Overview
Temperatures averaged 59.6 degrees in September, 4.8 degrees above normal and tied for the 9th warmest on record statewide.
Precipitation statewide in October was 2.67, 0.59 inches below the 30-year normal and the 67th driest October on record statewide.
Soil moisture at 2 inch depths averaged 0.26 water fraction by volume (wfv) at the end of October, 56% higher than the beginning of the month. Moisture levels increased in the top 8 inches.
Shallow groundwater levels were 1.85 feet below the long-term average at the end of October. Levels averaged 0.31 feet below September and 0.19 feet below last year.
Mean streamflow statewide was below the median for the month.
Mean provisional streamflow aggregated statewide was below the long-term median flow for October, about 80% of median (Figure 1). Monthly mean discharge values ranged mainly from normal to much below normal for October. The October 2025 monthly mean flow of the Sangamon River at Monticello was the lowest reported for any calendar month in the period of record of the gage.
Water surface levels at the end of October were below the full pool or target level at 18 of 19 reporting reservoirs. At the end of October, Lake Shelbyville was 2.3 feet below the seasonal target level, Carlyle Lake level was 0.7 feet below the seasonal target level, and Rend Lake was 0.3 feet below the spillway level.
Lake Michigan’s mean level was below its long-term mean for the month.
Weather/Climate Information (Trent Ford)
The following description of temperatures, 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.
October in Illinois was warmer and drier than normal statewide.
Temperatures averaged 59.6 degrees in September, 4.8 degrees above normal and tied for the 9th warmest on record statewide.
October average temperatures ranged from the high 50s in northern Illinois to the mid-60s in southern Illinois, between 2 and 7 degrees above average (Figure 2, Table 1). High temperatures regularly reached into the high 80s and low 90s in early October, including 93 degrees in Minonk and 92 in Charleston. However, low humidity helped nighttime temperatures dip into the 20s and 30s on m any nights, including 26 degrees in Moline and 31 in Mt. Vernon.
The coolest point in the state last month was Barrington in Lake County at 55.1 degrees, and the warmest point was Morrisonville in Christian County at 64.1 degrees. Last month was a top 10 warmest October on record in several places, including Champaign-Urbana (6th warmest). Unusually high temperatures in early October broke 28 daily high maximum temperature records and 7 daily high minimum temperature records. Two places, McHenry and Normal, broke all-time October high maximum temperature records with highs of 90 and 92 degrees, respectively, in the first week of the month.
Precipitation statewide in October was 2.67, 0.59 inches below the 30-year normal and the 67th driest October on record statewide.
The first half of October was quite dry and extended drought conditions statewide from September. A significant weather pattern shift that coincided with the mid-month cooldown brought more frequent and substantial rain, especially in southern Illinois. Overall, October total precipitation ranged from around 0.90 inches in western Illinois to over 6 inches in parts of southern and south-central Illinois. Most of the state south of Interstate 70 was 1 to 4 inches wetter than normal in October, while most of central and northern Illinois were 1 to 3 inches drier than normal (Figure 3, Table 1).
Drought: Below normal rainfall continued from August and September into October in central and northern Illinois. Most of central Illinois has been 5 to 10 inches drier than normal since August 1st, less than 50% of normal over that time. The dry weather helped harvest progress very quickly but also created some challenges with dry vegetation and high fire risk. Dozens of field fires were reported across the state in the first two weeks of October, including one that burned over 1,000 acres in north-central Illinois. Many rivers and streams remain at or near low flow, including extremely low levels on the Sangamon and Vermilion Rivers. In contrast, drought was eased or altogether broken in much of southern Illinois, thanks to abundant rainfall in October.
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 rose in October to an average of 5.6 mph, 2.3 mph higher than September but 0.9 mph lower than the long-term average. ICN Monmouth (Warren County) had the month’s highest average wind speed of 9.7 mph. The highest recorded wind gust was 42.0 mph, measured at ICN Stelle (Ford County) on October 21.
Temperatures average 58.9° for the month, 9.9° cooler than September and 4.1° warmer than the long-term average. Stations saw highs in the high 80s and low 90s and lows in the 20s and 30s. The highest recorded temperature was 92.5° at ICN Champaign (Champaign County) while the lowest was 25.8° at ICN DeKalb (DeKalb County).
Soil temperature fell 8 to 12° in October to averages in the low to mid 60s. Under bare soils, temperatures ranged from 33.9 to 96.1° at 2 inches and 34.4 to 91.2° at 4 inches. Temperatures under sod ranged from 46.0 to 82.6° at 4 inches and 48.4 to 91.9° at 8 inches.
October was wetter for most stations. The southern and most northern stations received higher than normal precipitation for the month. The far southern stations saw especially heavy totals as ICN Dixon Springs (Pope County) measured 6.54 inches, 2.86 inches higher than its long-term average.
Conditions were drier at the central stations as most stations recorded monthly totals less than 2 inches, more than an inch below their long-term averages.
Overall, the network averaged 3.09 inches for the month, 1.78 inches more than September but 0.19 inches below the long-term average.
Despite disparities in precipitation, soil moisture rose across the state in October. Levels at 2 inches rose 56%, on average, across the network. The highest increases were in the south, averaging 87% for the region. But even the drier central region saw moisture levels 44% higher at the end of the month.
Increases continued through the top 8 inches in all regions while soil moisture remained steady 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 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 October (approximately 80 percent of the median) and below the mean for October (approximately 35 percent of the mean). In October, monthly mean discharge values ranged mainly from normal to much below normal. The October 2025 monthly mean flows of the Vermilion River at Pontiac (which is downstream of the withdrawal intakes and impoundment for the Pontiac public water supply) and the Sangamon River at Monticello were near zero cfs. The October 2025 monthly mean flow of the Sangamon River at Monticello was the lowest reported for any calendar month in the period of record of the gage.
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-September water levels at 19 reservoirs for which levels were reported last month and this month, reported end-of-October water levels were lower at 15 reservoirs and higher at 4 reservoirs. For the 19 reservoirs with measurements reported for the end of October, water levels were below normal target pool or spillway level at all but one lake (Raccoon Lake, which is no longer a primary public water supply source).
Major Reservoirs. Compared to water levels at the end of September, at the end of October the water level at Lake Shelbyville was 0.5 feet lower, Carlyle Lake was 0.5 feet higher, and Rend Lake was 0.5 feet lower. At the end of October, Lake Shelbyville was 2.3 feet below the seasonal target level, Carlyle Lake level was 0.7 feet below the seasonal target level, and Rend Lake was 0.3 feet below 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 October 2025 mean level for Lake Michigan was 578.3 feet. The monthly mean level one year ago (October 2024) was 578.8 feet. The long-term average lake level for October is 579.0 feet, based on 1918-2023 data. In this period of record, the lowest mean level for Lake Michigan for October occurred in 1964 at 576.4 feet, and the highest mean level for October occurred in 1986 at 582.4 feet. The month-end level of Lake Michigan was 578.1 feet. All values are provided by the U.S. Army Corps of Engineers Detroit District.
Groundwater Information (Jennie Atkins)
Water tables were below the long-term average again in October, the 10th month in a row with lower-than-normal levels.
Seventeen of twenty-four reporting wells were lower at the end of the month with statewide average decrease of 1.85 feet. The largest decreases were in western Illinois with both the Perry (Pike County) and Good Hope (McDonough County) wells both declined 2.03 feet, the month’s largest.
However, increases were observed in the south where the Carbondale (Jackson County) and St Peter (Fayette County) wells rose 2.41 and 2.72 feet respectively.
Wells averaged 0.19 feet below October 2024, 1.95 feet below the 15-year average, and 1.85 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