Washington state has two distinctly different climates split by the Cascade Mountains. West of the Cascades, you get mild, wet winters and cool, dry summers typical of a maritime climate. East of the Cascades, the climate shifts toward continental: hotter summers, colder winters, and far less rain. This single mountain range, stretching 90 to 125 miles inland at elevations of 4,000 to 10,000 feet, acts as both a topographic and climatic wall that defines nearly everything about the state’s weather, agriculture, and daily life.
Western Washington: Mild, Wet, and Overcast
The western side of the state, home to Seattle, Olympia, and the Puget Sound region, has the classic Pacific Northwest feel. Winters are cloudy and wet but rarely bitterly cold. January average highs in Seattle sit around 45°F, with lows in the mid-30s. Snow at sea level is uncommon. Summers, by contrast, are pleasantly cool, with July and August highs in the upper 70s and lows in the mid-50s.
Seattle averages roughly 36 inches of rain per year, which is actually less than cities like New York or Atlanta. The difference is how that rain is distributed. During December and January, rain falls on 20 to 25 days or more each month, creating long stretches of gray, drizzly weather. Then summer flips the script: during July and August, it’s common for two to four weeks to pass with only a few scattered showers, giving western Washington some of the most reliably dry summer weather in the country.
That persistent winter overcast has real health effects. About 25% of Washington residents experience the “winter blues” during the darker months, and roughly 10% develop seasonal affective disorder, a clinical form of seasonal depression tied to reduced daylight.
The Olympic Peninsula: Rainforest Territory
Western Washington’s rainfall numbers get extreme on the Olympic Peninsula. The western-facing valleys and coastline of Olympic National Park receive 100 to 170 inches of rain annually. The Hoh and Quinault rain forests average around 140 inches per year, making them some of the wettest places in the contiguous United States. This rainfall fuels dense, moss-draped temperate rainforests that look more like something from the Pacific coast of South America than the rest of the Lower 48.
Meanwhile, just on the other side of the Olympic Mountains, the area northeast of the range sits in a rain shadow and receives as little as 20 inches per year. That kind of dramatic variation over a short distance is one of Washington’s defining quirks.
Eastern Washington: Hot Summers and Cold Winters
Once air masses cross the Cascades and descend the eastern slopes, they warm and dry out dramatically. The lowest sections of the Columbia Basin approach near-desert conditions, with annual rainfall as low as seven to nine inches near the confluence of the Snake and Columbia Rivers. Along the state’s eastern border, precipitation picks back up to 15 to 30 inches, but the overall character is semi-arid.
Temperatures swing much wider here than on the western side. Summers are genuinely hot. The state’s all-time record high of 120°F was set at Hanford in the Columbia Basin on June 29, 2021. Dry stretches during July and August commonly last four to eight weeks with only a few scattered showers. Winters can be harsh: the all-time state record low of -48°F was recorded at Mazama and Winthrop on December 30, 1968, both in the northeastern mountain valleys.
This temperature range, a 168-degree difference between the state’s all-time extremes, illustrates just how continental eastern Washington’s climate can be compared to the buffered, ocean-moderated conditions on the other side of the Cascades.
How Climate Shapes Washington’s Agriculture
The hot, dry summers and irrigated valleys of eastern Washington are what make the state one of the country’s top producers of apples, wine grapes, cherries, and hops. The Columbia Basin’s combination of long sunny days, low humidity, and available irrigation water from the Columbia River system creates ideal growing conditions for crops that need warmth and predictable dry weather during the growing season.
That same climate, though, introduces specific challenges. Apple color development, a key factor in marketability, suffers when fall nighttime temperatures stay too high. Warm winters can reduce the “chill hours” that tree fruits need during dormancy to produce good yields the following season. Washington’s orchards are currently more resilient on this front than growing regions in the Southeast and Southwest, but it’s a factor growers track closely.
Wildfire smoke has also become a seasonal concern for agriculture, particularly for wine grapes. Smoke exposure can taint grapes and affect the flavor of the resulting wine, adding a new variable to an industry built around predictable dry summers.
Wildfire Smoke Season
Smoke from wildfires, both within Washington and drifting in from Oregon, California, and British Columbia, has become a recurring feature of late summer. During bad smoke years, air quality can swing from “good” (AQI under 50) to “unhealthy” (AQI 151 to 200) or worse within a day or two. At the most extreme levels, with AQI readings above 200, health officials advise everyone to stay indoors and filter their air.
Eastern Washington tends to get hit harder and more frequently by smoke, but major events can blanket the entire state, including the Seattle metro area, in haze thick enough to block out the sun. The smoke season generally overlaps with the driest months of July through September, turning what is otherwise the most pleasant stretch of weather into an unpredictable period for outdoor activity and air quality.
Two States in One
The simplest way to think about Washington’s climate is as two very different states sharing one border. Western Washington offers mild temperatures year-round with heavy winter rain and dry summers, a pattern that supports evergreen forests and a lifestyle built around layering clothes and tolerating gray skies. Eastern Washington delivers wider temperature extremes, dramatically less precipitation, and a landscape that ranges from irrigated farmland to sagebrush steppe. Both sides share long summer daylight (Seattle gets about 16 hours of daylight at the solstice) and short, dark winters, but the day-to-day experience of weather is remarkably different depending on which side of the Cascades you call home.