July 2018: Warm & Dry in the Midwest

Posted: August 7, 2018, 10:38 am by jsullivan

The warmth we saw in May and June continued as a stretch of hot and very muggy conditions into the first week of July. This prolonged stretch of weather was a result of a large ridge in the jet stream that was firmly planted over the Ohio Valley and Northeast, which pushed the jet stream well north into Canada allowing tropical air northward.  A generally dry pattern was in place during the first week of the month, with only disorganized thunderstorms that dropped hit and miss rainfall across the Midwest. In most cases, the warmth was attention-grabbing but not record breaking, though Cincinnati hit a high of 96 degrees on July 4th, the hottest temperature they’ve seen since the summer of 2012.

The hot and humid weather was broken by a cold front that pushed through the region July 5th-6th.  It sparked normal summer thunderstorms, which were largely isolated and only produced spotty severe weather, with highly variable rainfall amounts.  Cincinnati and Dayton missed out on any rain, and Chicago only saw a meager 0.02”.  However, Indianapolis had a more substantial 0.41”, the most they would see until the end of the month.

Surface map and infrared satellite showing a cold front and storms affecting parts of the Midwest on the afternoon of July 5th, 2018.

Canadian high pressure slid in bringing a few days of cooler and less humid conditions.  Chicago, Rockford, Dayton, and Columbus all saw at least one night with lows in the 50s (normal lows in the mid 60s), with Chicago, Rockford, and Dayton also managing a day with highs below 80 (normal highs in the mid 80s).

The middle two weeks of July featured another large ridge in the jet stream which parked itself over the central U.S.  This brought another period of above-average temperatures, increased humidity, and a noted lack of significant rainfall.  

The combination of prolonged heat and lack of widespread rain resulted in a further drying out through the third week of July.  Luckily, a wet spring and early summer allowed only a few spots in Illinois, Indiana, and northwestern Ohio to settle into an “abnormally dry” state, depicted in light yellow in the most recent drought monitor. However, areas to the west were not as lucky!

U.S. Drought Monitor from July 24th, 2018, showing abnormally dry conditions in the light yellow regions and more significant drought over northern Missouri.

The pattern was broken by a strong area of low pressure that dropped from the Midwest into the Ohio Valley July 19th-20th.  For the first time in weeks, spots saw at least some rain.  Cincinnati was the “winner” seeing 1.70” on the 20th, though Columbus, Dayton, Indianapolis, Chicago, and Rockford all had at least a few tenths of measurable rain as well.

Severe weather stayed east of Chicago / Indianapolis, and west of Columbus / Dayton, but did affect Cincinnati with some wind damage. On the 20th, five tornadoes which traversed Indiana were confirmed as well as heavy rain, damaging wind and large hail which occurred farther southeast in the Ohio Valley.  This same system was also responsible for bringing a rash of tornadoes to Iowa on the 19th, along with severe storms that capsized a duck boat and killed 17 people in Missouri.  

Reports of severe weather from July 20th, 2018.

This low pressure then stalled over the Ohio Valley continuing occasional showers, particularly over parts of Ohio, where spots ended up with a little under 1.00” of rain by the end of the week. However, Columbus received a substantial 1.30” on the 23rd from a few storms carrying abundant moisture.  Temperatures also cooled for a few days, with many locations enjoying below-normal high temperatures in the 70s.  Aside from another cold front that brought some scattered storms to parts of eastern Indiana and Ohio on July 26th, it was a quiet end to what was generally a warm but dry month.

In the temperature department, Chicago and Indianapolis ended the month above average, while Rockford, Cincinnati, Columbus and Dayton finished near normal. Rainfall varied across the board, though most locations ended dry.  Chicago has a deficit of 2.56”, which is less than half their normal monthly total! Both Indy and Rockford had about 1.50” less than average while Dayton and Cincinnati finished near normal.  Columbus was the lone site that came in with more rain than normal with 0.67” more than the usual amount. 

 

Lead Long Range Meteorologist
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