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“Extraordinary” Pacific storms shatter records in Northwest; tornado near Seattle

Water vapor imagery shows “atmospheric river” in Pacific NW (Stu Ostro Facebook page)

Since Saturday, a series of storms has battered the Pacific Northwest bringing record rainfall, damaging winds and, today, a rare September tornado near Seattle.

The storminess has been embedded within what’s described as “an atmospheric river” – where a long ribbon of deep moisture streams across the Pacific.

The National Weather Service calls today’s storm “extraordinary for late September” and “much more like a November storm”.

Water vapor image of storm (Cliff Mass Weather Blog) Water vapor image of storm (Cliff Mass Weather Blog)

The center of the storm moved ashore the center of Vancouver Island (in British Columbia, Canada) early this morning with a minimum pressure of 970 mb, deeper than any hurricane to form in the tropical Atlantic this hurricane season. On West Vancouver Island, a wind gust was clocked at 76 mph (122 km/h) Sunday night. Link: More British Columbia wind gusts.

What the NWS called the “poisonous tail” of the storm whipped coastal Oregon and Washington, spawning a small tornado outside Seattle in Frederickson – about 40 miles to the south.

The twister hit near a Boeing plant “causing some damage to a building’s roof, tipping over rail cars, and causing debris-blown damage to cars in a nearby parking lot”, reports KOMONews, a local TV affiliate.


(A warning wasn’t issued for the storm, keeping Seattle’s National Weather Service forecast office (nationwide-leading) 16-year streak without issuing a tornado warning intact.)

Straight line winds of 50-70 mph were common in coastal Washington and 30-45 mph in the lowlands just inland, reports University of Washington meteorologist Cliff Mass.

Peak wind gusts from latest storm in Pacific Northwest (Cliff Mass Weather Blog)

Peak wind gusts from latest storm in Pacific Northwest (Cliff Mass Weather Blog)

While wind was last night’s and today’s weathermaker, this past Saturday it was rain. Both Seattle and Olympia had their wettest September days on record, the NWS said. Seattle received more rain in that single day, 1.71 inches, than it averages in an entire September (1.50 inches). It has now received more than 5.8 inches of rain this month.

The onslaught of rain has continued further down the coast into Oregon.

“Through this morning, Astoria, Oregon had broken century-plus records for all-time wettest September (by over 1″), wettest September day (by almost 1″), and wettest 2-day and 3-day totals for September,” writes Capital Climate.

Portland and Eugene have also had their wettest September on records.

Widespread rainfall totals of 2.5-5 inches have fallen in the region from the recent storminess.

Today’s storm is now weakening and, while showery weather is forecast through midweek as the jet stream transports ashore more Pacific moisture, this latest bout of extreme weather in the Pacific Northwest has ended.

Jason is the Washington Post’s weather editor and Capital Weather Gang's chief meteorologist. He earned a master's degree in atmospheric science, and spent 10 years as a climate change science analyst for the U.S. government. He holds the Digital Seal of Approval from the National Weather Association.
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Jason Samenow · September 30, 2013

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