October 2024 Overview
October was another warm and dry month for Illinois.
Temperatures averaged 58.8 degrees in October, 4.0 degrees above normal and 15th warmest on record statewide.
Precipitation statewide in October was 0.85 inches, 2.41 inches below the 30-year normal and 9th driest on record statewide.
Soil moisture at 2 inches averaged 0.23 water fraction by volume (wfv) at the end of October, 19% lower than the beginning of the month. Decreases were seen through 39 inches with average declines of 20% at 4 inches, 18% at 8 inches, 7% at 20 inches, and 5% at 39 inches.
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 75% of median (Figure 1). Monthly mean discharge values ranged mostly from much below normal to normal for October.
Water surface levels at the end of October were below the full pool or target level at 16 of 18 reporting reservoirs. At the end of October, Lake Shelbyville was 1.5 feet below the seasonal target level, Carlyle Lake level was 0.6 feet below the seasonal target level, and Rend Lake was 0.5 feet above the spillway level.
Lake Michigan’s mean level was slightly below its long-term mean for the month.
Shallow groundwater levels were 1.61 feet below the long-term average at the end of October. Levels averaged 1.14 feet below September and 1.07 feet above last year.
Weather/Climate Information
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 58.8 degrees in October, 4.0 degrees above normal and 15th warmest on record statewide.
October is the most quintessential fall month, weather-wise, as we transition from a more summer-like September to what is often a more winter-like November. This year, however, October temperatures were more akin to the first part of the season than the last part. October average temperatures ranged from the mid-50s in northern Illinois to the low 60s in southern Illinois, between 2 and 5 degrees above normal (Figure 2, Table 1). High temperatures reached the 80s well into the final week of the month, including the third latest 80-plus-degree high temperature on record in Rockford (Oct. 29). However, low humidity also helped nighttime temperatures dip into the 20s and 30s on many nights, including 20 degrees in Joliet and 24 in Monmouth. The coolest point in the state last month was Stockton in Jo Daviess County at 54.6 degrees, and the warmest point was Olmstead in Pulaski County at 63.5 degrees. Last month was a top 15 warmest October on record in many parts of the state and was the ninth warmest October on record in Chicago.
Precipitation statewide in October was 0.85 inches, 2.41 inches below the 30-year normal and 9th driest on record statewide.
Most of October was somewhat to extremely dry across Illinois. In fact, many parts of northern and central Illinois had less than a quarter of an inch of precipitation into the final week of the month. Freeport had 30 consecutive days with no measurable precipitation, the fourth longest dry streak in the city’s more than 100-year record. The dry weather desiccated soils and dropped flow on many rivers and their tributaries, including along the Mississippi and Illinois rivers. A third straight very dry fall season continued to challenge pasture conditions around the state and increased the risk of fire and blowing dust. Large field fires burned hundreds of acres of farmland in north central and northeast Illinois the final week of the month. The U.S. Drought Monitor expanded moderate to severe drought across northern and central Illinois in response. The dry weather accelerated harvest across Illinois. As of Oct. 27, the U.S. Department of Agriculture estimated nearly 90% of both corn and soybeans were harvested in Illinois, well ahead of the five-year averages by that time.
A strong low-pressure system moved across the region in the final couple of days in October, bringing more significant rainfall to the state. Total October precipitation ranged from less than a quarter of an inch in east central Illinois to over 3 inches in northwest Illinois. Only the Quad Cities and surrounding areas were near normal for October precipitation, while most of the rest of the state was 1 to 4 inches drier than normal last month (Figure 3, Table 1).
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 5.9 mph in October, 1.5 mph higher than September and 0.6 mph lower than the long-term average. ICN Monmouth (Warren County) had the windiest month again with a monthly average of 11.6 mph. The highest recorded wind gust was 44.5 mph, recorded at ICN Belleville (St Clair County) on October 31.
Temperatures fell 10° from September to an average of 58°, 3° above the long-term average. Station highs were in the mid to high 80s with lows in the mid-20s to low 30s. The network’s highest temperature was 89°, measured at ICN Snicarte (Mason County) on October 12. The lowest temperature was 26°, recorded at ICN St Charles (Kane County) and ICN Stelle (Ford County) on October 17.
Soil temperatures fell 10 to 12° to averages in the low 60s. Under bare soils, temperatures ranged from 32 to 91° at 2 inches and 33 to 85° at 4 inches. Temperatures under sod ranged from 47 to 78° at 4 inches and 50 to 74° at 8 inches.
October was dry across the network. Stations averaged 1.07 inches, 2.21 inches below the long-term average. Most of the rain fell in the last week of the month with the networking averaging 0.76 inches between October 25 and 31 or 71% of the month’s total.
Station totals ranged from 14 to 73% of their long-term averages. The highest totals were in central Illinois where ICN Monmouth (Warren County) recorded 2.01 inches, the month’s highest total. ICN Brownstown (Fayette County) had the month’s lowest total with only 0.44 inches.
The lack of rain caused soil moisture to fall across the network. Moisture levels at 2 inches fell 60% from October 1 through 24. Levels rose the last week of the month; however, it was not enough to offset the drying during the first three weeks of the month. Overall, soil moisture at 2 inches declined 19%, ending the month with an average level of 0.23 water fraction by volume (wfv).
Similar but smaller declines were seen through 39 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 75 percent of the median) and below the mean for October (approximately 35 percent of the mean). Monthly mean discharge values in October ranged mostly from much below normal to normal.
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 17 reservoirs for which levels were reported last month and this month, reported end-of-October water levels were lower at 15 reservoirs and about the same as at the end of September at 2 reservoirs. For the 18 reservoirs with measurements reported for the end of October, water levels were below normal target pool or spillway level at 16 reservoirs, and above normal target pool or spillway level at 2 reservoirs.
Major Reservoirs. Compared to water levels at the end of September, at the end of October the water level at Lake Shelbyville was 0.7 feet lower, Carlyle Lake was 0.4 feet lower, and Rend Lake was 0.7 feet lower. At the end of October, Lake Shelbyville was 1.5 feet below the seasonal target level, Carlyle Lake level was 0.6 feet below the seasonal target level, and Rend Lake was 0.5 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 October 2024 mean level for Lake Michigan was 578.8 feet. The monthly mean level one year ago (October 2023) was 579.3 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 578.6 feet. All values are provided by the U.S. Army Corps of Engineers Detroit District.
Groundwater Information (Jennie Atkins)
Water tables continued to decline in October. Wells averaged 1.14 feet lower at the end of the month with most monitored wells reporting lower levels.
The largest declines were in southern Illinois, a change from September when the well levels significantly rose. The Carbondale well (Jackson County) had the largest decline, falling 2.16 feet in October after a 2.49 feet increase in September.
Despite the falls, well levels at most wells ended the month higher than 2023. The Belleville well (St Clair County) was 9.54 feet higher than last year even after declining 1.84 feet in October.
Wells averaged 1.07 feet above October 2023, 1.81 feet below the 15-year average, and 1.61 feet below the long-term record (Table 4).
Data sources for the IWCS include the following:
CPC - Climate Prediction Center, https://www.cpc.ncep.noaa.gov/index.php
ISWS - Illinois State Water Survey, https://www.isws.illinois.edu
MRCC - Midwestern Regional Climate Center, https://mrcc.purdue.edu/
NCEI - National Centers for Environmental Information, https://www.ncei.noaa.gov
NWS - National Weather Service, https://www.nws.noaa.gov
SPC - Storm Prediction Center, https://www.spc.noaa.gov
USACE - U.S. Army Corps of Engineers, https://www.lre.usace.army.mil
USDM - U.S. Drought Monitor, https://droughtmonitor.unl.edu
USGS - U.S. Geological Survey, https://waterdata.usgs.gov/il/nwis
WARM - Water and Atmospheric Resources Monitoring Program, https://warm.isws.illinois.edu/warm/