A formidable bomb cyclone is churning off the Western U.S.

The comma-shaped storm is a suped-up mid-latitude cyclone, which is quite different than the tropical cyclones (like hurricanes) that form near the equator and are fueled by extremely warm waters. Instead, mid-latitude cyclones are much larger (some 900 to over 3,000 miles in diameter) than tropical cyclones, and form near the boundaries of the frigid poles and the warmer air of the mid-latitudes. These converging air masses create counter-clockwise circulating motions that can induce whirlpool-like movement. Add in the energy from some typical atmospheric instability to the mix (like rising and sinking air), and you’ve got a robust, spinning storm.

In this case, the storm is experiencing a rapid drop in pressure at its center, which stokes a potent cyclonic flow as winds blow toward the low pressure.

“It’s a rapidly intensifying low,” Joe Wegman, a National Weather Service meteorologist, told Mashable.

Conditions for a “bomb cyclone,” or “bombogenesis,” occur when a storm’s central pressure drops by at least 24 millibars in 24 hours. In this case, meteorologists are measuring pressure drops of seven millibars per hour, which if sustained over six hours, would be an all-time record for an extratropical storm (which is a storm created from the temperature contrast between warm and cold air masses).

“The system is deepening rapidly…possibly record setting!” Jeff Weber, a research meteorologist at the University Corporation for Atmospheric Research, emailed Mashable as he observed the storm’s evolution.

“The system is deepening rapidly…possibly record setting!”

The cyclone will have major impacts. There will be high winds and heavy mountain snow in the Northwest. But, as the images below show, the cyclone is also dragging along an atmospheric river — a formidable band of moisture (sometimes dubbed a “river in the sky”) tending to stream over the Pacific Ocean — that will douse Northern California by Wednesday. That means extreme rain. Some areas of Northern California and Oregon will receive in excess of 12 inches of rain, Weber said.

A view from the National Oceanic and Atmospheric Administration’s GOES-West satellite on Nov. 19, 2024 shows the comma-shaped bomb cyclone on upper left, and the atmospheric river (horizontal band of clouds) below.
Credit: NOAA

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Although atmospheric rivers are a crucial part of California’s water supply, scientists have found that they’re becoming more intense, meaning more billion-dollar flooding disasters. The key factor driving more intense atmospheric rivers is the physics of a warming globe. More heat on the planet means more water vapor in the air. The resulting deluges are especially amplified in the case of already strong atmospheric rivers, which deliver a colossal amount of water, many times the average flow of water through the vast mouth of the Mississippi River.

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For those in California and the Northwest, heed warnings from local officials and the National Weather Service. This storm means business.

https://mashable.com/article/bomb-cyclone-atmospheric-river-storm-west-coast