Local and Synoptic Environments Associated with Freezing Rain in the Contiguous United States

Abstract

Local and synoptic conditions associated with freezing-rain events in the continental United States, as well as the temporal and spatial variability of these conditions, have been documented for the period 1976?90. It had been postulated that the characteristics of the thermodynamic stratification observed during freezing rain would be similar regardless of geographical location. However, through hypothesis testing, it was found that some interregional variability exists in the magnitude of various sounding parameters that the authors felt characterized the important aspects of the thermodynamic profile of freezing-rain environments. This variability seems to be related not only to local effects resulting from terrain variations and nearby water sources, but also from regional differences in synoptic-scale atmospheric environments favorable for freezing rain. These results suggest that freezing-rain forecast techniques, which rely on critical parameters derived for specific geographical locations, may not be applicable if applied elsewhere. Therefore, forecasters evaluating the possibility of freezing rain over synoptic-scale areas should not expect one variable that characterizes a sounding to be an accurate indicator of freezing rain across the entire region. Algorithms that evaluate the entire thermodynamic profile and consider the effect of this profile on frozen and freezing precipitation may provide forecasters with a quick and more accurate method of evaluating the potential for freezing rain than traditional forecast techniques, such as partial thickness.