Pacific ‘Bomb Cyclone’ will initiate a strong atmospheric river to the west

On November 19, 2024By Littum

A strong storm will develop off the northwest coast, drawing in an atmospheric flood of moisture.
Heavy rains can trigger flash floods, mudslides and rock slides, especially in northern California and southwestern Oregon.
Strong winds will accompany the storm, and higher elevations will see feet of snow.

A powerful “bomb cyclone” developing off the West Coast will usher in a strong, long-lasting atmospheric river to the region, producing flooding rain, feet of snow and strong winds through the end of the week.

(MORE: Bomb Cyclones 101)

Rapidly intensifying storm kicks off the soaking pattern

On Tuesday, the low pressure will undergo what meteorologists call bombogenesis over the North Pacific, from which the term “bomb cyclone” originates. This means that its pressure will have dropped by 24 or more millibars in 24 hours or less, indicating a storm that is rapidly intensifying, which could result in more significant impacts than what a weaker storm would produce.

In this case, the storm will also draw in a long-lasting atmospheric river moisture plume filled with abundant rain and mountain snow, especially in northern California and parts of Oregon.

Peak impacts from this soaking pattern will unfold Tuesday through Friday, possibly lingering into Saturday.

(MORE: Atmospheric rivers 101)

Atmospheric river setup

(Later Tuesday into Wednesday, the strong low pressure will be positioned off the northwest coast, drawing in the pipeline of moisture from the atmospheric river, as shown above.)

Breakdown of the effects

Heavy rain – The heaviest amounts of precipitation through the end of the work week will target northern California (north of the Bay Area) into southwestern Oregon. Some areas could receive 8 to 12 inches of rain (locally up to 15 inches). Totals of 1 to 5 inches will extend north through the rest of western Oregon and western Washington, with the heaviest amounts in the coastal and foothills.

This can result in flooding for poor drainage areas as well as possible flooding of streams and rivers. Mudslides can also be a threat, especially in any recently burned wildfire. Rockslides are also possible along some mountain roads.

snowfall – With moisture pouring into the Northwest day after day, snow will be measured in feet from the higher elevations of the Cascades south into the Siskiyou Mountains of Northern California. Snow levels start low but then increase throughout the week, affecting travel in some passes.

Snowfall will at times affect Washington’s Snoqualmie Pass along Interstate 90 and Siskiyou Pass along Interstate 5 near the Oregon-California border.

Strong wind – The strongest winds from this storm pattern will arrive later Tuesday and last into early Wednesday. Coastal parts of Northern California, Oregon and Washington could see wind gusts above 60 or 70 mph at times. Stronger gusts will also affect inland areas through the Cascades and its foothills. Some power outages and downed trees are possible impacts.

After these peak winds occur, wind strength will at times continue for the rest of the week.

Wind warnings

(Issued by the National Weather Service.)

Chris Dolce has been a senior meteorologist at weather.com for over 10 years after starting his career with The Weather Channel in the early 2000s.