From the Radar-enhanced RUC to the WRF-based Rapid Refresh

In this paper, we summarize the testing toward a 2007 update (radar assimilation, physics, mesonet) to the operational Rapid Update Cycle (RUC). We also summarize testing and development toward the 2009 planned implementation of the Rapid Refresh (RR), a similar hourly update analysis/forecast cycle to the RUC but using versions of the WRF model and GSI assimilation code, including RUC-unique enhancements, over an extended North American domain. In late 2006, an initial RR cycle began cycling at NOAA's Earth System Research Laboratory over the extended North American domain. This was preceded by an extended period of WRF testing using RUC initial conditions beginning in 2003. Initial results from both the 2007 updates to the RUC and the Rapid Refresh testing will be summarized in this talk.

The Rapid Update Cycle in the U.S. continues to be the only 1-h assimilation and mesoscale forecast cycle in the world running operationally as part of an operational numerical prediction center (U.S. National Centers for Environmental Prediction - NCEP). Predictions from the RUC are used heavily as mesoscale guidance for short-range forecasts, especially for aviation, severe-weather forecasting and situational awareness. An effective assimilation technique for 3-d radar reflectivity has been developed and being used successfully by specifying latent heating and moistening in a pre-forecast diabatic digital filter initialization (DDFI) within the RUC model (summary in this paper, more detail in paper by Weygandt and Benjamin). The RUC update will also include use of the RRTM longwave radiation, improving RUC diurnal cycle behavior.

The Rapid Refresh version of the WRF model is in testing with partial RUC-like physics (NCAR-Thompson microphysics, Grell-Devenyi convection, Mellor-Yamada-Janjic PBL, RRTM longwave radiation) with both ARW and NMM dynamic cores. It is being cycled using the Gridpoint Statistical Interpolation (GSI) assimilation over the North American domain, 2.6 times larger than the RUC domain. Current testing results will be presented.