Overview
From September 6 to September 8, 2011, the remnants of Tropical Storm Lee interacted with a stalled frontal boundary and moisture from Hurricane Katia to produce an extreme, multi-day heavy rainfall event across central New York and northeast Pennsylvania. This event resulted in catastrophic flash flooding and record-breaking river flooding throughout the upper Susquehanna River Basin. A total of 146 NCEI records were documented for this event, with 9 direct deaths reported across the region.
Environmental Context
The flooding was driven by a complex meteorological scenario where the remnants of Tropical Storm Lee moved northward from the southern Appalachians, stalling over the Mid-Atlantic region by September 8. This system interacted with a frontal boundary and deep tropical moisture drawn in from Hurricane Katia. This interaction produced a prolonged period of heavy rainfall, with 48-hour totals of 6 to 12 inches common across the upper Susquehanna River Basin. Many climate sites, including Harrisburg (KMDT) and Williamsport (KIPT), recorded their wettest year on record in 2011, with both sites setting all-time 24-hour rainfall records for September on September 7, 2011, receiving 7.71 and 6.76 inches, respectively.
Storm Evolution
Radar data from the KBGM site between September 7 and September 8, 2011, consistently showed high reflectivity values, frequently reaching the 75 dBZ cap. Echo tops remained elevated throughout the event, with 18 dBZ tops frequently exceeding 40,000 feet and reaching as high as 65,500 feet at 18:10 UTC on September 7. The persistent nature of these high-reflectivity cores, combined with the synoptic-scale forcing, supported the extreme rainfall rates that led to the widespread flooding.
Warnings Issued
There were no warnings listed in the provided data for this event.
Impacts
The impacts of this flood were severe and widespread, with damages in the upper Susquehanna River Basin estimated at nearly $1 billion. Record-breaking crests were observed on the Susquehanna River and its tributaries, often exceeding previous records set in June 2006 or the historic Hurricane Agnes flood of 1972.
- Broome County, NY: Catastrophic flash flooding occurred in Binghamton, Vestal, Endicott, and Endwell. The Susquehanna River at Binghamton crested at 25.71 feet on September 8, topping levees and causing extensive downtown flooding. Property damage in Broome County was significant, with $170 million in damage recorded in Binghamton and $160 million in Vestal.
- Tioga County, NY: Record flooding occurred along the Susquehanna River near Waverly, cresting at 26.67 feet on September 8. Catastrophic flash flooding was reported in Owego, Nichols, and Apalachin, with $70 million in property damage in Owego and $25 million in Apalachin.
- Dauphin County, PA: Widespread flooding resulted in $150 million in property damage. The Susquehanna River at Harrisburg crested at 25.17 feet. Four deaths were reported in the county, including a 70-year-old man in Derry Township and an 81-year-old man in Middle Paxton Township.
- Lancaster County, PA: Three deaths were reported, including a 62-year-old woman and an 8-year-old boy. The Susquehanna River at Marietta crested at 58.16 feet. A total of 189 water rescues were performed, and 1,782 structures were impacted.
- Luzerne County, PA: Record flooding on the Susquehanna River at Wilkes-Barre reached 42.66 feet on September 8, exceeding the previous record from Hurricane Agnes. Property damage was estimated at $43.5 million.
- Schuylkill County, PA: Extensive flooding in Pine Grove resulted in $4.1 million in public facility damage. National Guard assistance was required for evacuations, and 741 structures were impacted.
Conclusion
The remnants of Tropical Storm Lee produced a historic flood event across the Susquehanna River Basin. The combination of extreme rainfall totals and saturated antecedent soil conditions led to record-breaking river crests and catastrophic flash flooding. The event resulted in 9 direct deaths and nearly $1 billion in damages across the affected counties in New York and Pennsylvania.