December Figure 1. Statewide departures from normal

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1 December 2006 December 2006 Overview (Bob Scott) Temperatures and precipitation in Illinois during December were well above average. Soil moisture within the top inches of soil was above the long-term statewide normal. Streamflows were above median heights. Shallow groundwater levels rose above long-term average depths for the first time in 21 months. Temperatures across Illinois (Figure 1) for December were well above average (a 5.4-degree departure). Crop Reporting District (CRD) temperatures ranged from 4.6 degrees above average (west-southwest) to 6.2 degrees above average (northwest). Precipitation amounts for Illinois in December were well above average (Figure 1). The statewide average of 3.67 inches represents a inch departure or 137 percent of average for the month. Rainfall totals varied from 2.48 inches (122 percent of average) in the northwest CRD to 4.72 inches (131 percent) in the southeast CRD. Divisional percent-ofnormal extremes ranged from 118 percent (west) to 171 percent (east). Soil moisture in the 0- to -inch (0- to -centimeter) layer at the end of December was above normal (Figure 1). Conditions were near normal in all layers at most sites. Larger departures from normal were observed across southern Illinois in the deepest layer. Values in deeper soils across central Illinois have increased to near normal levels over the very dry amounts observed in previous months. Those earlier, drier values were a reflection of the drought of Mean provisional streamflow statewide was above the median flow in December, 378 percent of median (Figure 1). Rivers in Illinois recorded monthly mean discharges in the normal to much above normal range. The Illinois River reached flood stage at several locations in December. Water surface levels at the end of December were below the normal pool/target operating level at 11 of 37 reporting reservoirs. At the end of the month, Rend Lake and Lake Shelbyville were 4.2 feet and 5.5 feet above their respective seasonal target levels, while Carlyle Lake was 0.8 feet above its seasonal target level. Lake Michigan s mean level remains below the long-term average. Statewide, shallow groundwater levels were above normal with an average departure of one foot. Levels averaged 2.2 feet higher than November levels. Combined with the change in normal monthly groundwater levels between November and December, a 1.4-foot increase in departures from last month was observed (Figure 1). Levels were approximately 4.4 feet above December levels of last year. 500 D05 J06 F M A M J J A S O N D06 Note: Extended network descriptions appear in the January and July issues. Network maps are available upon request. Figure 1. Statewide departures from normal

2 Weather/Climate Information (Jim Angel and Bob Scott) Temperatures across Illinois for December were well above normal (Figure 2 and Table 1). Extremes ranged from -7ºF on December 8 at Dixon (Lee County), Rochelle (Ogle County), and Havana (Mason County) to 69 F on December 18 at Grayville (White County). It was the 15th warmest December and the 9th warmest November December (2-month) and January December (12-month) period since Precipitation for December was well above normal statewide (Figure 2 and Table 1). Claremont (Richland County) reported the highest one-day precipitation, 2.93 inches on December 1. Grand Chain Dam (Pulaski County) reported the highest monthly total, 7.12 inches. It was the 13th wettest December in Illinois on record. Significant snowfall reported for December was almost exclusively from the November 30 December 1 winter storm. The highest official total for the event and the month was 15.3 inches at Peru (La Salle County). An unofficial report of 18 inches was made near Princeton (Bureau County). Besides snowfall, heavy and damaging ice accumulations were reported in a band extending to the northeast from St. Louis into central Illinois, including Springfield, Bloomington-Normal, and Decatur. No other significant snowfall event occurred in December. No severe weather was reported in Illinois during December. Illinois Climate Network (ICN) Data. Average daily wind speeds in Illinois for December ranged from 5 mph at Dixon Springs to approximately 12 mph at Bondville and Stelle (Figure 3). Highest wind gusts for the month were 46 mph at Stelle and 45 mph at Bondville (December 1). The prevailing wind direction was southwesterly across the state. Wind speeds in excess of 8 mph varied from a total of hours at Dixon Springs to 560 hours at Monmouth and Bondville. (December has 744 hours.) Average air temperatures in December ranged from 30 F at DeKalb to 42 F at Dixon Springs and Carbondale. Solar radiation totals in December varied from 144 Mega-Joules per square meter (MJ/m 2 ) at St. Charles to 223 MJ/m 2 at Belleville. Potential evapotranspiration totals ranged from 0.8 inches at Freeport and DeKalb to 1.4 inches at Belleville. Soil temperatures at the 4-inch level ranged from 33 F at Big Bend to 45 F at Carbondale. Similar soil temperatures at the 8-inch level varied from F at Big Bend to 47 F at Dixon Springs. Extended climate outlooks issued by the U.S. Department of Commerce, National Oceanic and Atmospheric Administration, Climate Prediction Center for January and for January March call for above normal temperatures across the state, especially in northern Illinois, and for below normal precipitation statewide Snowfall Figure 2. Illinois temperature, precipitation, and snowfall during December

3 Crop Reporting District Table 1. Illinois Precipitation (inches) and Temperature (ºF) by Crop Reporting District Dec 06 Amount Last Month Last 3 Months Last 6 Months Last 12 Months % Temp Oct 06- % Temp Jul 06- % Temp Jan 06- % Avg Dev Dec 06 Avg Dev Dec 06 Avg Dev Dec 06 Avg Northwest Northeast West Central East West-southwest East-southeast Southwest Southeast State Average Note: Data are provisional. Complete, quality-controlled data are available about six months after a given month. Temp Dev Soil Moisture Information (Bob Scott) Precipitation across Illinois was well above average during December. Combined with rainfall in prior months, soil moisture across Illinois was near normal at most sites in every layer, except for a wider range of conditions in the deepest layer in southern Illinois (Figure 4). Values ranged from 63 percent of normal at Belleville to 128 percent at Olney in the 0- to 6-inch layer, from 82 percent at Bondville to 123 percent at Olney in the 6- to 20-inch layer, and from 68 percent at Bondville to 133 percent at Rend Lake in the 20- to -inch layer. Amounts in the - to 72-inch layer were more variable, ranging from 60 percent at Dixon Springs to 159 percent at Rend Lake. Overall soil moisture in Illinois at the end of December was above normal (Figure 1). Compared to conditions at the end of November, soil moisture in Illinois during December generally increased across the state (Table 2). Moisture near the surface increased between 15 and 35 percent at half of the network sites, and decreased substantially at just Monmouth (17 percent). Small increases were common at most sites in the 6- to 20-inch layer. Brownstown and Belleville showed increases near 15 percent. Increases occurred in the 20- to -inch layer at Springfield (21 percent), East Peoria and Monmouth (15 percent), and DeKalb (14 percent). Changes were 10 percent or less at all remaining sites. 3

4 Average Wind Speed (mph) Average Wind Direction (deg) Hours Wind Speed Above 8 mph Average Temperature (deg F) Total Solar Radiation (MJ/m 2 ) Total Potential Evap. (in) Average 4 Inch Soil Temperature (deg F) Average 8 Inch Soil Temperature (deg F) Figure 3. December monthly averages and totals as collected by the Illinois Climate Network

5 0-6 inch Soil Layer 6-20 inch Soil Layer < inch Soil Layer - 72 inch Soil Layer Figure 4. January 1 observed percent-of-normal soil moisture based on mean 5

6 Location Table 2. Soil Moisture in Various Layers on January 1, 2007 Jan (inches) Change from Dec 1 (%) Jan (inches) Change from Dec 1 (%) Jan (inches) Change from Dec 1 (%) Freeport (NW) DeKalb (NE) Monmouth (W) East Peoria (C) Topeka (C) Stelle (E) Champaign (E) Bondville (E) Perry (WSW) Springfield (WSW) Brownstown (ESE) Olney (ESE) 2.8 N/A 4.9 N/A 7.1 N/A Belleville (SW) Carbondale (SW) Ina (SE) Fairfield (SE) Dixon Springs (SE) Note: N/A = Data not available. Surface Water Information (Bill Saylor and Vern Knapp) River and stream discharge and stage data are obtained from gaging stations operated by the U.S. Geological Survey (USGS) or the U.S. Army Corps of Engineers (USACE). The USGS gaging station network is supported, in part, by the Illinois Department of Natural Resources Office of Water Resources and the Illinois State Water Survey (ISWS), and the USACE. Provisional discharge data are obtained from the USGS. Table 3 lists the provisional peak stage for the current month compared to flood stage at selected streamgaging stations located on the Illinois, Mississippi, and Ohio Rivers. The peak stage is determined from the daily morning readings posted by the National Weather Service and/or the USACE. River levels at many Illinois River locations reached flood stage during the last week of December; levels along the Mississippi and Ohio Rivers were below flood stage. Provisional monthly mean flows for 26 streamgaging stations located throughout Illinois are shown in Table 4. Mean values posted by the USGS are listed if available; otherwise, daily mean discharge data posted by the USGS are used to estimate the mean flow for the month. The USGS publishes long-term mean flows for each month. The month s median flow for each station listed in Table 4 is determined by ranking the December mean flow for each year of record, and selecting the middle value, 50 percent exceedence probability. 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 4 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 4 contribute to their flow.) Mean provisional flow statewide was above the median value for December (378 percent of the median) and above the long-term mean for the month (235 percent of the mean). Mean streamflow conditions in December ranged from normal to much above normal throughout Illinois as observed at Table 4 stations. Monthly mean streamflow for the Vermilion River near Danville was the highest monthly mean streamflow observed for the month of December during the period of record at that station. 6

7 River Station River Illinois mile* Mississippi Ohio Table 3. Peak Stages for Major Rivers, December 2006 Flood stage (feet)* Peak stage (feet)** Date Morris La Salle Peoria Havana Beardstown Hardin Dubuque Keokuk Quincy Grafton St. Louis Chester Thebes Cairo Notes: *River mile and flood stage from River Stages in Illinois: Flood and Damage Data, Illinois Department of Natural Resources, Office of Water Resources, August 2004 (except as revised by the National Weather Service). **Peak stage based on daily a.m. readings, not instantaneous peak. Water-Supply Lakes and Major Reservoirs. Table 5 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 5), 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-november water levels at 32 reservoirs, end-of-december water levels had increased at 18 reservoirs, had decreased at 9 reservoirs, and were the same as last month at 5 reservoirs. For the 37 reservoirs with observations reported at the end of December, 19 reservoirs were above normal pool (or target operating level), 7 reservoirs were at normal pool or spillway elevation, and 11 reservoirs were below normal pool. Major Reservoirs. Compared to end-of-november water levels, end-of-december water levels had decreased 0.3 feet at Lake Shelbyville and 0.9 feet at Carlyle Lake, but the level at Rend Lake level had increased 2.0 feet. At the end of December, the water surface level was 4.2 feet above the seasonal target level at Rend Lake, 0.8 feet above the seasonal target level at Carlyle Lake, and 5.5 feet above the seasonal target level at Lake Shelbyville (relative to its decreased January 1 target level). Great Lakes. Current month mean and end-of-month values are provisional and are relative to International Great Lakes Datum The December mean level for Lake Michigan was feet, compared to a mean level of feet in December The long-term average lake level for December is feet, based on data. Historically, the lowest mean level for Lake Michigan in December occurred in 1964 at feet, and the highest level occurred in 1986 at feet. The month-end level of Lake Michigan was feet. 7

8 Table 4. Provisional Mean Flows, December 2006 Drainage Years 2006 Long-term flows Percent Days of area of mean flow Mean* Median chance of data this Station (sq mi) record (cfs) (cfs) (cfs) Flow condition exceedence month Rock River at Rockton much above normal 6 31 Rock River near Joslin much above normal 6 31 Pecatonica River at Freeport above normal Green River near Geneseo much above normal 3 31 Edwards River near New Boston much above normal 4 31 Kankakee River at Momence much above normal 4 31 Iroquois River near Chebanse much above normal 7 25 Fox River at Dayton much above normal 1 31 Vermilion River at Pontiac much above normal 2 31 Spoon River at Seville above normal LaMoine River at Ripley normal Bear Creek near Marceline normal Mackinaw River near Congerville much above normal 3 31 Salt Creek near Greenview much above normal 5 31 Sangamon River at Monticello much above normal 5 31 South Fork Sangamon near Rochester above normal Illinois River at Valley City 26,743 67,920 18,060 14,937 much above normal 6 31 Macoupin Creek near Kane above normal Vermilion River near Danville much above normal ** 31 Kaskaskia River at Vandalia normal Shoal Creek near Breese above normal Embarras River at Ste. Marie above normal Skillet Fork at Wayne City above normal Little Wabash below Clay City above normal Big Muddy at Plumfield above normal Cache River at Forman above normal Notes: Much below normal flow = 90-% chance of exceedence. Below normal flow = 70-90% chance of exceedence. Normal flow = 30-70% chance of exceedence. Above normal flow = 10-30% chance of exceedence. Much above normal flow = 0-10% chance of exceedence. *As reported in U.S. Geological Survey (USGS) Water Resources Data, Illinois, Water Year ** New high for December monthly mean flow for the period of record. 8

9 Table 5. Reservoir Levels in Illinois, December 2006 Current level Average November Normal pool difference from Monthly difference from Years reported or target normal or target change normal or target of pumpage Reservoir County level (feet) (feet) (feet) (feet) record (million gallons) Altamont Effingham Bloomington McLean N/A Canton Fulton Carlinville Macoupin Carlyle (1) Clinton For security 44 considerations, +0.8 statewide -0.9 tabular reservoir +1.9 data 28 are not N/A Coulterville Randolph available on the Internet. 0.0 Specific +0.9 data requests -2.0may be made 10 to 5.2 Crab Orchard Williamson +0.7 N/A Not PWS Bill Saylor at: Decatur (1,3) Macon ,08 Devils Kitchen Williamson N/A Not PWS Evergreen (4) Woodford N/A Glenn Shoals Montgomery w/hillsboro Greenfield Greene Highland Madison Hillsboro Montgomery Jacksonville (2) Morgan N/A w/mauvaise Terre Kinkaid Jackson Lake of Egypt Williamson N/A N/A N/A Little Grassy Williamson N/A Not PWS Mattoon Coles w/paradise Mauvaise Terre (2) Morgan N/A no meter Mt. Olive (new) Macoupin N/A N/A N/A N/A w/mt. Olive (old) Mt. Olive (old) Macoupin Nashville (3) Washington Pana Christian Paradise Coles Paris (east) Edgar Paris (west) Edgar w/paris (east) Pinckneyville Perry Pittsfield Pike Raccoon (1) Marion N/A N/A Rend Franklin N/A Salem (3) Marion Shelbyville (1) Shelby Not PWS Sparta (3) Randolph Spring (4) McDonough Springfield (1,3) Sangamon Taylorville Christian Vermilion (4) Vermilion Virginia Cass Not PWS Notes: Normal pool and target level datum is NGVD Current levels reported represent water surface levels at the end of the month, not the monthly average. Average difference from normal or target level is the arithmetic average of reported month-end values for the period of record indicated. Years of record = total number of monthly readings included in month-end average. Total period of record may be longer. Not PWS = not a public water supply. N/A = Data not available. (1) Target operating level may vary. Seasonal target levels this month represent January 1 values. (2) Instrumentation not available to measure height of water elevation above spillway. (3) Natural inflow can be supplemented by other sources. (4) Normal pool elevations have changed during period of record reported. 9

10 Groundwater Information (Ken Hlinka) Comparison to Average Levels. Shallow groundwater levels in 15 observation wells, which are remote from pumping centers, were above average for the first time in 21 months. December levels were a foot above normal and ranged from 3.4 feet below to 3.6 feet above normal levels (Table 6). The water level at Snicarte (Mason County) was again below the bottom of the well. Comparison to Previous Month. Shallow groundwater levels were above those of November. Levels averaged 2.2 feet higher and ranged from 0.6 feet below to 7.4 feet above levels last month. Comparison to Same Month, Previous Year. Shallow groundwater levels in December were above levels measured one year ago. Levels averaged 4.4 feet higher and ranged from 0.7 feet to 8.4 feet higher than during December Table 6. Month-End Shallow Groundwater-Level Data Sites, December 2006 Number Well name County Well depth (feet) This month s reading (depth to water, feet) 15-year avg. level (feet) Deviation from Period of record avg. (feet) Previous month (feet) Previous year (feet) 1 Galena JoDaviess Mt. Morris Ogle Crystal Lake McHenry Cambridge Henry N/A N/A N/A N/A N/A 5 Fermi Lab DuPage Good Hope McDonough Snicarte Mason.30.30* N/A N/A N/A N/A 8 Coffman Pike Greenfield Greene Janesville Cumberland St. Peter Fayette SWS #2 St. Clair N/A 13 Boyleston Wayne Sparta Randolph SE College Saline Dixon Springs Pope Bondville Champaign Notes: N/A = Data not available. *Water level below bottom of well. Averages Addendum (Nancy Westcott) Imperial Valley Precipitation. December 2006 precipitation amounts (Figure 5a) were moderate. Monthly gage totals were greatest in the northern and western regions of the network, and precipitation was lightest in the central portion of the network. Individual gage amounts ranged from 8 inches at site #2 to 1.68 inches at site #7. The 30-year, , average precipitation amounts for December at Havana and Mason City are 2.63 and 2.41 inches, respectively. The December 2006 network average of 2.16 inches was about 153 percent of the 14-year ( ) December network average of 1.41 inches. Cook County Precipitation. December 2006 precipitation amounts (Figure 5b) were fairly uniform and heavy for December. The greatest precipitation was in the southern portion of the network, and the lightest precipitation was in the northwestern region of the network. Precipitation values ranged from 3.53 inches at site #16 (Palos Park), to 2.72 inches at site #1 (Northbrook). The December 2006 network average of 7 inches was about 184 percent of the 17-year ( ) December network average of 1.67 inches. 10

11 a. Imperial Valley b. Cook County 3.25 Figure 5. Long-term raingage network precipitation totals (inches) for December 2006 Data sources for information in this publication include the following: CPC - Climate Predication Center, ISWS - Illinois State Water Survey, MRCC - Midwestern Regional Climate Center, NCDC - National Climate Data Center, NWS - National Weather Service, USACE - U.S. Army Corp of Engineers, USGS - U.S. Geological Survey, WARM - Water and Atmospheric Resources Monitoring Program, Equal opportunity to participate in programs of the Illinois Department of Natural Resources (IDNR) and those funded by the U.S. Fish and Wildlife Service and other agencies is available to all individuals regardless of race, sex, national origin, disability, age, religion, or other non-merit factors. If you believe you have been discriminated against, contact the funding source s civil rights office and/or the Equal Employment Opportunity Officer, IDNR, One Natural Resources Way, Springfield, IL ; 217/ ; TTY 217/