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What exactly is lake effect snow?

Katie Raymond
Michigan Radio
Cold air blows across the land, turning into heat and moisture once it passes over unfrozen lake water. The heat and moisture then begin to form a small cloud that precipates snow as it grows to be an even larger cloud over cold land.

As a Michigander, it’s likely that you’ve heard of and experienced lake effect snow. For those hailing from the West side or Northern parts of the state, it's not uncommon to hear the term whenever a big snowstorm is in the forecast. This winter has - so far - been fairly calm in terms of lake effect snowstorms, but that could change as large portions of the country prepare for a potentially hazardous snowstorm to hit over the weekend.

gif image showing weather patterns across the country
Credit NOAA

According to Accuweather, the storms forecast for this weekend could bring bouts of Arctic air with "staying power that could keep the lake effect snow machine running at full speed." The National Weather Service is calling for five to eight inches of snow in the Grand Rapids area, with winds up to 40 miles per hour. Southeast Michigan will see similar snow accumulation, but with slower wind gusts. 

The Keweenaw Peninsula is usually hit hard with lake effect snow and those living in Keweenaw and North Houghton counties can expect snow accumulation between 10 and 18 inches, with wind gusts up to 35 miles per hour. 

But for as much as we talk about lake effect snow, what exactly is it? 

A hazardous weather event 

According to theNational Oceanic and Atmospheric Administration, lake effect snow “is one of the most hazardous weather events in the Great Lakes region.”

“Lake effect snow is snow that’s not necessarily associated with an actual weather system," said Patrick Bak, a National Weather Service Warning Coordination Meteorologist. “It can happen when you have cold water moving over the relatively warm waters of the Great Lakes.”  

Randall Schaetzl, professor of Geography at Michigan State University, explains what happens once the cold air moves across warm water.

“[Cold air] picks up moisture, and that cold air can’t hold all that moisture and so when it gets to the land, the air is typically forced upward over low hills that forces the air to rise," he said. "Rising air typically cools and cool air can’t hold as much moisture, so the snow comes out.”

To simplify it, Accuweather explains that when "moist air from the Great Lakes is forced over the land and rises in elevation, the rain or snow is released."  With the warmer temperatures we've experienced so far this winter, there is less ice cover on the Great Lakes. Because of this, the fairly warm and open waters will "lead to towering clouds of moisture" which will, in turn, bring bands of snow across the region. 

When does it occur?

According to Scheaetzl, right now is prime time for lake effect snow. 

“Most of the strongest lake effect snow is going to be early in the winter when the lakes are still warm and can evaporate,” said Scheatzl. 

As we approach mid-winter and beyond, lake effect snow is less likely to occur because the temperature of the lakes have dropped too low, making them less able to provide water vapor for lake effect snow. 

What are the key characteristics?

“Lake effect snow comes in waves,” Schaetzl said. “You get real heavy snow and then you might get an opening in the clouds as you’re kind of between lake effect bands.” 

Basically, because of the gap between bands, lake effect snow can look very different depending on where you are. You could see clear skies in between a band, or you could experience heavy, potentially white-out conditions directly under a band.  

Which areas get hit the hardest? 

Certain areas get hit harder with lake effect snow.

“The areas that get hit the hardest with it are the northern half of the upper peninsula and northwest lower Michigan, also southwest lower Michigan can get some as well,” said Bak. 

Lake effect snow is greatest when you are upland, any downwind locations from the lake will get hit. The Keweenaw Peninsula is a huge lake effect snow area. 

"Not only is [the Keweenaw Peninsula] just down wind from an open water body, the air is colder up there than it is when it crosses Lake Michigan and you’ve got a lot of topographic bump because the spine of the Keweenaw is quite high," said Scheatzl.

With any potentially hazardous weather conditions, the National Weather Service warns drivers to slow down and use caution while driving. If you don't need to be outside, stay inside.

Here is some of our previous coverage on winter weather:

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