DULUTH, Minn. — Deep snow on the ground has been hampering deer movement in parts of northern Minnesota and, if current weather trends hold, the winter of 2019-20 could go down as a tough one for whitetails.

There’s 2 feet or more of snow on the ground across much of northeastern Minnesota and more than 3 feet in parts of Lake and Cook counties.

Tom Rusch, Minnesota DNR wildlife manager based in Tower, said the agency's winter severity index, or WSI, as of early February is indicating significant deer mortality if the deep snow holds into late March.

“And it could be really bad if the snow keeps well into April,’’ Rusch said.

WSI levels already sat in the mid-80s in northern St. Louis County as of Friday. With one point awarded for each day with at least 15 inches of snow on the ground, and one for each day with below-zero temperatures, those numbers likely will rise to near 150 by April, Rusch noted.

“And that (a WSI of 150 or above) is getting to be a severe winter,’’ he said.

In a normal winter, with final April WSIs below 100, about 10% of deer perish. In severe winters, more than 40% of adult does have perished. The most severe winter in recent years, 1995-96, saw WSI readings over 200 in some areas.

Rusch said deer already are reducing their movement to conserve energy because deep snow is so hard to move around in. And he said a lack of quality winter cover for deer, namely conifers and cedars, is making the problem much worse.

“Deer in our area traditionally wintered in old aspen that had a significant understory of balsam," he said, but added that the "habit is gone now’’ after the large aspen was logged off.

“Deer need food and cover," he said. "There’s plenty of young aspen for food. What they are lacking is winter cover.”

Deer numbers hit all-time highs after a series of low-snow winters in the late 1990s and early 2000s, Rusch noted. Now, after multiple deep-snow winters since 2013, winter has brought deer numbers back down.

“The wolves have always been there, even when we had record deer populations,’’ Rusch said. “The problem is wolves combined with deep snow and a lack of winter cover.”