February 2024 Overview
February temperatures were above and precipitation was below the long-term average in Illinois. Mean streamflow statewide was slightly above the median for the month. Shallow groundwater levels were below the long-term depths.
Air temperatures averaged 41.0 degrees F, 9.9 degrees above the 1991–2020 normal for February (Figure 1). February average temperatures ranged from the mid-30s in northern Illinois to the high 40s in southern Illinois, between 6 and 12 degrees above normal.
Precipitation statewide in February was 0.43 inches, 1.68 inches below the long-term statewide average (Figure 1). Total February precipitation ranged from less than half an inch in parts of western Illinois to around 3 inches in parts of northern Illinois.
Mean provisional streamflow aggregated statewide was slightly above the long-term median flow for February, about 103 percent of median (Figure 1). Monthly mean discharge values in February ranged from below normal in parts of southern Illinois to above normal in parts of northern Illinois.
Water surface levels at the end of February were below the full pool or target level at 7 of 19 reporting reservoirs. At the end of February, Lake Shelbyville was 2.5 feet above the seasonal target level, Carlyle Lake was 0.1 foot above the seasonal target level, and Rend Lake was 0.9 feet below the spillway level. Lake Michigan’s mean level was above its long-term mean for the month.
Shallow groundwater levels were 1.15 feet below the long-term average at the end of February (Figure 1). Levels averaged 0.76 feet below January’s and 2.46 feet below last year’s levels.
Weather/Climate Information
The following description of temperatures, precipitation, snow, and winter conditions 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.
February in Illinois was much warmer and much drier than average statewide.
Temperatures averaged 41.0 degrees F, 9.9 degrees above the 1991–2020 normal for February and the 2nd warmest on record (Table 1a, Figure 1). February average temperatures ranged from the mid-30s in northern Illinois to the high 40s in southern Illinois, between 6 and 12 degrees above normal (Figure 2). Several stations saw daily high temperatures in the 80s last month, including 83 degrees in Belleville and 80 in Springfield. A strong cold front in the last week of the month dropped temperatures from the 70s and 80s into the teens and 20s. Several places saw 50- to 60-degree declines in less than 24 hours. Overall, the warmest place in the state last month was Du Quoin, with an average temperature of 49.1 degrees, and the coldest place in the state was Stockton in Jo Daviess County with an average temperature of 34.8 degrees.
The mild weather in February broke 186 daily high maximum temperature records. These included a 75-degree high in DeKalb on February 28, which beat the previous daily high record by a full 12 degrees. There were also 43 daily high minimum temperature records broken last month. Twenty-two locations in Illinois set new all-time February high temperature records, including 77 degrees in Peoria, 77 in Charleston, 76 in Moline, and 73 in Rockford. Last month was the warmest February on record in Chicago, Rockford, Moline, and Peoria. It was a top 5 warmest February virtually everywhere in the state.
Precipitation statewide in February was 0.43 inches, 1.68 inches below the long-term statewide average and the 2nd driest February on record (Table 1a). Total February precipitation ranged from less than half an inch in parts of western Illinois to around 3 inches in parts of northern Illinois (Figure 3). Most of the state was 1 to 3 inches drier than normal last month, while only a narrow stretch of northern Illinois caught more than normal precipitation.
Last month was the 7th driest on record in Rockford (0.29 inches total), the 8th driest in Moline (0.26 inches total), the 6th driest in Springfield (0.51 inches total), the 3rd driest in Normal (0.14 inches total), the 3rd driest in Quincy (0.07 inches), and 4th driest in Carbondale (0.74 inches). In fact, February was the 7th driest month on record (for any month) statewide in Illinois, and the driest since January 1981.
Snow: February total snowfall ranged from less than two-tenths of an inch in northwest Illinois to just over 5 inches in central Illinois. Only the Interstate 70 corridor was above normal on February snowfall, while most of northern Illinois was 4 to 10 inches below normal. The big January snowstorm in the Quad Cities area keeps that region above normal on season-to-date snowfall, while most of the rest of the state is 5 to 15 inches behind normal snowfall by March 1.
Winter: February ended yet another very mild climatological winter season that featured only one truly cold air outbreak. The season began with the 3rd warmest December on record statewide, followed by a mostly mild January split in two by extreme cold. An incredibly mild February put a cap on a winter with average temperatures that were 4 to 8 degrees above normal in Illinois. Overall, the winter average temperature was 35.7 degrees, 6.0 degrees above normal and the 2nd warmest winter on record in Illinois (Table 1b).
The very dry February in Illinois followed a very wet January and a mixed bag of wetter and drier than normal conditions in December. Overall, winter total precipitation ranged from less than 5 inches in northwest Illinois to over 10 inches in far southern Illinois. Most areas north of Interstate 64 were near to 1 to 2 inches wetter than normal last season, while far southern Illinois was 1 to 2 inches drier than normal in winter. Overall, total winter precipitation in Illinois averaged 7.39 inches, 0.54 inches above the 30-year normal and the 38th wettest on record statewide (Table 1b).
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 7.4 mph in February, 0.1 mph lower than in January and 0.9 mph lower than the long-term average. ICN Bondville (Champaign County) had the windiest month with an average of 11.1 mph. The station also recorded the month’s highest wind gust of 44.5 mph on February 27.
Temperatures were higher than normal throughout the network, averaging 40 degrees, or 9 degrees above the long-term average. Station highs were in the 70s and 80s with lows in the single digits and teens. The month’s highest temperature was 83 degrees, recorded at ICN Belleville (St. Clair County) on February 27. The lowest was 1 degree, measured at ICN Bondville (Champaign County) on February 17.
Soil temperatures rose 5 to 7 degrees to averages in the low 40s. Under bare soils, temperatures at 2 inches ranged from 26 to 72 degrees and from 30 to 64 degrees at 4 inches. Temperatures under sod ranged from 33 to 62 degrees at 4 inches and 31 to 56 degrees at 8 inches.
February was dry for most stations with a network average of 0.66 inches, 1.53 inches below the long-term average. Only three stations (ICN Rend Lake, ICN Dixon Springs, and ICN DeKalb) reported monthly totals of an inch or greater. ICN DeKalb (DeKalb County) was the only station with a higher than normal total for the month, recording 2.44 inches.
Soil moisture data will be provided in Spring 2024.
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 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 slightly above the median value for February (approximately 103 percent of the median) and below the mean for February (approximately 85 percent of the mean). Monthly mean discharge values in February ranged from below normal in parts of southern Illinois to above normal in parts of northern 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 represent 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 an 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-January water levels at 17 reservoirs for which levels were reported last month and this month, reported end-of-February water levels were lower at 11 reservoirs, slightly higher at 4 reservoirs, and about the same as at the end of January at 2 reservoirs. For the 19 reservoirs with measurements reported for the end of February, water levels were below the normal target pool or spillway level at 7 reservoirs, above the normal target pool or spillway level at 10 reservoirs, and at about the target level or spillway level at 2 reservoirs. The Kinkaid Lake level reflects previous managed drawdown for annual maintenance.
Major Reservoirs. Compared to water levels at the end of January, at the end of February the water level at Lake Shelbyville was 8.3 feet lower, Carlyle Lake was 5.4 feet lower, and Rend Lake was 0.1 foot higher. At the end of February, Lake Shelbyville was 2.5 feet above the seasonal target level, Carlyle Lake’s level was 0.1 foot above the seasonal target level, and Rend Lake was 0.9 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 February 2024 mean level for Lake Michigan was 578.7 feet. The monthly mean level one year ago (February 2023) was 578.8 feet. The long-term average lake level for February is 578.4 feet, based on 1918–2023 data. In this period of record, the lowest mean level for Lake Michigan for February occurred in 1964 at 576.1 feet, and the highest mean level for February occurred in 2020 at 581.5 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)
Water tables fell at most wells in February, ending the month 0.76 feet below the January average.
Fourteen wells ended the month lower with declines ranging from 0.15 feet at the Brownstown well (Fayette County) to more than 2 feet. Janesville (Coles County) had the largest drop of 2.70 feet below January levels. Levels at the well had risen last October, but the lack of rain in February caused the water table to drop.
Levels were lower than in 2023 at 20 wells. One exception was Monmouth (Warren County), where levels declined 1.17 feet over the month but still remained 2.47 feet higher than in 2023. Wells averaged 2.46 feet below February 2023 levels, 1.39 feet below the 15-year average, and 1.15 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/
