Introduction

Union County lies along the northeastern part of Oregon. It is wholly within Climate Division 8 (Northest Oregon) established by the National Climatic Data Center. Below is a description of the climate of Division 8 followed by specific descriptions of Union County. Climate tables for various parameters, as observed at long-term climate stations in Union County, are included below.

Climate Division 8 — Northeast Oregon

Climate Zone 8 occupies the northeastern corner of Oregon, occupying all of Wallowa, Baker, and Union Counties as well as portions of Umatilla and Grant. The area includes several sizable mountain ranges with large valleys between them. Among the larger cities are La Grande, Baker City, John Day, and Enterprise, although the biggest of these (La Grande) has a population of only slightly above 10,000 residents.

Several million acres of Federal land are being utilized by ranchers for livestock which is the major industry in this region. Beef cattle are the main livestock raised, but sheep, dairy herds, poultry, and hogs are significant income sources as well. Field crops are also an important commodity and include wheat, potatoes, barley, oats, and grass seed. Lumber is also produced in significant quantities from the forested areas in the region.

Annual precipitation totals in Zone 8 valley areas are generally below 20 inches. Some locations surrounded by high mountains, such as Baker City and Unity, barely exceed 10 inches per year. High elevation sites, on the other hand, receive much larger annual totals. Locations near the top of the Wallowa Mountains, for example, may exceed 100 inches precipitation per year, much of it in the form of snow. Figure 1 shows NOAA climate stations in Zone 8, which were in operation during the 1961-1990 period. Figure 2 shows the Union County region from the Oregon annual precipitation map. Table 1 lists monthly and annual normal precipitation at Zone 8 sites. Highest normal precipitation totals tend to be in winter and late spring. Unlike most of Oregon, Zone 8's monthly distribution in comparison is remarkably uniform throughout the year. Tables 2a and 2b list the average number of days with precipitation amounts exceeding certain thresholds.

Zone 8's distance from the ocean causes its annual temperature variations to be rather large. Table 3 lists normal monthly temperatures at stations in the area. Mean maximum temperatures are mostly in the 80's in summer months and in the 30's in winter. The dry, clear summer days are usually followed by cool nights; nighttime lows generally average in the 40's. The coldest temperatures in the region (and probably in the state) are observed in Seneca, located in a deep valley surrounded by mountain ridges. January low temperatures in Seneca average a cold 8.4 deg F. Annually, Seneca experiences an average of 22 days with below-zero temperatures. Seneca is in a tie for the coldest temperature ever recorded in Oregon, -54 deg F, set in February 1933.

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

Tables 5 and 6 list median frost dates and mean growing seasons, respectively, for four different temperature thresholds. While some of the lower valley sites have fairly long growing seasons, a few of the colder locations have very short seasons. At Seneca, Austin, and Ukiah, the mean length of time between freezing temperatures is less than six weeks.

Tables 7 and 8 list average monthly and annual heating and growing degree days, respectively.

County Description

Established: Oct. 14, 1864
Population: 24,550
Area: 2,038 sq. mi.
Economy: Agriculture, forest products, education and government.
County Seat: La Grande

Union County was created in 1864 and named for the town of Union, which had been established two years before and named by its founders for patriotic reasons during the Civil War. The county comprised a part of the northern portion of Baker County and in 1899 Union County gave up its eastern portion to Wallowa County. The Grande Ronde Valley in Union County is nearly table flat and is covered with the rich silt of an old lake bed. Highly diversified, with a 160-day growing season and an annual rainfall of twenty inches, the valley boasts of never having had a general crop failure. The county's 1,092 farms average 473 acres a unit. Union County's front door opens to the rugged Wallowa Mountains. Its back door faces the Blue Mountains, which attract hikers, skiers, and hunters.

(County information obtained from Oregon Blue Book)

Climate Tables (Union County, Oregon)