January 2023 Overview
January temperatures and precipitation were above 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 34.6 degrees F, 7.9 degrees above the 1991–2020 normal for January (Figure 1). Average temperatures ranged from the mid-20s in northwest Illinois to the low 40s in southern Illinois, between 5 and 12 degrees above normal.
Precipitation statewide in January was 2.41 inches, 0.10 inches above the long-term statewide average (Figure 1). January’s total precipitation ranged from around 2 inches in west-central Illinois to over 7 inches in far southern Illinois.
Mean provisional streamflow aggregated statewide was slightly above the long-term median flow for January, about 110 percent of the median (Figure 1). Monthly mean discharge values in January ranged from below normal to above normal.
Water surface levels at the end of January were below the full pool or target level at 5 of 20 reporting reservoirs. At the end of January, Lake Shelbyville was 6.4 feet above the winter target level, Carlyle Lake was 2.1 feet above the winter 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 0.3 feet below the long-term average at the end of January. Levels averaged 1.5 feet above those in December and 0.1 foot above last year’s levels.
Weather/Climate Information
The following description of temperatures, precipitation, and snowfall 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.
January in Illinois was much warmer and slightly wetter than normal.
Temperatures averaged 34.6 degrees F, 7.9 degrees above the 1991–2020 normal for January (Table 1, Figure 2). Last month was the fifth warmest January on record statewide. Although temperatures were not warm by any means, they were noticeably milder than expected in the first month of the year. January average temperatures ranged from the mid-20s in northwest Illinois to the low 40s in southern Illinois, between 5 and 12 degrees above normal (Figure 1). Following long-term warming trends, the nighttime low temperatures last month were particularly unusual. The average nighttime low temperature in Peoria in January was the third highest on record. The variable January temperatures broke four daily high maximum temperature records, three daily low maximum temperature records, and two daily low minimum temperature records.
Precipitation statewide in January was 2.41 inches, 0.10 inches above the long-term statewide average (Table 1, Figure 3). January is not typically a wet month, but relative to its spring and summer counterparts, this past month brought wetter weather to most of the state. January’s total precipitation ranged from around 2 inches in west-central Illinois to over 7 inches in far southern Illinois. Most parts of northern and southern Illinois were between 0.5 and 2 inches wetter than normal, while much of central Illinois was near to 0.5 inches drier than normal.
Snow essentially requires two ingredients: (1) cold-enough temperatures to permit the snow to reach the ground and (2) enough moisture in the air to precipitate as snow. Illinois had plenty of moisture last month, but the milder January
temperatures kept heavy snow at bay. January snowfall totals ranged from around 3 inches in southern and south-central Illinois to just under 12 inches in northeast Illinois. Only southern and parts of northeast Illinois had near to above normal snowfall, while the rest of the state had 1 to 6 inches below normal snowfall for the month. The general lack of sizeable January snowfall added to November and December deficits. Season-to-date snowfall remains above normal in southern Illinois, but 3 to 13 inches below normal in central and 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.
Winds averaged 7.4 mph in January, 0.8 mph lower than in December and 0.9 mph lower than the network’s long-term average. ICN Bondville (Champaign County) had the windiest month with an average of 11.4 mph. The highest recorded wind gust was 40.6 mph, measured at ICN St. Charles (Kane County) on January 27.
Temperatures averaged 34 degrees F for the month, 3 degrees warmer than in December and 6 degrees higher than the long-term average. The month had a warm start with station temperatures 9 to 12 degrees higher than normal in the first half of January. ICN Belleville (St. Clair County) recorded a high of 68 degrees on January 3, 26 degrees higher than normal for the station. It was the network’s highest temperature for the month. The network saw colder weather at the end of January when temperatures dropped to the negatives in the north and teens in the south. ICN Freeport (Stephenson County) recorded the month’s lowest temperature, measuring -12 degrees on January 31.
Soil temperatures averaged in the high 30s, 4 to 5 degrees above the long-term average. Under bare soils, temperatures ranged from 14 to 66 degrees at 2 inches and 25 to 60 degrees at 4 inches. Temperatures under sod ranged from 31 to 58 degrees at 4 inches and 31 to 57 degrees at 8 inches.
Precipitation increased in January to an average of 3.05 inches, 0.23 inches more than in December and 0.72 inches greater than the long-term average. The highest totals were recorded in the south. ICN Dixon Springs (Pope County) measured 6.23 inches, 2.32 inches higher than the long-term average. Higher than normal precipitation was also seen at the northern stations. Central Illinois had a drier January with totals 10 to 30 percent below normal.
The soil moisture data summary will return in spring 2023.
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 the 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 the 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 January (approximately 110 percent of the median) and below the mean for January (approximately 75 percent of the mean). Monthly mean discharge values in January ranged from below 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 periods 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-December water levels at 20 reservoirs for which levels were reported last month and this month, reported end-of-January water levels were lower at 6 reservoirs, higher at 12 reservoirs, and about the same as at the end of December at 2 reservoirs. For the 20 reservoirs with measurements reported at the end of January, water levels were below normal target pool or spillway level at 5 reservoirs, above normal target pool or spillway level at 8 reservoirs, and at about full pool level at 7 reservoirs.
Major Reservoirs. Compared to water levels at the end of December, at the end of January the water level at Lake Shelbyville was 0.6 feet higher, Carlyle Lake was 1.3 feet higher, and Rend Lake was 1.8 feet higher. At the end of January, Lake Shelbyville was 6.4 feet above the winter target level, Carlyle Lake was 2.1 feet above the winter 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 January 2023 mean level for Lake Michigan was 578.9 feet. The monthly mean level one year ago (January 2022) was 579.4 feet. The long-term average lake level for January is 578.5 feet, based on 1918–2021 data. In this period of record, the lowest mean level for Lake Michigan for January occurred in 2013 at 576.0 feet, and the highest mean level for January occurred in 2020 at 581.6 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 24 monitored wells in January, ending the month 1.5 feet on average above December levels. The southern wells again saw large gains because of the region’s heavy precipitation. The Carbondale (Jackson County) well level had the highest increase with 8.83 feet as the station reported 5.62 feet for the month.
Levels continued to fall at the Perry (Pike County) well in western Illinois. The well ended the month 1.92 feet below December levels and 9.67 feet below those in January 2022.
Wells averaged 0.1 foot above last year’s levels. The northern wells showed the greatest improvements as the Mt. Morris (Ogle County) and Freeport (Stephenson County) wells ended the month 6.69 feet and 6.76 feet higher than their January 2022 levels, respectively.
Wells averaged 0.7 feet below the 15-year average and 0.3 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
