In light of the recent stretch of below average temperatures, I thought it might be of interest to share some facts about ice on the Great Lakes. The NOAA Great Lakes Environmental Research Laboratory, or GLERL, has been studying ice coverage on the Great Lakes for over 30 years. Their data help us to understand ice’s role in water level changes, water temperature, and even plankton blooms in Lake Erie. Why should we care so much about ice? Read on to find out more about ice and its impacts.
During winter months, lakes lose energy to the atmosphere as the water near the surface cools. The cold, dense water sinks to the bottom of the lake while warmer water rises, and this cycle continues until the surface water reaches 32 degrees. Freezing begins and then extends down into the lake as the ice thickens. On average, it takes until early February for Lake Erie to achieve over 60% ice coverage. The recent stretch of cold temperatures across the Great Lakes has made for some record-breaking ice generation – Lake Erie went from 1.5% coverage on December 24 to over 85% coverage on January 8. For comparison, last year in early January, Lake Erie had only 7.6% ice coverage.
Ice and Lake Effect Snow
More ice on Lake Erie generally means less lake effect snow. When Lake Erie freezes over, less water is readily available to be drawn up from the lake to the air above. The ice acts like a cap, preventing moisture from evaporating and/or condensing and therefore creating lake effect snow. While those in the “snow belt” may appreciate the decrease in snowfall once Lake Erie starts freezing over, this usually comes at a price – colder weather!
Ice and Lake Levels
Increased ice coverage means more protection from evaporation in the winter and theoretically higher water levels – but the connection between ice coverage and water levels is not that simple. While the amount of available open water in the winter for evaporation plays a role, data have shown that evaporation peaks in the fall, before ice cover forms. In extreme ice cover years, the thermal structure of the lake could be impacted for the rest of the year, potentially leading to less evaporation from the lakes (and possibly higher water levels) in the following fall. It is important to note that evaporation and precipitation are the major drivers of seasonal water level changes in the Great Lakes. A winter of low evaporation due to ice cover could be negated by a dry spring with little rainfall.
Ice and Harmful Algal Blooms
Harmful algal blooms typically require a water temperature of at least 60 degrees to bloom. The percentage of ice coverage does play a part in water temperatures later in the year – the spring temperatures will have to melt the ice first before the water below the ice is able to warm up. In a year with a greater extent of ice cover, it will take longer for the lake to warm up to 60 degrees, and this could lead to a shorter harmful algal bloom season. However, factors such as nutrient runoff and spring/summer weather patterns can impact the extent of harmful algal blooms as well.
Want to learn more about ice? Check out NOAA GLERL’s Coastwatch program – with real-time observation of ice on the Great Lakes.
NOAA GLERL Great Lakes Ice Cover page: https://www.glerl.noaa.gov/data/ice/#overview
National Weather Service Great Lakes Ice Analysis: https://www.weather.gov/cle/GreatLakesIce_Analysis
Great Lakes Coastal Forecasting System Annual Ice Cover Comparison: https://www.glerl.noaa.gov//res/glcfs/compare_years/