Midwest Overview - August 2014

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Shift to Above Average Temperatures during Latter Half of August

While the month of August overall saw near normal temperatures (Figure 1), the month was visibly split with temperatures trending cooler than normal during the first half of the month (Figure 2), with a hotter weather pattern emerging during the latter half of the month (Figure 3). The warm finish to August was significant since below normal temperatures had been trending this summer since early July. The above average temperatures in late August peaked on August 24th and 25th, when a late summer heat wave impacted the central and southwest portions of the Midwest (Figure 4). The maximum temperature during this event was 106°F in Eminence, MO (Shannon County) on August 25th. The humidity was repsonsible for pushing the heat index well over 100°F in Missouri and Illinois, even over 110°F in some areas.

Preliminary average temperatures for August show that statewide, Minnesota and Missouri experienced the greatest departures of 1°F and 0.9°F above average, respectively, while Michigan experienced the opposite with the statewide average temperature 0.9°F below average. In Kentucky, the statewide August average temperature was right at the 1981-2010 normal of 75.2°F.

Above Average August Precipitation

A majority of the region experienced above average August precipitation (Figure 5), with preliminary statewide data showing Kentucky the greatest departure from normal at 2.34" above average (see table below). Other states with significant above average precipitation include Iowa at +1.83" and Illinois at +1.52". Northern Minnesota, southern Missouri, and portions of Michigan, Iowa, and Ohio experienced below normal precipitation at only 25% to 75% of normal. Total accumulation ranged from just 1" to 1.5" in portions of northern Minnesota and southern Missouri to over 10" in central Iowa (Figure 6).

A significant precipitation event occurred in the Detroit Metro area, when 4" to 6" fell on August 11th in an 8 hour period, with the heaviest during evening rush hour. Widespread flooding occurred in this area, including major impacts on the interstate system. Read more about this event in the Week 2 Climate Watch. The above average August precipitation helped alleviate some drought concerns in the region. At the beginning of the month, 2.5% of the region was in drought and by early September, only 0.85% remained (Figure 7). Currently, western Kentucky and a small portion of western Missouri are in Moderate Drought (D1). Overall, 92% of the region is drought-free, with 7% classified as abnormally dry.


Summer 2014 Summary

The end of August marked the end of meteorological summer. A majority of the Midwest experienced a slightly cool and wet summer, but the cool conditions were mainly felt from early July through mid-August while June and the end of August were unseasonably warm. Average summer temperatures were near to 3°F below normal, with the greatest departures of 2°F to 3°F in portions of Iowa and Upper Michigan (Figure 8). Total precipitation values ranged from only 6" to 8" in northwest Michigan to 22" to 24" in southwest Iowa (Figure 9), resulting in summer precipitation departures from 75% to 100% of normal to over 175% of normal (Figure 10).

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Extension Climatologist for Illinois-Indiana Sea Grant and the Midwestern Regional Climate Center
The Iowa Climatology Bureau also contributed to this report.
The Missouri Climate Center also contributed to this report.