Here’s why the water level in Lake Michigan typically drops during the colder months

Weather Blog

Lake Michigan’s water levels have fallen below record levels, but still remain elevated as we head into the increasingly active fall and winter seasons.

The drop in water levels is in part the product of the overall dry weather which has dominated since July across the lake’s drainage basin, but lake water levels also decline every year during the fall and winter months as air and water temperatures cool.

It’s an interesting fact that lake levels drop more in the cool and cold months because the arrival of cooler/colder air masses actually increases the rate at which temperatures drop through the atmosphere with height. Meteorologists say the atmosphere “grows more unstable” when this takes place.

This graphic from the National Weather Service’s Sullivan, WI forecast office lays out the lake level decline

The increase in the vertical temperature drop drives the seasonal lake level declines by encouraging air to ascend more vigorously in the cold season, carrying more lake moisture into the atmosphere than in the warmer months.

So even though sunlight is stronger in the warmer months, it’s the destabilization of the atmosphere brought on by the arrival of colder temperatures that increases evaporation more in fall and winter than in spring and summer.

Unfortunately, we’re still going to have trouble when with the strong winds of cold season storms. Even though lake levels have come down off records, Lake Michigan is still just under three feet above the long term average covering the period since 1918. Shoreline erosion and flooding will remain a concern as winds blow the full length of the lake.

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