Water Resources of the United States

PROJECT ALERT NOTICE (WA) Major Flooding in Northwest Washington

Date: Tue, 16 Nov 2021 15:45:39 EST

Summary: Precipitation from a second atmospheric river event in a week has resulted in Peak Of Record (POR) and major flood stage in Northwest Washington and the Olympic Peninsula.

Precipitation from a second atmospheric river (atmospheric river description available at https://cw3e.ucsd.edu/) has ended. However, river levels are still at major flood stage in the lower reaches of larger basins. Some USGS precipitation gauges have recorded 13+ inches over the previous five days. Rain on snow increased runoff to both west (i.e., Nooksack, Skagit Rivers) and east (i.e., Similkameen River) of the Northern Cascades. Streamflow exceeded the current rating at 9 locations, with some PORs occurring (final POR count may require indirects). Major flood stage is still occurring at 2 streamgages located in the Nooksack and Skagit Basins Moderate flood stage is occurring at 1 location, with 2 more at minor flood stage. Forecast hydrographs from the Northwest River Forecast Center are available at https://www.nwrfc.noaa.gov/rfc/hydrographs/

Crews from the Northwest (Ferndale, WA) and Western Washington (Tacoma, WA) Field Offices are in the field again today. A total of 19 people (11 crews) are deployed. Several sites have lost data as sensors inundated or were damaged. One critical site (12200500) went down last night near the peak with a team working late into the evening to repair. Unfortunately, the repair did not hold, and the local office supervisor self-deployed at 4:30 a.m. PST to hand enter manual readings into NWISWeb until successful repairs could be completed. Local media were on site and interviewed the field crew attempting repairs. A follow-up live interview has been requested for this evening.

Media coverage of the impacts available at:

https://www.washingtonpost.com/weather/2021/11/15/atmospheric-river-seattle-vancouver-flooding/

Flooded roadways, high winds, and landslides made some sites inaccessible. Interstate 5 repeatedly closed north of Seattle and Hwy 101 on the Olympic Peninsula is still closed. The need for indirects for peak flow determination is still being evaluated. Nearby Centers have been contacted to determine their level of indirect expertise.

This will be the final project alert for this event.

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