NORTH SOUND, APRIL 15: Spring offers a unique weather feature that usually originates in the North Sound – the Puget Sound Convergence Zone. The Convergence Zone can occur anytime of the year, but spring time is when it occurs most often.
What is the Puget Sound Convergence Zone?
Imagine water in a stream flowing around a large rock. The water wraps around the rock and meets on the other side. On a grand scale, that’s what happens with westerly air flow off the Pacific Ocean wrapping around and colliding just east of the Olympics.
South Snohomish County is ground zero for the Convergence Zone. The westerly air flows thru the Strait of Juan de Fuca and along the south side of the Olympics, wrapping around the mountains, collides, rises, and produce clouds and then rain. If it is cold enough, it can snow. Even thunderstorms can develop. With frequent stronger flow through the Strait of Juan de Fuca, the Convergence Zone tends to drift south into King County.
Spring is also the peak time of year for thunderstorms, particularly involving the Puget Sound Convergence Zone. One key by-product of thunderstorms is tornadoes and the spring season is also prime time for North Sound tornadoes.
North Sound Tornadoes
In Snohomish County since 1969, there have been 7 tornados and two were F2 tornados with wind speeds between 110 and 135 mph.
Tornados are borne from thunderstorms. The Dec 2018 Port Orchard F2 tornado was generated from a thunderstorm. A tornado is a rapidly rotating column of air touching the ground. A funnel cloud does not touch the ground. A waterspout is a tornado over water like Puget Sound.
Washington State averages around two tornadoes per year. Some years have none. In 1997 though, a record 14 tornadoes occurred. Tornadoes can occur any time of the year, but the seasonal transition of spring and fall is when most tornadoes occur with May having the greatest number of tornadoes in the state.
Most Washington tornadoes are weak and last less than 2 minutes. Most are F0 or F1 events with wind speeds under 110 mph.
However, Washington has suffered three F3 tornadoes since 1950, two occurring on the same day – April 5th, 1972. Vancouver was hit by one, striking a school, grocery store and bowling house, killing 6 and injuring over 200. Washington led the nation in tornado deaths that year. Later that same day, another F3 tornado touched down outside of Davenport west of Spokane.
The other F3 tornado occurred in early Dec 1969, starting as a waterspout off Des Moines and tracked into the Green River valley. Fortunately, there were no injuries.
Like thunderstorms with lightning, head indoors if a thunderstorm approaches. The phrase to remember is – When Thunder Roars, Go Indoors. And for tornado safety, get into an interior room without windows or a basement if available.
Expect the Unexpected
North Sound spring weather usually offers a wide variety of weather, from the recent period of warm sunshine, to showers, hail, thunderstorms, and even tornadoes. Remember, when you are weather aware, you are weather prepared.
Visit and bookmark the Everett Post Weather page that offers site specific North Sound community forecasts including hourly forecasts for those who spend time in the garden or other outdoor activities. The Everett Post Weather page also offers the Doppler weather radar display, and the radar loop will help you dodge those pesky April showers too!
