EAGLE RIVER - For Greg Herfindahl, 20 degrees below zero is the magic number.
When temperatures are colder than that, Herfindahl's school buses don't always cooperate.
He owns Schilleman Bus Service in Eagle River, and the thermometer reached 30 below in Land O'Lakes overnight. In the morning, the buses, which serve the Northland Pines School District, just didn't go.
"As soon as we started pulling out of the yard, right away they're losing power," Herfindahl said. "We've got issues."
As the diesel fuel gelled in frigid temperatures, buses stopped running, and Herfindahl told Northland Pines he couldn't confidently get students to school. That led to a day off for students.
"We really run into problems when we get 20 below. It's kind of like the magic number. When it's colder than 20 below, we start to see some problems with losing our fuel rail pressure," Herfindahl said. "Stuff isn't really designed for it."
Herfindahl's newest buses, due to emissions regulations, struggle more in the deep cold. He and his team spent Monday replacing fuel filters and switching the diesel blend.
"With the filters we have on and the additives, that's about all we can do," Herfindahl said.
With school called off, most school buildings sat quiet. But handful of students still spent the day at school.
The district gave notice of class cancellation late in the morning, so it offered a special option.
"For some families, not having that extra daycare, or opportunities to have families in the area, they could drop their kids off," said Northland Pines District Administrator Scott Foster.
About 50 students took up Foster on the offer.
"Childcare and other things with families and their plans, we really felt that we could still give kids a productive day to meet their needs and also make it a positive instead of being at home today," he said.
As Herfindahl warmed his buses Monday, he had got an eye on the forecast, hoping the "magic number" is nowhere in sight.
"We really work hard to make sure that we don't have this problem. When [we do], it's really frustrating, but it is part of the game, part of the business when we're living in northern Wisconsin," Herfindahl said.
Counting Monday's cancellation, weather has caused Northland Pines to miss two days of school. The district has just three snow days built into its calendar.