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A powerful ‘bomb cyclone’ strengthening off the west coast is bringing a strong, long-lasting atmospheric river into the region, producing pouring rain, meters of snow and strong winds through the end of the week.
(MORE: Bomb Cyclones 101)
Rapidly intensifying storm sets the weekly pattern in motion
Low pressure off the northwest coast is undergoing what meteorologists call bombogenesis, which is where the term “bomb cyclone” comes from. That means that within 24 hours or less, pressure will have dropped by 24 or more millibars, indicating a storm that is rapidly intensifying, which could lead to greater impacts than what a weaker storm would cause.
You can see the storm starting to arrive off the northwest coast in the current radar, satellite and surface pressure snapshot below.
The storm also attracts a long-lasting atmospheric river moisture plume packed with copious amounts of rain and mountain snow, especially in Northern California and parts of Oregon.
The peak effects of this wet pattern will be felt through Friday, possibly lasting into the weekend for some.
(MORE: Atmospheric rivers 101)
Current radar, satellite and pressure
Breaking the consequences
Heavy rain – The heaviest rainfall through the end of the work week will be focused on Northern California (north of the Bay Area) into southwestern Oregon. Some areas may see 8 to 12 inches of rain in this region (up to 15 inches locally).
The heavy rainfall will result in flooding of areas with poor drainage and possible flooding of creeks and rivers. Mudslides can also pose a threat, especially in areas where wildfires have recently occurred. Rockslides are also possible along some mountain roads.
On Thursday, NOAA’s Weather Prediction Center issued a rare high risk of excessive rainfall in northwestern California, including Eureka, because of how severe the flooding threat could be in that area.
Elsewhere, totals of 1 to 5 inches will extend north through the rest of western Oregon and western Washington, with the heaviest amounts in coastal and foothill areas.
Additional rain and snow forecast
Snowfall – With moisture moving northwest day by day, snow is measured in feet from the higher elevations of the Cascades south to the Siskiyou and Sierra Mountains of Northern California. Snow levels will start low but will rise as the week progresses, impacting travel in some passes.
Snowfall and high winds at times will impact Washington’s Snoqualmie Pass along Interstate 90 and Siskiyou Pass along Interstate 5 near the Oregon-California border.
The National Weather Service has issued several winter weather warnings from the Cascades to California’s northern Sierra. That includes a blizzard warning in the Washington Cascades for late Tuesday through early Wednesday, where travel is strongly discouraged.
Winter weather warnings
Strong wind – The strongest gusts from this storm pattern will arrive later Tuesday and last until early Wednesday. The coastal areas of Northern California, Oregon and Washington can sometimes experience wind gusts of more than 100 to 120 km per hour. Stronger wind gusts will also hit inland through the Cascades and their foothills.
Some power outages and downed trees are possible impacts, especially in areas where high wind warnings are in effect on the map below.
After these peak winds occur, gusty winds will continue on and off for the remainder of the week.
Wind warnings
Chris Dolce has been a senior meteorologist at Weather.com for more than 10 years after starting his career at The Weather Channel in the early 2000s.
