Forecasting of Snowfall on the Southern Edge of the United States Snowfall Region in South Central Texas

Snow in South Texas is a relatively rare event but does occur once every three to five years. Therefore, forecasting such events is difficult. Since snowfall is rare, it is a major event with significant impact to the residents of the region. Every winter weather forecaster is faced with the challenge of determining the type of precipitation (snow, sleet, freezing rain, or rain) that will occur in a storm system. There are some general rules of thumb to aid the forecasters. Computer models provide some guidance, but often do not pick-up small-scale changes needed to determine the specific type of precipitation.

Slight changes in temperatures from the surface up to a few thousand feet can change snow to rain or freezing rain. (Harris, 1959, Baxter, et al. 2005, Groisman et al. 2016). The type of precipitation has a significant impact on the general population, city government, and several industries. The impacts of snow and freezing rain include delays in travel, increased number of accidents, and closures of schools and businesses. City officials must make critical decisions on closing facilities and applying anti-icing materials to road surfaces. Beside lost revenue and productive due to closures, industries, like aviation sector, must relocate aircraft, delay or cancel operations and conduct costly de-icing procedures. The public, city official and industry look to the weather forecaster to predict the type of precipitation, timing of precipitation, and the amount of precipitation that will fall. A few degrees of temperature difference in the layer of air above the ground can make a significant difference in type and amount of precipitation that falls.

This presentation reports on a research project using standard upper air and surface data for 14 different snow events in San Antonio, Texas used to determine common features that can be used to help determine if the atmosphere is conducive to a measurable snowfall.