September 2020
Monthly Overview - September 2020
Scattered Rainfall
Precipitation was scattered across the Midwest in September, with many areas drier than wet
(Figure 1). Total precipitation for the region was 2.86 inches which was 0.58 inches below normal. Significantly dry areas were observed across Minnesota, southern Illinois and southern Indiana. Some of the driest areas were across southern Indiana, where less than a quarter of normal was recorded (Figure 2). Meanwhile, wetter areas were observed across the Iowa, Illinois and Wisconsin tri-state area in September. Some in these areas had twice the normal amount for the month. Much of this precipitation fell through the second week of the month, where amounts of 4-5 inches were recorded
(Figure 3). Many of the more than 200 daily precipitation records were recorded during this week (Figure 4). However, the following week was almost completely dry across the entire region, as high pressure prevailed
(Figure 5). Drier conditions continued during the final week of the month and led to regionwide below-normal precipitation for the month.
Cooler Temperatures
Temperatures were slightly cooler across the Midwest in September (Figure 6). Average temperature for the region was 62.2°F which was 0.7°F below normal. Very few areas were significantly cooler for the month and were mainly focused in the Upper Midwest. Most of the Ohio River Valley was near normal. Significantly cooler temperatures were widespread during the second week of September in the Upper Midwest, however
(Figure 7). More than 975 daily low temperature records were broken across the Midwest in September (Figure 8), with more than 825 of these records from September 8-14
(Figure 9). However, a warm final week of September in the Upper Midwest counteracted this extreme cold and led to more than 60 daily high temperature records (Figure 10).
Upper Midwest Freezes
First fall freezes were observed across the Upper Midwest from September 8-11 as an extremely cold airmass swept into the region
(Figure 11). Some of the coldest temperatures were across northern Minnesota on September 9, when hard freezes were observed. Extensive areas in northern Wisconsin and Michigan reached freezing for the first time this fall on September 10-11. These freezes were on the eastern edge of a very intense temperature shift across the northern Great Plains and Rockies as temperatures went from as high as 100° F to below freezing in just two days.
Drought Decreases
Drought significantly improved in Iowa and northern Illinois during September (Figure 12). While Iowa and northern Illinois had widespread drought at the beginning of the month
(Figure 13), soaking rainfall from September 8-14 aided in eliminating extreme drought from Iowa and led to a 35 percent decrease in drought as of the September 29 U.S. Drought Monitor. However, drier weather across southern Missouri, southern Illinois and Indiana led to an expansion of drought and abnormally dry conditions in these areas. Overall, drought coverage dropped by five percent in September, while abnormally dry conditions increased by five percent.
Severe Weather
Severe weather was observed on several days in September. A total of 150 reports of strong winds or hail were reported in the month, with three reported tornadoes. Many of these reports occurred on September 5 and September 7 as storms impacted Minnesota, Iowa and central Ohio (Figure 14). On September 5, 2.5-inch diameter hail was reported near Olivia, MN (Renville County) and near Wanda, MN (Redwood County). Strong winds in Iowa included an 83-mph wind gust near Titonka, IA (Kossuth County). On September 7, 2-inch hail was also reported near Nashville, OH (Holmes County), while an EF-0 tornado was confirmed near Delaware, OH (Delaware County). Isolated severe weather was also reported in northern Wisconsin and the U.P. of Michigan on September 25-26
(Figure 15), which included a tornado near Upson, WI (Iron County), and 2-inch hail near Morse, WI(Ashland County).
-BJP-