Strathcona Wilderness Centre
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Strathcona Wilderness Centre clear sky chart from 2005-11-06 to 2025-07-21.

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	9% 9% 3 9% 6% 5% 5% 4 6% 8% 35%	124189
	Night	8% 9% 4 10% 6% 6% 5% 4 6% 8% 34%	123569
Transparency	Day	44% 7% 17% 23% 8% 1	123932
	Night	46% 7% 16% 21% 9% 1	123471
Seeing	Day	13% 7% 24% 31% 19% 7%	16433
	Night	12% 6% 29% 35% 16% 2	25365

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 11% 4 12% 8% 6% 6% 5% 8% 9% 26%	3179
	11th to 20th	Day	3 8% 3 11% 8% 7% 7% 5% 9% 10% 29%	3159
	21st to end	Day	8% 12% 3 9% 7% 5% 5% 3 5% 7% 35%	3707
February	1st to 10th	Day	8% 13% 5% 11% 9% 6% 6% 5% 6% 7% 24%	1600
	11th to 20th	Day	4 12% 7% 12% 7% 6% 6% 5% 6% 7% 27%	1715
	21st to end	Day	4 12% 5% 12% 8% 5% 8% 5% 5% 8% 28%	1518
March	1st to 10th	Day	4 9% 5% 12% 7% 5% 6% 5% 7% 10% 30%	4518
	11th to 20th	Day	5% 12% 5% 10% 6% 5% 5% 4 5% 10% 33%	4993
	21st to end	Day	9% 14% 5% 15% 6% 5% 5% 4 6% 7% 25%	5519
April	1st to 10th	Day	8% 12% 4 8% 6% 6% 6% 5% 6% 8% 32%	2516
	11th to 20th	Day	11% 12% 4 7% 5% 6% 5% 4 7% 8% 32%	2570
	21st to end	Day	11% 10% 4 8% 5% 6% 5% 5% 7% 7% 32%	2600
May	1st to 10th	Day	11% 8% 3 8% 6% 5% 5% 4 5% 6% 39%	6632
	11th to 20th	Day	14% 11% 4 8% 6% 6% 5% 5% 7% 8% 27%	6734
	21st to end	Day	10% 8% 3 7% 5% 5% 5% 4 6% 7% 40%	7405
June	1st to 10th	Day	14% 8% 3 9% 6% 5% 5% 4 6% 8% 32%	3000
	11th to 20th	Day	19% 10% 3 9% 7% 7% 5% 5% 7% 7% 23%	3000
	21st to end	Day	11% 6% 2 7% 6% 5% 6% 5% 8% 9% 36%	3035
July	1st to 10th	Day	8% 5% 2 7% 5% 5% 5% 4 7% 7% 46%	4890
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 4 6% 9% 46%	4890
	21st to end	Day	11% 6% 2 6% 4 4 4 4 6% 8% 44%	5139
August	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 5% 7% 9% 40%	4562
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 4 8% 10% 42%	4123
	21st to end	Day	11% 4 2 6% 4 5% 5% 4 7% 9% 44%	4521
September	1st to 10th	Day	12% 6% 2 6% 4 5% 4 4 6% 8% 42%	2421
	11th to 20th	Day	14% 7% 3 6% 4 4 4 4 5% 7% 41%	2090
	21st to end	Day	8% 7% 2 7% 5% 5% 5% 3 6% 8% 43%	2090
October	1st to 10th	Day	10% 8% 3 10% 6% 5% 4 4 6% 7% 38%	3271
	11th to 20th	Day	10% 9% 4 8% 5% 4 4 4 6% 9% 37%	2914
	21st to end	Day	7% 13% 4 7% 5% 6% 5% 4 6% 7% 37%	3022
November	1st to 10th	Day	9% 13% 6% 9% 7% 5% 6% 4 6% 8% 27%	1568
	11th to 20th	Day	6% 12% 4 13% 8% 6% 6% 3 6% 6% 29%	1458
	21st to end	Day	5% 12% 6% 13% 7% 4 5% 5% 5% 8% 30%	1400
December	1st to 10th	Day	7% 16% 5% 10% 8% 7% 7% 5% 6% 8% 22%	2290
	11th to 20th	Day	9% 14% 5% 11% 7% 7% 6% 5% 7% 8% 21%	2642
	21st to end	Day	3 6% 3 10% 6% 6% 6% 4 6% 8% 42%	3498
January	1st to 10th	Night	3 8% 5% 14% 8% 8% 8% 6% 7% 7% 26%	6766
	11th to 20th	Night	2 9% 4 11% 7% 7% 5% 5% 6% 6% 38%	6739
	21st to end	Night	7% 12% 4 10% 6% 5% 5% 4 6% 8% 33%	7292
February	1st to 10th	Night	5% 10% 5% 14% 8% 8% 7% 5% 5% 7% 26%	2800
	11th to 20th	Night	5% 12% 5% 9% 6% 7% 6% 5% 7% 8% 30%	2571
	21st to end	Night	4 10% 4 11% 8% 7% 6% 6% 7% 8% 31%	2110
March	1st to 10th	Night	4 10% 5% 11% 5% 5% 6% 5% 7% 10% 33%	5376
	11th to 20th	Night	4 9% 4 11% 8% 6% 6% 5% 7% 9% 32%	5005
	21st to end	Night	10% 14% 6% 14% 7% 6% 5% 4 6% 6% 24%	5452
April	1st to 10th	Night	7% 10% 3 9% 7% 6% 6% 5% 7% 7% 33%	1883
	11th to 20th	Night	9% 10% 5% 10% 7% 6% 6% 5% 6% 7% 28%	1781
	21st to end	Night	11% 11% 3 8% 5% 5% 4 5% 6% 8% 35%	1800
May	1st to 10th	Night	17% 7% 2 7% 4 5% 4 4 5% 5% 40%	3328
	11th to 20th	Night	13% 10% 3 10% 6% 7% 7% 4 6% 7% 26%	3159
	21st to end	Night	12% 8% 3 7% 6% 5% 6% 4 6% 8% 35%	3470
June	1st to 10th	Night	15% 8% 4 7% 7% 5% 6% 6% 5% 7% 30%	1400
	11th to 20th	Night	16% 9% 3 9% 8% 7% 7% 6% 8% 7% 23%	1400
	21st to end	Night	9% 7% 3 8% 4 5% 6% 4 7% 9% 38%	1302
July	1st to 10th	Night	8% 7% 3 7% 5% 5% 5% 4 6% 7% 43%	2290
	11th to 20th	Night	8% 5% 2 6% 5% 5% 5% 5% 7% 10% 40%	2290
	21st to end	Night	13% 6% 2 4 4 3 4 4 7% 10% 43%	2414
August	1st to 10th	Night	14% 6% 2 6% 4 5% 4 4 6% 8% 42%	2365
	11th to 20th	Night	11% 6% 3 6% 5% 5% 5% 4 7% 8% 40%	2711
	21st to end	Night	11% 5% 2 6% 5% 5% 4 4 6% 9% 43%	3146
September	1st to 10th	Night	12% 5% 3 8% 4 4 4 3 5% 8% 46%	1754
	11th to 20th	Night	12% 6% 2 6% 4 3 4 3 6% 8% 45%	2090
	21st to end	Night	9% 6% 2 7% 4 4 4 4 6% 8% 44%	2090
October	1st to 10th	Night	8% 7% 3 9% 5% 5% 5% 4 7% 8% 40%	3702
	11th to 20th	Night	9% 6% 3 7% 5% 4 5% 5% 7% 9% 40%	4010
	21st to end	Night	6% 9% 3 9% 6% 5% 5% 4 7% 9% 37%	4505
November	1st to 10th	Night	11% 16% 5% 9% 6% 5% 5% 4 5% 6% 28%	2730
	11th to 20th	Night	7% 14% 5% 11% 7% 6% 5% 4 6% 6% 27%	2940
	21st to end	Night	5% 12% 5% 12% 7% 7% 7% 4 6% 7% 28%	3000
December	1st to 10th	Night	8% 16% 5% 12% 7% 7% 6% 4 6% 7% 22%	4890
	11th to 20th	Night	7% 14% 6% 14% 7% 7% 6% 5% 6% 8% 21%	5550
	21st to end	Night	2 6% 3 9% 6% 7% 6% 5% 6% 8% 42%	7458

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	51% 7% 12% 20% 9% 1	3179
	11th to 20th	Day	46% 6% 14% 14% 19% 1	3180
	21st to end	Day	46% 7% 21% 22% 5%	3707
February	1st to 10th	Day	57% 6% 14% 14% 9% 1	1600
	11th to 20th	Day	52% 8% 15% 15% 9%	1724
	21st to end	Day	51% 7% 12% 21% 8%	1518
March	1st to 10th	Day	47% 6% 18% 20% 9%	4518
	11th to 20th	Day	47% 6% 15% 22% 9%	4994
	21st to end	Day	55% 7% 9% 22% 6%	5519
April	1st to 10th	Day	47% 8% 16% 19% 8% 1	2516
	11th to 20th	Day	47% 6% 15% 21% 10%	2570
	21st to end	Day	46% 8% 15% 23% 7% 1	2600
May	1st to 10th	Day	44% 5% 10% 24% 15% 1	6632
	11th to 20th	Day	51% 8% 12% 22% 6%	6738
	21st to end	Day	39% 9% 20% 20% 11% 1	7406
June	1st to 10th	Day	47% 7% 14% 21% 10% 1	3000
	11th to 20th	Day	55% 9% 16% 16% 4	3000
	21st to end	Day	40% 11% 21% 20% 7% 1	3035
July	1st to 10th	Day	34% 8% 17% 27% 13% 1	4816
	11th to 20th	Day	33% 8% 17% 28% 13%	4809
	21st to end	Day	37% 7% 22% 24% 10%	4977
August	1st to 10th	Day	38% 9% 19% 32% 2	4544
	11th to 20th	Day	33% 9% 23% 27% 8%	4164
	21st to end	Day	35% 7% 28% 26% 4	4520
September	1st to 10th	Day	37% 9% 19% 25% 7% 2	2421
	11th to 20th	Day	41% 7% 18% 28% 7%	2090
	21st to end	Day	38% 9% 17% 26% 8% 2	2090
October	1st to 10th	Day	44% 6% 21% 24% 5%	3271
	11th to 20th	Day	44% 5% 15% 26% 10%	2914
	21st to end	Day	44% 7% 18% 27% 4	3022
November	1st to 10th	Day	53% 8% 17% 15% 6% 1	1568
	11th to 20th	Day	55% 7% 15% 18% 5%	1458
	21st to end	Day	51% 8% 17% 18% 5% 1	1400
December	1st to 10th	Day	58% 8% 17% 12% 4 1	2290
	11th to 20th	Day	57% 7% 17% 14% 4	2644
	21st to end	Day	39% 5% 13% 29% 13% 1	3498
January	1st to 10th	Night	53% 7% 14% 15% 10% 1	6766
	11th to 20th	Night	45% 6% 15% 16% 17% 1	6780
	21st to end	Night	47% 6% 21% 21% 5%	7292
February	1st to 10th	Night	55% 7% 13% 16% 9% 1	2800
	11th to 20th	Night	49% 8% 14% 17% 11% 1	2572
	21st to end	Night	47% 8% 13% 21% 10% 1	2110
March	1st to 10th	Night	44% 6% 18% 22% 10%	5376
	11th to 20th	Night	46% 6% 18% 20% 10% 1	5005
	21st to end	Night	57% 8% 10% 17% 9%	5452
April	1st to 10th	Night	45% 8% 14% 19% 13%	1883
	11th to 20th	Night	51% 8% 12% 18% 10% 2	1781
	21st to end	Night	45% 7% 12% 23% 12% 1	1800
May	1st to 10th	Night	43% 5% 9% 24% 17% 3	3327
	11th to 20th	Night	52% 9% 14% 18% 7%	3159
	21st to end	Night	43% 9% 17% 22% 8% 1	3470
June	1st to 10th	Night	48% 8% 13% 20% 10% 1	1400
	11th to 20th	Night	56% 10% 14% 16% 5%	1400
	21st to end	Night	40% 9% 24% 21% 6% 1	1302
July	1st to 10th	Night	37% 8% 18% 20% 16% 1	2255
	11th to 20th	Night	36% 9% 15% 29% 9% 1	2248
	21st to end	Night	34% 7% 22% 28% 8%	2337
August	1st to 10th	Night	39% 8% 20% 31% 2	2358
	11th to 20th	Night	40% 7% 21% 24% 8%	2736
	21st to end	Night	36% 7% 24% 28% 5%	3146
September	1st to 10th	Night	36% 8% 17% 26% 11% 2	1754
	11th to 20th	Night	36% 7% 17% 29% 9% 2	2090
	21st to end	Night	35% 9% 15% 26% 13% 2	2090
October	1st to 10th	Night	38% 6% 22% 27% 7%	3702
	11th to 20th	Night	38% 6% 14% 34% 7%	4010
	21st to end	Night	41% 7% 22% 25% 5%	4505
November	1st to 10th	Night	55% 8% 11% 20% 6%	2730
	11th to 20th	Night	55% 7% 12% 18% 6% 1	2940
	21st to end	Night	53% 9% 15% 17% 5% 1	3000
December	1st to 10th	Night	60% 7% 16% 12% 5% 1	4890
	11th to 20th	Night	60% 6% 18% 11% 5%	5547
	21st to end	Night	38% 6% 16% 22% 16% 2	7458

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	11% 4 31% 32% 20% 4	200
	11th to 20th	Day	9% 9% 35% 29% 16% 4	200
	21st to end	Day	12% 8% 36% 29% 10% 5%	220
February	1st to 10th	Day	12% 8% 31% 33% 14% 3	200
	11th to 20th	Day	9% 6% 31% 33% 17% 4	280
	21st to end	Day	6% 7% 32% 30% 16% 9%	282
March	1st to 10th	Day	12% 5% 28% 33% 18% 4	500
	11th to 20th	Day	10% 4 27% 35% 17% 6%	500
	21st to end	Day	12% 4 26% 34% 20% 4	550
April	1st to 10th	Day	11% 7% 24% 34% 19% 5%	500
	11th to 20th	Day	14% 8% 20% 30% 21% 8%	492
	21st to end	Day	15% 8% 19% 31% 20% 7%	500
May	1st to 10th	Day	12% 9% 21% 33% 19% 6%	682
	11th to 20th	Day	12% 6% 22% 33% 20% 8%	725
	21st to end	Day	15% 5% 19% 31% 19% 10%	789
June	1st to 10th	Day	17% 9% 22% 32% 16% 5%	730
	11th to 20th	Day	20% 8% 22% 23% 19% 8%	730
	21st to end	Day	14% 5% 19% 28% 24% 11%	765
July	1st to 10th	Day	11% 4 15% 33% 27% 9%	721
	11th to 20th	Day	10% 5% 20% 30% 24% 11%	718
	21st to end	Day	10% 4 18% 31% 26% 10%	740
August	1st to 10th	Day	11% 5% 20% 29% 24% 12%	583
	11th to 20th	Day	10% 4 23% 32% 25% 6%	477
	21st to end	Day	12% 6% 21% 31% 21% 9%	539
September	1st to 10th	Day	14% 10% 24% 27% 18% 7%	490
	11th to 20th	Day	18% 8% 24% 30% 16% 4	490
	21st to end	Day	12% 15% 30% 26% 14% 4	490
October	1st to 10th	Day	15% 8% 32% 26% 13% 6%	362
	11th to 20th	Day	12% 12% 30% 31% 12% 3	300
	21st to end	Day	15% 11% 35% 25% 12% 3	330
November	1st to 10th	Day	17% 6% 31% 32% 12% 2	300
	11th to 20th	Day	11% 7% 36% 34% 11% 2	228
	21st to end	Day	5% 9% 38% 32% 13% 5%	200
December	1st to 10th	Day	10% 7% 33% 32% 15% 4	200
	11th to 20th	Day	10% 9% 31% 36% 12% 3	200
	21st to end	Day	8% 5% 24% 39% 20% 5%	220
January	1st to 10th	Night	9% 7% 34% 35% 13% 2	1000
	11th to 20th	Night	10% 8% 35% 33% 13% 2	1000
	21st to end	Night	13% 10% 35% 29% 11% 2	1025
February	1st to 10th	Night	9% 9% 25% 36% 18% 3	800
	11th to 20th	Night	9% 5% 33% 36% 16% 1	784
	21st to end	Night	7% 6% 30% 34% 18% 5%	660
March	1st to 10th	Night	9% 5% 29% 39% 15% 3	800
	11th to 20th	Night	12% 4 30% 36% 14% 3	800
	21st to end	Night	13% 6% 26% 37% 16% 3	880
April	1st to 10th	Night	11% 6% 27% 35% 18% 3	683
	11th to 20th	Night	12% 7% 27% 36% 17% 1	593
	21st to end	Night	16% 6% 24% 36% 16% 2	600
May	1st to 10th	Night	16% 6% 23% 36% 17% 2	450
	11th to 20th	Night	11% 6% 24% 38% 18% 3	394
	21st to end	Night	19% 7% 19% 34% 19% 2	433
June	1st to 10th	Night	19% 7% 23% 35% 14% 2	400
	11th to 20th	Night	20% 5% 21% 32% 20% 3	400
	21st to end	Night	11% 4 21% 36% 25% 4	400
July	1st to 10th	Night	14% 3 16% 43% 24% 1	390
	11th to 20th	Night	11% 3 20% 42% 23% 2	388
	21st to end	Night	12% 2 17% 40% 25% 4	416
August	1st to 10th	Night	12% 2 18% 33% 29% 6%	378
	11th to 20th	Night	13% 4 16% 39% 25% 3	500
	21st to end	Night	12% 2 20% 40% 24% 1	627
September	1st to 10th	Night	14% 3 21% 38% 23% 2	589
	11th to 20th	Night	15% 4 22% 41% 18% 1	760
	21st to end	Night	11% 6% 29% 38% 13% 2	760
October	1st to 10th	Night	14% 6% 28% 38% 13% 1	760
	11th to 20th	Night	13% 6% 32% 35% 12% 2	760
	21st to end	Night	13% 9% 34% 33% 12%	860
November	1st to 10th	Night	18% 7% 33% 30% 9% 2	975
	11th to 20th	Night	13% 8% 36% 30% 10% 3	1000
	21st to end	Night	10% 7% 38% 33% 11% 2	1000
December	1st to 10th	Night	13% 9% 34% 28% 13% 3	1000
	11th to 20th	Night	11% 7% 33% 33% 14% 2	1000
	21st to end	Night	10% 4 32% 35% 16% 3	1100

Page generated at 2025-07-17 23:10:03. Version ac07

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