The primary tool used by the National Weather Service (NWS) for the detection of stream flooding is the Flash Flood Monitoring and Prediction (FFMP) program. The initial implementation of FFMP in 2003 provided a small stream database for detecting flash flooding in small watersheds with rainfall time durations of less than 6 hours. In the spring of 2005 a database of “large watersheds” was provided to NWS forecasters to support the detection of larger scale stream flooding. The case studies presented will show FFMP type displays of these “large watersheds” to demonstrate how this new FFMP feature will support detection of flash floods in the larger streams.
While the 2006 version of FFMP has maximum time duration of 6 hours, future versions of FFMP will support time durations of 24 to 48 hours. These increased rainfall time durations will greatly aid in the detection of large stream areal flooding. The detection capability of FFMP for the widespread flooding typically caused by tropical storms will especially benefit from rainfall durations of 24 to 48 hours. The case study of Hurricane Ivan will demonstrate the improvement in flood detection resulting from changing the maximum rainfall duration of 6 hours to 24 hours.