You might want to consider the following (lodging oughtn't be a problem at
that time):
Long Beach area, including mouth of Columbia in the southwest corner of the
state
Skagit River Delta just west of Mt. Vernon (eat at Wildflowers in Mt. Vernon)
Dungeness Spit and environs just north of Sequim (pronounced squim)
All of these are under three hours from Seattle.
Have fun!
Steve Aronoff