9612487 Mullen The U.S. Weather Research Program (USWRP) is an interagency activity designed to perform and implement the research necessary to improve the delivery of weather services to the nation. Under this Program, the National Science Foundation and the National Oceanic and Atmospheric Administration are jointly evaluating and supporting research of high priority to the USWRP. It is well known that the atmosphere is a chaotic system. As a consequence, small errors in the initial conditions of any numerical weather prediction model amplify as the forecast evolves. Because the atmospheric state can never be measured exactly, initial conditions will always contain errors whose magnitude and structure can only be estimated. Hence an infinite spectrum of plausible initial conditions exists, all of which are consistent with analysis uncertainty. A procedure for defining the scope of forecasting uncertainty and improving forecasts is known as ensemble forecasting (EF). EF involves running multiple forecasts starting at the same time, but from different, equally-likely initial conditions. The Principal Investigator will address four fundamental aspects of short-range EF of quantitative precipitation forecasting (QPF) at the mesoscale: Estimate limits of predictability for QPF by current operational forecast models; Investigate minimum number of ensembles needed to robustly estimate forecast evolution of probability density function of QPF; For QPF forecasts, determine relative importance of model differences verses uncertainties in initial conditions; Determine the relative merit of using short range ensemble forecast at a lower resolution verses a single, high resolution deterministic forecast. The Principal Investigator will collaborate in this effort with scientists within the National Oceanic and Atmospheric Administration. Successful completion of this research could lead to substantial improvements in abili ty to forecast precipitation. ***
