Geography of Washington (state)

From the Cascade Mountains westward, Western Washington has a mostly Mediterranean climate, with mild temperatures and wet winters, autumns and springs, and relatively dry summers.

It includes large areas of semiarid steppe and a few truly arid deserts in the rain shadow of the Cascades; the Hanford reservation receives an average annual precipitation of 6 to 7 inches (150 to 180 mm).

Despite the limited amount of rainfall, agriculture is an extremely important business throughout much of Eastern Washington, as the soil is highly productive and irrigation, aided by dams along the Columbia River, is fairly widespread.

[10] The Okanogan Highlands and the rugged Kettle River Range and Selkirk Mountains cover much of the state's northeastern quadrant.

In the spring and summer, a high-pressure anticyclone system dominates the north Pacific Ocean, causing air to spiral out in a clockwise fashion.

[14] Despite Western Washington's marine climate similar to many coastal cities of Europe, there are exceptions such as the "Big Snow" events of 1880, 1881, 1893, and 1916,[15][16] and the "deep freeze" winters of 1883–1884, 1915–1916, 1949–1950, and 1955–1956, among others.

During the El Niño phase, the jet stream enters the U.S. farther south through California, therefore late fall and winter are drier than normal with less snowpack.

The La Niña phase reinforces the jet stream through the Pacific Northwest, causing Washington to have more rain and snow than average.

The Olympic Peninsula's western side receives as much as 160 inches (4,100 mm) of precipitation annually, making it the wettest area of the 48 conterminous states and a temperate rainforest.

The western slopes of the Cascade Range receive some of the heaviest annual snowfall (in some places more than 200 inches or 5,100 millimeters water equivalent) in the country.

While the Puget Sound lowlands are known for clouds and rain in the winter, the western slopes of the Cascades receive larger amounts of precipitation, often falling as snow at higher elevations.

Western Washington is known for its mild climate, considerable fog, frequent cloud cover, long-lasting drizzles in the winter and warm, temperate summers.

The eastern region, which does not benefit from the general moderating effect of the Pacific Ocean, occasionally experiences extreme climate.

In the Western region, temperatures have reached as high as 118 °F (48 °C) in Maple Valley[25] during the June 2021 heat wave, which was reported to be a 1000-year weather event and broke several records in the Pacific Northwest.

[46] Common trees and plants in the region are camassia, Douglas fir, hemlock, penstemon, ponderosa pine, western red cedar, and many species of ferns.

The Pacific shore surrounding the San Juan Islands is heavily inhabited by killer, gray, and humpback whales.

Mammals native to the state include the bat, black bear, bobcat, cougar, coyote, deer, elk, gray wolf, hare, moose, mountain beaver, muskrat, opossum, pocket gopher, rabbit, raccoon, river otter, skunk, and tree squirrel.

[50] There have also been a large number of species introduced to Washington, dating back to the early 18th century, including horses and burros.