Hydrometeorological Analysis of Widespread Flooding Throughout the Southeastern and Northeastern United States in Late January 2010

Floods occur throughout Eastern North American in all months of the year and can be generated by a variety of mechanisms. Not all annual maximum flows are generated by anomalous or exceptional meteorological events, but are often caused by rather mundane weather systems that operate in conjunction with hydrologic and landscape processes. To that end, this project documents widespread flooding, and flood types, that occurred throughout the southeastern and northeastern United States due to a less-than-exceptional, slow-moving synoptic-scale system that traversed the region in late January 2010.

The synoptic set up for widespread flooding throughout the southeast and northeast included a well-defined 500 mb trough moving towards the western Great Lakes region on the morning of the 24^th. This 500 mb low supported the development of a surface system with a series of fronts just to the east and southeast of the upper level trough. Southwesterly flow at lower levels (850 mb and 925 mb) around the low allowed for ample warm air advection and precipitable water vapor to be brought northward into southeastern and northeastern states on the 24^th and 25^th.

Total estimated rainfall and rain rates were not exceptional, but when combined with antecedent soil moisture conditions, snow ablation and topography, widespread flash and river flooding readily occurred in late January 2010. Flooding occurred from the Carolinas on January 24^th and 25^th, with the flooding progressing northward into the generally snow-covered northeastern United States on the 25^th through the 26^th, and even extending to the 27^th, and 28^th on some larger rivers. Snow was present in the higher elevations of West Virginia, Virginia and Maryland, and was more widespread and deeper throughout Pennsylvania northward into the Northeast. Snowpack ablation exacerbated flooding from West Virginia and Virginia northward into the northeast with much, but not all, of the snowpack being depleted between January 24^th and 26^th. In addition to river and flash flooding, ice-jam flooding was also reported in the more northerly states.

At numerous US Geological Survey Hydro-climate Data Network (USGS-HCDN) sites which are thought to be relatively minimally impacted by human disturbance, this widespread flood event was registered as the annual maximum flow for the 2009-2010 water year. With winters expected to be warmer and wetter, and the frequency of storm systems that impact eastern North America expected to increase into the future under a warming climate, widespread, and potentially high magnitude, mid-winter flooding such as observed in January 2010 may become more frequent.