Mild La Niña will likely mean a colder winter with average pile of snow in Wisconsin

Milwaukee Journal Sentinel

Bruce Bergman splits wood that will be tossed onto a pile of 60-70 cords at Michaels Tree Service in Fond du Lac, Wis. In an average year they will sell about 100 cords. Meteorologists are predicting colder than normal temperatures and an average amount of snow this winter because of a mild La Niña forming in the Pacific.

It might be hard to fathom just how much Pacific Ocean surface temperatures matter to folks in Wisconsin.

But they do. And as meteorologists carefully watch what could be a mild La Niña forming in the Pacific, the forecast for the Badger State is predicting colder than normal temperatures and an average amount of snow this winter.

Weak La Niña weather disturbances usually mean plunging thermometers in the Midwest and Great Lakes region, said Jack Boston, a senior meteorologist with AccuWeather.

"Late in December around Christmas time, that will be the first opportunity for an arctic air mass to come blasting in. That will be much more common in January and February where we'll get arctic shots," Boston said.

The forecast for the Badger State is predicting colder than normal temperatures and an average amount of snow this winter.

"That will be a whole lot different compared to last winter when temperatures averaged above normal. This winter will be noticeably colder than last winter because of La Niña."

Average high and low temperatures in Milwaukee are 33 and 20 degrees in December, 29 and 16 in January and 33 and 19 in February, according to the National Weather Service.

In Madison, the average high and lows are 31 and 16 degrees in December, 27 and 11 in January and 32 and 15 in February.

Winter snowfall for the months of December, January and February average 37.1 inches in Milwaukee and 37 inches in Madison.

Sea surface temperatures in the Pacific Ocean dictate the strength or weakness of jet streams passing over the United States, which in turn affect storms, Boston said. The difference between a weak and strong La Niña is how far below normal surface water temperatures in the Pacific are.

Atmospheric blocking is also a factor with La Niñas — when weather systems don't move for a period of time, locking Arctic air over a location.

"Everything is tied together. The atmosphere and ocean feed off each other," said Sarah Marquardt, a National Weather Service meteorologist based in Sullivan.

"What happens in the Pacific translates down into the United States. As things change in one part of the world, it affects things in another part," Marquardt said.