Synoptic climatology of heavy snow in West Texas and eastern New Mexico, 1955-56 to 1987-88
Lambert, Barry Christopher
Monthly and seasonal snowfall data for the winter seasons of 1955-56 to 1987-88 were compiled for 53 locations on the Southern High Plains of west Texas and eastern New Mexico. The monthly publications, Climatological Data and Hourly Precipitation Oat~ for Texas and New Mexico were used to distinguish 104 separate heavy snow events during the 33-year period. This information was used in conjunction with the publication Daily Weather Map to identify three 500-mb synoptic pattern types (A, B, and D) which were responsible for producing heavy snow within the study area. It was discovered that over 91% of all "heavy" snow events (i.e.,~ 4 in/12 hr, or~ 6 in/24 hr) were characterized by a split-flow regime at 500mb (i.e., types A and B). Synoptic pattern A was characterized by a "lifting" short wave or closed-contour low, embedded in the southern branch, approaching the study area from the west or southwest at the onset of the heavy snowfall. Pattern type B contained a "digging" short wave or closed low, within the southern branch, approaching the study area from the northwest. One-half of these type A and B events had a closed-contour 500-mb low present at the onset of the heavy snowfall. Split-flow 500-mb patterns accompanied by a closed-contour low produced the majority (96%) ofthe "heaviest" snowfalls (10 in or greater). The third synoptic pattern type (D), was characterized by a full-latitude trough. This flow pattern contained a single, strong jet stream rotating around the base of the trough in close proximity to the study area. Pattern type D storms generated less than 1 00/o of all heavy snow events, and only 4% ofthe heaviest snowfalls recorded during the period of study. Further investigation of all 1 04 heavy snow events showed that type B systems produced the greatest amount of average and maximum heavy snowfall per storm. Pattern type A and D systems deposited similar but lower amounts of average and maximum snowfall for a given storm. For the heaviest snowfalls, type A and B systems resulted in substantially higher amounts of average and maximum heavy snowfall than type D systems. The study also revealed a general inverse relationship between the minimum 500-mb height of a storm, and the amount of average and maximum heavy snowfall it produced. However, the majority of heavy snow events were caused by storms that fell within the intermediate height categories.