An especially strong jet stream over the Pacific Ocean is spinning off a series of five or six weather systems, including a massive “bomb cyclone” that is expected to arrive in Cowlitz County on Sunday.
The system is expected to bring heavy rain and gusty winds up to 50 mph. The National Weather Service issued a wind advisory for Cowlitz County from 8 a.m. to 5 p.m. Sunday.
“What is remarkable is how big it is in scale, how deep the center is and the speed with which it goes from an open wave to a super-intense low-pressure system,” said Joe Boomgard-Zagrodnik, an agricultural meteorologist for Washington State University. “Meaning it will seem to explode out of nowhere.”
Grab your coats and boots; temperatures are expected to drop and rain is in the forecast this weekend.
A bomb cyclone occurs when pressure quickly drops over a 24-hour period, said National Weather Service Meteorologist John Bumgardner in Portland. Portland models show pressure will drop nearly twice as much as the minimum amount needed to create the weather phenomenon.
Bumgardner said the Portland office forecasts winds reaching up to 100 mph far out over the ocean, while in Cowlitz County, winds will reach roughly half that amount. He said gusts will peak at around 40 to 50 mph locally mid-morning Sunday through Sunday night. The National Weather Service calls for rain locally through Thursday.
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Bumgardner said this weekend’s event is expected to have the lowest pressure of any bomb cyclone, 5 degrees of 130 degrees West and 40 degrees North, which is roughly 300 miles off the coast of Southwest Washington.
The National Hurricane Center reports tropical cyclones have a minimum wind speed of 74 mph over a one-minute average.
As with most extreme weather events in the Pacific Northwest, Boomgard-Zagrodnik explained on his blog The Convergence Zone, this series was set off in the tropics. It began with the relatively benign storm Namtheun that is “helping supercharge what was already an impressive jet stream,” he said.
Christine Clarridge of the Seattle Times also contributed to this story.