Windchill of 35 below.

That's the magic number, Minneapolis students.

For school to be canceled, that's how extreme the windchill must be under the school district's newly revised weather policy. As of Monday morning, the Twin Cities just missed that threshold.

As daybreak arrived and the winter holiday break ended, the National Weather Service (NWS) reported windchill readings in the 20s below zero across the metro. Actual temperatures ranged from minus 9 in Lake Elmo to 15 below in Lakeville, the NWS added.

By afternoon, highs in the metro will struggle to get into positive territory, and a modest dusting of snow is in the forecast late in the day.

Last year, more intense windchills prompted Gov. Mark Dayton to cancel what would have been the first day of school after students returned from winter break. So far, no districts in Minnesota have called off classes Monday, despite subzero temperatures throughout the state and windchills in the minus-40s in much of northern Minnesota.

There were few problems related to frigid weather Sunday, when the afternoon high reached only 1 below. John Ward, of CenterPoint Energy, said that calls for broken furnaces were up only a little bit, while the State Patrol said there weren't any big problems in northwestern Minnesota or in the Twin Cities on Sunday, despite icy roads and blowing snow on Saturday night.

In northern Minnesota, the high temperatures in Bemidji and International Falls were 12 below and 14 below, respectively. In Duluth, where the Spirit Mountain ski area was shut down Sunday, the high was 1 below.

In St. Paul, only a handful of people came to the outdoor skating rink at Rice Park on Sunday, the warming-house attendant said. About 2 p.m., just five or six people were on the ice. But on Lakes of the Isles in Minneapolis, about 40 people were enjoying the rink.

It shouldn't be quite as cold on Tuesday, with lows around 5 below and light winds, making for windchills in the 15- to 20-below range. The cold weather is expected to last at least through Wednesday, the National Weather Service's Andy Lahr said.

More certainty for parents

One thing is certain — Minneapolis and St. Paul public schools are heading into the new year armed with new, detailed weather policies that firmly identify the temperature threshold that would merit classes being canceled.

For Minneapolis, that's a 35-below windchill by 6:30 a.m., with wind gusts between 5 and 10 miles per hour or greater.

In St. Paul, classes would be canceled if the forecast for 6 a.m. called for windchills to reach 40 below or if the air temperature hits 25 below.

"Parents would know the day before by 6:30 p.m., according to our policy," said Toya Stewart Downey, assistant director of communications for the St. Paul district.

As of Sunday night, neither school district had canceled classes for Monday. Minneapolis Schools tweeted: "Bundle up tomorrow, it's going to be cold!"

The St. Paul district echoed that approach with its own tweet: "It's going to be cold, so please dress accordingly."

Last year's frigid temps

Consider it one good thing to come out of last year's polar vortex, the cold air mass that settled over Minnesota for much of January.

Last year, Dayton took the unusual step of canceling classes on Jan. 6 after temperatures fell to 22 below and windchills were 48 below in the Twin Cities. It felt like 63 below at the Grand Marais airport that day.

Most school districts canceled classes four more times that month, a rarity in cold-hardy Minnesota.

When windchills approach 30 below, exposed skin can freeze in about 10 minutes, making the thought of students waiting outside for a bus incomprehensible for most school leaders.

In fact, several Minnesota private schools last year began experimenting with holding classes online when weather conditions made it unsafe for students to travel to and from school. More have pledged to do likewise this year, should conditions warrant.

Star Tribune staff writers Paul Walsh and Pat Pheifer contributed to this report.

Kim McGuire • 612-673-4469