April 2022 Overview
Temperatures and precipitation were below the long-term average in Illinois in April. Mean streamflow statewide was above the median for the month. Shallow groundwater levels were below the long-term depths.
Air temperatures averaged 49.6 degrees F, 3.0 degrees below the 1991–2020 normal for April (Figure 1). April average temperatures ranged from the low 40s in northern Illinois to the mid-50s in southern Illinois, between 1 and 6 degrees below the 1991–2020 normal.
Precipitation statewide in April was 3.57 inches, 0.67 inches below the long-term statewide average (Figure 1). April total precipitation ranged from just under 3 inches in east-central Illinois to over 6 inches in far southern Illinois.
Soil moisture at 2 inches declined 18 percent in April to a state average of 0.35 water fraction by volume (wfv). Drying occurred at depths down to 20 inches. At 39 inches and deeper, moisture levels remained high with little change seen over the month.
Mean provisional streamflow aggregated statewide was above the long-term median flow for April, about 155 percent of median (Figure 1). Monthly mean discharge values in April were normal to above normal.
Water surface levels at the end of April were below the full pool or target level at 3 of 23 reporting reservoirs. At the end of April, Lake Shelbyville was 2.1 feet below the May 1 target level, the Carlyle Lake level was 0.8 feet below the May 1 target level, and Rend Lake was 5.0 feet above the spillway level. Lake Michigan’s mean level was above its long-term mean for the month.
Shallow groundwater levels were 0.16 feet below the long-term average at the end of April. Levels averaged 0.38 feet below March levels and 0.42 feet above those of last year.
The following description of temperatures, precipitation, snow, 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.
April in Illinois was cooler and slightly drier than average statewide.
Temperatures averaged 49.6 degrees F, 3.0 degrees below the 1991–2020 normal for April (Table 1, Figure 1). April average temperatures ranged from the low 40s in northern Illinois to the mid-50s in southern Illinois, between 1 and 6 degrees below the 1991–2020 normal (Figure 2). The coldest point in the state last month was Galena in Jo Daviess County with an average temperature of 40.8 degrees, 6 degrees below normal. The warmest point in the state was Cairo in Alexander County with an average temperature of 56.1 degrees, 2.5 degrees below normal. On some of the few warmer April days, many stations in Illinois hit highs in the mid-80s, including 86 degrees on April 23 in Chicago, Moline, and Quincy. Meanwhile, many stations in northern and central Illinois regularly experienced low temperatures in the mid- to low 20s, including 22 degrees on April 17 in Freeport, Rockford, and Normal.
Altogether, daily high maximum temperature records were broken last month at 9 stations, and daily high minimum temperature records were broken at 17 stations. Daily low maximum temperature records were broken last month at 12 stations, and daily low minimum temperature records were broken at 24 stations.
Precipitation statewide in April was 3.57 inches, 0.67 inches below the long-term statewide average (Table 1). April total precipitation ranged from just under 3 inches in east-central Illinois to over 6 inches in far southern Illinois. Most areas north of Interstate 80 and south of Interstate 64 were 1 to 2 inches wetter than normal in April. Meanwhile, most of central Illinois was near to slightly drier than normal.
Precipitation frequency last month was unusually high as most places recorded 12+ days with some measurable precipitation. Macomb had 22 days with measurable precipitation last month, Aurora had 20, Champaign had 19, and Cairo had 18. The 22 wet days in Macomb last month set a new record for April, which was the second highest frequency of any month on record, only less than the 23 wet days in Macomb in October 2009.
Snow: April snow is not unusual for the northern half of the state; however, this month the white stuff stayed mostly north of Interstate 80. April snowfall totals ranged from just over a tenth of an inch along and north of Interstate 74 to over 3 inches around the Rockford area. April snowfall was between 0.5 and 2.5 inches above normal in northern Illinois.
Drought: The persistently wet and cool April weather did make quite a dent in drought conditions in northern Illinois. Soil moisture and streamflow across northern Illinois have recovered to pre-drought conditions, and in response the U.S. Drought Monitor eliminated all drought across the state on April 26. That ended a 55-consecutive-week stretch of some drought in Illinois, the longest in the 20+ year Drought Monitor record.
Groundwater levels in northern Illinois are the lone remaining legacy of the drought as they have yet to fully recover. Groundwater levels tend to respond much more slowly going into and coming out of drought, so it is not unexpected to see groundwater drought conditions remaining. However, if the wet pattern continues, we should see more improvement in groundwater conditions in northern Illinois.
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.
It was a breezy April with wind speeds averaging 9.1 mph, 0.7 mph higher than in March and 0.3 mph higher than the network’s long-term average. ICN Bondville (Champaign County) had the windiest month, averaging 13.7 mph. The highest recorded wind gust was 51.9 mph, measured at ICN Stelle (Ford County) on April 13.
Air temperatures rose 8 degrees from in March to an average of 51 degrees, 2 degrees below the long-term average. All stations reported monthly lows below freezing with most in the mid- to high 20s. However, station highs were in the 80s. The month’s warmest temperature was 84 degrees, measured at ICN St. Charles (Kane County) on April 17. The lowest was 24 degrees, recorded at ICN Monmouth (Warren County) on April 23.
Soil temperatures increased 8 degrees from in March to averages in the low 50s, 1–2 degrees below long-term averages. Under bare soil, temperatures ranged from 33 to 88 degrees at 2 inches and 33 to 78 degrees at 4 inches. Temperatures under sod ranged from 37 to 70 degrees at 4 inches and 38 to 65 degrees at 8 inches.
Network precipitation was near normal in April, averaging 3.78 inches, or 0.75 inches less than in March and 0.18 inches above the long-term average. The northern stations had a wetter month as stations reported totals up to 74 percent higher than their long-term averages. ICN St. Charles (Kane County) received 5.09 inches of precipitation in April, 0.83 inches more than in March and 2.79 inches higher than normal.
ICN Rend Lake (Jefferson County) had the network’s wettest month with 5.53 inches, or 0.97 inches more than normal.
The warmer and drier weather caused soils to begin to dry after a wet March. Soil moisture at 2 inches declined 18 percent through April to an end-of-month network average of 0.35 water fraction by volume (wfv). Despite the drying, moisture levels were at or near field capacity for most of the soils monitored. This is especially true in the south where moisture levels declined 15 percent in April but remained above field capacity at most stations.
Drying extended down to the 20-inch depths. However, there was little change at 39 inches and deeper where moisture levels remained higher.
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 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 April (approximately 155 percent of the median) and above the mean for April (approximately 130 percent of the mean). Monthly mean discharge values in April were normal to 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 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-March water levels at 21 reservoirs for which levels were reported last month and this month, reported end-of-April water levels were lower at 12 reservoirs, higher at 1 reservoir, and about the same as at the end of March at 8 reservoirs. For the 23 reservoirs with measurements reported at the end of April, water levels were below normal target pool or spillway level at 3 reservoirs, above normal target pool or spillway level at 13 reservoirs, and at about full pool level at 7 reservoirs. (Target operating levels increase from April to May, and water levels are actively managed at Lake Shelbyville, Carlyle Lake, and Lake Decatur.)
Major Reservoirs. Compared to water levels at the end of March, at the end of April the water level at Lake Shelbyville was 3.7 feet lower, Carlyle Lake was 2.2 feet lower, and Rend Lake was 0.1 foot lower. At the end of April, Lake Shelbyville was 2.1 feet below the May 1 target level, the Carlyle Lake level was 0.8 feet below the May 1 target level, and Rend Lake was 5.0 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 April 2022 mean level for Lake Michigan was 579.6 feet. The monthly mean level one year ago (April 2021) was 580.5 feet. The long-term average lake level for April is 578.8 feet, based on 1918–2021 data. In this period of record, the lowest mean level for Lake Michigan for April occurred in 1964 at 576.2 feet, and the highest mean level for April occurred in 2020 at 581.7 feet. The month-end level of Lake Michigan was 579.8 feet. All values are provided by the U.S. Army Corps of Engineers Detroit District.
Groundwater Information (Jennie Atkins)
Water tables declined at 72 percent of monitored wells in April. On average, levels were 0.38 feet lower than in March. This was not unexpected as precipitation returned to near normal levels and soil moisture declined.
Improvements continued at the northern wells. The Freeport well (Stephenson County) rose 3.84 feet from in March. However, water table levels remained lower than normal with end-of-month totals 5.3 feet below 2021 levels and 4.2 feet below the 15-year average.
Water tables statewide averaged 0.42 feet above April 2021 levels, 0.54 feet below the 15-year average, and 0.16 feet below the period of 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