Hydrologic Outlook issued December 18 at 3:36AM PST by NWS Seattle WA

ESFSEW

An atmospheric river has brought 2 to 4 inches of precipitation
across the Cascades of Snohomish County northwards over the last 24
hours. This has led to a rise in area rivers. However, river
flooding is not expected for Whatcom, Skagit, and King Counties from
this event. Although river flooding is not expected for Snohomish
County, the Stillaguamish River continues to rise rapidly this
morning due to 1 to 2 inches of precipitation over the last 6 hours
in the Stillaguamish basin and vicinity. For this reason, the
Hydrologic Outlook remains for Snohomish County. However, current
river forecasts keep the Stillaguamish River below flood stage. We
will continue to monitor if conditions change.