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Atmospheric river continues to unleash drenching rainfall in the Northwest

AccuWeather meteorologists say that an atmospheric river plunging into the Northwest U.S. and British Columbia, Canada, over the upcoming days will usher in additional waves of heavy rain, with some locations projected to finish the month with around a foot of rainfall.

The risk for flooding will rise as the active pattern continues, especially for urban and poor-drainage areas, rivers and streams, some of which have already climbed above flood stage.The persistent flow of moisture soaking the Northwest over the last several days is projected to continue into the start of the new week, forecasters say.

An expansive hydrologic outlook was issued along all of western Washington and Oregon at the start of the weekend due to the heavy swath of rainfall expected to continue across the region and the ample snowmelt occurring as snow levels rise to 7,000 or 8,000 feet.

"The Skokomish River in northwest Washington rose from minor flood stage to moderate flood stage from Saturday to Sunday morning as heavy rain fell across the region," explained AccuWeather Meteorologist Elizabeth Danco.

Moderate flood stage on the Skokomish River is categorized as water levels between 17.5-17.9 feet. After peaking at 17.27 feet late Thursday, the river gauge declined to 16.9 feet by Saturday morning. By early Sunday morning, the river levels rose to 17.74 feet, coming dangerously close to major flood stage. According to recent data, the last time the Skokomish River reached moderate flood stage was early December 2023. However, during this time, the river quickly surpassed moderate flood levels and rose to major flood levels with a peak reading of 18.01 feet.

Based on the rainfall through Sunday, forecasters say that the river levels are not likely to surpass major flood stage and repeat what occurred last month, although levels may come close. Major flood stage is categorized as water levels higher than 18.0 feet.

Into early week, a break in the active pattern across the northeastern states can allow for a temporary window of dry weather.

"Residents in Seattle could experience a brief break in the wet weather Sunday night into Monday, although this reprieve may only last for 12-24 hours before showery and cooler conditions return," added Danco.

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Rain and showers can return to the region by Monday night, bringing the short-lived hint of dry weather to an end. Daytime temperatures in Seattle and Portland are projected to trend lower throughout the week, declining to the middle to lower 50s by midweek and 40s by Friday.

Another drenching and more expansive wave of moisture can arrive along the West Coast by late Tuesday into Wednesday, likely reaching areas from southwest Canada to Central California. This midweek storm can bring heavy rainfall and strong winds to locations farther south than storms over the last few days.

As a cooler air mass spreads across the region, snow levels will gradually fall throughout the week and heavy, high-elevation snowfall can occur as the next system tracks overhead. Snow levels are expected to come down significantly from Thursday to Friday across the Sierra Nevada range. Accumulating snowfall upwards of 6-12 inches can even occur around pass level, forecasters say.

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