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 2024-11-03.

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 6% 7% 41%	101918
	Night	7% 11% 4 8% 5% 5% 5% 4 7% 8% 37%	97118
Transparency	Day	39% 4 16% 21% 14% 5%	101686
	Night	42% 5% 19% 21% 10% 3	96996
Seeing	Day	16% 20% 33% 21% 9% 2	14650
	Night	14% 13% 34% 27% 11% 1	23267

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	11% 22% 7% 15% 7% 6% 5% 4 6% 5% 14%	2539
	11th to 20th	Day	8% 17% 5% 13% 5% 6% 5% 3 5% 5% 27%	2516
	21st to end	Day	20% 22% 4 9% 6% 5% 5% 4 6% 5% 15%	2794
February	1st to 10th	Day	5% 17% 5% 10% 7% 7% 5% 5% 7% 9% 22%	1676
	11th to 20th	Day	6% 15% 5% 10% 6% 5% 5% 5% 7% 9% 27%	1665
	21st to end	Day	5% 16% 5% 12% 7% 7% 7% 5% 8% 6% 21%	1536
March	1st to 10th	Day	4 14% 6% 10% 7% 7% 6% 4 7% 7% 27%	3138
	11th to 20th	Day	5% 12% 3 6% 5% 6% 5% 4 5% 6% 43%	3428
	21st to end	Day	10% 17% 4 10% 7% 6% 6% 5% 6% 6% 22%	4041
April	1st to 10th	Day	8% 14% 4 10% 8% 7% 6% 6% 7% 8% 22%	2280
	11th to 20th	Day	6% 11% 4 9% 8% 6% 6% 6% 8% 8% 29%	2252
	21st to end	Day	6% 10% 4 9% 7% 7% 6% 5% 8% 9% 29%	2532
May	1st to 10th	Day	6% 10% 3 7% 5% 6% 5% 4 8% 7% 40%	4420
	11th to 20th	Day	6% 8% 2 5% 4 5% 6% 4 8% 10% 43%	4377
	21st to end	Day	8% 12% 4 10% 7% 7% 7% 5% 7% 7% 27%	4813
June	1st to 10th	Day	11% 7% 3 7% 6% 5% 5% 5% 7% 8% 35%	2660
	11th to 20th	Day	6% 7% 3 8% 6% 5% 6% 6% 8% 11% 35%	2707
	21st to end	Day	4 4 2 5% 5% 5% 5% 6% 7% 9% 48%	2850
July	1st to 10th	Day	1 2 1 3 2 3 3 3 3 5% 74%	4548
	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	9% 5% 2 8% 5% 5% 5% 4 7% 7% 43%	1900
	11th to 20th	Day	9% 8% 3 8% 5% 5% 4 4 8% 9% 38%	1900
	21st to end	Day	13% 10% 3 8% 5% 6% 6% 5% 6% 7% 31%	1905
November	1st to 10th	Day	13% 13% 3 8% 6% 6% 4 5% 9% 8% 24%	1613
	11th to 20th	Day	11% 16% 4 11% 8% 6% 6% 4 5% 6% 22%	1520
	21st to end	Day	8% 15% 5% 11% 7% 7% 7% 4 7% 7% 23%	1520
December	1st to 10th	Day	8% 14% 4 9% 8% 7% 5% 5% 7% 8% 25%	1520
	11th to 20th	Day	8% 17% 5% 10% 6% 7% 7% 6% 7% 7% 20%	1925
	21st to end	Day	12% 17% 6% 14% 8% 5% 5% 3 5% 6% 19%	2794
January	1st to 10th	Night	11% 21% 7% 12% 7% 6% 6% 4 6% 6% 13%	4406
	11th to 20th	Night	11% 14% 8% 13% 6% 4 4 4 6% 9% 22%	4382
	21st to end	Night	16% 23% 5% 10% 6% 5% 4 4 6% 6% 14%	4862
February	1st to 10th	Night	7% 15% 5% 10% 7% 5% 7% 6% 7% 9% 22%	2499
	11th to 20th	Night	6% 12% 4 8% 6% 5% 6% 4 9% 9% 30%	2402
	21st to end	Night	5% 15% 4 11% 7% 6% 6% 6% 7% 8% 26%	1918
March	1st to 10th	Night	4 12% 5% 8% 6% 6% 7% 6% 9% 9% 27%	3736
	11th to 20th	Night	3 10% 3 7% 5% 4 5% 4 5% 6% 48%	3534
	21st to end	Night	8% 15% 4 9% 6% 7% 7% 6% 7% 7% 24%	3599
April	1st to 10th	Night	5% 12% 4 9% 8% 7% 7% 4 8% 10% 27%	1900
	11th to 20th	Night	4 8% 4 7% 5% 5% 6% 6% 8% 11% 37%	1879
	21st to end	Night	4 9% 3 7% 5% 6% 6% 7% 9% 10% 34%	1645
May	1st to 10th	Night	5% 9% 2 7% 5% 5% 4 4 5% 7% 46%	2540
	11th to 20th	Night	5% 7% 2 6% 4 4 5% 5% 7% 9% 46%	2516
	21st to end	Night	4 11% 3 8% 5% 6% 6% 6% 9% 12% 31%	2762
June	1st to 10th	Night	6% 6% 2 5% 6% 5% 5% 6% 9% 9% 40%	1520
	11th to 20th	Night	3 6% 2 7% 6% 6% 6% 7% 7% 11% 39%	1464
	21st to end	Night	3 3 2 4 4 5% 6% 5% 6% 10% 54%	1330
July	1st to 10th	Night	1 1 1 2 1 2 3 3 4 5% 76%	2402
	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	7% 6% 2 6% 5% 4 5% 4 7% 9% 45%	2280
	11th to 20th	Night	9% 8% 3 6% 5% 5% 5% 5% 7% 9% 39%	2280
	21st to end	Night	13% 8% 3 7% 4 4 4 5% 8% 9% 34%	2692
November	1st to 10th	Night	13% 13% 3 7% 5% 6% 6% 5% 8% 9% 24%	2507
	11th to 20th	Night	12% 14% 4 9% 7% 5% 5% 6% 8% 8% 22%	2660
	21st to end	Night	8% 14% 5% 12% 7% 6% 6% 5% 7% 8% 23%	2660
December	1st to 10th	Night	8% 16% 5% 9% 7% 5% 6% 5% 7% 8% 23%	2660
	11th to 20th	Night	11% 17% 5% 11% 9% 8% 6% 5% 6% 7% 17%	3280
	21st to end	Night	14% 17% 7% 14% 7% 5% 5% 4 6% 6% 15%	4862

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% 7% 14% 9% 2	2539
	11th to 20th	Day	57% 6% 14% 16% 5% 2	2540
	21st to end	Day	68% 4 14% 10% 3	2794
February	1st to 10th	Day	55% 8% 18% 14% 4 1	1676
	11th to 20th	Day	51% 8% 18% 15% 8% 1	1674
	21st to end	Day	58% 5% 17% 15% 4 1	1536
March	1st to 10th	Day	52% 4 14% 16% 13% 1	3138
	11th to 20th	Day	39% 3 18% 37% 3	3428
	21st to end	Day	58% 4 17% 17% 4	4041
April	1st to 10th	Day	54% 6% 19% 17% 3	2280
	11th to 20th	Day	46% 7% 20% 17% 8% 2	2252
	21st to end	Day	47% 5% 21% 18% 8% 1	2532
May	1st to 10th	Day	38% 3 17% 23% 18% 1	4420
	11th to 20th	Day	32% 3 23% 32% 10%	4380
	21st to end	Day	52% 4 23% 19% 3	4814
June	1st to 10th	Day	43% 5% 19% 22% 10% 2	2660
	11th to 20th	Day	37% 3 26% 24% 9% 1	2707
	21st to end	Day	29% 4 22% 27% 16% 2	2850
July	1st to 10th	Day	14% 2 10% 18% 27% 28%	4479
	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	38% 3 16% 30% 10% 2	1900
	11th to 20th	Day	40% 5% 20% 23% 13%	1900
	21st to end	Day	49% 4 15% 20% 11%	1905
November	1st to 10th	Day	53% 6% 18% 17% 7% 1	1613
	11th to 20th	Day	60% 8% 17% 10% 4 2	1520
	21st to end	Day	54% 9% 16% 13% 6% 1	1520
December	1st to 10th	Day	53% 8% 17% 17% 5%	1520
	11th to 20th	Day	57% 10% 18% 12% 2	1928
	21st to end	Day	65% 6% 12% 11% 6%	2794
January	1st to 10th	Night	66% 6% 14% 11% 4	4406
	11th to 20th	Night	59% 5% 13% 15% 7% 1	4420
	21st to end	Night	69% 5% 12% 10% 3	4862
February	1st to 10th	Night	54% 9% 18% 14% 4	2499
	11th to 20th	Night	45% 10% 22% 16% 6% 1	2404
	21st to end	Night	52% 8% 16% 17% 6%	1918
March	1st to 10th	Night	48% 4 19% 16% 11% 2	3736
	11th to 20th	Night	35% 4 25% 33% 4	3535
	21st to end	Night	54% 5% 21% 18% 1	3599
April	1st to 10th	Night	47% 8% 21% 20% 4	1900
	11th to 20th	Night	36% 8% 26% 19% 10% 1	1879
	21st to end	Night	39% 6% 23% 23% 8%	1645
May	1st to 10th	Night	34% 3 20% 26% 17% 1	2540
	11th to 20th	Night	32% 4 24% 33% 7%	2516
	21st to end	Night	40% 6% 34% 17% 3	2762
June	1st to 10th	Night	35% 6% 26% 22% 10% 1	1520
	11th to 20th	Night	33% 6% 31% 22% 9%	1464
	21st to end	Night	24% 5% 24% 31% 13% 3	1330
July	1st to 10th	Night	10% 4 12% 23% 27% 24%	2362
	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	35% 4 18% 30% 12% 1	2280
	11th to 20th	Night	40% 5% 20% 24% 11%	2280
	21st to end	Night	43% 5% 19% 22% 11% 1	2692
November	1st to 10th	Night	52% 8% 17% 17% 6%	2507
	11th to 20th	Night	54% 8% 19% 13% 4 2	2660
	21st to end	Night	54% 8% 18% 12% 6% 2	2660
December	1st to 10th	Night	56% 9% 14% 16% 5%	2660
	11th to 20th	Night	61% 7% 19% 10% 3	3276
	21st to end	Night	68% 5% 13% 12% 3	4862

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	23% 13% 23% 23% 16% 2	180
	11th to 20th	Day	21% 7% 29% 26% 15% 2	180
	21st to end	Day	25% 12% 29% 23% 11% 2	198
February	1st to 10th	Day	25% 24% 29% 17% 4	336
	11th to 20th	Day	28% 19% 30% 17% 4 1	365
	21st to end	Day	19% 27% 31% 16% 7% 1	366
March	1st to 10th	Day	18% 28% 30% 17% 5% 1	460
	11th to 20th	Day	20% 22% 28% 20% 10%	460
	21st to end	Day	23% 28% 29% 15% 4	506
April	1st to 10th	Day	25% 25% 31% 15% 3 2	460
	11th to 20th	Day	21% 27% 32% 15% 4 1	452
	21st to end	Day	20% 28% 30% 14% 6% 1	460
May	1st to 10th	Day	14% 24% 35% 21% 6%	463
	11th to 20th	Day	22% 15% 31% 23% 8% 2	488
	21st to end	Day	14% 22% 31% 23% 9% 1	529
June	1st to 10th	Day	15% 24% 33% 19% 8%	490
	11th to 20th	Day	16% 27% 37% 13% 5% 1	537
	21st to end	Day	9% 23% 37% 22% 9% 1	680
July	1st to 10th	Day	4 21% 44% 24% 7%	562
	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	22% 18% 29% 24% 5% 1	238
	11th to 20th	Day	23% 16% 26% 20% 11% 5%	180
	21st to end	Day	14% 13% 31% 23% 14% 6%	180
December	1st to 10th	Day	24% 9% 25% 20% 17% 4	180
	11th to 20th	Day	16% 13% 36% 23% 10% 3	180
	21st to end	Day	18% 12% 30% 26% 13% 1	198
January	1st to 10th	Night	27% 11% 29% 22% 11% 1	760
	11th to 20th	Night	20% 11% 32% 25% 11% 1	760
	21st to end	Night	19% 9% 29% 30% 11% 1	836
February	1st to 10th	Night	19% 13% 35% 25% 7% 1	760
	11th to 20th	Night	16% 14% 32% 28% 8% 1	744
	21st to end	Night	22% 11% 30% 24% 12%	628
March	1st to 10th	Night	14% 13% 32% 31% 9% 1	760
	11th to 20th	Night	13% 13% 36% 26% 11% 1	760
	21st to end	Night	17% 18% 39% 20% 6% 1	836
April	1st to 10th	Night	13% 18% 37% 24% 8% 1	760
	11th to 20th	Night	11% 19% 35% 26% 8% 1	751
	21st to end	Night	9% 23% 37% 23% 8%	505
May	1st to 10th	Night	10% 19% 32% 29% 9% 1	380
	11th to 20th	Night	10% 11% 37% 29% 12% 1	374
	21st to end	Night	9% 10% 41% 27% 11%	411
June	1st to 10th	Night	11% 14% 40% 25% 9%	380
	11th to 20th	Night	9% 24% 40% 21% 6%	380
	21st to end	Night	6% 17% 36% 31% 10% 1	380
July	1st to 10th	Night	4 12% 42% 34% 8%	370
	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% 38% 27% 5%	748
	11th to 20th	Night	26% 9% 32% 21% 11% 2	760
	21st to end	Night	17% 10% 35% 22% 13% 3	760
December	1st to 10th	Night	19% 10% 31% 28% 11% 1	760
	11th to 20th	Night	19% 7% 41% 25% 7% 1	760
	21st to end	Night	21% 11% 36% 26% 5% 1	836

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