As we settle into winter in the Great Lakes region, many people are looking to NOAA’s Great Lakes Environmental Research Laboratory for information about the 2025 ice season. Here are some common questions about this year’s ice and our ice research, answered by a team of NOAA GLERL scientists.
What is the Great Lakes ice forecast for 2025?
The U.S. National Ice Center’s official seasonal outlook for Great Lakes ice predicts slightly below normal ice conditions on Lakes Superior, Michigan, Huron and Erie this winter. Near normal ice conditions are predicted for Lake Ontario. Read the full outlook here.
How does NOAA GLERL research ice cover?
NOAA GLERL has been exploring the relationships between ice cover, lake thermal structure, and regional climate for over 30 years through historical model simulations and observations of ice cover, surface water temperature, and other variables. Studying, monitoring, and predicting ice cover on the Great Lakes is important because ice plays an important role in determining regional weather, timing of evaporation, water movement patterns, water temperature structure, and spring plankton blooms.
NOAA GLERL and the U.S. National Ice Center have been collecting detailed ice cover data via satellite imagery since 1973. When it comes to analyzing each year’s data, we compare the current year to historical data in two major ways. The annual maximum ice cover (AMIC) is simply the highest measurement of ice cover that we see in a single ice season. While it’s interesting to look at peak ice cover every year, we also look at average ice cover throughout the entire season. Generally, looking at seasonal average ice cover is more relevant than AMIC for studying long term trends. For example, a short-lived cold air outbreak can cause a peak in maximum ice cover, even if the seasonal average was low for the rest of the year.
When does the Great Lakes ice season start?
The northern Great Lakes can start to see ice as early as late November or early December. NOAA GLERL begins tracking ice cover and updating our ice products for the season in early December. Low ice cover in December is normal, with the majority of ice growth historically occurring in January and February. Ice cover for mid-December typically runs between 1-2%. Access lakewide ice cover data for the 2025 season here.
“We expect a mild ice season in 2025,” says Dr. Jia Wang, ice climatologist at NOAA GLERL. Interannual variability of Great Lakes ice cover is heavily influenced by four large-scale climate patterns, referred to as teleconnections: the North Atlantic Oscillation (NAO), the Atlantic Multidecadal Oscillation (AMO), the El Nino/Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO).
“This year, both AMO and PDO are bringing very strong warm weather conditions to the Great Lakes region,” says Dr. Wang. “This will overwhelm the cooling caused by this year’s neutral ENSO conditions, so a mild winter is likely.”
What ice products and resources does NOAA GLERL have?
*** Please note: NOAA GLERL is still in the process of updating some of the following products for the 2025 season. All 2025 products will be available soon. ***
The NOAA Great Lakes Coastwatch Program provides satellite environmental data and products for near real-time observation of the Great Lakes. CoastWatch products help support water-dependent industries such as hydropower, fishing, commercial shipping, and search and rescue operations. The CoastWatch Great Lakes Ice Concentration Statistics page includes graphs and datasets for lakewide average ice concentrations, as well as comparisons to historical data.
The CoastWatch Great Lakes Surface Environmental Analysis (GLSEA) is a digital map of Great Lakes surface water temperature and ice cover, and is produced daily and derived from NOAA satellite imagery. Lake surface temperatures and ice cover conditions are updated daily with information from the cloud-free portions of the previous day’s satellite imagery.
The Experimental Great Lakes Coastal Forecasting System (GLCFS) is an experimental set of hydrodynamic computer models that predict lake circulation and other physical processes, such as thermal structure, wind, short-term water level changes, and ice dynamics. Access GLCFS ice animations for each lake below.
GLERL’s 2025 Ice Cover page includes daily ice cover maps and a Great Lakes average ice cover graph.
Our Historical Ice Cover page provides graphs and datasets for historical Great Lakes ice cover back to 1973. Our historical ice data is critical to predictive modeling efforts and establishes a foundation for understanding the influence of ice on the regional economy and environment.
To better understand ice formation and the types of ice in the Great Lakes, NOAA GLERL and the U.S. Coast Guard use Synthetic Aperture Radar (SAR) data from the NOAA CoastWatch Great Lakes Node to monitor six different types of ice, ice thickness, and ice cover. This risk assessment tool is known as the Ice Condition Index (ICECON). The U.S. Coast Guard uses ICECON to identify areas that require ice breaking operations and ship transit assistance. These ice breaking operations allow government and commercial ships to travel through the Great Lakes unobstructed.
All of NOAA GLERL’s ice products are also accessible from our Great Lakes Ice Cover homepage.
Why do NOAA GLERL’s ice records only go back to 1973?
The early 1970s is when we first had reliable satellite data with which to construct more accurate and complete datasets. Before the satellite era, information during the winter about ice concentration away from the shoreline was very limited. This is why we only use the 52-year dataset for our calculations, as this represents the highest quality data.
Is ice cover related to evaporation and water levels?
To form ice, the lake’s surface requires a loss of heat and moisture from evaporation in the late fall and early winter. While Great Lakes water levels are generally lowest in the winter, most of the evaporation from the lakes actually happens in the fall. This is because in the fall, cooler and drier air flows over the warmer lake waters. This contrast in temperature and moisture between the air and water helps to increase the evaporation from the water, causing a decline in water levels. Once ice has formed on the lake, its presence does reduce the amount of evaporation at that time.
The graphic below illustrates the seasonal cycles that Great Lakes water levels undergo every year. Learn more about Great Lakes water levels and water temperatures in our recent pre-winter Q&A.
Why is ice cover important?
Great Lakes communities have strong economic ties to ice cover on the lakes, and changes in ice cover can have big impacts on the people living there. Many local businesses in the region rely on ice fishing and outdoor sports, which can only happen if the ice is thick and solid. Commercial shipping schedules are heavily impacted by the formation of ice as well.
Ice is a natural part of the Great Lakes yearly cycle and many animal species, from microbial to larger fauna, rely on the ice for protecting young and harboring eggs. There’s increasing evidence that the ice plays a role in regulating many biological processes in the water throughout the winter. The Great Lakes also see most of their significant storms and large wave events during the colder months of late fall through winter. The shorebound ice sheets act as an important buffer against these waves, protecting the coast from erosion and damage to shoreline infrastructure.
Additional Resources
Fact Sheet: Ice Cover Research at NOAA GLERL