Douglas County lies along the southwestern part of Oregon. It is both within Climate Division 1 (Oregon Coast) and Climate Division 3 (Southwestern Interior) established by the National Climatic Data Center. Below is a description of the climate of Division 1 and 3 followed by specific descriptions of Douglas County. Climate tables for various parameters, as observed at long-term climate stations in Douglas County, are included below.

Climate Division 1 -- Oregon Coast

Stretching along Oregon's Pacific border, the coastal zone is characterized by wet winters, relatively dry summers, and mild temperatures throughout the year. Coastal terrain features include a coastal plain (extending from less than a mile to a few tens of miles in width), numerous coastal valleys, and the Coast Range, whose peaks range from 2,000 to 5,500 feet above sea level and extend down the full length of the state. Rivers such as the Coquille, Umpqua, and Yaquina dissect the Coast Range and drain its slopes. The area's heavy precipitation results from moist air masses moving off the Pacific Ocean onto land, especially during winter months. The abundant moisture supports lush pastures for dairy and animal production as well as valley crops of grass seed, flower bulbs, nuts, and fruit.

Along the lower elevations of the immediate coast, normal annual precipitation is between 65 to 90 inches. However, spots high on the west slopes of the range may get up to 200 inches. Several days of abundant rainfall can cause strong flood events. In some locations, flood control dams have greatly reduced the incidence of damaging floods. As is typical of western Oregon, the highest monthly precipitation values for the coast occur in the winter months of November, December, and January. Table 1 is a summary of mean monthly and annual precipitation for recording stations in the coastal zone. Figure 1 shows NOAA climate stations in Zone 1, which were in operation during the 1961-1990 period. Figure 2 shows the Douglas County region from the Oregon annual precipitation map. Table 2a and 2b lists the average number of days with precipitation amounts exceeding certain thresholds.

Snowfall' in tcoastal vicinity is minimal, usually only one to three inches. Some of the higher elevations receive significant amounts of snowfall, however. For example, in January of 1982, Laurel Mountain (elevation 3,589') received 55 inches of snow. At Mary's Peak (elevation 4,097'), the highest peak in the Coast Range, snow often lasts into May. Table 4 lists average monthly and annual snowfall totals for various stations.

The months of July, August, and September tend to be the warmest, but average summer temperatures are only about 15 degrees above the coldest month, January.

Table 3 lists normal monthly temperature at stations in the area. Average heating and cooling degree days (base 65 deg F) are lower for the coastal region than any other Oregon region as a result of the mild temperatures.

Extremely high or low temperatures are rare, and the annual temperature range is lower than any other Oregon climate zone. Temperatures of 90 deg F or above occur, on the average, less than once per year, and freezing temperatures are infrequent. Newport, for example, records temperatures of 32 deg F or below an average of 30 times per year. Killing frosts are even less frequent. Most of the area averages more than 300 days between the last occurrence (in spring) and the first occurrence (in fall) of 28 deg F temperatures. Table 5 and 6 list median frost dates and mean growing seasons, respectively, for four different temperature thresholds.

Occasional strong winds strike the Oregon Coast, usually in advance of winter storms. Wind speeds can exceed hurricane force, and in rare cases have caused significant damage to structures or vegetation. Damage is most likely at exposed coastal locations, but it may extend into inland valleys as well. Such events are typically short-lived, lasting less than one day.

Skies are likely to be cloudy during winter, and only partly cloudy during summer. At Astoria, average winter cloud cover is over 80 percent, dropping only to about 65 percent in summer. Summer cloud cover is due mostly to fog and low clouds. As a result of the persistent cloudiness, total solar radiation is lower here than in any other part of the state.

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

Climate Division 3 -- Southwestern Interior

The southwestern interior of Oregon is one of the more rugged parts of the state. Deeply indented river valleys separate mountains and ridges, with most of the rivers flowing westward towards the Pacific Ocean. Although much of the area lies in somewhat of a rain shadow, sheltered from the Pacific by the Coast Range to the west, many of the higher elevation sites receive abundant precipitation with some locations receiving in excess of 120 inches per year.

Due to the ruggedness of the terrain, much of Zone 3 remains sparsely settled. The only major urban areas lie in the broader valley areas, particularly the Rogue and Umpqua valleys. Ashland, Medford, and Grants Pass are the major cities in the Rogue valley, while Roseburg is the primary urban area in the Umpqua valley.

Long an important forestry area, southwestern Oregon is perhaps best known for its fruit crop, particularly the Rogue River pear industry which covers more than 10,000 acres. Additional agricultural and livestock commodities of importance include hay, grain, seed crop, beef cattle, poultry, sheep, and the dairy industry.

As in the case of the rest of western Oregon, most precipitation in Zone 3 falls during the months of November through March. Of Medford's average annual precipitation of 18.8 inches, about 75 percent falls during that five month period. Occasional summer thunderstorms cause precipitation during the warmer months, but average monthly totals during summer are quite low. Table 1 lists monthly and annual normal precipitation at Zone 3 sites.

Total precipitation in a given area is strongly influenced by elevation, and Zone 3 is no exception. In general, the driest areas are those at the lowest valley locations, while precipitation increases steadily at higher elevations. The driest area in Zone 3 extends from Central Point through Medford and nearly to Ashland, all of which receive less than 20 inches per year. Not far south of Ashland, however, is Mount Ashland at 7,500 feet, which receives an excess of 50 inches per year. Perhaps the wettest area in Zone 3 is in the remote, mountainous area east of Roseburg near Quartz Mountain. Although precipitation data in that area is scarce, it has been estimated that some of the higher peaks receive an excess of 120 inches of rain per year. Another very wet area lies in the Klamath Mountains near Cave Junction in the southwestern part of Zone 3. Some of the higher peaks, such as Onion Mountain and Squaw Mountain, probably receive more than 120 inches per year, although lack of precipitation measurement stations makes this somewhat uncertain. Figure 1 shows NOAA climate stations in Zone 3, which were in operation during the 1961-1990 period. Figure 2 shows the Douglas County region from the Oregon annual precipitation map. Table 2a and 2b list the average number of days with precipitation amounts exceeding certain thresholds.

Table 4 lists average monthly and annual snowfall total for the various stations. Snow falls nearly every winter in southwestern Oregon. In the valleys, the annual total is about 20 to 30 inches per year , although snow on the ground seldom lasts more than a few days at a time. At higher elevations, a great deal more snow is reported. At Sexton Summit (3,836 feet), for example, the average annual snowfall is about 100 inches. The frequency of snowstorms also varies widely with elevation differences. Medford, for example, has an average of 3 days per year with at least one inch of snow while Sexton Summit averages 30 inches.

Due to its separation from the coast, Zone 3 has greater temperature extremes than the remainder of western Oregon. During summer, it is generally the warmest part of the state. Medford, for example, averages about 55 days per year with maximum temperatures of 90 deg F or above; in fact, the average daily maximum for July is above 90 deg F. Winter temperatures can be quite cold. The average extreme low temperature in Medford during December and January is about 18 deg F, and an average of twenty days in January have low temperatures of 32 deg F or below. Medford's monthly mean temperature ranges from 72.5 deg F in July to 37.7 deg F in December, a range greater than most other stations west of the Cascades. Table 3 lists the normal monthly temperature at stations in the area.

Table 5 and 6 lists median frost dates and mean growing seasons, respectively, for four different temperature thresholds. Valley locations such as Riddle, Drain, and Grants Pass have longer growing seasons than higher elevation sites such as Howard Prairie Dam and Prospect. Most of the valley locations have at least 140 days in between spring and fall 32 deg F temperatures. Length of time between 28 deg F temperatures is generally more than 200 days.

Cloud cover is greatest during the winter months, averaging more than 80 percent of total potential cloud cover during December and January. Mid-latitude storms generally produce extensive middle and high clouds, while fair weather periods between storms often produce extensive valley fog, sometimes lasting for many days. Summers, however, are mostly cloud-free, averaging only about 20 percent mean sky cover.

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

Climate Division 4 -- Northern Cascade

The Cascade Mountains, the dominant terrain feature in Oregon, encompass the entire length of the state from the California border to Washington. With average elevations in excess of 4,000 feet, the Cascades are crowned with a number of very high peaks. Mount Hood, near the Washington border, exceeds 11,000 feet, while Mt. Jefferson and the Three Sisters exceed 10,000 feet. Mt. McLoughlin near Medford is approximately 9,500 feet. The Cascades are a higher and more imposing topographic feature in the northern part of Oregon, however. Average elevations and the number of tall peaks (over 9,000 feet) are higher north of about 43.5 deg N latitude. The region extending northward from this latitude to the Columbia River and encompassing high elevations west of the Cascade crest is the fourth of nine Oregon climatic zones.

The northern Cascades exert a profound effect on Oregon climate and weather. Mid-latitude storms approaching from the west are forced to rise as they encounter the Cascades, resulting in large amounts of orographic (terrain-induced) precipitation on the western slopes. So effective are the Cascades in removing moisture from the Pacific air masses, however, that most of Oregon east of the Cascades lies in a "rain shadow," resulting in large areas with annual precipitation less than 12 inches. Most of the northern Cascades, on the other hand, receive an excess of 80 inches per year; the highest peaks collect more than 150 inches per year, most of it in the form of snow. As in the case of rest of western Oregon, most of the precipitation in the Northern Cascades falls during the winter months with November through March period accounting for more than 75 percent of the total annual precipitation. Spring and fall rain and snow and summer thunderstorms contribute to the annual precipitation total, but they are dwarfed by the winter precipitation totals. Table 1 lists monthly and annual normal precipitation at Zone 4 sites.

Tables 2a and 2b list the average number of days with precipitation amounts exceeding certain thresholds.

Table 4 lists average monthly and annual snowfall totals for various stations. Monthly mean snowfall totals vary significantly according to elevation. Since precipitation tends to increase with increasing elevation, more potential moisture for snowfall is available at higher elevations. Since temperatures generally decrease with increasing elevation, those high precipitation amounts are more likely to be in the form of snow. As an example, McKenzie Bridge (elevation 1400 feet) receives an average of about 42 inches snow per year, while Marion Forks (2,500 feet) receives about 150 inches and Government Camp (3,980 feet) about 300 inches per year. Figure 1 shows NOAA climate stations in Zone 4, which were in operation during the 1961-90 period. Figure 2 shows the Douglas County region from the Oregon annual precipitation map.

Table 3 lists normal monthly temperature at stations in the area. The correlation of temperature with elevation is quite strong, with the highest station (Government Camp) having consistently lower temperatures than the other sites. McKenzie Bridge has by far the highest annual mean maximum temperatures, but its annual average temperature is only slightly higher than Detroit Dam due to lower minimum temperatures at McKenzie.

Table 5 and 6 list median frost dates and mean growing seasons, respectively, for four different temperature thresholds. Detroit Dam, at an elevation of 1,220 feet, has an exceptionally long growing season. This is probably due to the fact that its location above the valley floor prevents significant accumulation of cold air on clear nights, and the presence of nearby Detroit Lake serves to moderate any low temperatures. The growing season at higher elevation sites such as McKenzie Bridge, Marion Forks, and Belknap Springs is only about 50 percent as long as at Detroit: for example, Marion Forks at 2,480 feet has an average of only 116 days between occurrences of 32deg F temperatures compared with 244 days at Detroit Dam.

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

County Description

Established: Jan. 7, 1852
Population: 101,200
Area: 5,071 sq. mi.
Economy: Forest products, mining, agriculture, fishing and recreation.
County Seat: Roseburg

Douglas County was named for U.S. Senator Stephen A. Douglas, Abraham Lincoln's opponent in the presidential election of 1860 and an ardent congressional advocate for Oregon. Douglas County was created in 1852 from the portion of Umpqua County which lay east of the Coast Range summit. In 1862, Douglas County absorbed what remained of Umpqua County. Douglas County extends from sea level at the Pacific Ocean to 9,182-foot Mt. Thielsen in the Cascade Range. The Umpqua River marks the dividing line between northern and southern Oregon, and its entire watershed lies within the county's boundaries. The county also contains nearly 2.8 million acres of commercial forest lands and the largest stand of old growth timber in the world, which still provides the region's main livelihood. Approximately 25 to 30 percent of the labor force is employed in the forest products industry. Agriculture includes field crops, orchards and livestock. Over 50 percent of the land area of the county is owned by the federal government.

Climate Tables (Douglas County, Oregon)