Good Question: Why Are We Seeing Frost If It's Not Freezing?
MINNEAPOLIS (WCCO) -- The Twin Cities has broken the official record for the latest freeze -- a temperature reading of 32 degrees at the Minneapolis-St. Paul International Airport.
But there are plenty of people who have noticed frost on the ground this fall. Mike from St. Peter and Ron from St. Paul asked: If it's not freezing, why are we seeing frost?
"If you see frost, you know it's 32 degrees," says Pete Boulay, a state climatologist with the Minnesota Department of Natural Resources.
Some parts of the state have seen temperatures drop below freezing.
First, it is important to know the official temperature is measured five feet above the ground, which is five feet above where the frost is usually located.
"Five feet is basically eye level," Boulay said. "In the 19th century, it was a glass and liquid thermometers they had to read in a box, so it was very convenient to read at eye level."
Second, cold air is denser and settles to the ground. That means it could be freezing at the ground level but a couple of degrees warmer five feet in the air. Depending on the wind, it could be a difference of five degrees or more.
"More specifically, it's the grass blades that hit 32 or colder," Boulay said. "The ground is still pretty warm, but the grass blades are where you're seeing the frost."
The latest 32-degree freeze in recent history was Oct. 30, 1973. We have now beaten the record for twelve days.
