Snow is piling up in parts of western New York, Michigan, Pennsylvania and Ohio thanks to an incursion of Arctic air blowing over the unusually warm waters of the Great Lakes. Totals are expected to be between several inches to more than a foot, and more could be in store next week.

The contrast between cold air and warm water fuels what is called the lake effect: As the air blows over the lakes, water evaporates into it and turns to snow that falls — sometimes in extreme amounts — on coastal areas.

It’s not unusual to see lake effect snow at this time of year because it is when the first bouts of cold air begin to descend over waters that still retain some of summer’s warmth. But in the future, lake effect snow could occur more often and later in the cold season as global warming raises water temperatures in the Great Lakes, preventing the formation of winter ice that normally eventually shuts down the lake effect mechanism.

Currently, waters in the Great Lakes are running up to about 8°F above the long-term average.

Great Lakes temperatures

How temperatures across the great lakes this fall compared to the long-term average (from 1995-2015), in Celsius.

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“You’re not going to form ice with those temperatures,” George Leshkevich, a physical scientist at the Great Lakes Environmental Research Laboratory, said.

Those elevated lake temperatures and the lack of ice meant conditions were ripe once this season’s first major incursion of Arctic air began earlier this week.

A very mild autumn helped to keep temperatures in the Great Lakes elevated; Wisconsin, Michigan and Minnesota all had their warmest autumn (as did the contiguous U.S. as a whole), with temperatures running about 6°F above average.

The Upper Midwest has the fastest warming winters of any region in the country, with average temperatures climbing 1.12°F per decade since 1970 and expected to rise another 5.4°F by mid-century.

That regional warming is also driving up the temperatures of the lakes and driving down ice cover. Since the early 1970s, total ice cover in the Great Lakes has declined by 71 percent.

“One pretty robust climate change outcome that we see in the future is warmer lakes,” Brent Lofgren, a GLERL climatologist, said.

Last year was emblematic of this decline, with warm winter conditions keeping total ice cover in the lakes below 30 percent for most of the season. The sparse ice cover helped lead to a lake effect event that brought 3 feet of snow to New York’s Oswego County in February, a very rare event.

 

 

How lake effect snow changes in the future, though, also depends on how patterns of atmospheric flow might change with warming, something that is still very uncertain. But it’s possible that while some places might see much more lake effect snow, and later in the winter, other spots could see less.

Also, temperatures may eventually warm too much to support the formation of snow, which could mean a transition to winter lake effect rain.

One other potential wrinkle in understanding how lake effect snow around the Great Lakes may change in the future is that ice cover on the lakes has seemed to become more variable in recent years.

The unusually warm conditions of last year were preceded by two winters that saw some of the highest ice totals in the records. But what is causing these bigger year-to-year swings isn’t clear.

In the short term, western New York and other areas could be in store for another round of lake effect snow next week, when another, even colder, surge of Arctic air is expected.

How the season progresses after that depends on whether temperatures stay cold enough for long enough to begin ice formation, Leshkevich said. If these bouts of cold weather are followed by a return to warmer conditions, that could stymie ice formation and make it more likely for coastal areas to see lake effect snow later in winter.