Lake effect snow (or LES), a common occurrence in Michigan during the late fall and early winter months, also happens frequently in the Midwest. It is a phenomenon that occurs when cold air moves over the relatively warm early season waters of the Great Lakes. Typically the temperature difference between the air and the lake needs to be at least 13 degrees Celsius, or around 23 degrees Fahrenheit. When this temperature difference occurs, the warmer lakes heat the air right above it, which then forces that moisture-rich air to rise through the surrounding cooler air. Wind direction is also a key factor in LES development. The most favorable conditions occur when winds run parallel to the lake, because the cold winds have the greatest fetch or the longest travel distance across the lake and gather the most moisture. Since the wind direction in North America frequently has a westerly component, locations east of the Great Lakes experience the greatest snowfall amounts.
So what does this mean for the Midwest? Michigan, northern Indiana and northeast Ohio are most prone to lake effect snow each season since west and northwest winds usher chilly Canadian air across 80 to 120 miles of the Great Lakes, leading to intense lake effect snow showers. When winds run north to northeast, the Chicago metro area can experience lake effect snow. A northeast wind may provide multiple, lighter lake effect snow bands into the windy city, but sometimes a N - NNE wind can bring a heavier, single band into the the metro area.
Just how much influence do lake effect snow events have on seasonal snowfall totals in the Midwest? The figure below represents the seasonal snowfall average over the last 30 years and it's no surprise the LES prone areas typically receive the highest seasonal snowfall. Places east of Lake Michigan generally receive 72 – 100+ inches every year and the bullseye over NE Ohio highlights 60 - 72 inches of snow on average in the Cleveland area, which is aided by the lake effect. Further west, the snowfall gradient across northeast Illinois, between Will and Lake County, shows Lake Michigan's minor influence.
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While the LES snow events in the Midwest typically are not as notable as those in Upstate New York, these snow bands can still pack a punch. LES snow bands are infamous for producing very intense snowfall and extremely tight snowfall gradients (large snowfall difference over a small area). For instance, take a look below at a notable LES event that occurred on Easter in 2007 below. Considering the month, it is a rare event but the incredible snow amounts made it even more memorable as NE Ohio received over 30 inches of snow! To put this in perspective, Chicago’s greatest LES event happened in 1973 with snow measurements between 5 – 12 inches. LES season typically ends once the shallower Lake Erie freezes which normally occurs in January or February (unless we have a mild winter). Lake Michigan is too deep to completely freeze over but once lake ice reaches its maximum extent (typically in February or early March), LES in northeast Illinois and Indiana becomes less likely.
