Snoqualmie Point Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Snoqualmie Point Park clear sky chart from 2005-11-06 to 2026-04-02.

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	24% 11% 3 7% 4 4 4 3 4 5% 31%	136280
	Night	27% 13% 3 7% 4 3 3 3 4 5% 29%	134267
Transparency	Day	55% 6% 12% 16% 9% 2	135999
	Night	59% 5% 11% 15% 9% 2	134126
Seeing	Day	29% 10% 22% 25% 11% 3	16637
	Night	34% 8% 16% 25% 15% 2	25133

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	40% 19% 3 8% 4 4 3 2 3 3 10%	4723
	11th to 20th	Day	20% 11% 3 7% 4 4 3 3 4 5% 35%	4716
	21st to end	Day	30% 10% 3 7% 4 3 3 2 3 4 30%	5284
February	1st to 10th	Day	33% 15% 5% 8% 4 4 3 3 4 4 16%	1890
	11th to 20th	Day	32% 19% 4 7% 4 3 3 3 4 4 18%	1845
	21st to end	Day	33% 19% 4 8% 4 4 3 2 3 3 18%	1650
March	1st to 10th	Day	22% 17% 4 9% 5% 6% 5% 4 4 5% 18%	4676
	11th to 20th	Day	22% 21% 5% 9% 5% 4 3 2 2 3 25%	5110
	21st to end	Day	31% 16% 4 8% 6% 5% 5% 4 5% 5% 11%	5829
April	1st to 10th	Day	29% 18% 4 8% 6% 4 5% 3 5% 4 14%	2413
	11th to 20th	Day	25% 16% 4 7% 5% 4 4 3 5% 5% 22%	2372
	21st to end	Day	28% 16% 4 9% 5% 4 4 3 4 5% 18%	2660
May	1st to 10th	Day	20% 11% 3 7% 5% 4 4 4 4 5% 33%	6320
	11th to 20th	Day	31% 11% 3 7% 5% 4 4 3 5% 6% 21%	6277
	21st to end	Day	28% 11% 3 7% 4 4 4 3 5% 7% 25%	6903
June	1st to 10th	Day	29% 11% 3 7% 4 4 4 4 5% 5% 25%	2800
	11th to 20th	Day	30% 13% 3 9% 5% 4 4 4 5% 5% 17%	2973
	21st to end	Day	17% 10% 3 7% 4 4 4 4 5% 7% 34%	3000
July	1st to 10th	Day	12% 5% 2 4 2 2 3 2 4 5% 60%	6780
	11th to 20th	Day	7% 4 2 4 3 2 3 2 3 4 66%	6325
	21st to end	Day	11% 5% 1 4 3 3 3 3 5% 6% 55%	6874
August	1st to 10th	Day	8% 4 1 4 3 3 4 3 5% 6% 59%	4495
	11th to 20th	Day	17% 7% 3 8% 4 4 5% 4 6% 7% 36%	4156
	21st to end	Day	21% 8% 2 6% 3 3 3 3 4 5% 41%	4440
September	1st to 10th	Day	14% 7% 2 6% 3 3 3 3 5% 6% 47%	2400
	11th to 20th	Day	20% 9% 3 6% 5% 4 3 3 4 6% 38%	2400
	21st to end	Day	22% 9% 3 6% 4 4 3 3 4 5% 38%	2123
October	1st to 10th	Day	21% 8% 2 5% 3 4 4 3 5% 8% 38%	3280
	11th to 20th	Day	33% 9% 2 7% 4 3 3 3 4 5% 26%	3261
	21st to end	Day	35% 11% 3 8% 4 4 4 3 4 5% 19%	3330
November	1st to 10th	Day	40% 12% 3 7% 4 3 4 4 3 5% 16%	1718
	11th to 20th	Day	39% 14% 3 6% 4 3 3 3 3 4 19%	1680
	21st to end	Day	36% 15% 4 6% 3 4 3 2 3 4 20%	1680
December	1st to 10th	Day	28% 10% 3 5% 4 4 3 3 5% 5% 31%	2700
	11th to 20th	Day	37% 15% 4 8% 5% 4 3 3 4 3 14%	3105
	21st to end	Day	34% 18% 4 9% 5% 4 4 3 4 4 13%	4092
January	1st to 10th	Night	40% 19% 3 8% 4 4 3 2 3 3 11%	8172
	11th to 20th	Night	22% 12% 3 7% 3 2 2 3 4 6% 36%	8182
	21st to end	Night	27% 10% 3 7% 4 4 3 2 4 5% 30%	8897
February	1st to 10th	Night	32% 17% 3 8% 5% 4 4 3 4 5% 16%	2730
	11th to 20th	Night	31% 16% 3 7% 4 4 3 2 4 4 21%	2662
	21st to end	Night	32% 20% 3 6% 4 3 3 3 4 4 17%	2155
March	1st to 10th	Night	21% 18% 4 8% 5% 5% 5% 4 6% 6% 20%	5434
	11th to 20th	Night	29% 18% 3 7% 3 3 3 2 3 4 26%	5109
	21st to end	Night	36% 16% 3 8% 4 3 3 4 5% 5% 13%	5387
April	1st to 10th	Night	30% 17% 4 8% 4 4 4 3 6% 5% 15%	2010
	11th to 20th	Night	26% 15% 3 7% 4 3 4 3 3 5% 26%	1979
	21st to end	Night	32% 12% 3 6% 5% 4 4 3 5% 5% 20%	1736
May	1st to 10th	Night	22% 10% 2 7% 4 3 3 2 3 4 39%	3640
	11th to 20th	Night	30% 14% 3 7% 4 3 3 3 4 5% 26%	3616
	21st to end	Night	28% 15% 3 8% 4 3 3 2 4 5% 23%	3972
June	1st to 10th	Night	26% 10% 3 7% 6% 5% 4 2 3 4 29%	1600
	11th to 20th	Night	29% 12% 4 8% 5% 4 4 4 3 5% 23%	1421
	21st to end	Night	19% 8% 2 6% 4 4 3 3 4 7% 39%	1400
July	1st to 10th	Night	16% 5% 1 4 2 2 2 2 3 5% 59%	3180
	11th to 20th	Night	6% 3 1 3 2 2 2 2 3 3 72%	3632
	21st to end	Night	14% 4 1 3 2 2 2 2 4 6% 59%	3969
August	1st to 10th	Night	7% 4 1 4 2 2 2 2 4 6% 65%	2641
	11th to 20th	Night	21% 6% 2 6% 3 3 3 2 3 5% 47%	2902
	21st to end	Night	24% 7% 2 5% 2 2 2 2 3 4 47%	3476
September	1st to 10th	Night	14% 5% 2 5% 3 3 3 3 3 5% 52%	2000
	11th to 20th	Night	21% 9% 2 6% 3 3 4 3 4 4 40%	2000
	21st to end	Night	21% 8% 3 7% 4 3 3 3 4 5% 39%	2273
October	1st to 10th	Night	21% 9% 2 5% 3 3 3 3 5% 8% 37%	3920
	11th to 20th	Night	34% 8% 2 5% 3 4 4 3 4 5% 29%	3897
	21st to end	Night	36% 13% 3 6% 3 3 3 3 4 5% 21%	4474
November	1st to 10th	Night	38% 12% 3 7% 4 4 4 3 4 4 17%	2795
	11th to 20th	Night	39% 13% 3 7% 4 3 3 2 3 3 19%	2940
	21st to end	Night	36% 13% 3 7% 4 4 4 2 3 4 20%	2940
December	1st to 10th	Night	26% 11% 2 6% 5% 4 3 3 4 5% 31%	4700
	11th to 20th	Night	35% 17% 4 9% 5% 3 3 2 3 4 14%	5320
	21st to end	Night	34% 20% 4 9% 5% 4 4 3 3 4 12%	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	80% 5% 5% 7% 3	4723
	11th to 20th	Day	51% 5% 9% 15% 17% 3	4740
	21st to end	Day	60% 3 5% 15% 16% 1	5285
February	1st to 10th	Day	73% 5% 9% 8% 4 1	1890
	11th to 20th	Day	71% 5% 7% 9% 7% 1	1854
	21st to end	Day	73% 4 7% 11% 4	1650
March	1st to 10th	Day	64% 8% 12% 10% 5%	4676
	11th to 20th	Day	66% 5% 8% 18% 2	5110
	21st to end	Day	73% 8% 11% 7% 1	5829
April	1st to 10th	Day	72% 7% 12% 7% 1	2413
	11th to 20th	Day	64% 7% 10% 12% 6% 1	2372
	21st to end	Day	71% 6% 10% 9% 4 1	2660
May	1st to 10th	Day	50% 7% 14% 20% 8%	6320
	11th to 20th	Day	62% 9% 16% 11% 2	6280
	21st to end	Day	59% 9% 20% 11% 1	6904
June	1st to 10th	Day	61% 7% 15% 12% 5%	2800
	11th to 20th	Day	68% 7% 12% 10% 3	2973
	21st to end	Day	50% 7% 17% 17% 8% 2	3000
July	1st to 10th	Day	28% 6% 17% 21% 18% 11%	6706
	11th to 20th	Day	22% 5% 13% 27% 31% 2	6249
	21st to end	Day	28% 6% 21% 32% 11% 1	6681
August	1st to 10th	Day	25% 5% 12% 35% 21% 2	4478
	11th to 20th	Day	46% 8% 16% 20% 9% 1	4195
	21st to end	Day	46% 5% 11% 24% 12% 1	4439
September	1st to 10th	Day	38% 6% 15% 23% 13% 5%	2400
	11th to 20th	Day	49% 6% 11% 17% 14% 3	2400
	21st to end	Day	48% 6% 15% 17% 10% 3	2123
October	1st to 10th	Day	44% 5% 13% 28% 9% 1	3280
	11th to 20th	Day	61% 5% 10% 14% 9% 1	3261
	21st to end	Day	68% 5% 10% 9% 7% 2	3330
November	1st to 10th	Day	71% 5% 9% 11% 3	1718
	11th to 20th	Day	71% 5% 7% 8% 6% 2	1680
	21st to end	Day	71% 5% 5% 9% 8% 2	1680
December	1st to 10th	Day	56% 4 8% 16% 14% 2	2700
	11th to 20th	Day	75% 5% 8% 9% 3	3108
	21st to end	Day	76% 5% 9% 7% 2	4092
January	1st to 10th	Night	80% 3 4 8% 3 1	8172
	11th to 20th	Night	48% 5% 9% 16% 18% 4	8220
	21st to end	Night	59% 3 7% 14% 15% 1	8897
February	1st to 10th	Night	72% 5% 9% 8% 5% 1	2730
	11th to 20th	Night	67% 6% 9% 9% 7% 2	2664
	21st to end	Night	71% 6% 9% 10% 4	2155
March	1st to 10th	Night	61% 8% 14% 11% 6%	5434
	11th to 20th	Night	63% 5% 12% 17% 3	5110
	21st to end	Night	73% 7% 11% 8% 1	5387
April	1st to 10th	Night	70% 9% 11% 8% 1	2010
	11th to 20th	Night	60% 7% 12% 13% 7% 2	1979
	21st to end	Night	68% 7% 10% 9% 5% 1	1736
May	1st to 10th	Night	50% 5% 14% 21% 10%	3637
	11th to 20th	Night	61% 9% 15% 13% 2 1	3616
	21st to end	Night	64% 8% 16% 11% 1	3972
June	1st to 10th	Night	59% 6% 16% 14% 4	1600
	11th to 20th	Night	64% 8% 15% 11% 3	1421
	21st to end	Night	47% 8% 19% 18% 6% 2	1400
July	1st to 10th	Night	31% 5% 17% 18% 15% 14%	3145
	11th to 20th	Night	18% 4 14% 28% 35% 1	3585
	21st to end	Night	28% 6% 21% 31% 13% 2	3857
August	1st to 10th	Night	21% 4 12% 37% 24% 2	2633
	11th to 20th	Night	42% 8% 20% 19% 9% 2	2929
	21st to end	Night	44% 4 13% 24% 14% 1	3476
September	1st to 10th	Night	35% 6% 16% 23% 15% 5%	2000
	11th to 20th	Night	49% 7% 9% 17% 13% 5%	2000
	21st to end	Night	49% 7% 14% 17% 11% 3	2273
October	1st to 10th	Night	46% 4 12% 28% 9% 1	3920
	11th to 20th	Night	59% 4 9% 15% 12% 1	3897
	21st to end	Night	67% 4 10% 11% 8%	4474
November	1st to 10th	Night	71% 6% 10% 10% 3	2795
	11th to 20th	Night	72% 4 8% 9% 5% 2	2940
	21st to end	Night	69% 5% 7% 9% 9% 1	2940
December	1st to 10th	Night	56% 5% 7% 13% 16% 2	4700
	11th to 20th	Night	75% 4 8% 9% 3	5316
	21st to end	Night	78% 5% 9% 6% 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	45% 9% 20% 16% 7% 4	220
	11th to 20th	Day	32% 14% 16% 21% 14% 2	220
	21st to end	Day	43% 11% 18% 18% 9% 2	275
February	1st to 10th	Day	41% 13% 20% 17% 7% 1	430
	11th to 20th	Day	44% 12% 24% 15% 6%	425
	21st to end	Day	41% 16% 20% 20% 4	405
March	1st to 10th	Day	37% 16% 21% 19% 6% 1	540
	11th to 20th	Day	36% 15% 20% 19% 7% 2	540
	21st to end	Day	41% 13% 26% 14% 6%	594
April	1st to 10th	Day	38% 12% 24% 16% 8% 1	505
	11th to 20th	Day	30% 19% 26% 16% 8% 2	492
	21st to end	Day	32% 13% 25% 21% 7% 2	500
May	1st to 10th	Day	25% 10% 29% 27% 8% 1	503
	11th to 20th	Day	33% 10% 22% 22% 10% 3	528
	21st to end	Day	32% 10% 23% 23% 9% 3	573
June	1st to 10th	Day	28% 8% 23% 27% 12% 2	530
	11th to 20th	Day	30% 13% 26% 21% 9% 2	703
	21st to end	Day	17% 7% 25% 34% 14% 3	730
July	1st to 10th	Day	16% 6% 23% 38% 16% 2	721
	11th to 20th	Day	13% 6% 24% 37% 17% 4	528
	21st to end	Day	10% 4 21% 41% 19% 5%	575
August	1st to 10th	Day	14% 5% 19% 37% 19% 6%	527
	11th to 20th	Day	9% 4 22% 38% 21% 6%	517
	21st to end	Day	17% 9% 22% 34% 12% 6%	583
September	1st to 10th	Day	14% 9% 24% 35% 14% 3	530
	11th to 20th	Day	22% 8% 20% 32% 16% 2	530
	21st to end	Day	23% 7% 25% 26% 16% 2	530
October	1st to 10th	Day	26% 10% 24% 20% 18% 2	530
	11th to 20th	Day	34% 10% 19% 21% 12% 3	530
	21st to end	Day	36% 13% 21% 19% 8% 3	443
November	1st to 10th	Day	40% 16% 16% 20% 7% 1	258
	11th to 20th	Day	44% 15% 11% 14% 13% 3	220
	21st to end	Day	40% 7% 20% 19% 9% 5%	220
December	1st to 10th	Day	46% 9% 12% 14% 14% 5%	220
	11th to 20th	Day	47% 11% 21% 15% 5%	220
	21st to end	Day	38% 13% 19% 19% 10% 1	242
January	1st to 10th	Night	49% 11% 17% 16% 6%	840
	11th to 20th	Night	40% 9% 16% 26% 8% 1	840
	21st to end	Night	38% 8% 17% 28% 9%	924
February	1st to 10th	Night	40% 8% 23% 22% 6%	840
	11th to 20th	Night	37% 9% 18% 28% 8%	824
	21st to end	Night	42% 9% 22% 20% 6% 1	692
March	1st to 10th	Night	36% 10% 19% 22% 12% 1	840
	11th to 20th	Night	39% 9% 20% 23% 9% 1	840
	21st to end	Night	40% 10% 19% 24% 6% 1	924
April	1st to 10th	Night	36% 10% 19% 24% 10% 1	804
	11th to 20th	Night	31% 9% 21% 27% 11% 1	791
	21st to end	Night	36% 7% 17% 27% 12%	536
May	1st to 10th	Night	29% 7% 14% 34% 16% 1	400
	11th to 20th	Night	29% 7% 12% 28% 20% 3	394
	21st to end	Night	31% 5% 16% 22% 23% 3	433
June	1st to 10th	Night	30% 5% 12% 30% 23% 2	400
	11th to 20th	Night	35% 6% 14% 28% 18% 1	400
	21st to end	Night	21% 4 12% 33% 28% 3	400
July	1st to 10th	Night	16% 4 11% 31% 35% 3	390
	11th to 20th	Night	14% 2 9% 35% 36% 4	388
	21st to end	Night	11% 4 7% 29% 44% 5%	438
August	1st to 10th	Night	13% 2 7% 27% 44% 7%	417
	11th to 20th	Night	13% 3 7% 26% 40% 10%	594
	21st to end	Night	19% 4 8% 29% 36% 4	800
September	1st to 10th	Night	16% 2 10% 37% 31% 4	800
	11th to 20th	Night	23% 5% 11% 27% 30% 5%	800
	21st to end	Night	25% 5% 12% 31% 25% 2	800
October	1st to 10th	Night	26% 5% 15% 30% 22% 2	800
	11th to 20th	Night	34% 7% 17% 24% 16% 3	800
	21st to end	Night	37% 9% 18% 25% 8% 2	880
November	1st to 10th	Night	42% 10% 22% 22% 4	820
	11th to 20th	Night	44% 9% 20% 21% 5% 1	840
	21st to end	Night	40% 10% 19% 23% 8%	840
December	1st to 10th	Night	38% 8% 19% 24% 10% 1	840
	11th to 20th	Night	48% 10% 21% 16% 4 1	840
	21st to end	Night	50% 11% 18% 18% 3	924

Page generated at 2026-03-29 23:18:42. Version ac07

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