Upcoming changes to the NCEP North American Mesoscale Modeling system: Transition to NEMS-NMMB and high resolution nests

As part of long-range plans to unify its modeling systems within a common infrastructure, NCEP is planning significant changes to the North American Mesoscale (NAM) forecast system and the NAM Data Assimilation System (NDAS). The next version of the NAM has been restructured to run within the NOAA Environmental Modeling System (NEMS) framework. As part of this effort, the current WRF-NMM forecast model will be replaced in the NAM with the Nonhydrostatic Multiscale Model on B-grid (NMMB). All other components of the NDAS/NAM, including the Gridspace Statistical Interpolation (GSI) analysis, have been modified to run with the B-grid configuration. In addition to the current NAM forecast output, four fixed one-way nests (4-km CONUS, 6-km Alaska, 3-km Hawaii, 3-km Puerto Rico) will run within the 12-km NAM domain out to 60-h. An additional “on-call” 1.33-1.5 km nest will be run inside the CONUS or Alaska domain from 0-36 h, primarily for support of fire weather forecasting. These changes are targeted for implementation into NCEP operations during the spring of 2011. Further details on these changes and results from real-time and retrospective testing of NDAS, NAM, and the high-resolution nests will be presented at the conference.