September 15-21, 2024

Temperature

Average temperatures were quite warm for the third week of September. Everywhere in the region was above normal, ranging from as much as 12-14°F above normal in northern Minnesota, to 3-6°F above normal in Kentucky (Figure 1).

Average minimum temperatures were also above normal, ranging from 3-5°F over the Ohio Valley to as much as 14°F above normal in northern Minnesota (Figure 2). Red Lake Falls, Minnesota observed two consecutive days of minimum temperatures at or above 66°F, which was both the longest and warmest stretch of September minimum temperatures at that station since 1914. Mora, Minnesota observed a minimum temperature of 65°F on September 19. This was the second latest minimum temperature at or above 65°F in the calendar year for that station since records began in 1895, with the first latest occurring as recently as 2017.

Maximum temperatures averaged very anomalous, with most of the region at least 10°F above normal for the week (Figure 3). They were least anomalous in the far southern reaches of Kentucky and Missouri. Muskegon, Michigan observed 8 consecutive days of maximum temperatures at or above 85°F from September 12-19, which was the longest stretch in September since records began in 1896. Chicago, Illinois had 11 consecutive days of maximum temperatures at or above 85°F, the longest stretch in September since records began there in 1871.

Precipitation/Drought

The pattern was dominated by high pressure for most of the period, which led to not only the anomalously warm temperatures but minimal precipitation as well. Precipitation was mainly observed in the far northern and southern reaches of the region, in both northern Minnesota and the Missouri Bootheel. Both areas received over 175 percent of normal precipitation (Figure 4). Much of the region west of the Mississippi River received 25-50 percent of normal precipitation, but for Illinois, Indiana, Kentucky, Michigan and Ohio, there was less than 25 percent of normal precipitation. Dayton, Ohio observed no measurable precipitation since September 1, making September 1-21, 2024 the second driest stretch of September weather since records began in 1893.

Unfortunately, the areas that received the least precipitation needed it the most, according to the Drought Monitor. There were no improvements with the September 17 update, only degradations in all categories (Figure 5). D4 conditions (exceptional drought) in Ohio grew from 0.7 percent to 0.79 percent of the state. All other categories increased in coverage as well, with at least a third of the region experiencing D1 conditions (moderate drought). Over 75 percent of the Midwest was abnormally dry.

Severe Weather

There were 111 storm reports this week, most of which were wind reports (Figure 6). There were 9 tornado reports. A low pressure system anchored over Canada dragged a cold front through the Upper Midwest on September 19, spawning a few supercells over Minnesota. An EF-1 tornado with estimated peak winds of 105 mph traveled for almost 6 miles through St. Louis County, Minnesota. At least 50 pine trees snapped as a result of the tornado, with debris in the form of metal sheets wrapped around some of the trees. There was also quite a bit of hail with this system, and damage to cars was reported as the result of quarter size hail.