Cool, Wet Start to May

The first half of May was both cool and wet. Preliminary data indicates that statewide temperatures were 1.4 °F below normal for the period May 1-17. Meanwhile, precipitation has been abundant. The statewide average precipitation was 4.15 inches, 1.79 inches above normal or 176 percent of normal. The heaviest rains have fallen in western and northern Illinois. The largest month-to-date total reported was 8.24 inches in Dallas City (along the Mississippi River between Quincy and Moline) by a CoCoRaHS observer.

Table 1. Precipitation totals by climate division in Illinois, along with the 1971-2000 normals, and percent of normal, for May 1-17, 2009.
Climate Region Precipitation (in) Normal (in) Departure (percent)
Northwest 4.64 2.25 206
Northeast 4.55 2.06 221
West 5.84 2.46 238
Central 4.17 2.32 179
East 3.17 2.21 143
South Southwest 4.26 2.43 175
South Southeast 3.67 2.46 149
Southwest 3.37 2.49 135
Southeast 3.51 2.66 132
State 4.15 2.36 176

Illinois was surrounded on three sides by very wet conditions in parts of Missouri, Iowa, Wisconsin, as well as Kentucky. The rains in Illinois have produced saturated soils in places and minor to moderate flooding along the Mississippi and Illinois Rivers and their tributaries.

May 1-16 precipitation
Precipitation totals for the Midwest for the period May 1-16, 2010 (click to enlarge).

May 1-16 percent of normal precipitation
Percent of normal precipitation across the Midwest for May 1-16, 2010 (click to enlarge).

Warmest April on Record for Illinois

Based on preliminary data, the statewide average temperature for Illinois in April was 58.4 degrees, 6.2 degrees above normal and the warmest April on record. This beats the old record of 58.2 degrees set in 1955. Official statewide average temperature records go back to 1895. The warm temperatures in April were not unique to Illinois – the entire Midwest was much above normal (see map below).
April rainfall was 3.5 inches, just 0.3 inches below normal. Areas in western Illinois around received the most precipitation, over 5 inches in some locations. A CoCoRaHS observer in Matherville (Mercer County) reported 6.50 inches for the month.

April temperature departures
Temperature departures for April across the Midwest (click to enlarge).

Midwest precipitation for April
Precipitation totals for April across the Midwest (click to enlarge).

Central IL tornado climatology updated

The NWS office in Lincoln, IL has updated their tornado climatology for central and southeastern Illinois for the period 1950-2009. During this period McLean County reported an incredible 100 tornadoes, the highest for any county in central Illinois. However, McLean County is the biggest county in this area (a bigger county means a bigger target). This can be partially overcome by calculating a tornado density instead. In that case, Logan County ranks highest in the area with an average of 9.385 tornadoes per 100 square miles. You can click on the individual counties and get more detailed reports of that county, including tracks, dates, magnitudes, deaths, injuries, and property/crop damage of each tornado.
Here is the track map for Champaign County:

Tornado tracks, Champaign County, 1950-2009.
Tornado tracks in Champaign County, IL, 1950-2009. See the NWS report for more details.

First Documented Radar Hook Echo

The Illinois State Water Survey is home to the first ever documented radar hook associated with an actual tornado. Water Survey staff captured the historic event on film on April 9, 1953. This was a major turning point in monitoring severe weather, demonstrating that tornadoes could be identified by radar. This discovery helped lead to the first national weather radar network in the United States.
The radar was located at Willard Airport, south of Champaign IL, and was being used along with a rain gauge network to relate radar signals with rain rates. Don Staggs, the radar technician, had stayed late to complete repairs on the radar. While testing the repairs, he noticed an interesting radar return and began recording the radar scope using the mounted 35 mm camera. As a result, he captured a well-defined hook echo (see photo) on film. Afterwords, researchers related this information to damage and photos along the tornado’s path. More images and information of this event are in the links provided under the photograph.

Radar hook echo
First recorded radar hook echo of a tornado, April 9, 1953, near Champaign, IL (photo courtesy of the Illinois State Water Survey, INRS, University of Illinois).

Additional information on this event:

I talked about this event when Tom Skilling, WGN-TV, hosted his annual Tornado and Severe Storm Seminar at Fermilab in Batavia, IL on April 10, 2010. The video of the presentation is on the WGN-TV web site.

Warm Start to April

April is off to a warm start with statewide temperatures 10.0 degrees above normal for the first 18 days of April. The statewide average precipitation is 1.66 inches, 76 percent of average. The warmer-than-normal temperatures were prevalent throughout the eastern two-thirds of US but were most intense in the Midwest and Northeast.
The combination of warm temperature, strong winds, and low humidity have aided in drying out fields. According to the National Agriculture Statistics Service, near the beginning of the month 50 percent of the fields in Illinois were rated with surplus moisture. By the April 19 report, this number had dropped to 7 percent.

US Temperature Departure, April 1-19, 2010.
US Temperature Departure, April 1-19, 2010 (click to enlarge).

March Was Warmer and Drier than Normal

Champaign, Ill. – Based on preliminary data in Illinois, the statewide average temperature for March was 43.6 degrees, 2.5 degrees above normal. This ends a three-month streak of colder than normal temperatures that occurred this winter, according to State Climatologist Jim Angel of the Illinois State Water Survey (http://www.isws.illinois.edu).
The statewide average precipitation was 2.8 inches, 0.4 inches below normal. A year ago, the March precipitation was 4.2 inches, an inch above normal, signaling the start of a very wet growing season.
This year, the January to March precipitation total was 5.8 inches, 1.4 inches below normal. Drier conditions this year have helped soil moisture return to conditions more typical for this time of year after an exceptionally wet fall.
The latest National Weather Service outlook for April calls for an increased chance of above normal temperatures across Illinois and the Corn Belt. An increased chance of above normal precipitation is indicated for the western Corn Belt, including western Illinois. The eastern half of Illinois has an equal chance of above, below, and near normal precipitation.
“March certainly came in like a lion and out like a lamb. The average statewide temperature on March 1 was 32 degrees but warmed up to 58 degrees on March 31,” concludes Angel.

Cold February Wraps Up a Cold Winter

CHAMPAIGN, Ill. – Based on preliminary data in Illinois, the statewide average temperature for February 2010 was 25.1 degrees, 5.1 degrees below normal. Snowfall for February was above normal. Amounts ranged from 6 inches in southern Illinois to over 18 inches in the Quad Cities and Chicago areas.
The cold February, along with colder-than-normal temperatures in December and January, made this the 19th coldest winter on record. The 3-month average temperature was 25.3 degrees, 2.9 degrees below average. Winters in the late 1970s were still much colder with a virtual tie between the winter of 1977-1978 at 19.6 degrees and the winter of 1978-1979 at 19.9 degrees.
Winter snowfall totals (December—February) ranged from about 45 inches in northeast Illinois to just under 15 inches in southern Illinois. This was 1 to 3 inches above normal for southern Illinois to over 10 inches above normal in northern and western Illinois. Wintertime precipitation, both rainfall and the water content of snow, measured 7.04 inches and was 0.35 inches above normal.
The latest National Weather Service outlook for March calls for an increased chance of below-normal temperatures in the southern two-thirds of Illinois. It also calls for an increased chance of drier-than-normal conditions for the month. See the Climate Prediction Center page.

January – Cold Start to 2010

Based on preliminary data, the average statewide temperature for January was 21.1 degrees, 3.7 degree below normal. The statewide average precipitation for January was 1.50 inches, 0.43 inches and 22 percent below normal.

Temperature Departures for January
Temperature Departures from Normal for January 2010

Temperature Departures for January
Temperature Departures from Normal for January 2010