Climate

Benton County is located in the central part of the Columbia Basin, which has a landform surrounded by mountain ranges that have a pronounced effect on the region's climate. The following are characteristics of the climate as summarized in Benton County’s Comprehensive Plan (1998; source National Weather Service):

· The Rocky Mountain Range and ranges in southern British Columbia protect the basin from the more severe winter storms.

· Occasionally an outbreak of severely cold weather will penetrate into the basin for damaging spring or fall freezes.

· The Cascade Range to the west obstructs easterly flows of moist air into the basin.

· The County experiences strong seasonal winds associated with rapidly moving weather systems.

· The growing season is approximately 185 days from mid-April to mid-October.

· The percent of possible sunshine each month is 20-30 percent in winter, 50-60 percent in spring, and 80-85 percent in mid-summer.

· The number of clear days each month increases from about 5 in winter to 20 in summer.

· Dry with mild winters and warm sunny summers, cool summer nights;

· Summer temperatures in the warmest summer months can exceed 90⁰ F from 26 to 77 days with nights dropping to 50⁰ F, day time

temperatures can exceed 103⁰ F for about four days in two out of 10 summers;

· Winter afternoon temperatures range from 35 to 45⁰ F with night time readings at 20 to 30⁰ F, minimum temperatures can be 6⁰ F

or lower on four nights in two out of 10 winters, afternoons remain below freezing on about one third of all January days;

· It can get cold. In 1949-50, night time winter temperatures were less than 0⁰ F on 18 nights, minus 15⁰ F or lower on seven nights,

And minus 23⁰ F on one night (sustained cold temperatures were also experienced January-February 1996);

· Warm winters do occur - in 1957-58, the lowest temperature was 19⁰ F;

· Number of days with maximum temperatures below freezing ranges from two to 46.

· Mean annual precipitation is from 5 to 10 inches, with from 10 to 15 inches in discrete areas on the Horse Heaven and Rattlesnake

hills.

· Approximately 70 percent of precipitation occurs between November and April averaging one inch per month as either rain or

snow in mid-winter months;

· There can be no rain from 3 to 6 weeks at a time in mid-summer.

· Thunderstorms occur on 10 to 15 days between March and October, usually accompanied by light rainfall, but hail and heavy

showers can occur;

· Winter season snowfall has ranged from less than ½ inch (1957-58) to 44 inches  (1915-16), accumulations have ranged from 4

inches to 21 inches (February 1916);

· Snow cover can melt rapidly by rain or warm Chinook winds;

· Severe winter and spring flooding of the lower Yakima River can occur as a result of snowmelt and/or river icing conditions, such

as occurred in December 1995 and February 1996;

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