Review of the influences of the Great Lakes on weather

The considerable influence of the masses of water in the Great Lakes on the weather over and around the Lakes is reviewed and the average lake-related weather alterations are indicated. Particular emphasis is placed on delineating the known facts and those that are inadequately known. The lack of extensive continuous weather measurements, particularly over the lakes, makes definitive areal assessments of lake influences on the weather around them difficult. Whether the lakes act as the energy sources or sinks on a daily or seasonal basis depends on the relative temperature of the waters and the overlying air. Over the lakes and their downwind shore areas, the lake-caused average changes in cloud and precipitation amounts represent 5–15% reductions in summer and 5–45% increases in winter in comparison with upwind values.