Lynnwood
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lynnwood clear sky chart from 2005-11-06 to 2025-07-21.

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	18% 10% 3 8% 5% 4 4 4 5% 6% 32%	124314
	Night	22% 11% 4 8% 5% 4 4 3 5% 5% 29%	123496
Transparency	Day	51% 9% 14% 17% 8% 1	124070
	Night	56% 8% 13% 16% 6% 1	123383
Seeing	Day	24% 9% 19% 26% 17% 5%	16005
	Night	28% 8% 14% 26% 20% 4	24340

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	33% 16% 4 12% 6% 4 4 3 4 4 9%	3179
	11th to 20th	Day	19% 10% 4 10% 6% 5% 5% 4 6% 7% 22%	3595
	21st to end	Day	28% 13% 3 8% 4 4 5% 3 4 5% 23%	4114
February	1st to 10th	Day	27% 14% 4 10% 6% 5% 5% 3 5% 7% 14%	1800
	11th to 20th	Day	23% 16% 5% 11% 6% 5% 5% 3 4 5% 19%	1755
	21st to end	Day	24% 16% 4 8% 6% 4 5% 3 5% 5% 21%	1549
March	1st to 10th	Day	19% 15% 4 10% 7% 6% 5% 4 6% 6% 17%	4623
	11th to 20th	Day	18% 14% 4 8% 6% 5% 4 3 5% 5% 26%	5000
	21st to end	Day	22% 13% 4 11% 7% 7% 7% 5% 6% 6% 14%	5661
April	1st to 10th	Day	23% 13% 3 8% 6% 5% 5% 4 7% 7% 19%	2400
	11th to 20th	Day	20% 11% 3 7% 6% 5% 6% 4 5% 7% 26%	2401
	21st to end	Day	17% 10% 4 9% 6% 5% 6% 4 6% 6% 25%	2650
May	1st to 10th	Day	15% 8% 3 6% 4 4 4 4 5% 7% 41%	6320
	11th to 20th	Day	18% 10% 4 8% 5% 4 5% 4 6% 8% 28%	6277
	21st to end	Day	21% 9% 3 7% 5% 4 4 4 6% 8% 30%	6903
June	1st to 10th	Day	19% 8% 2 7% 5% 4 5% 4 6% 7% 32%	2870
	11th to 20th	Day	20% 10% 3 9% 6% 5% 5% 4 6% 7% 26%	3000
	21st to end	Day	12% 8% 3 7% 5% 4 4 4 6% 7% 39%	3000
July	1st to 10th	Day	7% 4 2 4 3 3 3 3 4 5% 64%	4890
	11th to 20th	Day	5% 3 1 3 2 2 3 2 4 5% 69%	4704
	21st to end	Day	10% 4 2 5% 3 3 3 3 5% 6% 58%	4791
August	1st to 10th	Day	5% 3 1 4 2 3 3 3 5% 8% 63%	4341
	11th to 20th	Day	8% 7% 3 8% 5% 5% 4 3 6% 8% 43%	4026
	21st to end	Day	14% 8% 3 7% 4 4 4 3 4 6% 43%	4340
September	1st to 10th	Day	10% 6% 2 6% 3 4 4 3 5% 7% 50%	2280
	11th to 20th	Day	14% 8% 2 8% 5% 5% 5% 3 5% 8% 38%	2280
	21st to end	Day	17% 8% 3 7% 5% 4 4 3 5% 7% 36%	2009
October	1st to 10th	Day	14% 8% 3 6% 5% 5% 6% 4 7% 10% 33%	3180
	11th to 20th	Day	29% 11% 3 9% 4 4 4 3 4 6% 23%	3161
	21st to end	Day	24% 12% 5% 10% 6% 5% 4 3 5% 7% 18%	3241
November	1st to 10th	Day	31% 13% 3 8% 4 5% 5% 4 5% 5% 17%	1604
	11th to 20th	Day	31% 13% 3 7% 4 3 5% 4 5% 5% 21%	1600
	21st to end	Day	31% 12% 3 7% 5% 4 5% 4 6% 6% 17%	1600
December	1st to 10th	Day	20% 11% 3 9% 7% 6% 6% 4 6% 8% 19%	2620
	11th to 20th	Day	31% 15% 5% 10% 6% 5% 5% 4 4 5% 11%	3025
	21st to end	Day	28% 15% 5% 12% 7% 6% 5% 4 4 4 11%	3525
January	1st to 10th	Night	32% 15% 5% 12% 6% 5% 4 3 4 4 10%	6766
	11th to 20th	Night	19% 10% 4 6% 5% 4 5% 4 6% 8% 29%	6285
	21st to end	Night	26% 11% 4 8% 5% 4 4 3 4 5% 27%	6846
February	1st to 10th	Night	28% 14% 3 8% 6% 5% 4 4 4 6% 19%	2600
	11th to 20th	Night	25% 14% 4 8% 5% 4 5% 3 4 6% 22%	2532
	21st to end	Night	27% 14% 3 7% 4 4 5% 4 5% 6% 22%	2080
March	1st to 10th	Night	17% 14% 4 9% 6% 6% 6% 5% 7% 7% 18%	5256
	11th to 20th	Night	21% 13% 4 8% 4 4 4 3 4 5% 29%	4999
	21st to end	Night	28% 13% 4 10% 6% 5% 5% 4 5% 4 15%	5314
April	1st to 10th	Night	23% 11% 4 9% 5% 5% 7% 5% 6% 6% 20%	2000
	11th to 20th	Night	19% 10% 4 7% 6% 5% 4 4 5% 5% 32%	1946
	21st to end	Night	22% 11% 3 7% 5% 5% 5% 4 5% 6% 26%	1750
May	1st to 10th	Night	16% 9% 3 6% 4 4 3 3 4 4 43%	3640
	11th to 20th	Night	23% 9% 3 8% 5% 4 4 3 4 6% 32%	3616
	21st to end	Night	24% 9% 4 8% 5% 4 5% 4 6% 7% 25%	3972
June	1st to 10th	Night	20% 8% 3 6% 5% 4 5% 4 6% 6% 33%	1526
	11th to 20th	Night	22% 11% 5% 9% 5% 3 4 4 5% 5% 26%	1400
	21st to end	Night	13% 6% 3 6% 5% 4 5% 3 6% 8% 41%	1400
July	1st to 10th	Night	10% 5% 2 5% 3 2 3 2 3 3 61%	2290
	11th to 20th	Night	4 3 1 2 2 2 2 3 3 5% 72%	2473
	21st to end	Night	12% 5% 2 4 3 3 4 3 4 5% 55%	2762
August	1st to 10th	Night	5% 2 1 4 3 3 3 2 4 6% 68%	2587
	11th to 20th	Night	11% 6% 3 6% 4 3 3 2 4 6% 51%	2812
	21st to end	Night	16% 6% 3 6% 4 3 3 3 3 5% 48%	3333
September	1st to 10th	Night	9% 5% 2 5% 4 4 3 3 5% 5% 55%	1900
	11th to 20th	Night	16% 8% 3 7% 5% 4 4 3 5% 5% 41%	1900
	21st to end	Night	16% 8% 3 7% 4 5% 4 4 4 6% 38%	2169
October	1st to 10th	Night	14% 7% 3 7% 5% 4 5% 4 6% 8% 37%	3800
	11th to 20th	Night	26% 9% 3 6% 5% 4 4 4 5% 6% 30%	3777
	21st to end	Night	28% 13% 4 9% 5% 4 4 3 4 5% 21%	4321
November	1st to 10th	Night	32% 11% 3 6% 5% 5% 4 3 4 4 22%	2692
	11th to 20th	Night	31% 13% 3 8% 4 4 4 4 4 4 21%	2800
	21st to end	Night	29% 12% 4 8% 5% 5% 5% 4 4 5% 19%	2800
December	1st to 10th	Night	21% 11% 3 9% 6% 5% 5% 4 6% 5% 24%	4560
	11th to 20th	Night	30% 14% 5% 10% 6% 5% 5% 3 5% 4 13%	5180
	21st to end	Night	28% 18% 5% 11% 6% 5% 4 3 4 4 12%	7412

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	78% 7% 7% 6% 2	3179
	11th to 20th	Day	53% 11% 13% 16% 6% 1	3619
	21st to end	Day	62% 5% 10% 14% 9%	4114
February	1st to 10th	Day	69% 9% 9% 8% 4 1	1800
	11th to 20th	Day	68% 7% 9% 9% 7%	1764
	21st to end	Day	67% 8% 10% 11% 5%	1549
March	1st to 10th	Day	61% 10% 13% 12% 4	4623
	11th to 20th	Day	59% 9% 13% 17% 2	5000
	21st to end	Day	67% 11% 13% 8% 1	5661
April	1st to 10th	Day	64% 10% 15% 10% 1	2400
	11th to 20th	Day	58% 8% 12% 13% 7% 1	2401
	21st to end	Day	59% 10% 12% 13% 5% 1	2650
May	1st to 10th	Day	43% 8% 16% 23% 10%	6320
	11th to 20th	Day	51% 11% 18% 16% 3	6280
	21st to end	Day	51% 10% 23% 15% 1	6904
June	1st to 10th	Day	52% 9% 18% 15% 5% 1	2870
	11th to 20th	Day	59% 11% 14% 13% 3	3000
	21st to end	Day	45% 9% 19% 19% 7% 1	3000
July	1st to 10th	Day	24% 7% 11% 21% 24% 13%	4816
	11th to 20th	Day	20% 5% 10% 31% 32% 3	4624
	21st to end	Day	28% 7% 17% 32% 15% 2	4640
August	1st to 10th	Day	20% 7% 14% 39% 18% 1	4324
	11th to 20th	Day	38% 11% 21% 22% 7% 2	4065
	21st to end	Day	42% 7% 13% 26% 11%	4339
September	1st to 10th	Day	36% 7% 15% 25% 13% 4	2280
	11th to 20th	Day	46% 7% 14% 17% 14% 2	2280
	21st to end	Day	48% 7% 17% 17% 9% 2	2009
October	1st to 10th	Day	42% 10% 17% 25% 5%	3180
	11th to 20th	Day	62% 6% 12% 13% 7%	3161
	21st to end	Day	64% 9% 11% 9% 6% 1	3241
November	1st to 10th	Day	68% 8% 12% 9% 3	1604
	11th to 20th	Day	66% 8% 9% 9% 6% 2	1600
	21st to end	Day	66% 9% 8% 10% 6% 1	1600
December	1st to 10th	Day	57% 9% 10% 15% 10%	2620
	11th to 20th	Day	73% 9% 11% 6% 1	3028
	21st to end	Day	74% 9% 11% 5% 2	3525
January	1st to 10th	Night	76% 8% 7% 6% 2	6766
	11th to 20th	Night	49% 10% 14% 21% 6%	6323
	21st to end	Night	59% 6% 10% 16% 8%	6846
February	1st to 10th	Night	66% 8% 11% 10% 5% 1	2600
	11th to 20th	Night	65% 8% 10% 10% 7% 1	2534
	21st to end	Night	63% 8% 11% 13% 4	2080
March	1st to 10th	Night	59% 12% 12% 12% 4	5256
	11th to 20th	Night	56% 9% 15% 18% 2	5000
	21st to end	Night	71% 9% 12% 8%	5314
April	1st to 10th	Night	63% 12% 12% 12% 2	2000
	11th to 20th	Night	55% 9% 14% 14% 8% 1	1946
	21st to end	Night	58% 11% 12% 13% 5% 1	1750
May	1st to 10th	Night	44% 8% 12% 29% 8%	3637
	11th to 20th	Night	52% 10% 18% 16% 3	3616
	21st to end	Night	59% 11% 18% 12% 1	3972
June	1st to 10th	Night	52% 8% 17% 17% 6%	1526
	11th to 20th	Night	59% 9% 14% 15% 3	1400
	21st to end	Night	42% 8% 22% 20% 6% 3	1400
July	1st to 10th	Night	27% 6% 10% 21% 20% 16%	2255
	11th to 20th	Night	17% 5% 11% 27% 39% 2	2430
	21st to end	Night	28% 8% 14% 29% 19% 3	2674
August	1st to 10th	Night	19% 5% 14% 40% 21% 2	2579
	11th to 20th	Night	35% 8% 23% 23% 9% 2	2839
	21st to end	Night	40% 6% 15% 29% 10%	3333
September	1st to 10th	Night	31% 8% 16% 28% 14% 4	1900
	11th to 20th	Night	46% 6% 12% 19% 13% 4	1900
	21st to end	Night	46% 8% 13% 22% 10% 1	2169
October	1st to 10th	Night	42% 9% 20% 25% 4	3800
	11th to 20th	Night	56% 7% 14% 17% 6%	3777
	21st to end	Night	65% 8% 10% 11% 6%	4321
November	1st to 10th	Night	64% 9% 12% 11% 3 1	2692
	11th to 20th	Night	67% 6% 10% 11% 4 2	2800
	21st to end	Night	65% 9% 9% 9% 7%	2800
December	1st to 10th	Night	55% 9% 12% 17% 7%	4560
	11th to 20th	Night	72% 8% 11% 7% 2	5176
	21st to end	Night	74% 10% 8% 6% 2	7412

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	37% 11% 17% 16% 14% 7%	200
	11th to 20th	Day	34% 10% 17% 21% 15% 5%	200
	21st to end	Day	40% 12% 16% 15% 13% 5%	265
February	1st to 10th	Day	42% 11% 17% 19% 9% 3	400
	11th to 20th	Day	37% 15% 23% 15% 9% 2	395
	21st to end	Day	34% 15% 20% 19% 10% 2	364
March	1st to 10th	Day	30% 15% 24% 16% 13% 2	500
	11th to 20th	Day	29% 15% 19% 19% 13% 5%	500
	21st to end	Day	35% 13% 22% 20% 9% 1	550
April	1st to 10th	Day	30% 13% 24% 19% 11% 3	500
	11th to 20th	Day	24% 15% 27% 18% 9% 6%	492
	21st to end	Day	22% 13% 23% 26% 13% 2	500
May	1st to 10th	Day	16% 11% 23% 32% 16% 3	503
	11th to 20th	Day	24% 9% 18% 23% 17% 7%	528
	21st to end	Day	24% 9% 17% 27% 16% 8%	573
June	1st to 10th	Day	23% 7% 22% 29% 16% 4	600
	11th to 20th	Day	22% 8% 23% 29% 15% 3	730
	21st to end	Day	14% 5% 20% 33% 21% 5%	730
July	1st to 10th	Day	12% 4 18% 34% 27% 5%	721
	11th to 20th	Day	8% 4 19% 34% 29% 7%	611
	21st to end	Day	8% 3 16% 35% 30% 8%	532
August	1st to 10th	Day	11% 2 11% 36% 28% 12%	487
	11th to 20th	Day	8% 3 13% 34% 32% 11%	477
	21st to end	Day	15% 6% 17% 34% 19% 9%	539
September	1st to 10th	Day	14% 6% 20% 36% 19% 6%	490
	11th to 20th	Day	17% 9% 18% 28% 24% 5%	490
	21st to end	Day	21% 9% 20% 29% 16% 6%	490
October	1st to 10th	Day	23% 9% 19% 22% 20% 7%	490
	11th to 20th	Day	31% 8% 16% 23% 17% 6%	490
	21st to end	Day	31% 13% 18% 21% 13% 4	420
November	1st to 10th	Day	40% 13% 17% 17% 10% 3	218
	11th to 20th	Day	41% 11% 15% 14% 12% 9%	200
	21st to end	Day	31% 13% 20% 19% 8% 11%	200
December	1st to 10th	Day	38% 9% 13% 12% 16% 14%	200
	11th to 20th	Day	42% 13% 20% 15% 10% 1	200
	21st to end	Day	38% 12% 18% 19% 11% 2	220
January	1st to 10th	Night	42% 11% 14% 16% 13% 3	900
	11th to 20th	Night	35% 10% 12% 23% 18% 2	801
	21st to end	Night	35% 9% 14% 24% 15% 3	880
February	1st to 10th	Night	36% 11% 16% 25% 11% 2	800
	11th to 20th	Night	34% 10% 13% 25% 16% 2	784
	21st to end	Night	33% 10% 17% 25% 12% 2	660
March	1st to 10th	Night	31% 11% 18% 26% 14% 1	800
	11th to 20th	Night	32% 13% 15% 23% 14% 3	800
	21st to end	Night	32% 12% 20% 25% 10% 1	880
April	1st to 10th	Night	30% 11% 16% 25% 16% 2	800
	11th to 20th	Night	25% 9% 19% 29% 16% 3	758
	21st to end	Night	27% 8% 17% 31% 14% 3	550
May	1st to 10th	Night	21% 9% 14% 35% 21% 2	400
	11th to 20th	Night	22% 6% 13% 29% 26% 3	394
	21st to end	Night	24% 7% 13% 26% 25% 6%	433
June	1st to 10th	Night	22% 7% 18% 32% 19% 3	400
	11th to 20th	Night	26% 9% 17% 28% 18% 2	400
	21st to end	Night	15% 4 17% 33% 26% 5%	400
July	1st to 10th	Night	14% 4 12% 32% 34% 5%	390
	11th to 20th	Night	9% 3 12% 36% 37% 4	388
	21st to end	Night	8% 4 10% 31% 42% 5%	416
August	1st to 10th	Night	11% 1 4 30% 45% 9%	410
	11th to 20th	Night	9% 2 6% 26% 45% 12%	564
	21st to end	Night	15% 3 10% 31% 34% 7%	736
September	1st to 10th	Night	13% 3 9% 34% 35% 5%	760
	11th to 20th	Night	21% 4 9% 24% 34% 9%	760
	21st to end	Night	21% 7% 12% 28% 26% 6%	760
October	1st to 10th	Night	21% 6% 12% 29% 26% 6%	760
	11th to 20th	Night	29% 6% 16% 23% 21% 5%	760
	21st to end	Night	32% 10% 16% 23% 15% 3	836
November	1st to 10th	Night	38% 10% 15% 24% 12% 1	780
	11th to 20th	Night	39% 10% 17% 19% 13% 3	800
	21st to end	Night	37% 8% 16% 21% 14% 5%	800
December	1st to 10th	Night	32% 9% 12% 25% 19% 4	800
	11th to 20th	Night	40% 12% 16% 20% 11% 1	800
	21st to end	Night	44% 11% 16% 18% 9% 1	980

Page generated at 2025-07-17 22:10:01. Version ac07

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