The Record Meso-Snowfall Event of 1997 in Jackson, Mississippi

A preliminary 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 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. The snowfall was largely the result of interactions between these jets, the deformation zone associated with an upper level feature previously in existence (and as clearly indicated by, and diagnosed with, water vapor imagery), a direct frontogenetical circulation in mid and upper levels (i.e., 500 mb, 300 mb, and 250 mb), and isentropic lift of a moisture pool from the east. These same features help explain the limited extent and short duration of the event. The event is described in hindcast mode and in terms of what could have led to operational recognition, or at least suspicion, of an unfolding snowfall event. Evidence suggests that identification of the upper level disturbance and moisture pool using satellite imagery would have been crucial to raising suspicion of a possible event in spite of model forecasts. The use of model soundings, IPV, and cross-sections, within an isentropic framework, could have led forecasters to suspect some snowfall based on dynamic considerations and in spite of model output.