Increasing convection-allowing ensemble spread through diverse member configurations

What is it about?

We compare three convection-allowing NWP ensembles in terms of their skill in forecasting convective storms, with an emphasis on severe local storms. The operational HREF is a highly diverse ensemble comprised of members with drastically different model configurations, whereas the HRRRE and OU-MAP are unified ensembles with spread coming only from perturbed initial conditions. Important skill and spread differences relevant to convective forecasting (e.g., Storm Prediction Center outlooks) are explored and their implications discussed.

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Why is it important?

We show that the operational HREF, a convection-allowing ensemble using highly diverse member configurations, achieves much better spread in forecasts of convective storms than comparable-size ensembles with only perturbed initial conditions. This is important to consider as design choices are made for future convection-allowing ensembles.