A classification scheme for nor'easters and other winter storms (November–April) in the eastern and central United States provides real-time information on the potential impact of these storms. This scheme also may be applied to winter storms over the last century to provide a time series of trends and cycles in specific magnitude nor'easters along the East Coast and Colorado lows that migrate northward toward the Great Lakes (i.e., Witches of November). The classification scheme follows a 1–5 hierarchy with category 1 storms being the least severe and category 5 storms the most severe. Winter storm/nor'easter category is determined through the development of an intensity index (I) from surface synoptic charts. The 1–5 scale classification scheme of the storm's intensity is determined from the sum of central low pressure difference from 1013 mb, the deepening rate (millibars per 12 hours) and the maximum pressure gradient in millibars per 1000 kilometers. A five-scale (1–5) duration factor (DF), inversely related to the storm's forward speed, is combined with intensity in the classification scheme in the form I.DF. The DF takes into account the potential for high precipitation totals (snow or rain depending on storm track) from slow-moving weak to moderate storms. This twofold categorization allows a general estimation of potential snowfall/rain amounts and rates, wind speed, and the impact on communities (i.e., infrastructure, schools, businesses) with different intensity and storm duration. Impact on marine/coastal interests along the eastern seaboard and in the Great Lakes region also may be inferred from this classification scheme.
University of Maine, Orono, Maine