Lake Michigan water levels have begun their seasonal decline. Water levels are expected to continue to fall through February. Below average precipitation late this summer and increased evaporation led to a decreased water supply to Lake Michigan. Over the next 6-months the USACE predicts that Lake Michigan water levels will close to the long-term average. La Niña conditions are likely to emerge by November and persist in the Northern Hemisphere through winter.

Water Levels on Lake Michigan-Huron

Here are five things to know about water levels on Lake Michigan for Fall 2024.

What are the current water levels on Lake Michigan?

The water level of Lake Michigan as of September 27, 2024, was at an elevation of 579.17 feet above sea level (from the International Great Lakes Datum). To put this level into perspective, here are some statistics for Lake Michigan relative to the period of water level records measured from 1918 to present (statistics from USACE’s Weekly Water Level Update).

What is the outlook for future water levels?

Water levels have begun their seasonal decline. The USACE is projecting that water levels will continue to decline another three inches by the end of October. The USACE 6-month forecast of Great Lakes Water levels shows the seasonal decline to continue through the fall and winter, with water levels near the long-term average (see the water level forecast issued for October 2024 below).

USACE six-month water level forecast for Lake Michigan-Huron retrieved for October 2024 from: https://lre-wm.usace.army.mil/ForecastData/BulletinGraphics/mich_hrn.jpg

What are current and predicted climate conditions like?

NOAA’s Climate Prediction Center has issued a La Niña Watch for the late fall/early winter. La Niña conditions are likely to emerge by November and persist in the Northern Hemisphere through winter. Climate predictions for October – December temperatures in the Great Lakes region leaning above normal. After a dryer than average August, precipitation outlooks show precipitation in the Great Lakes region has a slight chance to be above normal October-December (see precipitation outlook map from NOAA Climate.gov below). Check out the NOAA Climate Prediction Center’s U.S. climate outlook.

Caption: The U.S. precipitation outlook for October – December 2024. Map by NOAA Climate.gov, based on data from the Climate Prediction Center. From: https://www.cpc.ncep.noaa.gov/

What is behind Great Lakes water level fluctuations?

The story of Great Lakes water level changes is told by Net Basin Supply. Net Basin Supply (NBS) accounts for the water going into a lake in the form of precipitation and runoff minus water leaving a lake due to evaporation of water from the lake surface.

NBS represents the net influence of precipitation over the lake, runoff from a lake’s watershed into the lake, and evaporation from the lake’s surface. Image credit: National Oceanic and Atmospheric Administration

In general, when Net Basin Supply is positive, more water enters the lake than leaves, causing a rise in lake levels. When Net Basin Supply is negative, more water leaves the lake than enters, causing a drop in lake levels. (Click here for more detail).

The annual peak Net Basin Supply occurs when runoff peaks in the spring and experiences its minimum when over-lake evaporation peaks in the winter. These maximums and minimums in Net Basin Supply correspond to the seasonal water level rise and fall. (Click here for more detail). 

Evaporation takes place when the Lake’s surface water temperature is warmer than the air temperature. Evaporation increases in the fall and winter as the difference between air temperature and water temperature increases. August precipitation was below average for Lake Michigan, which combined with above average evaporation to contribute to the below average water supplies.

What is making water levels go down?

Since monthly record highs in 2020, the Great Lakes water levels have been trending downwards. This trend has continued and water levels are lower than they were at the same time in 2023. However, water levels still remain slightly above the long term average. The graph below visualizes the monthly difference from the long-term average NBS for the past five years. Red bars represent below average NBS, whereas blue bars represent above average NBS.

Evaporation relative to long term average Evaporation for the past 5 years. Retrieved from: https://lre-wm.usace.army.mil/ForecastData/GLBasinConditions/monthlyNBSPast5Years.jpg

Water level fluctuation is a process that occurs annually due to changes in net basin supply. Water supplies fluctuated throughout the winter and spring, with no months extremely out of balance. This has led to a seasonal winter water level decline followed by a spring increase that has been relatively consistent with the long-term average trend.

Places you can find more relevant information:

1. In this Adapting to A Changing Coast PBS Special, Dr. Adam Bechle explains how fluctuations in rainfall, runoff, and evaporation cause the Great Lakes’ water levels and coastlines to vary.
2. NOAA’s Climate.gov site hosts climate data and information to help you understand climate processes and make decisions on how to manage climate-related risks and opportunities.
   • U.S. Climate outlook for June 2024
   • El Niño and La Niña
   • Great Lakes Chapter of the Climate Resilience Toolkit
3. Our Coastal Hazards page for details about the impacts of high water levels, including erosion, flooding, and navigation issues.
4. Our Policy, Planning, and Risk Reduction Strategies page has tools and resources to help local governments identify local resilience opportunities.