Introduction

Wasco County lies along the central part of the Columbia River. It is wholly within Climate Division 6 (North Central Oregon) established by the National Climatic Data Center. Below is a description of the climate of Division 6 followed by specific descriptions of Wasco County. Climate tables for various parameters, as observed at long-term climate stations in Wasco County, are included below.

Climate Division 6 — North Central Oregon

North Central Oregon, climatic Zone 6, is a relatively dry region lying east of the Cascade Mountains. The Cascades serve as an effective moisture barrier, causing storms to dump much of their moisture west of the peaks and leaving areas to the east in a "rain shadow." As a result, Zone 6 is generally rather dry. The region extends from the Columbia River southward over hill country to the forested mountain areas, which border climate Zone 7. The Columbia is used in irrigation, transportation and hydroelectric power, and therefore dominates the area.

This region is Oregon's major wheat producing area. Grain production on dry land farms is the main source of agricultural income except for the Hood River Valley, which produces mostly tree fruits. Despite relatively small dimensions, the latter is one of the most important production areas in the Northwest. Its annual income of approximately $60 million derives mostly from pears, apples, and cherries. Other important commodities produced in Zone 6 include green peas, irrigated truck crops, beef cattle, sheep, alfalfa, and poultry.

Just as most of Oregon, this region has a definite winter rainfall climate. The months of November through February generally receive the most precipitation due to winter storms, which bring rain to lower elevations and snow to higher ridges and peaks. Annual totals vary greatly and are proportional to elevation; some of the lower elevations receive less than 12 inches per year, while a few of the higher areas receive more than 40 inches. Occasional summer thunderstorms bring localized, occasionally heavy showers.

Figure 1 shows NOAA climate stations in Zone 6, which were in operation during the 1961-1990 period. Figure 2 shows the Wasco County region from the Oregon annual precipitation map. Table 1 lists normal monthly and annual precipitation for stations in Zone 6. Locations at the lowest elevations (adjacent to the Columbia) such as Arlington and Hermiston receive less than 10 inches per year. Precipitation increases steadily with elevation. Highest annual totals are found in the Blue Mountains along the extreme east border of the region, where totals exceeding 50 inches occur. Tables 2a and 2b list the average number of days with precipitation amounts exceeding certain thresholds.

The Columbia Gorge is a major east-west passageway connecting Zone 6 with the Willamette Valley and Oregon coast. Vigorous winds are common in and around the Gorge. During summer, wind direction is predominantly from the west, causing strong, steady winds within the Gorge and along the northern edge of Zone 6. These winds, in fact, make Hood River a world-renowned wind surfing location. Winter winds can blow from the west or the east and can reach speeds sufficient to cause widespread damage.

A major effect of the Gorge is a moderation of air temperatures near the Columbia by allowing maritime air to reach the area from the west; this can occur both in summer and winter. Occasionally, however, large-scale easterly flow brings very cold continental air to the region, resulting in extremely cold conditions. During such periods, the cold air passes westward through the Gorge, creating extreme conditions in the western valleys as well.

Table 3 lists normal monthly and annual temperatures in the region. Highest summer temperatures are observed at the low-lying points near the Columbia (i.e. Arlington, Hermiston, and Milton Freewater), while mean temperatures decrease with increasing elevation. Winter temperatures follow the same pattern with mildest temperatures at the lower elevation sites.

Table 4 lists average monthly and annual snowfall total for the various stations.

Median frost dates and length of the growing season are listed in Tables 5 and 6, respectively. These also follow the same elevation relationship evident in the temperature data: the longest growing seasons are in the mild and low elevation sites, while increasing elevation generally causes a shortening of the season. Arlington and Condon, both at nearly 3,000 feet above sea level, have much shorter growing seasons than lower sites such as The Dalles and Arlington.

Table 7 and 8 list average monthly and annual heating and growing degree days.

County Description

Established: Jan. 11, 1854
Population: 24,150
Area: 2,396 sq. mi.
Economy: Agriculture, forest products, manufacturing, electric power, aluminum and transportation.
County Seat: The Dalles

When the Territorial Legislature created Wasco County in 1854 from parts of Clackamas, Lane, Linn and Marion counties, it embraced all of Oregon east of the Cascade Range, most of Idaho and parts of Montana and Wyoming. It was named for the Wasco (or Wascopam) Indian tribe. Wasco's county seat is The Dalles. Now the trading hub of north-central Oregon, The Dalles gained earlier fame as the town at the end of the Oregon Trail. Thousands of years before that, humans scratched pictographs on rocks overlooking the Columbia River in this area. Later, Indian tribes gathered for generations near Celilo Falls to trade and fish. The county's Indian heritage continues in evidence today. Kah-Nee-Ta, a popular Oregon resort, is located on the Confederated Tribes of the Warm Springs Reservation in southern Wasco County.

(County information obtained from Oregon Blue Book)

Climate Tables (Wasco County, Oregon)