Walla Walla
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Walla Walla clear sky chart from 2005-11-06 to 2024-01-13.

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	12% 7% 3 6% 5% 3 5% 5% 5% 7% 44%	74800
	Night	15% 8% 3 6% 6% 3 4 4 5% 6% 38%	74956
Transparency	Day	39% 9% 13% 19% 15% 5%	74503
	Night	45% 8% 12% 18% 12% 5%	74774
Seeing	Day	14% 11% 24% 28% 18% 4	13254
	Night	18% 9% 21% 30% 18% 4	22496

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	24% 13% 4 9% 8% 4 6% 6% 6% 6% 13%	1519
	11th to 20th	Day	23% 11% 5% 9% 8% 5% 6% 5% 5% 6% 17%	1456
	21st to end	Day	18% 12% 5% 9% 8% 5% 7% 4 5% 7% 19%	1584
February	1st to 10th	Day	21% 12% 4 8% 6% 4 5% 5% 5% 7% 23%	1530
	11th to 20th	Day	20% 12% 4 8% 6% 3 4 5% 4 6% 28%	1677
	21st to end	Day	17% 12% 5% 8% 6% 3 7% 6% 5% 6% 25%	1480
March	1st to 10th	Day	16% 11% 4 8% 7% 4 5% 5% 6% 8% 27%	1800
	11th to 20th	Day	15% 8% 5% 7% 7% 4 6% 6% 6% 9% 26%	1839
	21st to end	Day	18% 10% 4 8% 7% 4 6% 7% 6% 7% 22%	2376
April	1st to 10th	Day	13% 8% 4 6% 7% 4 6% 6% 7% 10% 28%	2160
	11th to 20th	Day	12% 8% 2 7% 5% 3 5% 5% 6% 8% 40%	2129
	21st to end	Day	13% 6% 4 6% 6% 3 6% 5% 5% 7% 41%	2334
May	1st to 10th	Day	8% 6% 2 5% 5% 3 4 5% 6% 9% 48%	2465
	11th to 20th	Day	11% 5% 3 6% 6% 4 5% 5% 6% 8% 40%	2477
	21st to end	Day	11% 5% 3 6% 5% 3 5% 5% 7% 8% 41%	2723
June	1st to 10th	Day	13% 6% 2 5% 5% 3 5% 4 5% 7% 44%	2520
	11th to 20th	Day	11% 5% 2 5% 4 3 4 5% 5% 8% 49%	2520
	21st to end	Day	4 3 1 3 3 2 3 4 5% 6% 66%	2520
July	1st to 10th	Day	2 2 1 2 2 1 3 4 4 5% 74%	2520
	11th to 20th	Day	2 2 1 2 2 1 3 3 4 5% 75%	2520
	21st to end	Day	1 1 1 1 1 2 3 3 4 82%	2741
August	1st to 10th	Day	2 2 1 2 3 1 3 3 3 5% 75%	2507
	11th to 20th	Day	2 2 2 2 1 2 3 3 6% 76%	2325
	21st to end	Day	4 3 1 3 3 2 2 3 3 6% 69%	2376
September	1st to 10th	Day	3 2 1 2 2 1 2 3 4 6% 74%	2160
	11th to 20th	Day	7% 4 2 4 3 2 5% 5% 5% 6% 57%	2088
	21st to end	Day	9% 5% 2 5% 4 3 4 4 4 7% 54%	1980
October	1st to 10th	Day	11% 5% 3 4 4 3 4 4 5% 6% 51%	1872
	11th to 20th	Day	12% 6% 2 4 4 2 4 5% 8% 8% 45%	1754
	21st to end	Day	17% 7% 2 7% 6% 3 4 4 4 6% 38%	1782
November	1st to 10th	Day	23% 8% 2 6% 6% 3 6% 5% 5% 8% 28%	1674
	11th to 20th	Day	18% 10% 4 9% 8% 4 7% 6% 6% 8% 20%	1630
	21st to end	Day	20% 10% 5% 9% 7% 3 6% 6% 6% 7% 22%	1520
December	1st to 10th	Day	19% 10% 5% 9% 7% 4 5% 6% 7% 8% 20%	1520
	11th to 20th	Day	20% 12% 6% 14% 12% 6% 6% 5% 3 4 11%	1928
	21st to end	Day	18% 10% 5% 10% 12% 5% 8% 6% 5% 6% 15%	2794
January	1st to 10th	Night	26% 13% 5% 9% 8% 4 5% 5% 5% 6% 15%	2646
	11th to 20th	Night	22% 11% 6% 8% 8% 4 5% 4 4 6% 20%	2560
	21st to end	Night	20% 11% 6% 9% 7% 4 5% 4 6% 7% 20%	2772
February	1st to 10th	Night	22% 13% 4 8% 6% 2 4 4 5% 7% 26%	2427
	11th to 20th	Night	19% 14% 4 6% 6% 2 4 4 5% 5% 31%	2171
	21st to end	Night	18% 16% 5% 7% 7% 3 5% 4 4 6% 26%	1776
March	1st to 10th	Night	17% 9% 4 9% 6% 3 4 4 6% 8% 30%	2160
	11th to 20th	Night	15% 10% 4 7% 5% 3 5% 5% 6% 7% 32%	2117
	21st to end	Night	19% 12% 4 6% 5% 4 5% 5% 6% 9% 25%	1980
April	1st to 10th	Night	17% 11% 2 7% 4 4 5% 4 6% 8% 31%	1800
	11th to 20th	Night	16% 7% 3 5% 5% 3 5% 3 5% 6% 41%	1779
	21st to end	Night	13% 8% 3 6% 6% 3 6% 4 6% 7% 37%	1625
May	1st to 10th	Night	10% 5% 2 4 5% 3 5% 4 5% 7% 49%	1493
	11th to 20th	Night	12% 4 2 5% 5% 3 6% 5% 6% 9% 43%	1416
	21st to end	Night	12% 7% 3 6% 7% 3 4 5% 7% 8% 39%	1552
June	1st to 10th	Night	15% 5% 2 5% 5% 3 4 5% 6% 8% 42%	1440
	11th to 20th	Night	15% 5% 3 4 6% 2 4 4 4 6% 46%	1440
	21st to end	Night	6% 2 1 4 3 2 4 3 6% 6% 61%	1440
July	1st to 10th	Night	3 2 1 2 2 2 3 4 4 6% 71%	1440
	11th to 20th	Night	2 1 1 2 2 2 3 3 3 6% 75%	1440
	21st to end	Night	1 1 1 2 1 2 2 3 3 6% 79%	1576
August	1st to 10th	Night	4 2 1 2 1 2 3 3 5% 6% 72%	1432
	11th to 20th	Night	3 3 1 2 2 2 1 3 4 4 75%	1570
	21st to end	Night	4 3 1 2 3 2 3 3 4 6% 70%	1980
September	1st to 10th	Night	4 2 2 3 3 1 3 2 3 5% 73%	1800
	11th to 20th	Night	6% 4 1 4 3 3 3 4 5% 7% 60%	1872
	21st to end	Night	10% 4 2 4 4 2 3 4 5% 7% 55%	1980
October	1st to 10th	Night	11% 4 3 5% 4 3 4 4 4 6% 52%	2084
	11th to 20th	Night	13% 6% 3 5% 5% 3 4 4 6% 6% 46%	2205
	21st to end	Night	17% 7% 3 5% 5% 3 5% 4 5% 6% 40%	2574
November	1st to 10th	Night	22% 10% 3 6% 5% 3 4 4 4 6% 33%	2405
	11th to 20th	Night	23% 9% 5% 7% 7% 3 5% 4 5% 6% 27%	2546
	21st to end	Night	18% 10% 3 7% 8% 4 5% 4 6% 7% 28%	2660
December	1st to 10th	Night	20% 11% 4 8% 8% 5% 6% 6% 6% 5% 22%	2660
	11th to 20th	Night	22% 15% 5% 13% 10% 5% 5% 4 4 4 13%	3276
	21st to end	Night	21% 11% 4 10% 13% 4 5% 5% 4 5% 17%	4862

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	70% 9% 13% 6% 1	1519
	11th to 20th	Day	66% 8% 14% 10% 1	1456
	21st to end	Day	63% 10% 17% 9% 1	1584
February	1st to 10th	Day	60% 12% 15% 10% 3	1530
	11th to 20th	Day	57% 9% 17% 13% 4	1686
	21st to end	Day	58% 11% 13% 12% 5% 1	1480
March	1st to 10th	Day	54% 11% 15% 14% 6% 1	1800
	11th to 20th	Day	53% 10% 15% 17% 4	1839
	21st to end	Day	57% 12% 15% 13% 3	2376
April	1st to 10th	Day	48% 13% 16% 17% 7%	2160
	11th to 20th	Day	42% 10% 15% 19% 12% 2	2132
	21st to end	Day	42% 9% 14% 21% 13% 1	2334
May	1st to 10th	Day	32% 9% 15% 26% 17% 1	2465
	11th to 20th	Day	42% 9% 13% 21% 13% 2	2480
	21st to end	Day	40% 10% 14% 23% 12% 2	2724
June	1st to 10th	Day	40% 8% 11% 24% 15% 2	2520
	11th to 20th	Day	33% 8% 14% 26% 16% 3	2520
	21st to end	Day	19% 7% 11% 29% 26% 9%	2520
July	1st to 10th	Day	15% 4 9% 22% 32% 19%	2451
	11th to 20th	Day	13% 4 9% 14% 36% 25%	2445
	21st to end	Day	8% 2 5% 15% 42% 27%	2589
August	1st to 10th	Day	13% 4 9% 21% 37% 17%	2490
	11th to 20th	Day	12% 3 10% 24% 36% 15%	2325
	21st to end	Day	19% 4 8% 28% 33% 9%	2376
September	1st to 10th	Day	14% 4 12% 27% 29% 15%	2160
	11th to 20th	Day	27% 6% 12% 22% 25% 8%	2088
	21st to end	Day	31% 7% 15% 26% 17% 5%	1980
October	1st to 10th	Day	34% 7% 14% 26% 17% 2	1872
	11th to 20th	Day	34% 10% 16% 26% 12% 2	1754
	21st to end	Day	46% 9% 15% 22% 7% 1	1782
November	1st to 10th	Day	52% 10% 17% 17% 4	1674
	11th to 20th	Day	61% 11% 15% 11% 1 1	1630
	21st to end	Day	59% 12% 16% 11% 3	1520
December	1st to 10th	Day	61% 13% 12% 12% 1	1520
	11th to 20th	Day	63% 22% 9% 6%	1928
	21st to end	Day	59% 15% 15% 10% 1	2794
January	1st to 10th	Night	69% 9% 10% 10% 1	2646
	11th to 20th	Night	66% 8% 12% 11% 3	2560
	21st to end	Night	61% 10% 14% 13% 1 1	2772
February	1st to 10th	Night	59% 8% 16% 13% 4	2427
	11th to 20th	Night	56% 7% 14% 17% 6%	2173
	21st to end	Night	59% 8% 10% 16% 6% 2	1776
March	1st to 10th	Night	53% 8% 12% 19% 7% 1	2160
	11th to 20th	Night	48% 10% 13% 23% 6%	2117
	21st to end	Night	56% 10% 14% 17% 4	1980
April	1st to 10th	Night	51% 9% 14% 18% 9%	1800
	11th to 20th	Night	44% 6% 14% 21% 11% 4	1779
	21st to end	Night	44% 10% 14% 15% 14% 3	1625
May	1st to 10th	Night	35% 7% 13% 25% 19% 2	1493
	11th to 20th	Night	37% 9% 13% 23% 15% 3	1416
	21st to end	Night	41% 9% 13% 23% 13% 1	1552
June	1st to 10th	Night	38% 8% 12% 24% 16% 2	1440
	11th to 20th	Night	38% 6% 12% 27% 13% 4	1440
	21st to end	Night	23% 5% 11% 28% 22% 11%	1440
July	1st to 10th	Night	15% 5% 7% 18% 32% 24%	1400
	11th to 20th	Night	13% 4 8% 17% 28% 30%	1392
	21st to end	Night	9% 2 5% 14% 33% 37%	1488
August	1st to 10th	Night	14% 3 7% 19% 35% 21%	1424
	11th to 20th	Night	15% 4 6% 19% 34% 22%	1570
	21st to end	Night	17% 4 8% 23% 32% 16%	1980
September	1st to 10th	Night	17% 3 9% 24% 28% 19%	1800
	11th to 20th	Night	24% 6% 9% 24% 25% 13%	1872
	21st to end	Night	29% 6% 11% 26% 20% 8%	1980
October	1st to 10th	Night	34% 6% 11% 26% 20% 3	2084
	11th to 20th	Night	38% 8% 10% 22% 17% 4	2205
	21st to end	Night	45% 8% 12% 20% 13% 2	2574
November	1st to 10th	Night	52% 8% 12% 22% 6% 1	2405
	11th to 20th	Night	56% 10% 14% 16% 3 1	2546
	21st to end	Night	52% 11% 16% 16% 5%	2660
December	1st to 10th	Night	61% 11% 13% 13% 2	2660
	11th to 20th	Night	65% 14% 13% 7% 1	3276
	21st to end	Night	57% 16% 13% 11% 4	4862

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	32% 15% 21% 17% 13% 3	180
	11th to 20th	Day	27% 9% 25% 23% 12% 5%	164
	21st to end	Day	31% 9% 25% 23% 12%	176
February	1st to 10th	Day	30% 16% 28% 15% 10% 2	250
	11th to 20th	Day	30% 19% 22% 19% 10% 1	381
	21st to end	Day	22% 14% 25% 25% 12% 1	346
March	1st to 10th	Day	20% 18% 30% 21% 11% 1	420
	11th to 20th	Day	16% 18% 21% 25% 18% 2	420
	21st to end	Day	17% 18% 32% 23% 8% 1	462
April	1st to 10th	Day	20% 15% 27% 21% 12% 5%	420
	11th to 20th	Day	16% 19% 30% 22% 10% 3	412
	21st to end	Day	12% 18% 27% 25% 13% 5%	420
May	1st to 10th	Day	10% 15% 26% 30% 15% 4	423
	11th to 20th	Day	18% 7% 23% 27% 19% 6%	448
	21st to end	Day	11% 9% 23% 29% 21% 7%	485
June	1st to 10th	Day	16% 9% 18% 28% 22% 7%	450
	11th to 20th	Day	11% 15% 30% 28% 13% 2	450
	21st to end	Day	3 7% 27% 34% 23% 6%	450
July	1st to 10th	Day	3 4 21% 43% 28% 2	446
	11th to 20th	Day	3 5% 27% 43% 19% 3	444
	21st to end	Day	1 5% 22% 41% 25% 6%	487
August	1st to 10th	Day	3 4 20% 40% 26% 6%	447
	11th to 20th	Day	2 4 18% 33% 35% 8%	437
	21st to end	Day	5% 10% 23% 32% 23% 6%	495
September	1st to 10th	Day	5% 6% 21% 35% 26% 7%	450
	11th to 20th	Day	8% 8% 25% 27% 25% 7%	450
	21st to end	Day	9% 8% 25% 29% 24% 3	450
October	1st to 10th	Day	11% 10% 22% 30% 23% 4	450
	11th to 20th	Day	14% 13% 20% 28% 20% 6%	404
	21st to end	Day	23% 11% 25% 25% 11% 5%	297
November	1st to 10th	Day	27% 15% 25% 24% 8% 1	270
	11th to 20th	Day	21% 12% 22% 28% 14% 3	232
	21st to end	Day	19% 11% 22% 27% 19% 2	180
December	1st to 10th	Day	22% 16% 17% 23% 13% 9%	180
	11th to 20th	Day	29% 16% 26% 20% 8% 2	180
	21st to end	Day	25% 13% 27% 22% 12% 3	198
January	1st to 10th	Night	32% 13% 17% 23% 12% 2	760
	11th to 20th	Night	26% 11% 19% 27% 14% 3	732
	21st to end	Night	25% 6% 20% 30% 16% 2	792
February	1st to 10th	Night	28% 12% 19% 28% 11% 2	720
	11th to 20th	Night	26% 11% 19% 28% 15% 2	704
	21st to end	Night	22% 16% 21% 28% 10% 2	592
March	1st to 10th	Night	19% 11% 26% 28% 13% 3	720
	11th to 20th	Night	17% 13% 22% 28% 19% 2	720
	21st to end	Night	22% 13% 27% 26% 11% 2	792
April	1st to 10th	Night	22% 10% 23% 30% 13% 3	720
	11th to 20th	Night	16% 11% 26% 26% 17% 4	711
	21st to end	Night	15% 11% 26% 29% 16% 3	545
May	1st to 10th	Night	11% 8% 29% 30% 20% 3	413
	11th to 20th	Night	14% 6% 16% 34% 23% 7%	354
	21st to end	Night	13% 8% 17% 35% 21% 6%	389
June	1st to 10th	Night	13% 9% 23% 33% 18% 4	360
	11th to 20th	Night	14% 13% 27% 30% 14% 2	360
	21st to end	Night	5% 5% 23% 38% 26% 3	360
July	1st to 10th	Night	4 3 21% 40% 28% 4	350
	11th to 20th	Night	3 5% 29% 39% 20% 4	348
	21st to end	Night	1 5% 20% 38% 31% 5%	394
August	1st to 10th	Night	5% 2 20% 41% 26% 6%	358
	11th to 20th	Night	3 3 15% 35% 33% 12%	502
	21st to end	Night	5% 4 19% 37% 28% 7%	792
September	1st to 10th	Night	4 3 20% 39% 27% 8%	720
	11th to 20th	Night	8% 3 17% 30% 31% 10%	720
	21st to end	Night	11% 6% 17% 30% 27% 8%	720
October	1st to 10th	Night	14% 3 18% 38% 23% 4	720
	11th to 20th	Night	14% 10% 19% 28% 23% 7%	720
	21st to end	Night	19% 10% 20% 30% 15% 7%	792
November	1st to 10th	Night	24% 9% 22% 30% 13% 1	740
	11th to 20th	Night	26% 11% 21% 28% 10% 4	760
	21st to end	Night	21% 9% 19% 30% 17% 4	760
December	1st to 10th	Night	23% 8% 21% 28% 18% 4	760
	11th to 20th	Night	29% 11% 19% 28% 11% 1	760
	21st to end	Night	32% 12% 21% 24% 10% 1	836

Page generated at 2024-01-10 07:16:13. Version ac07

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