Midwest Weekly Highlights - August 15-21, 2012

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Widespread Below Average Precipitation

A majority of the Midwest experienced below normal precipitation during the third week of August (Figure 1). The areas with the largest deficits were in northern Missouri, where they received 0% to 10% of their normal precipitation. Despite the overall below average precipitation, some parts of the Midwest experienced significant precipitation throughout the week, resulting in values that were 175% to 300% above normal. Luckily, much of this above normal rainfall fell in the very dry regions of eastern Illinois, western Indiana, western Kentucky, and southern Missouri. Locations within these regions received anywhere from 0.75" to 1.75" of rainfall throughout the week (Figure 2). There were just over 75 daily precipitation records set, mainly in the early part of the week.
 

Unseasonably Cool Temperatures

For the second week in a row, average temperatures were below normal across the Midwest (Figure 3). A majority of the region experienced temperatures that were at least 2°F below normal, with the highest departures of 7°F to 9°F below normal in central Iowa and northern Minnesota. Average temperatures ranged from 75°F to 80°F in the Missouri Bootheel to only 55°F to 60°F in northern Minnesota, Wisconsin, and Upper Michigan (Figure 4). Minimum temperatures were especially cool in the western Midwest. Parts of Iowa, Missouri, western Illinois, and northern Minnesota experienced minimum temperatures that were 9°F to 13°F below normal (Figure 5).

As a result of the unseasonably cool temperatures, there were several daily temperature records set throughout the week, mainly record low maximum and minimum temperatures. A few monthly record low temperatures were also set. The August cool-down over the last two weeks is fairly evident when looking at the number of record highs versus the number of record lows throughout the month (Figure 6). At the beginning of the month, there were several record highs and few record lows. However starting around August 10th, the record lows have been plentiful and the record highs have been less frequent.
 

Drought Update

As mentioned previously, the regions in Illinois, Indiana, and Kentucky that have been dealing with drought for a few months now did receive some significant precipitation during the week. While it was not enough precipitation to drastically improve the drought conditions, there was a little bit of improvement on the August 21st release of the US Drought Monitor (Figure 7). The area experiencing the highest level of drought, exceptional drought (D4), reduced slightly in this region. However, there is still just over 7% of the region affected by exceptional drought. Currently, about two-thirds of the Midwest region is still being impacted by some level of drought.

Severe Weather

There were some reports of severe weather throughout the week, but in general it was fairly quiet (Figure 8). The most active days for severe weather were the first two days of the week. On the 16th, there was hail measuring 2.75" reported in Pierce City, Missouri (Lawrence County) and 2.5" hail reported in Gorham, Illinois (Jackson County). In addition, high winds of 74 mph and 78 mph were reported in Effingham, Illinois (Effingham County) and Gays, Illinois (Moultrie County), respectively.

-MW-