35 miles per hour.
That's the wind speed at which the Florida Department of Education has recommended school districts start pulling buses off the road, for safety's sake.
The department sent the message to districts as Hurricane Michael churned northward through the Gulf of Mexico. It arrived while emergency operation centers all along the coast began planning for the worst, and parents clamored to know whether their schools would be open.
Department school transportation director Robert Manspeaker wrote that his section had reviewed data from several sources, to determine when the buses would be unsafe.
"Many factors must be considered to determine when to cease school bus operation, such as vehicle size, wind speed, wind direction, road conditions, and the wind speed at which emergency response vehicles cease operations," Manspeaker wrote. "Based on these factors, it is recommended that the operation of school buses be limited to periods with sustained winds below 35 MPH."
That's one reason why, even if a hurricane doesn't appear pointed directly at a community, it still might call off schools. The need for shelters, for local residents or those fleeing the storm's path, is another of the major causes for closing schools.
And don't forget, once a school becomes a shelter, it takes time to clean it up. That could mean more days off.
Keep it in mind as the hurricane season moves into the busy part.
From the files: Irma's gone. Why isn't my child going back to school this week?