What is a bomb cyclone? Bay Area braces for wet weather

OAKLAND, Calif. - As winter is upon us, bomb cyclones will surely be a popular search term.

In fact, a bomb cyclone, as well as an atmospheric river, is supposed to hit the San Francisco Bay Area, and so we thought we'd explain what it is. 

A bomb cyclone is a low pressure system that experiences a fall in pressure of 24 millibars in 24 hours, according to the National Weather Service. 

They are often associated with atmospheric rivers and typically form in winter when cold and warm air masses collide. Other nicknames include "explosive cyclogenesis" or a "weather bomb." 

Put more simply, National Weather Service meteorologist Daltton Behringer told KTVU that a bomb cyclone is how quickly a storm strengthens.

In this particular case this week, the bomb cycle is going to accompany an atmospheric river, which is a steady stream of moisture coming from the tropics. 

You can have one without the other, but in this case, Behringer said, both are going to slam into the Bay Area, with the heaviest days of rain expected on Wednesday and Friday. 

This week's storm

An atmospheric river storm is expected to arrive in the North Bay late Tuesday before spreading to the rest of the Bay Area later this week, likely bringing several inches of rain and wind gusts of up to 45-50 mph, according to the National Weather Service.

 By the end of the week, many parts of the region are expected to receive about a month's worth of rain, with the North Bay forecast to receive up to 10 inches or more in some Sonoma County coastal mountain ranges, weather service meteorologist Dial Hoang said.