Location of heaviest rainfall relative to frontal boundaries during the warm season

A warm-season precipitation climatology for the months May-Sept (1950-1996) was performed for 3,342 heavy rain events across the eastern two-thirds of the United States in nine separate regions. Heavy rain events were examined with respect to nearest frontal boundary features including frontal orientation, distance to event, and event location on the warm or cold side of a front. Events were considered “non-frontal” when > 300km from nearest front. This data was used to detect regional trends in the “heaviest” and “lightest” precipitation events using three precipitation variables. Stationary, cold and warm fronts were associated with 45%, 36%, and 16% of the heavy rain events, respectively. Cold and stationary frontal events were most frequent in the southern regions, while warm fronts were most common in the northern regions. The highest number of the “lightest” precipitation events was associated with the cold side of cold fronts. The highest number of the “heaviest” precipitation events was associated with the warm side of stationary fronts. Events on the warm side of warm fronts showed no regional trend in precipitation intensity.