Prefrontal Wind-Shift Lines in the Plains of the United States

Abstract

In the central United States, cold fronts are sometimes preceded by a surface wind shift by several hours. These wind shifts are examined to determine their origins and characteristics. A climatology and a case study of an autumn ?prefrontal wind shift? are presented. Data collected by the recently implemented Oklahoma Mesonet and a network of wind profilers permit finescale analyses of the autumn prefrontal wind shift. It is found that prefrontal wind shifts are associated with both lee troughs and drylines. The climatology reveals that in the central United States fronts are most frequently (up to 60% of them) preceded by wind shifts just east of the Rockies, where lee troughs and drylines originate. This paper focuses on a case study of a prefrontal wind shift associated with a lee trough that forms when a front approaches the lee trough. The prefrontal wind shift associated with the lee trough forms in the lee of the mountains but propagates away from the mountains when downslope flow decreases and warm advection occurs ahead of the wind shift. A cyclone forms along the prefrontal wind shift and propagates southward in part like an edge wave. The front, however, across which there is no cyclonic wind shift, moves faster than the prefrontal wind shift and eventually catches up to it.