Overview
March was warm and wet across Illinois.
Temperatures averaged 48.6° for the month, 7.2° higher than normal (Figure 1). March 2026 was the fifth warmest March on record.
Precipitation averaged 4.60 inches, 1.66 above normal (Figure 1). The month was the 16th wettest March on record.
Mean streamflow statewide was below the median for the month.
Mean provisional streamflow aggregated statewide was below the long-term median flow for March, about 75% of median (Figure 1). Monthly mean discharge values in March ranged mostly from much below normal to normal.
Water surface levels at the end of March were below the full pool or target level at 11 of 18 reporting reservoirs. At the end of March, Lake Shelbyville was 0.8 feet below the April 1 target level, Carlyle Lake level was 0.6 feet below the April 1 target level, and Rend Lake was 1.2 feet above the spillway level. Lake Decatur water level recovered to the range of normal summer pool levels.
Lake Michigan’s mean level was below its long-term mean for the month.
Shallow groundwater levels were 2.26 feet below the long-term average at the end of March. Levels averaged 2.14 feet above February and 0.56 feet below last year (Figure 1).
Weather/Climate Information (Trent Ford)
March in Illinois was much warmer and wetter than normal.
Temperatures averaged 48.6°, 7.2° above the 1991-2020 normal for March (Table 1, Figure 2). Last month was the fifth warmest March on record statewide and the warmest March since 2012.
March average temperatures ranged from the high 30s in northwest Illinois to the high 50s in southern Illinois, between 5 and 11° above the 1991-2020 normal (Figure 2).
March brought waves of summer-like temperatures across the state, including daily highs of 93° in Jacksonville and 89 in Bloomington-Normal. Dozens of locations across the state set new all-time March high temperature records, including 88° in Champaign-Urbana, 92° in Springfield, and 86° in Carbondale. Many of the records, including those in Champaign-Urbana and Bloomington-Normal, were last broken well over 100 years ago. A few stations’ high temperatures last month were also higher than their all-time April high temperature records, including 93° in Jerseyville and 92° in Springfield. Speaking of Springfield, our state capital had its earliest 90° day on record last month. The previous earliest 90° day in Springfield was May 5th of 1943, a full 40 days after the new record of March 26th.
Very cold weather, while fleeting, did bring temperatures well below freezing across the state last month, including nighttime low temperatures of 4° in Monmouth and 9° in Aurora. The coldest place in the state last month was Stockton with an average of 39.0°, while the warmest place in the state last month was Dixon Springs with an average temperature of 56.3°.
Precipitation statewide in March was 4.60 inches, 1.66 inches above the 1991-2020 normal (Table 1). It was the 16th wettest March on record statewide and the wettest since 1985.
March total precipitation ranged from around 2.5 inches in northwest Illinois to over 8 inches in parts of east-central Illinois. The entire state was 0.50 inches to 4.5 inches wetter than the 1991-2020 normals last month. The wettest part of the state was right around and slightly south of the Interstate 72 corridor from Springfield to Champaign-Urbana (Figure 3). Last month was the 3rd wettest March on record in Springfield, the 8th wettest in Bloomington-Normal, and the 6th wettest in Aurora.
Drought: As expected, the wet March weather improved drought conditions that had stretched back to late summer 2025. The U.S. Drought Monitor reduced statewide coverage of all drought categories between March 3rd and March 24th, including 43% less of the state in at least moderate drought and 11% less of the state in extreme drought. Root zone soil moisture improved across the state, relieving some of the risk of early season agricultural drought. However, water table levels remained much deeper than typical for spring and streams also remained somewhat to very low as the calendar moved to April. These issues are lagged effects of the prolonged hydrologic drought in Illinois, and we will need continued wet weather through April and May to see consistent improvement in these conditions.
Severe Weather: As is often the case in spring, abundant precipitation also meant abundant severe weather. An active storm track and sufficient humid, warm air moving into the Midwest produced multiple severe weather outbreaks in March. In all, the Storm Prediction Center listed 35 tornado reports in Illinois last month, including an EF3 tornado that moved through parts of Kankakee County on March 10th. That same storm produced widespread gargantuan hail, including several stones reported to be as large as 5-6” in diameter. One of the hailstones that fell in Kankakee on March 10th was measured by scientists at Northern Illinois University with a diameter of 6.616 inches. The current Illinois state hailstone record is 4.75 inches, which fell near Minooka in 2015. However, the State Climate Extremes Committee is currently reviewing the March 10th storm and measured hailstone and will determine if it set a new state record. This year marked the fourth consecutive March with at least 29 tornado warnings issued by National Weather Service offices serving Illinois. Prior to 2023, only one year (2006) had over 29 warnings issued, illustrating the remarkable stretch of active March severe weather recently.
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.
March lived up to the month’s reputation with winds averaging 9.2 mph for the month, 1.9 mph higher than February and 0.6 mph above the network’s long-term average. ICN Bondville (Champaign County) continued its streak as the windiest station, averaging 14.4 mph. The highest recorded wind gust was 56.3 mph, recorded at ICN Dixon Springs (Pope County) on March 4.
Air temperatures were higher than normal in March with an average of 49.6°, 14.3° higher than in February and 7.5° above the long-term average. Station highs were in the 80s and 90s with lows in the teens and single digits. The highest recorded temperature was 93.1° at ICN Snicarte (Mason County) on March 26. The monthly low was 2.3°, measured at ICN Monmouth (Warren County) on March 17.
Soil temperatures rose 12 to 13° from February to averages in the high 40s. Temperatures were 4 to 6° higher than the long-term average. Under bare soils, temperatures ranged from 23.9 to 82.6° at 2 inches and 23.7 to 77.7° at 4 inches. Temperatures under sod ranged from 31.3 to 70.3° at 4 inches and 31.2 to 68.6° at 8 inches.
March was wet across the network. Precipitation averaged 5.22 inches, 4.58 inches more than February and 2.20 inches above the long-term average. ICN Dixon Springs recorded 9.40 inches, the month’s highest, but thirteen stations had monthly totals greater than 5 inches.
Soil moisture will return to the IWCS in Spring 2026.
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 weigh 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 below the median value for March (approximately 75 percent of the median) and below the mean for March (approximately 65 percent of the mean). Monthly mean discharge values in March ranged mostly from much below normal to normal in the north half of Illinois, and from below normal to above normal in southern Illinois.
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-February water levels at 18 reservoirs for which levels were reported last month and this month, reported end-of-March water levels were lower at 4 reservoirs and higher at 14 reservoirs. For the 18 reservoirs with measurements reported for the end of March, water levels were below seasonal target pool or spillway level at 11 reservoirs, above seasonal target pool or spillway level at 6 reservoirs, and at about the target level or spillway level at 1 reservoir. Lake Decatur water level recovered to the range of normal summer pool levels.
Major Reservoirs. Compared to water levels at the end of February, at the end of March the water level at Rend Lake was 1.8 feet higher, Lake Shelbyville was 1.0 foot higher, and Carlyle Lake was 0.1 foot lower. At the end of March, Lake Shelbyville was 0.8 feet below the April 1 target level, Carlyle Lake level was 0.6 feet below the April 1 target level, and Rend Lake was 1.2 feet above the spillway level. (Target operating levels at 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 March 2026 mean level for Lake Michigan was 577.7 feet. The monthly mean level one year ago (March 2025) was 577.9 feet. The long-term average lake level for March is 578.5 feet, based on 1918-2024 data. In this period of record, the lowest mean level for Lake Michigan for March occurred in 1964 at 576.1 feet, and the highest mean level for March occurred in 2020 at 581.4 feet. The month-end level of Lake Michigan was 577.9 feet. All values are provided by the U.S. Army Corps of Engineers Detroit District.
Groundwater Information (Jennie Atkins)
March rains brought rising water tables at most monitoring wells. Levels averaged 2.14 feet higher at the end of the month.
The Perry well (Pike County) increased 15.65 feet in March to an end of month level of 4.09 feet, the month’s highest. This was the well’s highest level since August 2025. Large increases also occurred at the Fermi Lab well (DuPage County) that rose 7.11 feet and the Belleville well (St Clair County) that increased 5.26 feet.
Six of the 25 reporting wells ended the month lower though most saw decreases of less than one foot. The largest drop was 1.38 feet at the Fairfield well (Wayne County).
However despite improvements, most wells were below the 15 and long-term averages for March.
Wells averaged 0.56 feet below March 2025, 2.37 feet below the 15-year average, and 2.26 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