Lake Michigan snowstorm spawns rare winter waterspouts and thundersnow

A person makes their way up a street during a snowstorm in Washington DC. File Photo / Matt McClain, The Washington Post

Intense lake-effect snow bands streamed off Lake Michigan in the United States early this week, dumping up to 35cm of snow in northern Indiana and snarling travel.

In addition to heavy snow, the lake-effect bands produced thunder and lightning, small hail and another phenomenon rarely documented – snowspouts.

Sometimes called “arctic sea spouts”, snowspouts are actually a type of waterspout – a tornado-size vortex that forms over water.

Like summertime spouts in the tropics, snowspouts aren’t terribly strong, but they do pose a danger to mariners.

The funnels likely contain swirling winds of 45 to 75m/h (72-120km/h), which would be enough to capsize smaller vessels.

That’s why the National Weather Service in Romeoville, Illinois, which serves the Chicago metropolitan area, issued an unusual warning yesterday: a special marine warning – ordinarily reserved for thunderstorms and warm-season waterspouts – for the spout-producing snow squall.

“ A lake effect snow band capable of producing waterspouts was located near Mariana Shores at Dune Harbour … moving south at 25 knots,” the warning said.

Several waterspouts were reported, including by storm chaser Ryan Scholl, who captured a funnel looming against a snowy backdrop. The vortex appeared to menace a nearby ship.

Dozens of others could have occurred beneath couplets of rotation seen on radar but may have been hidden by the heavy snow.

That same snow band was whipping up some wild winter weather.

In its morning technical forecast discussion, the Weather Service detailed “a band of intense lake effect snow with … tops near 20,000 feet, periods of graupel (soft hail), and lightning strikes [extending] from northern Lake Michigan southward into northeastern Illinois”.

Multiple tall structures in the Chicago metro area were struck by lightning during the heavy snowfall.

It might be only the second time a special marine warning was issued for snowspouts. On December 5, 2024, the Weather Service in Buffalo warned of a “band of thundersnow producing waterspouts”.

Yesterday’s swarm of snowspouts was well-predicted using a nomogram, or forecasting technique, first developed by Wade Szilagyi of the International Centre for Waterspout Research.

Great Lakes waterspouts commonly occur during the autumn and early winter months as frigid air blows down the still-warm lakes; it takes the lake waters several months to lose the heat they accumulated during the summer.

The warm lake waters heat the air directly above, allowing air pockets to rise and form rain or snow showers. Sometimes, that rising air vertically stretches small eddies or invisible twists of wind near the surface, forming waterspouts.

The greater that temperature contrast between the lake waters and the air above, the greater the “equilibrium level”, or the height to which lake-warmed air pockets can rise.

Given a near record-warm Lake Michigan and a near record-cold air mass, lake-effect snow showers were able to grow to heights nearing 25,000ft (7620m) – tall updrafts perfect for creating waterspouts.

Do winter waterspouts ever come ashore? Not really. They need the warm lake waters to sustain their air currents. Land temperatures are much cooler, so that contrast no longer exists.

But there have been a few cases of legitimate snow tornadoes.

A snow tornado hit Andros Island in Greece on January 24, 2022.

A tornado descended out of a snow squall near Tinian, New Mexico, on February 17, 2019.

And on November 23, 2013, a rotating snow-producing thunderstorm dropped an EF1 snow tornado that destroyed a barn in Ontario, Canada.

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