Mesoscale Features of the Michigan Land Breeze Using PAM II Temperature Data

Abstract

During the period 16?20 December 1983, the northern United States was enduring a record-breaking cold air outbreak. The cold air brought temperatures as low as ?40°C to some areas while bringing considerable lake-effect snows to locations in the Ice of the Great Lakes. In western Lower Michigan much of the snow fell from the wind-parallel snowbands that resulted as the cold, strong northwesterly winds crossed the relatively warm waters of Lake Michigan. Analysis of surface weather data from PAM II stations in the region showed that during daylight hours of 18 December, when the winds were fairly strong, temperatures across Lower Michigan were relatively uniform. By 19 December, the strong winds subsided and strong radiational cooling after sunset resulted in the formation of a very cold pool of air over western Lower Michigan. Separating this cold air from the warm areas near the shore was the land-breeze front. Along the south end of the lake, radiational cooling served to intensify an existing south-to-north temperature gradient that resulted as cold air sweeping around the south end of the lake stood in contrast to lake-warmed air over southwest Michigan. As a result of this intensification, the cold air pushed northward as a density current or land breeze. Eventually, radiationally cooled air would cover all of western Lower Michigan.