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Dopper radar of tornado site
Color-coded Doppler radar imagery shows where a tornado apparently touched down near Port Orchard, Wash. (NWS via @MorganKIRO7 / Twitter)

The Pacific Northwest is typically in the “bush league” when it comes to tornadoes, but the National Weather Service says a twister hit a grand slam today south of Port Orchard on Washington state’s Kitsap Peninsula.

Aerial views from Seattle television stations showed roofs ripped off houses, debris flying in the air and trees uprooted.

In a series of tweets, the Kitsap County Sheriff’s Office said the storm caused “catastrophic damage in the Port Orchard area.”

“Most of the damage is contained to the area and neighborhoods east and south of WalMart … Active power lines are down and gas companies are checking their supply lines for leaks,” the department tweeted at 3:30 p.m. PT. “STAY OUT OF THE AREA OR SHELTER IN PLACE! This area has not been deemed ‘safe.’ ”

The sheriff’s office said Port Orchard police and several fire agencies were assisting with emergency response. KIRO-TV reported that a construction worker went to a hospital emergency room tonight after being picked up and dropped by strong winds in Port Orchard.

The National Weather Service said the radar evidence and video views supported its view that a tornado touched down shortly before 2 p.m. PT, but it said it was still too early to assess how strong the twister was.

“We continue to work with [emergency management] partners on the extent of damage,” it said in a tweet. “We will not be able to survey the area before dark tonight — will send a team tomorrow morning.”

Here’s a sampling of video and photos from the scene:

The National Weather Service says Washington state averages 2.5 tornadoes per year. And it says the state experiences a tornado in December only once a decade on average.

Several years ago, University of Washington atmospheric scientist Cliff Mass noted that Oregon and Washington state were in the “junior leagues” for tornadoes.

“So why are we in the bush league when it comes to tornadoes and heavy duty convection,” Mass wrote at the time. “Well, the key reason is that we don’t get many thunderstorms and our thunderstorms are wimpy.”

The reason for that has to do with the cold waters of the North Pacific.

“Thunderstorms like two things: lots of moisture in the air and big change of temperature with height — normally from a warm surface,” Mass explained. “Well, the Pacific is COLD, even in the summer … and cold water cannot put much water vapor into the atmosphere and keeps the surface cold.”

But as today illustrates, there’s the occasional exception. The deadliest Pacific Northwest tornado on record left six people dead, injured hundreds and caused millions of dollars in damage in 1972 when it ripped through the area surrounding Portland, Ore., and Vancouver, Wash.

This week, the coastal Olympic Peninsula and an area ranging from the Kitsap Peninsula northward to Canada have been experiencing rain and high winds. Today’s tornado was spawned by a strong thunderstorm that swept across Kitsap this afternoon, the National Weather Service said.

Update for 10:55 a.m. PT Dec. 19: Thirty emergency responders from a variety of agencies took part in post-storm sweeps of the affected area overnight. “Miraculously, we did not treat any major or severe injuries in this storm,” Jeff Faucett, assistant chief of South Kitsap Fire and Rescue, told reporters during a morning-after briefing.

Meanwhile, Mass’ weather and climate blog has a detailed analysis of the meteorological factors that gave rise to the tornado, and an outlook for the hours ahead. Here are the bottom lines on those two issues:

  • Looking back: The thunderstorm cell sweeping over Kitsap spawned the tornado because of weak wind shear that popped up on the lee side of the Olympic Mountains. “Such weak tornadoes are relatively rare, since everything had to happen perfectly, with the shear and a strong storm coming together at the right time and place,” Mass wrote. Yes, that’s right: a perfect storm.
  • Looking ahead: More windstorms are in store for the area. “There is some variability in the exact landfall position, and small error could have a big impact on the winds, so keep watching the forecasts,” Mass said. “Make sure your batteries are fresh, your barbecue has gas, and your smartphone is charged.”

Update for 2:20 p.m. PT Dec. 19: The National Weather Service classified the tornado as an EF-2 on the Enhanced Fujita Scale, with peak winds in the range of 120 to 130 mph over a stretch of 1.4 miles:

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