Regional and Local Influences on Freezing Drizzle, Freezing Rain,and Ice Pellet Events

Abstract

Regional and local influences on frequency and type of freezing precipitation (freezing drizzle, freezing rain, and ice pellets) are investigated via in-depth climatologies of six continental United States (CONUS) sounding sites. For each site, wind roses of precipitation type occurrences are compared with those for nearby stations and the aggregate values for the CONUS. Synoptic scenarios and sounding structures are identified for prolonged events of each precipitation type and probable formation mechanisms are discussed. Station location relative to topographic features smaller than 1 km in height, water bodies ranging in size from oceans to small bays, and dominant wintertime storm tracks are shown to play a major role in the determination of the frequency and type of freezing precipitation at each site. Results help to explain the regional maxima and minima of freezing precipitation across the CONUS, as well as the dominance of certain precipitation types and formation mechanisms in different portions thereof. Understanding these differences is necessary for proper development of techniques used to diagnose and forecast surface precipitation type and the occurrence of hazardous aircraft icing conditions associated with freezing precipitation aloft.