Yakima
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Yakima clear sky chart from 2005-11-06 to 2025-09-04.

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	6% 6% 2 6% 4 4 4 3 5% 6% 52%	135272
	Night	8% 8% 3 6% 4 4 4 3 5% 7% 49%	130751
Transparency	Day	31% 5% 10% 24% 21% 9%	129979
	Night	35% 5% 13% 24% 17% 6%	127050
Seeing	Day	10% 9% 19% 30% 24% 8%	15446
	Night	11% 5% 20% 41% 21% 3	24390

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	14% 14% 5% 14% 8% 5% 5% 5% 5% 5% 20%	3639
	11th to 20th	Day	12% 11% 3 6% 4 4 4 3 5% 6% 42%	3640
	21st to end	Day	16% 13% 4 11% 5% 4 3 2 3 5% 32%	4004
February	1st to 10th	Day	11% 11% 4 10% 6% 4 6% 5% 6% 8% 31%	1795
	11th to 20th	Day	9% 11% 4 8% 4 5% 5% 4 6% 6% 38%	1755
	21st to end	Day	7% 10% 3 7% 5% 4 5% 4 7% 8% 39%	1650
March	1st to 10th	Day	5% 7% 3 8% 6% 6% 7% 5% 8% 9% 36%	4518
	11th to 20th	Day	5% 8% 3 8% 6% 5% 4 4 5% 7% 45%	4906
	21st to end	Day	7% 8% 4 10% 8% 7% 6% 5% 7% 9% 29%	5826
April	1st to 10th	Day	8% 9% 2 7% 7% 6% 5% 5% 7% 8% 36%	2400
	11th to 20th	Day	6% 8% 3 6% 5% 4 5% 4 6% 8% 45%	2369
	21st to end	Day	5% 6% 2 6% 5% 5% 5% 5% 7% 8% 46%	2595
May	1st to 10th	Day	7% 4 1 4 3 4 4 3 5% 6% 59%	6320
	11th to 20th	Day	5% 5% 2 5% 4 4 4 4 5% 8% 53%	6277
	21st to end	Day	6% 6% 2 6% 4 4 5% 4 6% 7% 49%	6902
June	1st to 10th	Day	8% 5% 2 5% 4 4 4 3 7% 8% 49%	2800
	11th to 20th	Day	5% 4 2 5% 4 4 5% 5% 6% 7% 53%	2800
	21st to end	Day	3 3 1 4 4 3 3 3 5% 6% 65%	2800
July	1st to 10th	Day	1 2 1 1 1 2 2 2 3 4 81%	6319
	11th to 20th	Day	2 1 1 1 1 1 2 1 2 3 84%	6320
	21st to end	Day	2 2 2 2 2 2 2 4 5% 77%	6880
August	1st to 10th	Day	2 2 1 3 2 3 3 2 4 6% 71%	6210
	11th to 20th	Day	2 2 1 3 2 2 3 3 4 6% 72%	5843
	21st to end	Day	4 5% 2 4 3 3 3 3 4 6% 62%	5982
September	1st to 10th	Day	3 2 1 2 2 2 3 3 5% 6% 71%	2317
	11th to 20th	Day	4 4 2 5% 4 4 4 4 5% 6% 59%	2280
	21st to end	Day	6% 4 2 5% 3 4 4 2 5% 6% 60%	2046
October	1st to 10th	Day	5% 3 2 3 3 3 3 3 6% 8% 63%	3180
	11th to 20th	Day	5% 5% 2 5% 4 4 6% 5% 6% 9% 49%	3161
	21st to end	Day	8% 6% 2 7% 6% 6% 5% 4 6% 7% 43%	3147
November	1st to 10th	Day	10% 9% 2 7% 6% 5% 5% 4 6% 7% 38%	1739
	11th to 20th	Day	10% 11% 3 11% 6% 6% 5% 4 6% 6% 34%	1600
	21st to end	Day	11% 11% 5% 9% 5% 5% 6% 4 6% 7% 31%	1600
December	1st to 10th	Day	9% 8% 3 10% 4 4 4 4 6% 7% 40%	2620
	11th to 20th	Day	15% 16% 6% 14% 8% 5% 5% 4 4 5% 18%	3028
	21st to end	Day	14% 17% 5% 13% 7% 6% 5% 4 5% 5% 20%	4004
January	1st to 10th	Night	14% 21% 7% 11% 5% 5% 5% 4 5% 5% 19%	6306
	11th to 20th	Night	11% 9% 3 6% 4 3 3 3 5% 8% 45%	6320
	21st to end	Night	15% 14% 5% 11% 4 3 3 2 4 5% 34%	6952
February	1st to 10th	Night	11% 12% 4 7% 5% 5% 5% 5% 6% 8% 33%	2600
	11th to 20th	Night	10% 9% 3 7% 5% 4 4 4 6% 7% 41%	2532
	21st to end	Night	7% 11% 4 8% 5% 4 4 5% 6% 8% 38%	1980
March	1st to 10th	Night	5% 7% 2 6% 5% 6% 7% 5% 8% 9% 40%	5376
	11th to 20th	Night	6% 7% 3 6% 4 4 4 4 7% 6% 48%	5092
	21st to end	Night	7% 7% 3 9% 6% 6% 6% 6% 7% 9% 35%	5148
April	1st to 10th	Night	9% 7% 3 6% 5% 4 5% 3 7% 9% 41%	2000
	11th to 20th	Night	6% 7% 2 7% 3 3 4 4 6% 6% 52%	1979
	21st to end	Night	5% 5% 2 5% 4 4 5% 5% 7% 9% 49%	1802
May	1st to 10th	Night	4 4 2 4 3 3 4 3 4 5% 64%	3640
	11th to 20th	Night	4 4 2 4 3 3 4 3 5% 7% 61%	3616
	21st to end	Night	5% 4 1 4 3 3 3 4 6% 8% 58%	3972
June	1st to 10th	Night	8% 4 2 6% 3 3 5% 4 6% 8% 53%	1600
	11th to 20th	Night	5% 4 1 3 3 3 4 3 4 7% 62%	1600
	21st to end	Night	2 3 1 4 4 3 3 4 5% 6% 66%	1600
July	1st to 10th	Night	1 1 1 1 1 1 1 2 3 4 83%	3640
	11th to 20th	Night	1 1 1 1 1 2 2 2 3 86%	3640
	21st to end	Night	1 2 2 1 1 2 1 4 5% 81%	3970
August	1st to 10th	Night	2 2 1 3 2 3 3 3 4 6% 71%	3582
	11th to 20th	Night	4 2 1 3 2 2 3 3 4 5% 71%	4000
	21st to end	Night	3 3 1 4 3 3 4 3 5% 7% 64%	5012
September	1st to 10th	Night	3 2 1 2 1 2 3 3 4 6% 73%	1930
	11th to 20th	Night	3 3 2 4 3 4 3 3 5% 7% 64%	1900
	21st to end	Night	5% 3 1 4 3 3 3 4 5% 7% 62%	2130
October	1st to 10th	Night	4 3 1 3 3 2 4 3 6% 7% 64%	3800
	11th to 20th	Night	5% 4 1 5% 3 4 4 5% 8% 8% 52%	3777
	21st to end	Night	9% 6% 3 6% 4 4 5% 4 5% 8% 46%	4410
November	1st to 10th	Night	12% 9% 2 7% 5% 5% 5% 3 6% 7% 39%	2557
	11th to 20th	Night	11% 9% 3 8% 6% 4 5% 4 6% 7% 37%	2800
	21st to end	Night	11% 10% 4 9% 5% 4 5% 4 5% 7% 37%	2800
December	1st to 10th	Night	7% 8% 3 8% 4 3 4 3 5% 6% 47%	4560
	11th to 20th	Night	18% 16% 7% 15% 6% 4 4 3 5% 6% 16%	5176
	21st to end	Night	17% 16% 5% 8% 5% 5% 5% 3 4 5% 25%	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	62% 8% 12% 12% 6%	3639
	11th to 20th	Day	42% 5% 19% 26% 7%	3640
	21st to end	Day	56% 4 10% 20% 10%	4004
February	1st to 10th	Day	49% 9% 18% 19% 5% 1	1795
	11th to 20th	Day	43% 7% 16% 23% 9% 1	1764
	21st to end	Day	38% 9% 19% 22% 9% 2	1650
March	1st to 10th	Day	38% 8% 10% 25% 19% 1	4518
	11th to 20th	Day	35% 6% 10% 34% 14% 1	4906
	21st to end	Day	47% 9% 16% 20% 8% 1	5826
April	1st to 10th	Day	41% 9% 14% 21% 14% 1	2400
	11th to 20th	Day	33% 7% 13% 24% 19% 4	2372
	21st to end	Day	32% 8% 11% 27% 19% 3	2595
May	1st to 10th	Day	24% 5% 5% 22% 35% 8%	6320
	11th to 20th	Day	26% 5% 11% 31% 24% 4	6280
	21st to end	Day	30% 7% 13% 32% 16% 2	6904
June	1st to 10th	Day	31% 6% 9% 28% 21% 6%	2800
	11th to 20th	Day	26% 6% 9% 29% 25% 4	2800
	21st to end	Day	19% 4 9% 33% 26% 9%	2800
July	1st to 10th	Day	9% 2 4 18% 31% 35%	6251
	11th to 20th	Day	8% 1 3 14% 31% 43%	6245
	21st to end	Day	10% 3 5% 25% 36% 22%	6681
August	1st to 10th	Day	13% 3 5% 14% 39% 27%	4524
	11th to 20th	Day	13% 3 7% 36% 31% 10%	4231
	21st to end	Day	22% 3 8% 25% 35% 7%	4312
September	1st to 10th	Day	13% 4 7% 30% 32% 14%	2317
	11th to 20th	Day	24% 6% 10% 26% 25% 10%	2280
	21st to end	Day	25% 4 12% 32% 21% 6%	2046
October	1st to 10th	Day	21% 3 11% 37% 26% 2	3180
	11th to 20th	Day	31% 5% 18% 26% 18% 2	3161
	21st to end	Day	37% 6% 12% 28% 14% 3	3147
November	1st to 10th	Day	42% 8% 16% 21% 10% 2	1739
	11th to 20th	Day	48% 8% 17% 18% 7% 1	1600
	21st to end	Day	49% 8% 18% 15% 8% 1	1600
December	1st to 10th	Day	42% 7% 20% 23% 8%	2620
	11th to 20th	Day	68% 6% 11% 10% 4	3028
	21st to end	Day	65% 7% 11% 12% 4 1	4004
January	1st to 10th	Night	65% 6% 13% 10% 5%	6306
	11th to 20th	Night	38% 5% 20% 27% 9%	6320
	21st to end	Night	54% 4 12% 19% 10% 1	6952
February	1st to 10th	Night	46% 7% 22% 18% 6% 1	2600
	11th to 20th	Night	41% 7% 17% 22% 11% 2	2534
	21st to end	Night	40% 8% 16% 21% 12% 2	1980
March	1st to 10th	Night	34% 8% 12% 28% 16% 2	5376
	11th to 20th	Night	33% 5% 13% 33% 15% 1	5092
	21st to end	Night	42% 7% 17% 26% 7%	5148
April	1st to 10th	Night	36% 8% 15% 27% 13% 2	2000
	11th to 20th	Night	31% 5% 14% 27% 19% 3	1979
	21st to end	Night	28% 8% 13% 32% 17% 3	1802
May	1st to 10th	Night	23% 4 5% 22% 39% 7%	3637
	11th to 20th	Night	23% 4 10% 33% 26% 4	3616
	21st to end	Night	21% 6% 22% 33% 16% 1	3972
June	1st to 10th	Night	28% 5% 9% 32% 21% 4	1600
	11th to 20th	Night	22% 5% 10% 35% 25% 3	1600
	21st to end	Night	18% 5% 8% 33% 27% 9%	1600
July	1st to 10th	Night	8% 2 5% 23% 30% 34%	3600
	11th to 20th	Night	6% 2 4 13% 36% 40%	3592
	21st to end	Night	8% 2 5% 26% 36% 23%	3857
August	1st to 10th	Night	12% 2 4 14% 41% 27%	2601
	11th to 20th	Night	13% 3 9% 39% 25% 11%	2889
	21st to end	Night	17% 4 10% 26% 34% 10%	3605
September	1st to 10th	Night	12% 3 7% 30% 30% 17%	1930
	11th to 20th	Night	20% 4 12% 27% 26% 12%	1900
	21st to end	Night	20% 4 12% 33% 23% 8%	2130
October	1st to 10th	Night	19% 4 9% 42% 25% 1	3800
	11th to 20th	Night	26% 7% 17% 30% 18% 2	3777
	21st to end	Night	35% 5% 12% 30% 16% 1	4410
November	1st to 10th	Night	43% 7% 15% 21% 12% 1	2557
	11th to 20th	Night	44% 8% 17% 21% 8% 1	2800
	21st to end	Night	46% 7% 19% 17% 10% 1	2800
December	1st to 10th	Night	37% 6% 20% 28% 8%	4560
	11th to 20th	Night	69% 6% 12% 9% 3	5176
	21st to end	Night	60% 6% 14% 13% 6% 1	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	24% 7% 19% 28% 19% 5%	200
	11th to 20th	Day	21% 7% 11% 30% 25% 7%	200
	21st to end	Day	19% 2 8% 38% 27% 6%	220
February	1st to 10th	Day	16% 10% 19% 36% 16% 2	395
	11th to 20th	Day	18% 10% 23% 30% 17% 2	395
	21st to end	Day	14% 9% 26% 32% 15% 4	414
March	1st to 10th	Day	14% 12% 26% 29% 16% 2	500
	11th to 20th	Day	11% 14% 18% 31% 20% 5%	500
	21st to end	Day	13% 16% 24% 30% 14% 3	550
April	1st to 10th	Day	18% 13% 22% 25% 17% 5%	500
	11th to 20th	Day	12% 16% 23% 29% 14% 5%	492
	21st to end	Day	9% 14% 26% 26% 17% 8%	500
May	1st to 10th	Day	9% 12% 25% 31% 18% 5%	503
	11th to 20th	Day	12% 10% 23% 27% 20% 9%	528
	21st to end	Day	10% 9% 19% 27% 26% 10%	573
June	1st to 10th	Day	9% 8% 20% 26% 24% 12%	530
	11th to 20th	Day	8% 11% 26% 33% 16% 6%	530
	21st to end	Day	3 9% 19% 29% 33% 8%	530
July	1st to 10th	Day	3 5% 15% 36% 34% 8%	526
	11th to 20th	Day	2 5% 19% 32% 32% 11%	524
	21st to end	Day	2 3 14% 29% 37% 15%	575
August	1st to 10th	Day	4 3 12% 29% 36% 15%	527
	11th to 20th	Day	1 4 13% 26% 38% 18%	517
	21st to end	Day	4 7% 16% 29% 29% 15%	583
September	1st to 10th	Day	4 5% 14% 30% 32% 16%	503
	11th to 20th	Day	7% 6% 15% 33% 28% 11%	490
	21st to end	Day	8% 8% 19% 31% 28% 7%	490
October	1st to 10th	Day	10% 9% 22% 26% 26% 8%	490
	11th to 20th	Day	12% 8% 18% 28% 26% 8%	490
	21st to end	Day	15% 6% 25% 30% 16% 7%	364
November	1st to 10th	Day	19% 9% 17% 36% 15% 5%	287
	11th to 20th	Day	19% 9% 20% 27% 17% 10%	200
	21st to end	Day	14% 5% 13% 32% 29% 8%	200
December	1st to 10th	Day	16% 2 12% 33% 23% 16%	200
	11th to 20th	Day	16% 5% 12% 46% 21% 2	200
	21st to end	Day	18% 7% 13% 40% 18% 5%	220
January	1st to 10th	Night	20% 7% 18% 37% 15% 3	800
	11th to 20th	Night	18% 4 17% 37% 21% 2	800
	21st to end	Night	18% 3 14% 40% 22% 2	880
February	1st to 10th	Night	16% 6% 22% 40% 14% 2	800
	11th to 20th	Night	15% 4 22% 39% 18% 3	784
	21st to end	Night	11% 10% 19% 42% 16% 2	660
March	1st to 10th	Night	13% 6% 19% 45% 15% 2	800
	11th to 20th	Night	9% 7% 21% 42% 19% 1	800
	21st to end	Night	8% 9% 24% 43% 15% 2	880
April	1st to 10th	Night	12% 6% 22% 41% 18% 2	800
	11th to 20th	Night	8% 7% 29% 36% 17% 3	791
	21st to end	Night	7% 5% 28% 40% 18% 2	602
May	1st to 10th	Night	5% 4 28% 44% 18% 2	400
	11th to 20th	Night	8% 6% 22% 40% 24% 1	394
	21st to end	Night	6% 2 20% 45% 24% 3	433
June	1st to 10th	Night	9% 4 26% 38% 22% 1	400
	11th to 20th	Night	7% 4 33% 41% 14% 1	400
	21st to end	Night	3 4 29% 45% 19% 1	400
July	1st to 10th	Night	3 2 24% 51% 20% 1	390
	11th to 20th	Night	1 3 27% 51% 18% 1	388
	21st to end	Night	1 2 22% 45% 28% 1	438
August	1st to 10th	Night	2 2 21% 46% 26% 3	398
	11th to 20th	Night	3 1 13% 39% 36% 8%	567
	21st to end	Night	3 4 17% 40% 32% 4	877
September	1st to 10th	Night	5% 2 14% 39% 35% 4	772
	11th to 20th	Night	4 2 13% 37% 34% 9%	760
	21st to end	Night	7% 3 17% 39% 29% 5%	760
October	1st to 10th	Night	10% 3 16% 42% 25% 3	760
	11th to 20th	Night	9% 3 16% 40% 26% 5%	760
	21st to end	Night	12% 3 19% 44% 17% 4	836
November	1st to 10th	Night	15% 4 16% 48% 16% 2	780
	11th to 20th	Night	15% 6% 22% 37% 17% 3	800
	21st to end	Night	14% 4 19% 41% 18% 4	800
December	1st to 10th	Night	16% 4 16% 39% 22% 5%	800
	11th to 20th	Night	21% 4 14% 44% 17% 1	800
	21st to end	Night	18% 5% 20% 43% 13% 1	880

Page generated at 2025-08-31 22:51:09. Version ac07

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