Modeling and Visualization of a Record Meso-Snowfall Event in Jackson, Mississippi

A further investigation of the record meso-snowfall event of 1997 in Jackson, Mississippi has revealed several features that may have made a difference in operational forecasts. The findings are based on a hindcast run of the MM5. The rare event was of particular interest given its extremely limited duration (several hours) and extent (across central Mississippi only) and its apparently "innocuous-look" prior to the snowfall (i.e., lack of model development of the positively tilted upper air system and the generation of any precipitation). Several features, including significant jet streaks through Mexico and another moving northward from the Gulf of Mexico, were poorly handled by operational models (ETA and AVN) resulting in large errors in the predicted strength of the upper level system responsible for the snow. In an attempt to "capture" the event in a forecast mode, the MM5 (version 3.2) was applied to the initialization datasets available from NCAR for 1200 UTC Saturday and 0000 UTC Sunday. The model domain consisted of a triple nest grid centered over Jackson, Mississippi with an outer domain of 27 km resolution, and inner grids of 9 and 3 km resolution. The model was run for a non-hydrostatic atmosphere and accumulation of precipitation in the grid was explicit. Of primary interest in the modeling was the generation of precipitation, particularly based on the 1200 UTC Saturday initial data, during the time of the actual event. The 0000 UTC Sunday initial data were also run for comparison to the Eta for the same initial time. Limited diagnostics were made and focused on vertical velocity, quantitative precipitation, frontogenesis, and cross-section analyses and forecasts. The intent was to determine whether a mesoscale model, based on the same initial data, might have provided forecasters with information that may have led them to consider the occurrence of a snowfall event. Modeling results from the application of the MM5 in combination with animations and other visualization techniques have provided a closer look at the dynamics of the event. These reveal more precisely the evolution and conceptualization of the snowfall which, had such information been available, could have assisted forecasters prior to its occurrence.