Kennewick-Pasco-Richland
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Kennewick-Pasco-Richland clear sky chart from 2005-11-06 to 2026-03-03.

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	7% 7% 3 6% 4 4 4 3 5% 6% 50%	139998
	Night	8% 8% 3 7% 5% 5% 5% 4 5% 7% 43%	138476
Transparency	Day	34% 4 11% 22% 20% 9%	134705
	Night	39% 5% 12% 21% 16% 7%	134773
Seeing	Day	9% 8% 20% 26% 24% 13%	15935
	Night	12% 6% 19% 36% 23% 3	25151

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	15% 18% 6% 14% 6% 6% 5% 4 5% 6% 15%	4722
	11th to 20th	Day	11% 11% 6% 9% 7% 7% 7% 5% 6% 6% 27%	4740
	21st to end	Day	14% 13% 6% 10% 6% 5% 7% 5% 5% 5% 24%	5187
February	1st to 10th	Day	14% 14% 6% 12% 8% 5% 5% 4 4 5% 23%	1824
	11th to 20th	Day	12% 13% 4 9% 5% 6% 4 4 4 6% 31%	1920
	21st to end	Day	9% 9% 3 9% 7% 5% 6% 5% 7% 8% 32%	1730
March	1st to 10th	Day	6% 7% 3 7% 5% 6% 6% 5% 8% 10% 37%	4539
	11th to 20th	Day	6% 9% 3 7% 5% 4 4 3 5% 6% 47%	4731
	21st to end	Day	9% 9% 3 9% 6% 6% 7% 5% 7% 9% 29%	5941
April	1st to 10th	Day	8% 8% 3 7% 5% 5% 5% 5% 7% 9% 39%	2400
	11th to 20th	Day	5% 7% 2 6% 4 5% 5% 4 7% 9% 47%	2369
	21st to end	Day	6% 6% 2 6% 4 4 4 4 6% 8% 50%	2560
May	1st to 10th	Day	7% 4 1 4 3 3 4 3 5% 7% 58%	6314
	11th to 20th	Day	5% 5% 2 5% 5% 5% 5% 4 6% 6% 53%	6277
	21st to end	Day	4 5% 2 5% 4 4 5% 4 6% 8% 55%	6902
June	1st to 10th	Day	9% 5% 2 6% 4 4 5% 3 5% 8% 50%	2800
	11th to 20th	Day	6% 4 2 4 4 4 5% 4 5% 8% 55%	2800
	21st to end	Day	3 3 1 3 3 3 3 3 4 6% 68%	2800
July	1st to 10th	Day	2 2 1 2 2 1 2 2 3 4 80%	6319
	11th to 20th	Day	1 1 1 2 2 1 2 1 2 3 84%	6320
	21st to end	Day	1 1 1 2 1 2 2 2 4 6% 78%	6880
August	1st to 10th	Day	3 3 1 4 2 3 2 2 4 6% 69%	6210
	11th to 20th	Day	2 1 1 2 2 2 2 2 4 6% 75%	5845
	21st to end	Day	4 4 1 4 3 3 3 3 5% 6% 65%	5984
September	1st to 10th	Day	2 1 2 2 2 3 2 5% 6% 73%	2400
	11th to 20th	Day	4 4 1 4 4 4 4 4 6% 6% 60%	2351
	21st to end	Day	6% 4 2 5% 4 4 3 3 5% 6% 59%	2200
October	1st to 10th	Day	5% 3 1 4 3 3 3 3 4 7% 64%	3322
	11th to 20th	Day	5% 4 2 5% 4 4 6% 5% 7% 10% 47%	3229
	21st to end	Day	10% 7% 2 8% 5% 6% 6% 5% 6% 7% 40%	3200
November	1st to 10th	Day	12% 9% 3 10% 6% 5% 5% 4 5% 7% 33%	1854
	11th to 20th	Day	12% 15% 4 10% 7% 6% 6% 4 6% 6% 24%	1748
	21st to end	Day	11% 14% 6% 14% 8% 7% 5% 4 5% 6% 20%	1680
December	1st to 10th	Day	9% 11% 7% 14% 10% 9% 6% 4 5% 5% 20%	2700
	11th to 20th	Day	16% 20% 8% 14% 7% 5% 4 3 4 4 15%	3108
	21st to end	Day	15% 16% 7% 17% 8% 6% 5% 3 3 4 17%	4092
January	1st to 10th	Night	18% 21% 7% 11% 6% 5% 5% 3 5% 5% 13%	8172
	11th to 20th	Night	10% 10% 4 7% 6% 6% 7% 5% 7% 8% 32%	8220
	21st to end	Night	11% 13% 6% 11% 6% 5% 7% 5% 6% 7% 23%	8994
February	1st to 10th	Night	13% 13% 4 8% 5% 5% 6% 5% 5% 7% 29%	2793
	11th to 20th	Night	10% 12% 3 8% 6% 5% 5% 4 6% 6% 34%	2585
	21st to end	Night	9% 10% 4 7% 7% 5% 5% 4 6% 6% 37%	2076
March	1st to 10th	Night	7% 7% 3 6% 4 5% 6% 5% 8% 9% 40%	5400
	11th to 20th	Night	8% 8% 3 7% 5% 4 4 4 5% 6% 45%	5264
	21st to end	Night	7% 9% 3 9% 6% 6% 7% 5% 9% 9% 30%	5033
April	1st to 10th	Night	11% 9% 3 7% 5% 4 5% 4 6% 8% 39%	2000
	11th to 20th	Night	8% 6% 3 6% 5% 4 3 4 5% 6% 50%	1979
	21st to end	Night	6% 5% 2 7% 5% 5% 5% 4 7% 7% 46%	1840
May	1st to 10th	Night	6% 4 1 4 3 4 4 4 6% 6% 57%	3644
	11th to 20th	Night	7% 5% 2 5% 4 4 4 3 6% 7% 53%	3616
	21st to end	Night	5% 4 2 5% 3 4 4 4 6% 8% 55%	3972
June	1st to 10th	Night	8% 4 1 4 4 4 6% 4 7% 9% 50%	1600
	11th to 20th	Night	6% 6% 3 6% 5% 4 4 3 5% 6% 54%	1600
	21st to end	Night	3 3 1 5% 5% 3 4 4 4 6% 63%	1600
July	1st to 10th	Night	1 2 1 2 1 1 2 2 4 5% 78%	3640
	11th to 20th	Night	1 1 1 1 1 1 2 2 4 84%	3640
	21st to end	Night	2 2 1 2 1 1 2 2 4 6% 78%	3970
August	1st to 10th	Night	3 3 1 3 3 3 3 3 5% 7% 66%	3582
	11th to 20th	Night	2 2 1 3 2 3 3 2 4 5% 72%	3998
	21st to end	Night	3 3 1 4 3 4 4 3 5% 6% 66%	5015
September	1st to 10th	Night	3 2 1 2 2 2 3 3 3 5% 73%	2000
	11th to 20th	Night	4 3 1 4 4 3 4 3 6% 6% 62%	2048
	21st to end	Night	6% 3 1 4 3 3 5% 2 5% 8% 60%	2200
October	1st to 10th	Night	5% 3 1 3 3 3 3 3 4 5% 67%	3874
	11th to 20th	Night	7% 4 1 5% 4 4 4 4 6% 8% 53%	3927
	21st to end	Night	10% 5% 2 6% 5% 5% 5% 4 7% 8% 45%	4600
November	1st to 10th	Night	14% 8% 3 8% 5% 6% 5% 4 5% 6% 36%	2665
	11th to 20th	Night	14% 11% 3 9% 6% 5% 5% 5% 5% 6% 30%	2867
	21st to end	Night	13% 11% 4 8% 6% 7% 6% 4 5% 8% 28%	2940
December	1st to 10th	Night	7% 11% 7% 10% 7% 7% 6% 5% 6% 8% 27%	4700
	11th to 20th	Night	17% 18% 7% 13% 7% 6% 6% 4 5% 5% 12%	5316
	21st to end	Night	15% 16% 5% 11% 7% 7% 5% 4 4 6% 20%	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	67% 7% 11% 10% 5%	4723
	11th to 20th	Day	55% 6% 16% 18% 4	4740
	21st to end	Day	59% 5% 14% 16% 6%	5187
February	1st to 10th	Day	61% 7% 16% 11% 5%	1824
	11th to 20th	Day	52% 7% 14% 19% 8%	1929
	21st to end	Day	47% 7% 15% 21% 9% 1	1730
March	1st to 10th	Day	38% 6% 13% 25% 17% 1	4539
	11th to 20th	Day	36% 4 13% 31% 16% 1	4731
	21st to end	Day	48% 5% 18% 21% 8% 1	5941
April	1st to 10th	Day	39% 6% 15% 24% 15% 1	2400
	11th to 20th	Day	33% 4 14% 27% 16% 6%	2372
	21st to end	Day	32% 3 13% 29% 19% 3	2560
May	1st to 10th	Day	25% 3 6% 27% 32% 8%	6314
	11th to 20th	Day	29% 4 9% 27% 24% 7%	6280
	21st to end	Day	27% 4 15% 30% 22% 3	6904
June	1st to 10th	Day	33% 3 9% 27% 22% 6%	2800
	11th to 20th	Day	26% 4 11% 28% 26% 6%	2800
	21st to end	Day	19% 2 8% 31% 29% 12%	2800
July	1st to 10th	Day	12% 1 3 15% 30% 38%	6251
	11th to 20th	Day	9% 1 2 10% 32% 46%	6245
	21st to end	Day	10% 2 4 23% 36% 25%	6681
August	1st to 10th	Day	15% 2 4 13% 37% 29%	4524
	11th to 20th	Day	11% 2 4 34% 36% 13%	4235
	21st to end	Day	19% 2 6% 28% 33% 12%	4311
September	1st to 10th	Day	13% 3 8% 29% 32% 16%	2400
	11th to 20th	Day	24% 4 11% 27% 27% 8%	2351
	21st to end	Day	27% 3 14% 33% 18% 5%	2200
October	1st to 10th	Day	21% 3 11% 38% 24% 3	3322
	11th to 20th	Day	29% 6% 21% 28% 14% 1	3229
	21st to end	Day	40% 5% 15% 28% 12% 1	3200
November	1st to 10th	Day	49% 6% 17% 20% 7% 1	1854
	11th to 20th	Day	57% 8% 15% 15% 4 1	1748
	21st to end	Day	62% 7% 15% 11% 5%	1680
December	1st to 10th	Day	64% 8% 12% 14% 3	2700
	11th to 20th	Day	73% 5% 10% 9% 2	3108
	21st to end	Day	72% 4 11% 12% 2	4092
January	1st to 10th	Night	71% 6% 12% 9% 3	8172
	11th to 20th	Night	46% 6% 19% 25% 4	8220
	21st to end	Night	55% 5% 17% 16% 6%	8994
February	1st to 10th	Night	52% 7% 20% 17% 4 1	2793
	11th to 20th	Night	47% 7% 15% 22% 7% 1	2587
	21st to end	Night	46% 7% 14% 22% 9% 2	2076
March	1st to 10th	Night	35% 5% 10% 30% 18% 1	5400
	11th to 20th	Night	38% 3 11% 31% 16%	5264
	21st to end	Night	45% 7% 16% 25% 7%	5033
April	1st to 10th	Night	43% 5% 14% 24% 14% 1	2000
	11th to 20th	Night	36% 4 10% 26% 19% 6%	1979
	21st to end	Night	34% 6% 13% 25% 19% 5%	1840
May	1st to 10th	Night	25% 4 6% 23% 37% 6%	3641
	11th to 20th	Night	29% 5% 7% 28% 27% 4	3616
	21st to end	Night	25% 5% 15% 33% 19% 3	3972
June	1st to 10th	Night	30% 5% 10% 26% 23% 7%	1600
	11th to 20th	Night	30% 4 6% 28% 25% 6%	1600
	21st to end	Night	23% 3 6% 26% 28% 15%	1600
July	1st to 10th	Night	11% 2 3 16% 27% 41%	3600
	11th to 20th	Night	7% 1 2 9% 31% 49%	3592
	21st to end	Night	10% 1 3 18% 36% 32%	3857
August	1st to 10th	Night	17% 1 3 10% 33% 36%	2601
	11th to 20th	Night	14% 2 4 30% 34% 17%	2885
	21st to end	Night	16% 2 6% 26% 31% 19%	3608
September	1st to 10th	Night	15% 3 7% 23% 31% 21%	2000
	11th to 20th	Night	22% 4 9% 26% 26% 14%	2048
	21st to end	Night	23% 4 9% 30% 25% 9%	2200
October	1st to 10th	Night	21% 2 8% 34% 32% 2	3874
	11th to 20th	Night	29% 4 15% 29% 22% 2	3927
	21st to end	Night	35% 5% 12% 32% 15% 2	4600
November	1st to 10th	Night	46% 7% 15% 22% 9% 1	2665
	11th to 20th	Night	53% 7% 14% 19% 6% 1	2867
	21st to end	Night	52% 8% 17% 16% 6% 1	2940
December	1st to 10th	Night	50% 9% 19% 18% 4	4700
	11th to 20th	Night	73% 7% 12% 6% 2	5316
	21st to end	Night	63% 6% 14% 12% 5%	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	27% 9% 21% 27% 14% 3	220
	11th to 20th	Day	20% 7% 17% 31% 20% 5%	220
	21st to end	Day	17% 6% 21% 30% 22% 4	242
February	1st to 10th	Day	19% 13% 24% 26% 14% 4	364
	11th to 20th	Day	19% 9% 20% 27% 19% 5%	465
	21st to end	Day	15% 11% 24% 28% 18% 4	446
March	1st to 10th	Day	14% 12% 28% 25% 17% 5%	509
	11th to 20th	Day	12% 10% 20% 28% 21% 9%	500
	21st to end	Day	15% 12% 27% 27% 16% 3	550
April	1st to 10th	Day	12% 15% 24% 24% 15% 10%	500
	11th to 20th	Day	8% 13% 29% 26% 15% 8%	492
	21st to end	Day	6% 10% 27% 27% 21% 9%	500
May	1st to 10th	Day	6% 9% 24% 27% 22% 11%	503
	11th to 20th	Day	10% 9% 23% 23% 22% 13%	528
	21st to end	Day	9% 5% 19% 25% 26% 16%	573
June	1st to 10th	Day	9% 8% 18% 23% 25% 17%	530
	11th to 20th	Day	7% 11% 27% 28% 18% 9%	530
	21st to end	Day	2 5% 19% 26% 30% 18%	530
July	1st to 10th	Day	3 2 11% 28% 40% 16%	526
	11th to 20th	Day	1 3 14% 29% 33% 21%	524
	21st to end	Day	1 2 11% 24% 33% 28%	575
August	1st to 10th	Day	3 3 10% 23% 34% 26%	527
	11th to 20th	Day	2 2 11% 24% 31% 31%	517
	21st to end	Day	4 6% 14% 26% 28% 21%	583
September	1st to 10th	Day	4 3 11% 26% 33% 25%	530
	11th to 20th	Day	5% 5% 16% 26% 28% 22%	530
	21st to end	Day	7% 7% 16% 27% 28% 15%	530
October	1st to 10th	Day	10% 5% 19% 26% 24% 15%	530
	11th to 20th	Day	10% 10% 16% 25% 25% 14%	510
	21st to end	Day	17% 8% 22% 31% 15% 7%	363
November	1st to 10th	Day	18% 9% 24% 28% 18% 3	330
	11th to 20th	Day	22% 11% 20% 25% 19% 2	256
	21st to end	Day	9% 12% 20% 29% 25% 5%	220
December	1st to 10th	Day	15% 9% 23% 25% 16% 11%	220
	11th to 20th	Day	19% 12% 22% 30% 15% 2	220
	21st to end	Day	17% 6% 32% 29% 13% 3	242
January	1st to 10th	Night	26% 9% 19% 28% 16% 2	840
	11th to 20th	Night	18% 7% 17% 35% 20% 3	840
	21st to end	Night	17% 5% 13% 38% 24% 3	924
February	1st to 10th	Night	18% 9% 20% 32% 20% 2	840
	11th to 20th	Night	13% 9% 20% 35% 20% 3	824
	21st to end	Night	13% 14% 20% 35% 17% 1	692
March	1st to 10th	Night	13% 7% 24% 36% 18% 2	808
	11th to 20th	Night	10% 9% 20% 35% 23% 2	800
	21st to end	Night	12% 9% 29% 34% 15% 1	880
April	1st to 10th	Night	16% 8% 20% 37% 17% 3	800
	11th to 20th	Night	10% 9% 29% 30% 19% 4	791
	21st to end	Night	7% 8% 27% 35% 21% 2	640
May	1st to 10th	Night	7% 6% 24% 38% 23% 3	404
	11th to 20th	Night	10% 6% 16% 36% 30% 3	394
	21st to end	Night	8% 3 20% 38% 27% 4	433
June	1st to 10th	Night	9% 5% 24% 35% 23% 4	400
	11th to 20th	Night	9% 6% 33% 34% 17% 2	400
	21st to end	Night	3 4 23% 39% 29% 3	400
July	1st to 10th	Night	4 2 18% 45% 29% 2	390
	11th to 20th	Night	4 2 20% 46% 27% 2	388
	21st to end	Night	1 2 17% 41% 36% 3	438
August	1st to 10th	Night	4 2 12% 42% 36% 4	398
	11th to 20th	Night	3 1 13% 36% 37% 10%	563
	21st to end	Night	3 2 14% 41% 34% 6%	880
September	1st to 10th	Night	3 3 14% 39% 37% 5%	800
	11th to 20th	Night	5% 2 12% 36% 38% 8%	800
	21st to end	Night	6% 4 17% 32% 35% 7%	800
October	1st to 10th	Night	10% 3 15% 39% 29% 4	800
	11th to 20th	Night	11% 8% 17% 33% 26% 6%	800
	21st to end	Night	10% 7% 23% 34% 21% 5%	880
November	1st to 10th	Night	16% 7% 21% 36% 19% 1	820
	11th to 20th	Night	18% 10% 21% 33% 17% 2	840
	21st to end	Night	16% 6% 17% 38% 20% 4	840
December	1st to 10th	Night	15% 8% 17% 35% 21% 3	840
	11th to 20th	Night	22% 9% 18% 35% 15% 1	840
	21st to end	Night	24% 7% 19% 35% 13% 1	924

Page generated at 2026-02-27 22:40:19. Version ac07

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