Average Basin Rainfall (ABR), the average rainfall that falls over a stream watershed in a specified period of time, is the key parameter in indicating the occurrence and severity of flash flooding. Paul Jendrowski, the Science and Operations Officer at the Honolulu National Weather Service(NWS) Office, has developed software to compute and display ABR in flash flood watersheds. The Areal Mean Basin Estimated Rainfall (AMBER) software, created with a Geographic Information System (AMBERGIS), produces a display of ABR graphics, tabular ABR output, and line graphs of ABR vs. flash flood guidance. AMBERGIS has been running operationally at the Pittsburgh NWS since 30 May 2001.

The NWS will be implementing AMBERGIS capabilities nationally as part of Flash Flood Monitoring and Prediction (FFMP) in upcoming software builds of the Advanced Weather Interactive Processing System (AWIPS). The Pittsburgh NWS Office will be a beta test site for the AMBERGIS version of the FFMP software during the summer of 2001.

The new AMBERGIS graphical output allows quicker and easier access to the ABR data. The following case study will examine the application of AMBERGIS output to the flash flood warning process. On 20 June 2001, a flash flood in Franklin, Pennsylvania (Venango County) resulted in the closure of the two main highways leading into the city. During this event, AMBERGIS was monitored in real time and a timely flash flood warning was issued with a 10-minute lead-time for a 30-minute rainfall event. The AMBERGIS graphics revealed rainfall rates in excess of 100 mm hr-1 with an ABR total of over 50 mm in 30 minutes. Monitoring of the ABR rate product and the 30-minute ABR summation were critical to the early detection of this flash flood. Small basin areas (down to 5 km2) combined with the short time intervals of the ABR data (5 minute) make AMBERGIS an excellent flash flood detection tool.