Wild Puget Sound Lightning Possible, But What About Tornadoes?

SEATTLE, WA — The lightning storm that swept across Puget Sound on Saturday was one of the biggest in recent memory, with some 2,200 lightning strikes that caused power outages, the evacuation of Husky Stadium, and the early closure of the Washington State Fair.

The storm happened because of a unique set of weather conditions, according to forecasters — so unique, that such a storm likely won't happen again for a while. This type of weather can also lead to one of the rarest local weather events: tornadoes.

According to the National Weather Service, there was a shortwave trough on Saturday over Puget Sound, a type of system associated with upward motion. There was cool air high up in the atmosphere, and warm air near sea level due to warmer Pacific Ocean temperatures. That warm air moving upward created the thunderstorm. The shortwave trough moved northwest over the region, bringing thunderstorms from the Cascades into central Puget Sound.

"So we had the trifecta for Puget Sound thunderstorms: great instability, a sharp trough aloft given strong lift, and the perfect winds to drift the storms over the lowlands," University of Washington Meteorologist Cliff Mass said in a blog post.

The weather since Saturday night has been similarly stormy (minus the lightning) with sudden heavy downpours, gusty winds, and ominous looking clouds. That got us thinking: what are the chances of a tornado hitting the Seattle-Tacoma area?

Tornadoes are not impossible in the Pacific Northwest. Port Orchard had an EF2 tornado on Dec 18, 2018. And on Sunday night, two possible tornadoes touched down in the Portland area.

But tornadoes in Washington are extremely rare, with only about three per year on average statewide, according to the NWS. That's less than states like Arizona (5 per year) and New York (10 per year).

There are two big reasons states like Kansas, Nebraska, and Texas see so many tornadoes, according to NWS Seattle Meteorologist Mike McFarland: warm, moist air from the Gulf of Mexico and dry air blowing off the Rocky Mountains. Those factors help form mesocyclones, or super cells.

Those ingredients don't typically exist in Puget Sound due to cool temperatures. Our tornadoes usually happen when unstable air rushes over the terrain and spins upward, McFarland said.

That might be what happened in Port Orchard last year, according to Mass. A thunderstorm traveling over the Kitsap Peninsula hit horizontal air flowing eastward off the Olympic Mountains, creating the relatively small EF2 tornado.

So tornadoes are possible, but not likely, and not the type seen in "The Wizard of Oz." McFarland said that there might be very isolated thunderstorms over Puget Sound this week, but the conditions for big storms just aren't right.