April 2025 Overview
April was another warm month in Illinois.
Temperatures averaged 54.1°, 1.4° above the 1991-2020 normal for April and the 32nd warmest April on record statewide (Figure 1).
Precipitation statewide in April was 5.12 inches, 0.88 inches above normal and the 25th wettest April on record statewide (Figure 1).
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 165% of median (Figure 1). Monthly mean discharge values in April ranged from below normal to normal in northern and central Illinois, to much above normal in southern Illinois.
Water surface levels at the end of April were below the full pool or target level at 2 of 18 reporting reservoirs. At the end of April, Lake Shelbyville was 0.7 feet above the May 1 target level, Carlyle Lake level was 2.4 feet above the May 1 target level, and Rend Lake was 5.3 feet above the spillway level.
Lake Michigan’s mean level was below its long-term mean for the month.
Soil moisture average 0.33 water fraction by volume (wfv) at the end of April, 8% lower than the beginning of the month. Levels were 5% lower at 4 inches. Soil moisture remained high at depths of 20 inches and greater.
Weather/Climate Information (Trent Ford)
The following description of temperatures, modified growing degree days, 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.
April in Illinois was warmer and wetter than normal.
Temperatures averaged 54.0°, 1.4° above the 1991-2020 normal for April and the 32nd warmest April on record statewide (Table 1). April average temperatures ranged from the high 40s in northern Illinois to the high 50s in southern Illinois, between 1 and 3° above normal (Figure 2). The short periods of warmer weather in April broke seven daily high maximum temperature records and three daily high minimum temperature records. Meanwhile, the colder weather in the first half of the month broke three daily low maximum temperature records and two daily low minimum temperature records. Waukegan was the coldest place in the state last month with an average temperature of 46.7°. Carbondale was the warmest with an average temperature of 60.3°.
Precipitation statewide in April was 5.12 inches, 0.88 inches above normal and the 25th wettest April on record statewide (Table 1). April this year brought a very active storm track and multiple rounds of heavy precipitation, especially in southern Illinois. April total precipitation ranged from around 2.5 inches in northwest Illinois to over 15 inches in southern Illinois. Most of central and northern Illinois were within 1 inch of normal precipitation last month, apart from areas round the Wisconsin border, which were closer to 2 inches drier than normal. Meanwhile, virtually all places south of I-70 were 4 to 8 inches wetter than normal in April (Figure 3).
Last month was the wettest April on record in St. Louis and Fairfield and was a top 10 wettest April on record for most places in southern Illinois. Overall, the preliminary statewide average total April precipitation was 5.46 inches, 1.22 inches above the 1991-2020 average and 18th wettest on record statewide.
Snow: The first 80-degree day in many parts of Illinois is on par with any of the great weather gifts we have, like Christmas morning snow or an October afternoon with winds below 20 mph. But if you’ve lived in Illinois for more than a year, you should be weary of the snow that inevitably follows that first taste of summer temperatures. This year, though, no measurable snow came to Illinois in April. Many stations in central and northern Illinois recorded trace snowfall in the first week of the month, but no accumulation.
Given the rarity of May snow in Illinois, I am confident in my proclamation of the end of the 2024-25 snowfall season. Snowfall totals in Illinois ranged from around 3 inches in far southern Illinois to nearly 25 inches in parts of southeast Illinois. An active winter stormtrack across the Interstate 70 corridor in January and February kept south-central Illinois 1 to 10 inches snowier than normal. Meanwhile, most of central and northern Illinois had between 3 and 25 inches below normal snowfall, with the largest negative departures in northeast Illinois.
Illinois Climate Network (ICN) (Jennie Atkins)
The Illinois Climate Network (ICN) consists of 19 stations across the state which collects hourly weather and soil information.
Winds averaged 8.1 mph in April, 0.9 mph lower than March and 0.6 mph lower than the network’s long-term average. ICN Bondville (Champaign County) had an average monthly wind speed of 12.4 mph, the network’s highest. The highest reported wind gust was 50.0 mph measured at ICN Belleville (St Clair County) on April 20.
Temperatures were 7.3° higher than March and 1.8° higher than the long-term average, averaging 54.9° in April. Station highs were in the 80s with lows below freezing. The highest temperature was 87.5°, recorded at ICN Belleville (St Clair County) on April 20. The lowest was 18.6°, measured at ICN St Charles (Kane County) on April 8.
Soil temperatures rose 9° on average from March to the mid-50s. Under bare soils, temperatures ranged from 30.7 to 92.6° at 2 inches and 33.6 to 81.5° at 4 inches. Temperatures under sod ranged from 40.1 to 75.9° at 4 inches and 41.1 to 69.8° at 8 inches.
April was wetter for the southern stations as five stations reported monthly totals greater than 10 inches. ICN Dixon Springs (Pope County) received 13.80 inches, 8.97 inches more than usual for the month.
The northern stations had a drier month, receiving only 64 to 75% of normal totals. ICN Freeport (Stephenson County) recorded 2.15 inches, 1.21 inches lower than the station’s long-term average.
Overall, the network averaged 6.13 inches in April, 2.17 inches more than March and 3.26 inches higher than the long-term average.
Soil moisture decreased 8% overall at 2 inches over April. The largest declines were in northern Illinois with levels 24% lower at the end of the month. However, soil moisture levels rose in the south, ending the month 8% higher.
Similar trends were observed through the top 8 inches. Soil moisture remained high across the state at depths of 20 inches and greater.
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 165 percent of the median) and above the mean for April (approximately 140 percent of the mean). Monthly mean discharge values in April ranged from below normal to normal in northern and central Illinois, to much above normal in southern Illinois. The April 2025 monthly mean flows at four of the five southernmost streamgaging stations listed in Table 2 were provisionally the highest values for the month of April in the respective periods of record (which in the case of the Big Muddy River at Plumfield is truncated to after the construction of Rend Lake, upstream).
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 lower at 1 reservoir, higher at 14 reservoirs, and about the same as at the end of March at 3 reservoirs. For the 18 reservoirs with measurements reported for the end of April, water levels were below normal target pool or spillway level at 2 reservoirs, above normal target pool or spillway level at 14 reservoirs, and at about the target level or spillway level at 2 reservoirs.
Major Reservoirs. Compared to water levels at the end of March, at the end of April the water level at Lake Shelbyville was 5.7 feet higher, Carlyle Lake was 3.1 feet higher, and Rend Lake was 1.8 feet higher. At the end of April, Lake Shelbyville was 0.7 feet above the May 1 target level, Carlyle Lake level was 2.4 feet above the May 1 target level, and Rend Lake was 5.3 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 April 2025 mean level for Lake Michigan was 578.4 feet. The monthly mean level one year ago (April 2024) was 578.9 feet. The long-term average lake level for April is 578.8 feet, based on 1918-2023 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 578.5 feet. All values are provided by the U.S. Army Corps of Engineers Detroit District.
Groundwater Information (Jennie Atkins)
Water tables rose 0.22 feet, on average, in March. Thirteen of the twenty-two reporting wells increased over the month.
The highest increase occurred at Good Hope well (McDonough County) which ended the month 1.36 feet higher than in March. Four other wells – Crystal Lake (McHenry County), Monmouth (Warren County), Rend Lake (Jefferson County), and SWS #2 (St. Clair County) – rose more a foot.
However, levels averaged more than a foot lower than last year. The Freeport well (Stephenson County) was more than 8 feet below 2024 despite rising 0.50 feet in April. Good Hope was 3.86 feet below last year even with its April increase. Only seven wells were higher than last year.
Wells averaged 1.21 feet below April 2024, 1.16 feet below the 15-year average, and 0.87 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