The calendar has turned to October, and with it, harvest and fall activities will accelerate over the next few weeks. We have already experienced a few chilly nights this past week with patchy frost in some areas, but when do we typically see our first freeze conditions? This first (last) official freeze is defined as the first fall (spring) day where the overnight low reaches 32 degrees F.
The Midwest Regional Climate Center (MRCC) has developed a new Freeze Date Tool (https://mrcc.purdue.edu/freeze/freezedatetool.html) that relies on historical temperature data at the county level back to 1950 and allows users to select a freeze temperature threshold between 20 degrees F and 40 degrees F to visualize the earliest, average, and latest fall or spring event. For instance, many of us are interested in the hard freeze threshold of 28 degrees F, the temperature at which our corn and soybean growing season comes to an end.
Temperatures are expected to flirt with 32 degrees F again Saturday and Sunday mornings. Still, most of the earliest dates and even the earliest 10% of dates on record occurred in late September, so we are beyond those thresholds. More recent first freeze dates have been occurring later in the year, with some counties reporting a trend of more than 3 days later per decade (~21 days later over the full period). The Freeze Tool also allows users to view these trends as well as more detailed analysis for individual counties.