A significant RUC upgrade bundle is planned at NCEP for spring 2008, of which the most important change is the hourly assimilation of 3-d radar reflectivity, followed closely by TAMDAR aircraft data and improved radiation and convective parameterizations. These upgrades will result in discernible improvements to aviation guidance using RUC grids, especially for improvements in shortrange convection forecasts (Weygandt et al. 2008a), winter storm forecasts, and surface forecasts in all seasons and at all times of day. Assimilation of 3-d radar reflectivity in the RUC is achieved primarily by specification of 3-d radar-based latent heating during a pre-forecast diabatic digital filter initialization (DFI). This change has been in testing at NOAA/ESRL/GSD in real-time RUC cycles since February 2007. A number of revisions have been developed during the testing since then, including more careful QC procedures for the radar reflectivity data, and in the specification of latent heating. A convection suppression technique has also been developed as part of the RUC radar assimilation to suppress erroneous convection in the RUC background forecast in echo-free regions. A secondary contribution of the RUC radar reflectivity assimilation is to complement satellite cloud-top and METAR ceiling/visibility so as to modify the background, 1-h RUC, 3-d hydrometeor/water vapor forecast (Benjamin et al. 2004c). Proxy reflectivity, calculated using lightning stroke density, supplements the radar reflectivity data in areas of no-radar coverage.
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