As part of the NOAA Hazardous Weather Testbed 2007 Spring Forecasting Experiment, a 30-member mesoscale short-range ensemble forecasting system using the Weather Research and Forecasting (WRF) model was developed for the contiguous 48 states at a horizontal grid spacing of 30 km (described in a companion abstract). The current study explores the possibility of using such mesoscale ensembles to initialize high-resolution ensemble convective forecasts. Specifically, the mesoscale ensemble analyses and forecasts provide initial and boundary conditions for ensemble forecasts employing a 3-km horizontal grid spacing.
Retrospective 3-km WRF ensemble forecasts with explicit convection have been produced for several severe weather cases in spring 2007, including 28 March 2007 (high plains tornado outbreak) and 4 May 2007 (Greensburg, Kansas tornadic storm). Ensemble forecasts have been produced out to about 6 hours, or roughly the same lead time as for severe weather watches. Some of the issues being explored are ensemble design (multi-parameterization approaches, initial condition perturbations, and boundary condition perturbations) and the influences that assimilating surface observations have on the ensemble forecasts. Initial results suggest that these convective-scale ensembles provide reasonable probabilistic information that could be used by forecasters for purposes such as issuing watches.