Two major heavy rain/flood events in the mid-Atlantic: June 2006 and September 2011

Abstract

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 slowmoving cold front. A 3-day period of heavy rain resulted in nearly 38.1 cm (15 in) of rain across portions of the northern mid-Atlantic with record flooding along the mainstem Susquehanna and Delaware Rivers. In September 2011, moisture associated with the remnants of Tropical Storm Lee resulted in a 24-h period of heavy rain over which rainfall totals approached 30.3 cm (12 in) across portions of central New York and northern Pennsylvania. Numerous river-stage records that were set in the June 2006 event were shattered along the mainstem Susquehanna River during the September 2011 flood. Damage estimates resulting from the flooding in both events were >2 billion dollars, and 22 lives were lost. Multiple counties across the northern mid-Atlantic were declared disaster areas. Both flood events were investigated to identify the similar meteorological features and patterns responsible for extreme rainfall. Several crucial similarities were identified that likely combined to produce historic socioeconomic and environmental impacts. One of the similarities was that each event had a well-established atmospheric river in place that provided the uninterrupted supply of deep tropical moisture. Additionally, although these events displayed many of the large-scale characteristics identified in previous flash flood classification schemes, both events were associated with the presence of coastal fronts that appeared to make these cases different from many otherwise similar and previously documented flood cases.