September 15-21, 2023

Above-Average Temperatures To The West, Below-Average Temperatures To The East

The past week was characterized by vast differences in temperatures from the Ohio Valley to the Upper Mississippi River Valley. Ohio, Indiana, and Kentucky saw average temperatures 3-5°F below normal for the period (Figure 1). Compare this with Minnesota, where parts of the state were nearly 6°F above normal.

Minimum temperatures were really below normal over parts of the Ohio Valley. The minimum temperature averaged as much as 7°F below normal in the Greater Cincinnati area (Figure 2). Surrounding parts of Indiana, Kentucky and Ohio were also a solid 3-6°F below normal.

Average maximum temperatures were quite noteworthy. Parts of Minnesota saw maximum temperatures that were 6-8°F above normal (Figure 3). Much of Minnesota saw a maximum temperature of 80-85°F, with isolated spots averaging 85-90°F (Figure 4). Most of the week’s daily high temperature records that were broken happened in Minnesota, and 80°F temperatures were recorded very close to the Canadian border (Figure 9). Hibbing, Minnesota, in the state’s Arrowhead region, recorded a maximum temperature of 81°F on September 21, which broke the previous record of 78°F set in 2015. This is quite remarkable, given that average maximum temperatures are between 60-65°F for much of northern Minnesota by September 20.

Well Below-Normal Precipitation, Except Chicago

It was another week of below normal precipitation for the Midwest. Most of Indiana, Michigan, Minnesota, Ohio and Wisconsin picked up 0-5 percent of normal precipitation for the past week (Figure 5). This is especially noteworthy due to the fact that this is already a dry time of year with little precipitation.

Of course, there were a few isolated pockets of extreme rainfall—one in Iowa, right along I-80, and the other in the Greater Chicago area. Both areas picked up 150 to 175 percent of normal rainfall for the period. While only 14 daily precipitation records were broken or tied this past week, seven occurred in Illinois alone (Figure 7). The Chicago area got hit hard by heavy rains on September 17, with an isolated pocket of three to six inches of rain through the south suburbs (Figure 6). Flash flooding was a frequent sight across many area roads, and engineers in Calumet City, Illinois established that it was a 500-year event.

Drought Has Expanded and Streamflow is Impacted

There was no drought improvement this past week. In fact, only about one-fifth of the Midwest wasn’t classified as drought-stricken as of September 21, most of which is in Michigan, Ohio and Kentucky (Figure 8). Even in those states, drought has been pushing back in, with abnormally dry intensity (D0) now in Ohio and Kentucky. Even moderate drought (D1) was added through northern Indiana. Almost 80 percent of the region is now in at least abnormally dry conditions (D0), with 50 percent reaching moderate intensity (D1). Another third of the region is now in at least severe drought conditions (D2).

Where D2-D4 drought is concerned, the focus has been on both the Mississippi and Missouri River Valleys. As a result, the aforementioned rivers and their adjacent tributaries were below normal streamflow across the region as if September 21 (Figure 12). Since every gauge along the Mississippi river from the Ohio River southward to Jackson, Mississippi is at or below the low water stage, there is increasing concern for water supply and barge deliveries during harvest season. The Mississippi River above Tiptonville, Missouri was at 0.04 feet on September 21, well below the low stage of 6 feet (Figure 10) and the Ohio River at Cairo, Illinois was already at 7 feet on the morning of September 21, which is two feet below the low stage of 9.2 feet (Figure 11).