Extended wet weather ended in July in Illinois with less rain and more heat

[August 15, 2019]    The seven-month historic stretch of abnormally wet weather in Illinois ended with drier than average conditions in July, according to Brian Kerschner, spokesperson for the Illinois State Climatologist Office at the University of Illinois’ Illinois State Water Survey.

The preliminary July average statewide precipitation was 3.23 inches, which is 0.85 inches below the long-term average.

Since November 2018, each month has been reported with above average statewide precipitation. Although the amount of rain in July was below average overall, the precipitation across Illinois was not evenly distributed.

Many in southern and northeastern Illinois experienced near to above average precipitation totals in July. A station near Highland in Madison County reported the highest monthly rainfall total of 9.02 inches.

In contrast, large regions of western and central Illinois saw below average rainfall. In fact, multiple localities near the Quad Cities and along the Mississippi River, as well as smaller regions in east-central Illinois, received only 10 to 25 percent of the average monthly precipitation.

Dating back to June 1, these same regions have reported precipitation departures of around 2 to 4+ inches below the long-term average. Because of this extended stretch of dry conditions, the August 1 map from the U.S. Drought Monitor continued to highlight areas of abnormally dry conditions across western and central Illinois.

The preliminary average statewide July temperature was 77.3°F, which is 1.9°F above the long-term average.

The first two to three weeks of July brought several extended periods of heat and humidity to Illinois. Most notable was the heat wave that affected the region from July 18-21, in which every county in Illinois was under an Excessive Heat Warning at some point during the weekend.

Throughout this event, daily maximum station temperatures soared into the 90s, with dew points in the mid- to upper 70s. This resulted in heat indices of over 100 for many and approached 110 degrees or higher in some locations.

Daily temperature departures of 8 to 10+ degrees above average were common across the northern half of the state.

Overnight low temperatures during this event did not bring much, if any, relief from the heat. With a daily minimum temperature of only 80 degrees on July 19, Rockford in Winnebago County set a new all-time record-high minimum temperature dating back to 1905.

Over the entire month of July, average station temperatures varied from the mid 70s to the low 80s, and monthly temperature departures of 1 to 4 degrees above the long-term average were common for the northern two-thirds of Illinois.

The highest temperature reading in the state of 98 degrees occurred at two stations, Flora (Clay County) on July 11, and Palestine (Crawford County) on July 21. The lowest minimum temperature of 51 degrees also occurred at two stations, one near Champaign (Champaign County) on July 23, and at a station near Paxton (Ford County) on July 25.

For the remainder of August, the monthly outlook from the Climate Prediction Center (CPC), issued on July 31, favors probabilities for below average temperatures across Illinois and most of the upper Midwest. The outlook also favors near equal chances for below, near, or above average precipitation.

[Lisa A. Sheppard]