Evaluation of the Areal Mean Basin Estimated Rainfall (AMBER) Flash Flood Algorithm at the Tulsa, OK and Sterling, VA NWSFOs

The Areal Mean Basin Estimated Rainfall (AMBER) program is a tool developed at the Pittsburgh National Weather Service Forecast Office (NWSFO) to assist in flash flood warning decisions. The AMBER program computes basin average rainfall rates and accumulations from radar precipitation estimates to alert forecasters to the potential for flash flooding. AMBER has been used in real-time operations for several years at the Pittsburgh and Honolulu NWSFOs, and was implemented in 1998 as part of the National Severe Storms Laboratory's (NSSL) Warning Decision Support System (WDSS) at the Tulsa, OK and Sterling, VA NWSFOs. Work is currently underway to implement an "AMBER-like" functionality in the Flash Flood Monitoring and Prediction (FFMP) Program, which will be included in Build 5.1 of the NWS Advanced Weather Interactive Processing System (AWIPS). To obtain quantitative feedback on AMBER's utility as a flash flood forecasting tool prior to its implementation in the FFMP, NSSL was tasked with providing an objective evaluation of AMBER's performance in nine case studies from the Tulsa and Sterling county warning areas. For each case study, archived Level II data from the KINX and KLWX radars, flash flood reports, rain gage data, and flash flood guidance (FFG) values were analyzed to determine the pre-existing hydrologic conditions, the nature of the precipitation event, the accuracy of the radar precipitation estimates, and the extent and severity of the resultant flash flooding. Average basin rainfall rates and accumulations from AMBER were analyzed to determine whether the algorithm would have indicated flash flood potential and, if so, the approximate lead time. This paper presents details of the evaluation methodology and discusses results and recommendations in reference to the effects of different basin scales and the utility of using average basin rainfall rate and/or ratio of average basin rainfall accumulation to FFG value to determine flash flood potential.