MMM SEMINAR NCAR
Morris L. Weisman
NCAR/MMM
The WRF model has been developed as a next generation mesoscale forecast model and data assimilation system with an overall goal of advancing both the understanding and prediction of important mesoscale weather, especially convection. Convective weather remains a significant challenge for numerical weather prediction systems, and is recognized as a major contributor to poor warm season quantitative precipitation forecasting (QPF). The success of a convective forecasting effort depends on many factors, including using sufficient resolution to represent the convective processes explicitly. To date, only limited testing has been completed for strong convective scenarios using explicit resolutions, and have only covered relatively small domains, due to the prohibitive expense in computer resources.
During the recent Bow Echo and MCV Experiment (BAMEX), 36h realtime forecasts were conducted daily with WRF using a 4 km horizontal grid resolution and explicit convection over the central US (2000x2000 km). These 4 km forecasts were then compared to equivalent 10 km WRF forecasts as well as to other operational models, which all employed convective parameterization. We found that the 4km simulations did a surprisingly good job at forecasting timing, location, and number of significant convective systems, and did a much better job at predicting convective system mode and propagational characteristics, as compared to the coarser resolution simulations. These improvements in convective forecast guidance were found to be extremely useful for operations planning each day, and were also highly praised by NWS forecasters, who used the WRF output for their daily severe weather outlooks. Challenges remain, however, as the 4 km simulations did not show corresponding improvements in overall QPF. Still, these results show much promise for explicit convective forecasting over a multi-day period. Based on last year's experience and success, we will be running explicit convective forecasts again this spring in collaboration with the Storm Prediction Center, CAPS, and NWS forecasters, using an updated version of the WRF code, and covering even a larger region of the US.
Tuesday, 6 April
2004, 3:30 PM
NCAR-Foothills
Laboratory
3450 Mitchell Lane