A short-lived cold front in the southwestern United States

A cold front developed in Arizona in a region of initially small temperatur e gradient, developing to great intensity, accompanied by damaging winds ov er New Mexico, and then losing strength over the high plains of Oklahoma an d Texas. The entire development of frontogenesis and frontolysis occurred i n no more than 24 h. The initial growth of temperature contrast was attributable mainly to horiz ontal variation of surface heat flux during the morning, with little heatin g in a region of dense cloud cover and scattered showers in the west and wi th intense heating in a region of only thin high clouds to the east. The ac companying ageostrophic circulation then resulted in a collapse toward disc ontinuity. The frontal zone maintained an approximately steady state for a few hours in early afternoon. At this time the westerly component of surfac e wind just ahead of the zone was not as strong as the eastward motion of t he zone. The passage of the zone was accompanied by a veering and strengthe ning of the surface wind so that westerly components were briefly larger th an 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 w eakened as the mixing then was unopposed. Severe convection developed durin g the evening as the convergent surface wind shift came into contact with h umid unstably stratified air.