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 2026-10-29.

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	5% 8% 2 6% 5% 5% 5% 4 6% 8% 45%	154422
	Night	6% 9% 3 7% 5% 5% 5% 4 7% 9% 41%	146354
Transparency	Day	34% 5% 16% 26% 14% 5%	154149
	Night	37% 6% 19% 25% 11% 2	146209
Seeing	Day	16% 20% 33% 21% 9% 2	17167
	Night	14% 13% 34% 27% 11% 1	25702

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	7% 17% 6% 13% 7% 6% 6% 5% 8% 9% 16%	4723
	11th to 20th	Day	5% 10% 3 8% 3 4 4 4 7% 7% 45%	4716
	21st to end	Day	11% 15% 3 7% 6% 6% 5% 3 5% 5% 34%	5186
February	1st to 10th	Day	5% 16% 5% 11% 7% 7% 4 5% 7% 10% 21%	1854
	11th to 20th	Day	5% 15% 5% 10% 6% 6% 6% 5% 7% 9% 27%	1845
	21st to end	Day	5% 16% 5% 12% 7% 7% 6% 5% 9% 6% 21%	1693
March	1st to 10th	Day	3 11% 4 8% 6% 6% 7% 5% 8% 9% 31%	4618
	11th to 20th	Day	4 13% 3 7% 6% 7% 6% 5% 7% 7% 34%	5020
	21st to end	Day	8% 15% 3 9% 7% 7% 7% 5% 8% 9% 22%	5921
April	1st to 10th	Day	7% 13% 3 9% 8% 7% 6% 6% 7% 8% 24%	2520
	11th to 20th	Day	6% 10% 4 8% 7% 6% 6% 6% 8% 9% 31%	2492
	21st to end	Day	5% 9% 4 9% 7% 7% 6% 5% 8% 9% 33%	2798
May	1st to 10th	Day	4 6% 2 5% 4 5% 5% 4 7% 8% 51%	8195
	11th to 20th	Day	5% 6% 2 5% 4 5% 6% 5% 9% 12% 39%	8160
	21st to end	Day	6% 8% 3 7% 5% 5% 6% 4 7% 10% 40%	8993
June	1st to 10th	Day	10% 7% 3 6% 6% 5% 5% 5% 7% 8% 37%	2940
	11th to 20th	Day	5% 6% 3 7% 6% 5% 5% 6% 7% 11% 39%	2993
	21st to end	Day	4 4 2 6% 5% 5% 5% 5% 7% 9% 48%	3150
July	1st to 10th	Day	1 2 2 2 2 3 2 3 5% 77%	8460
	11th to 20th	Day	2 2 1 2 2 2 3 2 3 4 77%	8220
	21st to end	Day	2 2 1 2 2 2 3 3 4 7% 74%	8916
August	1st to 10th	Day	1 1 1 2 2 2 2 3 5% 7% 74%	6441
	11th to 20th	Day	2 1 1 3 3 4 4 4 7% 9% 62%	6036
	21st to end	Day	4 3 1 5% 4 3 4 4 6% 9% 57%	6166
September	1st to 10th	Day	3 2 1 4 4 3 4 4 6% 8% 61%	2520
	11th to 20th	Day	5% 5% 2 5% 5% 5% 5% 5% 7% 8% 49%	2520
	21st to end	Day	7% 5% 2 6% 5% 5% 5% 4 7% 7% 48%	2252
October	1st to 10th	Day	5% 3 2 5% 4 4 5% 4 7% 9% 52%	3380
	11th to 20th	Day	8% 5% 2 7% 5% 6% 6% 5% 8% 9% 38%	3361
	21st to end	Day	13% 8% 2 6% 5% 5% 6% 4 8% 10% 33%	3310
November	1st to 10th	Day	14% 14% 3 8% 6% 6% 5% 5% 8% 9% 24%	1766
	11th to 20th	Day	11% 16% 4 11% 8% 6% 6% 4 5% 6% 22%	1680
	21st to end	Day	8% 15% 5% 10% 7% 7% 7% 4 7% 8% 23%	1680
December	1st to 10th	Day	6% 9% 3 7% 7% 8% 5% 5% 7% 10% 33%	2700
	11th to 20th	Day	7% 18% 5% 11% 6% 7% 7% 6% 8% 8% 16%	3105
	21st to end	Day	10% 18% 6% 13% 8% 5% 6% 4 6% 8% 17%	4092
January	1st to 10th	Night	9% 20% 6% 13% 7% 6% 6% 5% 7% 7% 14%	8172
	11th to 20th	Night	7% 8% 4 8% 4 3 4 4 6% 9% 43%	8182
	21st to end	Night	10% 15% 3 7% 6% 5% 5% 4 6% 6% 33%	8994
February	1st to 10th	Night	6% 14% 5% 10% 7% 5% 7% 6% 7% 9% 23%	2761
	11th to 20th	Night	6% 12% 4 8% 6% 5% 6% 4 9% 9% 31%	2662
	21st to end	Night	5% 15% 4 11% 7% 6% 6% 6% 6% 8% 26%	2113
March	1st to 10th	Night	3 9% 3 6% 5% 6% 7% 7% 10% 11% 33%	5496
	11th to 20th	Night	5% 13% 4 7% 4 5% 5% 4 6% 9% 40%	5182
	21st to end	Night	8% 13% 4 8% 6% 6% 7% 6% 8% 9% 24%	5283
April	1st to 10th	Night	5% 11% 4 8% 7% 6% 7% 4 8% 11% 29%	2100
	11th to 20th	Night	4 8% 3 7% 5% 5% 6% 6% 8% 11% 38%	2079
	21st to end	Night	4 8% 3 7% 5% 6% 5% 6% 9% 10% 38%	1818
May	1st to 10th	Night	4 6% 2 5% 3 4 4 4 5% 8% 54%	4724
	11th to 20th	Night	4 7% 2 6% 4 4 6% 6% 9% 13% 39%	4700
	21st to end	Night	4 7% 2 5% 4 5% 6% 6% 9% 13% 40%	5178
June	1st to 10th	Night	6% 6% 2 5% 6% 5% 5% 6% 9% 10% 42%	1680
	11th to 20th	Night	3 6% 2 6% 6% 6% 6% 6% 7% 10% 44%	1618
	21st to end	Night	2 2 2 4 5% 4 6% 5% 6% 9% 54%	1470
July	1st to 10th	Night	1 1 1 2 1 2 3 3 5% 8% 74%	4476
	11th to 20th	Night	1 1 1 1 1 2 2 3 5% 81%	4740
	21st to end	Night	1 1 1 2 2 2 3 3 4 8% 75%	5152
August	1st to 10th	Night	1 2 2 2 2 2 5% 6% 77%	3709
	11th to 20th	Night	2 1 1 2 2 3 3 3 6% 8% 70%	4021
	21st to end	Night	4 2 1 3 2 3 3 3 5% 10% 65%	5000
September	1st to 10th	Night	2 2 1 3 3 4 4 4 6% 8% 63%	2100
	11th to 20th	Night	5% 4 1 5% 4 4 5% 4 6% 8% 54%	2100
	21st to end	Night	6% 5% 2 4 4 4 5% 4 7% 10% 50%	2366
October	1st to 10th	Night	5% 5% 2 4 4 4 4 4 7% 11% 50%	4040
	11th to 20th	Night	8% 6% 2 5% 5% 5% 5% 5% 7% 10% 41%	4017
	21st to end	Night	11% 7% 2 5% 4 4 5% 5% 8% 12% 36%	4666
November	1st to 10th	Night	13% 13% 3 7% 5% 5% 6% 5% 9% 10% 24%	2749
	11th to 20th	Night	13% 14% 4 8% 7% 5% 5% 6% 8% 8% 22%	2940
	21st to end	Night	8% 14% 5% 11% 7% 6% 6% 5% 7% 8% 24%	2940
December	1st to 10th	Night	6% 9% 3 6% 7% 8% 6% 5% 7% 9% 33%	4700
	11th to 20th	Night	10% 17% 5% 11% 9% 7% 6% 5% 6% 8% 15%	5320
	21st to end	Night	14% 17% 6% 13% 7% 5% 5% 4 6% 8% 15%	7106

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	58% 9% 16% 14% 3	4723
	11th to 20th	Day	35% 6% 14% 31% 10% 3	4740
	21st to end	Day	49% 5% 14% 21% 10%	5187
February	1st to 10th	Day	55% 8% 17% 14% 5% 1	1854
	11th to 20th	Day	51% 8% 17% 15% 8% 1	1854
	21st to end	Day	57% 5% 18% 15% 3 1	1693
March	1st to 10th	Day	45% 4 17% 17% 16% 1	4618
	11th to 20th	Day	44% 3 15% 32% 6%	5020
	21st to end	Day	54% 6% 20% 16% 4	5921
April	1st to 10th	Day	51% 6% 20% 19% 3	2520
	11th to 20th	Day	44% 7% 20% 18% 9% 2	2492
	21st to end	Day	44% 5% 21% 21% 9% 1	2798
May	1st to 10th	Day	29% 3 14% 36% 17% 2	8195
	11th to 20th	Day	32% 4 27% 30% 8%	8163
	21st to end	Day	37% 4 23% 31% 5%	8994
June	1st to 10th	Day	41% 4 18% 24% 11% 2	2940
	11th to 20th	Day	35% 3 24% 25% 12% 1	2993
	21st to end	Day	29% 4 22% 27% 15% 2	3150
July	1st to 10th	Day	11% 2 12% 31% 25% 19%	8391
	11th to 20th	Day	12% 2 6% 24% 29% 27%	8145
	21st to end	Day	12% 3 8% 31% 36% 10%	8723
August	1st to 10th	Day	10% 2 7% 27% 34% 20%	6424
	11th to 20th	Day	18% 4 18% 42% 16% 2	6077
	21st to end	Day	24% 3 17% 32% 21% 3	6165
September	1st to 10th	Day	21% 3 16% 30% 24% 7%	2520
	11th to 20th	Day	30% 4 17% 25% 19% 5%	2520
	21st to end	Day	34% 4 19% 26% 14% 4	2252
October	1st to 10th	Day	27% 4 17% 38% 14% 1	3380
	11th to 20th	Day	38% 7% 16% 24% 15%	3361
	21st to end	Day	43% 5% 17% 21% 11% 3	3310
November	1st to 10th	Day	52% 5% 19% 16% 6% 1	1766
	11th to 20th	Day	60% 8% 16% 10% 4 2	1680
	21st to end	Day	54% 10% 16% 13% 6% 1	1680
December	1st to 10th	Day	40% 11% 21% 23% 6%	2700
	11th to 20th	Day	59% 9% 19% 11% 2	3108
	21st to end	Day	63% 6% 16% 10% 4	4092
January	1st to 10th	Night	63% 8% 14% 12% 3	8172
	11th to 20th	Night	37% 7% 15% 29% 11% 2	8220
	21st to end	Night	49% 7% 14% 21% 9%	8994
February	1st to 10th	Night	54% 9% 18% 14% 5%	2761
	11th to 20th	Night	44% 10% 21% 17% 7% 1	2664
	21st to end	Night	52% 9% 16% 18% 5%	2113
March	1st to 10th	Night	39% 5% 20% 24% 11% 1	5496
	11th to 20th	Night	40% 4 21% 28% 7%	5183
	21st to end	Night	51% 9% 20% 17% 3	5283
April	1st to 10th	Night	46% 8% 22% 21% 4	2100
	11th to 20th	Night	35% 8% 27% 19% 10% 1	2079
	21st to end	Night	37% 6% 23% 25% 8%	1818
May	1st to 10th	Night	27% 3 18% 37% 15%	4721
	11th to 20th	Night	31% 5% 28% 31% 5%	4700
	21st to end	Night	31% 6% 34% 26% 4	5182
June	1st to 10th	Night	33% 5% 26% 24% 11% 1	1680
	11th to 20th	Night	31% 5% 28% 25% 10%	1618
	21st to end	Night	24% 5% 24% 31% 12% 3	1470
July	1st to 10th	Night	11% 4 17% 32% 24% 13%	4436
	11th to 20th	Night	9% 2 10% 28% 30% 21%	4692
	21st to end	Night	10% 2 13% 38% 30% 8%	5040
August	1st to 10th	Night	9% 3 9% 31% 36% 13%	3701
	11th to 20th	Night	13% 4 30% 41% 11% 2	4046
	21st to end	Night	17% 4 21% 38% 18% 2	5000
September	1st to 10th	Night	18% 4 21% 31% 21% 5%	2100
	11th to 20th	Night	26% 5% 17% 28% 20% 4	2100
	21st to end	Night	28% 5% 22% 28% 13% 3	2366
October	1st to 10th	Night	27% 5% 18% 40% 9%	4040
	11th to 20th	Night	35% 6% 20% 26% 13%	4017
	21st to end	Night	37% 6% 23% 23% 9% 2	4666
November	1st to 10th	Night	51% 8% 18% 16% 6%	2749
	11th to 20th	Night	54% 8% 19% 14% 4 2	2940
	21st to end	Night	53% 8% 18% 13% 6% 1	2940
December	1st to 10th	Night	41% 12% 18% 25% 5%	4700
	11th to 20th	Night	62% 8% 16% 11% 2	5316
	21st to end	Night	65% 6% 16% 11% 2	7106

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	21% 13% 27% 23% 14% 2	220
	11th to 20th	Day	21% 5% 28% 29% 15% 2	220
	21st to end	Day	21% 11% 31% 24% 11% 2	242
February	1st to 10th	Day	22% 24% 30% 19% 5%	394
	11th to 20th	Day	26% 18% 32% 17% 5% 1	425
	21st to end	Day	21% 26% 31% 15% 6% 1	427
March	1st to 10th	Day	20% 28% 29% 17% 5% 1	540
	11th to 20th	Day	25% 22% 26% 18% 9%	540
	21st to end	Day	25% 27% 29% 15% 4	594
April	1st to 10th	Day	23% 24% 30% 16% 5% 2	540
	11th to 20th	Day	22% 26% 31% 15% 5% 1	532
	21st to end	Day	19% 26% 32% 14% 7% 2	540
May	1st to 10th	Day	15% 22% 34% 21% 7% 1	543
	11th to 20th	Day	24% 17% 29% 21% 7% 2	568
	21st to end	Day	15% 22% 31% 22% 9% 1	617
June	1st to 10th	Day	17% 23% 33% 19% 7% 1	570
	11th to 20th	Day	18% 26% 38% 13% 5% 1	623
	21st to end	Day	9% 23% 37% 21% 9% 1	780
July	1st to 10th	Day	4 22% 44% 22% 6% 1	650
	11th to 20th	Day	8% 19% 40% 22% 9% 1	564
	21st to end	Day	6% 15% 41% 27% 10% 2	619
August	1st to 10th	Day	8% 13% 37% 30% 10% 2	567
	11th to 20th	Day	6% 11% 35% 33% 11% 3	557
	21st to end	Day	10% 17% 35% 23% 13% 3	627
September	1st to 10th	Day	7% 19% 34% 26% 11% 3	570
	11th to 20th	Day	10% 19% 36% 22% 10% 2	570
	21st to end	Day	15% 21% 30% 24% 9% 2	570
October	1st to 10th	Day	16% 16% 27% 24% 13% 3	570
	11th to 20th	Day	18% 18% 30% 22% 10% 3	570
	21st to end	Day	24% 17% 28% 20% 8% 3	413
November	1st to 10th	Day	27% 18% 27% 22% 6% 1	283
	11th to 20th	Day	25% 16% 24% 20% 10% 5%	220
	21st to end	Day	15% 14% 31% 24% 12% 5%	220
December	1st to 10th	Day	25% 10% 23% 20% 19% 4	220
	11th to 20th	Day	21% 13% 32% 22% 10% 2	220
	21st to end	Day	18% 12% 29% 27% 14% 1	242
January	1st to 10th	Night	26% 11% 30% 22% 10% 1	840
	11th to 20th	Night	19% 11% 32% 25% 12% 1	840
	21st to end	Night	17% 9% 29% 31% 12% 1	924
February	1st to 10th	Night	17% 13% 35% 28% 7%	840
	11th to 20th	Night	15% 14% 32% 29% 9% 1	824
	21st to end	Night	23% 13% 30% 23% 11%	692
March	1st to 10th	Night	15% 14% 32% 30% 9%	840
	11th to 20th	Night	15% 16% 34% 25% 10% 1	840
	21st to end	Night	18% 19% 38% 19% 5% 1	924
April	1st to 10th	Night	13% 18% 36% 25% 8% 1	840
	11th to 20th	Night	12% 20% 34% 26% 7% 1	831
	21st to end	Night	10% 23% 37% 23% 8%	558
May	1st to 10th	Night	10% 19% 33% 29% 8% 1	420
	11th to 20th	Night	12% 14% 35% 27% 11% 1	414
	21st to end	Night	10% 12% 41% 26% 11%	455
June	1st to 10th	Night	12% 15% 40% 24% 9%	420
	11th to 20th	Night	10% 25% 39% 20% 6%	420
	21st to end	Night	6% 18% 36% 30% 10%	420
July	1st to 10th	Night	4 13% 43% 32% 7%	410
	11th to 20th	Night	3 18% 45% 28% 5%	408
	21st to end	Night	3 15% 40% 32% 11%	460
August	1st to 10th	Night	3 13% 38% 29% 17%	418
	11th to 20th	Night	4 9% 35% 33% 17% 2	566
	21st to end	Night	6% 14% 33% 32% 13% 1	882
September	1st to 10th	Night	5% 13% 33% 30% 17% 2	840
	11th to 20th	Night	8% 10% 30% 30% 19% 3	840
	21st to end	Night	11% 14% 29% 28% 15% 2	840
October	1st to 10th	Night	12% 9% 31% 29% 18% 1	840
	11th to 20th	Night	15% 13% 29% 28% 14% 2	840
	21st to end	Night	20% 13% 31% 24% 9% 2	912
November	1st to 10th	Night	20% 10% 37% 27% 5%	820
	11th to 20th	Night	27% 11% 31% 20% 10% 1	840
	21st to end	Night	17% 10% 35% 23% 13% 2	840
December	1st to 10th	Night	19% 11% 30% 27% 12% 1	840
	11th to 20th	Night	21% 9% 39% 24% 7%	840
	21st to end	Night	21% 12% 36% 26% 5% 1	924

Page generated at 2026-10-26 01:37:45. Version ac07

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