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What Causes Lake Effect Snow? | CNN


It takes just the right conditions to produce lake-effect snow, but when they come together it creates some of the most extreme winter weather anywhere in the world. Perfectly blue skies can turn into a blinding blizzard in minutes, producing amounts of snow that will bury your ruler in a matter of hours.

According to CNN meteorologist Brandon Miller, the Great Lakes are the only place in the United States where lake-effect snow occurs, except occasionally at the Great Salt Lake in Utah.

But what exactly is lake effect snow?

Miller said it happens when very cold, windy conditions form over a not-so-cold lake. The lake could be 40 degrees, he said, and the air zero degrees.

“That difference in temperature creates some instability, and the water provides a source of moisture,” Miller said. “When it comes over land, it deposits water vapor like snow.”

Lake-effect snow generally does not fall over water because it takes the friction and topography of the land to move the snow out.

Winds usually blow from west to east in the Northern Hemisphere, so lake-strengthened snow is pushed toward the eastern side of the Great Lakes, Miller said.

Lake-effect snow can be very localized, especially when hills and mountains can cause these small weather systems to fail and deposit a lot of precipitation in one place.

“You can have 20 to 30 inches of snow, and five miles away just a few inches,” Miller said.

The National Weather Service webpage on lake-effect snow says that “wind direction is a key component in determining which areas will receive lake-effect snow. Heavy snow can fall in one spot, while the sun shines only a few miles away in either direction. ”

Patrick Harden clears snow from the roof of his car in Erie, Pennsylvania.

Upstate New York and the cities of Rochester, Buffalo and Syracuse are the hot spots — perhaps they should be called cold spots — for lake-enhanced snow in the United States, Miller said.

That area is east of Lake Erie and Lake Ontario, which are oriented more east-west than the other Great Lakes. That means there’s more time and distance for the lake-enhanced snow to build up, Miller said. In meteorological parlance, that’s called a longer “fetch”.

And lake-effect snow can pile up with amazing speed.

The incidence of lake-effect snow decreases as we move deeper into winter, he said. The lake water becomes colder and there is less difference with the air temperature.

Lake Erie often freezes over because it is the smallest and shallowest of the Great Lakes. “When the lake freezes, the lake-effects machine effectively shuts down,” Miller said.

The Great Salt Lake sometimes produces lake-effect snow, but not much because it is not as large as the Great Lakes.

Japan is suffering from something even bigger and worse than lake-effect snow: ocean-effect snow, where the effects are amplified by mountain ranges.

“You can see a hundred centimeters in a week of the snow with the ocean effect,” Miller said.

Traffic in Buffalo, New York, came to a halt in January 2017 when lake-effect snow clogged the city's roads.

The link between lake-effect snow and the climate crisis is complicated, but scientists have observed a slight increase in the annual amount of lake-effect snow around the Great Lakes since 1930, and they expect it to continue to increase slightly through the middle of 2010. this century.

That increase is due to two things: warmer water temperatures in lakes and a shorter time that the lakes are covered with ice in winter.

When cold air blows over warmer lake water, it can absorb more moisture and lead to greater amounts of snow downstream. In the same vein, if lakes are ice-free for longer in the winter season, that creates the potential for more lake-effect snow events, as lake-effect snow generally requires the lakes not to be ice-covered.

Ultimately, scientists think the increase will stop — possibly around the middle of this century — if air temperatures continue to rise due to global warming from fossil fuel emissions. One of the most important requirements for a lake-effect blizzard is cold air. As that air warms, it will be less and less likely to be cold enough to produce snow.

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