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 2024-02-05.

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	13% 13% 4 8% 6% 3 5% 5% 5% 6% 32%	77836
	Night	14% 15% 5% 8% 6% 3 4 4 5% 6% 30%	80969
Transparency	Day	52% 7% 12% 17% 10% 2	77558
	Night	54% 7% 12% 16% 9% 2	80827
Seeing	Day	18% 14% 27% 25% 13% 3	13867
	Night	21% 7% 21% 32% 17% 2	23118

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	11% 29% 9% 15% 8% 3 4 3 3 3 10%	2454
	11th to 20th	Day	15% 17% 5% 7% 4 3 7% 8% 5% 6% 22%	2516
	21st to end	Day	22% 32% 6% 8% 5% 2 3 3 4 4 11%	2794
February	1st to 10th	Day	13% 20% 6% 11% 6% 4 4 5% 4 6% 22%	1472
	11th to 20th	Day	11% 19% 6% 10% 5% 4 5% 5% 4 7% 22%	1610
	21st to end	Day	11% 15% 7% 9% 7% 4 6% 6% 5% 5% 23%	1480
March	1st to 10th	Day	15% 19% 6% 10% 9% 4 5% 5% 5% 5% 17%	1800
	11th to 20th	Day	19% 17% 5% 7% 6% 3 5% 4 4 8% 23%	1837
	21st to end	Day	17% 20% 6% 9% 7% 4 6% 4 4 6% 17%	2367
April	1st to 10th	Day	15% 17% 5% 9% 7% 5% 6% 5% 5% 5% 22%	2160
	11th to 20th	Day	14% 13% 5% 9% 8% 4 6% 5% 5% 6% 24%	2207
	21st to end	Day	14% 12% 5% 9% 7% 5% 6% 6% 5% 6% 26%	2358
May	1st to 10th	Day	12% 9% 4 8% 6% 3 6% 5% 6% 8% 33%	2520
	11th to 20th	Day	13% 10% 4 9% 8% 4 6% 5% 5% 8% 30%	2477
	21st to end	Day	16% 9% 6% 9% 7% 4 6% 6% 6% 7% 25%	2846
June	1st to 10th	Day	22% 8% 4 8% 7% 3 6% 6% 6% 6% 26%	2700
	11th to 20th	Day	17% 9% 5% 9% 9% 5% 6% 6% 6% 6% 21%	2700
	21st to end	Day	10% 5% 3 6% 6% 4 5% 5% 6% 8% 41%	2700
July	1st to 10th	Day	6% 4 2 5% 5% 3 7% 6% 7% 9% 46%	2676
	11th to 20th	Day	5% 3 2 5% 5% 3 5% 5% 5% 7% 54%	2520
	21st to end	Day	4 2 1 3 4 3 4 5% 4 7% 63%	2741
August	1st to 10th	Day	4 3 2 5% 5% 3 5% 5% 6% 8% 54%	2507
	11th to 20th	Day	6% 3 1 3 4 3 4 3 6% 7% 61%	2421
	21st to end	Day	7% 4 2 6% 5% 3 4 6% 6% 7% 50%	2449
September	1st to 10th	Day	7% 4 1 5% 5% 3 4 5% 5% 7% 54%	2160
	11th to 20th	Day	11% 6% 3 6% 5% 4 4 4 5% 6% 47%	2076
	21st to end	Day	14% 7% 4 7% 6% 3 5% 4 4 6% 40%	1980
October	1st to 10th	Day	13% 7% 3 6% 6% 5% 5% 5% 5% 7% 37%	1878
	11th to 20th	Day	17% 9% 4 6% 5% 4 4 4 5% 7% 35%	1685
	21st to end	Day	19% 16% 3 5% 5% 3 6% 4 4 6% 27%	1782
November	1st to 10th	Day	23% 17% 5% 8% 6% 3 4 5% 5% 5% 20%	1674
	11th to 20th	Day	18% 18% 6% 9% 6% 3 4 4 4 4 23%	1505
	21st to end	Day	16% 20% 7% 9% 7% 3 5% 4 5% 6% 19%	1330
December	1st to 10th	Day	14% 15% 6% 12% 6% 4 5% 4 4 5% 25%	1330
	11th to 20th	Day	15% 28% 7% 10% 6% 2 4 3 4 6% 15%	1682
	21st to end	Day	14% 26% 7% 9% 6% 3 4 4 4 5% 19%	2442
January	1st to 10th	Night	17% 30% 8% 12% 6% 3 4 3 3 3 12%	4520
	11th to 20th	Night	13% 17% 7% 9% 7% 4 5% 5% 4 6% 22%	4382
	21st to end	Night	23% 30% 7% 10% 6% 2 3 3 3 3 9%	4862
February	1st to 10th	Night	14% 20% 5% 9% 7% 4 5% 4 5% 6% 20%	2582
	11th to 20th	Night	12% 18% 5% 9% 7% 3 4 3 5% 7% 27%	2233
	21st to end	Night	10% 16% 5% 7% 7% 5% 5% 6% 6% 9% 24%	1776
March	1st to 10th	Night	15% 17% 6% 9% 7% 3 5% 4 4 5% 24%	2160
	11th to 20th	Night	17% 16% 5% 7% 6% 3 5% 4 4 6% 28%	2121
	21st to end	Night	13% 16% 5% 8% 8% 4 6% 5% 5% 6% 25%	1985
April	1st to 10th	Night	13% 13% 4 6% 6% 3 6% 5% 5% 8% 32%	1800
	11th to 20th	Night	15% 9% 3 6% 7% 4 6% 5% 6% 7% 31%	1703
	21st to end	Night	10% 11% 3 8% 5% 4 6% 5% 6% 8% 35%	1600
May	1st to 10th	Night	8% 7% 3 5% 7% 4 7% 7% 6% 7% 38%	1440
	11th to 20th	Night	11% 8% 3 6% 5% 4 5% 5% 6% 8% 39%	1416
	21st to end	Night	15% 11% 5% 7% 6% 4 5% 5% 6% 8% 28%	1428
June	1st to 10th	Night	15% 7% 4 7% 4 3 5% 5% 8% 9% 33%	1260
	11th to 20th	Night	16% 5% 3 7% 7% 4 7% 6% 6% 7% 32%	1260
	21st to end	Night	9% 4 3 5% 4 3 6% 5% 7% 7% 48%	1260
July	1st to 10th	Night	5% 3 1 4 5% 4 4 5% 6% 7% 56%	1280
	11th to 20th	Night	3 3 2 3 5% 3 4 4 5% 8% 61%	1440
	21st to end	Night	2 2 1 2 2 1 3 3 5% 8% 70%	1576
August	1st to 10th	Night	4 3 2 3 4 2 3 4 4 7% 63%	1432
	11th to 20th	Night	4 3 1 3 3 2 3 5% 5% 8% 64%	1478
	21st to end	Night	6% 4 1 2 3 2 4 5% 7% 9% 58%	1903
September	1st to 10th	Night	5% 4 1 4 5% 3 4 4 6% 8% 57%	1800
	11th to 20th	Night	9% 6% 3 5% 4 4 4 4 6% 7% 49%	1883
	21st to end	Night	12% 5% 2 5% 5% 3 3 4 5% 7% 47%	1980
October	1st to 10th	Night	13% 7% 3 6% 6% 3 5% 4 5% 7% 42%	2078
	11th to 20th	Night	16% 9% 4 6% 5% 2 4 5% 4 6% 38%	2274
	21st to end	Night	20% 11% 3 6% 6% 3 4 4 4 6% 32%	2574
November	1st to 10th	Night	25% 16% 5% 8% 5% 4 5% 4 5% 5% 19%	2405
	11th to 20th	Night	18% 19% 6% 8% 7% 3 4 3 4 5% 22%	2654
	21st to end	Night	17% 20% 8% 10% 5% 2 4 4 4 6% 20%	2850
December	1st to 10th	Night	16% 18% 7% 11% 6% 3 4 3 5% 4 23%	2850
	11th to 20th	Night	16% 27% 8% 11% 7% 3 4 3 4 5% 12%	3510
	21st to end	Night	16% 25% 8% 9% 6% 3 4 4 4 5% 16%	5214

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	79% 8% 5% 6% 2	2454
	11th to 20th	Day	60% 9% 15% 10% 4 2	2540
	21st to end	Day	76% 9% 6% 7% 2	2794
February	1st to 10th	Day	65% 7% 12% 10% 5% 2	1472
	11th to 20th	Day	62% 9% 13% 11% 4	1619
	21st to end	Day	61% 9% 11% 11% 7%	1480
March	1st to 10th	Day	67% 9% 11% 8% 5%	1800
	11th to 20th	Day	61% 7% 11% 16% 5%	1837
	21st to end	Day	70% 6% 12% 9% 3	2367
April	1st to 10th	Day	62% 8% 12% 13% 4	2160
	11th to 20th	Day	60% 7% 13% 15% 5%	2207
	21st to end	Day	57% 8% 12% 18% 3 1	2358
May	1st to 10th	Day	48% 7% 18% 20% 6% 1	2520
	11th to 20th	Day	53% 7% 14% 20% 7%	2480
	21st to end	Day	57% 9% 14% 16% 4	2847
June	1st to 10th	Day	57% 7% 10% 14% 9% 2	2700
	11th to 20th	Day	61% 8% 12% 13% 7%	2700
	21st to end	Day	39% 7% 13% 24% 15% 2	2700
July	1st to 10th	Day	31% 7% 11% 25% 19% 7%	2603
	11th to 20th	Day	27% 6% 10% 22% 27% 7%	2445
	21st to end	Day	20% 5% 9% 25% 31% 9%	2589
August	1st to 10th	Day	26% 8% 11% 24% 23% 8%	2490
	11th to 20th	Day	21% 6% 12% 32% 25% 4	2421
	21st to end	Day	31% 7% 12% 30% 18% 2	2449
September	1st to 10th	Day	30% 6% 13% 29% 18% 4	2160
	11th to 20th	Day	38% 6% 11% 26% 16% 2	2076
	21st to end	Day	45% 7% 16% 18% 11% 1	1980
October	1st to 10th	Day	46% 7% 15% 24% 7%	1878
	11th to 20th	Day	51% 8% 14% 20% 7%	1685
	21st to end	Day	56% 8% 14% 16% 5% 1	1782
November	1st to 10th	Day	65% 10% 10% 12% 3 1	1674
	11th to 20th	Day	65% 9% 10% 11% 4 1	1505
	21st to end	Day	68% 8% 12% 9% 4	1330
December	1st to 10th	Day	62% 7% 13% 13% 4	1330
	11th to 20th	Day	73% 8% 10% 6% 3	1684
	21st to end	Day	68% 7% 9% 10% 6%	2442
January	1st to 10th	Night	79% 6% 6% 6% 2	4520
	11th to 20th	Night	62% 6% 9% 15% 5% 3	4420
	21st to end	Night	78% 7% 7% 5% 2	4862
February	1st to 10th	Night	63% 9% 12% 10% 5% 2	2582
	11th to 20th	Night	58% 7% 14% 15% 5%	2235
	21st to end	Night	56% 9% 13% 13% 8% 1	1776
March	1st to 10th	Night	62% 8% 13% 11% 6%	2160
	11th to 20th	Night	57% 8% 11% 16% 8%	2122
	21st to end	Night	58% 7% 15% 13% 7%	1985
April	1st to 10th	Night	50% 8% 17% 18% 7% 1	1800
	11th to 20th	Night	52% 6% 14% 20% 7% 1	1703
	21st to end	Night	47% 8% 14% 22% 8% 1	1600
May	1st to 10th	Night	42% 9% 16% 24% 9%	1440
	11th to 20th	Night	42% 7% 20% 22% 8% 1	1416
	21st to end	Night	53% 6% 15% 20% 6%	1428
June	1st to 10th	Night	45% 8% 15% 19% 11% 2	1260
	11th to 20th	Night	49% 9% 12% 20% 9% 1	1260
	21st to end	Night	33% 7% 14% 25% 19% 2	1260
July	1st to 10th	Night	25% 7% 10% 28% 22% 8%	1244
	11th to 20th	Night	21% 5% 13% 24% 25% 12%	1392
	21st to end	Night	13% 4 9% 26% 36% 12%	1488
August	1st to 10th	Night	20% 5% 10% 28% 27% 9%	1424
	11th to 20th	Night	18% 5% 12% 33% 27% 5%	1478
	21st to end	Night	22% 5% 14% 32% 22% 5%	1903
September	1st to 10th	Night	25% 5% 12% 29% 24% 5%	1800
	11th to 20th	Night	35% 6% 11% 25% 20% 4	1883
	21st to end	Night	37% 6% 20% 22% 13% 2	1980
October	1st to 10th	Night	42% 7% 14% 28% 8%	2078
	11th to 20th	Night	47% 7% 16% 20% 9% 1	2274
	21st to end	Night	54% 7% 14% 19% 6% 1	2574
November	1st to 10th	Night	65% 8% 10% 11% 5% 1	2405
	11th to 20th	Night	65% 9% 11% 10% 5% 1	2654
	21st to end	Night	66% 7% 11% 11% 5%	2850
December	1st to 10th	Night	64% 6% 11% 14% 5% 1	2850
	11th to 20th	Night	75% 7% 9% 6% 2	3507
	21st to end	Night	70% 9% 9% 7% 5%	5214

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	28% 16% 25% 18% 11% 2	180
	11th to 20th	Day	26% 15% 27% 18% 10% 4	180
	21st to end	Day	28% 11% 31% 21% 9% 1	198
February	1st to 10th	Day	22% 20% 35% 18% 5%	168
	11th to 20th	Day	21% 19% 35% 17% 7% 1	335
	21st to end	Day	15% 14% 36% 26% 8% 1	346
March	1st to 10th	Day	27% 21% 28% 15% 7% 2	420
	11th to 20th	Day	24% 18% 23% 21% 12% 2	420
	21st to end	Day	28% 18% 23% 18% 12% 2	462
April	1st to 10th	Day	27% 18% 23% 20% 9% 2	420
	11th to 20th	Day	24% 18% 26% 18% 9% 4	412
	21st to end	Day	20% 16% 28% 21% 12% 4	420
May	1st to 10th	Day	16% 13% 31% 27% 11% 2	423
	11th to 20th	Day	22% 11% 25% 24% 15% 3	448
	21st to end	Day	20% 12% 22% 25% 18% 4	608
June	1st to 10th	Day	23% 14% 23% 25% 12% 3	630
	11th to 20th	Day	19% 16% 27% 23% 13% 3	630
	21st to end	Day	13% 9% 24% 30% 20% 4	630
July	1st to 10th	Day	7% 11% 25% 34% 20% 3	598
	11th to 20th	Day	9% 14% 34% 29% 12% 3	444
	21st to end	Day	6% 9% 33% 30% 17% 4	487
August	1st to 10th	Day	7% 9% 30% 30% 19% 5%	447
	11th to 20th	Day	5% 10% 28% 33% 18% 6%	437
	21st to end	Day	8% 15% 27% 28% 16% 5%	495
September	1st to 10th	Day	12% 14% 30% 27% 14% 3	450
	11th to 20th	Day	16% 15% 26% 26% 14% 2	450
	21st to end	Day	20% 17% 27% 21% 11% 3	450
October	1st to 10th	Day	16% 12% 33% 23% 13% 2	450
	11th to 20th	Day	21% 15% 28% 20% 12% 4	335
	21st to end	Day	28% 14% 26% 22% 7% 2	297
November	1st to 10th	Day	27% 13% 23% 28% 8% 1	270
	11th to 20th	Day	32% 11% 22% 23% 8% 3	189
	21st to end	Day	26% 13% 23% 21% 11% 6%	180
December	1st to 10th	Day	25% 12% 20% 23% 14% 6%	180
	11th to 20th	Day	21% 16% 23% 28% 11% 2	180
	21st to end	Day	23% 12% 24% 33% 7% 1	198
January	1st to 10th	Night	33% 10% 23% 25% 7% 1	822
	11th to 20th	Night	28% 8% 25% 29% 9% 2	760
	21st to end	Night	23% 7% 28% 31% 10% 1	836
February	1st to 10th	Night	26% 9% 28% 28% 8% 1	738
	11th to 20th	Night	24% 7% 25% 33% 11%	704
	21st to end	Night	18% 8% 25% 32% 15% 2	592
March	1st to 10th	Night	24% 8% 22% 29% 15% 1	720
	11th to 20th	Night	26% 10% 19% 30% 15% 1	720
	21st to end	Night	21% 7% 24% 31% 15% 2	792
April	1st to 10th	Night	19% 8% 21% 33% 17% 2	720
	11th to 20th	Night	20% 6% 24% 35% 13% 2	635
	21st to end	Night	17% 8% 23% 36% 15% 1	520
May	1st to 10th	Night	12% 5% 21% 38% 23% 1	360
	11th to 20th	Night	15% 3 19% 32% 29% 2	354
	21st to end	Night	19% 7% 18% 26% 27% 2	389
June	1st to 10th	Night	21% 4 19% 35% 20% 1	360
	11th to 20th	Night	16% 7% 19% 38% 19% 3	360
	21st to end	Night	10% 4 18% 40% 23% 4	360
July	1st to 10th	Night	6% 2 11% 43% 37% 1	350
	11th to 20th	Night	3 3 19% 44% 27% 3	348
	21st to end	Night	3 1 13% 43% 37% 2	394
August	1st to 10th	Night	5% 2 12% 36% 42% 4	358
	11th to 20th	Night	5% 2 12% 38% 37% 6%	410
	21st to end	Night	8% 4 14% 38% 33% 3	715
September	1st to 10th	Night	7% 3 20% 39% 27% 4	720
	11th to 20th	Night	13% 3 16% 29% 33% 5%	720
	21st to end	Night	15% 6% 16% 39% 21% 4	720
October	1st to 10th	Night	17% 5% 21% 34% 22% 2	720
	11th to 20th	Night	24% 6% 16% 34% 19% 1	720
	21st to end	Night	26% 7% 25% 30% 10% 3	792
November	1st to 10th	Night	33% 9% 23% 29% 7%	740
	11th to 20th	Night	32% 9% 22% 25% 12% 1	774
	21st to end	Night	30% 9% 19% 29% 11% 2	950
December	1st to 10th	Night	25% 8% 25% 29% 13% 1	950
	11th to 20th	Night	31% 8% 24% 29% 7% 1	950
	21st to end	Night	28% 10% 28% 29% 5%	1045

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