“Flood Forecast Challenges in the Middle Atlantic Region During Hurricane Irene and Tropical Storm Lee”

In late August and early September of 2011, two tropical systems each produced in excess of ten inches of rain in portions of the Middle Atlantic Region resulting in back to back record flooding - a true rarity. In late August, Hurricane Irene brought 6 to 10+ inches of rain along the coast and further inland in southeast Pennsylvania and New Jersey. This excessive rainfall produced record flooding in New Jersey as well as significant flooding elsewhere. In early September, the remains of Tropical Storm Lee brought 6 to 14+ inches of rain from the west shore of the Chesapeake Bay north through the Susquehanna River Valley. As a result of this tropical system, record flooding occurred in portions of the Susquehanna River Basin as well as significant flooding elsewhere.

This presentation will describe significant challenges with river forecasting associated with the tropical systems Irene and Lee as well as actions taken by the National Weather Services' Middle Atlantic River Forecast Center (MARFC) in State College, PA to efficiently produce accurate river forecasts. Specific challenges under extreme conditions included quantitative precipitation forecasts (QPF), backwater effects, record flooding, and several unique hydrologic circumstances which, when combined, exacerbated an already demanding forecast environment.

These challenges were addressed and resolved during the events or, in some cases, retrospectively through close coordination with the United States Geological Survey (USGS), the US Army Corps of Engineers, local emergency managers, the media, and others. We will discuss those resolutions as well as recommend future improvements to the hydrologic forecast process that will mitigate similar challenges during future events.