Heavy rain will soak portions of Washington and British Columbia through Friday, leading to flash flooding before spreading inland through the weekend.
According to AccuWeather Senior Meteorologist Brett Anderson, "A fire hose of moisture extending from the western Pacific Ocean to western North America will focus over British Columbia to Washington state through Saturday."
The heaviest rain will fall across the Olympic and Cascade mountains of Washington as well as Vancouver Island and the Coastal Mountains of British Columbia, including Vancouver. Storm total rainfall could exceed 10 inches (250 mm) in some locations through this weekend.
"Seattle will not receive as much rainfall as the nearby mountainous regions, but could still pick up between 2 to 3 inches (50 to 75 mm) through Saturday," Anderson said.
Lesser amounts of rain will fall across northwest Oregon, northern Idaho and northwest Montana through Friday.
While this rain will be beneficial with the ongoing drought across the region, too much rain in a short period of time will lead to flash flooding concerns, especially across western Washington and southwest British Columbia.
Snow on the order of 1-3 inches (25 to 75 mm) could fall across the northern Cascades of Washington into the higher peaks of the Coastal Mountains of British Columbia through Saturday.
"Snow levels in the Cascades [of Washington] and coastal ranges [of British Columbia] will be above pass level for this storm," Anderson said.
While most of the passes will be free from snow, wet roads and strong winds could lead to some dangerous travel conditions.
"Gusts topping 60 mph (97 km/h) can occur, along with fog in some of the passes, so travel may still be hazardous," Anderson said.
This system will slowly progress south and east through the weekend, bringing rain to northern and central California and significant snowfall across the Cascades of Oregon and the Sierra Nevada.
As the cold air dives in Saturday night into Sunday, snow levels will drop significantly and could cause rain to change or mix with snow as far down in elevation as the Snoqualmie Pass (3,000 feet).
Another foot or more of snow can fall across the Sierra Nevada into early next week.
Snowfall could lead to chain laws going into effect for those driving through Donner Pass.
This storm may bring nothing but a sprinkle from Los Angeles to Las Vegas on Sunday night.
This storm will not only bring beneficial precipitation to the Intermountain West early next week but also another quick shot of chilly air.
High temperatures across the Intermountain West will fail to reach 40 F (4 C) in most areas on Monday.
Rain and higher elevation snow will move into the Four Corners region on Monday. Rain amounts will be much less than the amounts expected across western Washington.
Cities including Flagstaff to Salt Lake City will see the return of snow showers with minor accumulations possible.
The train of storm systems will continue as another storm brings drenching rain and mountain snow across the Northwest and British Columbia starting on Monday.
The heaviest rain from these two systems will fall across western portions of Washington, which are currently dealing with a moderate drought, according to the U.S. Drought Monitor. Locations across eastern Washington that could desperately use the rain will not receive the amount of rain to put any significant dent in the drought.
Rainfall totals from this storm and the storm early next week could lead to rainfall totals of over 18 inches (457 mm) across the Olympic and Cascade mountains of Washington and Coastal Ranges of British Columbia.
"The storms will be a boost for ski country," Anderson said.
Anderson also said that the stormy pattern in the Northwest and British Columbia will continue over the next few weeks.
There is the possibility that the drought across western Washington could be erased in some locations by the end of next week.