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Great Lakes ice cover forecast: Less than average, for third straight year

Posted Dec 6

By Kelly Reardon, cleveland.com

CLEVELAND, Ohio - For the third season in a row, Great Lakes ice coverage is forecast to remain below average through the upcoming winter, although the numbers are still highly debated.

Jia Wang, a climatologist with the National Oceanic and Atmospheric Administration, predicts the five lakes to peak at 44 percent ice coverage, after the past two winters of scarce coverage, he told Ideastream.

Historically, the mean maximum ice coverage for the Great Lakes is around 55 percent.

With less ice, more of the lake surface is exposed, leading to more lake-effect snow. Cold winds pick up moisture from the water and dump heavy snow when they hit land. For Northeast Ohio, that lake-effect band is generally targeted east of Cleveland.

The forecast

Lake Erie and Superior are expected to get the most ice coverage this year, at 82 and 54 percent, reports Ideastream. That's not surprising considering Lake Erie is the shallowest, and Lake Superior is one of the coldest lakes.

The Great Lakes Environmental Research Laboratory found the variability of Great Lakes ice cover is heavily influenced by two large-scale climate drivers: ENSO (the El Nino Southern Oscillation) and the North Atlantic Oscillation or Atlantic Oscillation.

The Great Lakes Integrated Sciences and Assessments team says other factors influence Great Lakes ice coverage as well, including recent air temperature trends and evaporation from the lakes preceding winter.

Overall, low ice cover years are preceded by less evaporation from the lake, leading to less heat loss. High ice cover years are marked by more evaporation from the lake surface, leading to higher heat loss. The warmer air is, the greater its ability to take in moisture from a lake. 

How temperature and evaporation affect Great Lakes ice coverage. (NOAA)

El Nino and La Nina are two of the three phases of a natural cycle called ENSO - the El Nino/Southern Oscillation - across the tropical Pacific. ENSO oscillates between El Nino conditions, neutral conditions, and La Nina conditions.

According to the National Oceanic and Atmospheric Administration, each full ENSO cycle lasts three to seven years, but within the cycle, weather patterns are irregular. La Nina generally follows El Nino with neutral conditions in between, but there are no guarantees. Sometimes the neutral condition break between El Nino and La Nina can be skipped.

The two phases have a global effect on both temperature and moisture conditions. El Nino typically leads to warmer, drier winters for the northern portion of the United States, while La Nina leads to the opposite conditions.

The Arctic Oscillation is a climate index of the state of atmospheric circulation over the Arctic, consisting of a positive and negative phase. With the negative phase, the polar vortex over the Arctic is weaker, resulting in weaker upper-level winds called the westerlies. When the westerlies weaken, cold, Arctic air is able to surge south into the United States. In the positive phase, the polar vortex circulation is stronger, forcing the cold air and storm tracks to remain farther north.

"The North Atlantic Oscillation and Atlantic Oscillation are two separate indices that are ultimately describing the same phenomenon of varying pressure gradients in the northern latitudes and the resultant effects on temperature and storm tracks across the continent," explains NOAA.

The NAO consists of two pressure centers in North America, one area of low pressure near Iceland and another area of high pressure near the Azores, an island chain located in the eastern Atlantic Ocean. "Variations in the strength of these features significantly alters the alignment of the jet stream, especially over the eastern United States, and ultimately affects temperature and precipitation distributions in this area," according to NOAA.

To read the story with photos and graphs, please visit: http://www.cleveland.com/weather/blog/index.ssf/2017/12/ice_cover_on_great_lakes_forec.html

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