The Evolution of an Oklahoma Dryline. Part I: A Meso- and Subsynoptic-Scale Analysis

Abstract

A study is made of the 8 June 1974 Oklahoma dryline and tornado outbreak case, using data synthesis 1) to fit existing concepts on dryline structure and behavior to this case, and 2) to identify processes contributing to moisture convergence along the dryline. The dryline undergoes a major transformation in structure (from sloped to slopeless) during the day, as implied from mesoscale (10?100 km) and subsynoptic scale (100?1000 km) analysis of virtual potential temperature fields. Mesoscale examination of dryline movement reveals the presence of wavelike perturbations which propagate along the dryline, irregardless of its slope, and contribute more to its eastward progression than does the downward slope of the terrain. All but one of 22 tornadoes reported in Oklahoma on this date were associated with thunderstorms that formed within a subsynoptic moisture convergence region at the dryline in central Oklahoma. Results indicate a downward transport of southwesterly momentum through a well-developed mixed-layer west of the dryline and isallobaric effects at the dryline contributed to the buildup of convergence.