August saw a continuation of July’s cooler than normal temperatures through much of the Midwest and Ohio Valley. The coolest departures from normal, 1 to 2 degrees, occurred across southern areas of Illinois, Indiana and Ohio. In fact, Indianapolis, Indiana did not reach 90 at all in August, the first such occurrence since August 2004!
The early summer pattern of Mesoscale Convective Systems (MCS) moving through every few days and bringing record rainfalls in July diminished significantly in August. Drier conditions dominated across much of the Midwest and Ohio Valley with many locations receiving below normal precipitation for the month. Northern Illinois, Central Indiana and Eastern Ohio had the largest deficits where rainfall was less than 75% of normal. In northeast Ohio, rainfall deficits were as large as 2” to 3” with Akron logging their 3rd driest August on record.
Temperature (left) and precipitation (right) departures from August 2015 via the Midwestern Regional Climate Center.
Despite the decreased MCS activity, there still was some severe weather, in particular on August 2nd / 3rd and the 18th. On August 2nd a strong low in southwest Wisconsin combined with unseasonably cool air at the mid-levels and created a very unstable atmosphere, which allowed powerful thunderstorms to fire across northern Illinois. Most of the reported severe weather was confined to the Chicago metro area, where even an EF-1 tornado (86 – 110 mph winds) was observed along with numerous reports of hail as large as 2 inches. Scattered severe storms continued on the afternoon of August 3rd across Indiana. Here, storms produced large hail In Delaware and Randolph counties with golf ball sized hail reported southeast of Muncie. The strong storms weren’t finished, however, as southwest corner of Ohio received 2” diameter hail, much like the Chicago area the day prior.
On August 18th another fairly intense low for August moved from Iowa into southern Minnesota and created a volatile environment, primed for t-storm development. The result, isolated supercell thunderstorms blossomed in the late afternoon and tracked northeast towards Chicago. The storms produced 4 confirmed EF-0 tornadoes (which pack 65 – 85 mph winds).
Also on August 18th, Rockford, Illinois set a new rainfall record for the date with 2.87”. Overall for August most locations across the Midwest and Ohio Valley averaged 1 to 3 degrees (F) below normal with a good portion also receiving normal rainfall. Looking ahead September will likely see some changes as above normal temperatures are expected with near or slightly above normal precipitation.
Overall for August most locations across the Midwest and Ohio Valley averaged 1 to 3 degrees (F) below normal with a good portion also receiving normal rainfall. Looking ahead September will likely see some changes as above normal temperatures are expected with near or slightly above normal precipitation.
