While Washington State is generally known for its mild climate and verdant landscapes, it is a misconception that tornadoes do not occur within its borders. Tornadoes do indeed touch down in Washington, though they are typically less frequent and weaker than those observed in other parts of the United States.
The Reality of Tornadoes in Washington
Tornadoes are a recognized weather event in Washington, despite their relative rarity compared to states in the central and southeastern U.S. On average, the state experiences between two and three tornadoes each year. This frequency places Washington among the states with the lowest number of tornado occurrences annually. These events can manifest at any time throughout the year.
Geographic and Seasonal Patterns
Tornado activity in Washington State shows distinct patterns concerning both time of year and geographic location. The peak season for tornadoes generally occurs during the spring months, specifically April, May, and June. While late spring and early fall also see increased chances, Eastern Washington can experience tornadoes into July and August.
Geographically, tornadoes have been observed across the state, with both Western and Eastern Washington recording events. Counties such as Clark, Pierce, Spokane, Lincoln, and Yakima have recorded the highest number of tornadoes since 2000. The state’s varied topography, including mountain ranges like the Olympics and Cascades, can influence wind flow and contribute to unique microclimates that support these formations.
Characteristics of Washington Tornadoes
Tornadoes in Washington State typically exhibit characteristics that differentiate them from their counterparts in Tornado Alley. The majority of these events are classified as weak, predominantly rated EF0 or EF1 on the Enhanced Fujita (EF) scale. These ratings correspond to wind speeds ranging from 65 to 110 miles per hour.
Washington tornadoes are generally brief in duration and small in size. Many last only a few minutes, making them challenging to detect and forecast. For instance, the EF2 tornado that struck Port Orchard in 2018 lasted approximately five minutes.
Their short lifespan and often shallow nature can make them difficult for radar systems to pick up, as they may occur between radar scans or be too low to the ground for effective detection. Despite their general weakness, the state has experienced stronger tornadoes, including an F3/EF3 in Vancouver in 1972, which remains the deadliest in the Pacific Northwest.
Understanding Tornado Formation in the Pacific Northwest
Tornado formation in Washington involves a specific combination of atmospheric conditions, often influenced by the region’s unique geography. The primary ingredients for tornado development include atmospheric instability, wind shear, and sufficient moisture. Instability arises when warm, moist air near the surface rises into an environment where colder, drier air is present aloft. This process is often enhanced by solar heating, particularly in the spring, which warms the surface and promotes rising air. Wind shear, defined as a change in wind speed or direction with increasing height, creates a horizontal rolling motion in the atmosphere. If this rotating air is then lifted vertically by a thunderstorm’s updraft, it can tighten and form a tornado.
The Pacific Northwest’s specific climate and terrain contribute to the unique nature of its tornadoes. The cooling influence of the Pacific Ocean tends to moderate the climate, which generally prevents the extreme instability needed for powerful tornado outbreaks seen in other parts of the country.
However, the interplay between the Olympic and Cascade Mountains, Puget Sound, and the Columbia River can create localized microclimates that are conducive to tornado development. For example, the Olympic Mountain velocity shear zone describes how onshore air flow, when forced around the mountains, can generate the low-level wind shear necessary for rotating storms.
Many of Washington’s tornadoes are landspouts, which form from the ground up and are typically weaker and shallower than supercell-driven tornadoes. The presence of a Pacific high-pressure system can also limit how high clouds can build, further impacting the strength and type of tornadoes that form in the region.