Malheur County lies along the southern part of the Idaho border. It is wholly within Climate Division 9 (Southeastern Oregon) established by the National Climatic Data Center. Below is a description of the climate of Division 9 followed by specific descriptions of Malheur County. Climate tables for various parameters, as observed at long-term climate stations in Malheur County, are included below.

Climate Division 9 — Southeastern Oregon

Oregon climate Zone 9 occupies the southeast corner of the state, and is limited to the confines of Malheur County, the state's second largest county. This is a region of high desert, mountain ranges, plateaus, and river valleys, with elevations ranging from slightly above 2,000 feet to nearly 8,000 feet above sea level. Less than 30,000 people occupy the nearly 10,000 square miles, which comprise Malheur County. Most reside in the Ontario - Nyssa - Vale areas near the northeast border. More than 90 percent of the county is range land, two-thirds of which is controlled by the Bureau of Land Management.

Principal industries in Zone 9 are agriculture, livestock, food processing, and recreation. Agriculture has played the dominant role in the economy, especially as irrigated acreage has increased. Extensive irrigation in the northeastern valleys is the center of very productive and diversified farming. Oregon State University's Malheur Experiment Station, west of Ontario, has been an active agricultural research center for many years, specializing in new farming practices and testing of alternative crops. Among the chief crops grown in the area are potatoes, sugar beets, onions, peas, tomatoes, berries, and sweet corn. Experiments with exotic melons, squash, and other cash crops (much of them for export to the Far East) are also continuing.

With the exception of a few of the higher mountain areas, Zone 9 receives low amounts of precipitation; most of the region averages less than 15 inches of total precipitation per year. The driest portions are in valleys near Rome and Burns Junction. These sites average 7.62 and 8.04 inches per year, respectively. On the other hand, locations in the Trout Creek Mountains in the southeast corner receive up to 30 inches per year. In even the wettest locations, however, annual precipitation is much lower than evaporation. Average annual evaporation at Malheur Experiment Station is well above 50 inches per year, most of it coming during the months of April through September.

Unlike most of Oregon, annual precipitation in Zone 9 is distributed rather evenly throughout the year. Figure 1 shows NOAA climate stations in Zone 9, which were in operation during the 1961-1990 period. Figure 2 shows the Malheur County region from the Oregon annual precipitation map. Table 1 shows normal monthly and annual precipitation values for Zone 9. Although winter months tend to have the highest total precipitation, the relative contribution of those months to the annual total is much lower than in areas further west. Some locations, such as McDermitt and Rome, report their highest precipitation values during the late spring. Others, such as Danner and Sheaville, have nearly uniform monthly normals for the entire period of October through June. The driest month throughout the region is July. Table 2a and 2b lists the average number of days with precipitation values for Zone 9.

Due to its distance from the Pacific Ocean, Zone 9 is characterized by large annual temperature variations. Table 3 lists normal monthly temperatures for Zone 9 measurement stations. Summers are quite warm with daytime highs averaging in the high 80's or low 90's from June through September. Malheur Experiment Station (MES) averages about 50 days per year with temperatures of 90 deg F or above, mostly during July and August. Summer nights are cool, however, due to the generally clear skies and dry air: even in the warmest months, nighttime lows average in the low to mid 50's.

Table 4 lists average monthly and annual snowfall total for the various stations. During winter, average highs are mostly in the 30's with lows in the teens. MES averages about 140 days per year with minimum temperatures of 32 deg F or below; on 26 of those days, maximum temperatures remain below freezing as well. Occasionally, very cold air reaches the area from the north, causing lows to drop below 0 deg F. MES averages about 6 sub-zero days per year.

Tables 5 and 6 list median frost dates and mean growing seasons, respectively, for four different temperature thresholds. While stations in the northeast (MES and Nyssa) have an average of 140-160 days between 32 deg F temperatures, some of the higher stations have much shorter growing seasons. Examples would be Sheaville (4,620 feet) with an average of 87 days between frost dates, and Danner (4,230 feet), which averages 92 days.

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

County Description

Established: Feb. 17, 1887
Population: 32,000
Area: 9,926 sq. mi.
Economy: Agriculture, livestock, food processing and recreation.
County Seat: Vale

Malheur County was created in 1887 from Baker County. Malheur County derives its name from the "Riviere au Malheur" or "Unfortunate River" (later changed to "Malheur River"), named by French trappers whose property and furs were stolen from their river encampment. Malheur County is a place filled with fascinating history, diverse landscape and friendly people. The landscape is enchanting and provides for a wide variety of excellent recreation such as hunting, fishing, hiking, rock climbing, rock hounding, boating and water skiing. The county is 94 percent rangeland. Basques, primarily shepherds, settled in Jordan Valley in the 1890s. Irrigated fields in the county's northeast corner, known as Western Treasure Valley, are the center of intensive and diversified farming.

(County information obtained from Oregon Blue Book)

Climate Tables (Malheur County, Oregon)