Anatomy of a Rare South Texas Snowstorm: 7–8 December 2017

Between the morning of 7 December 2017 and the morning of 8 December 2017, South Texas experienced a rare snowstorm. Two quasi-stationary snow bands produced up to 8 inches (20.32 cm) of snow across portions of Corpus Christi. The release of conditional symmetric instability and convective instability in the presence of frontogenesis played a key role in producing higher snowfall rates within these snow bands. Sufficient vertical motion resulted in charge separation that produced occasional thundersnow, during the early morning hours of 8 December across portions of South Texas.

The North American Mesoscale (NAM) Forecast System, the Canadian Meteorological Centre’s (CMC) Global Deterministic Prediction System (GDPS), the Short Range Ensemble Forecast (SREF), and the High Resolution Ensemble Forecast version 2 (HREFv2) all performed quite well in forecasting accumulating snow across South Texas, up to several days in advance. However, it will be shown that the Global Forecast System (GFS) and the European Centre for Medium-Range Weather Forecasts’ (ECMWF) High Resolution Model did not perform very well in predicting snow across South Texas. The boundary layer temperature forecasts from these two numerical weather prediction models were generally too warm to support frozen precipitation and thus underestimated the potential for snow.

Finally, a comparison using reanalysis data of broad synoptic scale factors associated with this snowstorm will be made with several South Texas snowstorms dating back to 1895.