A Short-Lived Cold Front in the Southwestern United States

Abstract

A cold front developed in Arizona in a region of initially small temperature gradient, developing to great intensity, accompanied by damaging winds over New Mexico, and then losing strength over the high plains of Oklahoma and Texas. The entire development of frontogenesis and frontolysis occurred in no more than 24 h. The initial growth of temperature contrast was attributable mainly to horizontal variation of surface heat flux during the morning, with little heating in a region of dense cloud cover and scattered showers in the west and with intense heating in a region of only thin high clouds to the east. The accompanying ageostrophic circulation then resulted in a collapse toward discontinuity. The frontal zone maintained an approximately steady state for a few hours in early afternoon. At this time the westerly component of surface wind just ahead of the zone was not as strong as the eastward motion of the zone. The passage of the zone was accompanied by a veering and strengthening of the surface wind so that westerly components were briefly larger than the frontal motion. The tendency of the convergent wind field to produce a frontogenesis was evidently balanced by small-scale mixing. Subsequently the pressure trough and surface wind shift propagated eastward more rapidly than the frontal temperature contrast. The contrast quickly weakened as the mixing then was unopposed. Severe convection developed during the evening as the convergent surface wind shift came into contact with humid unstably stratified air.