Active Weather Pattern Continues in July

Posted: August 3, 2017, 1:38 pm by ccastellano

Rain has been a big part of the summer across the Midwestern United States so far. A high level of activity continued into July, with a multitude of heavy thunderstorm events that led to another surplus of rainfall for the region. Some of these events were severe with the amount of rainfall, to the point of flooding issues in the surrounding areas of the region’s major cities.

Our high totals came courtesy of an active weather pattern that transferred from June into July. As a hot and dry ridge remained in the West, the eastern half of the country remained in a series of troughs that kept the region cool and dynamic. A frequent phenomenon was the presence of groups of thunderstorm complexes known as Mesoscale Convective Systems (or MCS). It can be typical to see these in summer across the United States, especially in flat territories such as the plains and Midwest. In July of 2017, however, these seemed to be a near-daily occurrence, leading to a high volume of impressive rain events and thusly, higher overall totals.

Storm Total Precipitation via KLOT radar, showing upwards of 8-10 inches of rain in the July 12th rain event in parts of Northeast Illinois! Image courtesy of WeatherTap

The sheer amount of rain in July eventually began to take its toll, especially given the wet June that preceded it. Cases of flooding began to pop up in Northern Illinois after a heavy MCS pounded the area with heavy rain on the 12th, with a daily record amount of rain being picked up at O’Hare Airport of 1.45”. Not to be outdone, another heavy complex of storms pushed through these areas again, with Rockford this time getting into the record books on the 21st with a whopping 2.45” of rain for the calendar day. This pailed in comparison to parts of Lake County, however which were crushed by over a half of a foot of rain, causing some parts of Northern Illinois to be declared disaster areas. Other parts of the Midwest also achieved daily records, including Indianapolis which took a 3.78” rain hit on the 11th and busted a previous record that stood for well over 100 years.  


As far as the rankings go from the start of the Meteorological summer, the placements were not necessarily overwhelming, but most of the Cornbelt’s major cities rose into the top-10 for June and July combined rainfall. Where normally these months average anywhere from 7 to 9 inches of rain, just about the whole region collected rainfall amounts in the double-digits. In some cases, anywhere from 7 to 12 inches of rain would be needed in August to break records for the summer (per the table provided). While this may sound like a tall feat, given the pattern that has held over the Midwest and some of the copious amounts so far, it is not completely out of the realm of possibility that it can be done.



Needless to say, with all of the activity and cloud cover, temperatures remained rather mild with no records broken. In fact, hitting the 90 degree mark almost seemed like a struggle. Between the major cities of Illinois, Indiana and Columbus, O’Hare airport recorded the hottest daily high temperature only at 93 degrees on the 6th. Indianapolis frequented the mark most often, with 4 days of 90 degree temperatures.

On the other side of the ledger, Dayton (or ASOS station KDAY) didn’t even see a single day reach the mark in July, which is a rare occurrence. How rare? This is only the 10th time in recorded history with records at this station going back to 1935 that a daily high temperature failed to reach 90 degrees, though perhaps surprisingly it is the 6th time it has happened since the turn of the millennium (data courtesy of SC ACIS). Despite all of this, temperatures in the Midwest were not all that short of average, with most within a degree or so on the either side of normal.

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