June 2023 Overview
June temperatures and precipitation were below the long-term average in Illinois. Mean streamflow statewide was well below the median for the month. Shallow groundwater levels were below the long-term depths.
Air temperatures averaged 71.6 degrees in June, 0.6 degrees below normal (Figure 1). June average temperatures ranged from the high 60s in northern Illinois to the high 70s in southern Illinois, between 1 and 3 degrees above normal in northwest and parts of central Illinois, and between 1 and 4 degrees below normal in eastern and most of southern Illinois.
Precipitation statewide in June was 1.81 inches, 2.84 inches below normal and the 9th driest on record statewide (Figure 1). June precipitation ranged from less than 1 inch in far western and southwest Illinois to isolated spots of over 7 inches in northwest and southeast Illinois.
Soil moisture at the end of June at 2 inches was 22 percent higher with a state average of 0.22 water fraction by volume (wfv). There was no significant change at 4 inches but an 8 to 16 percent decrease at depths from 8 to 39 inches.
Mean provisional streamflow aggregated statewide was below the long-term median flow for June, about 30 percent of median (Figure 1). Monthly mean discharge values in June ranged mostly from below normal to much below normal.
Water surface levels at the end of June were below the full pool or target level at 12 of 19 reporting reservoirs. At the end of June, Lake Shelbyville was 0.1 foot below the seasonal target level, Carlyle Lake was at the seasonal target level, and Rend Lake was 1.8 feet above the spillway level. Lake Michigan’s mean level was above its long-term mean for the month.
Shallow groundwater levels were 1.63 feet below the long-term average at the end of June. Levels averaged 1.74 feet below those in May and 0.68 feet below levels in June 2022.
The following description of temperatures, precipitation, 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.
June was slightly cooler and much drier than normal statewide, worsening drought in Illinois.
Temperatures averaged 71.6 degrees in June, 0.6 degrees below normal, but still the 52nd warmest on record statewide. June average temperatures ranged from the high 60s in northern Illinois to the high 70s in southern Illinois, between 1 and 3 degrees above normal in northwest and parts of central Illinois, and between 1 and 4 degrees below normal in eastern and most of southern Illinois (Table 1, Figure 2). The dry air in the Midwest for most of the month kept daytime temperatures high but allowed nighttime temperatures to regularly dip into the 50s. In fact, while daytime high temperatures in June were 1 to 4 degrees above normal, nighttime low temperatures were 1 to 4 degrees below normal, making for one of the most comfortable Junes in recent memory. The warmest place in the state last month was Olmstead in Pulaski County with an average temperature of 75.9 degrees, and the coolest place in the state in June was Waukegan with an average temperature of 65.5 degrees.
Altogether, 20 daily high maximum temperature records and 3 daily high minimum temperature records were broken in June. In addition, 13 daily low maximum temperature records and 24 daily low minimum temperature records were broken last month.
Precipitation statewide in June was 1.81 inches, 2.84 inches below normal and the 9th driest on record statewide. Last month was the driest June since 2012. June precipitation ranged from less than 1 inch in far western and southwest Illinois to isolated spots of over 7 inches in northwest and southeast Illinois (Table 1, Figure 3). Most places in the state had between 2 and 5 inches below normal rainfall in June.
Last month capped off an extremely dry start to the growing season, going back to April 1. The period between April 1 and June 30 was the 2nd driest on record in Quincy, the 3rd driest in Moline, the 5th driest in Champaign, the 8th driest in Peoria, and the 11th driest on record in Chicago. Quincy, for example, had 4.53 inches of rain in April, May, and June together, which was 0.80 inches less than that period in 2012 and 1.48 inches less than in 1988.
Drought: The dry weather from April through June put Illinois in its most serious drought since 2012. Soils throughout the state are somewhat to very dry down to 12 inches and in some places down to 20 inches. The 8-inch soil moisture at the Illinois Climate Network station in Champaign was at its driest point on record on June 28, with a daily record going back to 2004. Streams and ponds are much lower than normal across the state, but conditions have not progressed to affect rural wells or municipal water supply. Pasture conditions remain poor in many areas, with little regrowth since the first or second cutting of hay.
Rain in the last few days of June and first week of July have helped stop deteriorating drought conditions and have improved crop and stream conditions somewhat. We will need consistent, near to above normal precipitation through July and much of August to really begin to improve drought conditions and avoid worse impacts to agriculture, ecology, and hydrology.
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 5.0 mph in June, 0.8 mph lower than in May and 0.9 mph below the long-term average. ICN Bondville (Champaign County) was the windiest station again with a monthly average of 8.1 mph and the highest wind gust of 60.1 mph on June 29.
Temperatures rose 7 degrees from in May to an average of 72 degrees, 1 degree lower than the historical average. Station highs reached the 90s and 100s with ICN Carbondale (Jackson County) reporting 102 degrees on June 30, the network’s highest temperature of the month. Station lows fell into the 40s and 50s. The month’s lowest temperature was 42 degrees, recorded at ICN St. Charles (Kane County) on June 12.
Soil temperatures rose 8 to 9 degrees from in May to averages in the mid- to high 70s. Under bare soils, temperatures at 2 inches ranged from 50 to 108 degrees and from 50 to 100 degrees at 4 inches. Temperatures under sod ranged from 60 to 97 degrees at 4 inches and 61 to 88 degrees at 8 inches.
Precipitation was low across the network in June as all but one station had totals less than their historical average. ICN Dekalb (DeKalb County) recorded only 0.91 inches in June, 3.14 inches below its long-term average. Thirteen stations had monthly totals less than 2 inches. Only one station, ICN Olney (Richland County), reached its historical average, recording 4.26 inches, June’s highest total.
Overall, the network averaged 1.79 inches of rain for the month, 2.30 inches below the historical average. Thirty-seven percent of this was recorded during the storms on June 29 and 30.
The lack of rain kept soil moisture low for most of June. Levels averaged 0.18 water fraction by volume (wfv) at 2 inches on June 1 and fell 10 percent between June 1 to 28. Soils were close to or at the wilting points at most stations. However, the storms that passed through the state on June 29 and 30 caused moisture levels to jump 37 percent to 0.22 wfv. The highest increases were in central Illinois where 2-inch soil moisture increased more than 40 percent in two days. Overall, moisture levels ended the month 22 percent higher.
Impacts from the late June storms were seen down to 8 inches. At the end of June, moisture levels were down 8 percent for the month at 8 inches, 16 percent at 20 inches, and 10 percent at 39 inches. There were no significant overall changes at 4 and 59 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 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 below the median value for June (approximately 30 percent of the median) and below the mean for June (approximately 25 percent of the mean). Monthly mean discharge values in June ranged from normal to below normal in northern Illinois, and from below normal to much below normal elsewhere. The provisional June 2023 monthly mean streamflow of the Illinois River at Valley City was the second lowest mean flow in 85 years of record. (The lowest reported monthly mean streamflow of the Illinois River at Valley City in June was in 1988.)
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-May water levels at 19 reservoirs for which levels were reported last month and this month, reported end-of-June water levels were lower at 13 reservoirs, higher at 5 reservoirs, and about the same as at the end of May at 1 reservoir. For the 19 reservoirs with measurements reported for the end of June, water levels were below normal target pool or spillway level at 12 reservoirs, above normal target pool or spillway level at 4 reservoirs, and at about full pool level at 3 reservoirs. Salem Lake inflow was supplemented by occasional pumping from Carlyle Lake in June.
Major Reservoirs. Compared to water levels at the end of May, at the end of June the water level at Lake Shelbyville was 0.4 feet lower, Carlyle Lake was at about the same level as at the end of May, and Rend Lake was 1.5 feet lower. At the end of June, Lake Shelbyville was 0.1 foot below the seasonal target level, Carlyle Lake was at the seasonal target level, and Rend Lake was 1.8 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 June 2023 mean level for Lake Michigan was 579.7 feet. The monthly mean level one year ago (June 2022) was 580.1 feet. The long-term average lake level for June is 579.3 feet, based on 1918–2022 data. In this period of record, the lowest mean level for Lake Michigan for June occurred in 1964 at 576.6 feet, and the highest mean level for June occurred in 2020 at 582.2 feet. The month-end level of Lake Michigan was 579.7 feet. All values are provided by the U.S. Army Corps of Engineers Detroit District.
Groundwater Information (Jennie Atkins)
Water tables continued to fall with levels decreasing at 24 of the 25 monitored wells in June. Statewide, wells averaged 1.74 feet lower than in May.
Eighteen of the wells decreased more than 1 foot and seven decreased more than 2 feet. Only the Monmouth well (Warren County) had no significant change from in May.
Widespread rains at the end of June had little impact on water tables. While some wells, such as the one in Olney (Richland County), showed slight level increases, these were not enough to offset the earlier declines. For most wells, the rains had no impact.
Wells averaged 0.68 feet below those in June 2022, 2.12 feet below the 15-year average, and 1.63 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/