A Frost Advisory stretches across a wide swath of Minnesota, Wisconsin and Michigan’s Upper Peninsula from midnight tonight through Monday morning, with temperatures forecast to fall as low as 29 degrees in the coldest spots.
Northeast Minnesota and Northwest Wisconsin: Frost Advisory Details
The NWS Duluth office has the advisory in effect from midnight tonight to 8 AM CDT Monday across a broad stretch of its forecast area.
In Minnesota, that includes northern Aitkin, Pine, South Itasca, Carlton and South St. Louis counties, where temperatures as low as 35 degrees are expected, along with Koochiching, North Itasca, Central and North St. Louis, and northern Cook and Lake counties, where lows could reach the lower to middle 30s.
Across the state line in Wisconsin, Burnett County could see temperatures as low as 33 degrees, while Douglas, Bayfield, Ashland, Iron, Washburn, Sawyer and Price counties are forecast to drop into the lower to middle 30s.
Forecasters note that areas inland from Lake Superior, including southern Douglas and Bayfield counties, carry the greatest frost risk, while areas right around Superior are less likely to see it. Grand Rapids, Duluth, Hinckley, Grantsburg, Ashland, Hurley, Washburn, Bayfield, Spooner, Hayward and International Falls are among the cities covered.
Northern Wisconsin: The Northwoods Add to the Cold Pocket
The NWS Green Bay office extended the same overnight advisory into its territory, covering Langlade, northern Marinette and northern Oconto counties, where temperatures as low as 34 degrees are forecast, and Lincoln, Oneida, Vilas, Florence and Forest counties, where lows in the lower to middle 30s could dip a few degrees below freezing for a couple of hours around sunrise. Antigo, Rhinelander, Crandon, Merrill, Tomahawk and Eagle River are all included.
Michigan’s Upper Peninsula: The Coldest Numbers of the Night
The lowest temperatures in the advisory belong to the NWS Marquette office‘s territory. Baraga, Iron and Gogebic counties could see temperatures as low as 29 degrees, while Dickinson, Ontonagon and southern Houghton counties are forecast to bottom out near 30 degrees. Ironwood, Iron River, L’Anse, Ontonagon, Kenton and Iron Mountain are all in the advisory area.
A Clear, Calm Night Sets Up the Cold
The setup is a classic one for the Northland in mid-September: clear skies and light winds overnight allow the ground to radiate heat away quickly, letting temperatures fall well below the afternoon high. Areas away from the moderating influence of Lake Superior, and low-lying spots where cold air naturally settles, are seeing the advisory extend well outside the immediate lakeshore.
What It Means for Gardens and Farms
Frost can harm sensitive outdoor vegetation, and uncovered tender plants may not survive the night. Home gardens with tomatoes, peppers, squash, herbs and annual flowers are the most vulnerable, while hardier crops already nearing harvest are generally less affected.
How to Protect Tender Plants
Take steps now to protect tender plants from the cold. Covering garden beds with sheets, towels or frost cloth before dark can trap enough heat from the soil to keep plants a few critical degrees warmer overnight. Potted plants can be moved indoors, into a garage or under a covered porch until the sun is back up.
Anyone with a garden still producing frost-sensitive vegetables should consider harvesting what they can before nightfall, since even a light frost can end the season for the most tender plants.
What Comes Next
The cold snap is short-lived. Widespread showers with embedded thunderstorms are expected to move into the Northland on Monday, bringing warmer, more humid air behind the overnight chill and effectively closing out this round of frost risk as the pattern turns wetter into the new week.
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