IRON MOUNTAIN — Winter may turn much colder about a week from now.

“Changes are taking place in the atmosphere above the Arctic Circle that suggest the clock is ticking on the mild weather — for January standards — gripping much of the United States,” AccuWeather meteorologist Paul Pastelok said. “Signs are pointing toward cold air outbreaks that will begin during the third week of January.”

The polar vortex keeping Arctic air trapped is weakening, he explained. This will allow frigid air to push southward into the U.S.

“After the first surge of Arctic air, there are likely to be additional waves of cold air that spread from the Central states to the Eastern states during the latter part of January and into early February,” Pastelok said.

An active storm track and a lack of ice on the Great Lakes may bring increased chances for snowfall in the coming weeks, he added.

For the Iron Mountain-Kingsford area, a long-range forecast from the National Weather Service is neutral on temperature trends from now through end of March. The model slightly favors above-normal precipitation.

That forecast is partly based on La Nina conditions — a cooling of sea-surface temperatures in the central Pacific Ocean — that may persist into spring. La Nina winters typically favor increased snowfall in the upper Midwest.

To date, the local winter has been mild. Temperatures in December averaged 24.4 degrees at the Iron Mountain-Kingsford Wastewater Treatment Plant, which is more than 4 degrees above average.

It ranks as the fifth-warmest December this century, but well below the warmest December since record-keeping began around 1900. The warmest December was in 1913, at 31.9 degrees.

The highest temperature last month was 48 degrees on Dec. 12 and the lowest was minus-6 on Dec. 29 and Dec. 30.

Snowfall for the month totaled 6.4 inches, which was more than 6 inches below average. The maximum snow depth for the month was 5 inches — about 4 inches below normal. Water-equivalent precipitation last month measured 0.64 inches, which is 0.95 inches below average.

The dry December kept 2020 slightly below the ranks of record precipitation. As it is, the total of 36.97 inches was nearly 7 inches above average and ranks as the fifth-wettest year since the early 1900s.

The wettest year on record was 39.31 inches in 2017, while 2019 was a close second at 39.3 inches.

Temperatures during 2020 averaged 43.7 degrees, which was 1.8 degrees above the all-time historical average and 1.1 degrees above the average since 2000. It was the seventh-warmest year this century.

The warmest year on record at Iron Mountain-Kingsford was 1987, when temperatures averaged 46.9 degrees.

Jim Anderson can be reached at 906-774-3500, ext. 226, or janderson@ironmountaindailynews.com.