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 2024-12-24.

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%	105588
	Night	10% 11% 3 7% 4 4 4 4 6% 7% 40%	103113
Transparency	Day	39% 8% 13% 21% 14% 5%	105356
	Night	42% 8% 13% 20% 12% 4	102991
Seeing	Day	14% 13% 28% 28% 14% 3	14910
	Night	16% 6% 21% 34% 21% 3	24082

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% 24% 7% 13% 8% 6% 6% 2 4 5% 13%	2539
	11th to 20th	Day	17% 13% 5% 8% 6% 5% 6% 4 4 6% 24%	2516
	21st to end	Day	24% 25% 6% 12% 5% 4 3 3 4 4 10%	2794
February	1st to 10th	Day	12% 15% 5% 10% 6% 6% 6% 4 5% 7% 25%	1529
	11th to 20th	Day	11% 14% 4 8% 4 5% 5% 4 7% 8% 29%	1730
	21st to end	Day	11% 13% 4 8% 6% 6% 5% 5% 6% 7% 29%	1570
March	1st to 10th	Day	9% 13% 4 8% 5% 5% 6% 5% 7% 8% 28%	3138
	11th to 20th	Day	7% 8% 2 6% 4 4 3 3 6% 7% 50%	3254
	21st to end	Day	12% 12% 4 9% 7% 6% 6% 5% 7% 7% 24%	4165
April	1st to 10th	Day	11% 10% 3 9% 7% 7% 6% 5% 5% 9% 27%	2280
	11th to 20th	Day	9% 8% 3 8% 7% 6% 6% 5% 7% 7% 33%	2302
	21st to end	Day	9% 8% 3 8% 7% 6% 6% 4 6% 8% 35%	2487
May	1st to 10th	Day	7% 7% 2 7% 5% 5% 5% 5% 7% 10% 40%	4420
	11th to 20th	Day	6% 7% 3 7% 5% 5% 5% 4 8% 9% 42%	4377
	21st to end	Day	10% 9% 4 10% 7% 6% 6% 5% 7% 7% 27%	4859
June	1st to 10th	Day	14% 9% 3 6% 6% 5% 4 4 7% 7% 36%	2850
	11th to 20th	Day	10% 8% 3 8% 7% 6% 6% 5% 7% 8% 33%	2850
	21st to end	Day	5% 5% 2 5% 6% 5% 5% 4 6% 7% 50%	2850
July	1st to 10th	Day	2 2 1 3 2 2 4 3 5% 6% 71%	4487
	11th to 20th	Day	2 2 1 3 2 3 2 2 3 5% 75%	4420
	21st to end	Day	2 2 1 2 3 3 3 3 5% 6% 70%	4790
August	1st to 10th	Day	3 2 1 3 3 3 4 3 5% 8% 67%	4401
	11th to 20th	Day	2 2 1 4 3 3 4 4 6% 8% 63%	4237
	21st to end	Day	3 3 1 4 4 4 4 4 6% 7% 59%	4225
September	1st to 10th	Day	4 3 1 4 2 3 5% 3 5% 6% 64%	2280
	11th to 20th	Day	6% 4 2 6% 4 5% 5% 5% 7% 8% 49%	2204
	21st to end	Day	7% 4 2 7% 4 4 5% 4 6% 7% 50%	2090
October	1st to 10th	Day	6% 5% 1 5% 3 4 4 3 6% 8% 55%	3283
	11th to 20th	Day	6% 6% 2 6% 5% 5% 7% 4 7% 9% 43%	3002
	21st to end	Day	13% 8% 2 7% 5% 5% 7% 5% 8% 7% 33%	3101
November	1st to 10th	Day	17% 12% 3 9% 6% 5% 5% 3 5% 7% 28%	1764
	11th to 20th	Day	14% 15% 4 8% 7% 5% 4 3 5% 4 29%	1625
	21st to end	Day	15% 19% 5% 11% 8% 4 4 4 6% 5% 20%	1458
December	1st to 10th	Day	11% 15% 5% 14% 8% 5% 5% 5% 5% 6% 21%	1400
	11th to 20th	Day	18% 24% 6% 12% 6% 3 3 4 4 5% 15%	1752
	21st to end	Day	14% 22% 7% 11% 6% 5% 5% 4 6% 6% 14%	2559
January	1st to 10th	Night	17% 25% 6% 11% 5% 5% 5% 3 5% 4 14%	4406
	11th to 20th	Night	15% 15% 5% 10% 6% 4 4 3 5% 9% 23%	4382
	21st to end	Night	24% 29% 5% 9% 5% 4 4 3 3 3 12%	4862
February	1st to 10th	Night	12% 17% 4 9% 5% 4 5% 4 6% 7% 27%	2647
	11th to 20th	Night	10% 13% 4 8% 5% 6% 4 4 7% 6% 33%	2336
	21st to end	Night	7% 11% 4 8% 5% 5% 5% 4 7% 6% 36%	1884
March	1st to 10th	Night	6% 11% 3 7% 5% 5% 5% 4 8% 10% 36%	3736
	11th to 20th	Night	8% 8% 3 5% 4 3 4 3 4 5% 54%	3722
	21st to end	Night	13% 10% 4 8% 5% 6% 7% 6% 7% 8% 26%	3488
April	1st to 10th	Night	10% 8% 3 6% 6% 5% 5% 5% 8% 8% 37%	1900
	11th to 20th	Night	7% 8% 3 9% 7% 6% 5% 4 5% 7% 39%	1829
	21st to end	Night	6% 7% 3 7% 6% 6% 5% 5% 8% 7% 41%	1691
May	1st to 10th	Night	9% 6% 2 6% 5% 5% 6% 5% 8% 9% 39%	2540
	11th to 20th	Night	5% 4 2 5% 4 4 5% 5% 7% 8% 52%	2516
	21st to end	Night	10% 8% 3 8% 5% 5% 5% 5% 7% 8% 37%	2712
June	1st to 10th	Night	9% 6% 3 6% 5% 4 5% 5% 8% 7% 42%	1330
	11th to 20th	Night	7% 6% 2 8% 5% 4 5% 5% 7% 10% 41%	1330
	21st to end	Night	4 3 2 5% 4 3 5% 4 7% 8% 56%	1330
July	1st to 10th	Night	1 1 1 2 2 3 3 3 4 6% 75%	2468
	11th to 20th	Night	1 1 1 1 2 3 2 4 5% 80%	2540
	21st to end	Night	1 1 2 2 2 2 2 4 6% 78%	2762
August	1st to 10th	Night	3 3 1 3 2 2 3 2 5% 7% 70%	2529
	11th to 20th	Night	1 2 1 4 2 3 4 3 5% 9% 66%	2592
	21st to end	Night	3 2 1 4 3 3 5% 4 6% 7% 62%	3448
September	1st to 10th	Night	3 1 1 2 3 3 4 3 6% 7% 66%	1900
	11th to 20th	Night	5% 4 2 5% 4 3 5% 4 6% 9% 53%	1976
	21st to end	Night	7% 4 1 4 3 3 4 3 7% 7% 57%	2090
October	1st to 10th	Night	6% 3 1 5% 3 3 3 3 6% 8% 59%	3695
	11th to 20th	Night	8% 5% 2 5% 4 5% 4 4 6% 9% 48%	3931
	21st to end	Night	12% 8% 2 8% 4 5% 5% 5% 8% 7% 38%	4457
November	1st to 10th	Night	17% 13% 4 7% 4 4 5% 5% 6% 7% 29%	2535
	11th to 20th	Night	15% 14% 4 8% 5% 4 5% 5% 6% 5% 29%	2770
	21st to end	Night	16% 19% 6% 9% 5% 4 3 3 5% 5% 24%	2920
December	1st to 10th	Night	12% 17% 4 12% 6% 5% 5% 3 5% 6% 25%	3000
	11th to 20th	Night	16% 24% 8% 12% 6% 4 4 3 4 4 15%	3660
	21st to end	Night	16% 24% 5% 11% 5% 4 4 4 6% 5% 15%	5199

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	69% 11% 8% 9% 3	2539
	11th to 20th	Day	61% 7% 13% 13% 3 4	2540
	21st to end	Day	75% 9% 7% 7% 2	2794
February	1st to 10th	Day	58% 10% 14% 11% 6% 1	1529
	11th to 20th	Day	51% 11% 15% 14% 8%	1739
	21st to end	Day	54% 9% 13% 15% 9% 1	1570
March	1st to 10th	Day	48% 12% 14% 15% 11% 1	3138
	11th to 20th	Day	34% 9% 21% 30% 6%	3254
	21st to end	Day	52% 15% 14% 13% 5%	4165
April	1st to 10th	Day	52% 9% 15% 17% 6% 1	2280
	11th to 20th	Day	46% 10% 15% 19% 10% 1	2302
	21st to end	Day	45% 10% 14% 19% 8% 3	2487
May	1st to 10th	Day	35% 8% 13% 29% 15% 1	4420
	11th to 20th	Day	33% 9% 15% 29% 13% 1	4380
	21st to end	Day	46% 15% 15% 18% 6%	4860
June	1st to 10th	Day	45% 6% 11% 19% 14% 4	2850
	11th to 20th	Day	45% 10% 12% 19% 11% 3	2850
	21st to end	Day	30% 7% 13% 26% 19% 4	2850
July	1st to 10th	Day	13% 5% 8% 18% 30% 26%	4418
	11th to 20th	Day	13% 3 6% 12% 29% 37%	4345
	21st to end	Day	14% 4 7% 23% 30% 22%	4639
August	1st to 10th	Day	16% 5% 8% 28% 32% 11%	4384
	11th to 20th	Day	18% 6% 11% 39% 22% 4	4279
	21st to end	Day	22% 6% 14% 32% 22% 3	4224
September	1st to 10th	Day	19% 7% 12% 30% 25% 7%	2280
	11th to 20th	Day	31% 9% 12% 24% 20% 4	2204
	21st to end	Day	32% 8% 17% 27% 12% 3	2090
October	1st to 10th	Day	28% 6% 19% 35% 12%	3283
	11th to 20th	Day	36% 8% 18% 23% 14%	3002
	21st to end	Day	43% 13% 18% 17% 9% 1	3101
November	1st to 10th	Day	56% 10% 14% 14% 5% 1	1764
	11th to 20th	Day	59% 8% 14% 13% 4 2	1625
	21st to end	Day	65% 9% 11% 10% 3 1	1458
December	1st to 10th	Day	64% 8% 11% 12% 5%	1400
	11th to 20th	Day	72% 8% 10% 6% 3	1754
	21st to end	Day	68% 11% 10% 7% 4	2559
January	1st to 10th	Night	70% 9% 8% 9% 3	4406
	11th to 20th	Night	58% 7% 12% 16% 5% 2	4420
	21st to end	Night	76% 9% 8% 6% 2	4862
February	1st to 10th	Night	55% 9% 15% 13% 7% 2	2647
	11th to 20th	Night	50% 9% 15% 17% 8% 1	2338
	21st to end	Night	44% 9% 17% 16% 12% 1	1884
March	1st to 10th	Night	37% 11% 19% 21% 11% 1	3736
	11th to 20th	Night	32% 6% 21% 33% 7%	3723
	21st to end	Night	47% 15% 15% 17% 6%	3488
April	1st to 10th	Night	42% 8% 17% 24% 8% 1	1900
	11th to 20th	Night	44% 7% 14% 21% 13% 2	1829
	21st to end	Night	38% 8% 14% 24% 14% 2	1691
May	1st to 10th	Night	34% 8% 14% 25% 18% 1	2540
	11th to 20th	Night	25% 9% 13% 32% 18% 3	2516
	21st to end	Night	38% 12% 18% 22% 9%	2712
June	1st to 10th	Night	37% 9% 11% 22% 17% 5%	1330
	11th to 20th	Night	36% 8% 16% 22% 14% 4	1330
	21st to end	Night	23% 7% 12% 28% 24% 6%	1330
July	1st to 10th	Night	11% 4 7% 19% 33% 27%	2428
	11th to 20th	Night	9% 3 7% 14% 21% 47%	2492
	21st to end	Night	9% 2 5% 23% 32% 29%	2674
August	1st to 10th	Night	15% 4 7% 25% 33% 17%	2521
	11th to 20th	Night	16% 5% 11% 36% 28% 5%	2616
	21st to end	Night	20% 6% 13% 30% 26% 5%	3448
September	1st to 10th	Night	16% 6% 9% 30% 28% 11%	1900
	11th to 20th	Night	28% 7% 12% 25% 23% 6%	1976
	21st to end	Night	26% 7% 17% 32% 14% 5%	2090
October	1st to 10th	Night	24% 5% 17% 37% 16%	3695
	11th to 20th	Night	33% 8% 16% 27% 16%	3931
	21st to end	Night	41% 11% 17% 22% 8% 1	4457
November	1st to 10th	Night	53% 10% 17% 13% 6% 1	2535
	11th to 20th	Night	55% 10% 15% 14% 5% 2	2770
	21st to end	Night	62% 7% 12% 13% 5%	2920
December	1st to 10th	Night	60% 8% 13% 15% 3	3000
	11th to 20th	Night	72% 10% 8% 6% 3	3657
	21st to end	Night	68% 10% 9% 8% 5%	5199

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	29% 9% 22% 26% 12% 2	180
	11th to 20th	Day	30% 7% 28% 21% 11% 3	180
	21st to end	Day	29% 7% 26% 29% 8% 1	198
February	1st to 10th	Day	20% 16% 37% 21% 6%	189
	11th to 20th	Day	19% 14% 29% 29% 8% 1	396
	21st to end	Day	16% 15% 32% 25% 12% 1	382
March	1st to 10th	Day	20% 21% 29% 20% 10% 1	460
	11th to 20th	Day	17% 15% 24% 26% 17%	460
	21st to end	Day	19% 20% 28% 23% 8% 2	506
April	1st to 10th	Day	23% 14% 32% 21% 9% 2	460
	11th to 20th	Day	17% 22% 30% 18% 9% 3	452
	21st to end	Day	15% 20% 28% 27% 9% 2	460
May	1st to 10th	Day	12% 17% 32% 26% 10% 3	463
	11th to 20th	Day	16% 13% 29% 26% 13% 2	488
	21st to end	Day	12% 13% 28% 29% 15% 4	549
June	1st to 10th	Day	17% 13% 25% 28% 14% 3	680
	11th to 20th	Day	13% 16% 28% 28% 12% 3	680
	21st to end	Day	5% 10% 26% 34% 22% 3	680
July	1st to 10th	Day	5% 11% 30% 37% 15% 3	527
	11th to 20th	Day	4 11% 34% 33% 15% 3	484
	21st to end	Day	3 12% 29% 34% 17% 5%	531
August	1st to 10th	Day	6% 7% 26% 36% 19% 5%	487
	11th to 20th	Day	4 7% 28% 33% 20% 8%	477
	21st to end	Day	6% 12% 28% 29% 19% 6%	539
September	1st to 10th	Day	8% 10% 27% 28% 22% 6%	490
	11th to 20th	Day	9% 13% 27% 30% 17% 5%	490
	21st to end	Day	12% 18% 25% 27% 15% 3	490
October	1st to 10th	Day	12% 11% 30% 27% 17% 2	490
	11th to 20th	Day	17% 9% 29% 29% 14% 3	395
	21st to end	Day	24% 10% 28% 30% 5% 3	330
November	1st to 10th	Day	25% 8% 26% 31% 10% 1	300
	11th to 20th	Day	23% 14% 28% 23% 11%	213
	21st to end	Day	27% 10% 28% 22% 13% 2	200
December	1st to 10th	Day	22% 10% 23% 24% 18% 4	200
	11th to 20th	Day	24% 8% 27% 31% 10% 1	200
	21st to end	Day	23% 6% 26% 34% 10%	204
January	1st to 10th	Night	30% 7% 26% 26% 10% 2	760
	11th to 20th	Night	25% 5% 24% 30% 13% 3	760
	21st to end	Night	26% 3 19% 35% 15% 2	836
February	1st to 10th	Night	22% 6% 26% 31% 13% 3	760
	11th to 20th	Night	17% 6% 27% 34% 15% 1	744
	21st to end	Night	14% 9% 23% 34% 17% 4	628
March	1st to 10th	Night	16% 5% 26% 34% 18% 1	760
	11th to 20th	Night	16% 7% 24% 35% 18% 1	760
	21st to end	Night	17% 7% 26% 33% 15% 2	836
April	1st to 10th	Night	13% 8% 20% 34% 23% 2	760
	11th to 20th	Night	11% 9% 27% 35% 16% 2	701
	21st to end	Night	8% 11% 25% 36% 19% 2	551
May	1st to 10th	Night	10% 8% 20% 37% 24% 2	380
	11th to 20th	Night	11% 5% 17% 34% 28% 5%	374
	21st to end	Night	12% 7% 19% 32% 26% 4	411
June	1st to 10th	Night	10% 7% 23% 35% 22% 3	380
	11th to 20th	Night	10% 5% 23% 38% 20% 3	380
	21st to end	Night	4 4 18% 41% 30% 3	380
July	1st to 10th	Night	3 3 14% 41% 35% 4	370
	11th to 20th	Night	2 3 19% 44% 30% 2	368
	21st to end	Night	1 2 13% 42% 38% 4	416
August	1st to 10th	Night	4 2 12% 29% 44% 8%	378
	11th to 20th	Night	2 3 13% 32% 42% 7%	432
	21st to end	Night	4 5% 16% 36% 35% 5%	799
September	1st to 10th	Night	3 3 18% 36% 32% 8%	760
	11th to 20th	Night	7% 4 12% 34% 36% 7%	760
	21st to end	Night	10% 5% 15% 37% 27% 7%	760
October	1st to 10th	Night	12% 4 16% 38% 28% 1	760
	11th to 20th	Night	12% 8% 18% 34% 26% 2	760
	21st to end	Night	18% 5% 21% 37% 15% 3	836
November	1st to 10th	Night	25% 6% 17% 39% 11% 1	780
	11th to 20th	Night	25% 7% 24% 29% 14% 1	800
	21st to end	Night	25% 6% 21% 30% 17% 2	920
December	1st to 10th	Night	22% 5% 20% 35% 15% 3	1000
	11th to 20th	Night	28% 5% 21% 35% 10% 1	1000
	21st to end	Night	29% 6% 23% 32% 10% 1	1022

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