Current methods for estimating design windspeeds in non-hurricane regions of the United States do not distinguish between winds originating from large-scale extratropical pressure systems and small but intense thunderstorms. These two different meteorological phenomena have separate statistical distributions and, based on analyses of four stations, should not be analyzed using a single (mixed) distribution, as is currently the case. From the stations considered, it appears that there may be many sites in the United States where thunderstorm winds dominate the extreme wind climatology (for the return periods relevant to conventional structural design). For thunderstorm-dominated sites, the traditional approach tends to underestimate the design windspeeds and too narrowly models the wind directionality distribution. Since thunderstorms differ from large-scale extratropical winds in the details of wind structure, storm duration, frequency, and directionality, these differences could have an important influence on the future codification of design winds, the safety of structures, and wind tunnel testing. It is recommended that these results be extended to additional sites and include an investigation of thunderstorm wind-induced structural response for several categories of structures.