Midwest Weekly Highlights - April 17-23, 2004

---

‘Tis the Season….Severe Weather Visits the Midwest.

 
After two to three weeks of dry weather, rain returned to much of the Midwest and with it came the first significant severe weather of the season. Temperatures this week were above normal across all but the far nothern portions of the region (Figure 1), ranging from 6F to 8F above normal across the southeastern half to 2F to 4F below normal across northern Minnesota, northern Wisconsin, and the Michigan UP.  There were some 90F degree readings reported in Iowa and Missouri on April 18 and April19, and a few temperature records were tied or set. Rainfall for the period was well above normal across the northwestern half of the region, except for a small portion of southwestern Iowa/northwestern Missouri, and northwestern Minnesota (Figure 2).  The central portion of the region received  only 30 to 75 percent of normal rainfall, while the far southern portion of the region was well above normal.  However, rainfall for the month to date is still well below normal across most of the Midwest (Figure 3), with the exception being Kentucky, southeastern Ohio, and far northern Wisconsin.

The week of April 17-23 literally began with some severe weather in northeastern Illinois. A front draped across the region was the focus of thunderstorms early in the morning of April 17. There was some minor wind damage, with most of the severe storms sporting hail from 0.75 to 1 inch. Grayslake, IL (Lake County) received 0.75 inch hail for almost 4 minutes.

On April 18 a strong low pressure system was spinning over South Dakota, with a warm front extending across southern Iowa, Wisconsin, and low Michigan (Figure 4). Severe thunderstorms hit parts of lower Michigan during the early morning. Later in the day, thunderstorms developed from northwestern Iowa through southern Minnesota and eastward into Wisconsin. There were numerous reports of 0.5 to 1.75 inch hail. Thunderstorm related wind gusts in excess of 60 mph caused damage. Several tornadoes were sighted in Iowa and Minnesota during the late afternoon (Figure 5). Further east, wind damage and large hail were also observed in parts of Wisconsin. Two to three inches of rain in north central Wisconsin caused flash flooding. On top of it all, strong, gusty winds created by the strong low pressure system produced some damage on their own. There were numerous reports of gusts over 40 mph, and a gust of 62 mph was observed in Norway, IA (Benton County). The winds caused some minor damage and there a number of small power outages. In Madison, WI three downtown streets were closed off and about 100 inmates from the Dane County Jail were evacuated overnight when a 10-foot by 20-foot concrete form fell from the new Dane County courthouse construction site.

 
Tornado Outbreak over Illinois and Indiana

The cold front that moved through the Midwest on April 19 began to lift northward as a warm front again early on April 20 (Figure 6, Unisys). A broad area of showers and some thunderstorms developed along and ahead of the front early on April 20. This was the first significant rain of the month for much of the region, much to the delight of agricultural producers who were actively into spring planting activities. During the afternoon thunderstorms began developing from central Illinois northward. The first of these was a small, low topped supercell in Douglas and Champaign Counties east-central Illinois during the early afternoon (Figure 7). This storm spawned a small tornado. There were reports of multiple touchdowns by this tornado, and it produced some damage to a house, barn, and machine shed in its short lifetime.

More significant storms began to develop during the late afternoon. By 5:00 p.m. CDT a number of these storms were developing into small supercells. The supercell that eventually spawned the Utica tornado was just starting to intensify at the western edge of Stark County (Figure 8, University of Illinois). At approximately 5:45 p.m. CDT a tornado from this storm touched down over open country about 2 miles east of Hennipen, IL. The tornado then traveled northeast into Granville, causing significant damage estimated as high F2 to 60 homes and other structures in Granville. Eyewitnesses reported multiple vortices with this tornado. By 6:00 p.m. this storm was located just east of the intersection of Interstate 80 and Interstate 39. At 6:09 p.m. a large tornado struck Utica (Figure 9 and Figure 10, University of Illinois).  The tornado caused F3 damage and eight people were killed taking refuge in the basement of an old building housing a tavern in downtown Utica when the tornado collapsed the building. At least 10 people were injured and taken to hospitals. Several other tornadoes were reported with other storms as they moved through northeastern Illinois during the evening hours (Figure 11, College of DuPage). On April 21 Illinois Governor Rod Blagojevich declared Kankakee, LaSalle, Putnam, and Will Counties state disaster areas. On April 23 those four counties were declared federal disaster areas, and there was a possibility of adding at least one more.

Six tornadoes hit parts of western and central Indiana during the late afternoon (Figure 12, NWS). The first touched down east of Frankfort, IN at 5:15 p.m. producing F0 damage. At least 12 homes were damaged near Jamestown, IN, and another tornado removed the roof of a skating rink in Kokomo. 

By the time the night was over, 15 tornadoes had touched down in Illinois and five in Indiana (Figure 13). This number will like be revised as damage surveys are completed and final tornado tracks are determined.

 
Stalled Front Brings More Rain to Southern Missouri and OhioValley

The cold front that moved through the Midwest on April 21 stalled out just south of the Ohio River. A wave moving along this front brought rain over much of southern Missouri, southern Illinois, southern Indiana, and Kentucky on April 22, and widespread heavy rain over southwestern Missouri on April 23.  The rain in Missouri , which continued into April 24 and 25, caused wiidespread flash flooding. This event will be covered in more detail in next week's summary.