Atmospheric river to soak Pacific Northwest through Thanksgiving week
Several inches of rain falling over a few days through Thanksgiving will slow motorists during the busiest travel week of the year, as a surge of moisture arrives ashore from the Pacific.
Heavy rain and snow may cause travel impacts across the Pacific Northwest on the days leading up to and including Thanksgiving.
A surge of moisture called an atmospheric river will bring heavy rain and mountain snow that slows Thanksgiving travel across the Pacific Northwest this week, and can even last into the holiday itself, warn AccuWeather meteorologists.
Rain and snow fell over parts of Washington and Oregon on Sunday, but there has been a relative break from Monday into Tuesday. Heavier precipitation is slated to arrive later Tuesday through Thursday. Flooding, minor wind damage and slushy roads are all expected to occur.
"The heavy rain from the atmospheric river will likely slow travel on Interstate 5 leading up to the Thanksgiving holiday," said AccuWeather Senior Meteorologist Dan Pydynowski.
Several inches of rain may cause flooding
Following only spotty showers on Monday, a more significant bout of rain will arrive beginning on Tuesday.
"The first round of heavy rain looks to target western Washington and northwestern Oregon starting late Tuesday and Tuesday night," said Pydynowski.
A pedestrian makes his way along a waterfront as downtown Seattle is partially hidden in a steady rain beyond Monday, Nov. 18, 2019. (AP File Photo/Elaine Thompson)
Wednesday, traditionally the busiest travel day of the year, could feature some of the heaviest rain of the atmospheric river event. "Locally heavy rain can cause localized flooding and ponding on roads in cities such as Portland, Seattle and Olympia on Wednesday," added Pydynowski.
Rainfall amounts of 1-4 inches will be common in western Washington and northwestern Oregon, with locally higher amounts possible in the foothills and higher elevations below where it snows. This will be more than enough to cause flooding on roadways and rises on smaller creeks and streams.
In addition to the threat of heavy rain, atmospheric rivers also usually generate strong, gusty winds, especially near the coast. Such winds, locally in excess of 40 mph, can cause minor damage and act to slow travel even further.
Difficult travel possible over some passes, due to snow
It will not just be rain that will hamper holiday travel and outdoor plans on Thanksgiving, but snow in portions of the Cascades. While the Oregon Cascades will largely be dealing with rain at pass levels, travelers through the Washington passes may not be as fortunate.
Snow is expected for both U.S. Route 2 through Stevens Pass and Interstate 90 through Snoqualmie Pass. Several inches of snowfall accumulation is expected to slow motorists here during the pre-Thanksgiving travel period before snow levels rise above pass levels.
In the higher peaks in Washington, such as Mount Rainier, it will be a veritable winter wonderland during the atmospheric river event, with multiple feet of snow possible and temperatures falling to near zero amid strong winds and whiteout conditions.
Following the blast of snow and rain, quieter weather is ahead, beginning later in the week.
"The rain and snow are forecast to continue into Thanksgiving Day before drier air arrives in time for shoppers heading out on Friday," added Pydynowski.
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