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.
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.
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.
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:
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.
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.