NOAA/NASA

Do the Great Lakes freeze over?

The lakes are full of water (obviously)… and Ontario is cold during the winters… so the lakes should freeze over in the wintertime, right? Not quite! Read on to learn all about ice, ice baby.


Do the Great Lakes freeze over in winter?

The short answer? No, not completely. The lakes are so vast that it is very rare for them to entirely freeze over. Yet they do experience substantial ice coverage, with large sections of the lake freezing over in the coldest months.

Since water takes longer to warm up or cool down compared to land, the Lakes usually begin freezing in late December to early January. They usually reach their peak freeze by the end of February or early March.

Since the early 1970s, the Great Lakes have a long-term average of 55% ice coverage with certain areas reliably freezing over. In that time, the lakes have surpassed 80% ice coverage a mere five times. The lowest ice coverage was in 2002 when ice coverage was only 9.5%.

The last time that Lake Superior almost entirely froze over was in 1979 when the lake reached 94.7% ice coverage.

Records show that lakes Michigan and Ontario are the only lakes to have resisted freezing over since recording began in the early 1900s. This is due to their lower latitudes and large depths. The deep lakes provide massive heat storage and allow the lakes to better resist freezing.

Since the 1970s, ice coverage has generally decreased. However, we did experience one brutal winter in 2013/2014. That frigid year, the Great Lakes together reached 92% ice coverage, during which Lake Erie and the Straits of Mackinac (the region between Lakes Michigan and Huron) completely froze over and Lakes Huron and Superior nearly froze over. But this is an anomaly. Temperatures over the last few decades have generally increased, and we are unlikely to see a repeat performance of that deep freeze any time soon.

Since the early 1970s the annual average ice coverage on the great lakes has decreased by an astonishing 71%. Due to climate change, snow and ice depth have decreased on both the lakes and on land. This reduction in ice leaves the lakes uncovered and free to evaporate. And if you have read our article all about snow, you will know that when the lakes are warmer and water evaporates, the cold wind sweeps in and results in dense lake-effect precipitation. In other words, less ice coverage could mean heavier snow dumpings on land.

It is likely that the Great Lakes’ ice levels will continue to decrease in the coming years and we could see quite the shift in our usual winter weather.

More information:

For more information on snow in the Great Lakes region, click here.

For an up-to-date forecast of the Great Lakes ice coverage, click here.

To view historic ice coverage, click here.