Lake Wenatchee
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Wenatchee clear sky chart from 2005-11-06 to 2025-07-06.

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	6% 9% 3 7% 5% 5% 5% 4 7% 8% 41%	124383
	Night	7% 10% 3 7% 5% 5% 5% 4 7% 9% 38%	123095
Transparency	Day	38% 5% 17% 23% 13% 4	124151
	Night	40% 6% 19% 22% 10% 2	122970
Seeing	Day	16% 20% 33% 21% 9% 2	15449
	Night	14% 13% 34% 27% 11% 1	24101

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% 19% 7% 14% 6% 5% 6% 5% 7% 7% 17%	3639
	11th to 20th	Day	6% 12% 4 10% 4 4 4 4 6% 8% 40%	3616
	21st to end	Day	14% 16% 3 6% 4 4 4 3 5% 5% 34%	4004
February	1st to 10th	Day	5% 16% 5% 11% 7% 7% 5% 5% 7% 10% 22%	1765
	11th to 20th	Day	6% 15% 5% 10% 6% 5% 6% 5% 7% 9% 27%	1755
	21st to end	Day	5% 16% 5% 12% 7% 7% 7% 5% 9% 6% 20%	1615
March	1st to 10th	Day	3 11% 4 8% 6% 7% 7% 5% 8% 9% 31%	4518
	11th to 20th	Day	4 13% 3 7% 6% 7% 6% 5% 6% 7% 34%	4912
	21st to end	Day	8% 15% 3 9% 7% 7% 7% 5% 8% 9% 22%	5793
April	1st to 10th	Day	7% 13% 3 10% 8% 7% 7% 6% 8% 8% 23%	2400
	11th to 20th	Day	6% 10% 4 8% 7% 6% 6% 6% 8% 8% 31%	2372
	21st to end	Day	6% 9% 3 9% 7% 6% 6% 5% 8% 9% 31%	2665
May	1st to 10th	Day	5% 7% 2 5% 4 5% 4 4 7% 8% 48%	6320
	11th to 20th	Day	6% 7% 3 6% 5% 6% 6% 5% 9% 11% 36%	6277
	21st to end	Day	6% 8% 3 7% 5% 6% 6% 4 7% 10% 38%	6903
June	1st to 10th	Day	10% 7% 3 6% 6% 5% 5% 5% 7% 8% 38%	2800
	11th to 20th	Day	5% 7% 3 7% 6% 5% 6% 6% 8% 11% 37%	2850
	21st to end	Day	4 4 2 5% 5% 5% 5% 5% 7% 9% 49%	3000
July	1st to 10th	Day	1 2 1 3 2 3 3 3 3 5% 74%	4623
	11th to 20th	Day	2 2 1 2 2 2 3 2 4 4 75%	4420
	21st to end	Day	2 2 1 2 2 2 2 2 4 6% 76%	4790
August	1st to 10th	Day	1 2 1 2 2 3 3 4 6% 7% 69%	4401
	11th to 20th	Day	2 1 1 4 3 4 4 4 6% 10% 62%	4098
	21st to end	Day	5% 4 2 6% 4 4 4 4 6% 7% 55%	4242
September	1st to 10th	Day	3 2 1 3 3 3 4 4 6% 8% 63%	2280
	11th to 20th	Day	5% 5% 2 5% 5% 5% 5% 5% 7% 9% 47%	2280
	21st to end	Day	8% 6% 2 6% 5% 5% 5% 4 7% 7% 47%	2038
October	1st to 10th	Day	5% 3 2 5% 4 4 5% 4 7% 9% 51%	3180
	11th to 20th	Day	8% 6% 2 8% 5% 6% 5% 5% 8% 9% 37%	3161
	21st to end	Day	13% 8% 2 6% 4 5% 6% 4 7% 10% 33%	3137
November	1st to 10th	Day	13% 13% 3 8% 6% 6% 4 5% 8% 9% 24%	1680
	11th to 20th	Day	11% 16% 4 11% 8% 6% 6% 4 5% 6% 22%	1600
	21st to end	Day	8% 15% 5% 11% 7% 7% 7% 4 7% 8% 22%	1600
December	1st to 10th	Day	6% 9% 3 7% 7% 8% 5% 5% 7% 10% 34%	2620
	11th to 20th	Day	7% 18% 6% 11% 6% 7% 7% 6% 8% 8% 16%	3025
	21st to end	Day	10% 18% 6% 13% 8% 5% 6% 4 6% 7% 17%	4004
January	1st to 10th	Night	9% 21% 7% 14% 8% 6% 5% 4 6% 6% 14%	6306
	11th to 20th	Night	8% 10% 6% 10% 5% 3 4 3 6% 9% 36%	6282
	21st to end	Night	11% 17% 4 7% 6% 5% 4 4 5% 6% 31%	6952
February	1st to 10th	Night	7% 14% 5% 11% 7% 5% 7% 5% 7% 9% 22%	2630
	11th to 20th	Night	6% 12% 4 8% 6% 5% 6% 4 9% 10% 30%	2532
	21st to end	Night	5% 15% 4 11% 7% 6% 6% 6% 6% 8% 26%	2015
March	1st to 10th	Night	3 9% 3 6% 5% 6% 7% 6% 10% 11% 33%	5376
	11th to 20th	Night	5% 13% 4 7% 4 5% 5% 4 6% 8% 40%	5070
	21st to end	Night	8% 13% 4 8% 6% 6% 7% 6% 8% 9% 24%	5169
April	1st to 10th	Night	5% 11% 4 9% 7% 7% 7% 4 8% 11% 27%	2000
	11th to 20th	Night	4 8% 3 7% 5% 4 6% 6% 8% 11% 38%	1979
	21st to end	Night	4 8% 3 7% 5% 6% 5% 6% 9% 10% 36%	1731
May	1st to 10th	Night	5% 7% 2 6% 4 4 4 4 5% 8% 52%	3640
	11th to 20th	Night	5% 8% 3 7% 5% 5% 6% 5% 9% 11% 38%	3616
	21st to end	Night	4 8% 2 6% 4 5% 6% 6% 9% 12% 38%	3972
June	1st to 10th	Night	6% 6% 2 5% 6% 5% 5% 6% 9% 9% 42%	1600
	11th to 20th	Night	3 6% 2 6% 6% 6% 6% 6% 7% 10% 41%	1541
	21st to end	Night	2 2 2 4 4 4 6% 5% 6% 9% 54%	1400
July	1st to 10th	Night	1 1 1 2 1 2 3 3 4 6% 76%	2438
	11th to 20th	Night	1 2 2 2 2 2 3 5% 81%	2540
	21st to end	Night	1 1 1 1 2 3 3 4 7% 78%	2762
August	1st to 10th	Night	1 2 1 2 2 3 3 3 5% 8% 73%	2529
	11th to 20th	Night	2 1 1 3 2 3 3 3 6% 8% 68%	2736
	21st to end	Night	5% 2 1 4 3 3 4 4 6% 9% 60%	3434
September	1st to 10th	Night	2 2 1 3 3 4 4 4 6% 8% 63%	1900
	11th to 20th	Night	5% 4 1 5% 4 4 5% 4 7% 9% 52%	1900
	21st to end	Night	6% 5% 2 5% 4 4 5% 4 7% 9% 50%	2140
October	1st to 10th	Night	5% 5% 2 5% 4 4 4 4 7% 11% 50%	3800
	11th to 20th	Night	8% 6% 2 6% 5% 5% 5% 5% 7% 10% 41%	3777
	21st to end	Night	11% 7% 2 6% 4 4 5% 5% 8% 12% 36%	4421
November	1st to 10th	Night	12% 13% 3 7% 5% 5% 6% 5% 9% 10% 25%	2615
	11th to 20th	Night	12% 15% 4 9% 6% 5% 5% 5% 8% 8% 22%	2800
	21st to end	Night	8% 14% 5% 12% 7% 6% 6% 5% 7% 8% 24%	2800
December	1st to 10th	Night	6% 10% 3 6% 7% 8% 6% 5% 7% 9% 34%	4560
	11th to 20th	Night	10% 17% 5% 11% 9% 7% 6% 5% 6% 8% 15%	5180
	21st to end	Night	14% 17% 6% 13% 7% 5% 5% 4 6% 8% 15%	6952

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	60% 8% 15% 15% 3	3639
	11th to 20th	Day	41% 5% 16% 27% 10% 1	3640
	21st to end	Day	50% 4 16% 20% 10% 1	4004
February	1st to 10th	Day	55% 8% 17% 13% 5% 1	1765
	11th to 20th	Day	51% 8% 18% 14% 8% 1	1764
	21st to end	Day	57% 6% 18% 15% 4 1	1615
March	1st to 10th	Day	45% 4 17% 16% 16% 1	4518
	11th to 20th	Day	44% 3 15% 33% 6%	4912
	21st to end	Day	54% 6% 20% 16% 4	5793
April	1st to 10th	Day	53% 6% 19% 18% 3	2400
	11th to 20th	Day	44% 7% 20% 18% 9% 2	2372
	21st to end	Day	45% 5% 21% 20% 8% 1	2665
May	1st to 10th	Day	31% 4 14% 32% 18% 2	6320
	11th to 20th	Day	35% 4 27% 26% 8%	6280
	21st to end	Day	39% 3 24% 28% 6%	6904
June	1st to 10th	Day	41% 4 18% 24% 11% 2	2800
	11th to 20th	Day	36% 3 25% 25% 10% 1	2850
	21st to end	Day	29% 4 23% 27% 16% 2	3000
July	1st to 10th	Day	14% 2 10% 19% 27% 28%	4554
	11th to 20th	Day	13% 3 7% 17% 27% 33%	4345
	21st to end	Day	11% 3 8% 28% 36% 14%	4639
August	1st to 10th	Day	13% 3 9% 26% 35% 14%	4384
	11th to 20th	Day	19% 4 19% 38% 17% 3	4139
	21st to end	Day	29% 3 15% 26% 23% 4	4241
September	1st to 10th	Day	20% 3 16% 29% 24% 7%	2280
	11th to 20th	Day	31% 4 18% 23% 19% 5%	2280
	21st to end	Day	34% 4 19% 25% 14% 4	2038
October	1st to 10th	Day	27% 4 17% 37% 14% 1	3180
	11th to 20th	Day	39% 7% 17% 23% 14%	3161
	21st to end	Day	43% 4 17% 21% 12% 3	3137
November	1st to 10th	Day	52% 6% 19% 17% 6% 1	1680
	11th to 20th	Day	60% 8% 16% 10% 4 2	1600
	21st to end	Day	54% 9% 17% 13% 6% 1	1600
December	1st to 10th	Day	39% 11% 21% 23% 6%	2620
	11th to 20th	Day	60% 9% 19% 10% 2	3028
	21st to end	Day	64% 6% 16% 10% 4	4004
January	1st to 10th	Night	65% 7% 13% 12% 3	6306
	11th to 20th	Night	44% 5% 17% 25% 9% 1	6320
	21st to end	Night	52% 6% 13% 20% 9%	6952
February	1st to 10th	Night	54% 9% 17% 14% 5%	2630
	11th to 20th	Night	45% 10% 22% 16% 6% 1	2534
	21st to end	Night	52% 8% 16% 18% 5%	2015
March	1st to 10th	Night	39% 4 20% 24% 12% 1	5376
	11th to 20th	Night	40% 3 21% 28% 7%	5071
	21st to end	Night	52% 9% 20% 17% 3	5169
April	1st to 10th	Night	47% 8% 21% 20% 4	2000
	11th to 20th	Night	35% 8% 26% 20% 10% 1	1979
	21st to end	Night	37% 6% 23% 25% 8%	1731
May	1st to 10th	Night	29% 3 18% 32% 18% 1	3637
	11th to 20th	Night	35% 5% 24% 29% 6%	3616
	21st to end	Night	34% 6% 35% 22% 3	3972
June	1st to 10th	Night	34% 6% 27% 23% 11% 1	1600
	11th to 20th	Night	32% 6% 29% 23% 10%	1541
	21st to end	Night	24% 5% 25% 31% 12% 3	1400
July	1st to 10th	Night	11% 4 12% 23% 27% 23%	2398
	11th to 20th	Night	9% 2 10% 22% 32% 26%	2492
	21st to end	Night	8% 2 15% 31% 31% 13%	2674
August	1st to 10th	Night	12% 3 11% 31% 33% 10%	2521
	11th to 20th	Night	15% 4 30% 36% 13% 3	2761
	21st to end	Night	21% 5% 21% 31% 19% 3	3434
September	1st to 10th	Night	18% 4 20% 31% 21% 5%	1900
	11th to 20th	Night	27% 5% 17% 27% 20% 4	1900
	21st to end	Night	28% 5% 22% 27% 13% 4	2140
October	1st to 10th	Night	28% 5% 17% 40% 9%	3800
	11th to 20th	Night	36% 6% 20% 26% 12%	3777
	21st to end	Night	38% 6% 23% 22% 9% 2	4421
November	1st to 10th	Night	51% 8% 18% 17% 6%	2615
	11th to 20th	Night	54% 8% 19% 14% 4 2	2800
	21st to end	Night	54% 7% 19% 13% 6% 2	2800
December	1st to 10th	Night	40% 12% 17% 25% 5%	4560
	11th to 20th	Night	63% 7% 16% 11% 2	5176
	21st to end	Night	65% 6% 16% 11% 2	6952

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	22% 12% 26% 23% 15% 2	200
	11th to 20th	Day	21% 6% 30% 27% 15% 2	200
	21st to end	Day	23% 11% 29% 24% 11% 2	220
February	1st to 10th	Day	24% 25% 30% 18% 4	365
	11th to 20th	Day	27% 19% 32% 16% 5% 1	395
	21st to end	Day	19% 26% 32% 16% 7% 1	397
March	1st to 10th	Day	17% 29% 30% 17% 6% 1	500
	11th to 20th	Day	22% 23% 27% 19% 10%	500
	21st to end	Day	24% 28% 29% 15% 4	550
April	1st to 10th	Day	24% 25% 32% 14% 4 2	500
	11th to 20th	Day	21% 27% 31% 15% 4 1	492
	21st to end	Day	19% 27% 31% 14% 7% 2	500
May	1st to 10th	Day	16% 23% 34% 21% 6% 1	503
	11th to 20th	Day	23% 16% 30% 22% 7% 2	528
	21st to end	Day	15% 21% 31% 23% 9% 1	573
June	1st to 10th	Day	15% 24% 34% 19% 7% 1	530
	11th to 20th	Day	17% 27% 38% 13% 5% 1	580
	21st to end	Day	9% 23% 37% 22% 9% 1	730
July	1st to 10th	Day	4 21% 44% 24% 7%	587
	11th to 20th	Day	7% 18% 40% 24% 10% 1	484
	21st to end	Day	6% 13% 41% 28% 11% 2	531
August	1st to 10th	Day	7% 13% 37% 30% 11% 2	487
	11th to 20th	Day	6% 10% 35% 34% 13% 3	477
	21st to end	Day	10% 17% 35% 23% 12% 3	539
September	1st to 10th	Day	7% 20% 36% 24% 10% 2	490
	11th to 20th	Day	9% 20% 38% 23% 8% 1	490
	21st to end	Day	14% 21% 30% 24% 9% 2	490
October	1st to 10th	Day	17% 17% 27% 23% 13% 3	490
	11th to 20th	Day	18% 18% 30% 20% 11% 3	490
	21st to end	Day	25% 17% 28% 19% 8% 3	354
November	1st to 10th	Day	25% 18% 28% 23% 6% 1	257
	11th to 20th	Day	25% 17% 26% 19% 10% 5%	200
	21st to end	Day	14% 12% 32% 25% 13% 5%	200
December	1st to 10th	Day	23% 10% 24% 20% 20% 5%	200
	11th to 20th	Day	18% 12% 34% 24% 11% 3	200
	21st to end	Day	18% 11% 30% 27% 13% 1	220
January	1st to 10th	Night	26% 11% 30% 23% 10% 1	800
	11th to 20th	Night	20% 11% 32% 25% 11% 1	800
	21st to end	Night	18% 9% 30% 30% 12% 1	880
February	1st to 10th	Night	18% 13% 35% 26% 7% 1	800
	11th to 20th	Night	16% 14% 32% 28% 9% 1	784
	21st to end	Night	22% 11% 31% 24% 12%	660
March	1st to 10th	Night	14% 13% 33% 31% 9% 1	800
	11th to 20th	Night	14% 14% 35% 26% 10% 1	800
	21st to end	Night	18% 18% 39% 20% 6% 1	880
April	1st to 10th	Night	12% 18% 37% 24% 8% 1	800
	11th to 20th	Night	11% 20% 35% 25% 7% 1	791
	21st to end	Night	9% 22% 37% 24% 8%	531
May	1st to 10th	Night	11% 19% 32% 30% 8% 1	400
	11th to 20th	Night	11% 13% 36% 28% 11% 1	394
	21st to end	Night	10% 11% 40% 27% 11%	433
June	1st to 10th	Night	11% 15% 41% 24% 9%	400
	11th to 20th	Night	10% 24% 40% 20% 6%	400
	21st to end	Night	6% 18% 37% 30% 10% 1	400
July	1st to 10th	Night	4 13% 42% 33% 8%	380
	11th to 20th	Night	2 17% 45% 30% 6% 1	368
	21st to end	Night	3 14% 38% 32% 12%	416
August	1st to 10th	Night	3 12% 36% 31% 18% 1	378
	11th to 20th	Night	4 8% 34% 34% 18% 2	512
	21st to end	Night	6% 14% 35% 31% 13% 2	798
September	1st to 10th	Night	4 13% 34% 30% 17% 2	760
	11th to 20th	Night	8% 10% 29% 29% 21% 3	760
	21st to end	Night	10% 14% 29% 28% 16% 3	760
October	1st to 10th	Night	12% 9% 30% 28% 19% 1	760
	11th to 20th	Night	15% 12% 28% 28% 15% 2	760
	21st to end	Night	21% 12% 31% 24% 10% 2	836
November	1st to 10th	Night	19% 10% 37% 27% 6%	780
	11th to 20th	Night	26% 10% 32% 20% 10% 2	800
	21st to end	Night	17% 9% 35% 23% 13% 2	800
December	1st to 10th	Night	18% 11% 30% 28% 12% 1	800
	11th to 20th	Night	19% 8% 40% 25% 7% 1	800
	21st to end	Night	21% 12% 36% 26% 5% 1	880

Page generated at 2025-07-02 22:30:17. Version ac07

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