84th AMS Annual Meeting

Tuesday, 13 January 2004: 4:15 PM
Real-time explicit convective forecasts using the WRF model during the BAMEX field program
Room 605/606
Morris L. Weisman, NCAR, Boulder, CO; and C. Davis, J. Done, W. Wang, and J. Bresch
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, and promoting closer ties between the research and operational forecasting communities ( see http://wrf-model.org/.). 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). One of the primary objectives of the WRF developmental effort is to improve our ability to represent and forecast convective systems in the 6-48 hour time frame. The success of such an effort depends on many factors, including using sufficient resolution to represent the convective processes explicitly (nominally, 4 km horizontal grid resolution for strong, mid-latitude convective systems).

The BAMEX field program (Bow echo And Mcv EXperiment; see http://www.mmm.ucar.edu/bamex/science.html) took place between May 20 and July 6, 2003 in the central US, and offered a unique opportunity to advance these WRF objectives. Real-time runs out to 36 h were completed with the WRF model each day in support of the BAMEX field effort, using a 500x500x35 domain at 4 km horizontal grid resolution over the BAMEX domain (central US). Each simulation was initialized with 00 GMT data from the 40 km ETA model, with boundary conditions updated evey 3 h using the ETA model forecasts. These 4 km WRF forecasts were also compared to equivalent 10 km WRF forecasts, as well as other operational models. We found that the 4km simulations did a much better job at predicting convective mode, as well as the timing and location of convective initiation, but did not show improvements in overall QPF, due primarily to the inability to decay existing convection. Recurrent errors were also identified in the diurnal cycle of the boundary and surface layers, which might be related to the above noted QPF issues. These, as well as other experiences will be discussed during the presentation.

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