Physics in the HRRR and RAP: recent progress and future plans

The two situational awareness and very-short-range forecast systems at NCEP, the Rapid Refresh (RAP) and the High-Resolution Rapid Refresh (HRRR), both use the Advanced Research version of the Weather Research and Forecast model (WRF-ARW). They are both run hourly, the RAP with a full hourly assimilation cycle and the HRRR initialized from the previous 1-h RAP forecast combined with a 1-h spinup followed by an analysis. The convection-permitting HRRR, being run on a 3-km horizontal grid over the CONUS, uses the RAP, covering all of North America on a 13km grid, for lateral boundary conditions. The talk by Alexander in this conference will describe in more detail the analysis and initialization of RAP and HRRR.

The RAP and HRRR share a common physics package, including RRTMG long and shortwave radiation, the RUC (Smirnova) Land-surface model, the Mellor-Yamada-Nakanishi-Niino boundary and surface layer schemes (substantially modified by Olson—talk by Kenyon in this conference will cover some aspects of Olson's work), and the Grell-Freitas shallow and deep convection. (The deep convection is turned off in the cloud-permitting HRRR.)

Intensive work continues toward improving the performance of the RAP and HRRR, most of it focused on improving the physics, and much of this focussed on eliminating certain systematic biases. Chief among these is a warm and dry daytime bias over the central and eastern CONUS during the warm season, and a cold nighttime bias in winter over snow cover. We have made good progress toward alleviating these and other issues. This talk will summarize major improvements we are now testing at ESRL (and plan to be at NCEP by the time of this talk), in preparation for operational implementations of improved versions of the RAP and HRRR later in 2015.

This research is partially in response to requirements and funding by the Federal Aviation Administration (FAA). The views expressed are those of the authors and do not necessarily represent the official policy or position of the FAA.