Midlatitude cyclones in the southeastern United States: frequency and structure differences by cyclogenesis region

Abstract

ABSTRACTMidlatitude cyclones that affected the Southeast (SE) United States between 1998 and 2010 were classified into five types according to their region of origin: (1) Continental United States, (2) Canadian, (3) Gulf Low, (4) Hatteras Low, or (5) Stationary. A composite analysis was used to examine differences in the structure, evolution, and propagation of these cyclones during boreal winter, when the largest number of cyclones affect the SE United States. Most of the midlatitude cyclones that affect the SE in the wintertime formed within the continental United States (∼11 events/winter), followed by Gulf Lows (∼4 events/winter) and Canadian cyclones (∼4 events/winter). Hatteras Lows were relatively rare (∼1 events/winter), and Stationary events did not occur during winter. While Canadian and Continental US cyclones occurred year‐round the frequency of Gulf Low events peaked in the boreal winter when the upper‐level jet was strongest and located further south. Hatteras Lows peaked in the boreal fall and winter, and Stationary events occurred almost exclusively during the boreal summer. Overall, Gulf Low and Continental US cyclones were the only cyclones that brought wintertime precipitation to the SE United States. When integrated over the season, Continental US cyclones made the largest contribution to the wintertime precipitation in the SE United States. On a per‐event basis, however, Gulf Lows were the biggest wintertime precipitation makers in the SE United States while Canadian cyclones and Hatteras Lows did not bring much precipitation to the SE United States. Gulf Lows were more common during El Niño than La Niña years and tended to occur back‐to‐back with either another Gulf Low or with a Hatteras Low.