Higher elevations (northwestern parts of Frederick County) require 40 lb/ft².
Section 1608 Uniform Statewide Building Code(USBC)/International Building Code (IBC) 2009. T1608.2 IBC lists Frederick County as 'CS' Case Study. Loading is based on historical performance and Figure 1608.3(1) of the BOCA Building Code as published in the 1996 edition.
Ultimate Wind Design (Vult) & Risk Category (USBC 1609.3) 115 Vmph for Risk Category II
Exposure category: Exposure C, unless Exposure B definition applies. See USBC/IBC 1609.4.3.