The Importance of Summer Season Fronts in Extreme Precipitation Events

Previous research has shown that the fronts of extratropical cyclones are the single largest cause of heavy precipitation events in the continental United States. Analysis of 935 Cooperative Observer stations for the period of 1908-2013 produced a dataset of one-day heavy precipitation events exceeding a threshold for a 1-in-5-year recurrence interval and associated meteorological causes. Presented here, the data were further analyzed for only those events associated with fronts over the same time period. Historical, annual, seasonal, and monthly distributions were plotted to identify the spatial distribution of frontal frequencies and frontal characteristics. The analysis produced evidence of significance in summer season fronts, both in event intensities and concentrations for certain areas of the central and eastern United States. For example, the majority of these extreme events in the Midwest U.S. occur in the peak summer months of July and August and a majority of these are caused by fronts. Even in the southeast U.S., fronts in July and August, although weak, are responsible for up to 25% of all such extreme events. This talk will describe the statistical analysis of summer fronts and the synoptic-scale characteristics associated with such situations, with a focus on the southeast U.S.