The arrival of autumn's first killing frost could be just around the corner for Missouri farmers. "Where you live can make a big difference when to expect your first frost," says Pat Guinan, University of Missouri Extension climatologist.
A map showing the average date of the first frost (32 degrees) in Missouri can be found at agebb.missouri.edu/weather/frost2.htm. These are dates in the fall before which there is a 50% chance of a light killing frost.
"Typically, the first fall frost occurs over northern and central Missouri by the second and third week of October, respectively," he says.
Missouri's latitudinal variation, the Ozark Plateau, river bottomlands and hills and valleys are all factors contributing to frost potential. Frosts are more likely to be experienced earlier in the fall over the Ozarks when compared to central Missouri. This is due to the higher elevation of the Ozark Plateau, which causes cooler temperatures in the Ozark region than would be expected, he said.
In the Bootheel, with its lowlands, the average first fall frost occurs during the last week of October, or as late as the first week of November in the extreme southeastern tip of the state.
Local terrain is another factor in determining fall's first frost, Guinan notes. Temperatures can be highly variable within small distances due to topography. Minimum temperatures can vary as much as 10 degrees over a short distance from the bottom of a valley to a nearby hilltop.