Wednesday promises to be the coldest day of the season yet for the Twin Cities, with the potential for windchill readings closing schools.

Minneapolis went first Tuesday calling off school for Wednesday. Anoka-Hennepin, the state's largest district, soon followed, citing the extreme cold and "the safety of our students and staff." Others included Osseo.

No unnecessary travel is being advised Tuesday night in south central and southwest Minnesota.

A windchill warning from the National Weather Service (NWS) kicks in at 2 a.m. Wednesday and is expected to last late into the morning, forecasting what the agency describes as "dangerously cold windchills across all of central and southern Minnesota and into western Wisconsin."

Strong northwest winds, combined with a "surge of frigid arctic air … will produce windchill values between 35 and 40 degrees below zero," the warning read. "The worst conditions will be from 3 a.m. to 10 a.m." Blowing snow is being tossed in during this time frame as well.

Windchill of 35 below by 6:30 a.m. is the bar Minneapolis had set for calling off classes, according to the School District's newly revised policy.

St. Paul schools Superintendent Valeria Silva said via an e-mail Tuesday night that the district plans to be open Wednesday but that any absences will be excused. "I want to offer SPPS families the opportunity to do what they know is best for their own children," Silva said.

The St. Paul district's policy is to cancel classes if the forecast for 6 a.m. called for windchills to reach 40 below or if the air temperature hits 25 below. The latest NWS forecast calls for a low of minus-14 early Wednesday.

The Anoka-Hennepin School District, the state's largest, takes a different approach. If the NWS issues a windchill warning stating that exposed skin can become frostbitten in less than 15 minutes, then the district "will likely make a decision to close," according to the district's explanation on its website.

The NWS' pending windchill warning does not put a time on how quickly frostbite could occur Wednesday but warned of "frostbite and … hypothermia or death if precautions are not taken."

School officials in Austin and Winona in the southeast corner of Minnesota are getting ahead of the game, having already decided to start classes two hours late Wednesday. St. Thomas Academy in Mendota Heights joined the two-hour late march for Wednesday morning as well.

Monday's predawn deep freeze was not frigid enough to close any schools in Minnesota. There was a smattering of late starts.

Last winter, Gov. Mark Dayton took the unusual step of canceling classes statewide on Jan. 6 after temperatures fell to minus-22 windchills were 48 below in the Twin Cities. Most school districts canceled classes four more times that month, a rarity in cold-hardy Minnesota.

The Twin Cities weather forecast for the rest of the week offers no relief from subzero air temperature readings, with the best chance for a daytime high even into double digits above zero coming Thursday.

Star Tribune staff writer Kim McGuire contributed to this report. Paul Walsh • 612-673-4482