Overview
July temperatures and precipitation were above the long-term average in Illinois. Mean streamflow statewide was above the median for the month. Shallow groundwater levels were below the long-term depths.
Air temperatures averaged 75.8 degrees F, 0.4 degrees above the 1991–2020 normal for July (Figure 1). Average temperatures ranged from the low 70s in far northern Illinois to around 80 degrees in southern Illinois.
Precipitation statewide in July was 5.12 inches, 1.06 inches above the long-term statewide average (Figure 1).
Soil moisture levels at 2 inches increased 24 percent in June to an average of 0.22 water fraction by volume (wfv). Levels also increased at 4 and 8 inches but remained steady at depths of 20 inches and greater.
Mean provisional streamflow aggregated statewide was above the long-term median flow for July, about 145 percent of median (Figure 1). Monthly mean discharge values in July ranged from below normal to much above normal.
Water surface levels at the end of July were below the full pool or target level at 8 of 19 reporting reservoirs. At the end of July, Lake Shelbyville was 0.5 feet below the summer target level, Carlyle Lake was 3.6 feet above the summer target level, and Rend Lake was 2.5 feet above the spillway level. Lake Michigan’s mean level was above its long-term mean for the month.
Shallow groundwater levels were 0.49 feet below the long-term average at the end of July (Figure 1). Levels averaged 0.09 feet below those in June and 0.59 feet below last year’s levels.
Weather/Climate Information
The following description of temperatures, precipitation, severe weather, and drought comes from data compiled by networks that report to the National Oceanic and Atmospheric Administration (NOAA). These data are provisional and may change slightly over time.
July in Illinois was slightly warmer and much wetter than normal.
Temperatures averaged 75.8 degrees F, 0.4 degrees above the 1991–2020 normal for July, tying for the 51st warmest July on record (Table 1). July average temperatures ranged from the low 70s in far northern Illinois to around 80 degrees in southern Illinois (Figure 2). July was 1 to 3 degrees cooler than normal for most of northern Illinois, and 1 to 3 degrees warmer than normal in southern Illinois. The hottest point in the state last month was Cairo with an average July temperature of 82 degrees, and the coolest part of the state was Aurora with an average July temperature of 71 degrees.
Altogether, 2 daily high maximum temperature records were broken last month, and 15 daily high minimum temperature records were broken. Meanwhile, 7 daily low maximum temperature records were broken last year, including a 69-degree high temperature in Aurora on July 16. One daily low minimum temperature record was broken last month, a 52- degree low in Joliet on July 9.
Precipitation statewide in July was 5.12 inches, 1.06 inches above the long-term statewide average, and the 20th wettest July on record (Table 1). Multiple, intense rainfall events ran from northwest to southeast along and north of the Interstate 80 corridor and the Interstate 64 corridor in July, including the incredibly intense rain in the St. Louis metro area on July 26th. Between 6 and 8 inches of rain fell in just 10 hours in the Metro East. Meanwhile, parts of Clay, Richland, and Lawrence Counties in southeast Illinois had between 12 and 14 inches of rain in July, making the month the second wettest on record in Olney. While some parts of northern and south-central Illinois were 6 to 13 inches wetter than normal in July, most areas along the Interstate 74 corridor were 1 to 3 inches drier than normal (Figure 3). The wettest point in the state in July was Olney in Richland County, with over 13 inches of rain. In contrast, Homer in Champaign County received just 1.28 inches in July.
Drought: While rain was inundating the northern and south-central parts of the state, much of central Illinois from Monmouth to Danville remained somewhat to very dry. This area and parts of Alexander and Pulaski Counties in far southern Illinois were 1 to 3 inches drier than normal last month. In response, the U.S. Drought Monitor introduced and expanded the severe to moderate drought classifications in east-central and far southern Illinois. Since the beginning of summer, most of Champaign and Vermilion Counties have had less than 60 percent of normal rainfall, and some parts of eastern Champaign County are 6 to 7 inches below normal on summer-to-date rainfall. June and July total rainfall in Champaign-Urbana is 3.23 inches, the ninth lowest total on record and the lowest since 2012.
Illinois Climate Network (ICN) (Jennie Atkins)
The Illinois Climate Network (ICN) consists of 19 stations across the state that collect hourly weather and soil information.
Wind speeds were lower in July, averaging 4.5 mph or 0.8 mph lower than in June and 0.4 mph less than ICN’s long-term average. ICN Stelle (Ford County) had the highest monthly average with 3.8 mph. The highest recorded wind gust was 47.0 mph, measured at ICN Olney (Richland County) on July 16.
Temperatures rose to an average of 76 degrees F, 2 degrees higher than in June and 1 degree higher than the long-term average. July began warm as temperatures reached the mid- to high 90s throughout Illinois. ICN Champaign (Champaign County) recorded a high of 100 degrees on July 5, the network’s highest temperature of the month. However, temperatures cooled later in July. Station lows ranged from the low 50s in the north to the low 60s in the south. The month’s coolest temperature was 52 degrees, measured at ICN DeKalb (Dekalb County) on July 30.
Soil temperatures rose 3 to 4 degrees from in June to averages in the high 70s and low 80s. The warm temperatures, sunny skies, and dry soils, particularly in east-central Illinois, led to temperatures above 100 degrees at 2 and 4 inches. Temperatures at 8 inches reached the low 90s. Lows at all depths were in the 60s.
Precipitation averaged 5.22 inches for the network in July, 2.56 inches greater than in June and 1.86 inches more than the long-term average. A significant portion of that rain fell in southern Illinois. The region averaged 7.97 inches for the month with two stations, Belleville (St. Clair County) and Olney (Richland County), having totals of more than 12 inches.
In comparison, east-central Illinois averaged 2.23 inches for the month. ICN Stelle (Ford County) only received 1.88 inches, the month’s lowest.
Soil moisture at 2 inches increased 24 percent to a state average of 0.22 water fraction by volume (wfv). This was mainly due to heavy rains in the south that caused regional moisture levels to increase 61 percent in July at the 2-inch depths. Levels remained low in central Illinois. In east-central Illinois, levels averaged 0.13 wfv on July 31, which is at the wilting point of most of the soils monitored.
This pattern also occurred at the 4- and 8-inch depths with double-digit increases in the south and little change elsewhere. Soil moisture in all regions remained higher at depths of 20 inches and greater, showing little change over the month.
Surface Water Information (Bill Saylor)
Provisional monthly mean flows for this month for 26 streamgaging stations located throughout Illinois are shown in Table 2, compared to statistics of the past record of monthly mean flows at those stations for the same month. Both recent and long-term data are retrieved from U.S. Geological Survey (USGS) online data services following the end of the month. Years of record values in Table 2 represent the number of past monthly values included in the Table 2 statistics; at some stations, the available record may not be continuous. Additional source data may be available from USGS.
The statewide percent of historical mean flow and percent of historical median flow are calculated by dividing the sum of the average flows this month at stations in Table 2 by the sum of the historical mean and median flows calculated for the month, respectively, at the same stations. This method is intended to weight individual observations proportionately in the aggregate comparison. (The Illinois River and Rock River stations are excluded from the statewide calculation because other rivers listed in Table 2 contribute to their flow.)
Mean provisional flow aggregated statewide, using the available monthly mean data shown this month in Table 2, was above the median value for July (approximately 145 percent of the median) and about equal to the mean for July. Monthly mean discharge values in July ranged from below normal to much above normal.
Water-Supply Lakes and Major Reservoirs. Table 3 lists selected reservoirs in Illinois, their normal pool or target water surface elevation, and data related to observed variations in water surface elevations. Reservoir levels are obtained from a network of cooperating reservoir operators who report water levels each month. Current reservoir levels reported in Table 3 are representative of the end of the reported month and are presented as the difference in feet from the seasonal target level or from the full pool, as applies. Years of record represent the number of past reports for the same month used to calculate the average of the month-end values presented in Table 3. For some reservoirs, this average does not include the additional period of record prior to a substantial change in reservoir operation. Most reservoirs in Table 3 serve as public water supplies, with the exceptions noted in the last column.
Compared to end-of-June water levels at 19 reservoirs for which levels were reported last month and this month, reported end-of-July water levels were lower at 6 reservoirs, higher at 10 reservoirs, and about the same as at the end of June at 3 reservoirs. For the 19 reservoirs with measurements reported at the end of July, water levels were below normal target pool or spillway level at 8 reservoirs, above normal target pool or spillway level at 7 reservoirs, and at about full pool level at 4 reservoirs. The supply at Carlinville was pumped from their Lake 2.
Major Reservoirs. Compared to water levels at the end of June, at the end of July the water level at Lake Shelbyville was 0.7 feet lower, Carlyle Lake was 3.3 feet higher, and Rend Lake was 1.4 feet lower. At the end of July, Lake Shelbyville was 0.5 feet below the summer target level, Carlyle Lake was 3.6 feet above the summer target level, and Rend Lake was 2.5 feet above the spillway level.
Great Lakes. Current month mean and end-of-month values are provisional and are relative to International Great Lakes Datum 1985. The July 2022 mean level for Lake Michigan was 580.1 feet. The monthly mean level one year ago (July 2021) was 580.8 feet. The long-term average lake level for July is 579.4 feet, based on 1918–2021 data. In this period of record, the lowest mean level for Lake Michigan for July occurred in 1964 at 576.7 feet, and the highest mean level for July occurred in 2020 at 582.2 feet. The month-end level of Lake Michigan was 580.1 feet. All values are provided by the U.S. Army Corps of Engineers Detroit District.
Groundwater Information (Jennie Atkins)
Heavy rains in the south caused water tables to rise in the region. The water table at the Olney (Richland County) well rose 3.1 feet in July because of the more than 12 inches of rain received at the site over the month. The SWS #2 (St. Clair County) well increased 3.7 feet in July. Parts of the county recorded over 13 inches of rain for the month.
Yet, this trend was not seen in wells in central and northern Illinois or even in all southern wells. The well at Good Hope (McDonough County) fell 1.9 feet from in June. Overall, levels averaged 0.09 feet below June levels.
Water tables were slightly lower than last year’s, averaging 0.59 feet below July 2021 levels and ranging from 2.7 feet below to 3.0 feet above July 2021 levels.
Levels averaged 1.03 feet below the 15-year average and 0.49 feet below the period of record.
Data sources for the IWCS include the following:
CPC - Climate Prediction Center, https://www.cpc.ncep.noaa.gov/index.php
ISWS - Illinois State Water Survey, https://www.isws.illinois.edu
MRCC - Midwestern Regional Climate Center, https://mrcc.purdue.edu/
NCEI - National Centers for Environmental Information, https://www.ncei.noaa.gov
NWS - National Weather Service, https://www.nws.noaa.gov
SPC - Storm Prediction Center, https://www.spc.noaa.gov
USACE - U.S. Army Corps of Engineers, https://www.lre.usace.army.mil
USDM - U.S. Drought Monitor, https://droughtmonitor.unl.edu
USGS - U.S. Geological Survey, https://waterdata.usgs.gov/il/nwis
WARM - Water and Atmospheric Resources Monitoring Program, https://www.isws.illinois.edu/warm
