	2616
	11th to 20th	Day	36% 9% 27% 23% 4	2398
	21st to end	Day	40% 9% 24% 22% 4	2574
September	1st to 10th	Day	43% 8% 20% 22% 6% 1	2314
	11th to 20th	Day	42% 9% 22% 22% 6%	1980
	21st to end	Day	37% 8% 20% 25% 9% 1	1980
October	1st to 10th	Day	47% 7% 20% 19% 6%	1859
	11th to 20th	Day	45% 7% 18% 24% 6%	1638
	21st to end	Day	56% 7% 12% 20% 4	1720
November	1st to 10th	Day	55% 9% 15% 17% 5%	1487
	11th to 20th	Day	53% 7% 20% 14% 5%	1330
	21st to end	Day	53% 9% 16% 18% 4 1	1330
December	1st to 10th	Day	52% 9% 14% 17% 8% 1	1330
	11th to 20th	Day	52% 9% 18% 16% 5%	1684
	21st to end	Day	40% 6% 12% 29% 11% 1	2113
January	1st to 10th	Night	59% 7% 13% 14% 6% 1	4878
	11th to 20th	Night	47% 7% 14% 19% 12% 1	4740
	21st to end	Night	52% 7% 21% 14% 5%	5168
February	1st to 10th	Night	54% 7% 14% 17% 7% 1	2660
	11th to 20th	Night	54% 6% 13% 18% 9%	2477
	21st to end	Night	46% 9% 16% 21% 9%	2017
March	1st to 10th	Night	49% 7% 15% 22% 7%	2280
	11th to 20th	Night	46% 7% 13% 23% 10% 1	2088
	21st to end	Night	51% 7% 16% 18% 7% 1	2147
April	1st to 10th	Night	44% 6% 14% 22% 12% 1	1692
	11th to 20th	Night	51% 7% 10% 18% 12% 2	1601
	21st to end	Night	50% 6% 10% 22% 11% 1	1609
May	1st to 10th	Night	45% 6% 15% 21% 12% 2	1260
	11th to 20th	Night	39% 6% 11% 27% 15% 1	1239
	21st to end	Night	48% 7% 12% 20% 11% 1	1358
June	1st to 10th	Night	50% 6% 16% 19% 9% 1	1206
	11th to 20th	Night	52% 8% 14% 21% 6%	1080
	21st to end	Night	39% 9% 22% 23% 5% 1	1080
July	1st to 10th	Night	37% 11% 20% 24% 6% 2	1050
	11th to 20th	Night	38% 12% 22% 26% 2	1192
	21st to end	Night	32% 10% 24% 29% 5%	1302
August	1st to 10th	Night	36% 11% 25% 26% 2	1295
	11th to 20th	Night	35% 8% 25% 25% 7% 1	1502
	21st to end	Night	42% 7% 18% 25% 7%	1782
September	1st to 10th	Night	39% 7% 22% 24% 6% 2	1643
	11th to 20th	Night	37% 6% 20% 27% 9%	1980
	21st to end	Night	35% 8% 17% 27% 12% 2	1980
October	1st to 10th	Night	44% 6% 15% 25% 9%	2101
	11th to 20th	Night	44% 7% 16% 26% 6%	2318
	21st to end	Night	50% 7% 14% 21% 8%	2618
November	1st to 10th	Night	58% 6% 12% 20% 5%	2590
	11th to 20th	Night	57% 8% 16% 15% 4	2850
	21st to end	Night	55% 8% 18% 15% 4 1	2850
December	1st to 10th	Night	51% 7% 12% 20% 9% 1	2850
	11th to 20th	Night	59% 9% 14% 13% 5%	3507
	21st to end	Night	39% 6% 16% 24% 14% 2	5538

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% 4 28% 36% 19% 3	180
	11th to 20th	Day	12% 7% 32% 28% 16% 5%	180
	21st to end	Day	12% 9% 36% 26% 14% 4	198
February	1st to 10th	Day	13% 8% 38% 29% 11% 2	180
	11th to 20th	Day	12% 7% 30% 32% 15% 4	234
	21st to end	Day	7% 7% 35% 32% 14% 6%	248
March	1st to 10th	Day	8% 9% 32% 32% 16% 3	460
	11th to 20th	Day	8% 8% 34% 29% 17% 5%	449
	21st to end	Day	17% 5% 30% 28% 16% 4	462
April	1st to 10th	Day	9% 11% 34% 30% 12% 5%	420
	11th to 20th	Day	16% 7% 26% 29% 16% 6%	412
	21st to end	Day	16% 9% 33% 28% 12% 2	426
May	1st to 10th	Day	12% 10% 23% 31% 20% 5%	603
	11th to 20th	Day	13% 6% 24% 30% 21% 6%	625
	21st to end	Day	16% 7% 18% 32% 19% 8%	679
June	1st to 10th	Day	19% 6% 25% 31% 15% 4	681
	11th to 20th	Day	20% 6% 18% 26% 24% 6%	810
	21st to end	Day	11% 4 18% 31% 26% 10%	810
July	1st to 10th	Day	12% 4 18% 34% 25% 7%	796
	11th to 20th	Day	14% 4 19% 31% 25% 6%	642
	21st to end	Day	10% 5% 19% 29% 27% 11%	684
August	1st to 10th	Day	14% 4 16% 28% 24% 14%	574
	11th to 20th	Day	9% 5% 29% 30% 22% 5%	437
	21st to end	Day	12% 6% 22% 31% 22% 6%	495
September	1st to 10th	Day	18% 11% 25% 26% 14% 5%	450
	11th to 20th	Day	20% 7% 25% 30% 15% 3	450
	21st to end	Day	12% 10% 29% 28% 17% 4	450
October	1st to 10th	Day	14% 10% 29% 26% 16% 4	329
	11th to 20th	Day	15% 4 34% 30% 14% 2	270
	21st to end	Day	18% 12% 29% 25% 12% 3	297
November	1st to 10th	Day	20% 5% 29% 31% 14% 1	269
	11th to 20th	Day	12% 7% 40% 25% 13% 3	180
	21st to end	Day	7% 7% 42% 28% 12% 4	180
December	1st to 10th	Day	6% 8% 33% 31% 17% 6%	180
	11th to 20th	Day	12% 9% 32% 34% 11% 2	180
	21st to end	Day	8% 4 24% 37% 22% 6%	198
January	1st to 10th	Night	12% 6% 29% 39% 13% 1	991
	11th to 20th	Night	11% 6% 32% 37% 13% 2	950
	21st to end	Night	14% 7% 34% 32% 10% 2	1012
February	1st to 10th	Night	12% 7% 27% 34% 18% 2	760
	11th to 20th	Night	12% 4 28% 38% 18% 1	744
	21st to end	Night	6% 4 29% 38% 20% 4	628
March	1st to 10th	Night	10% 5% 28% 39% 16% 2	760
	11th to 20th	Night	12% 4 27% 40% 16% 1	752
	21st to end	Night	14% 5% 26% 35% 18% 2	792
April	1st to 10th	Night	10% 4 24% 39% 18% 3	612
	11th to 20th	Night	13% 4 26% 39% 16% 2	533
	21st to end	Night	15% 7% 21% 38% 17% 1	536
May	1st to 10th	Night	11% 7% 20% 38% 21% 3	360
	11th to 20th	Night	13% 5% 18% 40% 21% 3	354
	21st to end	Night	20% 3 19% 34% 22% 2	389
June	1st to 10th	Night	18% 4 18% 40% 18% 2	360
	11th to 20th	Night	19% 6% 14% 36% 22% 3	360
	21st to end	Night	10% 5% 13% 43% 26% 4	360
July	1st to 10th	Night	13% 2 17% 39% 28%	350
	11th to 20th	Night	13% 4 18% 41% 22% 2	348
	21st to end	Night	9% 3 14% 41% 30% 4	394
August	1st to 10th	Night	9% 3 15% 37% 30% 6%	358
	11th to 20th	Night	11% 2 20% 39% 26% 1	434
	21st to end	Night	14% 3 18% 42% 23% 2	594
September	1st to 10th	Night	17% 3 21% 35% 22% 2	556
	11th to 20th	Night	15% 4 18% 43% 19% 2	720
	21st to end	Night	11% 3 29% 38% 17% 1	720
October	1st to 10th	Night	16% 3 26% 36% 18% 2	720
	11th to 20th	Night	14% 4 31% 36% 13% 3	720
	21st to end	Night	17% 7% 31% 33% 11% 1	836
November	1st to 10th	Night	17% 5% 30% 34% 11% 2	925
	11th to 20th	Night	14% 7% 34% 31% 11% 3	950
	21st to end	Night	11% 6% 37% 33% 12% 2	950
December	1st to 10th	Night	13% 7% 32% 32% 13% 3	950
	11th to 20th	Night	11% 7% 31% 36% 14% 2	950
	21st to end	Night	9% 4 30% 36% 18% 3	1137

Page generated at 2024-03-15 12:01:41. Version ac07

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