Extended Autumn Possible — When Will the Cold Weather Arrive?
The days have become noticeably shorter to the point of starting to infringe on evening activities. With winter fast approaching, it’s time to prepare. Part of that preparation for weather-sensitive folks is trying to discern the signs for clues of the fall and early winter temperature pattern.
Autumn Trends Over Past 25 Years
The Midwestern corn belt has tended to have fall seasons that are more often warmer than normal and more often wetter than normal since the mid-1990s. Here are some details from the climatology.
Looking at the three months of Fall (September, October, and November) since 1995, we find seven of the 11 warmest autumn seasons in the past 125 years. Only two of the past 25 autumns averaged one degree or more below normal. The warming trend has not been a steady one. The region had several very cold autumns between 1985 and 1996, including both 1991 and 1993 when wintery cold and substantial snow arrived by the start of November.
Most recently, fall of 2020 brought an early cold snap with some frost in northwest areas as soon as mid-September. The autumn season overall was a little warmer than normal. At 93% of normal, It was also the region’s driest fall since 2012.
In recent years both the early and late portions of autumn have been seeing above normal temperatures. In the 22 years from 1999 to 2020, September temperatures were well above normal 12 times (but well below normal just twice). On the other end of autumn, only three of the past 22 years had Novembers in which temperatures were well below normal. That 22-year period not only contained the five warmest Novembers in the past 125 years, but nine others which weren’t quite as warm yet still classified as well above normal.
Minnesota just completed its 8th warmest September on record. In the past thirty years, when Septembers have been among the top ten warmest in Minnesota, October has also had a strong tendency to be warmer than normal. Most of the medium range weather models agree that the central and eastern US have excellent prospects of a warm first two weeks of October, and this is reflected in the 30-day outlooks released by NOAA’s CPC on October 2nd.
Soil Moisture Sees an Autumn Recharge
Most autumns of the past 25 years have been near to above normal for Corn Belt moisture. Though 2020 brought the driest fall season since 2012, both 2018 and 2019 had very wet autumns in the Corn Belt. September and October have tended to bring the wetter conditions with respect to normal. The timing of early autumn rains has tended to boost yields for late developing soybean crops. At the same time, lighter late autumn rain and snow have allowed an extended window in which late harvest progress has been good.