New Atmospheric River Expected To Arrive Late Sunday In The Flood-Wary Pacific Northwest

Rescue Crews Brave Floodwaters In Washington

The Pacific Northwest will have much of the weekend to dry out after days of flooding rainfall, but there is another atmospheric river set to wash ashore by early in the week ahead.

Flooding will continue as runoff from previous events continues to move through the Cascades and down toward Puget Sound.

(MORE: Latest News From Washington State)

Drier weather will persist across the region through at least the first half of Sunday.

Here's a current look at the atmospheric river off the Pacific Coast:

Timing Through Early Week

Arrival: Late Sunday in Washington State; Tuesday in Northern California

Peak Flood Potential: Late Sunday to Monday in Washington, Oregon; Tuesday in Northern California

Departure: Early Tuesday in Washington, but with potential for a reinforcing shot late in the day

How This Event Compares

• This singular event will have a shorter duration compared to the back-to-back events that occurred on Monday and Wednesday of this past week

• Rainfall totals appear to be lighter than the event that occurred Wednesday.

• Rainfall rates may be slightly lower due to the change in orientation of this upcoming atmospheric river, which will come in less perpendicular to the mountain ranges.

• The upcoming event is likely to be classified as a Category 4 event, which is the same rating given to the previous atmospheric river that came ashore Wednesday.

• Snow levels appear to be similarly high compared to previous events, although they could come down quicker on the backside of this event.

(MORE: Where It Isn't Raining, It Is Record Warmth Forecast In The West)

Rainfall Totals

Rainfall will generally be lighter than what was seen in the Pacific Northwest over the last week, but it also won’t take as much rainfall to create significant issues, especially in Washington.

This atmospheric river will drop further south into Northern California than those of the previous week, so some new areas will pick up rainfall there, but totals will be light.

Snowfall will be confined to the highest elevations of the Cascades and Northern Rockies, but over a foot is possible, especially in the Washington Cascades.

More Atmospheric Rivers Later This 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 later in 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 a sort of an atmospheric nozzle that will likely steer additional moisture to the already waterlogged Northwest.

I guess a slight silver lining here is that most models are suggesting that the heaviest rain is expected across southwestern Oregon and northwestern 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 snow for skiiers and snowboarders planning to hit the slopes to end 2025.

Jonathan Belles has been a digital meteorologist for weather.com for 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.