Climate of Oregon

Climate zones of the Continental United States.

Oregon's climate varies greatly from the western and eastern regions of the state. An oceanic climate (also called "west coast marine climate") predominates in Western Oregon, and a much drier semi-arid climate prevails east of the Cascade Range in Eastern Oregon. Major factors determining Oregon's climate include the large semi-permanent high pressure and low pressure systems of the north Pacific Ocean, the continental air masses of North America, and the Cascade mountains. Oregon's population centers, which lie mostly in the western part of the state, are generally moist and mild, while the lightly populated high deserts of Central and Eastern Oregon are much drier.

Precipitation

Precipitation in the state varies widely: the deserts of eastern Oregon, such as the Alvord Desert (in the rain shadow of Steens Mountain), get as little as 200 mm (8 inches) annually, while some western coastal slopes approach 5000 mm (200 inches) annually.

Temperature range

Snowfall in Oregon is concentrated along the Cascade Range.

Few states have greater temperature extremes than Oregon where they have ranged from a low of 54° F below zero to a high of 119° F. Seldom, however, do daily extremes occur even closely approaching these absolute records. In 80 percent of recent years the highest temperature recorded in the State has not exceeded 114° F, nor was the absolute minimum lower than -37° F. In 50 percent of those years no temperature was recorded higher than 110° mark. Here the mean of the coldest month, January, is 45° F only 15° less than that of July, the warmest month.

In the Willamette Valley few stations have had a maximum temperature greater than 98° F, or a minimum temperature lower than 16° F for over half of their years Fahrenheit record. Temperature of 90° F or more, occurs only about six to eight days a year and those below zero occur on an average of once every 25 years. Here the mean temperatures average 38° F in January and 66° F in July. In the inland valleys of the southwest the average summer temperatures are about 5° F higher than in the northwest and maximums of 90° F or more occur 40 to 50 days a year.

The High Desert region of Oregon.

In south-central Oregon the median annual maximum temperatures over a period of years have been between 95° F and 100° F, varying, of course, with the different stations; in most other areas east of the Cascades this variance is between 100° and 105° F. Median annual minimum temperatures for eastern Oregon vary from near zero in the more protected areas of the Columbia Basin to -26° F in the high mountain and plateau regions. The minima for majority of these stations, however, lies in the range of –1 to -10° F. The normal mean January temperature in southeast Oregon is 25° to 28° F and in the northeast 29° to 33° F; July normal means range between 65° and 70° F in the central valleys and plateau regions and 70° to 78° F along the eastern border.

See also

• Climate of the United States