A 10-Year Survey of Extreme Rainfall Events in the Central and Eastern United States Using Gridded Multisensor Precipitation Analyses

Extreme rainfall events in the central and eastern United States during 2002-11 were identified using NCEP stage-IV precipitation analyses. Precipitation amounts were compared against established 50- and 100-yr recurrence interval thresholds for 1-, 6-, and 24-h durations. The authors identified points where analyzed precipitation exceeded the threshold, and combined points associated with the same weather system into events. At shorter durations, points exceeding the thresholds were most common in the Southeast, whereas points were more uniformly distributed for the 24-h duration. Most 24-h events have more points than the other durations, reflecting the importance of organized precipitation systems on longer temporal scales. Though monthly peaks varied by region, the maximum (minimum) usually occurred during the summer (winter); however, the 24-h point maximum occurred in September owing to tropical cyclones. The maximum (minimum) in hourly extreme rainfall points occurred at 2300 (1100) LST, though there were regional differences in the timing of the diurnal maxima and minima. Over half of 100-yr. 24-h events were a result of mesoscale convective systems (MCS), with synoptic and tropical systems responsible for nearly one-third and one-tenth, respectively. Of the 10 events with the most points exceeding this threshold, 5 were associated with tropical cyclones, 3 were synoptic events, and 2 were MCSs. Among the MCS events, 7 of the top 10 were training line/adjoining stratiform (TL/AS). While the 49 TL/AS events investigated further had similar moisture availability, the more widespread events had stronger low-level winds, stronger warm air advection, and stronger and more expansive frontogenesis in the inflow.