September 19-25, 2001:

The period of September 19-25 was very active in the Midwest, with at least three distinct low pressure centers passing through the region. More than 3 inches of rain fell in much of northern Illinois and Michigan, and heavy rain for the week was also noted for northern Missouri, parts of eastern Iowa and Minnesota, southern Wisconsin, and other portions of Michigan (Figure 18). Only the westernmost portions of Minnesota and Iowa and easternmost Ohio were dry relative to normal (Figure 19). Temperatures remained above normal for much of the week, only to fall far below normal at the end of the period. Overall, the western Midwest near Iowa was 2-4°F below normal for the week, and the northern Great Lakes area was 1-2°F above normal (Figure 20). At the beginning of the period, a low pressure center traveled northeastward from the Texas panhandle, dropping copious amounts of rain through Kansas, Missouri, and northern Illinois, exiting the region through northern Michigan on the 20th. Another frontal boundary and small disturbance traveled eastward across Iowa on the 20th and 21st, triggering some severe weather and dropping very heavy rain in isolated bands in northern Iowa and Illinois, southeastern Iowa, and central Missouri (Figure 21, Storm Prediction Center). Storm-caused winds of 30 to 60 mph and hail up to in size damaged row crops in a number of states. This second low passed by Chicago on the 22nd, but brought only weak precipitation to the eastern Midwest. The final system of the week was associated with a strong low pressure center traveling from west to east across the Midwest with a powerful fall-like cold front. Heavy rain fell in southern Minnesota and southwestern Wisconsin, with moderate rain elsewhere.

The front also brought the first truly cold low temperatures of the season. The temperatures plunged to mid-fall levels, with numerous low temperature readings in the mid-20s the first morning after the frontal passage in Minnesota and Iowa (Figure 22). Some low lying areas experienced a freeze sufficient to end the growing season. The low temperature record of 25°F was tied at International Falls, MN, on the morning of the 24th, and coop stations at Embarrass and Tower, MN, recorded even colder temperatures on the morning of the 25th, 19°F and 20°F, respectively. Frost and freeze warnings were issued over much of Minnesota, Iowa, and parts of Wisconsin. Record low maximum temperatures were set on the 25th at Louisville, Lexington, and Jackson, KY, and Flint and Detroit, MI, as an upper level low cloud deck combined with the Canadian air mass to keep daytime temperatures very cold.