The Paradox of Lake-Effect Snow: Why Warming Could Bring the Great Lakes More, for a While

In late autumn and early winter, cold air from the north pours over the still-warm Great Lakes, and snow streams off them onto the shores downwind. What happens to this snow machine as the climate warms? Counter-intuitively, it may produce more lake-effect snow, at least for a while.

Lake-effect snow on January 6, 2017: cloud bands stream off the lakes, with snow along the southern shore of Lake Erie and the eastern end of Lake Ontario. NASA/NOAA, Suomi NPP.

How lake-effect snow works

When cold air crosses a long stretch of relatively warm, ice-free lake water, it warms enough to rise and picks up enough moisture to form clouds and then snow. How much snow falls depends on how warm and ice-free the lakes are and on the temperature difference between the water and the air. Once the lakes freeze over, the moisture supply shuts off and the season ends. All else equal, as long as there is warm water and cold air, there will be lake-effect snow.

Snowfall from September 30, 2016, to January 7, 2017: the heaviest totals mark the lake-effect belts. NOAA Climate.gov, from National Operational Hydrologic Remote Sensing Center data.

Heavily ice-covered Great Lakes on February 14, 2014; ice sharply reduces lake-effect snow. NASA/NOAA, Suomi NPP.

Has it changed already?

Probably, though with less certainty than for many other trends. Temperature is read from a thermometer, but snow is usually measured by hand with a ruler, so methods vary between people, places and storms, and snow records are generally less reliable.

Still, a study that applied strict quality standards to station records found lake-effect snow increased along Lake Superior and Lake Michigan from 1927 to 2007; too few stations around the other lakes met its standards to say much about them. An earlier study with looser standards found increases across the whole Great Lakes region between 1931 and 2001.

Lake-effect snow on January 22, 2014, with bands south of the Finger Lakes in upstate New York. NASA, Terra MODIS.

Not a contradiction

More snow does not disprove warming. As the air warms, the lakes warm too and stay ice-free longer, which in theory means more snow per storm and a longer season, as long as the air stays cold enough for snow. But the cold air crossing the lakes is also warming, which favours less lake-effect snow. It is a climate tug-of-war.

What the models say

The answer is uncertain: many climate models represent the Great Lakes coarsely and struggle with the conditions that make lake-effect snow. Several studies have tried anyway.

• Coupling a climate model with a lake model showed that complete ice cover drastically cuts lake-effect precipitation.
• As global temperatures rise, ice cover shrinks, and by 2050 heavy lake-effect snowstorms become more frequent around Lake Superior, whose colder climate can keep supporting snow longer than the other lakes.
• Higher-resolution weather models with warmer, less icy lakes produced more lake-effect snow downwind and farther inland.

Projected change in average surface air temperature (°F) for 2071–2099 compared with 1970–1999 under a higher-emissions scenario. NOAA Climate.gov, adapted from the 2014 National Climate Assessment.

Any increase would be temporary. As greenhouse gases keep pushing temperatures up, the lake-effect snow will eventually turn to rain.

Sources

• NOAA Climate.gov, "The paradox of lake effect snow: global warming could bring the Great Lakes more of it, at least for a while"; rewritten in hubnx's own words. Images: NASA and NOAA Climate.gov.
• Kunkel and others (2009), Journal of Great Lakes Research; Notaro, Bennington and Vavrus (2015), Journal of Climate.