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'Perfect storm' of conditions leads to above-normal ice cover

Feb 26, 2018 09:16AM ● Published by Editor

Graphic from N.O.A.A.

By Steve Zucker of The Petoskey News

With this winter's wide weather swings, it may be surprising for some to learn that the Great Lakes saw their ice cover percentage reach well above the average yearly peak.

Although this winter has chilled Northern Michigan residents at times with stretches of below-zero temperatures, those have been punctuated by several mid-season warm-ups featuring numerous days with well-above-normal temperatures.

Although this year's Great Lakes peak ice coverage did not approach the nearly completely frozen-over conditions the lakes saw in the winters of 2013-14 and 2014-15, the lakes did see a peak ice coverage at about 69 percent around Feb. 11, according to data collected by the National Oceanic and Atmospheric Administration's Great Lakes Environmental Research Laboratory.

In fact, on that date, the agency reported that Lake Erie was about 91 percent frozen over, Lake Michigan was at 51 percent, Lake Huron was at about 81 percent, Lake Ontario was at 15 percent, Lake Superior was at 77 percent and Lake St. Clair was nearly 94 percent covered.

Indeed, even as of Saturday, the Great Lakes were reported to be nearly 49 percent covered by ice. Last year at the same time, the lakes were just 6.2 percent covered and at the same time in 2016 they were just 12.9 percent covered by ice.

The average peak ice coverage for the Great Lakes since officials began recording data around 1973 is about 55 percent. As for yearly maximum ice coverage, the highest was recorded in 1979 at 94.7 percent and the lowest was in 2002 at 11.9 percent. The second-highest (92.5 percent) and second-lowest (12.9 percent) yearly maximums for ice cover both occurred more recently — in 2014 and 2012, respectively.

Scott Rozanski, a meteorologist at the National Weather Service office in Gaylord, said the Great Lakes owes much of its ice cover this winter to a "perfect storm" of ideal ice-forming conditions that started in to mid- to late- January.

Rozanski explained there are numerous factors that impact how much and how quickly ice forms on the Great Lake.

He said a period of very cold weather in late December and early January primed the Great Lakes to "create a lot of ice very quickly."

He said the two other main factors that come into play are water temperatures and wind. He said the absence of wind during really cold spells not only provides a calm surface on which ice can form more quickly, but also keeps the water temperature at the surface more consistent, because wave action doesn't stir mix the colder layers with warmer layers of lake water.

When those cold temperatures came in, we did not have a lot of waves and ice was able to grow very, very quickly.

This was particularly noticeable during a period in early February from about Feb. 2 to Feb. 12, when daily highs were in the teens or low 20s and overnight lows were regularly in the single digits. During that same approximate time frame, from Jan. 28 to Feb. 12, the ice coverage on the Great Lakes grew from about 15 percent to the season peak of 69 percent.

Rozanski said now, even as ice coverage begins to wane for the season as spring approaches, winter's ice coverage can have multiple impacts that linger into spring and summer.

He said it can have an impact on lake levels, as water is lost by evaporation during the winter when there is more ice cover. Similarly, when ice is in place, it greatly reduces the potential for lake effect snow. He said it will also have an impact on how quickly the lakes warm up when warmer weather arrives. Correspondingly, cooler lakes often translate into somewhat cooler spring temperatures, especially near the lakeshore.

That means the common Northern Michigan springtime weather forecast of "cooler near the lakes" could be especially common this coming spring.

"Generally speaking, when you break a mid-winter pattern that trends toward what we seen recently, you will have a spring that last a little longer and it's a little harder to break toward warmer weather, especially near the lakes," Rozanski said

Lake Superior Ice Coverage Map. Click on map to enlarge. [GLERL Ice Concentration for Lake Superior]

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