The leading cause of weather related property damage and death in southeast Arizona is flash flooding and frequently occurs during the Southwest Monsoon season (mid June through September). For the NWS Tucson WFO, the probability of detection of a flash flood is 82%. However, the false alarm rate is high at 61% and the lead time a relatively low 24 minutes.

The Areal Mean Basin Estimated Rainfall (AMBER) algorithm was installed at the Tucson WFO to assist forecasters in issuing timely flash flood warnings. AMBER uses the 1 degree x 1 km Digital Hybrid Reflectivity Scan from the WSR-88D to estimate the average basin rainfall (ABR) for six periods and the basin rate of accumulation. The algorithm also compares the ABR to flash flood guidance values that alerts the forecaster to basins near or exceeding flash flood guidance. Forecasters can then examine the alerting status of the particular basin and decide if a flash flood warning is necessary. The results of AMBER’s performance and its impact on the flash flood warning verification program at the NWS Tucson WFO are presented.