Mild Winter Result of Positive Phase of North Atlantic Oscillation

The sun is shining and the temperature is in the 50’s, but that will all change tomorrow, and meteorologists are forecasting snow and cooler temperatures.

The change comes on the heels of the 15th warmest December on record, with an average temperature of 35 degrees Fahrenheit, according to the National Weather Service.

Ryan Zimmerman, meteorologist and Patch contributor, said he expects this winter season to relatively mild overall. The weather consultant said this is due to the shift in phase of the North Atlantic Oscillation from negative to positive. In general, the last four years were in the negative phase.

“The jet stream is configured in a way where cold air is forced down from Canada and in a positive phase it’s the complete opposite, where the air mass is coming in from the Pacific Ocean,” Zimmerman said. “The jet stream is more west to east than coming in from Canada.”

Earlier:

The jet stream is a river of air in the atmosphere 30,000 feet in the air that guides storm systems, Zimmerman said.

Local businesses are noticing different weather-related patterns.

Jack Capozzoli, owner of , said the weather definitely affects his business.

Because there hasn't been a lot of snowfall, patrons aren't buying as many boots, Capozzoli said, but it has been easier for his older customers to get to his store.

The ideal winter weather for the shoe business is some snow and slush mixed in with warmer weather, Capozzoli said. Road salt destroys shoes and when weather conditions are manageable, customers will come in to buy "everyday shoes" to replace salted or wet shoes.

The lack of snow cover this season over the northern part of the country was another cause of the overall higher temperatures, Zimmerman said. The lack of snow cover blocks arctic air masses from coming down from Canada.

“With a lack of snow you also get more sunlight that can radiate down and increase temperatures,” Zimmerman said. “When you have snow on the ground it reflects light back up into the atmosphere.”

Zimmerman said he wasn’t sure how long the positive phase will last, and that sometimes the weather switches back and forth between the two phases within a single season.

Generally speaking, we were in the negative phase from 2007 to 2011, and in the positive phase from 2005 to 2007, Zimmerman said.

“It’s really hard to forecast, especially looking farther out, because you don’t know how long the cycle will last,” Zimmerman said. “It’s really hard to determine. It would seem we’re on a four to five year cycle, but it could flip flop in the future.”

Zimmerman forecasted three to five inches of snow for Thursday. He said in an average winter season, Nov. 1 to April 30, we usually pick up about 36 to 37 inches of snow, last year we had 57 inches, and he forecasted 20 to 25 for this season.

Des Plaines resident Frank Floss, 34, said he took his dog Rocky to the Park Ridge dog park more in December because the weather was warmer.

Floss is a project manager for a local construction company and welcomes the warmer weather.

“Keep your fingers crossed for all of us who work outside,” Floss said.

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