There can hardly be a better day to start the Winter Carnival, wouldn't you say?

Temperatures bottomed out before dawn Thursday at 20 below zero in the Twin Cities, but the metro is about to experience a warm-up of nearly 50 degrees.

Now put away those thoughts of convertible tops down and jogging with bare legs. Once the anticipated warm-up to 33 above comes and goes Friday, the National Weather Service says there's a below-zero high waiting around the corner in the Twin Cities come Monday.

But as for the here and now: A blast of cold air means that most every school kid has yet another day off, with some having to settle for a late start to class.

Lakeville was reporting minus 20 shortly after sunrise, with Crystal, Eden Prairie and Lake Elmo close behind at 17 below.

Elsewhere in Minnesota, there was not a single reading above zero: 36 below in Crane Lake in far northern Minnesota, minus 31 in Crookston and Ely, 24 below just outside the Twin Cities in Princeton and minus 17 in Rochester and Austin.

With many schools closed, traffic was lighter than usual Thursday morning around the Twin Cities, but "black ice" caused trouble for motorists, especially on the bottoms of entrances to freeways and highways.

At least 10 rollovers in the metro were reported by 8:30 a.m., including on the ramps from County Road 42 to northbound Interstate 35W in Burnsville and 42nd Avenue to southbound Hwy. 100 in Robbinsdale.

At 8:30 a.m., westbound I-94 travelers in the east metro were slipping and sliding with crashes blocking lanes at White Bear Avenue, Hwy. 52 and Lexington Avenue.

A multivehicle crash tangled traffic on northbound 35W at County Road I in Mounds View. At 8:30 a.m., the State Patrol was dealing with 11 separate incidents.

An eastbound Burlington Northern Santa Fe (BNSF) train had a mechanical failure and blocked the tracks at Ramsey Boulevard and Hwy. 10 in Ramsey. That forced Metro Transit to scrub the third run of the Northstar commuter line. The fourth inbound run from Big Lake to downtown Minneapolis was moved to the other set of tracks and also ran late.

The fifth and final inbound train also ran late, officials said.

BNSF spokeswoman Amy McBeth said operations returned to normal about 8:40 a.m., and she attributed the mechanical difficulties to the extreme cold.

Ice cold beer at the park

The annual Winter Carnival in St. Paul gets started Thursday evening with the Moon Glow Parade. Venture out — if you dare — and gather at the St. Paul Chamber of Commerce lobby at 5 p.m. for hot chocolate, cookies and a chance to mingle. Then, according to the planners' plan, the assembled will be encouraged to participate in the walking parade to Rice Park for live music and an "ice bar," stocked with beer and wine.

One hitch: Outdoor ice carvings scheduled to start at 9 a.m. have been pushed back to noon.

With even colder temperatures predicted through the end of the month, Minnesota is on pace to have its coldest January in 33 years, said Mark Seeley, a University of Minnesota climatologist who publishes a weekly weather newsletter.

"Gosh, you have to say that we've been predominantly wimpy in the wintertime," Seeley said. "Since 1982, we've had very few occurrences like this month."

Star Tribune staff writer Joy Powell contributed to this report. • 612-673-4482 • 612-673-7768