Colville Flats
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Colville Flats clear sky chart from 2005-11-06 to 2026-04-17.

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	8% 9% 3 7% 5% 5% 5% 4 6% 7% 42%	135006
	Night	9% 11% 3 8% 5% 4 5% 4 6% 7% 37%	135862
Transparency	Day	39% 9% 13% 21% 14% 5%	134733
	Night	43% 9% 13% 20% 12% 4	135713
Seeing	Day	14% 13% 28% 28% 14% 3	16543
	Night	16% 6% 20% 35% 21% 3	25798

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	12% 21% 7% 14% 8% 6% 6% 3 4 5% 14%	4723
	11th to 20th	Day	9% 7% 3 9% 8% 7% 7% 5% 6% 8% 30%	4716
	21st to end	Day	16% 17% 4 10% 5% 6% 5% 4 7% 6% 19%	5186
February	1st to 10th	Day	11% 15% 6% 10% 6% 5% 5% 4 5% 7% 25%	1691
	11th to 20th	Day	10% 14% 4 8% 5% 5% 5% 4 7% 8% 28%	1918
	21st to end	Day	10% 13% 4 8% 6% 6% 5% 5% 6% 7% 29%	1730
March	1st to 10th	Day	7% 10% 4 7% 5% 5% 7% 6% 9% 9% 31%	4618
	11th to 20th	Day	7% 10% 3 7% 5% 5% 4 3 6% 8% 42%	4762
	21st to end	Day	11% 12% 4 9% 6% 6% 6% 5% 8% 8% 25%	6101
April	1st to 10th	Day	11% 10% 3 9% 6% 6% 6% 5% 6% 9% 30%	2520
	11th to 20th	Day	9% 8% 3 8% 7% 6% 6% 5% 7% 7% 34%	2498
	21st to end	Day	9% 8% 3 8% 6% 6% 6% 4 6% 8% 36%	2618
May	1st to 10th	Day	5% 6% 2 6% 4 5% 5% 5% 7% 9% 45%	6320
	11th to 20th	Day	7% 8% 4 9% 6% 6% 6% 4 8% 9% 33%	6277
	21st to end	Day	7% 7% 3 8% 6% 5% 5% 5% 6% 8% 39%	6963
June	1st to 10th	Day	13% 8% 2 6% 6% 5% 4 4 7% 7% 38%	3000
	11th to 20th	Day	9% 7% 3 8% 6% 6% 6% 5% 7% 8% 35%	3000
	21st to end	Day	5% 5% 2 5% 6% 5% 5% 4 6% 8% 49%	3000
July	1st to 10th	Day	2 3 1 3 2 2 3 3 5% 6% 70%	6415
	11th to 20th	Day	2 2 1 3 2 2 2 2 3 5% 75%	6320
	21st to end	Day	4 2 1 3 3 3 3 3 5% 6% 67%	6874
August	1st to 10th	Day	3 2 1 3 3 3 4 3 5% 8% 66%	4541
	11th to 20th	Day	2 2 1 4 3 3 4 4 6% 8% 63%	4374
	21st to end	Day	3 3 1 4 4 4 4 4 6% 7% 59%	4359
September	1st to 10th	Day	4 3 1 4 2 3 5% 3 5% 6% 65%	2400
	11th to 20th	Day	5% 4 2 6% 4 5% 5% 4 7% 8% 49%	2320
	21st to end	Day	7% 4 2 7% 4 4 5% 4 6% 7% 50%	2200
October	1st to 10th	Day	6% 4 1 5% 3 4 4 3 6% 8% 55%	3386
	11th to 20th	Day	6% 6% 2 6% 5% 5% 7% 4 7% 9% 43%	3097
	21st to end	Day	12% 8% 2 7% 5% 5% 7% 5% 8% 7% 33%	3200
November	1st to 10th	Day	17% 12% 3 9% 6% 5% 4 3 6% 6% 29%	1854
	11th to 20th	Day	15% 16% 4 9% 7% 5% 4 3 5% 4 28%	1706
	21st to end	Day	14% 19% 5% 11% 8% 4 4 3 6% 5% 20%	1531
December	1st to 10th	Day	10% 11% 4 15% 9% 8% 6% 5% 6% 6% 20%	2360
	11th to 20th	Day	17% 24% 6% 12% 6% 3 4 3 4 4 16%	2712
	21st to end	Day	15% 27% 8% 14% 6% 5% 4 3 4 4 10%	3716
January	1st to 10th	Night	16% 23% 6% 12% 6% 5% 4 3 5% 6% 13%	8172
	11th to 20th	Night	8% 8% 3 11% 8% 6% 5% 5% 9% 13% 23%	8182
	21st to end	Night	15% 19% 4 8% 5% 6% 7% 5% 7% 8% 16%	8994
February	1st to 10th	Night	11% 18% 5% 9% 5% 4 5% 4 6% 7% 27%	2925
	11th to 20th	Night	9% 14% 5% 9% 5% 6% 4 4 7% 6% 32%	2588
	21st to end	Night	8% 11% 4 8% 5% 5% 5% 4 7% 7% 35%	2076
March	1st to 10th	Night	5% 9% 2 7% 5% 5% 5% 5% 9% 12% 36%	5496
	11th to 20th	Night	10% 11% 3 6% 4 3 4 3 5% 6% 45%	5454
	21st to end	Night	11% 9% 4 9% 6% 7% 8% 6% 8% 8% 23%	5116
April	1st to 10th	Night	9% 7% 3 6% 5% 5% 6% 5% 8% 8% 38%	2100
	11th to 20th	Night	7% 8% 3 9% 7% 6% 5% 4 5% 7% 40%	1986
	21st to end	Night	6% 7% 3 6% 6% 5% 5% 5% 8% 7% 42%	1780
May	1st to 10th	Night	7% 5% 2 5% 4 4 5% 5% 8% 9% 47%	3640
	11th to 20th	Night	7% 6% 2 7% 5% 5% 5% 4 7% 7% 43%	3616
	21st to end	Night	7% 6% 2 6% 4 4 4 4 7% 9% 46%	3908
June	1st to 10th	Night	9% 6% 3 6% 4 4 5% 5% 8% 8% 43%	1400
	11th to 20th	Night	7% 6% 2 8% 5% 4 6% 5% 7% 9% 42%	1400
	21st to end	Night	4 4 2 5% 4 4 5% 4 6% 8% 55%	1400
July	1st to 10th	Night	2 2 1 2 2 2 2 2 4 6% 76%	3540
	11th to 20th	Night	3 2 2 1 2 3 2 3 4 78%	3640
	21st to end	Night	2 2 1 3 2 2 2 2 4 7% 73%	3969
August	1st to 10th	Night	3 3 1 3 2 2 3 2 5% 7% 69%	2609
	11th to 20th	Night	2 2 1 4 2 3 4 3 5% 9% 66%	2675
	21st to end	Night	4 2 1 4 3 3 5% 4 6% 6% 62%	3556
September	1st to 10th	Night	3 2 1 2 3 3 4 3 6% 8% 66%	2000
	11th to 20th	Night	5% 3 2 5% 4 3 5% 4 6% 8% 54%	2080
	21st to end	Night	7% 4 2 4 3 3 4 3 7% 6% 57%	2200
October	1st to 10th	Night	5% 3 1 5% 3 3 3 3 6% 8% 59%	3812
	11th to 20th	Night	8% 5% 2 5% 4 5% 4 4 6% 9% 48%	4056
	21st to end	Night	11% 8% 2 8% 4 5% 5% 5% 8% 7% 38%	4600
November	1st to 10th	Night	17% 13% 3 7% 4 4 5% 5% 7% 7% 28%	2665
	11th to 20th	Night	15% 14% 4 8% 5% 4 5% 5% 6% 5% 28%	2909
	21st to end	Night	15% 19% 6% 9% 6% 4 3 3 5% 6% 24%	3066
December	1st to 10th	Night	8% 12% 4 14% 7% 8% 8% 5% 6% 6% 22%	5040
	11th to 20th	Night	16% 22% 7% 12% 6% 5% 4 3 5% 5% 14%	5700
	21st to end	Night	17% 25% 6% 12% 5% 4 4 3 5% 5% 13%	7512

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	68% 10% 8% 11% 3	4723
	11th to 20th	Day	47% 13% 19% 15% 5% 2	4740
	21st to end	Day	60% 11% 13% 12% 4	5187
February	1st to 10th	Day	58% 10% 13% 11% 7% 2	1691
	11th to 20th	Day	51% 11% 15% 14% 8%	1927
	21st to end	Day	53% 10% 14% 15% 8% 1	1730
March	1st to 10th	Day	41% 13% 15% 16% 14% 1	4618
	11th to 20th	Day	40% 9% 18% 27% 7%	4762
	21st to end	Day	51% 14% 14% 15% 5% 1	6101
April	1st to 10th	Day	49% 9% 16% 18% 7%	2520
	11th to 20th	Day	45% 9% 15% 19% 10% 1	2498
	21st to end	Day	44% 10% 14% 21% 9% 3	2618
May	1st to 10th	Day	32% 7% 11% 27% 23% 1	6320
	11th to 20th	Day	41% 10% 13% 26% 10% 1	6280
	21st to end	Day	38% 12% 16% 26% 8% 1	6964
June	1st to 10th	Day	43% 6% 11% 20% 16% 4	3000
	11th to 20th	Day	44% 10% 12% 19% 13% 3	3000
	21st to end	Day	30% 8% 14% 26% 19% 4	3000
July	1st to 10th	Day	15% 4 9% 21% 28% 22%	6346
	11th to 20th	Day	13% 4 6% 24% 28% 26%	6245
	21st to end	Day	17% 5% 8% 29% 26% 16%	6681
August	1st to 10th	Day	16% 5% 8% 29% 31% 11%	4524
	11th to 20th	Day	18% 6% 11% 39% 22% 4	4416
	21st to end	Day	22% 6% 14% 32% 22% 3	4358
September	1st to 10th	Day	19% 6% 11% 31% 25% 7%	2400
	11th to 20th	Day	30% 9% 13% 25% 20% 4	2320
	21st to end	Day	32% 8% 17% 27% 12% 3	2200
October	1st to 10th	Day	28% 6% 19% 35% 11%	3386
	11th to 20th	Day	36% 8% 18% 23% 15%	3097
	21st to end	Day	43% 13% 18% 17% 8% 1	3200
November	1st to 10th	Day	56% 10% 14% 14% 5% 1	1854
	11th to 20th	Day	59% 8% 14% 13% 4 2	1706
	21st to end	Day	65% 9% 11% 10% 4 1	1531
December	1st to 10th	Day	61% 11% 14% 10% 3	2360
	11th to 20th	Day	71% 9% 8% 8% 3	2714
	21st to end	Day	75% 9% 8% 5% 3	3716
January	1st to 10th	Night	70% 10% 10% 8% 2	8172
	11th to 20th	Night	49% 15% 15% 15% 5% 1	8220
	21st to end	Night	59% 14% 13% 10% 3	8994
February	1st to 10th	Night	56% 9% 14% 12% 8% 2	2925
	11th to 20th	Night	50% 10% 14% 17% 8% 1	2590
	21st to end	Night	45% 10% 17% 16% 11% 1	2076
March	1st to 10th	Night	35% 12% 19% 20% 13% 1	5496
	11th to 20th	Night	39% 6% 17% 28% 10% 1	5455
	21st to end	Night	49% 15% 14% 17% 5%	5116
April	1st to 10th	Night	40% 8% 18% 24% 8% 1	2100
	11th to 20th	Night	42% 7% 14% 22% 14% 2	1986
	21st to end	Night	37% 8% 13% 25% 15% 2	1780
May	1st to 10th	Night	28% 7% 12% 27% 24% 2	3637
	11th to 20th	Night	34% 9% 13% 29% 13% 2	3616
	21st to end	Night	30% 10% 18% 32% 9% 1	3908
June	1st to 10th	Night	35% 9% 10% 22% 18% 6%	1400
	11th to 20th	Night	35% 8% 16% 22% 16% 4	1400
	21st to end	Night	24% 7% 12% 28% 23% 6%	1400
July	1st to 10th	Night	11% 3 8% 22% 32% 24%	3500
	11th to 20th	Night	11% 3 6% 25% 22% 33%	3592
	21st to end	Night	13% 4 4 29% 30% 20%	3857
August	1st to 10th	Night	15% 4 7% 26% 32% 16%	2601
	11th to 20th	Night	16% 5% 11% 36% 28% 5%	2699
	21st to end	Night	20% 6% 13% 29% 26% 6%	3556
September	1st to 10th	Night	16% 5% 9% 30% 28% 11%	2000
	11th to 20th	Night	27% 7% 11% 26% 23% 6%	2080
	21st to end	Night	26% 6% 16% 32% 15% 5%	2200
October	1st to 10th	Night	24% 5% 17% 37% 16%	3812
	11th to 20th	Night	34% 7% 16% 27% 16%	4056
	21st to end	Night	41% 12% 17% 22% 8% 1	4600
November	1st to 10th	Night	53% 10% 17% 13% 6% 1	2665
	11th to 20th	Night	56% 10% 15% 13% 5% 2	2909
	21st to end	Night	62% 8% 13% 12% 5%	3066
December	1st to 10th	Night	58% 14% 14% 13% 2	5040
	11th to 20th	Night	71% 12% 8% 6% 3	5697
	21st to end	Night	71% 11% 8% 7% 3	7512

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% 10% 24% 25% 12% 2	220
	11th to 20th	Day	25% 6% 27% 27% 13% 3	220
	21st to end	Day	26% 6% 24% 33% 10% 1	242
February	1st to 10th	Day	17% 17% 33% 23% 10% 1	231
	11th to 20th	Day	18% 14% 29% 28% 10% 1	464
	21st to end	Day	16% 16% 30% 25% 11%	446
March	1st to 10th	Day	18% 19% 27% 23% 11% 1	540
	11th to 20th	Day	20% 16% 23% 26% 16%	540
	21st to end	Day	19% 20% 29% 24% 8% 2	594
April	1st to 10th	Day	21% 15% 29% 21% 11% 3	540
	11th to 20th	Day	16% 23% 29% 18% 10% 3	517
	21st to end	Day	14% 19% 27% 27% 12% 2	500
May	1st to 10th	Day	11% 17% 31% 26% 10% 4	503
	11th to 20th	Day	16% 14% 30% 26% 13% 2	528
	21st to end	Day	13% 12% 26% 29% 15% 5%	594
June	1st to 10th	Day	16% 12% 25% 29% 15% 3	730
	11th to 20th	Day	12% 16% 28% 28% 13% 3	730
	21st to end	Day	5% 9% 26% 34% 22% 3	730
July	1st to 10th	Day	5% 11% 30% 36% 16% 3	569
	11th to 20th	Day	4 12% 33% 32% 15% 3	524
	21st to end	Day	4 11% 29% 34% 18% 5%	575
August	1st to 10th	Day	6% 7% 26% 36% 19% 6%	527
	11th to 20th	Day	5% 8% 28% 32% 21% 7%	517
	21st to end	Day	6% 11% 27% 29% 19% 7%	583
September	1st to 10th	Day	7% 9% 25% 26% 24% 7%	530
	11th to 20th	Day	8% 12% 25% 30% 19% 5%	530
	21st to end	Day	12% 18% 25% 27% 16% 3	530
October	1st to 10th	Day	11% 12% 31% 27% 17% 2	530
	11th to 20th	Day	18% 9% 29% 28% 13% 3	430
	21st to end	Day	22% 10% 29% 31% 6% 2	363
November	1st to 10th	Day	24% 9% 26% 31% 9% 1	330
	11th to 20th	Day	23% 14% 28% 24% 11%	234
	21st to end	Day	26% 9% 29% 23% 12% 1	220
December	1st to 10th	Day	22% 11% 24% 24% 16% 4	220
	11th to 20th	Day	25% 9% 28% 29% 9% 1	220
	21st to end	Day	24% 8% 24% 32% 11%	242
January	1st to 10th	Night	29% 7% 25% 27% 10% 2	840
	11th to 20th	Night	23% 5% 24% 32% 14% 3	840
	21st to end	Night	24% 3 19% 36% 17% 1	924
February	1st to 10th	Night	20% 6% 26% 32% 13% 2	840
	11th to 20th	Night	16% 6% 25% 35% 16% 1	824
	21st to end	Night	14% 10% 22% 34% 17% 3	692
March	1st to 10th	Night	15% 6% 25% 34% 19% 2	840
	11th to 20th	Night	16% 8% 24% 34% 17% 1	840
	21st to end	Night	17% 8% 28% 32% 14% 2	924
April	1st to 10th	Night	13% 8% 20% 35% 22% 3	840
	11th to 20th	Night	11% 9% 27% 36% 16% 2	762
	21st to end	Night	8% 11% 24% 36% 19% 2	580
May	1st to 10th	Night	9% 8% 20% 37% 24% 2	400
	11th to 20th	Night	11% 5% 18% 34% 27% 5%	394
	21st to end	Night	11% 6% 19% 33% 26% 5%	433
June	1st to 10th	Night	9% 7% 23% 36% 23% 3	400
	11th to 20th	Night	10% 5% 23% 40% 20% 3	400
	21st to end	Night	4 4 17% 41% 31% 4	400
July	1st to 10th	Night	3 3 14% 40% 36% 4	390
	11th to 20th	Night	3 3 18% 45% 30% 2	388
	21st to end	Night	1 2 13% 42% 38% 4	438
August	1st to 10th	Night	4 2 11% 30% 44% 8%	398
	11th to 20th	Night	3 3 13% 34% 41% 7%	455
	21st to end	Night	5% 4 15% 36% 36% 5%	841
September	1st to 10th	Night	3 3 17% 36% 34% 8%	800
	11th to 20th	Night	7% 4 12% 34% 37% 7%	800
	21st to end	Night	10% 5% 15% 37% 27% 6%	800
October	1st to 10th	Night	12% 4 17% 39% 27% 2	800
	11th to 20th	Night	12% 8% 19% 34% 25% 2	800
	21st to end	Night	18% 6% 20% 38% 15% 3	880
November	1st to 10th	Night	25% 6% 18% 39% 11%	820
	11th to 20th	Night	26% 7% 23% 28% 14% 1	840
	21st to end	Night	24% 6% 21% 32% 16% 2	966
December	1st to 10th	Night	22% 6% 20% 35% 15% 3	1050
	11th to 20th	Night	28% 6% 21% 35% 10% 1	1050
	21st to end	Night	29% 7% 22% 32% 10% 1	1109

Page generated at 2026-04-13 23:44:28. Version ac07

Copyright © 2026 Attilla Danko.