Great Lakes' water levels plunge with rapid drought

The very dry September combined with the typical seasonal decline in water levels are bringing Great Lakes' water levels down to lowest level in several years.

In September the precipitation was less than half the normal amount for most of the Great Lakes' drainage basins. Each Great Lake has its own surrounding area where rainfall drains into rivers and streams and then into that particular Great Lake.

Lake Superior dropped so quickly and has been in such a dry area in the past few months. The Lake Superior drainage basin had the driest situation in September with only 38 percent of normal precipitation. The very warm September also increased evaporation to higher than normal amounts.

As a result the water level on the largest Great Lake has plunged below the long-term monthly average for September.

On Lake Superior there was a short four month period at the beginning of 2022 when the lake water level dropped below the monthly average. Since then the water level has been running higher than normal. In looking at a longer timeframe Lake Superior hasn't been below average on water levels since 2014.

Lake Michigan and Lake Huron are considered one lake when talking about water levels. These two lakes haven't dipped below the long-term monthly average since September 2014. During this past September the Lake Michigan-Huron drainage basin only had 44 percent of its usual rainfall. There was only 1.50 inches of rain in September. Also over the Lake Michigan-Huron area September was very warm with the dry weather. This lead to increase evaporation.

Lake Erie is still about eight inches higher than its long-term monthly average. The Lake Erie basin wasn't quite as dry compared to a September normal, receiving 55 percent of normal. Lake Erie continues a long stretch of above normal water levels dating back to March 2015.

Lake Ontario's water level fluctuates the most of any Great Lake due to the human ability to regulate some of the outflow into the St. Lawrence Seaway. Lake Ontario also had the most rainfall in September, receiving 80 percent of normal rainfall. That's dry, but not in a meaningful amount.

Lake Ontario has been below the monthly average water levels in seven stretches of time since 2014. Lake Ontario is right at the long-term monthly average right now and is expected to remain near normal for the next six months.

The Great Lakes are all in a normal seasonal water level decline from now through March. The winter weather doesn't bring as much liquid precipitation as spring, summer and fall. The colder air over warmer water in fall and early winter leads to the most evaporation at this time of year. Those two factors lead to water level declines through winter until the spring rains and snow melt start in March.