What is a ‘bomb cyclone’? Storm approaches West Coast, bringing rain, wind, possible flooding


SACRAMENTO, Calif. (KTXL) — The storm that will bring heavy rain and gusty winds into the Northern California and Pacific Northwest regions through Tuesday will undergo the process of bombogenesis, becoming what’s known as a “bomb cyclone.”

A bomb cyclone occurs when a mid-latitude cyclone rapidly intensifies, dropping in atmospheric pressure at least 24 millibars (a measure of pressure) over 24 hours. The lower the pressure, the stronger the storm.

This weekend’s storm, specifically, is forecast to drop from 984 millibars to 942 millibars between 4 p.m. Saturday to 4 p.m Sunday. Once this happens, it will officially be classified as a bomb cyclone.

In Northern California, the storm is forecast to provide two to four inches of rain and gusts of 30 to 40 mph on Sunday. Snow levels will drop Sunday night into Monday, allowing for one to three feet of snow above 6,000 feet in elevation.

Winds off the coast of Oregon will gust 70 to 90 mph — as strong as a Category 1 hurricane. 

In turn, the winds will create offshore waves of 40 to 50 feet in the Pacific. This will cause shipping disruptions, rough surf and beach erosion. Along the Pacific Northwest coastline, waves are expected to be 10 to 20 feet high.

The storm is also expected to bring heavy rain to parts of the West Coast, making it a near “certainty” that metro areas including San Francisco and Sacramento will be affected by flooding, according to AccuWeather.

AccuWeather Chief Meteorologist Jon Porter also acknowledged that the rainfall may help put an end to the remaining wildfires scattered throughout the region, but warned of mudslides, especially in charred areas previously affected by the fires.

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