Overview
Another warm, wet month in Illinois.
Temperatures averaged 58.8 degrees, 6.2 degrees above the 1991-2020 normal for April. Last month was the warmest April on record statewide.
Precipitation statewide in April was 5.80 inches, 1.56 inches above the 1991-2020 normal. It was the 14th wettest April on record statewide.
Two-inch soil moisture rose 7%, on average, in April to a statewide average of 0.35 water fraction by volume. Increases occurred through the 20-inch depths while moisture levels remained steady at 39 inches and deeper.
Shallow groundwater levels were 0.86 feet below the long-term average at the end of April. Levels averaged 1.56 feet above March and 0.93 feet above last year.
Mean streamflow statewide was above the median for the month.
Mean provisional streamflow aggregated statewide was above the long-term median flow for April, about 145% of median (Figure 1). Monthly mean discharge values in April ranged mostly from normal to above normal. Monthly mean streamflow was much below normal in southernmost Illinois, and much above normal at some northern Illinois stations.
Water surface levels at the end of April were below the full pool or target level at 1 of 19 reporting reservoirs. At the end of April, Lake Shelbyville was 0.9 feet above the May 1 target level, Carlyle Lake level was 2.0 feet above the May 1 target level, and Rend Lake was 1.5 feet above the spillway level.
Lake Michigan’s mean level was slightly below its long-term mean for the month.
Weather/Climate Information (Trent Ford)
April in Illinois was the warmest on record and was also much wetter than normal.
Temperatures averaged 58.8 degrees, 6.2 degrees above the 1991-2020 normal for April (Table 1). Last month was the warmest April on record statewide.
April average temperatures ranged from the mid-50s in northwest Illinois to the mid-60s in southern Illinois, between 5 and 10 degrees above the 1991-2020 normal (Figure 1).
Prolonged periods of warmth broke 29 daily high maximum temperature records and broke an astounding 167 daily high minimum temperature records last month. Only one daily low minimum temperature record was broken, with a 24-degree low in Elgin on April 20th. Eight places broke their all-time April high minimum temperature records last month, including a 70-degree low temperature in Mt. Vernon and a 68-degree low temperature in Peoria. Waukegan was the coolest place in the state in April with an average temperature of 50.5 degrees, and Smithland Lock & Dam in Massac County was the warmest place in the state with an average temperature of 65.2 degrees.
Precipitation statewide in April was 5.80 inches, 1.56 inches above the 1991-2020 normal (Table 1). It was the 14th wettest April on record statewide.
April this year brought a very active storm track and multiple rounds of heavy precipitation, especially in northern and central Illinois. April total precipitation ranged from around 2.5 inches in far southern Illinois to over 12 inches in northwest Illinois. April was 1 to 3 inches drier than average in far southern Illinois and was 1 to 8 inches wetter than normal in most places north of Interstate 70 (Figure 2).
Flooding: Multiple rounds of very heavy rain across northern Illinois and southern Wisconsin caused widespread flooding on several rivers, including the Fox and Des Plaines. The Fox River at Algonquin reached a peak of 12 feet for the first time since 2017, as communities sand-bagged to minimize flood damage. Meanwhile, the wet weather in central Illinois continued the region’s drought recovery, as all drought in the U.S. Drought Monitor was removed from the region by the end of the month. Last month was the wettest April on record in Freeport with 8.92 inches; a full inch above the previous wettest April in 2013. Last month was also the 7th wettest April on record in Chicago and Rockford, and the 6th wettest April on record in Peoria.
Severe Weather: April advanced what has been an incredibly active severe weather year for Illinois. As of May 1st, Illinois had 108 tornadoes in 2026. For perspective, our state has averaged around 60 tornadoes per year over the past 30 years. Mississippi is the next most tornado-active state this year with 61. There were simply too many tornado events last month to highlight them all. Among many notable storms was a group of tornadoes that tore through Bloomington-Normal, leaving significant damage especially on the north and west sides of the metro area. An EF-2 tornado caused significant damage in Lena, Illinois on April 17th. While multiple homes were substantially damaged, there were no reported injuries or fatalities. 2026 is the third consecutive year with over 100 tornadoes in Illinois, continuing a remarkably active period of severe weather for our state.
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 averaged 9.3 mph in April, 0.6 mph above the month’s long-term average but 0.1 mph lower than March. ICN Bondville (Champaign County) once again had the highest monthly average of 14.4 mph. ICN DeKalb (DeKalb County) recorded the highest wind gust, measuring 58.3 mph of April 27.
Air temperatures were once again higher than normal, averaging 59.5° or 6.4° above the long-term average. Temperatures averaged 6.6° higher than in March. Station highs were in the 80s with lows from the 20s to the 40s. The highest recorded temperature was 88.1, measured at ICN Snicarte (Mason County) on April 14. The lowest temperature was 24.8°, recorded on April 7 at ICN Freeport (Stephenson County).
Soil temperatures rose 11° to averages in the high 50s to low 60s. Temperatures were 6 to 7° warmer than the long-term averages. Under bare soils, temperatures ranged from 27.2 to 91.1° at 2 inches and 31.4 to 87.2° at 4 inches. Temperatures under sod ranged from 42.7 to 78.1° at 4 inches and 43.6 to 71.3° at 8 inches.
April was wet at most ICN stations. The network averaged 6.18 inches for the month, 2.22 inches more than its long-term average. Only three stations, all in southern Illinois, had monthly totals less than normal. The northwest stations were the wettest with ICN Freeport (Stephenson County) recording 9.93 inches, the month’s highest.
Soil moisture at 2 inches rose 7%, on average, during the month. The largest increases were in southern Illinois where stations ended April 32% higher partially due to significant rain at the end of the month. Increases continued to 20 inches. Moisture levels at 39 and 59 inches remained steady.
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 April (approximately 145 percent of the median) and above the mean for April (approximately 120 percent of the mean). Monthly mean discharge values in April ranged mostly from normal to above normal across Illinois; however, monthly mean streamflow was much below normal in southernmost Illinois, and much above normal at some northern Illinois stations.
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-March water levels at 18 reservoirs for which levels were reported last month and this month, reported end-of-April water levels were higher at 16 reservoirs, lower at 1 reservoir, and about the same as at the end of March at 1 reservoir. For the 19 reservoirs with measurements reported for the end of April, water levels were below normal target pool or spillway level at 1 reservoir, above normal target pool or spillway level at 13 reservoirs, and at about the target level or spillway level at 5 reservoirs.
Major Reservoirs. Compared to water levels at the end of March, at the end of April the water level at Lake Shelbyville was 5.4 feet higher, Carlyle Lake was 3.6 feet higher, and Rend Lake was 0.3 feet higher. At the end of April, Lake Shelbyville was 0.9 feet above the May 1 target level, Carlyle Lake level was 2.0 feet above the May 1 target level, and Rend Lake was 1.5 feet above the spillway level. (The seasonal target levels of Lake Shelbyville and Carlyle Lake increase from March to May.)
Great Lakes. Current month mean and end-of-month values are provisional and are relative to International Great Lakes Datum 1985. The April 2026 mean level for Lake Michigan was 578.6 feet. The monthly mean level one year ago (April 2025) was 578.4 feet. The long-term average lake level for April is 578.8 feet, based on 1918-2024 data. In this period of record, the lowest mean level for Lake Michigan for April occurred in 1964 at 576.2 feet, and the highest mean level for April occurred in 2020 at 581.7 feet. The month-end level of Lake Michigan was 579.0 feet. All values are provided by the U.S. Army Corps of Engineers Detroit District.
Groundwater Information (Jennie Atkins)
Water levels continued to rise across Illinois in April as 20 out of 25 reporting wells showed increases over the month.
Both Bondville wells (Champaign County) and the Freeport well (Stephenson County) rose more than 5 feet over the month, April’s highest increases. All wells are co-located at ICN stations and reported precipitation totals of 5.92 and 9.79 inches, respectively.
However, despite the rise, the Freeport well ended below both the 15 and period of record long-term averages.
Five wells reported decreases in April, most less than a foot. The Sparta well (Randolph County) was 1.33 feet lower than March but remains more than 4 feet above the lows observed in January 2026.
Wells averaged 0.93 feet above April 2025, 0.99 feet below the 15-year average, and 0.86 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