SEATTLE – Heavy rain overnight has increased flooding concerns across western Washington and Oregon after an atmospheric river storm known as a Pineapple Express slammed into the Pacific Northwest on Monday.
Multiple rivers across the region are on Flood Warnings and some rivers near populated areas in the foothills of Western Washington are forecast to near or reach major flood stage by midweek. Already, as much as 4-8 inches of rain have fallen in the mountains, and more is on the way.
A Pineapple Express is when the jet stream dips to the south into the tropical Pacific Ocean near Hawaii, gathers warm, moist air and carries it across the ocean where it dumps heavy rain in either the Pacific Northwest or California.
And the air in Washington is indeed warm. Seattle recorded a temperature of 59 degrees early Tuesday morning, which already broke its old record of 58 degrees. Olympia, Washington, hit 63 degrees on Tuesday morning which is now its second-warmest December temperature on record. Snow levels are near 10,000 feet.
The precipitation is expected to remain heavy into later Tuesday before finally letting up Tuesday evening as the band of moisture slowly pushes inland, but the stage has been set for significant river flooding.
The FOX Forecast Center says that the combination of several inches of rain on top of the 2-4 feet of snow on the ground in the Cascades and Olympics from winter storms over the weekend is resulting in extensive runoff. Numerous rivers, creeks and streams are expected to reach flood stage – with major flooding possible in some spots.
Water levels are expected to climb significantly on Tuesday and will crest either late Tuesday night or Wednesday.
Moderate to major flooding is expected along the Skagit, Snohomish, Snoqualmie and Skokomish rivers in Western Washington, and communities along those rivers should prepare for the possibility of flooded roads and water creeping into buildings.
The Skagit River at Mt. Vernon is expected to crest at 34.51 feet on Thursday. The Snoqualmie River near Carnation is expected to crest at 58.4 feet on Wednesday. Both those crests are considered major flood stage.
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The National Weather Service in Seattle says several inches of rain have already fallen in the region and up to 5 inches of additional rain is possible over the Olympics, 2-4 inches over the Cascades, 1-2 along the coast and 1-2 over the interior lowlands by late Tuesday.
This will be on top of the already impressive rainfall totals reported in the region over the past 24 hours.
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The NWS says Olympic National Park recorded 8.67 inches of rain. Duvall and Granite Falls, which both are near the foothills of the Cascades, picked up several inches of rain. Duvall recorded 7.12 inches while Granite Falls reported 5.87 inches. Skykomish, in the heart of the Cascades along Stevens Pass, was just over 7 inches and counting.
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The Flood Watches have covered much of western Washington and Oregon for days, but have expanded to the south to include portions of Northern California, including Eureka, through Thursday.
Flood Watches include the cities of Bellingham, Seattle and Spokane in Washington. In Oregon, the cities of Portland, Eugene, Coos Bay and Medford are included in the Flood Watch.
The bulk of the heavy precipitation is expected to wind down as we head into Wednesday.
However, the flood risk will continue throughout the day as the copious amounts of water continue to flow downstream. More rain is in the forecast later in the week but snow levels will return to more typical December levels, mitigating any future flood threat.