White Salmon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the White Salmon clear sky chart from 2005-11-06 to 2025-10-04.

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	8% 7% 3 7% 5% 4 5% 4 5% 6% 46%	135688
	Night	11% 9% 3 7% 5% 4 4 4 5% 6% 41%	131019
Transparency	Day	23% 38% 8% 16% 10% 4	130436
	Night	26% 38% 9% 16% 8% 3	127270
Seeing	Day	17% 14% 33% 22% 11% 3	15688
	Night	15% 10% 24% 33% 17% 2	24620

By Month

Percentage Cloud Cover SW (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	22% 21% 6% 14% 7% 5% 6% 4 5% 4 5%	3639
	11th to 20th	Day	18% 12% 3 9% 6% 5% 6% 4 6% 6% 25%	3640
	21st to end	Day	23% 14% 5% 9% 4 4 4 3 4 4 26%	4203
February	1st to 10th	Day	15% 15% 4 9% 7% 7% 6% 4 7% 6% 20%	1800
	11th to 20th	Day	13% 11% 4 9% 8% 7% 6% 5% 8% 8% 23%	1755
	21st to end	Day	11% 11% 4 10% 7% 7% 7% 5% 6% 6% 24%	1619
March	1st to 10th	Day	8% 9% 4 9% 8% 6% 7% 6% 8% 8% 27%	4559
	11th to 20th	Day	10% 11% 4 10% 6% 5% 5% 4 6% 5% 33%	5000
	21st to end	Day	11% 11% 4 10% 7% 7% 8% 6% 9% 9% 19%	5722
April	1st to 10th	Day	10% 10% 3 9% 7% 7% 7% 5% 8% 7% 27%	2400
	11th to 20th	Day	7% 10% 3 9% 6% 6% 5% 5% 6% 7% 36%	2369
	21st to end	Day	5% 7% 3 8% 5% 6% 6% 6% 7% 10% 39%	2553
May	1st to 10th	Day	9% 5% 2 5% 4 4 5% 4 5% 6% 52%	6320
	11th to 20th	Day	5% 7% 3 7% 5% 5% 5% 4 5% 8% 47%	6277
	21st to end	Day	6% 5% 2 6% 4 4 5% 4 6% 9% 49%	6902
June	1st to 10th	Day	8% 6% 2 6% 5% 5% 5% 4 6% 7% 45%	2800
	11th to 20th	Day	4 5% 2 6% 5% 5% 5% 5% 7% 8% 49%	2800
	21st to end	Day	3 2 1 3 4 4 4 3 5% 7% 63%	2800
July	1st to 10th	Day	1 1 1 2 1 1 1 2 3 4 83%	6319
	11th to 20th	Day	1 1 1 1 2 2 2 2 3 84%	6320
	21st to end	Day	2 1 1 2 1 2 2 1 3 5% 81%	6880
August	1st to 10th	Day	2 2 1 3 2 3 3 3 4 5% 72%	6044
	11th to 20th	Day	1 2 1 3 2 3 4 3 4 6% 70%	5796
	21st to end	Day	5% 4 2 3 3 3 4 3 5% 8% 59%	6037
September	1st to 10th	Day	2 1 1 3 3 2 2 3 5% 8% 70%	2400
	11th to 20th	Day	4 2 1 5% 4 4 5% 4 5% 7% 58%	2400
	21st to end	Day	7% 4 2 6% 4 4 4 3 5% 7% 55%	2133
October	1st to 10th	Day	5% 4 2 5% 3 4 4 4 6% 8% 54%	3211
	11th to 20th	Day	7% 7% 3 8% 5% 6% 6% 5% 8% 8% 38%	3161
	21st to end	Day	13% 9% 4 9% 6% 5% 6% 4 7% 8% 27%	3260
November	1st to 10th	Day	15% 11% 4 9% 7% 5% 6% 6% 8% 7% 22%	1717
	11th to 20th	Day	15% 14% 5% 13% 7% 7% 7% 5% 6% 6% 16%	1600
	21st to end	Day	13% 14% 3 10% 7% 6% 7% 5% 6% 7% 20%	1600
December	1st to 10th	Day	9% 14% 5% 9% 6% 5% 5% 4 7% 8% 26%	2620
	11th to 20th	Day	24% 20% 8% 14% 6% 5% 4 3 4 4 7%	3028
	21st to end	Day	21% 22% 8% 13% 7% 5% 5% 3 4 4 7%	4004
January	1st to 10th	Night	22% 19% 6% 14% 7% 5% 5% 4 5% 5% 8%	6306
	11th to 20th	Night	18% 14% 4 9% 5% 4 4 3 4 7% 29%	6320
	21st to end	Night	24% 12% 4 10% 4 3 3 2 3 4 30%	6759
February	1st to 10th	Night	15% 14% 3 8% 6% 6% 6% 6% 7% 6% 23%	2600
	11th to 20th	Night	15% 10% 3 9% 6% 5% 6% 4 6% 6% 29%	2532
	21st to end	Night	11% 13% 3 9% 6% 5% 6% 6% 8% 8% 25%	2010
March	1st to 10th	Night	7% 10% 4 10% 7% 6% 7% 6% 8% 9% 28%	5332
	11th to 20th	Night	11% 10% 3 9% 6% 6% 5% 4 6% 6% 35%	5000
	21st to end	Night	11% 11% 4 10% 7% 7% 7% 5% 7% 8% 21%	5253
April	1st to 10th	Night	9% 9% 3 7% 6% 6% 6% 6% 7% 8% 33%	2000
	11th to 20th	Night	8% 7% 2 6% 5% 6% 7% 5% 6% 6% 42%	1979
	21st to end	Night	7% 5% 3 6% 4 4 6% 6% 8% 9% 42%	1843
May	1st to 10th	Night	10% 6% 2 4 3 3 3 3 5% 6% 55%	3640
	11th to 20th	Night	4 6% 2 6% 4 4 4 4 6% 7% 52%	3616
	21st to end	Night	6% 4 1 4 4 4 5% 4 8% 10% 49%	3972
June	1st to 10th	Night	8% 6% 2 5% 6% 5% 5% 3 6% 7% 46%	1600
	11th to 20th	Night	5% 4 2 4 3 4 3 4 6% 10% 56%	1600
	21st to end	Night	3 2 1 3 4 3 3 3 5% 6% 66%	1600
July	1st to 10th	Night	1 1 1 1 1 2 2 4 5% 82%	3640
	11th to 20th	Night	1 1 1 1 1 1 1 2 3 86%	3640
	21st to end	Night	1 1 1 1 1 1 1 1 3 6% 83%	3970
August	1st to 10th	Night	2 2 1 3 2 3 3 3 5% 7% 70%	3752
	11th to 20th	Night	4 3 1 3 2 2 3 2 4 6% 71%	4052
	21st to end	Night	3 3 1 3 3 2 4 3 5% 6% 66%	4959
September	1st to 10th	Night	2 1 1 4 2 2 3 3 4 6% 74%	2000
	11th to 20th	Night	4 3 1 4 3 3 4 4 4 7% 61%	2000
	21st to end	Night	6% 4 1 4 3 4 3 4 4 7% 59%	2262
October	1st to 10th	Night	6% 3 2 5% 3 4 4 3 5% 6% 58%	3836
	11th to 20th	Night	8% 5% 1 6% 4 5% 6% 5% 7% 8% 44%	3777
	21st to end	Night	12% 9% 4 10% 6% 5% 5% 4 6% 7% 32%	4301
November	1st to 10th	Night	16% 9% 3 7% 5% 5% 6% 4 7% 8% 28%	2580
	11th to 20th	Night	17% 11% 5% 10% 8% 6% 5% 5% 6% 6% 22%	2800
	21st to end	Night	11% 11% 4 10% 6% 6% 7% 5% 8% 6% 25%	2800
December	1st to 10th	Night	10% 11% 4 9% 6% 5% 5% 4 6% 8% 31%	4560
	11th to 20th	Night	26% 16% 7% 14% 7% 5% 5% 4 4 4 7%	5176
	21st to end	Night	25% 18% 7% 12% 5% 4 5% 3 5% 4 11%	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	58% 27% 7% 7% 1	3639
	11th to 20th	Day	35% 27% 16% 17% 4	3640
	21st to end	Day	45% 27% 4 15% 9%	4203
February	1st to 10th	Day	26% 63% 6% 4 1	1800
	11th to 20th	Day	26% 63% 4 4 1	1764
	21st to end	Day	23% 63% 5% 3 6%	1619
March	1st to 10th	Day	32% 31% 8% 17% 11%	4559
	11th to 20th	Day	32% 30% 8% 23% 6%	5000
	21st to end	Day	41% 31% 12% 13% 4	5722
April	1st to 10th	Day	20% 63% 7% 8% 1	2400
	11th to 20th	Day	17% 62% 7% 8% 5%	2372
	21st to end	Day	14% 63% 7% 10% 5%	2553
May	1st to 10th	Day	18% 31% 6% 25% 19% 1	6320
	11th to 20th	Day	21% 32% 11% 23% 12% 1	6280
	21st to end	Day	18% 31% 21% 26% 5%	6904
June	1st to 10th	Day	10% 62% 6% 14% 7% 1	2800
	11th to 20th	Day	10% 62% 5% 15% 8% 1	2800
	21st to end	Day	8% 60% 6% 15% 9% 1	2800
July	1st to 10th	Day	5% 25% 3 18% 25% 25%	6251
	11th to 20th	Day	4 24% 2 11% 27% 31%	6245
	21st to end	Day	8% 24% 8% 27% 23% 9%	6681
August	1st to 10th	Day	11% 35% 3 11% 22% 18%	4403
	11th to 20th	Day	11% 36% 11% 30% 10% 3	4195
	21st to end	Day	17% 36% 8% 17% 19% 4	4352
September	1st to 10th	Day	7% 57% 7% 16% 10% 3	2400
	11th to 20th	Day	13% 57% 7% 12% 9% 3	2400
	21st to end	Day	13% 57% 6% 13% 8% 2	2133
October	1st to 10th	Day	15% 37% 8% 23% 16% 1	3211
	11th to 20th	Day	27% 39% 11% 15% 6%	3161
	21st to end	Day	34% 39% 7% 17% 4	3260
November	1st to 10th	Day	24% 58% 6% 9% 2	1717
	11th to 20th	Day	29% 59% 4 5% 3	1600
	21st to end	Day	26% 58% 4 6% 5% 1	1600
December	1st to 10th	Day	28% 37% 16% 16% 3	2620
	11th to 20th	Day	57% 33% 5% 4	3028
	21st to end	Day	54% 28% 10% 7% 1	4004
January	1st to 10th	Night	59% 27% 6% 6% 2	6306
	11th to 20th	Night	36% 27% 13% 20% 3	6320
	21st to end	Night	42% 28% 6% 15% 9%	6759
February	1st to 10th	Night	26% 62% 5% 5% 1	2600
	11th to 20th	Night	25% 63% 4 6% 1	2534
	21st to end	Night	19% 62% 6% 8% 4	2010
March	1st to 10th	Night	28% 31% 10% 20% 11%	5332
	11th to 20th	Night	30% 30% 9% 25% 6%	5000
	21st to end	Night	39% 32% 16% 13% 1	5253
April	1st to 10th	Night	16% 64% 9% 8% 2	2000
	11th to 20th	Night	13% 63% 7% 11% 5%	1979
	21st to end	Night	12% 63% 7% 13% 4	1843
May	1st to 10th	Night	19% 30% 3 27% 21% 1	3637
	11th to 20th	Night	19% 31% 12% 27% 9% 1	3616
	21st to end	Night	18% 29% 26% 23% 4	3972
June	1st to 10th	Night	11% 62% 5% 16% 5% 1	1600
	11th to 20th	Night	8% 62% 5% 15% 9% 1	1600
	21st to end	Night	7% 61% 6% 16% 9% 2	1600
July	1st to 10th	Night	6% 25% 4 20% 23% 22%	3600
	11th to 20th	Night	6% 24% 3 10% 31% 26%	3592
	21st to end	Night	6% 24% 9% 29% 23% 9%	3857
August	1st to 10th	Night	9% 35% 3 13% 22% 19%	2722
	11th to 20th	Night	8% 37% 14% 28% 10% 3	2929
	21st to end	Night	12% 37% 10% 19% 17% 6%	3565
September	1st to 10th	Night	8% 57% 7% 15% 10% 3	2000
	11th to 20th	Night	13% 58% 6% 12% 8% 3	2000
	21st to end	Night	13% 57% 6% 15% 8% 1	2262
October	1st to 10th	Night	13% 39% 5% 26% 17%	3836
	11th to 20th	Night	22% 39% 15% 16% 7%	3777
	21st to end	Night	33% 39% 6% 18% 4	4301
November	1st to 10th	Night	23% 58% 5% 10% 3	2580
	11th to 20th	Night	27% 58% 6% 6% 3	2800
	21st to end	Night	22% 58% 6% 8% 5% 1	2800
December	1st to 10th	Night	25% 37% 17% 19% 3	4560
	11th to 20th	Night	55% 34% 6% 4 1	5176
	21st to end	Night	51% 29% 9% 10% 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	28% 13% 30% 24% 6% 1	200
	11th to 20th	Day	34% 7% 25% 23% 11% 2	200
	21st to end	Day	28% 7% 23% 26% 15% 1	302
February	1st to 10th	Day	28% 16% 26% 22% 8% 1	400
	11th to 20th	Day	28% 17% 32% 18% 5% 1	395
	21st to end	Day	27% 14% 33% 19% 6% 1	399
March	1st to 10th	Day	26% 15% 33% 17% 7% 1	500
	11th to 20th	Day	21% 18% 30% 22% 8% 2	500
	21st to end	Day	26% 19% 32% 16% 7%	550
April	1st to 10th	Day	26% 20% 30% 15% 7% 1	500
	11th to 20th	Day	21% 20% 34% 15% 7% 3	492
	21st to end	Day	20% 19% 35% 18% 5% 3	500
May	1st to 10th	Day	20% 19% 31% 19% 9% 2	503
	11th to 20th	Day	18% 15% 35% 20% 9% 3	528
	21st to end	Day	16% 16% 34% 22% 9% 2	573
June	1st to 10th	Day	17% 17% 34% 18% 12% 2	530
	11th to 20th	Day	19% 23% 36% 14% 7% 2	530
	21st to end	Day	8% 16% 38% 25% 11% 2	530
July	1st to 10th	Day	6% 12% 48% 23% 10% 1	526
	11th to 20th	Day	4 14% 45% 23% 11% 3	524
	21st to end	Day	4 10% 43% 23% 15% 5%	575
August	1st to 10th	Day	6% 8% 39% 25% 16% 7%	527
	11th to 20th	Day	4 12% 34% 27% 15% 7%	517
	21st to end	Day	8% 15% 30% 25% 15% 6%	583
September	1st to 10th	Day	5% 11% 32% 29% 17% 6%	530
	11th to 20th	Day	9% 11% 34% 30% 13% 4	530
	21st to end	Day	13% 12% 31% 28% 14% 3	530
October	1st to 10th	Day	17% 12% 29% 24% 16% 2	503
	11th to 20th	Day	16% 13% 24% 26% 14% 5%	490
	21st to end	Day	26% 12% 25% 22% 12% 4	426
November	1st to 10th	Day	28% 8% 22% 32% 9% 1	275
	11th to 20th	Day	30% 9% 31% 25% 5% 2	200
	21st to end	Day	26% 6% 28% 30% 11% 1	200
December	1st to 10th	Day	20% 11% 26% 25% 17% 3	200
	11th to 20th	Day	32% 9% 28% 27% 4 1	200
	21st to end	Day	26% 14% 21% 28% 10% 1	220
January	1st to 10th	Night	25% 10% 20% 29% 14% 1	800
	11th to 20th	Night	24% 8% 19% 33% 14% 2	800
	21st to end	Night	20% 6% 18% 36% 18% 2	880
February	1st to 10th	Night	22% 12% 20% 31% 15% 1	800
	11th to 20th	Night	24% 9% 20% 31% 15% 2	784
	21st to end	Night	22% 12% 21% 33% 11% 1	660
March	1st to 10th	Night	16% 11% 22% 37% 13% 1	800
	11th to 20th	Night	15% 10% 20% 39% 15% 2	800
	21st to end	Night	18% 14% 22% 32% 11% 2	880
April	1st to 10th	Night	18% 14% 25% 29% 13% 1	800
	11th to 20th	Night	14% 14% 29% 27% 14% 2	791
	21st to end	Night	13% 13% 31% 29% 14% 1	643
May	1st to 10th	Night	11% 16% 27% 30% 16% 2	400
	11th to 20th	Night	11% 12% 27% 29% 19% 2	394
	21st to end	Night	8% 10% 30% 36% 15% 2	433
June	1st to 10th	Night	14% 13% 29% 28% 15% 1	400
	11th to 20th	Night	10% 17% 40% 24% 9%	400
	21st to end	Night	6% 12% 35% 31% 16% 1	400
July	1st to 10th	Night	5% 8% 37% 35% 15% 1	390
	11th to 20th	Night	2 8% 44% 35% 10% 1	388
	21st to end	Night	3 8% 35% 36% 17% 2	438
August	1st to 10th	Night	3 6% 31% 40% 17% 3	467
	11th to 20th	Night	4 4 23% 34% 29% 6%	594
	21st to end	Night	4 10% 30% 32% 20% 4	850
September	1st to 10th	Night	4 7% 27% 32% 27% 3	800
	11th to 20th	Night	6% 7% 27% 30% 26% 5%	800
	21st to end	Night	9% 8% 17% 36% 27% 4	800
October	1st to 10th	Night	11% 6% 18% 40% 22% 3	772
	11th to 20th	Night	12% 6% 18% 36% 23% 4	760
	21st to end	Night	17% 8% 19% 37% 18% 3	836
November	1st to 10th	Night	18% 7% 17% 41% 16% 1	780
	11th to 20th	Night	23% 9% 20% 34% 12% 2	800
	21st to end	Night	15% 9% 19% 38% 18% 2	800
December	1st to 10th	Night	18% 8% 21% 34% 16% 2	800
	11th to 20th	Night	25% 6% 22% 34% 13%	800
	21st to end	Night	23% 11% 24% 33% 8% 1	880

Page generated at 2025-09-30 22:39:03. Version ac07

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