Rain set to return with a vengeance as January weather flips overnight
SEATTLE - January weather is poised to do an about-face, switching from subfreezing cold to heavy rain virtually overnight.
The National Weather Service warns that Western Washington is about to get slammed with a double-barreled blast of steady rain and wind, along with much milder temperatures, starting Monday night and continuing for 48 hours or more.
The combination could trigger flooding on some rivers and a high avalanche danger in the mountains.
A winter storm warning has been posted for the Cascades from 6 a.m. Tuesday to 6 p.m. Wednesday. Such areas as Stevens and Snoqualmie passes could get up to 5 inches of snow through Tuesday morning. Ice accumulations of one-half inch to 1 inch below for 5,000 feet.
The heavy rain is expected to develop Monday night and early Tuesday morning, lasting into early Wednesday evening. The mountains and coast could see 4 to 8 inches of rain with locally higher amounts, while the interior lowlands of Western Washington could see 1 to 4 inches in that 48-hour period.
It will also be locally windy during this time, especially for the Washington coast and north interior areas around San Juan and Whatcom counties, where downed tree limbs and local power outages are possible.
If rainfall amounts are as heavy as expected, it could lead to some flooding on the more flood-prone rivers flowing out of the Olympics and Cascades, as well as the Chehalis River in southwest Washington.
At the same time, high temperatures will warm into the low 50s Tuesday and Wednesday around Puget Sound - which will seem subtropical after weeks of frigid low temperatures and wind chills in the single digits.
The snow level will rise to 7,000 to 8,000 feet through Tuesday night, then fall to around 6,000 feet late Wednesday as precipitation begins to decrease.
The exception to warmer temperatures - at least for a time - will be the Portland-Vancouver metro area, the Columbia Gorge and the valleys of southwest Washington, where a major ice storm is possible for several hours Monday night and Tuesday before temperatures finally warm above freezing.
Meanwhile, the Northwest Avalanche Center is warning of a high avalanche danger in both the Olympics and Cascades from Monday night through Tuesday as heavy rain and snow create unstable layers. Also, strong southwest winds will build new and unstable wind slab on lee slopes at higher elevations throughout Tuesday.
The change in weather pattern is courtesy of a 120-knot jet stream aimed directly at the Pacific Northwest.