Front-mountain interactions in the long-lived, intense surface front of 28 February through 4 March 1972 over the United States

The focus of this presentation is on the structure and evolution of an intense long-lived surface front from 28 February through 4 March 1972. The front was noteworthy for four reasons: 1) it affected most of the United States from the Rockies to the Atlantic coast, 2) a 50°C temperature contrast between Kansas and southern Manitoba was observed, 3) diurnally varying differential diabatic heating and cooling across complex terrain played an important role in frontogenesis, and 4) mountain-induced cold-air damming and downslope warming strongly influenced frontal intensity and propagation.

The large-scale environment in the February-March 1972 case favored the accumulation of bitterly cold arctic air in Canada. Frontal formation occurred over northern Montana and North Dakota as the arctic air moved slowly southward as surface pressures rose east of the Canadian Rockies. The arctic air accelerated southward subsequent to lee cyclogenesis-induced pressure falls ahead of an upstream trough that crossed the Rockies. The southward acceleration of the arctic air was also facilitated by dynamic anticyclogenesis in southern Canada beneath a poleward jet-entrance region.

Three types of cyclogenesis events were observed over the lifetime of the event: 1) low-amplitude frontal waves with no upper-level support, 2) low-amplitude frontal waves that formed in a jet-entrance region, and 3) cyclones that formed ahead of advancing upper-level troughs. All cyclones were either non-developing or weak developments despite extreme baroclinicity, likely the result of large atmospheric static stability in the arctic frontal zone and unfavorable along-front stretching deformation. Significant front-mountain interactions were observed over the Rockies and the Appalachians and are the focus of this presentation