0- to 2-hour convective storm nowcasts and is currently in use at the Aviation Weather Center in Kansas City. Forecasters use this regularly updated (every 10 minutes), automated weather product as guidance in anticipating enroute aviation weather hazards. The United Kingdom Meteorology Office has run a system called Nimrod (Golding, 1998) operationally for several years. This system, which combines radar and satellite information with numerical model output, produces 0- to 6-hour precipitation rate and accumulation forecasts every 10 minutes for both meteorological and hydrological purposes; accurate warning for flash floods are a primary goal in the use of this tool.

Recommendation: To increase the accuracy and lead time of flash flood forecasts and warnings, the NWS should continue to implement new technologies and techniques including (a) the Flash Flood Monitoring and Prediction program at all Weather Forecast Offices, (b) polarimetric modifications to NEXRAD, (c) data assimilation systems that integrate radar and other operational datasets into coupled hydrometeorological and hydrological models, and (d) data fusion systems.

Extensive opportunities exist for forecasters to take advantage of the rapid advancement of technology to improve forecasts, watches, and warnings. The FFMP system, which requires adaptation to the specific watersheds served by each WFO, would facilitate more specific flash flood warnings. In addition, as part of its new Advanced Hydrologic Prediction Services, the NWS is encouraged to continue its effort to develop and evaluate hydrologic and coupled meteorological-hydrologic models to advance technologies useful for improved flash flood guidance and warnings. The polarimetric modification would improve the data quality and quantitative precipitation measurement capabilities of NEXRAD. Real-time data assimilation systems that incorporate observations into high-resolution mesoscale numerical models provide rapidly updated wind and precipitation forecasts. Data fusion systems, such as the Auto-Nowcast system, incorporate all available observation datasets together with numerical model output to produce very short range (0- to 2-hour), site-specific forecasts. These advances can produce improved forecasts, including ensemble and probabilistic forecasts, of precipitation rate and accumulation that are essential for flash flood forecasting. To enhance the usefulness of the forecast, quantification of uncertainty (e.g., probability forecasts) should be an integral component of these products (NRC, 2003).

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