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Minnesota State University students heading to their Wednesday classes had their heads in a frigid fog created by the campus heating plant.

The year was 1994 and it’s well remembered in the annals of Minnesota weather history.

That was when, almost 15 years ago exactly, then-Gov. Arne Carlson canceled all public schools in the state because of extreme cold, including wind chills of minus 50. The announcement was met with a mixture of approval and harsh criticism, prompting school districts to take future cold-weather cancellations into their own hands.

Since then, Supt. Ed Waltman said, Mankato schools have closed only a couple times due to extreme temperatures. Today, he said, might be the next.

“If forecasts show it’s going to be cold all day,” Waltman said, “then we might have to close school.”

As late as Wednesday afternoon, the National Weather Service was still predicting a high of minus-9 with wind chills exceeding minus-40. And while the arctic air responsible for the cold is expected to begin waning by this afternoon, that may not be in time for schools.

Like most area superintendents, Waltman uses the NWS’ wind chill index to guide school closings.

Due to technological and scientific advancements, the NWS updated its windchill chart in 2001. The chart is now more accurate, but generally reads warmer than the previous index. For that reason, Waltman said, schools do not set any kind of windchill threshold, below which school would absolutely be canceled. Instead, schools consider a combination of factors, the most important being the danger level associated with a particular wind chill.

The new chart is separated into four zones, based on the number of minutes it takes for frostbite to take hold. But because wind works differently at different temperatures, not all wind chills are created equal.

For instance, a temperature of minus 25 with a wind speed of 5 mph produces a wind chill of -40. Under those variables, frostbite takes 30 minutes to set in.

But if the temperature is minus 5 with a wind speed of 45 mph, the -37 wind chill will cause frostbite in 10 minutes — which is the zone superintendents generally look at to make weather cancellations.

“That’s when you really need to think about not having school at all,” said St. Peter Supt. Jeff Olson. “At that point, it’s getting very dangerous for kids.”

The last time the National Weather Service headquarters in Minnesota registered three consecutive days of sub-zero temperatures was in February 1996. So far this winter, there have been 17 days of sub-zero temperatures. Last winter, there were five in the same stretch.

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