While the climate structure and overall suitability for growing winegrapes is typically focused on growing season temperatures or heat accumulation, risk associated with frost timing and the length of the growing season can severely limit site suitability in many regions. To assess regional risk due to frost and short growing seasons, this research uses PRISM 400m grids from the 1971-2000 climate normals for median last spring and first fall freeze dates and the frost-free period. The analysis focuses on wine regions in the Pacific Northwest (Oregon, Washington, and Idaho) and known cultivar growth characteristics of bud break and time to maturity to help establish cultivar suitability to regions based upon their frost timing and length of the frost-free period.