Atmospheric River to advance into the West Coast this week
Following a welcome lull in the stormy pattern early week across the Pacific Northwest, AccuWeather forecasters warn that an Atmospheric River is on the way later in the week that will raise the risk for flooding, damaging winds.
A dusting of snow fell across parts of Utah, leaving the red rock canyon partially covered.
A series of storms will bring a deluge of moisture into the Pacific Northwest later this week, sparking a threat for flooding rainfall, mountain snowfall, blustery conditions and travel disruptions across the region.
While some locations across Washington, Oregon, Idaho, Montana and Wyoming already experienced a storm diving southeastward into the U.S. from western Canada at the start of the week, AccuWeather meteorologists warn there is much storminess to come as the week progresses.
Early-week pattern
The first storm already impacted the Northwest Sunday afternoon and night with rain and high elevation snow.
There will be a lull in storm activity for most locations in the Pacific Northwest through Tuesday night.
The early-week break between storms will also provide temperatures near the historical average, or seasonal norm. Cities like Seattle and Portland, Oregon, are projected to have daytime highs in the lower to middle 60s approaching the midweek period.
GET THE FREE ACCUWEATHER APP
•Have the app? Unlock AccuWeather Alerts™ with Premium+
An Atmospheric River to drench areas late week
The latter half of the week will feature a more tumultuous pattern across the West compared to the late weekend storm. Additional waves of rainfall are on the docket with multiple storms expected between Wednesday and the upcoming weekend.
Later Wednesday, the next storm will advance into parts of southwest British Columbia, Canada, Washington and portions of northern Oregon with occasional showers and breezy conditions at the direct coastline.
A potent storm will follow in quick succession across the Northwest U.S. on Thursday, advancing first into western British Columbia as early as Wednesday evening with drenching rainfall and snow across the higher terrain. Wind gusts associated with this storm can range upwards of 50 mph over the ocean and the immediate coastal areas to 30-40 mph farther inland.
While a portion of the interior Northwest U.S. is expected to observe between 1-2 inches of rain from the late-week storminess, coastal regions in Washington and Oregon and the Cascades are projected to pick up higher amounts on the order of 2-4 inches. Localized pockets of around 6 inches will not be off the table, particularly in zones along the coast that see repeated downpours from Thursday into the weekend.
A continued pattern of storms into the Northwest states will gradually help to aid the zones facing severe and extreme drought. Area river levels in need of moisture can benefit from a pattern such as this. However, it will come at a cost, with travel disruptions likely and days of rain generating flooding from the Northwest coast into Northern California.
“The pattern setting up along the Northwest to Northern California coast is indicative of an Atmospheric River as the moisture can be traced back to Southeast Asia. This type of a pattern typically yields heavy rain and flooding with only very high-elevation snow in the Sierra given the warm air bleeding into the storm," AccuWeather Senior Meteorologist Chad Merrill said.
In addition to the rain and wind, a heavy, wet snow will fall in the highest crests of the Cascades and Sierra, likely above pass level during the late-week period. The potential will remain for cooler conditions through the weekend to lower snow levels and impact heavily-traveled roadways and passes across the region.
“Atmospheric Rivers are most common from November to January in the Northwest into Northern California. They also usually dump heavy rain in a short time period; within 24 hours, several inches can trigger flooding and mudslides. The upcoming late-week and early weekend storm will likely be no exception to that rule.”
Want next-level safety, ad-free? Unlock advanced, hyperlocal severe weather alerts when you subscribe to Premium+ on the AccuWeather app. AccuWeather Alerts™ are prompted by our expert meteorologists who monitor and analyze dangerous weather risks 24/7 to keep you and your family safer.
Report a Typo
