13 th Conf. Aviation, Range and Aerospace Meteorology, Jan 2008, New Orleans, LA, Amer. Meteor. Soc. 1 6.2 IMPLEMENTATION OF THE RADAR-ENHANCED RUC Stan Benjamin, Stephen S. Weygandt, John M. Brown, Tanya Smirnova 2 , Dezso Devenyi 2 , Kevin Brundage 3 , Georg Grell 2 , Steven Peckham 2 , William R. Moninger, Thomas W. Schlatter 2 , Tracy L. Smith 2 , and Geoff Manikin 1 NOAA Earth System Research Laboratory / Global Systems Division, Boulder, CO 1 Environmental Modeling Center, National Centers for Environmental Prediction, NOAA, Camp Springs, MD 2 Collaboration with the Cooperative Institute for Research in Environmental Sciences (CIRES), Boulder, CO, USA 3 Collaboration with the Cooperative Institute for Research in the Atmosphere (CIRA), Fort Collins, CO, USA 1. I ntroduction 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 short- range 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. 2. Motivation for improved high-frequency data assimilation By 2025, the number of aircraft flying globally is expected to increase by a factor of 2-3x. Crowded airspace will necessitate much higher accuracy for aviation forecast accuracy than even now. With the anticipated proliferation of decision-support tools for aviation and other situational awareness user groups, the requirement for accuracy and spatial coverage of very-high-frequency updating of numerical weather prediction (NWP) models using latest observations will increase. Figure 1. Observations assimilated into RUC as of 2008 after upgrade, new observations in bold and with leading arrows. The Rapid Update Cycle (RUC, Benjamin et al. 2004a,b), covering 2/3 of North America, continues to be the only 1-h (hourly updating) assimilation and mesoscale forecast cycle in the world running as part of an operational numerical prediction center (US National Centers for Environmental Prediction - NCEP). RUC prediction grids are used heavily as mesoscale guidance for short-range forecasts, especially for aviation, severe-weather, and situational awareness forecast users. The current improvements to the RUC and future transition to the Rapid Refresh reflects the need for hourly (at least) NWP updating over a larger area with improved accuracy via, in part, improved data assimilation of radar, satellite, aircraft, profiler, GPS moisture, surface, and other observation types. The Rapid Refresh hourly-updating cycle will play a key role in the planned Next Generation Air Transportation System (NextGen), under design by a consortium of government agencies. 3. Summary of Spring 2008 Changes to RUC The final major change upgrade to the operational RUC includes the following key characteristics, in testing at NCEP since November 2007. Real-time comparisons between the operational RUC and the Corresponding author address: Stan Benjamin, NOAA/ESRL/GSD, R/E/GS1, 325 Broadway, Boulder, CO 80305, stan.benjamin@noaa.gov