The Blue Mountains in spring (first picture) and winter (second picture)

All data originally measured at the Walla Walla Regional Airport, at an elevation of 1,204 ft and located at N46º05'40", W118º17'17".

Mean annual temperature:
47.6º F

Mean annual minimum temperature (average daily low temperature for a whole year):
35.9º F

Mean annual maximum temperature (average daily high temperature for a whole year):
59.3º F
 

Temperature (°F)	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
mean maximum	35.5	41.6	49.8	58.4	67.0	75.4	83.5	82.6	72.7	58.9	42.9	36.3
monthly mean	30.0	34.6	40.1	46.2	52.9	60.0	65.1	64.7	57.2	47.4	37.1	31.1
mean minimum	24.5	27.7	30.5	34.0	38.8	44.6	46.7	46.7	41.7	36.0	30.9	25.8

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Average annual precipitation total:
19.53 inches

Median date of last occurrence in spring of
24º F: March 19
28º F: April 19
32º F: May 19
36º F: June 8

Median date of first occurrence in fall of
24º F: November 16
28º F: October 17
32º F: October 2
36º F: September 12

Growing Season:
Average days between occurrences of
24º F: 243
28º F: 183
32º F: 121
36º F: 100

Mean number of days per year with 0.01 inches or more precipitation:
106

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Precipitation (inches)	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Sep
monthly precipitation	2.18	1.97	1.94	1.71	1.62	1.09	0.54	0.78	0.98	1.55	2.65	2.52

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	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
mean days w/at least 0.01" precipitation	13	11	12	9	9	7	3	3	5	9	11	12

Mean percentage of possible sunshine:
60%
 

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
mean percentage sky cover	81	74	63	54	50	45	24	27	40	52	74	84

The mean percentage of sky cover is calculated as the amount of clear sky versus the area of sky that is covered in clouds. Measurements are taken only during daylight hours.
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	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
fastest wind (MPH)	42	47	62	41	32	37	36	26	51	54	67	47

Mean sea level pressure:
30.03 inches
 

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
mean sea level pressure (inches)	30.12	30.09	30.03	30.00	29.97	29.94	29.94	29.97	30.06	30.15	30.12	30.03

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Mean annual number of days that the maximum temperature is 90º F or above:
37

Mean annual number of days that the minimum temperature is 32º F or below:
66
 

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
avg highest monthly high (°F)	54.18	59.24	64.88	76.71	84.88	90.24	97.82	97.59	88.12	77.59	60.71	54.94
avg lowest monthly low (°F)	13.06	12.00	26.25	33.94	38.19	44.56	49.94	51.25	40.63	31.63	22.19	12.50

 

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
max temperature 90° F or above	0	0	0	0	1.75	6.50	15.81	13.81	4.50	0	0	0
min temperature Below 32° F	18.88	12.94	4.56	0.19	0	0	0	0	0.06	1.50	7.94	20.38

Average inches of snowfall per year:
17.63 in
 

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
average snowfall (inches)	5.73	4.23	1.33	0.00	0.00	0.00	19.32	0.00	0.00	0.13	2.03	5.86

Mean Relative Humidity (Percent)	7am	1pm	7pm
Annual	70	51	51
January	82	73	80
April	69	44	43
July	54	29	24
October	72	50	54

 

Resources

Environmental Data Service, 1968, Climatic atlas of the United States: U.S. Department of Commerce: Environmental Science Services Administration.

Taylor, G.H. and R.R. Hatton, 1999, The Oregon weather book: a state of extremes: Corvallis, Oregon State University Press.

Taylor, G.H. and C. Hannon, 1999, The climate of Oregon: from rain forest to desert:
Corvallis, Oregon State University Press.

Taylor, G. H. and A. Bartlett, 1993, The climate of Oregon: climate zone 8, northeast area: Corvallis, Oregon Climate Service, Oregon State University.

Walla Walla Weather, http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?wawall.
 

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