Overview
A wet June for most of Illinois.
Temperatures averaged 71.9° for the month, 0.3° below normal.
Precipitation averaged 7.14 inches, 2.49 inches above normal. June 2026 was the 6th wettest June on record.
Soil moisture rose in the first 20 inches in June. Moisture levels at 2-inches rose 33%, ending the month with an average of 0.32 water fraction by volume (wfv). The most significant increases were in the north where moisture levels were 89% higher at the end of the month.
Mean streamflow statewide was above the median for the month.
Mean provisional streamflow aggregated statewide was above the long-term median flow for June, about 275% of median (Figure 1). Monthly mean discharge values in June ranged mostly from normal to much above normal for the month.
Water surface levels at the end of June were below the full pool or target level at 3 of 19 reporting reservoirs. At the end of June, Lake Shelbyville was 10.5 feet above the summer target level, Carlyle Lake level was 2.9 feet above the summer target level, and Rend Lake was 0.9 feet above the spillway level.
Lake Michigan’s mean level was slightly above its long-term mean for the month.
Shallow groundwater levels were 0.76 feet below the long-term average at the end of June. Levels averaged 0.25 feet above May and 0.88 feet above last year.
Weather/Climate Information (Trent Ford)
June was slightly cooler and much wetter than normal in Illinois.
Temperatures averaged 71.9 degrees, 0.3 degrees below the 1991-2020 normal for June (Table 1, Figure 2). Last month was the 66th coolest June on record statewide.
June average temperatures ranged from the high 60s in northern Illinois to the mid-70s in southern Illinois. Most of the northern half of the state was near normal to 2 degrees cooler than normal, while much of southern Illinois was around 1 degree warmer than normal last month (Figure 2).
Below average temperatures in mid-June brought a few sub-50-degree nighttime lows in central and northern Illinois, including 43 degrees in Danville and 45 in Rockford. Extreme heat in the last two days of June pushed daytime highs well into the 90s, including highs of 96 degrees in Alton and 94 in Chicago. The warmest place in the state last month was Morrisonville in Christian County with an average temperature of 76.9 degrees. The coolest place in the state last month was Waukegan with an average temperature of 66.8 degrees. Last month was the coolest June in Peoria since 2013.
Precipitation statewide in June was 7.14 inches, 2.49 inches above the 1991-2020 normal (Table 1). It was the 6th wettest June on record in Illinois and the wettest since 2015.
The same upper-level trough that brought us cooler weather mid-month also kept an active storm track in central Illinois, particularly, producing seriously high rainfall totals. Total June rainfall ranged from over 12 inches in parts of central Illinois to less than 2 inches in southern Illinois (Figure 3).
Flooding: Last month was the 5th wettest June on record in Peoria and the 3rd wettest on record in Bloomington-Normal and Galesburg. The heavy rainfall caused widespread flooding on the Illinois, Mackinaw, and Vermilion Rivers among others in central Illinois last month. The Illinois River at Havana reached its highest stage (19.82 feet) since 2020. Meanwhile, the rain was harder to come by in southern Illinois, especially around the Carbondale-Marion area. Carbondale has amassed quite a precipitation deficit this year so far, with the driest first half of the year there since 2012.
Severe Weather: June is one of our most active severe weather months; however, this month was next level. Last month saw multiple, very large tornado outbreaks across Illinois, producing at least 65 tornadoes. Among these were multiple large, EF-3 tornadoes in Effingham County and Jefferson County, and unfortunately related fatalities and injuries. The incredibly active severe weather month continued a record-breaking tornado year in Illinois. As of July 1st, our state had 178 tornadoes, smashing the previous annual record of 142 in 2024, and doubling the next most active state this year. Illinois has now had over 100 tornadoes four years in a row after only surpassing the century mark four times between 1950 and 2022.
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.
Winds were lower again in June, averaging 6.0 mph for the month or 0.7 mph lower than May and 0.1 mph higher than the network’s long-term average. ICN Monmouth (Warren County) was the windiest station with a monthly average of 9.2 mph. The highest recorded wind gust was 67.5 mph, measured at ICN DeKalb (DeKalb County) on June 10.
Air temperatures were 9.0° higher than May with a monthly average of 72.8°. Temperatures were 0.2° warmer than the long-term average. Station highs ranged from the high 80s to mid-90s. Station lows in the 40s and 50s.
June’s highest temperature was 95.4°, recorded on June 30 at ICN Rend Lake (Jefferson County). The lowest temperature was 46.4°, measured at ICN St Charles (Kane County) on June 15.
Soil temperatures were 8 to 9° warmer in June to averages in the mid-70s. Under sod temperatures were 1° above the long-term averages while the bare soil temperatures were 2-4° below. Under bare soils, temperatures ranged from 47.6 to 108.2° at 2 inches and 52.9 to 98.2° at 4 inches. Temperatures under sod ranged from 62.3 to 93.3° at 4 inches and 61.1 to 86.8° at 8 inches.
June was wetter at all ICN stations. The network averaged 6.50 inches of rain, 3.79 inches more than May and 2.41 inches higher than the long-term average. Two stations – ICN Peoria (Tazewell County) an ICN Charleston (Coles County) – received more than 10 inches recording 10.91 and 10.06 inches, respectively.
Soil moisture rose in the top 20 inches. Levels increased 33%, on average, at 2-inch depths. The largest increases were at the northern stations where levels rose from near wilting points to an average 0.24 water fraction by volume (wfv), an 89% increase. In comparison, the moisture declined 4% at the southern stations, ending the month with an average of 0.36 wfv.
Soil moisture increases were observed to the 20-inch depths. Moisture levels remained high at 39 and 59 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. Both recent and long-term data are retrieved from 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 June (approximately 275 percent of the median) and above the mean for June (approximately 200 percent of the mean). Monthly mean discharge values at Table 4 streamgage locations ranged mostly from normal to much above normal for the month. Monthly mean streamflow of the Big Muddy River at Plumfield (downstream of Rend Lake) remained below normal in June.
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-May water levels at 16 reservoirs for which levels were reported last month and this month, reported end-of-June water levels were lower at 6 reservoirs, higher at 8 reservoirs, and about the same as at the end of May at 2 reservoirs. For the 19 reservoirs with measurements reported for the end of June, water levels were below normal target pool or spillway level at 3 reservoirs, above normal target pool or spillway level at 11 reservoirs, and at about the target level or spillway level at 5 reservoirs.
Major Reservoirs. Compared to water levels at the end of May, at the end of June the water level at Lake Shelbyville was 8.3 feet higher, Carlyle Lake was 1.0 foot higher, and Rend Lake was 0.6 feet lower. At the end of June, Lake Shelbyville was 10.5 feet above the summer target level, Carlyle Lake level was 2.9 feet above the summer target level, and Rend Lake was 0.9 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 June 2026 mean level for Lake Michigan was 579.4 feet. The monthly mean level one year ago (June 2025) was 578.8 feet. The long-term average lake level for June is 579.3 feet, based on 1918-2025 data. In this period of record, the lowest mean level for Lake Michigan for June occurred in 1964 at 576.6 feet, and the highest mean level for June 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)
A wetter month led to increasing water tables. Fifteen of 25 reporting wells were higher at the end of June.
The increases were small for most wells, less than a foot. However, the Fermi Lab (DuPage County) well increased 2.09 feet in June, the highest of the month. The well has risen almost 10 feet in 2026 so far from a low of 15.1 feet in December 2025.
Water table decreases were seen in southern Illinois where precipitation was 1 to 3 inches below normal. The Carbondale (Jackson County) well fell 1.81 feet, the month’s largest. Similar drops were also observed at Belleville (St Clair County) and Southeast College (Saline).
Wells averaged 0.88 feet above June 2025, 0.85 feet below the 15-year average, and 0.76 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