Revelstoke
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Revelstoke clear sky chart from 2005-11-06 to 2025-11-18.

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	11% 14% 5% 11% 6% 5% 5% 4 5% 6% 26%	131422
	Night	11% 18% 6% 14% 6% 5% 5% 3 5% 5% 22%	127558
Transparency	Day	55% 7% 15% 16% 6% 1	131131
	Night	62% 7% 13% 13% 4	127426
Seeing	Day	19% 11% 25% 26% 14% 5%	17010
	Night	22% 7% 23% 31% 16% 1	25366

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	9% 29% 12% 25% 8% 5% 4 2 3 1 3	3153
	11th to 20th	Day	7% 16% 7% 13% 6% 6% 5% 4 7% 9% 20%	3616
	21st to end	Day	14% 20% 8% 18% 8% 6% 4 2 3 3 14%	4004
February	1st to 10th	Day	12% 25% 7% 14% 8% 6% 4 3 4 4 13%	1600
	11th to 20th	Day	8% 22% 7% 15% 9% 6% 5% 3 4 5% 17%	1715
	21st to end	Day	6% 24% 7% 17% 8% 7% 6% 4 4 5% 12%	1650
March	1st to 10th	Day	6% 17% 8% 19% 8% 6% 5% 3 5% 6% 16%	4518
	11th to 20th	Day	5% 18% 7% 14% 8% 6% 5% 4 5% 6% 23%	4660
	21st to end	Day	9% 22% 7% 14% 7% 6% 6% 4 5% 5% 14%	5969
April	1st to 10th	Day	10% 22% 6% 14% 8% 7% 5% 4 5% 5% 15%	2400
	11th to 20th	Day	10% 18% 5% 12% 7% 7% 5% 4 6% 7% 20%	2466
	21st to end	Day	13% 16% 5% 12% 7% 6% 6% 4 7% 6% 18%	2703
May	1st to 10th	Day	10% 11% 4 9% 5% 5% 5% 3 5% 8% 35%	6320
	11th to 20th	Day	14% 15% 5% 10% 6% 6% 6% 4 6% 7% 20%	6295
	21st to end	Day	17% 13% 3 9% 6% 5% 5% 4 6% 7% 25%	7405
June	1st to 10th	Day	21% 11% 4 9% 8% 6% 5% 4 5% 6% 23%	3023
	11th to 20th	Day	23% 13% 5% 11% 7% 6% 6% 4 5% 6% 15%	3200
	21st to end	Day	15% 10% 4 10% 7% 6% 5% 4 6% 6% 28%	3200
July	1st to 10th	Day	8% 6% 2 5% 4 4 4 4 5% 7% 51%	7240
	11th to 20th	Day	7% 5% 2 4 4 5% 4 4 7% 8% 52%	6555
	21st to end	Day	6% 5% 2 6% 4 4 5% 5% 8% 10% 47%	6874
August	1st to 10th	Day	5% 4 2 5% 4 5% 5% 5% 7% 9% 50%	4541
	11th to 20th	Day	8% 6% 2 6% 5% 5% 6% 5% 7% 9% 41%	4470
	21st to end	Day	12% 7% 3 9% 5% 5% 5% 4 6% 7% 36%	4458
September	1st to 10th	Day	11% 9% 3 8% 5% 5% 5% 3 5% 7% 39%	2400
	11th to 20th	Day	16% 8% 3 8% 6% 4 5% 4 5% 6% 33%	2332
	21st to end	Day	19% 12% 3 11% 7% 5% 5% 4 6% 5% 24%	2200
October	1st to 10th	Day	14% 12% 4 11% 6% 7% 6% 4 6% 6% 24%	3349
	11th to 20th	Day	20% 14% 4 9% 5% 5% 6% 3 4 5% 23%	3041
	21st to end	Day	14% 20% 7% 13% 8% 7% 5% 4 5% 5% 12%	3200
November	1st to 10th	Day	21% 24% 8% 15% 7% 5% 4 2 3 3 8%	1780
	11th to 20th	Day	17% 25% 8% 14% 7% 6% 4 3 3 3 11%	1549
	21st to end	Day	13% 27% 8% 19% 9% 5% 5% 2 3 3 8%	1400
December	1st to 10th	Day	10% 18% 7% 21% 10% 7% 5% 4 4 3 11%	2290
	11th to 20th	Day	8% 33% 11% 22% 8% 5% 4 2 2 2 3	2642
	21st to end	Day	9% 26% 10% 19% 8% 4 4 3 4 4 8%	3204
January	1st to 10th	Night	9% 33% 12% 23% 6% 4 3 2 2 2 3	6799
	11th to 20th	Night	7% 14% 6% 18% 8% 7% 7% 5% 6% 6% 15%	6282
	21st to end	Night	14% 26% 9% 14% 7% 4 4 3 3 3 12%	6952
February	1st to 10th	Night	11% 25% 8% 21% 8% 5% 4 3 3 3 8%	2800
	11th to 20th	Night	10% 22% 8% 17% 8% 6% 4 3 4 4 15%	2569
	21st to end	Night	8% 23% 7% 17% 9% 7% 5% 3 5% 5% 11%	1980
March	1st to 10th	Night	6% 17% 8% 17% 7% 6% 5% 4 5% 7% 18%	5376
	11th to 20th	Night	5% 19% 6% 15% 7% 5% 5% 3 5% 6% 25%	5336
	21st to end	Night	11% 24% 7% 13% 6% 4 4 4 5% 6% 17%	5006
April	1st to 10th	Night	8% 19% 6% 13% 7% 7% 6% 4 6% 5% 19%	2000
	11th to 20th	Night	11% 15% 5% 10% 6% 6% 6% 5% 7% 7% 23%	1884
	21st to end	Night	13% 15% 4 9% 5% 5% 4 4 5% 6% 30%	1695
May	1st to 10th	Night	9% 9% 3 8% 6% 5% 6% 4 6% 6% 38%	3640
	11th to 20th	Night	16% 13% 4 11% 6% 5% 5% 5% 7% 7% 20%	3583
	21st to end	Night	17% 11% 3 8% 4 4 4 4 5% 7% 33%	3470
June	1st to 10th	Night	20% 9% 3 7% 5% 5% 4 3 5% 7% 31%	1372
	11th to 20th	Night	21% 12% 5% 8% 7% 5% 5% 4 6% 7% 21%	1200
	21st to end	Night	14% 7% 3 8% 5% 5% 5% 6% 7% 8% 32%	1200
July	1st to 10th	Night	7% 5% 2 6% 4 4 4 4 5% 5% 54%	2720
	11th to 20th	Night	8% 6% 2 5% 4 3 4 3 5% 7% 53%	3400
	21st to end	Night	7% 5% 2 6% 5% 4 5% 4 6% 8% 48%	3969
August	1st to 10th	Night	4 3 2 5% 4 4 5% 4 7% 10% 53%	2609
	11th to 20th	Night	8% 5% 2 6% 3 4 6% 4 8% 9% 45%	2577
	21st to end	Night	14% 7% 3 7% 4 4 5% 3 5% 7% 41%	3440
September	1st to 10th	Night	12% 7% 3 8% 4 4 5% 4 4 5% 44%	2000
	11th to 20th	Night	16% 10% 3 6% 4 3 4 3 5% 5% 42%	2067
	21st to end	Night	18% 8% 3 9% 6% 5% 5% 4 5% 5% 33%	2200
October	1st to 10th	Night	11% 10% 4 11% 7% 6% 8% 6% 7% 7% 23%	3849
	11th to 20th	Night	20% 13% 4 9% 5% 5% 5% 4 5% 6% 26%	4110
	21st to end	Night	17% 17% 7% 14% 8% 6% 5% 4 4 4 14%	4600
November	1st to 10th	Night	23% 24% 7% 14% 7% 5% 4 2 3 3 8%	2735
	11th to 20th	Night	15% 29% 7% 17% 6% 5% 4 3 3 3 9%	2983
	21st to end	Night	14% 26% 10% 19% 7% 5% 4 3 2 3 7%	3000
December	1st to 10th	Night	9% 19% 7% 21% 10% 8% 5% 3 5% 4 8%	4890
	11th to 20th	Night	9% 29% 11% 24% 9% 6% 4 2 2 2 2	5550
	21st to end	Night	10% 30% 11% 20% 7% 5% 4 2 3 2 5%	7715

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	88% 6% 3 2 1	3153
	11th to 20th	Day	59% 8% 16% 9% 6% 3	3640
	21st to end	Day	73% 8% 10% 8% 1	4004
February	1st to 10th	Day	76% 4 6% 7% 7%	1600
	11th to 20th	Day	70% 7% 10% 7% 5%	1724
	21st to end	Day	75% 6% 10% 5% 3	1650
March	1st to 10th	Day	67% 6% 12% 12% 3	4518
	11th to 20th	Day	56% 8% 16% 17% 2	4660
	21st to end	Day	68% 8% 10% 10% 4	5969
April	1st to 10th	Day	70% 7% 12% 9% 2	2400
	11th to 20th	Day	62% 7% 16% 12% 4	2466
	21st to end	Day	64% 8% 14% 13% 2	2703
May	1st to 10th	Day	45% 7% 16% 25% 6%	6320
	11th to 20th	Day	57% 9% 18% 13% 2	6298
	21st to end	Day	53% 10% 19% 16% 2	7406
June	1st to 10th	Day	60% 8% 11% 14% 6% 1	3023
	11th to 20th	Day	67% 8% 9% 13% 3	3200
	21st to end	Day	54% 7% 12% 18% 7% 1	3200
July	1st to 10th	Day	30% 5% 13% 27% 20% 5%	7161
	11th to 20th	Day	29% 5% 20% 26% 15% 5%	6473
	21st to end	Day	29% 6% 25% 26% 11% 3	6681
August	1st to 10th	Day	27% 6% 16% 38% 12% 1	4524
	11th to 20th	Day	36% 7% 27% 22% 8% 1	4512
	21st to end	Day	44% 8% 23% 20% 6%	4457
September	1st to 10th	Day	44% 7% 17% 24% 8% 1	2400
	11th to 20th	Day	49% 7% 14% 21% 8% 1	2332
	21st to end	Day	60% 7% 14% 13% 5%	2200
October	1st to 10th	Day	54% 9% 20% 15% 3	3349
	11th to 20th	Day	60% 7% 18% 14% 1	3041
	21st to end	Day	70% 7% 14% 7% 1	3200
November	1st to 10th	Day	82% 5% 6% 5% 1	1780
	11th to 20th	Day	80% 7% 6% 5% 3	1549
	21st to end	Day	81% 8% 4 4 2 1	1400
December	1st to 10th	Day	74% 10% 9% 6% 1	2290
	11th to 20th	Day	89% 4 4 2 1	2644
	21st to end	Day	78% 7% 8% 5% 2	3204
January	1st to 10th	Night	87% 6% 4 2 1	6799
	11th to 20th	Night	65% 9% 10% 10% 5% 1	6320
	21st to end	Night	74% 8% 10% 6% 1	6952
February	1st to 10th	Night	80% 5% 5% 5% 6%	2800
	11th to 20th	Night	73% 5% 8% 8% 4 1	2571
	21st to end	Night	75% 6% 7% 8% 3 1	1980
March	1st to 10th	Night	62% 9% 12% 14% 4	5376
	11th to 20th	Night	56% 8% 18% 15% 3	5337
	21st to end	Night	65% 9% 11% 13% 3	5006
April	1st to 10th	Night	63% 9% 14% 11% 3	2000
	11th to 20th	Night	57% 8% 15% 14% 6% 1	1884
	21st to end	Night	54% 7% 17% 18% 4	1695
May	1st to 10th	Night	43% 7% 23% 22% 5%	3637
	11th to 20th	Night	56% 9% 19% 13% 2	3583
	21st to end	Night	46% 10% 23% 19% 3	3470
June	1st to 10th	Night	51% 7% 15% 20% 6% 1	1372
	11th to 20th	Night	62% 8% 14% 13% 4	1200
	21st to end	Night	48% 8% 18% 19% 6% 1	1200
July	1st to 10th	Night	31% 5% 16% 23% 23% 2	2690
	11th to 20th	Night	31% 5% 16% 31% 14% 3	3359
	21st to end	Night	31% 4 25% 27% 11% 2	3857
August	1st to 10th	Night	24% 6% 17% 40% 12% 1	2601
	11th to 20th	Night	31% 7% 30% 22% 8% 1	2601
	21st to end	Night	42% 7% 27% 17% 6% 1	3440
September	1st to 10th	Night	41% 7% 15% 27% 10% 1	2000
	11th to 20th	Night	43% 5% 16% 23% 12% 1	2067
	21st to end	Night	52% 6% 19% 15% 8% 1	2200
October	1st to 10th	Night	52% 12% 17% 16% 4	3849
	11th to 20th	Night	55% 8% 18% 16% 3	4110
	21st to end	Night	68% 10% 11% 9% 1	4600
November	1st to 10th	Night	80% 6% 7% 5% 2	2735
	11th to 20th	Night	80% 6% 6% 5% 2	2983
	21st to end	Night	82% 7% 4 4 3	3000
December	1st to 10th	Night	75% 11% 8% 5% 1	4890
	11th to 20th	Night	89% 5% 3 2 1	5547
	21st to end	Night	85% 6% 4 4 1	7715

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	20% 11% 27% 24% 15% 5%	200
	11th to 20th	Day	18% 9% 26% 31% 14% 3	200
	21st to end	Day	16% 6% 31% 31% 12% 3	220
February	1st to 10th	Day	21% 13% 34% 22% 10% 2	200
	11th to 20th	Day	14% 14% 30% 26% 12% 3	348
	21st to end	Day	16% 14% 32% 26% 11% 2	414
March	1st to 10th	Day	16% 21% 28% 20% 10% 4	500
	11th to 20th	Day	20% 17% 25% 20% 12% 5%	500
	21st to end	Day	21% 14% 28% 22% 10% 6%	550
April	1st to 10th	Day	20% 14% 31% 25% 7% 3	500
	11th to 20th	Day	17% 16% 27% 25% 10% 5%	492
	21st to end	Day	18% 12% 27% 23% 13% 6%	500
May	1st to 10th	Day	19% 12% 26% 25% 13% 5%	503
	11th to 20th	Day	16% 11% 21% 27% 17% 8%	533
	21st to end	Day	22% 9% 16% 27% 20% 6%	789
June	1st to 10th	Day	23% 12% 27% 25% 10% 2	753
	11th to 20th	Day	25% 9% 27% 26% 11% 2	930
	21st to end	Day	18% 10% 23% 31% 16% 2	930
July	1st to 10th	Day	18% 9% 21% 31% 18% 4	916
	11th to 20th	Day	13% 8% 26% 29% 19% 6%	622
	21st to end	Day	7% 8% 23% 31% 22% 9%	575
August	1st to 10th	Day	12% 6% 24% 29% 17% 11%	527
	11th to 20th	Day	10% 9% 25% 31% 17% 9%	517
	21st to end	Day	14% 10% 22% 26% 17% 11%	583
September	1st to 10th	Day	15% 10% 22% 25% 17% 10%	530
	11th to 20th	Day	22% 9% 20% 25% 18% 6%	530
	21st to end	Day	22% 13% 28% 22% 13% 3	530
October	1st to 10th	Day	22% 8% 24% 25% 15% 5%	530
	11th to 20th	Day	28% 10% 21% 22% 14% 7%	400
	21st to end	Day	29% 8% 29% 22% 9% 2	363
November	1st to 10th	Day	28% 9% 31% 19% 11% 2	291
	11th to 20th	Day	30% 10% 24% 21% 9% 5%	214
	21st to end	Day	24% 9% 29% 20% 13% 7%	200
December	1st to 10th	Day	17% 10% 23% 23% 19% 9%	200
	11th to 20th	Day	23% 8% 29% 27% 10% 4	200
	21st to end	Day	19% 3 30% 32% 13% 3	220
January	1st to 10th	Night	31% 11% 23% 25% 8% 1	988
	11th to 20th	Night	24% 6% 30% 30% 9% 1	800
	21st to end	Night	26% 9% 26% 29% 10% 1	880
February	1st to 10th	Night	23% 9% 31% 26% 11%	800
	11th to 20th	Night	20% 6% 27% 33% 14% 1	784
	21st to end	Night	18% 8% 28% 28% 17% 1	660
March	1st to 10th	Night	21% 8% 28% 29% 14% 1	800
	11th to 20th	Night	21% 9% 26% 27% 16% 1	800
	21st to end	Night	21% 8% 24% 29% 14% 4	880
April	1st to 10th	Night	17% 6% 22% 38% 16% 2	800
	11th to 20th	Night	18% 6% 25% 38% 12% 1	696
	21st to end	Night	19% 5% 25% 34% 15% 1	495
May	1st to 10th	Night	16% 6% 21% 35% 22% 1	400
	11th to 20th	Night	17% 5% 23% 36% 18% 1	394
	21st to end	Night	19% 5% 18% 38% 21%	433
June	1st to 10th	Night	22% 6% 24% 39% 10%	400
	11th to 20th	Night	24% 7% 20% 33% 16% 1	400
	21st to end	Night	15% 6% 20% 36% 23% 1	400
July	1st to 10th	Night	14% 4 17% 38% 27% 1	390
	11th to 20th	Night	14% 4 18% 37% 26% 1	388
	21st to end	Night	10% 1 11% 43% 33% 2	438
August	1st to 10th	Night	7% 2 11% 37% 39% 3	398
	11th to 20th	Night	9% 3 12% 39% 35% 3	396
	21st to end	Night	13% 3 15% 39% 29% 1	777
September	1st to 10th	Night	16% 4 17% 31% 29% 3	800
	11th to 20th	Night	20% 5% 13% 31% 29% 3	800
	21st to end	Night	23% 4 20% 36% 15% 1	800
October	1st to 10th	Night	23% 5% 18% 35% 18% 1	800
	11th to 20th	Night	27% 5% 21% 33% 12% 2	800
	21st to end	Night	31% 6% 23% 28% 10% 1	880
November	1st to 10th	Night	37% 7% 23% 25% 7%	820
	11th to 20th	Night	32% 11% 28% 18% 10% 1	913
	21st to end	Night	26% 9% 29% 24% 10% 2	1000
December	1st to 10th	Night	23% 7% 29% 27% 12% 1	1000
	11th to 20th	Night	27% 8% 32% 25% 8% 1	1000
	21st to end	Night	25% 11% 29% 28% 7% 1	1156

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