Using Short Range Ensemble Forecasts and High Resolution Model Guidance to Assess the Potential for Tornadoes across Southeast Virginia on 28 April 2008

Short Range Ensemble Forecast (SREF) products are used with high resolution model output to identify the severe weather potential associated with a tornado outbreak across southeast Virginia on April 28, 2008. This study will illustrate that SREF probability forecasts and deterministic high resolution model solutions shouldn't be considered as mutually exclusive approaches to forecasting. Rather, the strengths of each approach can lead to a value added forecast when assessing the potential for severe weather.

The concentrated severe weather outbreak across southeast Virginia on April 28 resulted in 11 tornadoes and multiple injuries, including an EF3 rated tornado in the city of Suffolk. Although cloudy conditions ahead of an advancing cold front were expected to limit destabilization across the mid-Atlantic region, persistent low-level moisture inflow coupled with increasing low- to mid-level wind fields were expected to provide sufficient vertical wind shear to increase the potential for low-topped supercells and bowing line segments along a pre-frontal trough.

This study demonstrates a forecast strategy that utilizes 1) SREF probability forecasts to assess the likelihood, storm type potential, and predictability of the event; 2) SREF departures from climatology to evaluate the climatological context of the event; and 3) high resolution model output to determine the details of moisture, instability, lifting/forcing mechanisms, and convective mode (e.g., cellular, linear, etc.).