June 2024 Overview
June was warmer and drier than normal. Streamflows were below the median while soil moisture and water tables were lower than in May.
Temperatures averaged 74.5 degrees in June, 2.3 degrees above normal and tied for the 17th warmest June statewide record (Figure 1). Average temperatures ranged from the low 70s in northern Illinois to the high 70s in southern Illinois, between 1 and 4 degrees above normal.
Precipitation statewide in June was 3.09 inches, 1.56 inches below average and the 34th driest on record (Figure 1). Totals ranged from over 8 inches in East Dubuque to only 0.63 inches in Macomb.
Soil moisture at 2 inches averaged 0.24 water fraction by volume (wfv) at the end of June, 29% lower than at the beginning of the month. Declines continued, on average, through 39 inches.
The mean streamflow statewide was below the median for the month.
Mean provisional streamflow aggregated statewide was below the long-term median flow for June, about 85% of the median (Figure 1). Monthly mean discharge values in June were above normal in northern Illinois and below normal to normal elsewhere in Illinois.
Water surface levels at the end of June were below the full pool or target level at 9 of 21 reporting reservoirs. At the end of June, Lake Shelbyville was 0.3 feet above the summer target level, Carlyle Lake level was 0.1 feet above the summer target level, and Rend Lake was 2.5 feet above the spillway level.
Lake Michigan’s mean level was slightly above its long-term mean for the month.
Shallow groundwater levels were 1.40’ below the long-term average at the end of June (Figure 1). Levels averaged 1.30’ below May and 0.31’ above last year.
Weather/Climate Information (Trent Ford)
The following description of temperatures, precipitation, severe weather, 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 much warmer and drier than normal statewide.
Temperatures averaged 74.5 degrees in June, 2.3 degrees above normal and tied for the 17th warmest June on record statewide (Table 1). June began with relatively mild temperatures across the state, including a few days with average temperatures that were 3 to 10 degrees below normal. However, summer heat kicked in mid-month and persisted until the final few days of June. The heat wave in mid-to late June was not particularly extreme in the actual temperatures. Most places in the state reached the mid-to upper-90s several days, and a few places, including Salem and Cahokia Heights, saw high temperatures above 100 degrees. However, the heat wave was extreme in how long it lasted, with temperatures 5 to 15 degrees above normal for 10 to 14 consecutive days. For example, Charleston got above 90 degrees on half of the days in June, the most since 1988.
Overall, June average temperatures ranged from the low 70s in northern Illinois to the high 70s in southern Illinois, between 1 and 4 degrees above normal (Figure 2). Most places had daytime high temperatures in the upper 90s and a few places hit or exceeded 100 degrees during the heat wave last month. This included Mt. Vernon, which peaked over 100 degrees for the first time in June since 2012. Meanwhile, many spots in northern Illinois saw nighttime low temperatures dip into the low 40s in early June, including 41 degrees in Lisle and 43 in McHenry. The warmest place in the state last month was Cahokia Heights with an average temperature of 78.3 degrees, and the coolest place in the state in June was Waukegan with an average temperature of 70.2.
Precipitation statewide in June was 3.09 inches, 1.56 inches below average and the 34th driest on record (Table 1).
June totals ranged from over 8 inches in East Dubuque to only 0.63 inches in Macomb. In fact, last month was the third driest June on record in Macomb, and the driest since 1991. The preliminary statewide total June precipitation was 3.39 inches, 1.26 inches below normal and the 46th driest June on record statewide (Figure 3).
The stretch of hot and dry weather in June quickly depleted soil moisture in much of central and south-central Illinois. However, rain from the remnants of Hurricane Beryl produced widespread totals of 1.5 to 5 inches in the second week of July and largely assuaged drought concerns across most of the state.
June is one of our most active severe weather months, and while last month was not especially active with severe weather, the northern half of the state was still affected by tornadoes, hail, and severe winds. The NOAA Storm Prediction Center’s preliminary June numbers had 13 tornado reports, including an EF-1 on June 13th that did damage outside of Gibson City in Ford County and four EF-0 tornadoes in the Chicago western suburbs on June 22nd. Strong storms also caused several reports of storm damage from strong winds on June 16th. The airport in Moline recorded 65 mph wind gusts that afternoon.
Illinois Climate Network (ICN) (Jennie Atkins)
The Illinois Climate Network (ICN) consists of 19 stations across the state which collects hourly weather and soil information.
Winds averaged 6.1 mph in June, 0.2 mph lower than the month’s long-term average. ICN Monmouth (Warren County) had the windiest month again with a monthly average at 10.9 mph. The highest wind gust was 60.3 mph, recorded at ICN Bondville (Champaign County) on June 25.
Temperatures rose to an average of 75°, 8° warmer than May and 2° warmer than the long-term average. Highs were in the 90s at most stations with lows in the 40s and 50s. The highest temperature was 101°, measured at ICN Belleville (St Clair County) on June 25. The lowest temperature was 42° on June 11 at ICN St Charles (Kane County).
Soil temperatures rose 7 – 9° in June to averages in the mid to high 70s. Under bare soils, temperatures at 2 inches ranged from 57 to 110° and from 58 to 102° at 4 inches. Temperature under sod ranged from 62 to 102° at 4 inches and 62 to 91° at 8 inches.
Precipitation averaged 3.24 inches across the network, 1.18 inches less than May and 0.85 inches below the long-term average. The northern stations averaged 4.63 inches for the month with ICN Freeport (Stephenson County) and ICN St Charles (Kane County) receiving 4.96 and 5.90 inches, respectively.
However, ICN Dixon Springs (Pope County), once again, had the wettest month, recording 7.29 inches. The station has received 37.26 inches in the first half of 2024, 11.79 inches above its long-term average.
The network saw 2-inch soil moisture levels fall 29% across the network in June to an average of 0.24 water fraction by volume (wfv). The largest decreases were in southern Illinois where levels were 52% lower at the end of the month. However, levels remained above the wilting points of the measured soils.
Soil moisture rose 24% at the northern stations, ending the month with a regional average of 0.31 wfv.
Decreases in moisture levels were seen down to 39 inches at the southern and central stations while northern stations showed increases through 20 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 past record of monthly mean flows at those stations for the same month. Both recent and long-term data are retrieved from 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 85 percent of the median) and below the mean for June (approximately 65 percent of the mean). Monthly mean discharge values in June were above normal in northern Illinois and below normal to normal elsewhere in 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 the 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 21 reservoirs for which levels were reported last month and this month, reported end-of-June water levels were lower at 16 reservoirs, higher at 3 reservoirs, and about the same as at the end of May at 2 reservoirs. For the 21 reservoirs with measurements reported for the end of June, water levels were below normal target pool or spillway level at 9 reservoirs, above normal target pool or spillway level at 8 reservoirs, and at about the target level or spillway level at 4 reservoirs.
Major Reservoirs. Compared to water levels at the end of May, at the end of June the water level at Lake Shelbyville was 1.9 feet lower, Carlyle Lake was 1.2 feet lower, and Rend Lake was 0.7 feet lower. At the end of June, Lake Shelbyville was 0.3 feet above the summer target level, Carlyle Lake level was 0.1 feet above the summer target level, and Rend Lake was 2.5 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 2024 mean level for Lake Michigan was 579.6 feet. The monthly mean level one year ago (June 2023) was 579.7 feet. The long-term average lake level for June is 579.3 feet, based on 1918-2023 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 declined at most monitoring wells in June.
Wells were 1.30’ lower at the end of June with 22 out of the 25 monitored wells reporting decreases (Table 4). Seven wells had drops of more than 2’ and the SE College (Saline County) reported a decline of 3.09’, the month’s largest.
Only three wells in northern Illinois – Galena (JoDaviess County), Mt Morris (Ogle County), and St Charles (Kane County) – showed increases for the month.
Wells averaged 0.31’ above June 2023, 1.79’ below the 15-year average, and 1.40’ 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/
