Great Lakes warmer than usual; will that be a recipe for lake-effect snow this winter?

MICHIGAN - Michigan's start to winter should be wet, scientists say. But it's still unclear whether you will need a snow shovel or umbrella.

Great Lakes surface-water temperatures are significantly warmer than usual for this time of year, the result of a late August and September that felt more like July. That means there will be more water vapor above the lakes.

That's often a formula for heavy lake-effect snow, scientists say. But it all depends on the temperature of the air flows over the lakes.

"You get a greater temperature difference between the lake water and the air above it, in general, you would expect heavier lake-effect precipitation," said Jonathan Erdman, senior meteorologist with The Weather Channel and weather.com. "The trick is, is the air above the lakes cold enough to support snow?"

Very often in Michigan, winter air patterns send very cold air from the Canadian Arctic southeast over the Great Lakes. And warm surface waters, with frigid air passing over them, generally act like a snow-making machines, particularly in the northern Upper Peninsula, the northwestern Lower Peninsula and along Lake Michigan's eastern shoreline.

Last year, lake-effect snow was "relatively a dud" in most of the region's typical snow belts, even though the lakes were warm and there was little ice cover, Erdman said.

That was despite last year's La Niña, a condition of colder temperatures in equatorial regions of the Pacific Ocean that have significant impacts on global weather, and that typically mean colder air over the Great Lakes region.

That didn't happen last year because the jet stream didn't cooperate, Erdman said.

 

The jet stream, narrow bands of strong wind in the upper atmosphere that typically move west to east over North America and drive weather conditions, dipped in such a way last winter that cold air was mostly confined to the Pacific Northwest, leading to one of the tamest winters in recent memory in the Great Lakes region and elsewhere.

Absent a large area of high pressure in the atmosphere blocking the jet stream's west-to-east flow and pushing cold air south over the Great Lakes, temperatures might be too warm for lake-effect snow this winter, too, at least to start, Erdman said.

"(Tuesday) in Buffalo, they had a really nice lake-effect band coming off Lake Erie — it was as close to classic lake-effect snow conditions as you can see," he said. "But the temperatures were too warm, so they basically had rain — they had maybe a tenth of an inch of wet snow at the airport.

"Wetter can mean a lot of things. Does it mean more rain? Snow? System snow as opposed to lake-effect snow? It's kind of a mixed signal this year."

Michigan's rainy autumn hasn't featured much snow yet, because colder air has been "bottled up" in the Plains states and northern Rocky Mountains, Erdman said.

"It will be wetter (in the Great Lakes region), but from November into early December, how much of these events are rain events instead of snow events? It's a tough call," he said.

The Climate Prediction Center predicts a 55% to 65% chance that a La Niña will develop during the fall and winter of 2017-18. 


Nikk Baxter, 27 of Fenton enjoys the record-setting weekend weather at Pontiac Lake Recreation Area in Waterford, Michigan, on Feb. 28, 2017. A repeat of last year's La Niña weather conditions could mean mild conditions to come again -- but only if the jet stream and the cold, Canadian Arctic air it carries in winter are mostly held above the Great Lakes. (Photo: Eric Seals, Detroit Free Press)

According to scientists, as of Oct. 31, surface water temperatures in the Great Lakes ranged from 3.2 degrees Fahrenheit warmer than average on Lake Superior to almost 6 degrees warmer on Lake Erie. Three of the five Great Lakes — Huron, Erie and Ontario — are even warmer this year than they were last year at this time, when a mild fall transitioned into one of the more mild winters in recent memory.

"It looked for awhile this year like the temperature was way below normal on Lake Erie; but then we got that August and September warm spell and, zip! Up it goes," said George Leshkevich, a physical scientist at the National Oceanic and Atmospheric Administration's Great Lakes Environmental Research Laboratory in Ann Arbor.


Archie Tharrett, 30, shovels snow for his grandmother, aunt, and a couple of neighbors on Sunday, Dec. 11, 2016 in the Woodbridge neighborhood in Detroit. (Photo: Elaine Cromie, Elaine Cromie, Detroit Free Pres)

For snow-haters, the worst scenario is periods of cold, followed by warm-ups, Leshkevich said.

Consistently cold air can very quickly draw the warmth from the Great Lakes surface waters, helping ice cover to develop that lessens the ability for lake-effect snows, he said.

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© 2017 Detroit Free Press


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