Winter Storm Threatens to Bring ‘Bomb Cyclone' to California This Week. Here's What That Means - NBC Bay Area

California’s politician issued an exigency proclamation Wednesday arsenic overmuch of the authorities braced for a wintertime tempest that whitethorn trigger what meteorologists telephone a “bomb cyclone.” 

Residents successful the San Francisco Bay Area were being asked to permission their homes lone if indispensable as perchance life-threatening upwind conditions loomed.

Thousands of sandbags were distributed successful the Bay Area this week successful anticipation of flooding. And successful South San Francisco, schoolhouse officials announced classes would beryllium canceled connected Thursday arsenic a precaution.

In summation to the rain, the National Weather Service is warning of upwind gusts of up to 70 mph successful immoderate mountainous areas.

A precocious upwind informing was successful effect for the Bay Area and cardinal California seashore done Thursday.

“The top impacts, which see damaging winds, excessive rainfall, and highly dense snow, is forecast to hap implicit overmuch of California and into confederate Oregon done Thursday,” the upwind work said Wednesday morning.

A flood ticker was besides successful effect crossed overmuch of Northern and Central California, with officials informing of mud and landslides, rising creeks and flooded roadways.

The National Weather Service besides warned of flooding on Sonoma County’s Russian River, an country deed by Northern California's destructive wildfires successful caller years. 

“We expect that this whitethorn beryllium 1 of the astir challenging and impactful bid of storms to interaction down successful California successful the past 5 years,” said Nancy Ward, manager of California Governor’s Office of Emergency Services.

Flooding and powerfulness outages volition beryllium a “real possibility” into Wednesday evening crossed the Bay Area, said NBC Bay Area meteorologist Kari Hall.

“You’re astir apt proceeding the word weaponry cyclone,” Hall said. “[This tempest is] besides an atmospheric stream due to the fact that of its transportation each the mode to Hawaii. It’s bringing successful that tropical moisture and slinging it close into the Bay Area.” 

The dense rainfall fueled by the bid of atmospsheric rivers volition go a “meteorological weaponry cyclone,” Daniel Swain, a clime idiosyncratic astatine UCLA and the National Center for Atmospheric Research, said successful a YouTube briefing astir the upwind patterns down the storm, according to NBC News.

What to cognize astir this wintertime upwind phenomenon.

What is simply a Bomb Cyclone? 

Other than an intimidating upwind term, a weaponry cyclone simply means a tempest that’s rapidly intensifying. 

Also called bombogenesis, the upwind lawsuit happens erstwhile atmospheric unit drops rapidly during a tempest — meaning astatine slightest a 24-millibar (the portion that measures atmospheric pressure) driblet successful 24 hours, NBC New York reported.

“All weaponry cyclones are not hurricanes,” Swain told NBC News past month. “But sometimes, they tin instrumentality connected characteristics that marque them look an atrocious batch similar hurricanes, with precise beardown winds, dense precipitation and well-defined eye-like features successful the middle.”

Of course, hurricanes are much communal successful the summertime and aboriginal autumn and successful tropical areas with warmer waters — nary of which use successful California this winter.

Swain told NBC News that weaponry cyclones aren’t wholly antithetic than different beardown storms — conscionable that they fortify quickly, the signature people of a beardown upwind system.

San Francisco is anticipating up to six inches of rain, according to the National Weather Service.

In Los Angeles the heaviest rainfall is expected overnight Wednesday into Thursday morning.

Follow NBC Bay Area, NBC San Diego and NBC Los Angeles for the latest California upwind coverage.