Large-Amplitude Mesoscale Wave Disturbances Within the Intense Midwest Extratropical Cyclone of 15 December 1987

Abstract

On 15 December 1987 several long-lived, large-amplitude mesoscale wave disturbances embedded within a rapidly intensifying extratropical cyclone traversed the Midwest and created life-threatening blizzard conditions. Within the wave disturbances, which likely were atmospheric gravity waves, pressure fails of up to 11 mb in 15 min were accompanied by winds in excess of 30 m s?1 (60 kt), cloud-to-ground lightning and heavy snowfall. One of the large-amplitude mesoscale wave disturbances, characterized by a surface pressure minimum lower than the cyclone's central pressure, propagated through the cyclone center during the rapid intensification stage of the storm system. The rapid changes in weather conditions associated with these wave disturbances played havoc with attempts to make short-range forecasts at the height of the 15 December 1987 snowstorm. To help forecasters anticipate and identify mesoscale wave disturbances, basic forecast guidelines based on gravity wave principles and recent research results are discussed.