2018 Illinois Climate Recap

 A Climatologic Review: 2018

Now that 2019 is well underway, lets take a moment to reflect back on the climate averages and departures from 2018.

Note:  Data are provisional and may change slightly over time


2018 was a year marked with several climatologically dramatic temperature swings.  The chart below shows monthly temperature departures from the 1980 – 2010 long term average for Illinois.  The most noteworthy feature is the -7.8°F departure that occurred in April, ranking April 2018 as the second coldest April on record for the state (records extend back to 1895).  And with the turn of a calendar page, May saw a +8.0°F departure from the long term mean, ranking May 2018 as the warmest May in state history.

The plot below shows the average statewide temperature (F) by month for 2018, the colors represent meteorological seasons.

The map below shows spatially average temperature departures for the year 2018.   Despite several dramatic temperature swings throughout the seasons, the year as whole finished right around the long term mean statewide.  A few regions in the northwest were a degree below, and a few regions in the south/southeast were a degree above the long term mean.

The statewide average temperature for 2018 was 52.5°F which is 0.2°F  above the long term average.

  • The highest temperature recorded in the state: MORRIS 1 NW in Grundy County with 100°F on May 28th, 2018
  • The lowest temperature recorded in the state:  MORRISON in Whiteside County with -24°F on January 1st, 2018
  • The warmest mean temperature: LAWRENCEVILLE 2WSW in Lawrence County with 59.3°F
  • The coldest mean temperature: PALESTINE in Crawford County with 43.1°F


The chart below shows monthly precipitation departures from the 1980 – 2010 long term average for Illinois in inches.  February saw the wettest departure from average at 2.82 inches.  April saw the driest departure from average at -1.36 inches,

The plot below shows the average statewide precipitation (in) by month for 2018, the colors represent meteorological seasons.

The map below shows precipitation as a percent of normal for the year 2018 in inches.  It was a rather wet year statewide, the highest percentages above average were reported in numerous regions across the extreme northern and southern portions of Illinois, where 125 to 150 percent of normal precipitation was measured.

The statewide estimated average precipitation for 2018 stands at 45.75 inches which is an impressive 5.79  inches above the long term average.

  • The highest yearly precipitation in the state: NASHVILLE 1E in Washington County, with 66.79 inches
  • Largest one day maximum event: CISNE 2.5 in Wayne County with 8.54 inches on September 8th, 2018
  • Snowiest location in the state: BULL VALLEY 2.5 WNW with 55.4 inches, the one day maximum snowfall for the site was 13.1 inches on November 26, 2018

Severe Weather

Severe weather reports for Illinois in 2018 from the NOAA Storm Prediction Center. Note: It is possible to generate multiple report for the same storm/event

Month Total Reports Tornado Hail Wind
January 2 0 2 0
February 1 0 0 1
March 0 0 0 0
April 20 9 4 7
May 170 6 48 116
June 184 11 15 158
July 54 0 6 48
August 40 2 7 31
September 40 2 1 37
October 3 0 0 3
November 0 0 0 0
December 52 34 11 7
Total 566 64 94 408

Illinois Climate Minute: 2018 Recap

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Warm and Stormy December for Illinois

In contrast to November, December 2018 finished warmer than the long term average, was lacking in major winter storms, and brought a historic late season severe weather outbreak.

  • The statewide average temperature for December was 34°F, which is 4.1°F above the long term average.
  • The statewide average precipitation for December was 3.35 inches, which is 0.66 inches above the long term average.
  • The highest temperature recorded for the month was 71°F on December 2nd at the Kaskaskia River Lock and Dam in Randolph County.
  • The lowest temperature recorded for the month was 6°F on December 28th at both the Altona and Mount Carroll stations in Knox and Carroll Counties.
  • The highest monthly rainfall total of 6.83 inches occurred at a station near Chester, which is located in Randolph County.
  • The highest monthly snowfall total was only 3.1 inches, and was recorded at a station near Patoka in Marion County.
  • The National Weather Service confirmed 29 tornadoes in Illinois during the historic December 1st severe weather outbreak.

Data are provisional and may change slightly over time


December favored above average temperatures for the entire Midwest, including Illinois  The map below shows that the largest temperature departures were felt in the upper Midwest, and extending down into much of northern Illinois where several locations finished the month 6 to 7 degrees above the long term average.  Overall, the statewide average temperature for December was 34°F which is 4.1°F above average.


Statewide precipitation totals for December were at or above the long term average. Two storm systems impacting the state during the last week of December helped to bring the monthly totals above normal for much of central and northern Illinois, where precipitation was lacking in the middle of the month.  The highest widespread precipitation totals occurred around and south of I-70.  The maps below show total December precipitation, as well precipitation departures for Illinois.

December was not an ideal month for snow lovers as warmer temperatures, and a combination of environmental factors kept December snow accumulation to a minimum.  The highest accumulations were in the northeast, and in central/west central portions of the state –  where a quick moving cold front brought a majority of the snow accumulation during the first week of December. Total snow accumulations are shown in the map below.

Severe Weather

The National Weather Service confirmed 29 tornadoes across Illinois during the December 1st tornado outbreak, ranking this as the largest December outbreak in state history.  The previous three largest outbreaks are listed below:

  • December 18-19, 1957 with 21 tornadoes
  • December 23, 2015 with 6 tornadoes
  • December 4, 1973 with 5 tornadoes

Most notable was the Taylorsville Tornado in Christian County.  This tornado had a path width over 1/2 mile wide, and estimated wind speeds of 155 mph, ranking it as an EF-3 on the Enhanced Fujita Scale, The Taylorsville tornado caused major damage to 100 homes, and 22 reported injuries.

The map below, from the Storm Prediction Center, pinpoints locations of all severe weather reports from 12/1/2018.  It is evident that the worst of the severe weather, and tornadoes, were confined to west central Illinois.

SPC Storm Reports

In total, 52 severe weather reports were recorded for Illinois this December; 34 reports for tornadoes, 11 for severe hail, and 7 for severe wind.  Note:  It is possible for multiple reports to be created for the same event/storm.

Check out the Twitter link from Kevin Lightly, capturing aerial images of damage in Taylorsville the day after the tornado outbreak:

Outlook for January

Looking ahead at the rest of January 2019, the Climate Prediction Center is forecasting an above normal chance for a drier than average January for a majority of the state. The highest probabilities are centered over northern Illinois and the Great Lakes.  Focusing on temperatures, the highest probabilities for above average temperatures are concentrated over the upper Midwest and North Dakota, with a smaller probability extending into northwest Illinois.

January 2019: CPC One Month Precipitation Outlook
January 2019: CPC One Month Temperature Outlook

Be sure to check back in the coming week for the ‘Illinois 2018 Climate and Weather Recap’ blog entry.



Cold, Snowy November in Illinois

It was a cold and snowy November in Illinois.

  • The statewide average temperature for November was  35.2°F, which is an impressive 7.3°F below normal, ranking November 2018 as the 8th coldest on record.
  • The statewide average rainfall for November was 3.11 inches, which is 0.36 inches below normal.
  • The highest temperature recorded for the month was 70°F at a station in Du Quoin on the 1st day of the month.
  • The coldest temperature recorded for the month was a chilly 1°F at three stations in Lee, Carrol, and Knox County on the night of the 28th.
  • The highest monthly rainfall total of 7.50 inches occurred at a station in Belknap, which is located in Massac County.  5.51 inches of the total was recorded during a one-day event on the 1st of the month.
  • The highest monthly snowfall total of 18.5 inches was recorded at a station in Bull Valley, which is located in McHenry County.

November was an exceptional month for snow lovers statewide, with virtually the entire state seeing it’s first accumulating snow of the season before the month’s end.  In fact by the 15th, with half the month still to go, Springfield Abraham Lincoln Airport had already broken the record for the snowiest November.
Overall monthly snowfall accumulation totals averaged around an inch in southeastern Illinois, up to 15 inches in the northwest, near the Quad Cities, with several locally higher amounts reported.


Several outbreaks of unseasonably cold conditions throughout the month helped in bringing the statewide averaged November temperature to a chilly 35.2°F.
Temperatures across Illinois were typically on the order of 5 to 10 degrees below normal, a trend that was felt across most of the Midwest.  The map shows the bullseye for the below normal cold concentrated in sections of northeast Missouri, southeast Iowa, and west-central Illinois.

Seasonal Review

Looking at meteorological Fall (Sept, Oct, Nov), temperatures for the season ended up near normal in southeastern Illinois, and between 2 to 4°F below normal as you head northwest toward Rockford and the Quad Cities (see map).

Precipitation for the same period is near normal for the central portion of the state, with above normal totals in the northwest and southeast.  Precipitation totals at Chicago O’Hare and Rockford Airports are currently ranked as the 4th wettest years on record, with a month still to go.

December Outlook

Finally, here is the outlook for December that was released by the National Weather Service (NWS) Climate Prediction Center (CPC) on November 30th.  The precipitation maps show an increased chance of above normal precipitation statewide, becoming more likely as you head westward towards Nebraska.  Temperature wise, there is a slightly increased chance of above normal temperatures statewide, a trend which is noted for much of the eastern half of the country.

Notable November Events:

Rainy Start to November for Southern Illinois.

November started with several substantial rain events bringing a half to an inch and a half of precipitation to most of the state, with the largest amounts in southeastern Illinois.  Two CoCoRaHs stations in Massac County, and a COOP station in Pope County recorded over 6 inches of rain during the first week of November.

Mid-month Snowstorm and Canadian air outbreak.

An early season plowable snowstorm, accompanied by unseasonably cold temperatures affected much of the state November 14-15th.  As much as a half foot of snow was reported in locations south and west of Springfield.  The official total at Springfield Abraham Lincoln Airport was 5.3 inches. Total monthly snowfall accumulation in Springfield measured 11.4 inches, ranking November 2018 the snowiest November on record.

Northern Illinois November Blizzard.

A potent low-pressure system tracked through central Illinois to finish off the Thanksgiving weekend, bringing a wide range of weather to the state.  Thunder, rain, ice, snow, wind, and blizzard conditions were all reported in varying locations on Sunday 11/25/2018.  The map below shows station interpolated snowfall  totals for this event.
Peak wind gusts of 55 mph were reported at Champaign Willard Airport, and 52 mph at Chicago O’Hare.

The measured snowfall totals of 11.7 inches at Rockford, and 13.3 inches at Moline, ranks this event as the largest November snowstorm on record for both locations.  The total November accumulated snowfall in Rockford of 15.8 inches, and Moline of 18.4 inches ranks November 2018 as the snowiest November on record for both locations.
A fresh snow pack, coupled with cold air behind this system allowed temperatures to plummet during the start of the last week in November.  Both Moline, and Chicago O’Hare set a record low maximum temperature on 11/27/2018, with recordings of 22°F at Moline and 25°F at O’Hare.
This post was written by Brian Kerschner, who will be taking over the blog next month.