Up to 8 inches of rain to threaten flooding in northwestern US

By Kristina Pydynowski, AccuWeather senior meteorologist

January 16,2017, 11:10:08AM,EST

 

 Storms will return to the northwestern United States as more storms are set to deliver drenching rain and wintry travel hazards this week.

“An atmospheric river of moisture originating near the tropics in the West Pacific Ocean will stretch across the Pacific and help fuel heavy rain across the Northwest Monday night through Wednesday,” according to AccuWeather Meteorologist Jordan Root.
Travel delays to both motorists and airline passengers can be anticipated.
Along the coast, there will be the risk of flash and urban flooding, strong winds, mudslides and erosion. Farther inland, travel problems will result from snow, ice and rain.
Unlike last week when Portland, Oregon, endured ice and then one of its snowiest 24-hour periods on record, the track of the storms will bring milder conditions and mostly rain to the I-5 corridor of the Northwest.
Lingering cold should cause the rain to briefly begin as a period of ice and slick travel in Portland on Monday evening.

Rainfall generally totaling 2 to 4 inches will otherwise soak Portland and the other I-5 cities of Seattle and Olympia, Washington, and Salem and Eugene, Oregon.
Widespread flash flooding will threaten places along the coast and the western slopes of the northern Cascade Mountains, where rainfall should total 4-8 inches. Some rivers and streams may overflow their banks.
However, many of the rivers in western Washington are running at their lowest levels since the end of the summer, according to the National Weather Service in Seattle.
The rain will be windswept at times. The strength of the winds toward midweek could lead to sporadic tree damage and power outages along the coast. Seas will build as the winds howl, threatening to cause beach erosion.
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Snow levels will rise well above the mountain passes early this week, meaning motorists traveling through Snoqualmie Pass along I-90 will face water on roads and reduced visibility from downpours and fog instead of a snowcovered highway.
“This will not be a big snow event for the Cascades except for the highest peaks as snow levels will rise to between 7,000 and 7,500 feet on Tuesday,” AccuWeather Senior Meteorologist Dan Baker said.
However, motorists venturing eastward out of the Cascades will face greater hazards due a more extended period of ice in the valleys of northern Oregon and Washington.
Travel will be treacherous around Ellensburg and Wenatchee, Washington. Travel will become slippery and dangerous, including for a few hours after temperatures rise above freezing.

If enough moisture can survive over the mountains and into these areas, the ice could accumulate enough to cause power outages and tree damage.
The risk of ice will also expand along I-84 from Portland to Pendleton, Oregon, as well as along I-90 to Spokane, Washington, and into western Montana on Monday night into Tuesday, before an eventual changeover to rain.
Wintry weather may become more extensive over the Northwest by this weekend.
“The jet stream (a fast-moving river of air along which storms travel) will take a dip across the West during the midweek and will help bring colder air farther south,” Root said. “That will lower snow levels and allow snow to pile up across the Cascades later in the week.”
Periods of rain, albeit not as heavy as earlier in the week, will continue to dampen the I-5 corridor late this week.
While dry weather will hold across California early this week, the second half of the week will turn stormy.