In terms of significant weather and overall temperatures, the Midwest behaved rather mildly in the month of August. Still, the region had its fair share of warm days, with a couple of standout weather events over the period.
Overall, northern Illinois finished right around normal for the month, only around a few tenths above normal courtesy of several warmer than average nights. Much of the Ohio Valley topped out warmer than normal as well, by as much as 1 – 2 degrees. A bulk of the above normal temperatures came in the first 3 weeks, with Chicago 1 – 2 degrees on the warm side for the initial 21 days, and 2 – 4 degrees over the average from Indianapolis to Columbus. This roughly translated to daily high temperatures from the 1st through the 21st between 83 and 89 degrees. The drop was significant however after this, falling below normal for the remaining days.
SUMMERTIME STORMS, AND A CHANGE IN AIRMASS
The warm weather during the first 2/3 of the month was about to undergo a gradual transition by the 4th week. A frontal boundary worked in from the northwest on the 18th into Iowa, eventually stalling over Northern Illinois on the 19th. This brought thunderstorms to Chicago which resulted in reports of wind damage not only the nearby suburbs, but quite close to the downtown Metro as well. This complex of storms also reached the I-70 corridor, pushing some of these impacts (even with a bit of hail) to Indianapolis.
This front was then on the move a day or two later as a transition in the weather pattern was getting set to take place between the 20th and 21st. Cooler air behind it provided the transition to at or slightly below average temperatures that held the rest of the month. It also provided some of the most notable weather of the month with several rounds of thunderstorms before its passage.
Radar image from KIND radar showing storms that passed through Indianapolis on 8/20/2019, with Base Reflectivitiy (left) and Base Velocity (right) side by side. The radar site is the approximate location of the KIND observation station (Indianapolis Internatoinal Airport), which recorded a thunderstorm wind gust clocked in at 73 mph!
Indianapolis received the worst thrashing from these storms. A bowing line of thunderstorms moved south and east quickly across Illinois into Indiana on the 20th. The storms passed through the city between 2 PM and 3 PM that afternoon. Gusts topped 70 mph or higher for a widespread area. The reporting station at Indianapolis International Airport clocked in with a peak gust of 73 mph, with gusts reaching the 60s and 70s frequently from 2:43 PM to 3 PM. The strength of these winds led to numerous reports of downed trees and structural damage. This same line was even able to survive the trip to reach southwest Ohio, with similar reports through Cincinnati a couple of hours later.
Despite the severe outbreak, to say that August was your average summer month would not be too far off. Temperature departures were rather mundane in a sense, though on the plus side by a degree or two. For the summer as a whole, precipitation followed in the same manner. After a wet and active June (highlighted by the soaker through the Ohio Valley), July and August received near normal precipitation overall. From Chicago, to Indianapolis and Columbus, most areas stayed within a range of 75% - 125% of average for the period.
Most in the Midwest started the summer with 100% of their normal rainfall, even going up to as much as 200% for June. Precipitation leveled off in the season's middle and remaining months.