From the 13km RUC to the Rapid Refresh

The last major upgrade to the Rapid Update Cycle (RUC) was implemented in June 2005, including 13km resolution, assimilation of new observations, and improved precipitation physics. First, a summary of the RUC13 unique aspects is summarized in this paper.

The RUC is evolving into a new 1-h update cycle configuration called the Rapid Refresh (RR), using a version of the WRF model over a North American domain. This paper will also summarize the RR development at this point, especially emphasizing the effects on aviation forecasting.

The Rapid Refresh is to be implemented in 2007, and has been undergoing preliminary testing from 2003-2005 with twice-daily real-time testing of the WRF-ARW model using RUC initial conditions, called the ‘WRF-RUC'. Testing will begin this fall with the WRF-NMM as another possible alternative for the Rapid Refresh model. The RR will use a RR-version of the NCEP-developed Gridpoint Statistical Interpolation (GSI), with RUC-specific enhancements (e.g., cloud analysis, use of surface observations) but also taking advantage of the extensive capability for satellite radiance assimilation in the GSI. This work is now underway and will be reported at the conference.

The Rapid Refresh domain is about 2.6x larger than the RUC CONUS domain, expanding to coverage of Alaska, Puerto Rico, the Caribbean, and most of Canada. It will provide a common, hourly updated mesoscale analysis and model forecast over the full North American area, and a common basis for subsequent aviation products over this larger region. The horizontal resolution will be about 13 km, the same as the now current 13-km RUC.

While the RR will use a version of the WRF model, its physical parameterizations will be similar to those used successfully with the RUC, including the mixed-phase cloud microphysics parameterization developed largely by NCAR for improved depiction of supercooled liquid water. The Rapid Refresh, like the RUC, will continue hourly cycling of full 3-d hydrometeor fields correcting previous 1-h forecasts with satellite cloud and METAR cloud observations and adding radar reflectivity. This paper will describe the Rapid Refresh configuration, plans, and initial development and testing as of the conference date.