When Can We Expect Our First Autumn Frost in Missouri?
Commercial Agriculture/University of Missouri Extension
With summer winding down, memories of autumn are just around the corner - fall colors, shorter days harvest moon, and frost on the pumpkin to name a few. If Mother Nature acts accordingly, Missouri's growing season typically comes to an end in October. Depending on where you live, however, can make a big difference when to expect your first frost. Missouri's latitudinal variation, the Ozark Plateau, river bottomlands and hills and valleys are all factors contributing to frost potential. If you have an established climate record of temperatures for your region and an idea of how local topography can affect temperature, you can use that knowledge in determining when, on average, to expect your first fall frost.
The following map displays the average date of the first fall frost (=32°F) in Missouri. These are dates in the fall before which there is a 50 percent 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. Frosts are more likely to be experienced earlier in the fall over the Ozarks when compared to central Missouri. The reason for this is due to the higher elevation of the Ozark Plateau which causes cooler temperatures in the Ozark region than would be expected. As the Ozark Plateau transitions to the southeastern lowlands of the Bootheel, the average first fall frost occurs during the last week of October and as late as the first week of November in the extreme southeastern tip of the state.
As mentioned earlier, another item to consider is local terrain. Temperatures can be highly variable within small distances due to topography and this map is only a generalized view of expected last spring frost dates. Minimum temperatures can vary as much as 10° F over a short distance, say, from the bottom of a valley to a nearby hilltop. Cool air, being denser than warm air, moves down the slopes of hills, accumulating in the valleys. This is why low lying areas, such as river bottoms, will likely be colder than their surroundings on clear, calm nights. Therefore, while referring to this map, consider your local landscape when determining your average first frost date.