What you need to know about the powerful ‘bomb cyclone’ approaching Northern California, Oregon, Washington

On November 20, 2024By Littum

Upper line

A powerful storm is expected to bring heavy rain, strong winds and snow to the Pacific Northwest and Northern California this week, potentially producing life-threatening weather hazards and power outages over the next few days.

The storm is expected to last through Friday. (AP Photo/Elaine Thompson)

Key facts

The storm system, known as a “bomb cyclone“, is intensifying and will near the Pacific Northwest Tuesday evening, according to National Weather Servicewhich warned of damaging winds (gusts between 60 and 70 mph) from Northern California to Western Washington, which began experiencing heavy rain from the system Tuesday afternoon.

Heavy rainfall will continue into Friday, with more than 10 inches of rain and flooding expected in some regions between northern California and southwestern Oregon.

The NWS is predicting heavy snow and strong winds to produce whiteout conditions and almost impossible journey in parts of the Cascades into the northern Sierra Nevada.

ONE flood watch in California’s Sonoma, Napa and Marin counties is valid until 4 Saturday as the NWS Bay Area increased its forecast confidence Tuesday afternoon.

NWS Seattle warned of damaging, gusty winds Tuesday afternoon into Wednesday morning in Western Washington, noting that the winds could cause widespread power outages, road closures and damage to temporary structures.

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What is a bomb cyclone?

The term “bomb cyclone” is derived from the process of bombogenesis, which describes a low-pressure system in which the pressure drops by at least 24 millibars (a pressure unit) within a 24-hour period – signaling significant intensification. The NWS in Medford, Ore., said Tuesday that a storm as strong as this week’s “occurs on average about once every ten years” and that it will produce “some of the strongest winds we’ve seen in years.” Bomb cyclones have hit the US a few times in recent years, with two materializing in 2018 and 2022 and another forming last month in the form of Hurricane Milton, according to Associated Press.

How strong is the bomb cyclone?

The system’s minimum pressure is expected to drop to 943 millibars Tuesday evening, according to The Washington Post, far low enough to rival the pressure of powerful major hurricanes. Lower pressure in storm systems is associated with stronger intensity.

How to prepare for the bomb cyclone

The NWS advises people in affected areas to secure loose outdoor items, trim branches near their homes and prepare for power outages. Ready.gov advises those experiencing power outages to only use generators outdoors and away from windows, not to use gas stoves or furnaces to heat homes, and to plan for alternate power sources that may be needed during an outage.

What closures has the bomb cyclone caused?

Probable strong winds have closed classes, events and services at Bellevue College and resulted in closure of the Lake Washington Institute of Technology campus.

Key background

The NWS predicted last month that seasonal temperatures in Northern California and the Pacific Northwest would remain roughly the same between November and January. That too forecasts parts of the Pacific Northwest to receive above average rainfall. However, the western United States could potentially see less rainfall this year as scientists give La Niña, a cooling of sea surface temperatures in the eastern Pacific associated with dry winters in the region, a 57% chance appear late this year.