A new storm system will march across the northwestern U.S. into Wednesday with locally flooding rainfall and mountain snow.
"The onslaught of heavy rain will continue across the Northwest this week," AccuWeather Meteorologist Matt Rinde said.
A storm system which spread rain and mountain snow across the West Coast on Sunday will continue to track eastward across the Rockies through Monday, allowing the new system to move in.
The heaviest of the rain will move into coastal British Columbia, Washington and Oregon on Monday afternoon and last through Tuesday.
While much of the region would enjoy any precipitation it can take due to the significant drought, there has been a large amount of rain that has fallen in a short period of time this month.
|City, State||Rainfall (inches)||Normal Rainfall for Month (inches)|
|Crescent City, Calif.||6.18||10.18|
Some locations have received nearly the same amount of rain they normally see for the entire month of November in just the first 15 days.
Seattle has received the most rain this month than any calendar month since October 2014. Astoria, Oregon, hasn't seen more than 11 inches of rain since over 14 inches of rain fell in December of 2012.
The coming pockets of heavy rain can lead to areas of flooding from coastal British Columbia into northern California.
Rainfall totals of 3 to 6 inches will fall from the British Columbia coast to the Oregon Coast with a general 1 to 3 inches along the Interstate 5 corridor from Medford, Oregon, to the Canadian border and into Vancouver, British Columbia.
"Mudslides are even possible in some valley regions," Rinde said.
With chilly air already in place, snow will continue across the Cascades through Monday night.
According to AccuWeather Meteorologist Michael Doll, "When the next wave of precipitation arrives later Monday, snow levels will already be below pass level through the Cascades."
"Snow will accumulate quickly along Interstate 90 through Snoqualmie Pass and U.S. 2 through Stevens Pass and create treacherous driving conditions Monday afternoon into Monday night," Doll added.
Enough snow could fall to put chain laws and driving restrictions into effect.
Mild Pacific air will slowly build eastward from the coast through the Northwest, causing snow to changeover to rain across the passes on Tuesday.
"Snow levels will rise above pass level early Tuesday morning and roads will go from snow covered to wet and slushy," Doll said.
Over 3 inches of rain could fall across portions of the Cascades on Tuesday into Wednesday, leading to flooding concerns.
Snow will either change or mix with rain across the Bitterroot Mountains and Rockies of northern Idaho and western Montana.
While rain will clip the northwest portion of California, an area of high pressure over the Southwest will prevent any significant precipitation to reach the drought-striken areas of Nevada and central and Southern California.
The highest peaks of the Cascades will receive feet of snow by Wednesday morning.
A cold front will swing through the area during the day on Wednesday as a small area of high pressure will dry things out for a short period of time.
The next storm will approach the Northwest by Thursday.