[Mizar]

Welcome Sharkmelon;
I appreciate your concern about your location, however lets use the 1980 Mount St. Helens eruption as a model for a nuclear explosion, the effects are strikingly similar
on 18 May 1980, Mt. St. Helens erupted
Energy released = 24 Megatons
Temperature of Ashcloud = 660 d F, 349 degrees C
Altitude of explosion 8000 feet ( equivalent to nuclear airburst)
Altitude of ashcloud = 12 miles
Speed of ashcloud 680 MPH ( just subsonic)
Look up the ashcloud distribution pattern on Wikipedia, this would be equivalent to a radiation fallout pattern ( Image 1980 Mount St. Helens ash distribution.svg)
If the cities of Seattle, and Tacoma were nuked, the event would be likely be smaller than the Volcano blast, but with more Radiation fallout downstream. Notice that although the blast wave was felt in Vancouver, the Ashcloud mostly went East and South of the blast.
Hope you can sleep better now.
M