STRUCTURE AND EVOLUTION OF WINTER CYCLONES IN THE CENTRAL UNITED-STATES AND THEIR EFFECTS ON THE DISTRIBUTION OF PRECIPITATION .2. ARCTIC FRONTS

The structure and evolution of a shallow but intense cold front (commo nly referred to as an arctic front) and its associated precipitation f eatures that passed through the central United States from 0000 UTC 9 March to 0000 UTC 10 March 1992 are studied with the aid of observatio ns and outputs from a numerical simulation using the Pennsylvania Stat e University-National Center for Atmospheric Research Mesoscale Model MM4. Located above the arctic front was a region of midtropospheric, f rontogenetical confluence that was attended by a thermally direct vert ical circulation. A large banded precipitation feature, for the most p art located behind the arctic front, was produced by ice crystals from upper-level clouds (formed by the frontogenetical confluence) falling into low-level stratocumulus associated with the arctic front. The ar ctic front at the surface separated a region where the precipitation r eaching the ground was solid from an adjacent region where the precipi tation was liquid. A westward-moving, low-level jet behind the arctic front produced upslope flow over the high terrain of the northern Grea t Plains, which contributed to heavy snowfalls in this region. A porti on of the arctic front that moved southward, west of a low pressure ce nter, was characterized by sharp drops in temperature and dewpoint and an increase in wind speed. However, the arctic front was not associat ed with either a pressure trough or much change in wind direction. The proximity of arctic fronts to such nonfrontal features as tee troughs and/or drylines often leads to the latter being misanalyzed as cold f ronts.