Record highs cool off quickly
Last Friday, Des Moines, Iowa, reached 104 F., setting a record-high temperature for the day and also the hottest temperature for so late in the season. According to the record books, temperatures in Iowa have reached 100 F. in early September, but it is a rare event last seen in 1939. The hours of sunshine have diminished by over two hours from the peak in late June.
The shorter days allow more cooling at night; it is easier to cool to the 50s and 40s at night particularly in the river valleys across the Midwest in early September. This morning, temperatures have cooled to the 40s over a large section of Minnesota, Wisconsin, eastern Iowa, and portions of western Illinois. Fog is reducing visibility in the river valleys in some cases to a quarter-mile. The lower sun angle and light winds will help to keep these valleys cooler until later in the day. Still, dry topsoils allow surface temperatures to warm rapidly.
The latest Drought Monitor indicates that severe drought has returned to some parts of western and central Iowa as well as north-central Missouri with abnormally dry conditions over the rest of Iowa, much of northern Illinois, Wisconsin, Minnesota, and the eastern Dakotas. Fortunately for some areas of western Iowa and northwestern Missouri across central Missouri into southern Illinois, some good rains occurred Saturday night and Sunday. Red Oak, Iowa, received over 1 inch, and St. Louis, Missouri got nearly 2 inches.
This week, we expect a gradual warming trend over the Midwest and particularly for the northwestern Corn Belt. By this weekend, hot weather is forecast on Saturday and Sunday particularly for portions of Iowa, Missouri, Nebraska, and Kansas, possibly expanding over parts of western Illinois early next week, before some cooler air begins to return next week to the Midwest.
Beneficial rains are forecast for portions of the northern Corn Belt beginning this weekend, however, there are likely to be areas across the western Corn Belt that do not receive much rain. The warm days will help speed the crops toward maturity, but the lack of rain will hurt grain filling and possibly reduce yields, especially for soybeans now.
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