Occasionally, Mother Nature brings us autumn weather unlike any we have ever measured in the history of Minnesota.
Such was the case on Oct. 11, 2015. The day was dominated by clear skies, southwest winds, summerlike temperatures and desertlike relative humidity readings.
The daylong bright sunshine and dry landscape allowed temperatures to warm dramatically. For example, at Moorhead, the temperature was just 53 degrees F at 8 a.m. but reached 88 degrees by 2 p.m. Many weather observers in Minnesota reported their warmest day of the entire year, including Wheaton and Moorhead with afternoon readings of 95 degrees, and Rothsay with a reading of 93 degrees. This had never happened before, that October brought the warmest day of the year, so it was a singularity in our Minnesota climate history.
In addition, at least 12 Minnesota climate stations broke the all-time state high temperature record for Oct. 11, which dated back to 92 degrees at Canby in 1928. Breckenridge and Browns Valley reached all-time state record highs for the date at 96 degrees. These temperature readings were also the highest ever measured for so late in the autumn season.
Across the state, 84 daily high temperature records were tied or broken, and more than 35 climate stations reached at least 90 degrees, including 91 degrees at Lake Kabetogama along the Canadian border. These record-high temperature readings for the day were 30 to 35 degrees above normal, a remarkable aberration.
Low humidity, too
With such high afternoon temperatures and a dry air mass, the relative humidity bottomed out at record low values as well. At Appleton, the 3 p.m. temperature was 95 degrees with a relative humidity of just 13%, while at Breckenridge at the same time of day, the temperature was 95 degrees with a relative humidity reading of just 10%.
For comparison, Phoenix, located in the Arizona desert, was showing a temperature of 97 degrees and a relative humidity of 22% at 3 p.m. on Oct. 11, 2015. So the air in western Minnesota was even drier than the air over Phoenix!
In such an environment, mature cornfields in Minnesota dried down at a remarkable rate. Some measurements taken of kernel moisture content showed a moisture drop of 3% to 4% in just one day. As a result of this weather, many farmers reported little need for artificial drying before putting the crop in storage.
Seeley is an Extension climatologist with the University of Minnesota.