Abstract
AbstractSince 2013, the Met Office have run a 2.2 km horizontal gridlength version of the Unified Model (MetUM) as part of the National Oceanographic and Atmospheric Administration's Hazardous Weather Testbed Spring Forecasting Experiment. In this study, we perform high resolution MetUM simulations of the 20 May 2013 Oklahoma tornado outbreak at horizontal gridlengths between 2.2 km and 100 m. Here we present results showing that at 2.2 km gridlength the MetUM is able to simulate supercell‐like storms whereas at O(100 m) gridlength it is able to simulate realistic‐looking supercells with tornado‐like vortices. This opens up the opportunity for using such simulations to highlight areas of enhanced tornado risk ahead of time.
Highlights
Accurate forecasting of severe thunderstorms is crucially important for providing spatially and temporally correct warnings of the convective-scale hazards they can cause, e.g. squall lines and tornadoes
All of the National Oceanographic and Atmospheric Administration’s (NOAA’s) National Weather Service (NWS) tornado warnings are based upon detection by observers or the presence of a tornado vortex signature in radar data (Brotzge and Donner, 2013) meaning that the threat has to exist before a warning is issued, which limits further improvements in lead time unless an alternative method is found to warn before the threat exists
The main aim here is to investigate whether an order 100 m gridlength simulation, down-scaled from a free-running 2.2 km gridlength Numerical Weather Prediction (NWP) simulation, can resolve tornado-like vortices and potentially identify enhanced risk regions where tornadoes may occur many hours in advance of what could be obtained if assimilating radar data in the driving model
Summary
Accurate forecasting of severe thunderstorms is crucially important for providing spatially and temporally correct warnings of the convective-scale hazards they can cause, e.g. squall lines and tornadoes. The main aim here is to investigate whether an order 100 m gridlength simulation, down-scaled from a free-running 2.2 km gridlength Numerical Weather Prediction (NWP) simulation, can resolve tornado-like vortices and potentially identify enhanced risk regions where tornadoes may occur many hours in advance of what could be obtained if assimilating radar data in the driving model. To our knowledge, this is the first study to simulate a tornado-like vortex over the US Great Plains in a high resolution NWP model at several hours lead-time
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