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 2024-11-11.

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	10% 7% 2 6% 4 4 4 4 5% 6% 47%	105362
	Night	14% 9% 3 7% 5% 4 4 3 5% 6% 41%	102462
Transparency	Day	19% 48% 6% 11% 9% 6%	105108
	Night	22% 49% 6% 11% 8% 4	102305
Seeing	Day	13% 11% 24% 29% 18% 4	14384
	Night	17% 9% 21% 31% 18% 4	23483

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% 17% 6% 13% 7% 5% 5% 4 5% 5% 10%	2539
	11th to 20th	Day	22% 17% 6% 11% 5% 5% 7% 4 5% 4 13%	2540
	21st to end	Day	23% 15% 5% 11% 7% 6% 6% 4 5% 5% 12%	2794
February	1st to 10th	Day	21% 13% 4 8% 6% 5% 5% 4 5% 7% 23%	1615
	11th to 20th	Day	20% 13% 4 10% 4 5% 3 4 4 6% 27%	1772
	21st to end	Day	16% 14% 4 8% 5% 5% 6% 5% 5% 6% 25%	1570
March	1st to 10th	Day	10% 11% 3 9% 5% 5% 5% 5% 7% 9% 31%	3138
	11th to 20th	Day	10% 7% 3 6% 4 3 4 3 5% 8% 47%	3258
	21st to end	Day	17% 11% 4 11% 6% 6% 5% 5% 6% 7% 22%	4165
April	1st to 10th	Day	13% 9% 3 8% 5% 6% 5% 5% 7% 10% 29%	2280
	11th to 20th	Day	11% 8% 2 7% 5% 4 5% 4 6% 7% 40%	2249
	21st to end	Day	12% 6% 3 7% 5% 4 5% 4 6% 7% 40%	2464
May	1st to 10th	Day	13% 6% 2 5% 4 4 4 3 6% 8% 46%	4326
	11th to 20th	Day	6% 4 2 5% 3 3 3 3 4 6% 61%	4377
	21st to end	Day	10% 6% 2 6% 5% 4 6% 5% 7% 9% 40%	4813
June	1st to 10th	Day	13% 7% 2 6% 5% 4 4 4 5% 7% 43%	2660
	11th to 20th	Day	11% 5% 2 5% 4 4 4 4 6% 7% 49%	2660
	21st to end	Day	4 3 1 4 3 2 3 3 5% 6% 66%	2660
July	1st to 10th	Day	1 1 1 2 2 2 2 2 2 3 83%	4420
	11th to 20th	Day	1 1 2 2 2 2 2 3 4 81%	4420
	21st to end	Day	1 1 2 2 2 2 2 3 5% 79%	4790
August	1st to 10th	Day	2 2 1 3 2 2 3 3 4 5% 72%	4400
	11th to 20th	Day	2 2 1 3 2 2 3 3 4 6% 74%	4063
	21st to end	Day	3 3 1 4 2 2 3 3 3 5% 70%	4180
September	1st to 10th	Day	3 2 1 2 2 2 2 3 4 7% 73%	2280
	11th to 20th	Day	7% 5% 2 5% 3 4 5% 3 5% 6% 56%	2204
	21st to end	Day	8% 5% 2 5% 3 4 3 3 4 7% 55%	2090
October	1st to 10th	Day	8% 4 2 4 3 3 3 3 4 6% 61%	3304
	11th to 20th	Day	9% 6% 2 5% 3 4 5% 4 9% 8% 44%	3074
	21st to end	Day	15% 8% 3 7% 5% 5% 6% 3 6% 7% 35%	3101
November	1st to 10th	Day	22% 9% 2 7% 5% 4 6% 4 5% 8% 28%	1764
	11th to 20th	Day	18% 11% 3 10% 7% 6% 6% 5% 6% 8% 20%	1630
	21st to end	Day	19% 11% 4 10% 7% 4 6% 5% 6% 6% 22%	1520
December	1st to 10th	Day	18% 11% 4 11% 6% 5% 5% 5% 7% 8% 20%	1520
	11th to 20th	Day	20% 12% 6% 16% 11% 7% 6% 4 4 4 11%	1928
	21st to end	Day	18% 11% 5% 12% 10% 8% 7% 4 5% 6% 15%	2794
January	1st to 10th	Night	26% 17% 5% 12% 7% 5% 4 3 4 4 12%	4406
	11th to 20th	Night	23% 17% 6% 10% 5% 5% 5% 3 4 6% 16%	4420
	21st to end	Night	21% 12% 4 10% 7% 7% 6% 4 6% 7% 16%	4862
February	1st to 10th	Night	21% 14% 4 9% 5% 4 4 3 5% 6% 25%	2562
	11th to 20th	Night	19% 14% 3 7% 6% 3 3 4 5% 5% 31%	2296
	21st to end	Night	17% 17% 4 8% 6% 5% 4 3 4 5% 26%	1884
March	1st to 10th	Night	11% 12% 3 9% 5% 4 4 4 6% 8% 36%	3736
	11th to 20th	Night	11% 9% 3 6% 3 4 3 3 4 5% 49%	3718
	21st to end	Night	18% 11% 3 9% 5% 6% 6% 4 7% 8% 22%	3488
April	1st to 10th	Night	17% 12% 2 7% 4 5% 4 3 5% 8% 31%	1900
	11th to 20th	Night	15% 8% 2 6% 5% 4 4 3 5% 7% 41%	1879
	21st to end	Night	13% 9% 3 7% 5% 4 5% 4 6% 7% 37%	1715
May	1st to 10th	Night	16% 5% 2 5% 4 4 5% 3 5% 6% 46%	2621
	11th to 20th	Night	11% 3 2 4 3 3 4 3 5% 7% 55%	2516
	21st to end	Night	18% 8% 2 6% 5% 3 3 3 6% 7% 40%	2762
June	1st to 10th	Night	15% 6% 2 6% 4 4 4 4 6% 8% 41%	1520
	11th to 20th	Night	14% 6% 3 5% 5% 3 4 3 4 6% 47%	1520
	21st to end	Night	6% 3 1 4 3 3 4 3 5% 6% 61%	1520
July	1st to 10th	Night	1 1 1 2 2 1 2 2 4 4 81%	2540
	11th to 20th	Night	1 1 1 1 2 2 2 3 5% 82%	2540
	21st to end	Night	2 1 2 1 2 2 2 3 5% 79%	2761
August	1st to 10th	Night	3 3 1 3 2 3 3 2 4 6% 70%	2529
	11th to 20th	Night	2 2 1 3 2 3 3 3 5% 5% 72%	2769
	21st to end	Night	3 3 1 3 2 2 2 2 4 6% 71%	3498
September	1st to 10th	Night	4 2 2 3 2 3 3 2 3 5% 72%	1900
	11th to 20th	Night	6% 4 1 5% 3 3 3 3 6% 7% 58%	1976
	21st to end	Night	10% 4 2 4 3 3 3 3 5% 7% 56%	2090
October	1st to 10th	Night	7% 4 2 5% 3 3 3 2 3 5% 64%	3672
	11th to 20th	Night	10% 5% 2 5% 4 4 5% 4 7% 7% 47%	3860
	21st to end	Night	16% 7% 3 6% 4 4 5% 3 6% 7% 38%	4457
November	1st to 10th	Night	22% 10% 3 7% 4 4 4 3 4 6% 33%	2535
	11th to 20th	Night	22% 10% 4 9% 6% 4 4 4 5% 5% 26%	2552
	21st to end	Night	18% 11% 3 8% 7% 5% 4 3 6% 6% 28%	2660
December	1st to 10th	Night	19% 12% 4 9% 8% 6% 5% 5% 6% 5% 22%	2660
	11th to 20th	Night	22% 16% 4 14% 9% 6% 4 3 4 4 13%	3276
	21st to end	Night	21% 12% 4 13% 10% 6% 5% 3 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	46% 46% 6% 2 1	2539
	11th to 20th	Day	45% 42% 8% 5%	2540
	21st to end	Day	46% 43% 6% 4	2794
February	1st to 10th	Day	26% 67% 4 2	1615
	11th to 20th	Day	25% 67% 3 4 1	1781
	21st to end	Day	22% 67% 3 4 2 1	1570
March	1st to 10th	Day	25% 44% 8% 17% 7%	3138
	11th to 20th	Day	15% 42% 9% 26% 8%	3258
	21st to end	Day	32% 48% 8% 8% 4	4165
April	1st to 10th	Day	18% 67% 7% 5% 2	2280
	11th to 20th	Day	15% 68% 5% 7% 5% 1	2252
	21st to end	Day	14% 67% 4 8% 5%	2464
May	1st to 10th	Day	19% 45% 9% 15% 11% 1	4326
	11th to 20th	Day	11% 40% 7% 20% 18% 4	4380
	21st to end	Day	19% 47% 16% 14% 4	4814
June	1st to 10th	Day	10% 66% 5% 11% 7% 1	2660
	11th to 20th	Day	11% 66% 4 9% 8% 2	2660
	21st to end	Day	7% 64% 4 11% 12% 2	2660
July	1st to 10th	Day	6% 35% 2 5% 16% 36%	4351
	11th to 20th	Day	5% 35% 3 4 15% 38%	4345
	21st to end	Day	7% 35% 4 12% 22% 21%	4639
August	1st to 10th	Day	11% 36% 3 5% 22% 22%	4384
	11th to 20th	Day	9% 38% 4 28% 19% 3	4105
	21st to end	Day	13% 37% 5% 19% 20% 6%	4179
September	1st to 10th	Day	6% 61% 5% 12% 11% 4	2280
	11th to 20th	Day	14% 61% 5% 8% 10% 2	2204
	21st to end	Day	14% 62% 5% 13% 6% 1	2090
October	1st to 10th	Day	14% 38% 4 23% 18% 3	3304
	11th to 20th	Day	23% 39% 11% 18% 9%	3074
	21st to end	Day	30% 39% 4 20% 6%	3101
November	1st to 10th	Day	24% 59% 7% 9% 1	1764
	11th to 20th	Day	26% 63% 5% 4 1 1	1630
	21st to end	Day	25% 61% 7% 6% 2	1520
December	1st to 10th	Day	27% 63% 6% 4	1520
	11th to 20th	Day	32% 61% 3 3	1928
	21st to end	Day	33% 47% 11% 8% 1	2794
January	1st to 10th	Night	45% 45% 6% 4	4406
	11th to 20th	Night	44% 41% 9% 5% 1	4420
	21st to end	Night	39% 46% 11% 4	4862
February	1st to 10th	Night	27% 66% 4 2 1	2562
	11th to 20th	Night	24% 65% 4 6% 1	2298
	21st to end	Night	23% 66% 3 5% 1 1	1884
March	1st to 10th	Night	24% 44% 5% 15% 11% 1	3736
	11th to 20th	Night	17% 42% 5% 26% 10%	3718
	21st to end	Night	32% 48% 8% 8% 3	3488
April	1st to 10th	Night	19% 66% 6% 6% 3	1900
	11th to 20th	Night	15% 66% 5% 8% 5% 1	1879
	21st to end	Night	15% 67% 4 7% 6% 1	1715
May	1st to 10th	Night	22% 43% 7% 14% 11% 2	2621
	11th to 20th	Night	13% 41% 6% 25% 14% 1	2516
	21st to end	Night	21% 46% 12% 16% 4	2762
June	1st to 10th	Night	9% 66% 3 12% 9% 1	1520
	11th to 20th	Night	13% 65% 3 10% 7% 2	1520
	21st to end	Night	9% 64% 3 11% 9% 4	1520
July	1st to 10th	Night	4 35% 2 7% 16% 37%	2500
	11th to 20th	Night	3 35% 3 5% 12% 42%	2492
	21st to end	Night	7% 34% 2 11% 19% 27%	2674
August	1st to 10th	Night	12% 36% 3 6% 17% 27%	2521
	11th to 20th	Night	9% 37% 4 26% 21% 3	2793
	21st to end	Night	11% 37% 5% 22% 15% 11%	3498
September	1st to 10th	Night	9% 60% 4 11% 11% 6%	1900
	11th to 20th	Night	12% 61% 5% 10% 9% 4	1976
	21st to end	Night	12% 61% 5% 12% 9%	2090
October	1st to 10th	Night	14% 37% 5% 18% 24% 2	3672
	11th to 20th	Night	19% 39% 10% 15% 16% 1	3860
	21st to end	Night	29% 39% 4 21% 7%	4457
November	1st to 10th	Night	24% 58% 5% 10% 4	2535
	11th to 20th	Night	22% 64% 4 7% 2 1	2552
	21st to end	Night	21% 62% 6% 8% 4	2660
December	1st to 10th	Night	28% 61% 6% 4	2660
	11th to 20th	Night	33% 56% 7% 3 1	3276
	21st to end	Night	31% 48% 9% 8% 3	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% 20% 17% 13% 3	180
	11th to 20th	Day	25% 11% 23% 27% 11% 4	180
	21st to end	Day	29% 10% 24% 24% 13%	198
February	1st to 10th	Day	28% 17% 29% 16% 9% 1	275
	11th to 20th	Day	29% 19% 22% 21% 10% 1	416
	21st to end	Day	21% 15% 26% 25% 12% 2	382
March	1st to 10th	Day	20% 18% 29% 22% 11% 1	460
	11th to 20th	Day	15% 17% 21% 25% 18% 3	460
	21st to end	Day	17% 18% 32% 24% 8% 1	506
April	1st to 10th	Day	20% 16% 27% 21% 12% 5%	460
	11th to 20th	Day	14% 19% 31% 22% 11% 3	452
	21st to end	Day	12% 19% 27% 25% 13% 5%	460
May	1st to 10th	Day	10% 15% 27% 30% 15% 4	463
	11th to 20th	Day	17% 7% 24% 27% 19% 6%	488
	21st to end	Day	11% 9% 23% 29% 21% 6%	529
June	1st to 10th	Day	16% 10% 18% 28% 22% 6%	490
	11th to 20th	Day	11% 16% 30% 27% 14% 2	490
	21st to end	Day	4 8% 26% 33% 23% 6%	490
July	1st to 10th	Day	3 4 21% 43% 28% 2	486
	11th to 20th	Day	2 5% 26% 42% 21% 4	484
	21st to end	Day	1 5% 21% 42% 25% 6%	531
August	1st to 10th	Day	3 4 20% 40% 27% 7%	487
	11th to 20th	Day	2 4 18% 34% 34% 8%	477
	21st to end	Day	6% 10% 23% 31% 23% 8%	539
September	1st to 10th	Day	5% 6% 20% 33% 26% 9%	490
	11th to 20th	Day	9% 8% 24% 28% 24% 7%	490
	21st to end	Day	9% 9% 24% 30% 25% 4	490
October	1st to 10th	Day	11% 9% 22% 29% 23% 5%	490
	11th to 20th	Day	13% 13% 20% 27% 20% 6%	441
	21st to end	Day	23% 11% 25% 27% 11% 5%	330
November	1st to 10th	Day	26% 15% 25% 24% 9% 2	300
	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	25% 11% 19% 28% 14% 3	760
	21st to end	Night	24% 6% 21% 31% 15% 2	836
February	1st to 10th	Night	27% 12% 21% 27% 10% 2	760
	11th to 20th	Night	25% 11% 19% 29% 14% 2	744
	21st to end	Night	22% 17% 21% 28% 11% 2	628
March	1st to 10th	Night	19% 11% 27% 28% 13% 3	760
	11th to 20th	Night	16% 12% 22% 28% 19% 2	760
	21st to end	Night	21% 13% 28% 27% 10% 1	836
April	1st to 10th	Night	22% 10% 23% 30% 13% 3	760
	11th to 20th	Night	16% 12% 27% 26% 16% 3	751
	21st to end	Night	14% 12% 26% 29% 15% 3	575
May	1st to 10th	Night	11% 9% 28% 30% 19% 3	435
	11th to 20th	Night	14% 6% 17% 34% 23% 6%	374
	21st to end	Night	13% 9% 17% 35% 21% 5%	411
June	1st to 10th	Night	13% 9% 23% 33% 18% 4	380
	11th to 20th	Night	14% 12% 27% 31% 14% 2	380
	21st to end	Night	6% 5% 23% 38% 26% 2	380
July	1st to 10th	Night	4 3 21% 40% 27% 4	370
	11th to 20th	Night	3 4 28% 40% 21% 4	368
	21st to end	Night	1 6% 20% 38% 30% 5%	416
August	1st to 10th	Night	5% 2 19% 41% 26% 6%	378
	11th to 20th	Night	3 3 15% 36% 31% 11%	531
	21st to end	Night	5% 4 20% 37% 28% 7%	836
September	1st to 10th	Night	4 3 19% 38% 27% 8%	760
	11th to 20th	Night	8% 3 18% 31% 30% 10%	760
	21st to end	Night	11% 6% 17% 30% 27% 8%	760
October	1st to 10th	Night	13% 3 19% 39% 23% 4	760
	11th to 20th	Night	14% 9% 19% 29% 23% 6%	760
	21st to end	Night	19% 10% 20% 31% 15% 6%	836
November	1st to 10th	Night	24% 10% 22% 29% 14% 1	780
	11th to 20th	Night	26% 11% 21% 28% 10% 4	762
	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 2024-11-08 03:44:44. Version ac07

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