“Bomb cyclone” is the term used to describe a process that meteorologists often refer to as “bombogenesis.” The term refers to a storm that intensifies in a short period of time, which can happen in powerful storms like the one expected to hit northern California and the Pacific Northwest this week.
According to the National Oceanic and Atmospheric Administration, a bomb cyclone occurs during the rapid intensification of a storm between the tropics and the polar regions. It can occur when a cold air mass collides with a warm air mass and usually occurs over the ocean.
The measurements needed to determine whether a storm is a bomb cyclone are complex, but they mostly involve a rapid drop in pressure. Barometric pressure is measured in millibars by the National Weather Service. If a storm drops 24 millibars or more in less than 24 hours, it can be classified as a bomb cyclone, said Stephen Baron, a forecaster with the weather service in Gray, Maine.
The National Weather Service’s Weather Prediction Center has issued a severe rain warning for northern California and the Pacific Northwest starting on November 19 and lasting through November 22. The storm is expected to hit as the region experiences a strong atmospheric river — a long stream of moisture over the Pacific Ocean.
The Weather Forecast Center warned that the storm intensified so rapidly that it was considered a "bomb cyclone."
Bomb cyclones can occur in many places and are not unique to the West Coast of the United States. Bomb cyclones can occur in several oceans around the world, including the northwest Pacific and the north Atlantic.
The “bomb cyclone” hitting the West Coast is expected to bring heavy rain, which could lead to flash flooding in many areas, depending on elevation. High winds are also expected in parts of the West Coast.
Due to the impact of the "bomb cyclone", travel will be hazardous and power outages may occur. Trees and infrastructure are also likely to suffer significant damage.
Bomb cyclones have been linked to notable extreme weather events in recent years, the AP notes. Hurricane Milton, which hit Florida last month as a Category 3 hurricane, is a recent example of a bomb cyclone.
A 2018 “bomb cyclone” brought snow to the southeastern United States and hurricane-force winds. Another “bomb cyclone” in 2022 brought severe weather and extreme cold to much of the United States.
