Week 3: May 15-21, 2023

Near-Normal Temperatures; Strong, Back Door Cold Front

As high pressure was generally widespread throughout the course of the week, average temperatures remained near normal (Figure 1). Statewide, Michigan recorded the largest average temperature deviation of 3.6°F below normal. Maximum temperatures ranged from 5°F below normal in western Missouri to 10°F above normal in northwestern Minnesota; most of the region, however, was within a few degrees of normal values (Figure 2). Minimum temperatures for much of the Midwest were slightly below normal, with departures of up to 8°F below normal in Michigan (Figure 3). The southern and far northwestern areas observed slightly above normal minimum temperatures. In the evening on May 16, a strong, back door cold front began to move south through the Midwest and caused temperatures to drop 15°F in 10 minutes (Figure 4, 5/16 5pm EDT, WPC). This week, there were two high maximum, five low maximum, 20 high minimum, and eight low minimum temperature records broken or tied (Figure 5a, Figure 5b).

Spotty Storms for Most

Compared to the past few weeks, this week’s weather was relatively uneventful. Only the south and a few pockets throughout the region received above-normal precipitation, but even those areas were just slightly above normal (Figure 6). Some scattered precipitation was present throughout the south on May 15, but stronger storms did not ramp up until around 1pm EDT in Missouri. One EF-0 tornado occurred in Greene County, Missouri, and hail ranging from quarter (1 inch) to golf ball (1.75 inches) size fell in Wayne and Stoddard counties. This precipitation continued overnight into the 16 and lingered over Illinois through the morning. Storms became somewhat linear around noon (EDT) as they entered Kentucky and intensified over the next few hours; numerous reports of high wind speeds and hail were received through Kentucky, and four weak tornadoes touched down (Figure 7a: 5/16, 12pm EDT, NCEI; Figure 7b: 5/16 4pm EDT, NCEI). Only one of the tornadoes occurred on the Kentucky side of its shared border with Virginia, in Magoffin County.

Not much of note happened in the remainder of the week. Some convective precipitation popped up throughout the Midwest along frontal boundaries, but no more severe weather was reported in the last five days of the week. Overall, only 23 precipitation records were broken or tied this week (Figure 8).

Canadian Wildfires Cause a Smoky Midwest

Historically large wildfires in Alberta have been burning since early this week; a cold front and placement of the jet stream over the northern Midwest has brought smoky and hazy conditions to much of the United States. As smoke settled in, air quality alerts were issued across multiple states, including Illinois, Minnesota, and Wisconsin. Residents of these areas were encouraged to limit time outdoors and to keep windows shut overnight to prevent harmful respiratory effects from the smoke and it was also suggested to cut back on vehicle emissions as to not worsen conditions.

Streamflow and Drought Update

When compared with last week, streamflow conditions in southern Minnesota and northern Iowa increased and reached high levels in some areas (Figure 9). Conditions in Wisconsin, the UP, northern Indiana, Ohio, central Kentucky, and parts of Missouri trended towards normal levels. Conditions in central and northeast Illinois, Michigan, parts of Indiana, and northern Kentucky worsened slightly. Limited rainfall this week led to worsened drought conditions throughout the Midwest (Figure 10). Abnormally Dry (D0) conditions were expanded in Indiana, Illinois, and Minnesota, and small areas were added in Wisconsin, Michigan, Ohio, and Kentucky. The Moderate Drought (D1) was expanded in Iowa and Missouri, and a small pocket was added in northeastern Illinois. A small area of Severe Drought (D2) was added in northeastern Missouri.