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 2024-11-02.

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 9% 6% 5% 5% 5% 6% 8% 33%	102418
	Night	9% 10% 4 9% 6% 6% 5% 4 6% 8% 33%	96628
Transparency	Day	47% 7% 18% 22% 7%	102154
	Night	47% 7% 16% 21% 8% 1	96538
Seeing	Day	14% 7% 25% 30% 19% 6%	16138
	Night	13% 5% 27% 37% 17% 2	24519

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 16% 6% 15% 11% 6% 5% 5% 6% 7% 18%	2063
	11th to 20th	Day	5% 9% 3 9% 8% 6% 6% 9% 8% 12% 26%	2199
	21st to end	Day	6% 13% 5% 11% 6% 6% 4 4 6% 7% 33%	2519
February	1st to 10th	Day	7% 14% 4 11% 8% 7% 6% 4 7% 8% 23%	1520
	11th to 20th	Day	7% 11% 5% 13% 8% 6% 6% 5% 6% 8% 27%	1592
	21st to end	Day	4 12% 6% 11% 8% 7% 7% 6% 8% 8% 24%	1436
March	1st to 10th	Day	3 11% 5% 12% 9% 6% 7% 4 6% 8% 28%	3138
	11th to 20th	Day	5% 9% 5% 10% 6% 5% 5% 4 6% 10% 36%	3457
	21st to end	Day	10% 15% 5% 16% 7% 4 4 3 5% 7% 22%	3879
April	1st to 10th	Day	8% 12% 4 9% 7% 6% 5% 6% 7% 7% 28%	2394
	11th to 20th	Day	11% 12% 3 8% 6% 7% 5% 4 6% 7% 31%	2440
	21st to end	Day	12% 12% 4 9% 7% 5% 6% 5% 7% 8% 26%	2481
May	1st to 10th	Day	18% 9% 3 7% 5% 5% 5% 3 6% 7% 31%	4740
	11th to 20th	Day	14% 12% 3 8% 5% 4 5% 5% 5% 7% 32%	4694
	21st to end	Day	11% 9% 3 9% 7% 7% 7% 6% 8% 9% 26%	5161
June	1st to 10th	Day	16% 7% 3 8% 6% 6% 6% 5% 6% 7% 30%	2904
	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	11% 10% 4 9% 6% 4 4 4 5% 7% 35%	1962
	11th to 20th	Day	12% 11% 3 6% 5% 5% 6% 4 5% 8% 36%	1729
	21st to end	Day	12% 13% 5% 10% 6% 5% 6% 4 4 6% 29%	1815
November	1st to 10th	Day	11% 16% 5% 9% 6% 5% 5% 4 5% 7% 26%	1495
	11th to 20th	Day	6% 13% 6% 13% 6% 7% 5% 3 6% 8% 28%	1330
	21st to end	Day	5% 13% 4 13% 9% 5% 5% 4 5% 7% 30%	1330
December	1st to 10th	Day	4 12% 4 11% 8% 6% 7% 5% 7% 8% 27%	1330
	11th to 20th	Day	9% 11% 4 10% 6% 7% 7% 5% 7% 7% 27%	1682
	21st to end	Day	3 7% 3 9% 7% 6% 6% 4 7% 8% 39%	2113
January	1st to 10th	Night	5% 13% 7% 17% 8% 6% 6% 4 6% 6% 22%	4878
	11th to 20th	Night	4 10% 4 8% 7% 8% 8% 7% 6% 7% 32%	4699
	21st to end	Night	6% 12% 4 12% 8% 6% 6% 4 5% 7% 30%	5168
February	1st to 10th	Night	7% 12% 5% 11% 7% 6% 7% 5% 6% 7% 25%	2660
	11th to 20th	Night	7% 11% 4 12% 7% 6% 6% 5% 6% 7% 29%	2475
	21st to end	Night	3 10% 4 10% 7% 6% 6% 7% 8% 8% 31%	2017
March	1st to 10th	Night	4 10% 5% 11% 7% 7% 7% 5% 7% 10% 29%	3736
	11th to 20th	Night	5% 8% 3 8% 7% 6% 5% 4 7% 10% 38%	3522
	21st to end	Night	8% 15% 7% 14% 6% 5% 5% 4 5% 7% 25%	3772
April	1st to 10th	Night	8% 9% 3 8% 6% 7% 5% 4 6% 9% 34%	1785
	11th to 20th	Night	9% 11% 3 8% 7% 6% 7% 5% 6% 7% 30%	1691
	21st to end	Night	11% 13% 3 8% 5% 4 5% 5% 6% 8% 32%	1697
May	1st to 10th	Night	19% 7% 3 7% 5% 5% 5% 4 6% 6% 33%	2220
	11th to 20th	Night	14% 11% 3 8% 5% 5% 5% 4 6% 6% 32%	2199
	21st to end	Night	12% 7% 3 8% 7% 5% 6% 6% 8% 9% 29%	2414
June	1st to 10th	Night	15% 7% 3 9% 6% 6% 5% 4 6% 8% 31%	1272
	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	11% 8% 3 8% 5% 5% 5% 4 6% 8% 36%	2218
	11th to 20th	Night	9% 9% 3 8% 5% 5% 5% 4 6% 8% 36%	2447
	21st to end	Night	11% 12% 4 10% 5% 5% 5% 4 6% 6% 32%	2764
November	1st to 10th	Night	12% 14% 5% 10% 7% 5% 5% 4 5% 5% 27%	2617
	11th to 20th	Night	9% 13% 6% 12% 8% 6% 6% 5% 6% 7% 25%	2850
	21st to end	Night	6% 12% 5% 13% 8% 6% 5% 4 6% 8% 26%	2850
December	1st to 10th	Night	7% 12% 4 10% 8% 6% 5% 5% 6% 8% 30%	2850
	11th to 20th	Night	8% 13% 5% 14% 8% 6% 6% 5% 7% 7% 22%	3510
	21st to end	Night	4 8% 3 8% 6% 6% 6% 4 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	52% 6% 16% 20% 6%	3138
	11th to 20th	Day	43% 7% 22% 21% 7%	3458
	21st to end	Day	60% 7% 12% 18% 3	3879
April	1st to 10th	Day	50% 9% 17% 17% 8% 1	2394
	11th to 20th	Day	50% 6% 14% 21% 8%	2440
	21st to end	Day	53% 8% 13% 18% 7% 1	2481
May	1st to 10th	Day	50% 7% 10% 23% 10%	4740
	11th to 20th	Day	49% 7% 10% 24% 10%	4698
	21st to end	Day	49% 10% 17% 16% 7%	5162
June	1st to 10th	Day	50% 7% 15% 21% 6%	2904
	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	47% 7% 21% 19% 6%	1962
	11th to 20th	Day	46% 7% 18% 24% 6%	1729
	21st to end	Day	56% 7% 13% 20% 4	1815
November	1st to 10th	Day	56% 8% 15% 17% 4	1495
	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	48% 7% 18% 22% 5%	3736
	11th to 20th	Night	39% 7% 22% 22% 9% 1	3522
	21st to end	Night	55% 8% 12% 18% 6%	3772
April	1st to 10th	Night	45% 6% 14% 22% 12% 1	1785
	11th to 20th	Night	50% 7% 10% 18% 12% 2	1691
	21st to end	Night	49% 6% 11% 21% 12% 1	1697
May	1st to 10th	Night	48% 6% 10% 21% 13% 1	2220
	11th to 20th	Night	48% 8% 10% 23% 10% 1	2199
	21st to end	Night	46% 10% 20% 16% 8% 1	2414
June	1st to 10th	Night	50% 6% 15% 19% 9% 1	1272
	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	44% 6% 16% 25% 9%	2218
	11th to 20th	Night	44% 6% 17% 26% 6%	2447
	21st to end	Night	50% 7% 15% 21% 7%	2764
November	1st to 10th	Night	58% 6% 12% 19% 5%	2617
	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% 9% 35% 28% 16% 5%	460
	21st to end	Day	17% 6% 30% 28% 15% 4	506
April	1st to 10th	Day	9% 12% 35% 28% 11% 4	460
	11th to 20th	Day	16% 8% 27% 28% 16% 6%	452
	21st to end	Day	17% 9% 31% 28% 12% 2	467
May	1st to 10th	Day	13% 10% 23% 30% 19% 5%	653
	11th to 20th	Day	14% 7% 24% 30% 19% 5%	675
	21st to end	Day	15% 7% 18% 31% 20% 8%	734
June	1st to 10th	Day	20% 7% 25% 30% 14% 4	734
	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% 28% 31% 15% 2	272
	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% 5% 28% 39% 15% 1	760
	21st to end	Night	14% 5% 27% 36% 17% 2	836
April	1st to 10th	Night	11% 5% 25% 38% 18% 3	645
	11th to 20th	Night	13% 4 26% 39% 16% 2	563
	21st to end	Night	15% 7% 22% 39% 17% 1	565
May	1st to 10th	Night	12% 7% 21% 38% 20% 3	380
	11th to 20th	Night	14% 5% 18% 40% 20% 3	374
	21st to end	Night	19% 4 18% 34% 22% 2	411
June	1st to 10th	Night	19% 4 18% 39% 17% 2	380
	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% 12% 1	883
November	1st to 10th	Night	17% 5% 30% 34% 11% 2	935
	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 2024-10-30 11:19:18. Version ac07

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