Whatcom County lies entirely within the 85 MPH 3-second gust wind zone, per table 6-1 of the American Society of Civil Engineers (ASCE) / Structural Engineering Institute (SEI) engineering design manual.
Wind Exposure Zones
Depending on your location, the wind exposure (openness) would be B or C and because Washington has areas categorized as special wind zones, and if you are within 600 feet of an open body of water, it could be exposure D.
There are also a few areas that can fall under the area of wind up-speeding. This is where the mile per hour measurement of the wind is actually increased if your site is located on a steep slope, mountain areas, or bluff areas. For definitions of exposure refer to current codes or consult your local jurisdiction.
It is possible to design your structure prescriptively in zones B and C, but if your site is located in an exposure D zone or if the effects of up-speeding are present you will need to have your structure analyzed by an engineer to handle the wind loads that could affect your structure.