8.6      Evaluation of HRRR boundary layer structure via high-resolution radiosondes.

Fovell, Robert, University at Albany, SUNY

Along with the surface layer treatment, the planetary boundary layer (PBL) scheme represents one of the most important parameterizations in a numerical weather prediction (NWP) model.  Among other things, PBL schemes are responsible for determining the depth, stability and vertical profiles of humidity and horizontal wind in the boundary layer. These are subject to observational uncertainty and also the validity of assumptions that can vary widely among parameterizations. 

NOAA's operational High Resolution Rapid Refresh (HRRR) model is run at convection-permitting (3 km) horizontal resolution and utilizes the Mellor–Yamada–Nakanishi–Niino level 2.5 (MYNN2) PBL scheme.  This is a state-of-the-art treatment that has been substantially upgraded and expanded in recent years.  HRRR forecasts of boundary layer wind, temperature, and specific humidity are being evaluated using 60 high-resolution radiosondes across the contiguous US (CONUS) that can provide roughly 5 m vertical resolution near the surface.  Challenges in employing this underutilized resource have been mitigated or overcome and the spatially- and temporally-averaged composites are revealing shortcomings in the forecasts that can be addressed with further improvements to the scheme.