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On the lookout: Lake-effect snows

When knee-deep snow and whiteouts are winter fixtures

So much of meteorology is a matter of scales. Weather can be as small as a brief onshore flow of wind (an example of a microscale event) or as big as a 3,000-nautical-mile dip in the jet stream (definitely a global scale event).


Lake-effect snows often form in bands of varying density. Some areas can be completely clear, but just a few miles away there could be white-out conditions.In between those extremes are smaller events that escalate in size and impact—from supercell thunderstorm clusters (mesoscale) to frontal systems, hurricanes, and extra-large high- and low-pressure centers, which fit in what are called synoptic scale events.

Various types of mesoscale and synoptic scale weather are often associated with the geography that helps them thrive. So, we have tornado alley in the Midwest, southwest monsoons in Arizona, and an area famous for lots of lightning east of Tampa, Florida.

The Great Lakes make news as home of lake-effect snows, which are well known for their ability to suddenly dump several feet of snow on the windward shores of the states bordering them, as well as reducing visibilities to low-IFR status—or lower. That’s when airports like those around Buffalo, Watertown, Erie, Cleveland, and many other nearby locations shut down until conditions improve.

This surface analysis chart identifies areas of lake-effect snow with white and gray stripes. Lake-effect snows are mainly caused by synoptic features, like the low pressure systems to the north and northwest. When cold fronts pass over the warmer water of the Great Lakes, the conditions are right for lake-effect snows.So how did we get the term “lake-effect” to describe these snows? It helps to know that the worst of these snows happen in November and early December. In late autumn the lakes haven’t yet had a chance to become cold enough to freeze, and the water temperature may be in the 50-degree range. So any subfreezing, fast-moving winds aloft passing over them encounter the warmer lake air below. Cold air aloft paired with warm air beneath is a setup for instability, so the warmer lake air is drawn into the colder air aloft, where it condenses into clouds, creating snow crystals.

Typically, strong cold fronts descending from Canada start the process, which can last several days. Sometimes several lakes will generate lake-effect snows, other times the snowfalls are more localized. In extreme cases, strong winds can blow lake-effect snows deeper into Michigan, Ohio, Pennsylvania, and New York state, and even reach the Appalachian Mountains. Whatever the case, lake-effect snows are well-advertised in aviation weather reports and briefings, so they shouldn’t be a surprise for any well-briefed pilot. And as winter progresses the lakes can freeze over, ending moisture transport to the air and ending the lake-effect snow season.

Lake-effect snows are well-advertised in aviation weather reports and briefings, so they shouldn’t be a surprise for a well-briefed pilot.

Lake-effect snows aren’t the only aviation hazards around the Great Lakes. Winter weather can also feature clear, mixed, and supercooled large droplet (SLD) icing conditions. These are other types of synoptic scale events native to the region, and why NASA’s Glenn Research Center spent so much time pioneering the study of SLD—and flying in it. Of course, The Glenn Center is located on the Cleveland-Hopkins International Airport (CLE). At its icing wind tunnel facility, the slogan is “We Freeze to Please.”

As a newly minted instrument pilot I had an up-front view of lake-effect snow and icing conditions. Lake-effect clouds can have low tops, so my approach to Erie, Pennsylvania’s International Airport/Tom Ridge Field (ERI) began at 6,000 feet, where I was in clear air. But the airport was experiencing instrument conditions, so I had to descend to fly the ILS to Runway 24. Into the clouds I went. It took but two or so minutes to break out, but my Skyhawk was covered with an inch-thick encrustation of mixed ice. Before I left for the hotel, I went back to the airplane to lock it. There on the ground was the Skyhawk’s perfect, icy outline on the ramp.

I was feeling pretty embarrassed about the sight. But then an arriving Beechcraft Duke taxied in and shut down next to me. Its long, pointy nose was adorned with what looked like a bucket-shaped cone of solid ice. After the pilot climbed out of the airplane, he said “I took off, this happened, so I turned right around, came back, and I’m staying until this is over.” So did I.

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Thomas A. Horne

Thomas A. Horne

AOPA Pilot Editor at Large
AOPA Pilot Editor at Large Tom Horne has worked at AOPA since the early 1980s. He began flying in 1975 and has an airline transport pilot and flight instructor certificates. He’s flown everything from ultralights to Gulfstreams and ferried numerous piston airplanes across the Atlantic.

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