February 2023 Overview
February 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 above the long-term depths.
Air temperatures averaged 36.4 degrees F, 5.4 degrees above the 1991–2020 normal for February and the 12th warmest on record (Figure 1). February average temperatures ranged from the high 20s in northern Illinois to the mid-40s in southern Illinois, between 2 and 8 degrees above normal.
Precipitation statewide in February was 2.64 inches, 0.53 inches above the long-term statewide average and the 23rd wettest February on record (Figure 1). Total February precipitation ranged from around 2 inches in south-central Illinois to over 4 inches in southern Illinois.
Mean provisional streamflow aggregated statewide was slightly above the long-term median flow for February, about 110 percent of median (Figure 1). Monthly mean discharge values in February ranged from normal to above normal.
Water surface levels at the end of February were below the full pool or target level at 3 of 22 reporting reservoirs. At the end of February, Lake Shelbyville was 1.2 feet above the winter target level, Carlyle Lake was 0.3 feet above the winter target level, and Rend Lake was 2.6 feet above the spillway level. Lake Michigan’s mean level was above its long-term mean for the month.
Shallow groundwater levels were 1.30 feet above the long-term average at the end of February (Figure 1). Levels averaged 2.35 feet above those in January and 0.76 feet above last year’s levels.
Weather/Climate Information
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.
February in Illinois was warmer and wetter than average statewide.
Temperatures averaged 36.4 degrees F, 5.4 degrees above the 1991–2020 normal for February and the 12th warmest on record (Table 1a, Figure 2). February average temperatures ranged from the high 20s in northern Illinois to the mid-40s in southern Illinois, between 2 and 8 degrees above normal. Several stations saw daily high temperatures in the 70s last month, including 74 degrees in Williamson County. Meanwhile, a brief period of extreme cold at the start of the month pushed stations in northern Illinois well below zero, including nighttime low temperatures of -14 degrees in Kane County. The warmest place in the state in February was Carbondale, with an average temperature of 44.1 degrees, and the coldest place in the state was Stockton in Jo Daviess County with an average temperature of 25.2 degrees.
Figure 3. February 2023 Precipitation and Departures from Normal
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Altogether, 17 daily high maximum temperature records and 11 daily high minimum records were broken in February. No daily low maximum or daily low minimum temperature records were broken.
Precipitation statewide in February was 2.64 inches, 0.53 inches above the long-term statewide average and the 23rd wettest February on record (Table 1a, Figure 3). Total February precipitation ranged from around 2 inches in south-central Illinois to over 4 inches in southern Illinois (Figure 3). The Interstate 70 corridor between St. Louis Metro East and Effingham was near normal to half an inch drier than normal, while most areas north and south were 1 to 3 inches wetter than normal in February. Last month was the second wettest February on record in Rockford, third wettest in Freeport, and fourth wettest in Quincy.
Table 1a. February 2023 Temperature and Precipitation Summaries
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Snow: February added to existing snowfall deficits across the state. This past month’s mild temperatures precluded significant snowfall accumulation, so the above normal precipitation across much of the state came mostly as rain. Overall, only areas north of Interstate 72 saw any measurable snowfall in February, with totals ranging from less than half an inch from Adams to Iroquois County up to 12 inches in far northwest Illinois. All but the northwest tip of the state saw below normal snowfall, 2 to 8 inches less than normal.
Some of the more impressively weak snowfall totals in February included 0.1 inches in Peoria (fourth lowest on record). Both Springfield and Champaign recorded only trace snowfall for the entire month, meaning no snowfall accumulated to the point at which it could be measured.
Drought: While the lack of snowfall in February was disappointing for snow lovers, the abundant precipitation in most of the state eradicated any remaining drought. The February 28 U.S. Drought Monitor map for Illinois was completely empty for the first time since June 2020. Drought recovery in southern Illinois was particularly remarkable given that each of the southern seven counties were in severe to extreme drought as recently as December 1.
Winter: February wrapped up a very mild climatological winter season (December–February), with only a handful of cold air outbreaks and below normal snowfall for most of the state. The near record cold around Christmas pushed December slightly cooler than normal statewide, but the 6th warmest January on record and the 12th warmest February on record tilted the winter season warmer than normal in Illinois. In fact, the statewide average winter temperature was 33.7 degrees, 3.9 degrees above normal and the 8th warmest winter on record (Table 1b).
Wetter than normal conditions in both January and February brought this climatological winter into the top 40 wettest on record statewide. This past season’s statewide total precipitation was 7.62 inches, 0.77 inches wetter than normal and the 34th wettest winter on record.
Illinois Climate Network (ICN) (Jennie Atkins)
The Illinois Climate Network (ICN) collects hourly weather and soil information from 19 stations across the state.
Winds averaged 8.1 mph in February, 0.7 mph higher than in January but 0.2 mph lower than the long-term average. ICN Bondville (Champaign County) had the windiest month, averaging 12.4 mph. The highest recorded wind gust was 52.7 mph measured at ICN Perry (Pike County).
Temperatures increased from in January to an average of 37 degrees F, 3 degrees warmer than last month and 6 degrees higher than the network’s long-term average. The month began with cold weather with temperatures falling to the negatives in northern Illinois. ICN Freeport (Stephenson County) recorded a low of -9.8 degrees on February 3, the month’s lowest temperature.
The network saw higher temperatures after the first week with averages in the 30s and 40s for most of February. Highs even reached the 70s in southern Illinois the last week of the month when ICN Dixon Springs (Pope County) recorded the month’s high of 75 degrees on February 22.
Soil temperatures averaged in the high 30s at all depths, 3 to 4 degrees above the long-term averages. Under bare soils, temperatures ranged from 13 to 69 degrees at 2 inches and 22 to 61 degrees at 4 inches. Temperatures under sod ranged from 27 to 58 degrees at 4 inches and 28 to 55 degrees at 8 inches.
Precipitation averaged 3.36 inches, 0.31 inches more than in January and 1.17 inches higher than the network’s long-term average. Seven stations recorded more than 4 inches during the month. ICN Dixon Springs (Pope County) was the month’s wettest with 5.54 inches, bringing its 2023 total to 11.77 inches so far, or 4.14 inches above the station’s 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 slightly above the median value for February (approximately 110 percent of the median) and slightly below the mean for February (approximately 90 percent of the mean). Monthly mean discharge values in February were above normal in northern Illinois and far southern Illinois, and 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 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 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-January water levels at 20 reservoirs for which levels were reported last month and this month, reported end-of-February water levels were lower at 4 reservoirs, higher at 7 reservoirs, and about the same as at the end of January at 9 reservoirs. For the 22 reservoirs with measurements reported at the end of February, 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 6 reservoirs.
Major Reservoirs. Compared to water levels at the end of January, at the end of February the water level at Lake Shelbyville was 5.1 feet lower, Carlyle Lake was 1.9 feet lower, and Rend Lake was 0.7 feet higher. At the end of February, Lake Shelbyville was 1.2 feet above the winter target level, Carlyle Lake was 0.3 feet above the winter target level, and Rend Lake was 2.6 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 February 2023 mean level for Lake Michigan was 578.8 feet. The monthly mean level one year ago (February 2022) was 579.2 feet. The long-term average lake level for February is 578.4 feet, based on 1918–2021 data. In this period of record, the lowest mean level for Lake Michigan for February occurred in 1964 at 576.1 feet, and the highest mean level for February occurred in 2020 at 581.5 feet. The month-end level of Lake Michigan was 578.7 feet. All values are provided by the U.S. Army Corps of Engineers Detroit District.
Groundwater Information (Jennie Atkins)
Water tables rose at 18 of the 25 monitored wells in February, ending the month 2.35 feet on average above January levels (Table 4).
The Perry (Pike County) well stopped its decline in February, rising 12.78 feet during the month. Similar but smaller increases occurred at other west-central wells; Good Hope (McDonough County) rose 7.33 feet and Monmouth (Warren County) rose 4.30 feet.
Wells averaged 0.76 feet above last year’s average level. Increases at the northern wells continued with the Freeport (Stephenson County) well rising 6.08 feet in February and ending the month 13.32 feet higher than in February 2022. Mt. Morris (Ogle County), Fermi Lab (DuPage County), and DeKalb (Dekalb County) wells ended the month with water levels higher than last year’s levels.
Wells averaged 0.97 feet above the 15-year average and 1.30 feet above 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