This post was originally published on snow.news, my free Substack on snow science and the state of the snowpack.
When cold air passes over a relatively warmer lake, prodigous snowfall totals may be experienced downwind. This phenomenon, known as lake effect snow, is a prominent feature of winter weather around the Great Lakes, but it also affects other regions, such as the Wasatch Mountains near Utah’s Great Salt Lake.
The graphic below from the National Weather Service explains how lake effect snow works. When a cold air mass sweeps across a lake, moisture evaporates from the lake’s surface and rises in the atmosphere. As the moisture rises, it cools and condenses into clouds, eventually producing snowflakes. The effect really takes hold on the lee side of the lake as the wind pushes the moisture-laden clouds over land, especially if there’s any elevation gain.
Here’s another diagram, this one from the National Snow and Ice Data Center.
The satellite image below shows the effect at work over the Great Lakes.
“Lake effect snow usually occurs during the late fall and winter months and is capable of producing as much as 2-3 inches of snow an hour with event totals ranging from 60-100 inches,” according to NASA. The process is known as bay effect snow and sea effect snow when the cold air passes over those types of water bodies.
Narrow, intense bands of precipitation are a hallmark of lake effect snow, and these squalls can lead to vastly different conditions over short distances.
“It is not uncommon for sunny skies at a particular location to be quickly replaced by blinding, wind-driven snowfall in a matter of minutes,” according to the National Weather Service. “Similarly, snowfall accumulations can vary from a trace to several inches over a short distance.”
Lake effect snow is why some areas around the Great Lakes are known as “snowbelts,” as shown in the map below.
The map below shows an example of a November 2022 storm that dumped up to 81.2 inches in New York.
In the American West, the most famous example of lake effect snow takes place downwind of the Great Salt Lake. I recently enjoyed reading Jim Steenburgh’s Secrets of the Greatest Snow on Earth, in which he devotes an entire chapter to explaining how the lake can amplify snowfall in the nearby Wasatch Mountains.
“Conventional wisdom and marketing hype suggest that the Great Salt Lake effect is the holy grail of Utah powder skiing,” writes Steenburgh.
But the truth is more complicated.
“No Wasatch weather phenomenon is more misunderstood than the Great Salt Lake effect,” he writes, noting that the effect is “incredibly difficult” to forecast.
“In fact, it is so difficult that meteorologists call it the dreaded lake effect (DLE), although we use saltier language in private,” writes Steenburgh, professor of atmospheric sciences at the University of Utah and creator of the wonderfully named blog, Wasatch Weather Weenies.
The lake’s high salinity lowers the freezing point of water, so it never freezes except near freshwater inlets, but that salt water also doesn’t evaporate as readily as freshwater. It takes a special combination of atmospheric conditions to get the Great Salt Lake to produce lake effect snow, and Steenburgh makes a good case for discounting the influence.
“On average, lake-effect periods generate about 5 percent of the snow that falls in the Cottonwoods each winter,” he writes, referring to the two canyons that are home to Alta, Snowbird, Brighton, and Solitude ski areas. “Most skiers and snowboarders are surprised the percentage isn’t higher, but marketers and industry promoters suffer from delusions when it comes to the Great Salt Lake effect.”
