**October 1-7, 2023 **

Summer Temperatures To Start

It was a record-breaking start to the first week of October. Temperatures were above normal for the entire period, especially in the Upper Midwest, where the average daily temperature was 10-13°F above normal (Figure 1). Down in Illinois, Indiana and Ohio, average daily temperatures were also above normal, albeit only 4-8°F above normal, which is still noteworthy for October.

Minimum temperatures were anomalously warm for the period. Parts of Minnesota saw average minimum temperatures up to 16°F above normal (Figure 2). Wisconsin and Minnesota also had minimum temperatures that averaged 10-15°F above normal. In Minnesota specifically, minimum temperatures averaged 65-70°F in the Twin Cities, and 55-65°F in much of the rest of the state for October 1-3 (Figure 3). Normal minimums for all locations in Minnesota are below 50°F by October 1. International Falls, Minnesota observed a record high minimum temperature of 62°F for October 1, which was 26°F above normal for that date. Hibbing, Minnesota also set a record high minimum temperature on October 1, with a temperature of 59°F, which was 24°F above normal for that date.

Maximum temperatures were just as anomalous. In most of Minnesota, Wisconsin, and Iowa, the average maximum temperature for just October 1-4 was 15-25°F above normal (Figure 4). In the rest of the region, average maximum temperatures were still a solid 10-15°F above normal. In Iowa, Illinois, and Missouri, the first four days of October brought average maximum temperatures of 85-90°F (Figure 5). In Sioux City, Iowa, a record maximum temperature of 92°F was set for October 1. In Minnesota, the tempurature reached 95°F in the town of Milan on October 1, which was both 25°F above normal and a record for that day. In Minneapolis, the Twin Cities Marathon was canceled as a result of the anomalously warm conditions. Daily maximum temperature records were also broken for October 1 in Green Bay and Eau Claire in Wisconsin, Iowa City and Waterloo in Iowa, and Muskegon, Michigan. In Michigan, Alpena and Marquette both observed maximum temperature records on October 2, coming in at 85°F and 87°F, respectively. Findlay, Ohio observed a maximum temperature of 89°F on October 2, another record for that day.

Temperatures cooled rapidly by the end of the period. In fact, temperatures were 5-15°F below-normal by the end of the week (Figure 6). In northern Michigan, where record temperatures nearing 90°F were observed earlier in the week, highs were in the mid-40s to mid-50s by October 7. In Indianapolis, the maximum temperature was 11°F below normal on October 7, reaching only 58°F. In Louisville, Kentucky the temperature was 63°F on the same date, a solid 10°F below normal.

Another Week of Scattered Precipitation

It was another week of negligible rain totals for some areas, and healthy rainfall for others. Almost no areas received rain October 1-4. It wasn’t until a low pressure system, anchored in Canada, spread east with a cold front October 5-7 that most of the area started to see rain.

Much of Iowa, Wisconsin, southeast Minnesota, and northwestern Illinois saw less than 0.1 inches of rain (Figure 7). Meanwhile, Michigan, northern Indiana and southern Missouri were the big winners, with parts of these areas having received 2-4 inches of rain. In Michigan, rain from the aforementioned low pressure system started as early as the morning of October 5 and didn’t end until October 7. This left towns like Kalamazoo with over 3 inches of rain and some suburbs with over 4 inches. The same system brought over two inches of rain to southern Missouri and Michigan’s UP.

Drought Persists and Intensifies for Most

There was generally very little change in drought conditions heading into the first week of October. Rain was sparse, with the only significant rain occurring in areas with little to no drought, such as West Michigan and southern Missouri. There were negligible decreases of 0.5-1 percent in every drought category, and no decrease in exceptional drought (D4) which persists through eastern Iowa (Figure 8). Iowa was one of only three U.S. states where 100% of land is considered abnormally dry (D0). Drought removal occurred in Minnesota’s Arrowhead region, specifically in the Greater Duluth area. Elsewhere in the state, drought persisted. In Indiana, Kentucky and Ohio, abnormally dry and moderate drought (D1) conditions expanded due to a lack of rain in those states.

As a result of continued drought, streamflow was below average again for many river basins and tributaries across the Midwest. This is especially the case for the Upper Mississippi River Basin. Most gauges in Iowa were running at less than 10 percent of average streamflow as of October 7 (Figure 9). There were also some running at 10-25 of average in western Illinois and southern Minnesota. There have also been some low water levels in the Ohio River Valley, specifically in Indiana and Ohio. The Wabash River at New Harmony was well below the low water stage of 3.3 feet, sitting at 0.75 feet by October 7 at 8:00am (Figure 10).