Castlegar
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Castlegar clear sky chart from 2005-11-06 to 2026-06-01.

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% 12% 4 8% 5% 4 5% 4 5% 7% 38%	135816
	Night	10% 14% 4 8% 5% 4 4 4 5% 6% 35%	136051
Transparency	Day	45% 7% 14% 21% 11% 3	135539
	Night	48% 7% 15% 19% 9% 2	135907
Seeing	Day	18% 14% 28% 25% 12% 3	16896
	Night	20% 7% 23% 32% 16% 2	26034

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	8% 26% 9% 16% 7% 5% 4 2 3 3 16%	4584
	11th to 20th	Day	10% 12% 3 5% 3 4 5% 4 4 6% 44%	4716
	21st to end	Day	13% 22% 4 7% 4 3 4 3 4 5% 31%	5186
February	1st to 10th	Day	11% 20% 5% 11% 6% 4 5% 4 5% 6% 23%	1680
	11th to 20th	Day	10% 19% 7% 10% 5% 5% 5% 4 5% 6% 24%	1887
	21st to end	Day	11% 17% 6% 11% 6% 5% 6% 5% 5% 5% 22%	1730
March	1st to 10th	Day	7% 17% 5% 10% 6% 5% 5% 4 7% 7% 27%	4618
	11th to 20th	Day	8% 16% 5% 9% 5% 4 4 3 4 6% 35%	4764
	21st to end	Day	12% 20% 6% 11% 6% 6% 6% 4 5% 6% 19%	6092
April	1st to 10th	Day	13% 17% 4 9% 6% 5% 5% 4 6% 6% 25%	2520
	11th to 20th	Day	12% 13% 4 10% 6% 5% 6% 4 6% 6% 27%	2581
	21st to end	Day	11% 12% 4 9% 6% 6% 6% 5% 5% 7% 28%	2751
May	1st to 10th	Day	7% 7% 3 8% 5% 5% 6% 5% 6% 8% 40%	6460
	11th to 20th	Day	9% 10% 5% 12% 7% 6% 7% 5% 7% 8% 24%	6417
	21st to end	Day	10% 9% 3 9% 5% 5% 6% 4 6% 8% 33%	7383
June	1st to 10th	Day	20% 8% 3 8% 6% 5% 5% 4 6% 6% 28%	3001
	11th to 20th	Day	16% 9% 4 10% 8% 6% 5% 5% 6% 7% 23%	3000
	21st to end	Day	10% 6% 3 7% 6% 5% 5% 5% 7% 7% 40%	3000
July	1st to 10th	Day	3 3 1 3 3 3 4 3 5% 7% 65%	6700
	11th to 20th	Day	3 2 1 3 3 3 3 3 4 6% 69%	6320
	21st to end	Day	4 3 1 4 3 4 4 4 5% 9% 60%	6874
August	1st to 10th	Day	3 2 1 4 3 3 4 4 6% 9% 61%	4541
	11th to 20th	Day	4 3 1 4 3 3 4 3 7% 8% 59%	4374
	21st to end	Day	5% 5% 2 5% 3 4 5% 4 7% 8% 51%	4441
September	1st to 10th	Day	6% 4 1 5% 4 3 4 3 6% 8% 55%	2400
	11th to 20th	Day	10% 6% 2 6% 4 4 4 3 6% 6% 48%	2306
	21st to end	Day	12% 7% 3 8% 5% 4 5% 4 4 6% 42%	2200
October	1st to 10th	Day	8% 5% 2 6% 5% 4 4 4 6% 7% 47%	3414
	11th to 20th	Day	12% 8% 3 7% 5% 5% 5% 4 5% 7% 39%	3042
	21st to end	Day	14% 14% 4 8% 5% 5% 6% 4 6% 7% 27%	3200
November	1st to 10th	Day	21% 18% 5% 8% 5% 4 4 3 4 5% 22%	1854
	11th to 20th	Day	17% 21% 6% 11% 5% 4 4 3 4 4 22%	1663
	21st to end	Day	15% 22% 5% 11% 6% 4 4 3 5% 6% 18%	1470
December	1st to 10th	Day	9% 13% 5% 11% 4 3 3 3 5% 8% 37%	2360
	11th to 20th	Day	11% 26% 8% 13% 6% 5% 4 3 4 6% 15%	2712
	21st to end	Day	11% 28% 9% 16% 5% 3 3 2 3 4 14%	3575
January	1st to 10th	Night	10% 26% 9% 15% 6% 4 4 3 3 4 15%	8366
	11th to 20th	Night	8% 12% 4 7% 4 4 6% 6% 5% 7% 36%	8182
	21st to end	Night	13% 21% 5% 8% 4 3 4 4 4 5% 29%	8994
February	1st to 10th	Night	13% 20% 5% 10% 6% 6% 5% 3 6% 6% 21%	2940
	11th to 20th	Night	11% 18% 5% 10% 5% 4 4 3 5% 8% 28%	2616
	21st to end	Night	9% 18% 6% 9% 6% 5% 5% 5% 6% 9% 23%	2076
March	1st to 10th	Night	6% 16% 6% 9% 6% 5% 5% 3 5% 6% 34%	5496
	11th to 20th	Night	9% 17% 5% 9% 5% 4 4 3 4 5% 36%	5454
	21st to end	Night	12% 18% 5% 10% 6% 6% 6% 4 6% 6% 20%	5121
April	1st to 10th	Night	12% 14% 3 7% 5% 4 5% 4 6% 8% 33%	2100
	11th to 20th	Night	12% 10% 3 7% 6% 6% 6% 3 6% 7% 33%	1989
	21st to end	Night	9% 11% 2 8% 5% 5% 5% 4 6% 8% 37%	1866
May	1st to 10th	Night	6% 6% 2 6% 4 5% 5% 5% 7% 9% 46%	3720
	11th to 20th	Night	7% 9% 3 9% 7% 6% 6% 5% 6% 8% 34%	3696
	21st to end	Night	11% 10% 3 7% 5% 4 4 3 6% 8% 39%	3733
June	1st to 10th	Night	14% 8% 3 7% 3 4 5% 4 8% 9% 36%	1400
	11th to 20th	Night	15% 6% 3 8% 6% 6% 6% 5% 7% 7% 33%	1400
	21st to end	Night	8% 5% 3 6% 3 4 5% 5% 7% 8% 47%	1400
July	1st to 10th	Night	3 2 1 3 2 2 2 2 5% 6% 71%	3242
	11th to 20th	Night	3 3 1 3 3 3 3 2 4 5% 70%	3640
	21st to end	Night	2 3 1 3 2 2 3 3 5% 8% 68%	3969
August	1st to 10th	Night	3 2 1 3 3 4 3 4 6% 8% 63%	2609
	11th to 20th	Night	2 2 1 3 3 3 5% 4 7% 10% 61%	2676
	21st to end	Night	4 3 1 4 3 4 5% 4 7% 8% 55%	3471
September	1st to 10th	Night	4 4 1 5% 3 4 3 4 5% 8% 58%	2000
	11th to 20th	Night	8% 6% 3 5% 4 4 4 3 6% 7% 50%	2093
	21st to end	Night	11% 5% 2 7% 4 3 4 3 5% 7% 49%	2200
October	1st to 10th	Night	7% 4 2 5% 4 3 4 3 7% 8% 52%	3782
	11th to 20th	Night	13% 8% 3 7% 4 3 4 3 4 7% 44%	4108
	21st to end	Night	13% 10% 4 9% 5% 5% 5% 5% 6% 6% 32%	4600
November	1st to 10th	Night	22% 17% 5% 9% 5% 5% 4 4 5% 6% 20%	2665
	11th to 20th	Night	18% 21% 5% 9% 6% 5% 4 3 4 5% 20%	2934
	21st to end	Night	15% 22% 6% 12% 5% 4 3 3 4 6% 19%	3150
December	1st to 10th	Night	10% 13% 5% 12% 5% 4 5% 4 6% 7% 31%	5040
	11th to 20th	Night	12% 26% 8% 13% 6% 4 5% 4 5% 5% 12%	5700
	21st to end	Night	13% 28% 9% 14% 6% 4 3 3 4 4 13%	7623

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	73% 6% 9% 10% 1	4584
	11th to 20th	Day	39% 9% 26% 18% 7% 1	4740
	21st to end	Day	56% 7% 14% 18% 5%	5187
February	1st to 10th	Day	62% 8% 11% 9% 7% 2	1680
	11th to 20th	Day	60% 9% 13% 12% 6% 1	1896
	21st to end	Day	61% 9% 12% 11% 7%	1730
March	1st to 10th	Day	56% 7% 11% 14% 12%	4618
	11th to 20th	Day	50% 5% 19% 21% 5%	4764
	21st to end	Day	64% 8% 12% 12% 4	6092
April	1st to 10th	Day	58% 8% 15% 14% 5%	2520
	11th to 20th	Day	56% 6% 14% 18% 5% 1	2581
	21st to end	Day	55% 7% 12% 21% 4 1	2751
May	1st to 10th	Day	42% 7% 13% 25% 12% 1	6460
	11th to 20th	Day	53% 9% 14% 19% 5%	6420
	21st to end	Day	47% 9% 17% 23% 4	7384
June	1st to 10th	Day	54% 7% 10% 15% 11% 2	3001
	11th to 20th	Day	57% 8% 11% 15% 9%	3000
	21st to end	Day	39% 7% 13% 24% 14% 2	3000
July	1st to 10th	Day	20% 4 12% 26% 27% 11%	6627
	11th to 20th	Day	16% 4 12% 26% 27% 16%	6245
	21st to end	Day	22% 4 13% 30% 21% 10%	6681
August	1st to 10th	Day	20% 5% 10% 32% 26% 6%	4524
	11th to 20th	Day	22% 5% 18% 38% 16% 2	4416
	21st to end	Day	29% 7% 18% 29% 15% 2	4440
September	1st to 10th	Day	28% 5% 13% 30% 19% 5%	2400
	11th to 20th	Day	37% 6% 12% 28% 16% 2	2306
	21st to end	Day	43% 7% 17% 20% 11% 1	2200
October	1st to 10th	Day	37% 5% 20% 32% 6%	3414
	11th to 20th	Day	47% 7% 13% 25% 9%	3042
	21st to end	Day	53% 8% 17% 16% 6%	3200
November	1st to 10th	Day	64% 9% 11% 12% 3 1	1854
	11th to 20th	Day	67% 8% 10% 10% 4 1	1663
	21st to end	Day	68% 8% 11% 8% 4	1470
December	1st to 10th	Day	48% 10% 27% 13% 3	2360
	11th to 20th	Day	70% 8% 13% 7% 3	2714
	21st to end	Day	75% 6% 8% 7% 4	3575
January	1st to 10th	Night	73% 7% 11% 8% 1	8367
	11th to 20th	Night	44% 7% 21% 19% 7% 1	8220
	21st to end	Night	55% 8% 16% 18% 3	8994
February	1st to 10th	Night	62% 8% 11% 10% 7% 1	2940
	11th to 20th	Night	57% 7% 14% 16% 7% 1	2618
	21st to end	Night	57% 9% 14% 12% 7% 1	2076
March	1st to 10th	Night	52% 7% 13% 17% 11%	5496
	11th to 20th	Night	51% 5% 17% 22% 5%	5455
	21st to end	Night	60% 10% 14% 11% 4	5121
April	1st to 10th	Night	49% 7% 18% 19% 6%	2100
	11th to 20th	Night	49% 6% 15% 21% 7% 1	1989
	21st to end	Night	45% 8% 13% 24% 9% 1	1866
May	1st to 10th	Night	33% 8% 13% 31% 14% 1	3717
	11th to 20th	Night	45% 8% 16% 24% 7% 1	3696
	21st to end	Night	39% 9% 20% 27% 5%	3733
June	1st to 10th	Night	43% 8% 14% 20% 13% 2	1400
	11th to 20th	Night	48% 9% 12% 20% 10% 1	1400
	21st to end	Night	33% 7% 14% 25% 18% 2	1400
July	1st to 10th	Night	16% 4 11% 29% 26% 15%	3206
	11th to 20th	Night	17% 3 12% 23% 25% 20%	3592
	21st to end	Night	17% 3 10% 32% 26% 12%	3857
August	1st to 10th	Night	19% 4 10% 32% 28% 7%	2601
	11th to 20th	Night	19% 5% 19% 38% 17% 3	2700
	21st to end	Night	27% 5% 18% 28% 19% 3	3471
September	1st to 10th	Night	24% 5% 12% 30% 24% 5%	2000
	11th to 20th	Night	33% 6% 12% 26% 19% 3	2093
	21st to end	Night	35% 6% 20% 24% 13% 2	2200
October	1st to 10th	Night	30% 6% 21% 35% 8%	3782
	11th to 20th	Night	43% 6% 15% 28% 8%	4108
	21st to end	Night	50% 7% 17% 22% 4	4600
November	1st to 10th	Night	64% 8% 12% 11% 4	2665
	11th to 20th	Night	67% 9% 11% 9% 4 1	2934
	21st to end	Night	66% 7% 12% 10% 4	3150
December	1st to 10th	Night	50% 10% 21% 16% 3	5040
	11th to 20th	Night	73% 7% 13% 6% 2	5697
	21st to end	Night	74% 7% 8% 7% 3	7623

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	27% 16% 28% 17% 10% 2	220
	11th to 20th	Day	23% 13% 31% 21% 9% 3	220
	21st to end	Day	26% 10% 30% 25% 9% 1	242
February	1st to 10th	Day	19% 19% 35% 20% 7%	220
	11th to 20th	Day	18% 21% 33% 19% 8% 1	432
	21st to end	Day	20% 16% 34% 23% 7%	446
March	1st to 10th	Day	25% 21% 27% 18% 7% 1	540
	11th to 20th	Day	26% 19% 21% 19% 12% 2	540
	21st to end	Day	28% 19% 23% 19% 10% 1	594
April	1st to 10th	Day	25% 19% 24% 21% 9% 1	540
	11th to 20th	Day	21% 18% 28% 20% 8% 4	532
	21st to end	Day	18% 15% 28% 24% 12% 3	540
May	1st to 10th	Day	14% 15% 32% 27% 10% 1	543
	11th to 20th	Day	21% 13% 27% 23% 14% 2	568
	21st to end	Day	18% 13% 24% 26% 16% 3	761
June	1st to 10th	Day	21% 14% 26% 26% 11% 2	731
	11th to 20th	Day	19% 15% 27% 24% 12% 2	730
	21st to end	Day	13% 10% 25% 30% 18% 3	730
July	1st to 10th	Day	7% 11% 26% 36% 19% 3	694
	11th to 20th	Day	8% 13% 33% 31% 13% 2	524
	21st to end	Day	6% 10% 34% 29% 17% 3	575
August	1st to 10th	Day	7% 9% 30% 31% 18% 4	527
	11th to 20th	Day	6% 11% 29% 32% 18% 5%	517
	21st to end	Day	9% 14% 27% 29% 17% 5%	583
September	1st to 10th	Day	10% 12% 27% 27% 20% 3	530
	11th to 20th	Day	14% 14% 27% 28% 15% 2	530
	21st to end	Day	20% 17% 28% 23% 10% 2	530
October	1st to 10th	Day	16% 12% 35% 23% 12% 2	530
	11th to 20th	Day	21% 15% 28% 22% 11% 3	401
	21st to end	Day	26% 16% 28% 21% 7% 2	363
November	1st to 10th	Day	26% 14% 26% 27% 7% 1	330
	11th to 20th	Day	35% 12% 23% 21% 7% 3	231
	21st to end	Day	26% 14% 26% 19% 10% 5%	220
December	1st to 10th	Day	25% 11% 20% 23% 14% 6%	220
	11th to 20th	Day	23% 17% 24% 25% 9% 1	220
	21st to end	Day	23% 14% 25% 31% 7% 1	242
January	1st to 10th	Night	31% 12% 24% 25% 7% 1	908
	11th to 20th	Night	26% 8% 28% 29% 8% 1	840
	21st to end	Night	22% 7% 29% 32% 9% 1	924
February	1st to 10th	Night	25% 9% 28% 29% 8%	840
	11th to 20th	Night	22% 7% 27% 33% 11%	824
	21st to end	Night	20% 10% 25% 30% 14% 2	692
March	1st to 10th	Night	23% 8% 23% 30% 14% 1	840
	11th to 20th	Night	25% 11% 19% 30% 14% 1	840
	21st to end	Night	21% 8% 27% 29% 13% 1	924
April	1st to 10th	Night	19% 8% 24% 32% 15% 2	840
	11th to 20th	Night	18% 7% 27% 35% 12% 1	741
	21st to end	Night	16% 9% 23% 37% 14% 1	606
May	1st to 10th	Night	11% 6% 24% 37% 21% 1	420
	11th to 20th	Night	14% 5% 21% 32% 26% 1	414
	21st to end	Night	18% 8% 20% 27% 25% 2	455
June	1st to 10th	Night	19% 4 20% 37% 19% 1	400
	11th to 20th	Night	15% 7% 21% 38% 18% 2	400
	21st to end	Night	10% 5% 21% 40% 21% 5%	400
July	1st to 10th	Night	6% 3 12% 44% 35% 1	390
	11th to 20th	Night	3 3 19% 45% 27% 3	388
	21st to end	Night	3 2 14% 45% 35% 2	438
August	1st to 10th	Night	5% 2 12% 38% 39% 4	398
	11th to 20th	Night	5% 2 14% 39% 35% 5%	456
	21st to end	Night	8% 4 16% 39% 31% 2	795
September	1st to 10th	Night	6% 3 19% 41% 27% 4	800
	11th to 20th	Night	13% 3 16% 32% 32% 5%	800
	21st to end	Night	14% 6% 18% 40% 19% 3	800
October	1st to 10th	Night	16% 5% 24% 34% 20% 2	800
	11th to 20th	Night	23% 6% 18% 34% 18% 1	800
	21st to end	Night	26% 7% 27% 29% 10% 2	880
November	1st to 10th	Night	31% 9% 25% 29% 6%	820
	11th to 20th	Night	32% 11% 22% 24% 11% 1	856
	21st to end	Night	28% 11% 20% 28% 11% 1	1050
December	1st to 10th	Night	24% 8% 26% 29% 13% 1	1050
	11th to 20th	Night	31% 10% 24% 29% 7%	1050
	21st to end	Night	27% 11% 29% 28% 5%	1155

Page generated at 2026-05-28 22:53:31. Version ac07

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