Cooler Weather Spreads Across the Midwest Cooler weather moved into the Midwest in the second week of September, bringing temperatures averaging more than 10°F below normal to several states. The first frost or freeze of the season affected the northwest part of the region as hundreds of Midwest stations set or tied their record lows. ••• Heavy rains fell over a large swath of southern Iowa, northern Missouri, and central Illinois where rainfall was three to five times normal for the week. Lack of heat stress and sufficient moisture have played a role in the high yields expected in many areas. However, in some states there is concern about reaching maturity prior to a fall freeze. Read more in the September 16th Midwest Climate Watch.