A parade of Pacific storms, accompanied by atmospheric rivers, will continue to march into the West Coast, bringing a threat of more rain to already flooded areas of western Washington, and an increasing flood threat to Oregon and Northern California into this weekend.
The latest atmospheric river Monday dumped another 2 to 5 inches of rain in the Cascades and Olympics of Washington state, which were still recovering from 10 to 18 inches of rain during last week's procession of atmospheric rivers.
(MORE:What Is An Atmospheric River?)
This lead to a pair of levee breaches in King County, one along the Green River in Tukwila, just east of SeaTac Airport, Monday, then early Tuesday morning in the town of Pacific, east of Tacoma.
(MORE:Evacuations Prompted From Washington Levee Breaches)
Timing Through This Weekend
Unfortunately, there are more weather systems targeting the West into this weekend, and even beyond. Here is a rough daily timeline.
Late Tuesday Into Wednesday:A strong, windy storm will lash the Northwest and far Northern California with heavy rain and high winds. In the Washington Cascades and Olympics, this precipitation will be mainly snow. This precipitation should diminish to showers in these areas by Wednesday afternoon.
Thursday:Another atmospheric river arrives. The heaviest rain will be focused in Oregon but some rain and high-elevation snow will also fall in Washington into Idaho and western Montana.
Friday:The atmospheric river shifts into southern Oregon and Northern California. The main impacts will remain mainly north of the Bay Area. Showers and mountain snow may linger in Washington, northern Oregon and the northern Rockies.
Weekend:The main concern is for Northern California Sunday, though some locally heavy rain could also return to parts of Oregon. Showers in western Washington Saturday could increase by Sunday.
Impacts
First, we expect secondary crests either Wednesday or Thursday on many of the rivers that flooded western Washington last week, including stretches of the Skagit, Snohomish, Green, White, Cowlitz, Chehalis and Yakima Rivers.
In most of these cases, the crests will be significantly lower than last week, however major flooding is once again forecast along the Skagit River in bothConcreteandMt. Vernon, Washington.
The heaviest additional rainfall totals through this weekend will be in the western Oregon and Northern California, particularly in the foothills of the Cascades, Siskiyous and Sierra as well as the coastal ranges, where over 5 inches of rain is likely.
This heavy rain will likely trigger flash flooding and some landslides, particularly in areas recently burned by wildfires.
The late Tuesday - Wednesday storm system will dump up to 18 inches of snow in the Cascades and Olympics of Washington state and up to a foot of snow over the higher elevations of the northern Rockies of western Montana and western Wyoming.
Much of the Northwest and Northern Rockies will also be blasted by strong wind gusts over 60 mph, particularly in the interior Northwest and over the higher elevations. This could lead to tree damage and power outages, particularly in areas where heavier snow weighs down tree branches and power lines.
More Atmospheric Rivers Later This Week, Month?
Most people in the Pacific Northwest, and probably people around the country who know people who live in the Pacific Northwest, are likely wondering if a more long-term dryness is in the forecast.
I hate to be the bearer of bad news, but we may have more atmospheric rivers on the way. After several rounds of rain this week, expect more as we head into the last few weeks of December.
The atmospheric conditions, including a mid-level ridge over the Bering Sea and a downstream trough in the northeastern Pacific, will serve as a sort of an atmospheric nozzle that will likely steer additional moisture to the already waterlogged West Coast.
I guess a slight silver lining here is that most models are suggesting that the heaviest rain is expected across Oregon and California, however, should any new rainfall hit Washington, it could easily cause flooding due to saturated soils.
Another slight sign of good news is that temperatures may not be as warm in the coming weeks across the West as they are currently, which means snowfall is more likely across the Cascades and Sierra Nevada.
Note that snowmelt across the Cascades exacerbated the flooding from the heavy rainfall across the Pacific Northwest, so more of the precipitation across the mountains falling as snow will help to reduce some river flooding and can also help rebuild the snowpack for skiiers and snowboarders planning to hit the slopes to end 2025.
Jonathan Belleshas been a digital meteorologist forweather.comfor 9 years. His favorite weather is tropical weather, but also enjoys covering high-impact weather and news stories and winter storms. He's a two-time graduate of Florida State University and a proud graduate of St. Petersburg College.