3.1 Toward 1-km ensemble forecasts over large domains

Schwartz, Craig S., Glen S. Romine, Kathryn R. Fossell, Ryan A. Sobash, and Morris L. Weisman, National Center for Atmospheric Research

This presentation will describe precipitation forecasts from convection-allowing ensembles with 3- and 1-km horizontal grid spacing that were produced between 15 May and 15 June 2013 over central and eastern portions of the United States. Probabilistic forecasts produced from 10- and 30-member 3-km ensembles were consistently better than forecasts from individual 1-km ensemble members. However, 10-member, 1-km probabilistic forecasts usually produced the best forecasts, especially over the first 12 hours and at rainfall rates >= 5.0 mm/hr at later times. Further object-based investigation revealed that better 1-km forecasts at heavier rainfall rates were associated with more accurate placement of mesoscale convective systems compared to 3-km forecasts. The collective results indicate promise for 1-km ensembles once computational resources can support their operational implementation.