The preliminary statewide average July temperature was 77.1degrees, 1.7 degrees above the 1991-2020 average and tied for 35th warmest on record going back to 1895. The preliminary statewide total July precipitation was 3.41 inches, 0.65 inches below the 1991-2020 average and the 57th wettest on record.
Data are provisional and may change slightly over time.
Plentiful July Heat
July is the hottest month of the year in Illinois and last month was no exception. Daily temperatures from Carlyle in Figure 1 show the very warm start to July where temperatures were 5 to 10 degrees above normal around the Fourth of July holiday. However, temperatures moderated later in the month, swinging between warmer and cooler than normal conditions.
July average temperatures ranged from the mid-70s in northern Illinois to the low 80s in southern Illinois, between 1 and 4 degrees above normal (Figure 2). Strong southerly flow kept Gulf of Mexico moisture moving in virtually all month. Some of the more impressive daily high temperatures last month included 99 degrees in Belleville and 98 in Marseilles. Persistently high humidity kept nighttime temperatures elevated as well, with nighttime lows of 82 degrees in Belleville and 80 in Chicago. Springfield recorded its highest dewpoint temperature on record last month: 84 degrees on July 26. The state capital also suffered through an unprecedented run of 11 straight hours with a dewpoint above 80 degrees, which was three times the previous consecutive streak.
The heat and humidity last month broke 16 daily high maximum temperature records and 68 daily high minimum temperature records. Morris set a new all-time high minimum temperature record of 81 degrees on July 2. Meanwhile, some of the cooler weather mid-month broke seven daily low maximum temperature records and eight daily low minimum temperature records.
Overall, the preliminary statewide average July temperature was 77.1 degrees, 1.7 degrees above the 1991-2020 average and tied for 35th warmest on record going back to 1895
Another July with Air Quality Problems
Even though July is almost always the hottest month of the year, Illinois does usually benefit from a handful of weak cold fronts in July that bring some cooler and less humid weather. Unfortunately, the northwesterly air flow behind these fronts in recent years ushered in smoke and very poor air quality from wildfires burning in the northwest United States and southern Canada. Once again, we dealt with air quality issues this year, as northerly to northwesterly flow pushed in very poor air quality mid-month. The EPA’s Air Quality Index exceeded 600 on multiple days in northern Illinois (Figure 3), including in Chicago, which is twice the level considered hazardous for all people.
Drier July for Most, Extremely Wet for Few
The northern two-thirds of the state, outside of the Chicagoland area, was somewhat to significantly drier than normal in July, while both Chicago and far southern Illinois were much wetter than normal (Figure 4). Total precipitation ranged from around 1 inch in west-central Illinois to over 10 inches in far southern Illinois, between 1 to 3 inches drier than normal and 1 to 7 inches wetter than normal. While last month was not a record setting dry July, it was much drier than in recent years. In fact, Peoria, Champaign-Urbana, and Jacksonville all had their driest July since 2012, each with less than 2 inches total. Dry July weather does not portend a great crop year; however, more than abundant June rainfall kept sufficient soil moisture through the dry stretches of last month.
Meanwhile, Carbondale had its third wettest July on record with 9.34 inches of total precipitation. A few CoCoRaHS stations south of Carbondale and Marion had over 12 inches of precipitation last month.
Heavy Rain and a Few Tornadoes
It seems that every July brings one or more extreme rainfall events that cause significant flooding damage. Chicagoland, as is often the case, was a centerpoint of heavy precipitation and flooding last month. This included a round of very heavy rainfall during the Fourth of July weekend, when more than 8 inches of rain fell around Sugar Grove and Aurora, causing significant flash flooding in the west and southwest parts of the region. Storms on July 27 brought more heavy rainfall and flooding to Chicago, including a widespread area of 3-4 inches from the city to northwest Indiana. This same storm produced at least seven tornadoes in Chicagoland and reports of more than 100 mile per hour wind gusts causing significant damage across the area. Multiple rounds of thunderstorms produced extremely heavy rainfall in southeast Missouri and southern Illinois from July 9 to July 11. Parts of southern Jackson County and northern Union County received more than 10 inches in just two days, nearly reaching the all-time two-day rainfall record in Jackson County.
Outlooks
August is the beginning of the end of summer but can certainly bring its fair share of heat. It is also an important month for the growing season as we move toward fall. Climate Prediction Center outlooks for August don’t have much information for us, with slightly higher chances of warmer than average temperatures, and equal chances of wetter and drier weather (Figure 5).
The newest climatological fall (September through November) outlooks are even less certain, with no strong signals for temperature or precipitation. As El Niño strengthens, we will look for a “typical” El Niño fall weather signal, which tends to be a bit drier in Illinois. That said, El Niño tends to have its strongest impact in winter.
