Seattle, Washington, is not a typical location for severe weather, but tornadoes do occur. These events are extremely rare in the Puget Sound area and are typically weak, short-lived circulations that pale in comparison to the powerful tornadoes seen in the American Midwest. The region’s unique geography and prevailing atmospheric conditions provide a natural defense against destructive storms associated with Tornado Alley. Understanding Seattle’s tornado risk means looking at the few times they have occurred and the reasons why they almost never happen.
The Historical Record of Tornado Activity
Tornadoes in Washington state are infrequent, averaging only about two to three confirmed touchdowns per year. The vast majority of these events are classified as F0 or F1 on the Fujita scale, or EF0 or EF1 on the Enhanced Fujita scale, corresponding to wind speeds under 110 miles per hour. These weak tornadoes account for nearly all of the recorded activity in the Seattle and greater Puget Sound region. Between 1950 and 2005, Washington recorded 94 tornadoes, a number significantly lower than states in the central United States.
The most notable recent event was an EF-2 tornado that struck Port Orchard, just west of Seattle, in December 2018, causing considerable damage. Even this relatively strong event was short-lived, highlighting the difference between Pacific Northwest tornadoes and those in other parts of the country. Tornadoes that do form in the Puget Lowland are often associated with localized weather phenomena like the Puget Sound Convergence Zone. Washington ranks 43rd in the nation for tornado frequency.
Atmospheric Conditions That Limit Tornadoes
The primary reason Seattle rarely experiences strong tornadoes is the moderating influence of the Pacific Ocean and the presence of significant mountain ranges. Tornadoes require a specific combination of warm, moist air near the surface and strong wind shear in a highly unstable atmosphere. The cold Pacific Ocean is the most significant limiting factor, as it keeps the air temperatures near the coast relatively cool and stable. This stability prevents the buildup of the intense heat and humidity necessary to fuel violent thunderstorms.
The Olympic and Cascade Mountains also play a major role in disrupting the atmospheric ingredients needed for powerful storms. The Olympic Mountains effectively block and strip moisture from weather systems moving eastward off the Pacific, creating a rain shadow effect over the Puget Sound basin. Meanwhile, the Cascade Range acts as a formidable barrier, preventing the clash of warm, moist air from the south with cold, dry air from the interior. This clash is the mechanism that drives large-scale tornado outbreaks elsewhere, meaning the limited atmospheric instability prevents significant tornadic activity.
Severe Weather Events That Are More Common
Residents of the Seattle area should focus their preparedness on the far more common severe weather threats. Strong windstorms, particularly extratropical cyclones that form over the Pacific, are the most frequent and damaging weather events in the region. These storms, sometimes known as mid-latitude cyclones, can bring sustained winds between 60 and 70 miles per hour and gusts up to 90 miles per hour in exposed areas of the Puget Sound. These windstorms often occur in late fall and winter, leading to widespread power outages and property damage from falling trees due to the soil being saturated with heavy rain.
Heavy rainfall and the resulting flooding and landslides are also major hazards, often tied to atmospheric river events, sometimes called Pineapple Express storms. These systems carry large amounts of tropical moisture to the region, leading to prolonged periods of intense rain and subsequent erosion. Waterspouts, which are essentially tornadoes over water, are another fairly common occurrence over the Puget Sound. While visually dramatic, these typically dissipate or weaken significantly upon making landfall, rarely causing damage. The overall risk profile for Seattle is defined by wind and water, not the rotational force of a strong tornado.