Doppler Radar Observation of a Land-Breeze Cold Front

Abstract

During the early morning hours of Ii January 1981, a very narrow, intense band of snow which had formed along the leading edge of a land-breeze cold front was viewed by CP-4 radar near Muskegon, Michigan. The front formed well inland and moved through the area from the northeast shortly after dawn. The driving force for the land breeze was the large temperature contrast that existed between radiationally-cooled air over the Northern Highlands of Lower Michigan, and the relatively warm, lake-modified air near the shore of Lake Michigan. The possibility that the observed snowband was associated with a mesoscale feature other than the land breeze is investigated. An analysis of minimum temperatures in the Great Lakes Region for 11 January 1981 shows that a strong temperature gradient existed over western Lower Michigan.This gradient reached a maximum value well inland rather than at the lake shore. Radar observations show the band to be over 80 km long and only 4 km wide, oriented roughly parallel to the lake shore. The band was very uniform in both reflectivity and velocity structure along its length. Assuming horizontal homogeneity, the band-normal wind field was computed. Northerly winds were present at all levels on the warm side of the front and above the advancing cold air mass. Northeasterly winds were present in the cold air. Aircraft measurements revealed that the cold air extended to a height of 430 m. A gravity current model was applied to the motion of the land-breeze front and good agreement was found between the observed and predicted speeds of advance.