A rare West Coast “bomb cyclone” is forecast to sweep into southern Oregon and northern California later Tuesday and into Wednesday, bringing 100-mph wind gusts to the coast and multiple feet of snow to the mountains.
"This is a unprecedented storm given the track and strength and will being very dangerous conditions to the area," the National Weather Service in Medford, Oregon, said. "High winds and heavy snow is expected to impact the area."
As it approaches the coast, the storm is forecast to undergo what's known as bombogenesis, which is said to occur when a storm's central barometric pressure drops at least 24 millibars in 24 hours. (A millibar is a way of measuring air pressure.) The lower the pressure, the more powerful the storm.
"This can happen when a cold air mass collides with a warm air mass, such as air over warm ocean waters," the National Oceanic and Atmospheric Administration said. "The formation of this rapidly strengthening weather system is a process called bombogenesis, which creates what is known as a bomb cyclone."
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The word bombogenesis is a combination of cyclogenesis, which describes the formation of a cyclone or storm, and bomb, which is, well, pretty self-explanatory.
In the 1940s, some meteorologists began informally calling some big coastal storms "bombs" because they develop "with a ferocity we rarely, if ever, see over land," said Fred Sanders, a retired MIT professor, who brought the term into common usage by describing such storms in a 1980 article in the journal Monthly Weather Review.
Many nor'easters – big storms that wallop the East Coast – are the product of bombs. The contrast in temperature between polar air spilling over the eastern U.S. and the relatively warm Gulf Stream waters sets the stage for cyclogenesis on the boundary between these air masses.
What's rare about Tuesday's bomb cyclone is that it's hitting the West Coast. The weather service said this storm could rival some of the most intense storms on record for that part of the country.
While images of the cyclone looked impressive or even cool, it was causing havoc around Northern California.
Interstate 5 was closed due to heavy snow and the California Highway Patrol's traffic incident page Tuesday was flooded with reports of spin-outs and fender benders on all roads leading through the mountains of Northern California.
While not a tropical system, Oregon and Northern California getting their version of a hurricane landfall today.— Ryan Maue (@RyanMaue) November 26, 2019
Powerful "bomb cyclone" with wind gusting to 100 mph, heavy rain and mountain snows.
Simulated radar from HRRR (13z)https://t.co/XcmEbF18bW pic.twitter.com/7WkJE7u8sB
This article originally appeared on USA TODAY: Bomb cyclone: Storm to become bombogenesis in California, Oregon