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 2024-01-13.

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	14% 15% 6% 10% 8% 4 5% 4 5% 6% 23%	74879
	Night	14% 17% 7% 12% 8% 4 5% 4 4 5% 20%	74810
Transparency	Day	62% 7% 12% 14% 5% 1	74564
	Night	66% 6% 10% 12% 5%	74643
Seeing	Day	20% 11% 25% 26% 14% 5%	14478
	Night	23% 7% 24% 30% 15% 1	23101

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	18% 26% 8% 15% 10% 4 5% 3 3 2 6%	1316
	11th to 20th	Day	15% 22% 9% 15% 8% 6% 4 3 4 6% 7%	1456
	21st to end	Day	10% 21% 11% 20% 11% 5% 4 4 3 3 9%	1584
February	1st to 10th	Day	13% 24% 8% 13% 10% 5% 5% 3 3 4 13%	1440
	11th to 20th	Day	9% 20% 8% 14% 11% 5% 5% 5% 4 4 15%	1539
	21st to end	Day	7% 19% 10% 14% 11% 5% 6% 5% 4 5% 13%	1480
March	1st to 10th	Day	11% 22% 7% 14% 11% 4 4 3 4 6% 13%	1800
	11th to 20th	Day	10% 22% 8% 11% 8% 4 4 4 5% 6% 16%	1835
	21st to end	Day	11% 22% 9% 13% 9% 4 6% 4 4 5% 13%	2376
April	1st to 10th	Day	11% 21% 8% 13% 9% 5% 6% 4 5% 4 14%	2160
	11th to 20th	Day	12% 17% 6% 11% 9% 5% 5% 5% 5% 6% 19%	2216
	21st to end	Day	15% 15% 6% 10% 9% 5% 6% 5% 6% 6% 17%	2432
May	1st to 10th	Day	16% 14% 5% 9% 6% 4 6% 4 6% 7% 24%	2520
	11th to 20th	Day	13% 11% 4 7% 6% 4 5% 5% 7% 6% 32%	2481
	21st to end	Day	17% 13% 4 8% 7% 3 5% 5% 5% 7% 26%	2917
June	1st to 10th	Day	22% 11% 4 8% 9% 4 5% 4 5% 5% 22%	2720
	11th to 20th	Day	25% 12% 6% 10% 8% 4 6% 5% 5% 5% 14%	2880
	21st to end	Day	15% 9% 4 8% 8% 4 6% 4 5% 6% 29%	2880
July	1st to 10th	Day	14% 8% 3 6% 5% 4 5% 5% 6% 8% 36%	2880
	11th to 20th	Day	10% 8% 2 6% 6% 5% 6% 5% 6% 8% 38%	2615
	21st to end	Day	7% 4 2 5% 5% 3 4 5% 7% 7% 51%	2741
August	1st to 10th	Day	8% 6% 3 5% 5% 5% 5% 6% 6% 8% 44%	2507
	11th to 20th	Day	9% 5% 2 5% 5% 3 4 4 6% 8% 49%	2475
	21st to end	Day	14% 7% 3 8% 7% 5% 6% 5% 6% 7% 33%	2465
September	1st to 10th	Day	12% 9% 3 7% 7% 3 6% 4 5% 6% 37%	2160
	11th to 20th	Day	18% 8% 4 7% 7% 3 5% 5% 5% 6% 32%	2100
	21st to end	Day	19% 11% 3 9% 9% 4 5% 4 6% 5% 24%	1980
October	1st to 10th	Day	18% 15% 4 8% 6% 4 5% 4 4 6% 27%	1841
	11th to 20th	Day	19% 17% 5% 10% 6% 4 5% 5% 5% 5% 20%	1684
	21st to end	Day	21% 20% 7% 10% 7% 3 4 4 3 5% 16%	1782
November	1st to 10th	Day	23% 23% 8% 13% 9% 4 4 3 3 2 8%	1608
	11th to 20th	Day	19% 22% 9% 13% 8% 4 5% 3 3 3 12%	1421
	21st to end	Day	14% 23% 10% 17% 10% 3 6% 3 3 3 8%	1330
December	1st to 10th	Day	14% 21% 8% 15% 10% 5% 6% 4 3 2 12%	1330
	11th to 20th	Day	12% 29% 12% 19% 9% 3 4 3 1 3 4	1682
	21st to end	Day	12% 24% 8% 14% 9% 4 5% 4 4 5% 12%	2246
January	1st to 10th	Night	17% 29% 10% 13% 8% 4 5% 4 3 3 5%	2856
	11th to 20th	Night	16% 23% 8% 19% 11% 5% 6% 4 3 3 3	2548
	21st to end	Night	13% 25% 11% 19% 11% 5% 4 3 2 2 6%	2772
February	1st to 10th	Night	12% 23% 10% 20% 11% 4 4 4 2 3 7%	2520
	11th to 20th	Night	11% 21% 9% 15% 10% 4 5% 3 5% 4 12%	2305
	21st to end	Night	9% 18% 9% 15% 11% 6% 6% 4 5% 5% 12%	1776
March	1st to 10th	Night	12% 22% 9% 15% 10% 4 5% 4 3 4 13%	2160
	11th to 20th	Night	11% 22% 6% 10% 8% 4 5% 5% 5% 6% 19%	2121
	21st to end	Night	10% 21% 7% 12% 9% 4 5% 6% 4 5% 18%	1980
April	1st to 10th	Night	9% 17% 6% 11% 9% 5% 8% 5% 5% 6% 19%	1800
	11th to 20th	Night	12% 14% 6% 9% 7% 4 7% 6% 7% 7% 22%	1694
	21st to end	Night	12% 14% 4 8% 6% 4 4 5% 6% 6% 30%	1526
May	1st to 10th	Night	12% 12% 5% 8% 6% 3 5% 5% 7% 7% 30%	1440
	11th to 20th	Night	11% 8% 2 7% 6% 4 5% 6% 8% 9% 36%	1411
	21st to end	Night	14% 8% 3 7% 6% 4 5% 5% 5% 8% 33%	1358
June	1st to 10th	Night	22% 8% 3 7% 6% 3 5% 4 5% 7% 30%	1236
	11th to 20th	Night	23% 10% 5% 7% 8% 3 5% 4 6% 6% 20%	1080
	21st to end	Night	14% 6% 3 7% 6% 3 6% 6% 7% 8% 33%	1080
July	1st to 10th	Night	11% 6% 3 5% 5% 3 5% 5% 5% 6% 45%	1080
	11th to 20th	Night	10% 7% 2 5% 5% 3 4 5% 6% 8% 44%	1340
	21st to end	Night	8% 3 1 3 3 2 3 5% 5% 8% 57%	1576
August	1st to 10th	Night	7% 3 2 5% 5% 3 5% 5% 6% 8% 52%	1432
	11th to 20th	Night	7% 4 2 3 3 2 4 4 5% 9% 57%	1424
	21st to end	Night	10% 6% 2 6% 5% 3 6% 6% 6% 9% 42%	1887
September	1st to 10th	Night	13% 7% 3 7% 6% 3 5% 5% 5% 5% 42%	1800
	11th to 20th	Night	17% 10% 3 5% 5% 2 4 4 5% 5% 41%	1859
	21st to end	Night	18% 8% 3 7% 7% 4 5% 5% 5% 6% 33%	1980
October	1st to 10th	Night	15% 12% 4 8% 7% 3 5% 5% 5% 6% 31%	2117
	11th to 20th	Night	20% 14% 5% 9% 7% 3 4 4 5% 5% 23%	2276
	21st to end	Night	20% 19% 8% 12% 8% 3 4 4 4 4 14%	2574
November	1st to 10th	Night	25% 23% 8% 13% 8% 3 4 3 3 3 8%	2467
	11th to 20th	Night	16% 26% 8% 14% 8% 3 5% 4 3 3 9%	2738
	21st to end	Night	15% 24% 11% 17% 8% 4 4 4 2 3 8%	2850
December	1st to 10th	Night	14% 20% 8% 17% 12% 6% 5% 3 4 3 8%	2850
	11th to 20th	Night	13% 28% 11% 19% 11% 4 4 2 2 2 3	3510
	21st to end	Night	13% 24% 10% 18% 9% 4 5% 3 3 3 8%	5387

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	85% 6% 4 3 2	1316
	11th to 20th	Day	79% 5% 9% 4 2 1	1456
	21st to end	Day	82% 5% 5% 5% 3 1	1584
February	1st to 10th	Day	78% 5% 7% 7% 4	1440
	11th to 20th	Day	73% 7% 10% 7% 3	1548
	21st to end	Day	75% 6% 10% 5% 4 1	1480
March	1st to 10th	Day	75% 4 11% 6% 3 1	1800
	11th to 20th	Day	70% 5% 11% 12% 2	1835
	21st to end	Day	75% 7% 10% 7% 2	2376
April	1st to 10th	Day	72% 7% 11% 8% 1	2160
	11th to 20th	Day	65% 6% 14% 11% 3	2216
	21st to end	Day	65% 8% 12% 12% 2	2432
May	1st to 10th	Day	59% 9% 16% 12% 5%	2520
	11th to 20th	Day	51% 9% 17% 19% 4	2484
	21st to end	Day	58% 8% 13% 17% 4	2918
June	1st to 10th	Day	63% 7% 11% 13% 5% 2	2720
	11th to 20th	Day	70% 8% 9% 11% 2	2880
	21st to end	Day	54% 8% 12% 19% 7% 1	2880
July	1st to 10th	Day	45% 8% 12% 21% 12% 2	2801
	11th to 20th	Day	44% 7% 16% 21% 11% 1	2533
	21st to end	Day	30% 7% 14% 30% 17% 1	2589
August	1st to 10th	Day	37% 7% 16% 24% 14% 1	2490
	11th to 20th	Day	33% 8% 18% 27% 14% 1	2475
	21st to end	Day	49% 8% 13% 22% 8%	2465
September	1st to 10th	Day	47% 7% 15% 23% 8% 1	2160
	11th to 20th	Day	51% 7% 13% 21% 9% 1	2100
	21st to end	Day	60% 7% 14% 13% 5%	1980
October	1st to 10th	Day	57% 7% 15% 18% 3	1841
	11th to 20th	Day	66% 7% 14% 12% 1	1684
	21st to end	Day	72% 6% 9% 10% 2	1782
November	1st to 10th	Day	84% 5% 6% 5% 1	1608
	11th to 20th	Day	79% 7% 6% 5% 3	1421
	21st to end	Day	80% 8% 5% 5% 3 1	1330
December	1st to 10th	Day	78% 5% 6% 9% 2	1330
	11th to 20th	Day	88% 4 4 2 2	1684
	21st to end	Day	73% 9% 9% 7% 3	2246
January	1st to 10th	Night	84% 6% 4 4 2	2856
	11th to 20th	Night	86% 5% 5% 3 1 1	2548
	21st to end	Night	85% 5% 3 4 2	2772
February	1st to 10th	Night	82% 5% 5% 5% 4	2520
	11th to 20th	Night	76% 6% 8% 8% 3	2307
	21st to end	Night	74% 6% 7% 9% 4 1	1776
March	1st to 10th	Night	76% 5% 7% 8% 4	2160
	11th to 20th	Night	67% 6% 12% 12% 3	2122
	21st to end	Night	68% 8% 12% 9% 3	1980
April	1st to 10th	Night	63% 9% 14% 11% 3	1800
	11th to 20th	Night	59% 8% 14% 12% 6% 1	1694
	21st to end	Night	54% 8% 17% 16% 4	1526
May	1st to 10th	Night	50% 8% 21% 15% 5%	1440
	11th to 20th	Night	42% 9% 23% 21% 5%	1411
	21st to end	Night	48% 7% 18% 22% 4	1358
June	1st to 10th	Night	53% 7% 15% 20% 5% 1	1236
	11th to 20th	Night	63% 8% 14% 12% 3	1080
	21st to end	Night	48% 8% 18% 19% 6% 1	1080
July	1st to 10th	Night	37% 9% 16% 24% 11% 2	1050
	11th to 20th	Night	37% 8% 18% 25% 12%	1299
	21st to end	Night	23% 7% 19% 33% 17% 2	1488
August	1st to 10th	Night	28% 8% 18% 28% 17% 1	1424
	11th to 20th	Night	24% 7% 23% 31% 14% 1	1424
	21st to end	Night	37% 8% 17% 28% 9% 1	1887
September	1st to 10th	Night	43% 7% 13% 25% 10% 1	1800
	11th to 20th	Night	45% 5% 15% 22% 13% 1	1859
	21st to end	Night	52% 5% 19% 15% 8% 1	1980
October	1st to 10th	Night	54% 6% 15% 20% 5%	2117
	11th to 20th	Night	61% 8% 13% 15% 3	2276
	21st to end	Night	72% 7% 10% 9% 2	2574
November	1st to 10th	Night	81% 6% 6% 5% 2	2467
	11th to 20th	Night	80% 6% 6% 5% 2	2738
	21st to end	Night	82% 7% 4 4 3	2850
December	1st to 10th	Night	80% 5% 5% 8% 2	2850
	11th to 20th	Night	89% 4 3 2 2	3507
	21st to end	Night	81% 7% 5% 5% 2	5387

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	22% 11% 26% 22% 14% 4	180
	11th to 20th	Day	20% 10% 28% 25% 13% 4	164
	21st to end	Day	16% 7% 31% 31% 11% 4	176
February	1st to 10th	Day	22% 12% 38% 21% 6% 1	160
	11th to 20th	Day	15% 16% 33% 24% 10% 2	292
	21st to end	Day	13% 12% 34% 28% 12% 2	346
March	1st to 10th	Day	17% 22% 30% 17% 10% 4	420
	11th to 20th	Day	22% 18% 25% 19% 12% 5%	420
	21st to end	Day	23% 14% 27% 20% 11% 5%	462
April	1st to 10th	Day	21% 14% 31% 24% 7% 3	420
	11th to 20th	Day	18% 16% 28% 23% 9% 6%	412
	21st to end	Day	19% 13% 27% 22% 12% 6%	420
May	1st to 10th	Day	21% 11% 24% 26% 13% 5%	423
	11th to 20th	Day	14% 10% 20% 28% 18% 10%	452
	21st to end	Day	23% 7% 16% 27% 21% 6%	679
June	1st to 10th	Day	25% 12% 26% 25% 10% 2	650
	11th to 20th	Day	26% 9% 27% 26% 10% 1	810
	21st to end	Day	17% 10% 23% 31% 16% 2	810
July	1st to 10th	Day	19% 9% 20% 32% 16% 4	796
	11th to 20th	Day	14% 8% 27% 28% 18% 5%	532
	21st to end	Day	7% 8% 23% 32% 22% 8%	487
August	1st to 10th	Day	12% 7% 25% 31% 15% 10%	447
	11th to 20th	Day	10% 9% 24% 32% 16% 9%	437
	21st to end	Day	14% 11% 23% 27% 15% 9%	495
September	1st to 10th	Day	18% 12% 25% 26% 14% 6%	450
	11th to 20th	Day	25% 9% 21% 26% 15% 4	450
	21st to end	Day	21% 12% 26% 24% 14% 4	450
October	1st to 10th	Day	25% 8% 23% 22% 15% 6%	450
	11th to 20th	Day	28% 10% 21% 21% 13% 7%	334
	21st to end	Day	31% 8% 28% 22% 9% 2	297
November	1st to 10th	Day	31% 7% 27% 21% 12% 3	239
	11th to 20th	Day	30% 9% 23% 22% 11% 6%	180
	21st to end	Day	24% 8% 28% 19% 14% 7%	180
December	1st to 10th	Day	17% 11% 23% 22% 18% 8%	180
	11th to 20th	Day	24% 6% 28% 27% 11% 4	180
	21st to end	Day	18% 3 29% 35% 14% 3	198
January	1st to 10th	Night	32% 11% 24% 23% 8% 1	938
	11th to 20th	Night	26% 7% 31% 26% 9% 1	728
	21st to end	Night	27% 8% 28% 27% 9% 1	792
February	1st to 10th	Night	24% 8% 32% 26% 10%	720
	11th to 20th	Night	21% 5% 29% 32% 12% 1	704
	21st to end	Night	17% 6% 29% 29% 18% 2	592
March	1st to 10th	Night	23% 8% 28% 28% 11%	720
	11th to 20th	Night	22% 10% 28% 24% 15% 1	720
	21st to end	Night	22% 7% 25% 29% 14% 4	792
April	1st to 10th	Night	17% 7% 22% 36% 16% 1	720
	11th to 20th	Night	20% 6% 25% 36% 12% 1	626
	21st to end	Night	19% 5% 26% 35% 13% 1	446
May	1st to 10th	Night	17% 6% 21% 34% 22% 1	360
	11th to 20th	Night	14% 4 25% 38% 19%	354
	21st to end	Night	18% 4 19% 39% 20%	389
June	1st to 10th	Night	24% 5% 24% 38% 9%	360
	11th to 20th	Night	25% 8% 21% 31% 15% 1	360
	21st to end	Night	15% 5% 21% 36% 23% 1	360
July	1st to 10th	Night	15% 4 17% 39% 24% 1	350
	11th to 20th	Night	15% 4 20% 38% 22% 1	348
	21st to end	Night	10% 1 12% 45% 31% 1	394
August	1st to 10th	Night	7% 2 12% 38% 39% 1	358
	11th to 20th	Night	8% 3 13% 40% 34% 2	356
	21st to end	Night	13% 3 16% 40% 27% 1	699
September	1st to 10th	Night	18% 5% 18% 33% 26% 1	720
	11th to 20th	Night	21% 5% 14% 31% 26% 3	720
	21st to end	Night	23% 4 21% 34% 16% 1	720
October	1st to 10th	Night	24% 4 19% 33% 19% 1	720
	11th to 20th	Night	28% 5% 22% 32% 11% 2	720
	21st to end	Night	31% 6% 24% 28% 9% 1	792
November	1st to 10th	Night	38% 7% 24% 23% 8% 1	740
	11th to 20th	Night	32% 11% 29% 19% 10% 1	838
	21st to end	Night	28% 9% 30% 23% 9% 2	950
December	1st to 10th	Night	24% 7% 30% 26% 12% 1	950
	11th to 20th	Night	27% 8% 32% 25% 7% 1	950
	21st to end	Night	25% 11% 29% 28% 7% 1	1095

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