"Rivers and streams throughout Pennsylvania (fig. 1) experienced major flooding during January 1996. Flood stages (water-surface heights) and discharges (flows) in many of the Commonwealth's waterways were measured by the U.S. Geological Survey (USGS) and approached or exceeded record levels established during previous floods. Setting the stage for the flooding was an unusually cold beginning to the winter of 1995-96, which resulted in the early formation of ice in streams statewide. The anomaly of early ice was followed by a sequence of unusual meteorological events in January 1996, which, in many areas, resulted in the most widespread and severe flooding since that produced by tropical storm Agnes in June 1972. Locally, the flooding was the worst since August 1955 and, in some areas, since March 1936. In approximately 50 localities throughout Pennsylvania, flood effects were magnified when ice jams caused temporary damming of stream channels, resulting in the rapid rise of water levels and the subsequent overflow of water and ice onto flood plains. During the floods, the USGS collected stream-stage information on a near real-time basis at 189 stream flow-gaging stations across the Commonwealth. This information was used by various Federal, State, and local agencies to prepare flood forecasts and develop plans for emergency response."
U.S. Geological Survey: http://www.usgs.gov/