Midwest September 2018 Summary: Rainy and Warm!

Summer was slow to depart this September, with all locations in the Midwest finishing much warmer than average.  It was an odd month rainfall-wise as there were extended dry periods; but when it rained, it poured, with large parts of Ohio, Indiana, and Illinois doubling their average rainfall for the month.

The first in a series of fronts sagged into Illinois on Labor Day, bringing locally heavy rain and severe weather to the area.  Brief tornadoes touched down in both Cook and Winnebago Counties, disrupting the holiday in both Rockford and Chicago. As a whole, the entire holiday weekend was very rainy in northern Illinois with Rockford seeing 4.22” over the weekend (including over 1” on Labor Day) and Chicago receiving 1.97” over the weekend (with a whopping 1.79” on Labor Day).  Elsewhere, Labor Day weekend was mainly dry but warm, with Indianapolis, Columbus, Dayton, and Cincinnati each experiencing high temperatures which soared into the low 90s (more than 10 degrees warmer than average).

 

The work-week following Labor Day started dry but warm across the region, with highs in many areas surpassing 90 before a cold front pushed in from the north on Thursday and Friday, September 6th-7th.  This front produced spotty heavy rain with Columbus, Dayton, and Chicago all getting 0.50” to 1.00” of rain on the 6th. 

The front stalled over the Ohio Valley for the weekend, and set the stage for more rainfall extending from southern Illinois, east into Indiana and Ohio. This was due to the remnants of Tropical Storm Gordon, and all of its moisture, which moved along the front bringing an extended period of rain between the 7th and 9th. While Rockford escaped the rain, Chicago was on the fringe and saw another 0.30” of rain on the 7th.  Indianapolis was soaked by 4.71” of rain, with Cincinnati also seeing 4.73”.  Dayton joined the 4” club, with 4.31” resulting from the event, while Columbus received a much more pedestrian 2.69”.  Spotty higher totals upwards of 7” were realized across parts of southern Illinois, Indiana, and Ohio, resulting in locally significant flooding.  Chicago, Indianapolis, Columbus, Dayton, and Cincinnati all failed to reach 70 degrees at least once as Gordon’s rain moved through, which is well below the averages of around 80.

 

After Gordon moved through the region, high pressure built in and brought an extended period of dry weather which lasted through the following weekend.  Rockford did not have any measurable rainfall between September 7th and September 17th, Chicago from September 8th through the 18th, and Indianapolis was rain-free from the 10th through the 24th.  Cincinnati, Dayton, and Columbus saw their rainless streak cut short on Monday, September 17th, when the remnants of Hurricane Florence moved into the Upper Ohio Valley bringing generally less than 0.25" of rain to the area.  During this stretch, temperatures warmed back up with Chicago, Rockford, Indianapolis, Cincinnati, and Columbus all experiencing a late-season 90-degree day yet again (average highs in the 70s). 

More substantial weather occurred on the 21st of September when a truly strong cold front swept through the entire region.  Thunderstorms produced strong winds and spotty tree damage across the Columbus area, with Chicago and Rockford also seeing a light amount of rain.  Temperatures fell into the 70s (near normal) behind this front.

Another front pushed through September 25th and 26th.  This sparked a line of intense storms that brought widespread wind damage to northern Illinois, including both the Rockford and Chicago areas.  The activity generally weakened as it moved east overnight, though a brief tornado did touch down on the east side of Columbus during the early morning hours of the 26th.  The coolest air of the season to this point moved in behind this front, with much of the region falling into the 40s for overnight lows (a bit below average).  Rockford was the cold spot, bottoming out at a frosty 35 degrees on September 29th as parts of northern Illinois saw their first frost of the season.