March 2024 Overview
March temperatures and precipitation were above the long-term average in Illinois. Mean streamflow statewide was below the median for the month. Shallow groundwater levels were below the long-term depths.
Air temperatures averaged 47 degrees, 5.6 degrees above the 1991–2020 normal for March and the 10th warmest March on record statewide (Figure 1). March average temperatures ranged from the low 40s in northern Illinois to the low 50s in southern Illinois, between 2 and 5 degrees above normal.
Precipitation statewide in March was 2.83 inches, -0.11 inches above normal and the 59th driest March on record statewide (Figure 1). March total precipitation ranged from over 6 inches in north-central Illinois to less than 2 inches in southern Illinois.
Soil moisture at 2 inches averaged 0.33 water fraction by volume (wfv) at the end of March. Moisture levels averaged near field capacity at most locations.
Mean provisional streamflow aggregated statewide was below the long-term median flow for March, about 65 percent of median (Figure 1). Monthly mean discharge values in March ranged mostly from below normal to normal, except for much below normal flow conditions in southernmost Illinois.
Water surface levels at the end of March were below the full pool or target level at 7 of 20 reporting reservoirs. At the end of March, Lake Shelbyville was 1.9 feet below the April 1 target level, Carlyle Lake was 0.7 feet below the April 1 target level, and Rend Lake was 1.3 feet above the spillway level. Lake Michigan’s mean level was slightly above its long-term mean for the month.
Shallow groundwater levels were 0.89 feet below the long-term average at the end of March (Figure 1). Levels averaged 0.31 feet above February levels and 2.05 feet below last year’s levels.
Weather/Climate Information
The following description of temperatures, precipitation, severe weather, and snow 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.
March in Illinois was much warmer and slightly drier than normal.
Temperatures averaged 47 degrees, 5.6 degrees above the 1991–2020 normal for March and the 10th warmest March on record statewide (Table 1). March average temperatures ranged from the low 40s in northern Illinois to the low 50s in southern Illinois, between 2 and 5 degrees above normal (Figure 2). The warmest place in the state last month was Du Quoin at 53.4 degrees on average, and the coldest place in the state last month was Stockton at 39.6 degrees. It was the 5th warmest March on record in Peoria, the 6th warmest in Freeport, and the 9th warmest in both Moline and Rockford.
The mild weather in the first half of the month broke 77 daily high maximum temperature records and 32 daily high minimum temperature records in Illinois. The colder weather that settled in the back half of March broke three daily low minimum temperature records, including 21 degrees in Kaskaskia.
Precipitation statewide in March was 2.83 inches, -0.11 inches above normal and the 59th driest March on record statewide (Figure 3, Table 1). The first two months of the year included a top 15 wettest January on record and the 2nd driest February on record in Illinois. March gave us a little taste of both worlds, with wetter conditions in the north and drier conditions in the south. March total precipitation ranged from over 6 inches in north-central Illinois to less than 2 inches in southern Illinois. Most of the state north of Interstate 70 had a near-normal to wetter than normal March, while much of southern Illinois was 1 to 3 inches drier than normal.
Severe weather: Unfortunately, not all March precipitation was rain. While March wasn’t nearly as active for severe weather as last year, we did get quite a bit of hail across Illinois. The Storm Prediction Center’s preliminary count had 68 severe hail reports across Illinois last month, including eight reports of 2-inch (i.e., hen egg size) or larger diameter hail. Each of the past two years have had more than 45 severe hail reports across the state, following a stretch of five years between 2018 and 2022 with only 37 severe hail reports total.
Snow: Meanwhile, as it often does, March brought some snowfall to northern Illinois. Most places north of Interstate 80 saw some accumulation in March, with some isolated 8- to 9-inch totals in Boone and McHenry Counties. Despite the impressive totals, March still ended with below normal snowfall for the entire state, adding to deficits from the rest of the snow season.
Illinois Climate Network (ICN) (Jennie Atkins)
The Illinois Climate Network (ICN) consists of 19 stations across the state that collect hourly weather and soil information.
Winds averaged 8.8 mph in March, 1.4 mph higher than in February and 0.2 mph higher than the network’s long-term average. ICN Bondville (Champaign County) had the windiest month once again with a monthly average of 13.6 mph. The highest wind gust was 56.1 mph, measured at ICN Monmouth (Warren County) on March 14.
Temperatures continued to be warmer than normal in March. Air temperatures averaged 47 degrees, 7 degrees higher than in February and 5 degrees higher than the long-term average. The month’s highest temperature was 80 degrees, recorded at ICN Dixon Springs (Pope County). ICN Freeport (Stephenson County) reported 19 degrees on March 23, the month’s lowest temperature.
Soil temperatures rose 7 to 8 degrees in March to averages in the high 40s. Under bare soils, temperatures at 2 inches ranged from 32 to 80 degrees and from 32 to 73 degrees at 4 inches. Temperature under sod ranged from 35 to 67 degrees at 4 inches and 36 to 65 degrees at 8 inches.
March was wetter at all stations. Precipitation averaged 3.21 inches for the network, 2.55 inches more than in February and 0.19 inches higher than the long-term average. The highest totals were at the northern stations where ICN Freeport (Stephenson County) recorded 5.30 inches.
Soil moisture averaged 0.33 wfv at 2 inches at the end of March, slightly below field capacity for most of the soils monitored. Slight declines of 5 percent or less were seen in central and southern Illinois, while levels at the northern stations rose an average of 11 percent.
Moisture levels rose in the north from depths of 4 inches to 5 feet, while remaining relatively steady in the central and southern regions.
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 the past record of monthly mean flows at those stations for the same month. Both recent and long-term data are retrieved from U.S. Geological Survey (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 the 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 below the median value for March (approximately 65 percent of the median) and below the mean for March (approximately 55 percent of the mean). Monthly mean discharge values in March ranged mostly from below normal to normal, except for much below normal flow conditions in southernmost 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 20 reservoirs for which levels were reported last month and this month, reported end-of-March water levels were lower at 7 reservoirs, higher at 10 reservoirs, and about the same as at the end of February at 3 reservoirs. For the 20 reservoirs with measurements reported for the end of March, water levels were below normal target pool or spillway level at 7 reservoirs, above normal target pool or spillway level at 9 reservoirs, and at about the target level or spillway level at 4 reservoirs.
Major Reservoirs. Compared to water levels at the end of February, at the end of March the water level at Lake Shelbyville was 2.4 feet lower, Carlyle Lake was 0.2 feet higher, and Rend Lake was 0.4 feet higher. At the end of March, Lake Shelbyville was 1.9 feet below the April 1 target level, Carlyle Lake was 0.7 feet below the April 1 target level, and Rend Lake was 1.3 feet above the spillway level. (The target operating levels at Lake Shelbyville and Carlyle Lake increase from March to April.)
Great Lakes. Current month mean and end-of-month values are provisional and are relative to International Great Lakes Datum 1985. The March 2024 mean level for Lake Michigan was 578.7 feet. The monthly mean level one year ago (March 2023) was 578.8 feet. The long-term average lake level for March is 578.5 feet, based on 1918–2023 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 578.7 feet. All values are provided by the U.S. Army Corps of Engineers Detroit District.
Groundwater Information (Jennie Atkins)
The shallow groundwater water table levels improved in March.
Eleven out of 23 wells monitored ended the month with higher levels, giving a statewide average that was 0.31 feet higher than at the end of February. The largest change was at the Belleville well (St. Claire County), where the water table level was 9.24 feet higher at the end of March. The Fermi (DuPage County) and Freeport (Stephenson County) wells also rose significantly with increases of 1.93 feet and 1.99 feet, respectively.
However, water tables remained lower than in March 2023 at all but two wells, Fermi and Crystal Lake (McHenry County).
Wells averaged 2.05 feet below March 2023 levels, 1.18 feet below the 15-year average, and 0.89 feet below the long-term record.
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/
