What is a bomb cyclone? Sacramento storm may ease but expert says ‘don’t be fooled’

Northern California is experiencing a heavy atmospheric river which has already caused an onslaught of damage through flooding, power outages, mudslides and fallen trees.

Wednesday’s storm — an atmospheric river and bombogenesis — could bring up to 3 inches of rain to the region with winds exceeding 50 mph, even more powerful than the last.

“Atmospheric rivers are relatively long, narrow regions in the atmosphere – like rivers in the sky – that transport most of the water vapor outside of the tropics,” according to the National Oceanic and Atmospheric Administration.

The latter part is a bomb cyclone, said meteorologist Scott Rowe from the National Weather Service.

What exactly is a bomb cyclone?

“A bomb cyclone is essentially a storm, a low pressure system that strengthens by a matter of 24 millibars in 24 hours,” said Rowe. “The lower the pressure, the stronger the storm.”

A millibar is a unit of atmospheric pressure.

Cold air mass collides with a warm air mass and creates a bomb cyclone, also known as a bombogenesis, according to the weather service website.

Wednesday’s storm will bring strong winds, heavy rain and heavy mountain snow.

Wind gusts are expected to be at 50 to 60 mph, Rowe said.

“We’re having a wave of precipitation go through right now,” Rowe said. “There will probably be a period this afternoon where it lightens up. There may even be no rain falling from the sky but don’t be fooled. The rain will return tonight.”

This story was originally published January 4, 2023 at 11:30 AM with the headline "What is a bomb cyclone? Sacramento storm may ease but expert says ‘don’t be fooled’."