Illinois State Water Survey - University of Illinois at Urbana-Champaign

State Climatologist Office for Illinois

Climate Events of 2009 in Illinois

Dr. Jim Angel, State Climatologist

Fourth Wettest Year on Record

Based on preliminary numbers, the annual precipitation for 2009 in Illinois was 50.27 inches, 11 inches above normal. This ranks as the fourth wettest year on record since statewide records began in 1895.

Top 5 Wettest Years on Record
Rank Year Precipitation (inches)
1. 1993 51.19
2. 2008 50.46
3. 1990 50.37
4. 2009 50.27
5. 1927 49.64

All four wettest years have been in the last 20 years of the record. The normal statewide annual precipitation in Illinois is 39.2 inches. The outstanding feature is the two back-to-back exceptionally wet years of 2008 and 2009. Together they account for 100.8 inches of precipitation. That is an extra 22.4 inches of precipitation over the two-year period.

As it now stands, the annual temperature for 2009 in Illinois was 51.2 degrees, 0.8 degrees below normal. The outstanding colder-than-normal months in 2009 were January, July, August, and October.

Cold, Wet December Finishes Out Cold, Wet Year

Based on preliminary data, the average statewide temperature for December in Illinois was 28.9 degrees, 1.0 degree below normal. The statewide average precipitation for December was 4.11 inches, 1.42 inches and 53 percent above normal. Here are the maps for December 2009: temperature departure and precipitation departure and snowfall totals.

Dreaming of a White Christmas? Odds Slim in Illinois

Based on historical reports of snow on the ground Christmas morning, people in northern Illinois have the highest odds of 30 to 50 percent. Naturally the odds decrease farther south but even southern Illinois sees one every once in a while. Your best place for having a white Christmas in Illinois? That would be Freeport in the northwest corner of the state at 56 percent.

The Christmas Day with the most snow on the ground in recorded history was 1951, according to long-term records. Aurora had an incredible 31 inches piled up that day from 12 days of nearly non-stop snow and temperatures below freezing... more on the 1951 Christmas and the odds of a white Christmas.

First Major Winter Storm of the Season Hits Midwest

The first major winter storm of the season struck the Midwest on December 8-9, 2009. A strong low-pressure system moved out of the southwestern US, into the central Plains states, across the Midwest and Great Lakes, and on into eastern Canada. This system produced impressive amounts of snow and high winds, leading to blizzard warnings in many locals. Cold, Arctic air moved in behind this system, causing temperatures that were 15 to 25 degrees below normal across Illinois on December 10... more on the 2009 blizzard.

Seventh Warmest November on Record

November rainfall in Illinois

Based on preliminary data, the state-wide average temperature for November was 46.9 degrees, 5.1 degrees above normal. This makes it the seventh warmest November on record (tied with 1913). The warmest November on record is a tie between 1931 and 2001, both with 49.8 degrees. State-wide records go back to 1895.

The state-wide precipitation for November was 2.6 inches, 0.7 inches below normal. While rainfall totals of 1.5 to 3 inches were common in far southern and northern Illinois, the heaviest rains of 3 to 4 inches fell across central Illinois.  

The statewide January to November precipitation total for 2009 is 46.2 inches, the third wettest on record. In fact, 2009 is already the tenth wettest year on record, even if no precipitation fell in December.

Second Wettest October on Record

The state-wide precipitation for October was 8.90 inches. This is 6.0 inches above normal. Based on preliminary data, this is the second wettest October on record. The wettest October was 1941 with 9.23 inches. The heaviest rains fell in the southern half of the state with totals ranging from 6 to 12 inches. Here are more details on October.

Statewide temperatures for October have been 4.8 degrees below normal, making this the seventh coldest October on record. Statewide records of temperature and precipitation go back to 1895.

Check out the map of Midwestern stations that set or almost set their October rainfall records, courtesy of the Midwestern Regional Climate Center.

Cool, Wet Growing Season Delays Harvest

Illinois corn harvest

According to statistics from the Illinois office of USDA's National Agricultural Statistics Service, the percent of corn harvest as of October 25 was only 14 percent. This is by far the slowest harvest for corn by this date in Illinois when compared to records dating back to 1980 (click to enlarge graph).

The first weather challenge for the 2009 growing season was the much above normal rainfall in March-June, which slowed planting and related field work. Statewide rainfall during this period was 21.0 inches, 5.5 inches above normal and the 7th wettest March-June on record.

This was followed by the coldest July on record when the statewide average temperature was only 70.3 degrees, 5.1 degrees below normal. August was cool as well, 2.1 degrees below normal. Rainfall was closer to normal in July-September with the statewide average at 10.4 inches, only 0.5 inches below normal. However, this was followed by the second wettest October's on record (see below).

September Brings Uneven Rainfall across State

Illinois rainfall in September, departure from normal

The state-wide precipitation for September was 2.4 inches, 0.8 inches below normal. This breaks the string of months with above-normal precipitation that started in February 2009 and ended in August 2009. While much of southern and western Illinois received above normal precipitation, northern and eastern Illinois were drier than normal.

Rainfall was heaviest in southeast Illinois with Lawrenceville reporting 10.53 inches for the month. Many sites in northern and eastern Illinois reported totals of less than an inch of rain.

Temperatures were slightly below normal with a state-wide temperature average of 65.8 degrees, compared to a normal of 66.2 degrees.  As of September 30, no station had reported a freezing temperature (32 degrees or less). See the press release.

Impacts of El Niño on Temperature and Precipitation

Illinois Temperature Departures for December

The NOAA Climate Prediction Center has identified a weak El Niño event in the Pacific Ocean. This event is expected to strengthen and last through this winter (2009-2010). Here is a series of maps on the historical impacts of El Niño on monthly temperature and precipitation (pdf).

In general, El Niño produced warmer-than-normal temperatures in September and during December-March. In contrast, cooler-than-normal temperatures prevailed in August and April-May. The impact on monthly precipitation was both weaker and less consistent. Somewhat wetter conditions prevailed in August, October, and December while drier conditions were found in September.

Tracking the First Fall Freeze Across the Midwest

The Midwestern Regional Climate Center has an interesting map showing the progression of frost across the Midwest, in other words, places that have already hit 32 and 28 degrees this fall. The map is updated daily by 11:30 am. Speaking of frost, here are the average frost dates in Illinois. As of September 28, the USDA report for Illinois stated that only about 2 percent of the corn and 1 percent of the soybeans were harvested - well behind the 5-year average.

Illinois Agricultural Disaster Declaration

On September 13, 2009, 88 counties in Illinois were declared as natural disaster areas because of too much rainfall during the first half of the growing season. See press release. Rainfall during the April-July period totaled 20.94 inches, 4.74 inches above normal. Here are the preliminary rainfall totals for individual sites in Illinois during this period.

Cool, Wet Summer in Illinois

Illinois cornfield during storm, Mike Kruk MRCC staff

Based on preliminary statewide numbers, this is the 11th coolest and 8th wettest summer since statewide record began in 1895. The average temperature for June-August was 71.4 degrees, 2.4 degrees below normal. The total precipitation for June-August was 15.2 inches, 3.6 inches above normal.

The coolest summer on record was 1915 with 69.3 degrees. In recent years, 1992 was ranked third with 70.2 degrees and 2004 was ranked fourth with 70.4 degrees. The wettest summer on record was 1993 with 18.3 inches of rain.

The statewide August average temperature was 71.0 degrees, 2.6 degrees below normal and the 15th coolest August on record. The statewide August total precipitation was 5.0 inches, 1.4 inches above normal and the 17th wettest August on record.

Departure map links for summer temperature and precipitation and for August temperature and precipitation

This may be the cloudiest summer on record. According to long-term records of sunshine kept by Frank Wachowski, weather observer for Chicago/Midway, the percent sunshine this summer was 53 percent, a new low for Chicago. Normal summer sunshine is 67 percent.

Average Wind Speed Maps

Link: New web page on average wind speed in Illinois

El Niño Not Likely to Affect First Fall Freeze

An Illinois State Water Survey press release from last week indicates that the developing El Niño in the Pacific Ocean will likely not affect the first freeze this fall in Midwest. Even cool summer weather does not appear to change the odds of an early freeze.

The average first fall freeze (32F) can be found here. Generally, it is early October in northern Illinois, mid-October in central Illinois, and late October in southern Illinois. However, the actual freeze date from year to year can vary by a week or two from those dates.

Coldest July on Record in Illinois

Illinois Temperature Departures for July 2009

Statewide temperature: Based on preliminary data for Illinois, the statewide average temperature for July was 70.4 degrees, 5.3 degrees below normal. This ranked as the coldest July statewide by more than a degree (see list below for five coldest Julys). Statewide records go back to 1895. While cooler than normal temperatures prevailed throughout the Midwest and East Coast in July (click on map to the right), the Southwest and West were warmer than normal.

Coldest Julys in Illinois

  1. 2009 - 70.4°F
  2. 1924 - 71.5°F
  3. 1967 - 72.0°F
  4. 1950 - 72.4°F
  5. 1915, 1947 (tie) - 72.5°F
Illinois Days Above 90F

Lack of hot weather: While southern Illinois reported a few days with temperatures in the 90s in July, much of the rest of the state saw none. The normal range of days in the 90s is typically between 5 in northern Illinois to 15 in southern Illinois. Click on map to the left. In Champaign-Urbana this was only the fourth time in its 121 year history that the thermometer failed to reach 90°F in July. The other three times were 2000, 2007, and 2008.

Illinois Days Above 90F

Consistently cold: Another remarkable feature of July was the consistency of the colder than normal temperatures. On a statewide basis, every day was below normal except for July 11. Click on map at right. In addition, 33 record daily low temperatures as well as 218 record low high temperatures were set for July. New records from around the US can be found on the National Centers for Environmental Information website.

Fewer degree days: One clear impact was lowered energy demand for cooling homes and businesses during July; cooling degree days (CDD) were down 48 percent from normal. Meanwhile, modified growing degree days (a measure of corn development) were down 17 percent from normal, suggesting less favorable growing conditions. Degree day definitions can be found here.

Outlook: Historically, a cool July is most often followed by a cool August. The specific odds on August temperatures after a cool July are 45 percent cooler-than-normal, 34 percent near-normal, and 21 percent above-normal. The NOAA Climate Prediction Center indicates that cooler than normal temperatures are likely to prevail for August across Illinois, and for the northern two-thirds of Illinois for the August-October period.

Statewide precipitation: The statewide average precipitation for July was 4.9 inches, 1.1 inches above normal. Precipitation since January 1 stands at 29.0 inches, 5.6 inches above normal. See map for more details.

June - Another Wet Month for Illinois

Illinois Precipitation for June 2009

Based on preliminary data for Illinois, the statewide precipitation for June was 5.25 inches, 1.2 inches above normal and the 25th wettest June since statewide records began in 1895 (click on map at right). The precipitation total for the first half of 2009 was 24.2 inches, 4.8 inches above normal and the 14th wettest on record.

The statewide average temperature for June was 72.6 degrees, 0.7 degrees above normal. However, the first half of June was significantly cooler (2.6 degrees below normal) than the second half (4.1 degrees above normal).

Hot, humid weather arrives in Illinois

According to NOAA, heat is the number one weather-related killer. According to one study more than 1,500 people in the US die each year on average from heat. The combination of warm weather and high humidity has caused the NWS to issue heat advisories in Illinois in recent days. So here are some sites with information on summer heat.

5th Wettest Spring on Record

Illinois Precipitation for Spring 2009

Based on preliminary data for Illinois, the statewide precipitation this spring was 15.9 inches, 4.5 inches above normal and the 5th wettest spring since statewide records began in 1895 (see map). May precipitation was 6.0 inches, 1.7 inches above normal and the 19th wettest May on record.  Spring includes the months of March, April, and May.

The wettest site this spring has been St. David (near Peoria) with 27.7 inches. The wettest site in May was Edwardsville with 11.7 inches. Both Peoria and Galesburg reported their wettest spring on record, impressive given their much longer period of record.

At 15.9 inches, this spring is almost two inches wetter than the 14.1 inches of last spring (2008). Historically, wet springs do not lead to wet summers. In fact, of the other nine wettest springs in the list below, the rainfall of the following summers was above normal in 4 cases and below normal in 5 cases with an overall average of 1 inch below normal.

Wettest Springs on Record in Illinois

  1. 1927 - 18.59"
  2. 1945 - 17.32"
  3. 1973 - 17.22"
  4. 1898 - 16.82"
  5. 2009 - 15.86"
  6. 1933 - 15.83"
  7. 2002 - 15.82"
  8. 1908 - 15.65"
  9. 1995 - 15.63"
  10. 1957 - 15.45"

6th Wettest April on Record

Illinois Precipitation for April 2009

Based on preliminary data for Illinois, the statewide average precipitation was 6.2 inches, 2.4 inches above normal and tied for the 6th wettest April since statewide records began in 1895. This April shares the record with April 1983. The wettest April on record was 7.1 inches in 1957. Normal statewide April rainfall is 3.8 inches.

Cooler than normal temperatures accompanied the wet weather, leading a statewide average temperature of 51.3 degrees (1 degree below normal). While the first 22 days of April were 4 degrees below normal, the last 8 days partially compensated by being 7 degrees above normal.

As of May 1, the 1-5 day forecast from the NWS shows chances of rain across the state almost every day with the southern half of Illinois having the potential of 1 to 4 inches of rainfall. Amounts in the northern half are expected to be less than an inch. The 6-10 day and 8-14 day forecast shows above-normal rainfall. The NWS outlook for May shows an increased chance of above-normal rainfall.

March '09 - Wet in the North, Dry in the South

Illinois Precipitation Departure

Based on preliminary data for Illinois, the statewide average precipitation was 4.2 inches, 1 inch above normal (figure on the left - click to enlarge). However, much of that precipitation (both rain and snow) fell in the northern half of Illinois. Some areas received twice their normal March amounts. Meanwhile, drier conditions prevailed in southern Illinois. Some areas in far southern Illinois received only 70 percent of their normal March precipitation.

Overall, March temperatures in Illinois were 2 degrees above normal. Temperature departures in the southern half of the state were 2 to 3 degrees above normal while only 1 to 2 degrees above normal in the northern half.

More images for March: precipitation (percent of normal), snowfall, temperature (departures)

Where is Spring?

A cold and wet first half of April has farmers still waiting to get into the fields and homeowners waiting to get into their gardens. Temperatures in the first two weeks of April were 4.5 degrees below normal and precipitation was 58 percent above normal. Many places in northern Illinois reported measureable snowfall from an April 5-6 storm. Press Release.

The statewide average temperature for April 1-14, 2009 was 44 degrees, while the statewide average precipitation was 2.7 inches.

The coldest April on record in Illinois had an average temperature of 43 degrees, set in 1907, while the second coldest was in 1926 with 45 degrees. While temperatures are expected to be warmer in the second half of this month, it may still end up being one of the colder April’s on record.

See the second post below for more information on the last spring freeze in Illinois.

Average Last Spring Frost in Illinois

The average date of the last spring occurrence of 32°F ranges from April 7 in far southwestern Illinois to Apri 28 in far northern Illinois. The actual date can vary from year to year. I would suggest adding 2 weeks on to this date before planting tender annuals. See map here.

February '09 - More Rain, Less Snow

Illinois Total Precipitation for February 2009

Based on preliminary data for Illinois, the statewide average precipitation was 2.45 inches, 0.52 inches above normal or 127 percent of normal. Ft. Massac State Park reported the highest precipitation total of 6.03 inches. Click on figure at right for larger image.

Meanwhile, statewide snowfall was below normal with only the northern third of the state receiving any significant amounts. Barrington reported the highest snowfall total of 8 inches.

The statewide average temperature was 31.4 degrees, 1.2 degrees above normal. The cold spot in the state was McHenry with a low of -9 degrees, while the warmest spot was Cairo with a high of 72 degrees.

Illinois Temperature Roller Coaster

Illinois Daily Temperature Departure

Usually we look back at a winter and remember unrelenting cold weather. However, in many cases in Illinois we get short breaks from the cold weather. The figure on the left (click to enlarge) illustrates this well using our current 2008-09 winter with warmer-than-normal periods in late December/early January and in the middle of February. Many of the colder-than-normal periods show a sharp negative departure that moderates over the course of a few days. This is not a surprise because cold, Arctic air rushes into the region and then is slowly warmed over the course of the next few days.

Former Champaign-Urbana weather observer passes away

My friend and colleague, Maria Peters, passed away on February 5, 2009. She was the Champaign-Urbana weather observer from September 1999 to May 2004. She then worked for the Midwestern Regional Climate Center until her death. An online message can be found at

Cold January in Illinois

The January statewide average temperature was 20 degrees, 4.5 degrees below normal with some low temperatures approaching the state record on January 16.

Arctic Air Grips Illinois

Cold arctic air caused temperatures and wind chills to plummet in Illinois. Lows on the morning of January 15 and 16 were in the minus teens and 20s across much of central and northern Illinois. Only far southern Illinois managed to remain above zero.

The coldest official report in the state on January 15 was -28°F at Mt. Carroll. The coldest report on January 16 was -33° at both Mt. Carroll and Elizabeth. See the minimum temperature map for January 15 and January 16. The official state record of -36°F, held at Congerville IL on January 5, 1999, still stands.

New records from around the US can be found at the National Centers for Environmental Information.

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