August 2021: Hot and Stormy in the Midwest

Chicago Area:

It was the 6th warmest August on record in Chicago and the 8th warmest summer overall (meteorological summer ended on August 31st). The average high for the month was 86.2° with an average low of 68.1°. Total precipitation for August was 4.51", just about a quarter of an inch above normal.

Overall, the first week of the month was rather pleasant with low humidity and a fair amount of sunshine. A few showers and storms returned for the first weekend of August, but nothing out of the ordinary for the dog days of summer.

August 9th offered a few rounds of heavy storms that not only produced some severe weather, but localized rainfall amounts of 2 – 5”. This resulted in flooding issues across several parts of the state, including the Chicago area. The next day was quiet, hot, and humid as the heat index peaked at 105 – 110°. This “set the stage” for another round of late day storms that produced wind gusts of 50 – 70 mph along with several downed trees and powerlines. 

 

West Dundee, IL tree damage from August 10th.

The stormy pattern then continued into August 11th. A squall line raked across much of northern Illinois during the morning and produced a broad swath of wind damage to trees and crops. After a break during the afternoon, another area of storms produced wind gusts of 40 – 60 mph during the evening and early overnight hours.

A cold front then pushed through the Midwest on August 12th. This was followed by a much quieter pattern for the next several days with just a few isolated showers and storms around during the afternoon. After a relatively quiet spell, another cold front then made its way across Illinois on the 21st. This produced scattered showers and a few gusty storms in the afternoon, but nothing severe.

Beyond that, the Chicago area saw “typical” weather for late August. Days were quite warm and humid with afternoon highs in the mid to upper 80s. There were a few storms around, but these were mainly confined to later in the day. Finally, a stronger cold front swept across the region on the 29th. This was followed by cooler and less humid weather for the end of the month with highs in the upper 70s to low 80s.

Central Indiana into Ohio:

Similar to the Chicago region, a warm August also ensued for areas around Indianapolis, IN, Cincinnati and Columbus, OH. The average high temperature was 86-87°, which was 1-3° above normal. Average low temperatures were 67-68°, which was also above normal by 3-4°. Total precipitation varied from region to region. Rain totaled 1.99" in Indianapolis for the month, where the normal is usually 3.20". Meanwhile, in Cincinnati, 5.06" was the rainfall total, coming in above the usual average of 3.43". Columbus had the highest precipitation total for the month, though, totaling 7.16", well above the 3.74" average.

Aside from a few afternoon showers and storms around on August 1st, the month started off relatively mundane in Indiana and Ohio. High pressure overhead resulted in dry and quiet weather from August 2nd through the 5th, with low humidity and high temperatures in the low-to-mid 80s (slightly below average for the time of year). Starting on the 6th, a warming pattern occurred with temperatures climbing into the mid-to-upper 80s. Humidity also increased too, resulting in daily isolated-to-scattered shower and storm chances from the 6th through the 9th. Beginning on the 10th and through the 12th, temperatures climbed into the low 90s during the day, resulting in heat indices just above 100. With this increased heat and humidity, more numerous showers and storms developed, with localized areas of severe weather, too. This was especially true for the Columbus metro, where a line of severe storms rolled through during the evening of the 11th, resulting in wind gusts up to 60 mph.

Damage from severe weather evening of August 11th in Columbus, OH-Courtesy of NWS Wilmington, OH

Humidity and temperatures dropped slightly for the 13th, but were still very warm with high temps in the upper 80s to near 90. Widely scattered showers and storms were featured during the afternoon and evening hours, with high pressure building across the region in its wake. This resulted in dry, much less humid, and cool weather for August 14th and 15th, with highs in the upper 70s to low 80s. While primarily dry and quiet weather persisted around Indianapolis for the 16th, a system brought periods of scattered showers and storms to Cincinnati and Columbus in the late evening of the 15th through the 16th, resulting in 1.79" and 1.55" of rain, respectively. This actually broke a new daily precipitation record in Columbus.

Scattered showers and storms resumed across the entirety of the region for the afternoon and evening of the 17th as conditions continued to warm and turn more humid. Locally heavy rainfall and flash flooding occurred on the eastern side of Columbus, with 4.50" of rain falling in 90 minutes. Similar conditions persisted from the 18th through the 21st, though shower/storm activity turned more and more isolated as the days progressed. Humidity persisted and heat continued to build too, reaching the upper 80s to around 90 by the end of the period.

Following a dry but rather hot period from the 22nd to 24th, with heat indices once again reaching the low 90s, a more unsettled pattern existed across the region from the 25th through the end of the month. Several disturbances/frontal passages brought periods of slow-moving scattered showers and storms, with locally gusty winds and heavy rain (especially on the 25th, 26th, 30th, and 31st). In fact, Indianapolis airport received 1.24" of rain in only 50 minutes on August 25th.