Results of initial WRF-based turbulence and icing algorithm testing

The HQ Air Force Weather Agency (AFWA) Air and Space Sciences Division has embarked on a multi-faceted project to transition from the MM5 to the WRF model. Testing all parameters and algorithms is required, and we took advantage of a period when parallel cycles of the operational MM5 (run four times per day) and a test WRF CONUS theater was run once per day at AFWA (0600 UTC cycle). When WRF tests began, we added this data with our ongoing winter 2004-2005 icing and turbulence algorithm tests that already included MM5 (15km and 45km) and GFS model data, and PIREPs. The AFWA-modified Panofsky Index (PI) is used to assess low-level turbulence for a layer from the surface to 4,500 ft AGL. The PI algorithm consists of buoyancy, wind speed, and wind shear terms. The Ellrod-Knapp turbulence index (TI2) is used for 10K ft MSL and above. The TI2 algorithm consists of vertical wind shear, convergence, deformation due to stretching, and deformation due to shearing terms.

The icing algorithm applied to MM5 and WRF data is an AFWA-modified NCAR-RAP algorithm that calculates four potential icing regimes. It is modified by the use of total cloud water mixing ratio to estimate forecast icing severity. For the GFS, the RAOB icing technique developed by the Air Force is used. Over 1000 PIREPs over the CONUS were used to access model and algorithm performance, and subsequently provide important feedback to the WRF developers. We will present some statistics calculated from our winter and spring 2005 analysis to date.