Frost line depth in Whatcom County, WA
How deep the ground freezes in Whatcom County, WA
13 in. Dig to 14 in, just below the frost. Nearest NOAA station: Upper Baker Dam, 14.7 mi.
Your building department sets the legal frost line depth (IRC Table R301.2(1)); footings must go below it (R403.1.4.1). Call them before you dig.