Overview
July saw higher temperatures and streamflows in Illinois but lower precipitation and water tables.
Temperatures averaged 76.8°, 1.4° above the long-term average.
Precipitation was 3.35 inches, 0.71 inches below the long-term average.
Soil moisture was lower across Illinois with the largest declines in central Illinois.
Mean streamflow statewide was above the median for the month. Two-inch moisture levels ended the month 26% lower with a state-wide average of 0.22 water fraction by volume (wfv). Declines were seen through the top 20 inches.
Mean provisional streamflow aggregated statewide was above the long-term median flow for July, about 175% of median (Figure 1). Monthly mean discharge values in July mostly ranged from normal to above normal.
Water surface levels at the end of July were below the full pool or target level at 9 of 21 reporting reservoirs. At the end of July, Lake Shelbyville was 4.7 feet above the summer target level, Carlyle Lake level was 0.5 feet above the summer target level, and Rend Lake was 0.4 feet above the spillway level.
Lake Michigan’s mean level was slightly above its long-term mean for the month.
Shallow groundwater levels were 1.07 feet below the long-term average at the end of July. Levels averaged 1.18 feet below June and 0.26 feet below last year.
Weather/Climate Information (Trent Ford)
July was warmer and drier than normal in Illinois.
Temperatures averaged 76.8°, 1.4° above the 1991-2020 normal for July (Table 1, Figure 2). Last month was the 33rd warmest July on record statewide.
July average temperatures ranged from the mid-70s in northern Illinois to the low 80s in southern Illinois, between 1 and 4° 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° in Belleville and 98 in Marseilles. Persistently high humidity kept nighttime temperatures elevated as well, with nighttime lows of 82° in Belleville and 80 in Chicago. Springfield recorded its highest dewpoint temperature on record last month: 84° on July 26. The state capital also suffered through an unprecedented run of 11 straight hours with a dewpoint above 80°, 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° 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.
Precipitation statewide in July was 3.35 inches, 0.71 inches below the 1991-2020 normal (Table 1). It was the 57th driest July on record in Illinois and the driest since 2019.
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 3). 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.
Flooding & Severe Weather: 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 center point 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.
Illinois Climate Network (ICN) (Jennie Atkins)
The Illinois Climate Network (ICN) consists of 20 stations across the state which collects hourly weather and soil information.
July was calmer for Illinois with winds averaging 4.2 mph, 1.8 mph lower than June and 0.6 mph below the network’s long-term average for the month. Winds averaged 6.1 mph at ICN Stelle (Ford County) making it the month’s windiest station. The highest recorded wind gust was 43.4 mph, recorded at ICN Big Bend (Whiteside County) on July 20.
Air temperatures were higher in July, averaging 76.9° or 4.1° higher than June and 1.7° above the long-term average. Stations highs were in the 90s with lows ranging from the mid-40s to low 60s. The highest network temperature, 97.9°, was recorded at ICN Belleville (St Clair County) on July 26. The lowest was 46.2°, measured at ICN Stelle (Ford County) on July 23.
Soil temperatures were 6° warmer than June as averages were in the high 70s to low 80s. Under bare soils, temperatures ranged from 52.4 to 110.7° at 2 inches and 58.9 to 101.1° at 4 inches. Temperatures under sod ranged from 68.2 to 98.4° at 4 inches and 70.0 to 91.0° at 8 inches.
The network received 3.96 inches of rain in July, 2.54 inches less than June and 0.17 inches more than the long-term average. The average, though, is heavily skewed by very wet months for the southern stations. ICN Dixon Springs (Pope County) received 10.25 inches, 6.04 inches above its long-term average.
However the month’s highest was 12.18 inches, measured at ICN Carbondale (Jackson County). This is 8.36 inches over the station’s normal. 78% of the rain, 9.55 inches, fell over just four days from July 8 -11.
In comparison, ICN Stelle (Ford County) recorded only 1.13 inches, the network’s lowest July total.
Soil moisture dropped at depths from 2 to 20 inches during July. At 2 inches, moisture levels were 26% lower, on average, at the end of the month. The declines were largest at the central stations, which averaged 38% lower by July 31. ICN Stelle (Ford County) saw a 40% drop.
For the central stations, the declines continued through 59 inches while soil moisture remained steady at the deeper depths (39 and 59 inches) in the north and south.
On average, levels were 68% lower at 4 inches, 26% at 8 inches, and 12% at 20 inches.
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 past record of monthly mean flows at those stations for the same month. Streamflow data is retrieved from USGS online data services. 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 175 percent of the median) and above the mean for July (approximately 120 percent of the mean). Monthly mean discharge values in July ranged mostly from normal to above normal. The monthly mean streamflow of the Big Muddy River at Plumfield remained below 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 seasonal target level or from 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 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 21 reservoirs for which levels were reported last month and this month, reported end-of-July water levels were lower at 13 reservoirs, higher at 3 reservoirs, and about the same as at the end of June at 5 reservoirs. For the 21 reservoirs with measurements reported for the end of July, water levels were below normal target pool or spillway level at 9 reservoirs, and above normal target pool or spillway level at 12 reservoirs.
Major Reservoirs. Compared to water levels at the end of June, at the end of July the water level at Lake Shelbyville was 5.8 feet lower, Carlyle Lake was 2.5 feet lower, and Rend Lake was 0.6 feet lower. At the end of July, Lake Shelbyville was 4.7 feet above the summer target level, Carlyle Lake level was 0.5 feet above the summer target level, and Rend Lake was 0.4 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 2026 mean level for Lake Michigan was 579.5 feet. The monthly mean level one year ago (July 2025) was 579.0 feet. The long-term average lake level for July is 579.4 feet, based on 1918-2025 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 579.5 feet. All values are provided by the U.S. Army Corps of Engineers Detroit District.
Groundwater Information (Jennie Atkins)
More normal precipitation with declining soil moisture led to lower water tables at the end of July. Twenty-two of the 26 reporting wells were lower at the end of July.
Most decreases were more than a foot with seven wells seeing drops of two feet or more. The Olney (Richland County) well was 3.22 feet lower at the end of the month. This site received less than half of its normal rainfall in July and saw a 29% decrease in 2-inch soil moisture.
The two largest increases for the month were in the southwest where rainfall totals were greater than 6 inches. The Carbondale (Jackson County) and Sparta (Randolph County) wells both rose more than a foot.
Wells averaged 0.26 feet below July 2025, 1.31 feet below the 15-year average, and 1.07 feet below the long-term record (Table 4).
Data sources for the IWCS include the following:
CPC - Climate Prediction Center
ISWS - Illinois State Water Survey
MRCC - Midwestern Regional Climate Center
NCEI - National Centers for Environmental Information
NWS – National Weather Service
SPC – Storm Prediction Center
USACE – U.S. Army Corps of Engineers
USDM – US Drought Monitor
USGS – US Geological Survey
WARM – Water and Atmospheric Resources Monitoring Program