Agriculturally, October tends to be dominated by crop harvesting across Minnesota, most often associated with the corn and soybean crops, as well as the last cutting of alfalfa in some southern counties.

Our state climate history shows that October also tends to bring some of the driest days of the year and, more often than not, the National Weather Service issues some red flag warnings for a high risk of wildfires at least somewhere in the state on one or more days. These observations are backed up by historical climate data.

Over the past 30 years, half of all Octobers have brought at least one day with dew points in the single digits or teens and afternoon relative humidity readings lower than 20%. In the Octobers of 1997, 1999, 2000, 2003, 2010, 2011, 2012 and 2022, there were days when the relative humidity levels were at record-setting low values in the single digits — as low as just 6%, with afternoon high temperatures ranging from 80 degrees F to 93 degrees F. Such days are about equivalent to the dry environment of the desert Southwest (places such as Phoenix, Ariz.).

When combined with moderate to strong winds (usually from the Southwest), these environmental conditions prompt the National Weather Service to issue red flag warnings indicating that the weather is favorable for wildfire combustion and rapid spread. In Minnesota’s climate history, there are no other months when the frequency of extreme low relative humidity readings is as prevalent as October.

Dry silver lining

There is a silver lining benefit to crop producers from these extremely dry days in October, and that is the field drying of crops before harvest. When such days occur, crops lose a great deal of moisture to the dry air. From historical reports by farmers who provide data for the USDA National Agricultural Statistics Service Weekly Crop-Weather Reports, there have been cases when these unusually dry October days cause sampled corn kernel moisture content to drop by several percentage points, sometimes in just a few days.

Such was the case in both 2011 and 2012, when kernel moisture content dropped by over 4 percentage points in some cases just before harvest. In addition, soybeans drop their leaves faster, and pods dry faster in the field under these dry conditions. Sometimes, field drying of these crops is significant enough in October that little or no artificial drying is required before putting them in storage.

Current National Oceanic and Atmospheric Administration Climate Prediction Center seasonal outlook models favor a warmer and drier October in 2024. Perhaps we will see the occurrence of such dry days with extremely low relative humidity again this year.

More on Minnesota’s weather history is available in my book, “Minnesota Weather Almanac: Second Edition,” available at most bookstores or through the Minnesota Historical Society Press.