The Major June 2006 and September 2011 East Coast Flash Flood Events: A Comparison Study

The two costliest flash flood events in the history of the Binghamton, NY Weather Forecast Office (WFO) are compared in an effort to assist forecasters in recognizing favorable synoptic and mesoscale patterns capable of producing historic flooding across central New York and northeastern Pennsylvania. In June 2006, significant flooding and flash flooding impacted much of the Mid-Atlantic region as a continuous supply of deep tropical moisture moved north from the subtropical Atlantic ahead of a slow moving cold front. A three-day period of heavy rain resulted in nearly 38.1 cm (15 in.) of rain across portions of the Binghamton, NY County Warning Area (CWA) and record flooding along the main stem Susquehanna and Delaware Rivers. In September of 2011, tropical moisture associated with the remnants of Tropical Storm Lee resulted in a 24-hour period of heavy rain over which rainfall totals approached 30.3 cm (12 in.) across the Binghamton CWA. Although the areal coverage of flooding was smaller in the Tropical Storm Lee event, numerous river level records set in the June 2006 event were easily shattered along the main stem Susquehanna River. Combined, both events produced over $2-billion worth of damage with multiple counties in both New York and Pennsylvania officially declared as federal disaster areas.

Using NCEP/NCAR Global Reanalysis and the WFO Binghamton Weather Event Simulator (WES), both flood events were investigated to identify meteorological features and patterns responsible for such extreme rainfall. Though some differences were noted, several crucial similarities were present which likely combined to allow both events to be regarded as “historic” in terms of both socioeconomic and environmental impacts. Using integrated water vapor imagery, it will be shown that each event had a well-established atmospheric river in place which allowed for the uninterrupted supply of deep tropical moisture. Additionally, both events displayed mesoscale features which departed from normally accepted flash flood conceptual models. Documentation of key similarities and departures from traditional flash flood conceptual models will allow for the assessment and recognition of similar patterns capable of historic flooding in the future.