The Mesoscale Temperature and Dew Point Fields of a Very Cold Airflow Across the Great Lakes

Abstract

The mesoscale air temperature and dew point fields in a synoptic situation where air with a temperature at least 25°C colder than lake water temperature passed over the western Great Lakes is investigated. The airflow experienced an average temperature rise of 8°C and a dew point rise of 15°C from one shore of Lake Michigan to the other. Leeward of Lake Michigan the surface air temperature and dew point of the airflow decreased approximately 2°C and 4°C, respectively, as the air moved inland. Strong temperature gradients, referred to as lake–end pseudofronts, were found perpendicular to the flow downwind from the end of the lakes. The lake-end pseudofront at the southern end of Lake Michigan was 25–50 km wide, extended over 100 km downstream, and had an average magnitude of 0.5°C (5 km)⁻¹. A band of heavy snow was associated with it. Ice on the lakes, coupled with a transitory wind shift, allowed unmodified cold air to penetrate into lower Michigan for several hours. Low dew points accompanied this cold air penetration with the region covered by low dew points being greater than that covered by low temperatures.