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 2025-02-06.

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	10% 12% 4 8% 5% 4 5% 4 5% 7% 37%	111949
	Night	11% 14% 4 8% 5% 4 4 4 5% 6% 34%	114961
Transparency	Day	47% 7% 13% 19% 11% 3	111713
	Night	50% 7% 14% 18% 9% 2	114843
Seeing	Day	18% 14% 27% 25% 13% 3	15158
	Night	20% 7% 22% 32% 17% 2	24387

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% 25% 9% 18% 6% 4 3 2 3 3 17%	3526
	11th to 20th	Day	10% 13% 4 6% 4 4 6% 4 4 6% 39%	3616
	21st to end	Day	15% 25% 5% 7% 4 3 3 3 4 4 28%	4004
February	1st to 10th	Day	12% 20% 5% 11% 6% 4 4 3 5% 6% 23%	1560
	11th to 20th	Day	11% 20% 6% 10% 5% 5% 4 4 5% 6% 23%	1701
	21st to end	Day	11% 17% 6% 11% 6% 5% 6% 5% 5% 5% 22%	1570
March	1st to 10th	Day	10% 21% 6% 11% 7% 5% 5% 3 5% 5% 22%	3138
	11th to 20th	Day	11% 15% 3 5% 4 3 3 2 4 6% 43%	3256
	21st to end	Day	13% 21% 6% 11% 7% 6% 6% 4 4 6% 16%	4156
April	1st to 10th	Day	14% 19% 4 10% 6% 6% 5% 4 5% 5% 22%	2280
	11th to 20th	Day	13% 14% 4 11% 6% 5% 6% 4 6% 6% 25%	2332
	21st to end	Day	13% 13% 4 10% 7% 6% 6% 5% 5% 6% 26%	2489
May	1st to 10th	Day	10% 10% 4 10% 6% 6% 6% 4 6% 8% 31%	4420
	11th to 20th	Day	10% 10% 3 9% 6% 5% 5% 5% 7% 10% 30%	4377
	21st to end	Day	15% 13% 4 11% 6% 6% 6% 4 6% 7% 22%	5034
June	1st to 10th	Day	21% 9% 3 9% 6% 5% 5% 4 6% 6% 26%	2850
	11th to 20th	Day	16% 10% 4 10% 8% 6% 6% 5% 6% 7% 22%	2850
	21st to end	Day	10% 6% 3 7% 6% 5% 5% 4 7% 7% 40%	2850
July	1st to 10th	Day	3 3 1 4 3 3 4 3 5% 7% 64%	4688
	11th to 20th	Day	3 2 1 4 3 3 3 3 4 5% 70%	4420
	21st to end	Day	3 2 1 4 3 4 3 4 5% 8% 64%	4790
August	1st to 10th	Day	3 2 1 4 3 3 4 4 6% 9% 61%	4401
	11th to 20th	Day	4 3 1 4 3 3 4 3 7% 8% 59%	4237
	21st to end	Day	5% 5% 2 5% 3 4 5% 5% 7% 8% 51%	4305
September	1st to 10th	Day	6% 4 1 5% 4 3 4 4 5% 8% 55%	2280
	11th to 20th	Day	10% 6% 2 6% 4 4 4 4 6% 6% 47%	2191
	21st to end	Day	13% 7% 3 8% 5% 4 5% 3 4 6% 41%	2090
October	1st to 10th	Day	8% 5% 2 7% 5% 4 4 4 6% 7% 47%	3310
	11th to 20th	Day	12% 8% 3 7% 5% 5% 5% 3 5% 8% 39%	2949
	21st to end	Day	15% 15% 4 8% 5% 5% 6% 4 6% 6% 27%	3101
November	1st to 10th	Day	22% 19% 5% 8% 5% 4 4 4 4 5% 20%	1764
	11th to 20th	Day	17% 21% 6% 11% 5% 4 4 3 4 4 22%	1584
	21st to end	Day	16% 22% 5% 11% 6% 4 4 3 5% 6% 18%	1400
December	1st to 10th	Day	8% 12% 4 11% 4 3 3 3 5% 8% 37%	2290
	11th to 20th	Day	11% 26% 8% 13% 6% 5% 4 3 4 6% 15%	2642
	21st to end	Day	12% 29% 9% 16% 5% 3 3 2 3 4 13%	3498
January	1st to 10th	Night	12% 27% 9% 15% 6% 4 4 2 3 3 16%	6462
	11th to 20th	Night	9% 12% 4 8% 4 4 6% 5% 6% 7% 34%	6282
	21st to end	Night	16% 24% 5% 8% 4 3 4 4 4 5% 24%	6952
February	1st to 10th	Night	14% 21% 5% 10% 6% 6% 5% 3 6% 6% 20%	2730
	11th to 20th	Night	12% 19% 5% 10% 6% 4 4 2 5% 7% 27%	2362
	21st to end	Night	9% 18% 5% 9% 6% 6% 5% 5% 6% 9% 23%	1884
March	1st to 10th	Night	9% 20% 7% 10% 6% 4 4 3 5% 5% 27%	3736
	11th to 20th	Night	11% 16% 3 6% 4 3 3 2 3 5% 45%	3722
	21st to end	Night	13% 20% 5% 11% 7% 6% 5% 3 5% 5% 20%	3493
April	1st to 10th	Night	13% 14% 4 7% 5% 4 5% 4 5% 8% 32%	1900
	11th to 20th	Night	13% 10% 3 7% 6% 6% 6% 3 6% 7% 32%	1798
	21st to end	Night	10% 12% 3 8% 5% 5% 6% 4 6% 8% 34%	1688
May	1st to 10th	Night	8% 7% 2 8% 6% 6% 6% 6% 7% 8% 35%	2540
	11th to 20th	Night	7% 7% 3 6% 5% 4 4 4 6% 9% 46%	2516
	21st to end	Night	16% 14% 4 8% 6% 5% 4 4 6% 8% 25%	2540
June	1st to 10th	Night	15% 8% 3 8% 4 4 5% 4 8% 8% 34%	1330
	11th to 20th	Night	15% 6% 3 8% 6% 6% 6% 5% 6% 7% 32%	1330
	21st to end	Night	8% 4 2 5% 3 4 5% 5% 7% 7% 48%	1330
July	1st to 10th	Night	3 2 3 3 3 3 3 5% 6% 71%	2268
	11th to 20th	Night	2 2 1 2 3 2 3 2 4 6% 73%	2540
	21st to end	Night	2 2 1 2 2 2 3 3 5% 7% 71%	2762
August	1st to 10th	Night	2 2 1 3 3 4 3 4 5% 8% 64%	2529
	11th to 20th	Night	2 2 1 3 3 3 5% 4 7% 10% 61%	2593
	21st to end	Night	4 3 1 4 3 4 5% 5% 8% 9% 54%	3365
September	1st to 10th	Night	5% 4 1 5% 3 4 3 4 5% 8% 58%	1900
	11th to 20th	Night	9% 6% 3 6% 4 5% 4 3 6% 7% 49%	1988
	21st to end	Night	11% 5% 2 7% 4 4 4 3 5% 7% 48%	2090
October	1st to 10th	Night	7% 4 2 5% 4 3 4 3 7% 8% 52%	3666
	11th to 20th	Night	13% 8% 3 7% 4 3 4 3 4 7% 44%	3981
	21st to end	Night	13% 10% 4 9% 5% 5% 5% 5% 6% 6% 32%	4457
November	1st to 10th	Night	23% 16% 5% 9% 5% 5% 4 4 5% 5% 19%	2535
	11th to 20th	Night	17% 21% 5% 9% 6% 4 4 3 4 5% 21%	2794
	21st to end	Night	16% 22% 6% 12% 5% 4 3 3 4 6% 19%	3000
December	1st to 10th	Night	10% 13% 4 11% 5% 4 5% 4 6% 7% 31%	4890
	11th to 20th	Night	13% 26% 8% 13% 6% 4 5% 4 5% 5% 13%	5550
	21st to end	Night	13% 28% 9% 14% 6% 4 3 3 4 4 12%	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	73% 7% 8% 11% 1	3526
	11th to 20th	Day	44% 9% 24% 14% 7% 1	3640
	21st to end	Day	59% 7% 11% 18% 5%	4004
February	1st to 10th	Day	63% 8% 12% 9% 6% 2	1560
	11th to 20th	Day	61% 9% 13% 11% 5% 1	1710
	21st to end	Day	62% 9% 11% 11% 7%	1570
March	1st to 10th	Day	65% 7% 7% 11% 10%	3138
	11th to 20th	Day	44% 6% 22% 24% 5%	3256
	21st to end	Day	69% 7% 10% 9% 4	4156
April	1st to 10th	Day	62% 8% 13% 13% 4	2280
	11th to 20th	Day	59% 7% 13% 16% 6%	2332
	21st to end	Day	58% 8% 12% 18% 4 1	2489
May	1st to 10th	Day	49% 9% 14% 22% 5%	4420
	11th to 20th	Day	46% 10% 13% 24% 7%	4380
	21st to end	Day	58% 12% 12% 15% 3	5035
June	1st to 10th	Day	56% 7% 10% 14% 10% 2	2850
	11th to 20th	Day	60% 8% 11% 13% 7%	2850
	21st to end	Day	39% 7% 13% 24% 15% 2	2850
July	1st to 10th	Day	20% 4 9% 24% 29% 13%	4615
	11th to 20th	Day	17% 4 6% 17% 35% 22%	4345
	21st to end	Day	18% 4 9% 26% 28% 14%	4639
August	1st to 10th	Day	19% 5% 10% 33% 27% 6%	4384
	11th to 20th	Day	22% 5% 18% 38% 16% 2	4279
	21st to end	Day	29% 7% 19% 29% 15% 1	4304
September	1st to 10th	Day	29% 5% 13% 29% 18% 5%	2280
	11th to 20th	Day	38% 6% 11% 27% 16% 2	2191
	21st to end	Day	43% 7% 17% 19% 12% 2	2090
October	1st to 10th	Day	37% 5% 19% 32% 6%	3310
	11th to 20th	Day	47% 7% 13% 26% 8%	2949
	21st to end	Day	53% 8% 16% 16% 6%	3101
November	1st to 10th	Day	65% 10% 10% 12% 3 1	1764
	11th to 20th	Day	65% 8% 10% 11% 4 1	1584
	21st to end	Day	68% 9% 11% 8% 4	1400
December	1st to 10th	Day	47% 10% 27% 13% 3	2290
	11th to 20th	Day	70% 8% 13% 7% 2	2644
	21st to end	Day	76% 6% 8% 7% 4	3498
January	1st to 10th	Night	74% 6% 8% 9% 2	6462
	11th to 20th	Night	48% 8% 17% 18% 8% 2	6320
	21st to end	Night	60% 7% 14% 14% 4	6952
February	1st to 10th	Night	63% 9% 11% 10% 6% 2	2730
	11th to 20th	Night	58% 7% 13% 15% 6% 1	2364
	21st to end	Night	56% 10% 13% 12% 8% 1	1884
March	1st to 10th	Night	58% 8% 12% 13% 8%	3736
	11th to 20th	Night	43% 7% 21% 24% 5%	3723
	21st to end	Night	61% 11% 12% 10% 5%	3493
April	1st to 10th	Night	51% 8% 17% 18% 6% 1	1900
	11th to 20th	Night	51% 7% 14% 20% 7% 1	1798
	21st to end	Night	48% 8% 13% 22% 8% 1	1688
May	1st to 10th	Night	41% 11% 15% 24% 8%	2540
	11th to 20th	Night	34% 8% 16% 30% 10% 1	2516
	21st to end	Night	52% 11% 14% 18% 5%	2540
June	1st to 10th	Night	45% 8% 15% 19% 11% 2	1330
	11th to 20th	Night	49% 9% 12% 19% 9% 1	1330
	21st to end	Night	32% 7% 14% 25% 19% 2	1330
July	1st to 10th	Night	15% 4 8% 30% 26% 17%	2232
	11th to 20th	Night	14% 3 8% 15% 32% 28%	2492
	21st to end	Night	14% 3 7% 26% 32% 17%	2674
August	1st to 10th	Night	18% 4 9% 33% 29% 7%	2521
	11th to 20th	Night	19% 5% 18% 38% 17% 3	2617
	21st to end	Night	26% 5% 19% 29% 18% 3	3365
September	1st to 10th	Night	24% 5% 12% 29% 24% 6%	1900
	11th to 20th	Night	34% 6% 11% 26% 19% 3	1988
	21st to end	Night	36% 6% 20% 23% 13% 2	2090
October	1st to 10th	Night	31% 6% 21% 34% 8%	3666
	11th to 20th	Night	43% 6% 15% 28% 7%	3981
	21st to end	Night	50% 7% 17% 22% 4	4457
November	1st to 10th	Night	65% 8% 11% 11% 5% 1	2535
	11th to 20th	Night	66% 9% 11% 9% 5% 1	2794
	21st to end	Night	67% 7% 11% 10% 5%	3000
December	1st to 10th	Night	49% 11% 21% 16% 3	4890
	11th to 20th	Night	73% 7% 13% 6% 2	5547
	21st to end	Night	75% 7% 8% 7% 3	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	26% 16% 27% 19% 11% 3	200
	11th to 20th	Day	24% 14% 29% 21% 10% 4	200
	21st to end	Day	25% 10% 31% 23% 9% 1	220
February	1st to 10th	Day	20% 19% 36% 18% 6% 1	190
	11th to 20th	Day	20% 20% 34% 17% 9% 1	366
	21st to end	Day	17% 15% 34% 25% 8% 1	382
March	1st to 10th	Day	26% 21% 28% 16% 8% 2	460
	11th to 20th	Day	22% 17% 23% 21% 14% 2	460
	21st to end	Day	27% 17% 24% 19% 12% 2	506
April	1st to 10th	Day	27% 20% 23% 20% 9% 2	460
	11th to 20th	Day	22% 18% 27% 19% 9% 4	452
	21st to end	Day	19% 17% 28% 21% 11% 3	460
May	1st to 10th	Day	15% 14% 31% 27% 11% 2	463
	11th to 20th	Day	22% 12% 25% 24% 15% 3	488
	21st to end	Day	19% 13% 22% 25% 17% 4	659
June	1st to 10th	Day	23% 13% 25% 25% 11% 3	680
	11th to 20th	Day	19% 15% 27% 23% 13% 3	680
	21st to end	Day	13% 10% 25% 30% 19% 4	680
July	1st to 10th	Day	7% 10% 25% 35% 20% 3	646
	11th to 20th	Day	8% 12% 33% 30% 13% 2	484
	21st to end	Day	6% 10% 34% 29% 16% 4	531
August	1st to 10th	Day	7% 9% 30% 32% 18% 4	487
	11th to 20th	Day	5% 10% 28% 33% 18% 6%	477
	21st to end	Day	9% 15% 29% 27% 16% 5%	539
September	1st to 10th	Day	11% 13% 29% 27% 17% 3	490
	11th to 20th	Day	15% 15% 26% 27% 14% 2	490
	21st to end	Day	20% 18% 27% 22% 10% 2	490
October	1st to 10th	Day	16% 12% 34% 23% 13% 2	490
	11th to 20th	Day	21% 14% 28% 23% 11% 4	368
	21st to end	Day	28% 15% 27% 21% 7% 2	330
November	1st to 10th	Day	26% 13% 25% 28% 7% 1	300
	11th to 20th	Day	34% 11% 21% 22% 8% 3	210
	21st to end	Day	26% 15% 23% 21% 11% 5%	200
December	1st to 10th	Day	24% 11% 20% 25% 16% 7%	200
	11th to 20th	Day	20% 18% 23% 28% 10% 2	200
	21st to end	Day	24% 13% 24% 31% 6% 1	220
January	1st to 10th	Night	32% 11% 24% 25% 7% 1	865
	11th to 20th	Night	26% 8% 27% 29% 8% 2	800
	21st to end	Night	22% 7% 28% 32% 10% 1	880
February	1st to 10th	Night	26% 9% 28% 28% 8% 1	780
	11th to 20th	Night	23% 7% 26% 32% 11%	744
	21st to end	Night	19% 9% 24% 31% 15% 2	628
March	1st to 10th	Night	23% 9% 22% 30% 15% 1	760
	11th to 20th	Night	25% 10% 18% 31% 16% 1	760
	21st to end	Night	21% 7% 24% 31% 15% 2	836
April	1st to 10th	Night	20% 8% 22% 32% 16% 2	760
	11th to 20th	Night	19% 7% 25% 35% 13% 2	670
	21st to end	Night	17% 8% 23% 36% 15% 1	548
May	1st to 10th	Night	12% 6% 21% 38% 23% 1	380
	11th to 20th	Night	14% 5% 19% 33% 28% 2	374
	21st to end	Night	19% 8% 18% 26% 26% 2	411
June	1st to 10th	Night	20% 4 19% 36% 19% 1	380
	11th to 20th	Night	16% 7% 19% 37% 18% 2	380
	21st to end	Night	10% 4 20% 40% 22% 4	380
July	1st to 10th	Night	6% 2 12% 44% 36% 1	370
	11th to 20th	Night	3 3 19% 45% 27% 3	368
	21st to end	Night	3 2 14% 43% 36% 2	416
August	1st to 10th	Night	4 2 13% 37% 40% 4	378
	11th to 20th	Night	5% 2 13% 38% 36% 6%	433
	21st to end	Night	8% 4 15% 39% 32% 3	755
September	1st to 10th	Night	7% 3 19% 40% 27% 4	760
	11th to 20th	Night	13% 3 17% 30% 33% 5%	760
	21st to end	Night	14% 6% 17% 39% 20% 4	760
October	1st to 10th	Night	16% 5% 23% 34% 20% 2	760
	11th to 20th	Night	24% 6% 16% 34% 19% 1	760
	21st to end	Night	26% 7% 26% 29% 10% 3	836
November	1st to 10th	Night	31% 8% 24% 30% 7%	780
	11th to 20th	Night	32% 10% 22% 24% 11% 1	815
	21st to end	Night	29% 11% 19% 29% 11% 2	1000
December	1st to 10th	Night	24% 7% 25% 30% 13% 1	1000
	11th to 20th	Night	31% 9% 24% 30% 7% 1	1000
	21st to end	Night	27% 11% 29% 28% 5%	1100

Page generated at 2025-02-03 00:05:50. Version ac07

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