Relative Warm Great Lakes Modify Incoming Cold Air Masses

The U.S. Heating Degree Day Forecast Adjusts Colder for December
12/03/2017, 7:24 pm EDT
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A colder weather pattern is ahead beginning in the 6-10 day period with following waves of cold in both the 11-15 and 16-20 day period(s). Causing the cold waves are emergence of the displacement of the polar vortex from northern latitudes toward the Great Lakes region.

While the upper air forecasts by all models look formidable we’re early enough in meteorological winter for moderating influence (on the cold upper trough) by the relative warm waters of the Great Lakes. During this polar vortex weather pattern the Great Lakes should cool dramatically.

However, leading into the approaching colder pattern the Great Lakes are somewhat warmer than normal especially Lakes Michigan, Erie and Ontario. Surface temperatures are near or warmer than 50F across eastern Erie and Ontario and near 50 over eastern Michigan. Lake Superior and Huron are closer to normal 40’s.

The incoming cold air masses will modify due to the warming influence of the relative warm water. Dramatic lake-effect snow events are likely with location of heavy snow dependent on wind direction. Forecasts indicate waves of cold in the medium/extended-range implying lake-effect snow events also occur in dramatic/short period occurrences.

As the Great Lakes cool during this much colder weather pattern the modifying effects weaken. Therefore coldest anomalies are likely after mid-December in the eastern U.S.