A Vortex Relocation Method for Improving Initial Conditions and Subsequent Predictions of Tornadoes


A time-space shift method is developed for relocating model-predicted tornado vortices to radar observed locations to improve the model initial conditions and subsequent predictions of tornadoes. The method consists the following three steps: (i) Use the vortex center location estimated from radar observations to sample the best ensemble member from tornado-resolving ensemble predictions. Here, the best member is defined in terms of the predicted vortex center track that has a closest point, say at the time of t = t*, to the estimated vortex center at the initial time t0 (when the tornado vortex signature is first detected in radar observations). (ii) Create a time-shifted field from the best ensemble member in which the field within a circular area of about 10 km radius around the vortex center is taken from t = t*, while the field outside this circular area is transformed smoothly via temporal interpolation to the best ensemble member at t0. (iii) Create a time-space-shifted field in which the above time-shifted circular area is further shifted horizontally to co-center with the estimated at t0, while the field outside this circular area is transformed smoothly via spatial interpolation to the non-shifted field at t0 from the best ensemble member. The method is applied to the 20 May 2013 Oklahoma Newcastle–Moore tornado case, and is shown to be very effective in improving the tornado track and intensity predictions.