March 2023 Overview
March temperatures were below and precipitation was above the long-term average in Illinois. Mean streamflow statewide was above the median for the month. Shallow groundwater levels were above the long-term depths.
Air temperatures averaged 41.0 degrees F, 0.4 degrees below the 1991–2020 normal for March (Figure 1). March average temperatures ranged from the low 30s in far northern Illinois to the high 40s in southern Illinois, within 1 degree of normal virtually everywhere in the state.
Precipitation statewide in March was 4.17 inches, 1.23 inches above normal (Figure 1). Total March precipitation ranged from just over 3 inches in northwest Illinois to nearly 12 inches in far southern Illinois.
Mean provisional streamflow aggregated statewide was above the long-term median flow for March, about 180 percent of median (Figure 1). Monthly mean discharge values in March ranged from normal to much above normal.
Water surface levels at the end of March were below the full pool or target level at 1 of 22 reporting reservoirs. At the end of March, Lake Shelbyville was 2.4 feet above the April 1 target level, Carlyle Lake was 3.8 feet above the April 1 target level, and Rend Lake was 5.4 feet above the spillway level. Lake Michigan’s mean level was above its long-term mean for the month.
Shallow groundwater levels were 1.34 feet above the long-term average at the end of March (Figure 1). Levels averaged 0.58 feet above those in February and 0.46 feet above last year’s levels.
The following description of temperatures, precipitation, 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 slightly cooler and much wetter than normal.
Temperatures averaged 41.0 degrees F, 0.4 degrees below the 1991–2020 normal for March (Table 1). Due to the long-term warming trend in March, last month was cooler than normal but still 1.2 degrees above the 20th century average. March average temperatures ranged from the low 30s in far northern Illinois to the high 40s in southern Illinois, within 1 degree of normal virtually everywhere in the state (Figure 2). Last month, four daily high maximum temperature records were broken, and two daily high minimum temperature records were broken. The extreme cold in the middle of the month broke 19 daily low maximum temperature records and 26 daily low minimum temperature records.
Snow: As the active storm track carried multiple systems through the Midwest in March, the dividing line between rain and snow seemed locked in northern Illinois. Along and north of Interstate 88, quickly accumulating wet and heavy snowfall occurred, and areas south of Interstate 88 mostly saw rain. Overall, only the northern half of the state saw any snowfall last month, with totals ranging from less than half an inch along Interstate 70 to nearly 15 inches in northwest Illinois. Rockford and Freeport picked up more than 14 inches of snow last month, the snowiest March on record in those places since 1972 and 1943, respectively.
Above normal March snowfall in northwest Illinois pushed the 2022–2023 season-to-date snowfall 2 to 8 inches above normal, while the rest of the state has seen between 2 and 15 inches below normal snowfall this season. Snowfall deficits have been especially large this season in parts of central and northeastern Illinois. If Champaign sees no additional snowfall before May, its 7 inches total will be the second lowest seasonal total on its 120+ year record.
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 8.7 mph in March, 0.6 mph higher than in February and 0.1 mph higher than the networks’ long-term average. ICN Bondville (Champaign County) was the windiest station of the month with a monthly average of 13.7 mph. The highest recorded wind gust was 68.7 mph, recorded at ICN Dekalb (DeKalb County) during the severe weather of March 31.
Temperatures averaged 41 degrees F, 4 degrees higher than in February but 1 degree lower than the long-term average. The month’s highest temperature was 79 degrees, recorded at ICN Snicarte (Mason County) on March 31. The lowest was 9 degrees, measured at ICN Freeport (Stephenson County) on March 18.
Soil temperatures rose 4 to 5 degrees from February to averages in the mid-40s. Under bare soils, temperatures ranged from 22 to 73 degrees at 2 inches and 28 to 66 degrees at 4 inches. Temperatures under sod ranged from 32 to 64 degrees at 4 inches and 34 to 58 degrees at 8 inches.
Precipitation averaged 5.20 inches for the network in March, 1.84 inches higher than in February and 2.18 inches higher than the long-term average. The southern stations had another wet month as all seven recorded totals of greater than 6 inches. ICN Dixon Springs (Pope County) had the wettest month again in March, recording 9.46 inches. The station’s 2023 total is 21.23 inches so far, 9.23 inches above its long-term average.
The soil moisture summary will return in the spring.
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 above the median value for March (approximately 180 percent of the median) and above the mean for March (approximately 155 percent of the mean). Monthly mean discharge values in March ranged from normal to much above 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 the 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-February water levels at 22 reservoirs for which levels were reported last month and this month, reported end-of-March water levels were lower at 5 reservoirs, higher at 14 reservoirs, and about the same as at the end of February at 3 reservoirs. For the 22 reservoirs with measurements reported at the end of March, water levels were below normal target pool or spillway level at 1 reservoir, above normal target pool or spillway level at 18 reservoirs, and at about full pool level at 3 reservoirs.
Major Reservoirs. Compared to water levels at the end of February, at the end of March the water level at Lake Shelbyville was 3.2 feet higher, Carlyle Lake was 4.6 feet higher, and Rend Lake was 2.8 feet higher. At the end of March, Lake Shelbyville was 2.4 feet above the April 1 target level, Carlyle Lake was 3.8 feet above the April 1 target level, and Rend Lake was 5.4 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 March 2023 mean level for Lake Michigan was 578.8 feet. The monthly mean level one year ago (March 2022) was 579.2 feet. The long-term average lake level for March is 578.5 feet, based on 1918–2021 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 578.9 feet. All values are provided by the U.S. Army Corps of Engineers Detroit District.
Groundwater Information (Jennie Atkins)
Water tables rose at 19 of the 25 monitored wells in March, ending the month with an average of 0.58 feet above February levels (Table 4).
The Sparta (Randolph County) well rose 4.24 feet in March, the month’s highest increase. The well has risen over 9 feet in the past four months from a low of 11.64 feet in November 2022.
Wells averaged 0.46 feet higher than March 2022 levels. The Freeport (Stephenson County) well continued to rise, ending the month 1.92 feet higher than in February and 14.11 feet higher than last year’s levels. Mt. Morris (Ogle County) also ended the month with levels higher than the average in 2022, measuring 12.36 feet above last year’s levels. However, other northern wells, including Fermi Lab (DuPage County) and DeKalb (Dekalb County), showed declines.
Wells averaged 0.87 feet above the 15-year average and 1.34 feet above 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://www.isws.illinois.edu/warm