After days of unseasonably warm weather, the Pacific Northwest faces a threat of isolated severe thunderstorms Wednesday that could unleash lightning, large hail, damaging winds and heavy downpours of rain — and possibly even spawn a rare but brief tornado.

Early Wednesday morning, signs of the weather to come were already apparent with a thunderstorm and a few lightning strikes reported over Washington’s Olympic Peninsula.

“The big show is coming later this afternoon,” said Dana Felton, a meteorologist with the National Weather Service office in Seattle.

The Storm Prediction Center issued what the Weather Service calls a level-two threat rating for the Interstate 5 corridor that straddles western Washington and Oregon and includes Seattle and Portland. Other areas of the states and portions of Idaho are in a slightly lower threat level.

While the thunderstorm risk may be only slight, it’s significant in a region where severe thunderstorms are rare. Even rarer are the potential for tornadoes and hail more than two inches in diameter, forecasters said.

“This is about as high-end of an outlook as we typically get here in the Pacific Northwest, only once or less per year west of the Cascades,” said Lee Picard, a meteorologist with the Weather Service office in Portland.

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