High resolution UM simulations of supercell storms

For the past two years the Met Office have run both 4.4 and 2.2 km horizontal grid length versions of the Unified Model (UM) as part of the NOAA Hazardous Weather Testbed Spring Forecasting Experiment. In this study we perform high resolution UM simulations of the 20 and 31 May 2013 Oklahoma tornado outbreaks by nesting 500, 200 and 100m grid length domains within the 2.2km domain. Here we present results comparing the simulated storms in the different resolution models, showing that at 2.2 km grid length the UM is able to produce supercell-like storms where as at O(100 m) grid length the UM is able to produce realistic-looking supercells with tornado-like vortices. The structure and realism of these simulated tornado-like vortices will be discussed along with predictability issues relating to number of tornadoes and their location