That is how cold the air temperature has to be before schools are closed in St. Paul this winter, with classes also canceled if the forecasted wind chill is minus-40 or lower.
As the first signs of snow appeared in Minnesota Wednesday, St. Paul Public Schools took the unusual step of setting a temperature at which children will have a "cold day," the Pioneer Press reports. This comes after many Minnesota students missed multiple days of school last winter because of the extreme temperatures.
The decision on whether to cancel will be made no later than 6.30 p.m. the evening before and will be based on National Weather Service forecasts for 6 a.m., the newspaper notes.
Meanwhile, decisions on snow days are a little bit more flexible and will be made in the morning once road conditions for school buses are properly assessed.
School districts or principals make their own decisions on whether cold weather or snow should force closures, with USA Today noting that policies across Minnesota vary wildly and depends on what kids are used to, with some schools sending children outside for recess even when temperatures hit 15-below zero.
School closures were a regular occurrence last winter as the state suffered particularly harsh conditions because of the polar vortex that swept the Midwest, and the St. Paul Public Schools spokeswoman Toya Stewart Downey told the Press they wanted to remove the ambiguity over when schools should shut their doors.
In January, Gov. Mark Dayton announced statewide school closures ahead of forecasted severe temperatures with a wind chill of 50-below zero, according to ABC 6.
Individual school districts made separate decisions to cancel classes at various times during the winter, with Anoka-Hennepin among those canceling when weather forecasts predicted air temperatures of minus-20 with a windchill of minus-40, the Star Tribune reported.
Prolonged exposure to extreme low temperatures could put school children at serious risk, with the Washington Post reporting that the risk of frostbite increases greatly at temperatures of more than minus 18 degrees.
When wind chill is greater than minus 50, skin can freeze in just five minutes, the newspaper adds.
Minnesota Department of Natural Resources figures ranked the winter of 2013-14 as among the top 10 coldest in recorded history in the state, with an average temperature of just 9.7 degrees between December and January – the coldest it's been since 1978-79.