November 2021 Overview
Temperatures and precipitation were below the long-term average in Illinois in November. Mean streamflow statewide was above the median for the month. Shallow groundwater levels were above the long-term depths.
Air temperatures averaged 41.0°F, 1.2° below the 1991–2020 normal for November (Figure 1). November average temperatures ranged from the high 30s in northern Illinois to the low 40s in southern Illinois.
Precipitation statewide in November was 0.87 inches, 2.21 inches below the long-term statewide average (Figure 1).
Soil moisture declined across the state. On average, levels fell 11% at 2 inches, with the largest drops seen in northern and central Illinois.
Mean provisional streamflow aggregated statewide was above the long-term median flow for November, about 240% of median (Figure 1). Monthly mean discharge values in November ranged mostly from normal to above normal for the month.
Water surface levels at the end of November were below the full pool or target level at 9 of 23 reporting reservoirs. At the end of November, Lake Shelbyville was 4.6 feet above the target level, Carlyle Lake was 0.2 feet above the target level, and Rend Lake was 0.5 feet above the spillway level. Lake Michigan’s mean level was above its long-term mean for the month.
Shallow groundwater levels statewide were 0.52 inches above the long-term average at the end of November. Levels averaged 0.62 inches below those in October 2021 and 0.01 inches above the November 2020 average.
Weather/Climate Information (Trent Ford)
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.
November in Illinois was cooler and drier than average statewide.
Temperatures averaged 41.0°F, 1.2° below the 1991–2020 normal for November (Table 1a, Figure 1). November average temperatures ranged from the high 30s in northern Illinois to the low 40s in southern Illinois, between 1° and 4° below the 1991–2020 normal (Figure 2). Several stations saw daily high temperatures in the 70s in early November, including a 75° high in Randolph County. Meanwhile, several stations in northern and central Illinois reached nighttime minimum temperatures well below 20°, including 10° lows in Knox and Warren Counties.
Mild temperatures in November did not break any local daily high maximum or high minimum temperature records in Illinois; however, the daily low minimum temperature records on November 4 and 5 were broken in Casey in Cumberland County.
Precipitation statewide in November was 0.87 inches, 2.21 inches below the long-term statewide average (Table 1a). The entire state was drier than normal, as November totals ranged from less than a quarter of an inch in northwest Illinois to just over 2 inches in southeast Illinois. Last month was the second driest November on record in Rockford (0.45 inches) and the third driest in St. Louis (0.35 inches).
Snow has been scant so far this season. Only the northern third of the state saw snowfall in November, and totals ranged from just over a quarter of an inch in northwest Illinois to less than a tenth of an inch in northeast and central Illinois. November total snowfall was between 0.5 inches and 2 inches below normal in the northern half of the state.
Drought: The dry conditions added to existing precipitation deficits in northern Illinois, and in response there was not much change in the U.S. Drought Monitor this past month. Most areas between Whiteside County in northwest Illinois and Lake County in northeast Illinois remain in moderate to severe drought as year-to-date precipitation deficits of 6 to 12 inches remain.
January 1 through November 30 was the second driest of that period on record in Rockford, greater only than in 2012. Rockford will need at least 1.11 inches of precipitation in December to keep 2021 from being the driest calendar year on record there. The dryness in southwest Illinois was noted as the Drought Monitor introduced abnormally dry conditions across much of the St. Louis Metro East area from Calhoun to Monroe Counties.
Fall (September–November) was overall warmer than normal across most of Illinois. Seasonal temperatures averaged 56.9°F, 2.3° above the 1991–2020 normal (Table 1b), ranging from the low 50s in northern Illinois to the high 50s in central and southern Illinois. Fall temperatures were 1° to 4° above normal in northern and central Illinois and within 1° of normal in southern Illinois.
Fall precipitation averaged 9.22 inches statewide, 0.47 inches below average (Table 1b). Seasonal totals were highest in east central Illinois, ranging from 10 to 14 inches. Meanwhile, northern and southwest Illinois were the dry spots in the fall, with totals between 6 and 8 inches. The very wet October and very dry November offset each other, resulting in a fall season that was just slightly drier than normal.
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.
Wind speeds averaged 6.9 mph for November, an increase of 1.0 mph from in October but 1.0 mph less than the long-term monthly average. ICN Monmouth (Warren County) had the windiest month with the highest monthly average at 11.4 mph and the highest recorded wind gust, measuring 40.2 mph on November 11.
Air temperatures fell 19° to a November average of 41°, 2° lower than the long-term network average. Station highs were in the 60s and 70s, ranging from 14 to 20° higher than normal. The month’s highest temperature was 74°, recorded at ICN Belleville (St. Clair County) on November 18. Lows fell into the 10s and 20s. ICN Monmouth measured 11° on November 26, the month’s lowest temperature.
Soil temperatures declined 17 to 20° to monthly averages in the low to mid-40s. Under bare soil, temperatures ranged from 29 to 72° at 2 inches and 31 to 65° at 4 inches. Temperatures under sod ranged from 36 to 62° at 4 inches and 34 to 60° at 8 inches.
November precipitation was low across the entire network as stations recorded totals 18 to 48% of normal. Eleven stations had monthly totals less than one inch. The month’s highest was 2.00 inches recorded at ICN Dixon Springs (Pope County).
With the drier weather, soil moisture declines were seen across the state. Soil moisture levels at 2 inches averaged 0.32 water fraction by volume on November 30, a decrease of 11% from the first of the month. The largest drops were in western and central Illinois where levels fell 15 and 18%, respectively, over November.
Similar declines occurred through depths of 20 inches, while moisture levels remain high at 39 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 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 above the median value for November (approximately 240 percent of the median) and above the mean for November (approximately 140 percent of the mean). Monthly mean discharge values in November ranged mostly from normal to above normal for the month.
Water-Supply Lakes and Major Reservoirs. Table 3 lists reservoirs in Illinois, their normal pool or target water surface elevation, and other data related to observed variations in water surface elevations. Reservoir levels are obtained from a network of cooperating reservoir operators who are contacted each month by ISWS staff for the current water levels. Reservoir levels are reported in terms of their difference from normal pool (or target level). The average of the month-end readings for the period of record is reported in terms of the difference from normal pool or target level (column 6 of Table 3), and the number of years of record for each reservoir also is given (column 7). Most reservoirs serve as public water supplies, with the exceptions noted in the last column.
Compared to end-of-October water levels at 23 reservoirs for which levels were reported last month and this month, reported end-of-November water levels were lower at 16 reservoirs, slightly higher at 1 reservoir, and about the same as at the end of October at 6 reservoirs. For the 23 reservoirs with measurements reported at the end of November, water levels were below normal target pool or spillway level at 9 reservoirs, above normal target pool or spillway level at 9 reservoirs, and at about full pool level at 5 reservoirs. The Kinkaid Lake level was intentionally drawn down in November. Seasonal target operating levels of Lake Decatur and Lake Springfield decrease at the beginning of December.
Major Reservoirs. Compared to water levels at the end of October, at the end of November the water level at Lake Shelbyville was 3.0 feet lower, Carlyle Lake was 0.6 feet lower, and Rend Lake was 0.6 feet lower. At the end of November, Lake Shelbyville was 4.6 feet above the December 1 target level, the Carlyle Lake level was 0.2 feet above the December 1 target level, and Rend Lake was 0.5 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 November 2021 mean level for Lake Michigan was 580.0 feet. The monthly mean level one year ago (November 2020) was 581.5 feet. The long-term average lake level for November is 578.7 feet, based on 1918–2020 data. In this period of record, the lowest mean level for Lake Michigan for November occurred in 1964 at 576.3 feet, and the highest mean level for November occurred in 1986 at 582.0 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 decreased at most monitoring wells in November. On average, well levels declined 0.62 inches from in October with individual well changes ranging from 2.87 inches below to 1.35 inches above last month’s levels. The largest decline was at the Perry well in Pike County, which was drying out from a very wet October.
Levels were 0.01 inch above last year, 0.10 inches above the 15-year average and 0.52 inches above the period of record. Water tables are still lower in northern Illinois as drought continues in the region. The Freeport well level in Stephenson County was 22.61 inches on November 30, a decline of 4.04 inches from last year and 4.48 inches below the 15-year average.
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, http://rivergages.com, 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