Midwest Weekly Highlights - April 10-16, 2006

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Summer Warmth Makes Early Appearance

Midwest residents enjoyed a few days of mild, quiet weather the second week of the month.  However, respite was brief as the increasing warmth combined with increasing moisture to produce several rounds of severe weather across the region.  Temperatures this week were much above normal across the entire region, although there was a distinct east to west gradient (Figure 1).  Average temperatures ranged from 9°F above normal in eastern Ohio to 16°F above normal over southwestern Minnesota and northwestern Iowa.   The precipitation pattern reflected the the northwesterly upper level wind flow across the Midwest as thunderstorms moved along frontal boundaries across the central Midwest.  Rainfall was well above normal across northern Iowa, and then from central Indiana to southern Ohio (Figure 2).  North and south of this band, rainfall was well below normal for the week.  Rainfall for the month to date reflects a similar pattern, but with more rain across southern Wisconsin into southern Michigan, and over eastern Kentucky (Figure 3).  The northern halves of Minnesota and Wisconsin as well as most of Missouri have been rather dry this month.  The April 11 U.S. Drought Monitor, issued early in this period continues to depict severe to extreme drought over southwestern Missouri, and moderate to severe drought over southern Iowa and northern Illinois (Figure 4).


Turning Up the Heat

A warm front lifted northeastward through the Midwest on April 11, and strong southerly winds behind pulled unseasonably warm air well north into the region.  By April 13 high temperatures reached the mid 80s as far north as central Minnesota, some 25°F to 30°F above normal (Figure 5).  In western Missouri, afternoon temperatures topped out in the low 90s, breaking records in a number of locations by 4°F to 5°F.  This was the first day of four consecutive days with record warm temperatures in the Midwest (Figure 6). Numerous maximum temperature records were set, and many locations also set new high minimum temperature records.   Some of the high temperatures records set or tied during the period can be found in Table 1 .

Four Days of Severe Weather

April 13 - Iowa Hit Hard

The unusually warm and more humid weather helped set the stage for several episodes of severe weather that affected most of the Midwest the last four days of the period.  On April 13 a cold front was pushing through the northern portions of the Midwest providing a focus for thunderstorm development (Figure 7).  Storms first developed during the late afternoon in central Iowa, and moved east through the state and into Illinois through the evening hours.  The storms reached severe levels in eastern Iowa, spawning 11 tornadoes in Iowa and one in western Illinois.  The first tornado touched down near in Johnson County and moved into Muscatine County.  It only had a one quarter mile damage path, but a woman in a mobile home near Nichols, IA was killed when the tornado struck.  The most significant of the 12 tornadoes was a F2 tornado which touched down in Iowa City (Johnson County).  The tornado was on the ground for four and a half miles, tearing through downtown Iowa City and the University of Iowa campus.  The tornado caused extensive damage to the University of  Iowa campus.  Thirty people were injured and treated at local hospitals. Iowa Governor Tom Vilsack declared state of emergency in Johnson County on April 14 in order to allow the local governments to seek state and federal aid.  Initial estimates were that damage in Iowa City would top $12 million, with the figure likely to rise.  There were 212 buildings damaged, and of those, 14 buildings were destroyed and 96 suffered major damage.  

The storms continued to drive southeast into Illinois, where the storms were mostly hail producers with hail as large as golf balls.  Shortly after midnight two separate tornadoes touched down near Lincoln, IL (Logan County) producing some damage to buildings and trees.  The storms pushed into southwestern Indiana during the early morning hours.

Severe thunderstorms also rolled through central and southern Wisconsin where high winds caused downed power lines and damage to trees.  At 9:55 pm CDT law enforcement in Jefferson County, WI reported a 4.25" diameter hail stone about three miles north of Lake Mills.

April 14 - Illinois, Indiana, and Ohio  

The cold front in the northern Midwest on April 13 began pushing through the remainder of the region on April 14 (Figure 8).  During the late afternoon storms erupted over northern and eastern Illinois. The storms in central and northern Illinois produced 0.75 to 1.25 inch hail. A storm that over Iroquois County, IL dropped 2.50 inch hail stones that cracked numerous automobile windshields. This storm intensified as it moved into western Indiana, producing 2.75 inch (baseball size) hail and spinning off several tornadoes as it traveled southeast.  There was damage to buildings and trees from the tornadoes, but no major damage and no injuries. Straight-line winds of 68 mph in Warren County, IN resulted in some building and tree damage and downed power lines.

April 15 - Back to Missouri, Iowa

The next major weather system began spinning up over the Central Plains on April 15 (Figure 9).  A frontal boundary extending east from the low through Missouri, Illinois, and southern Indiana was again the focus of thunderstorms.  The storms developed first in Kansas, then across western Missouri and western Iowa during the evening.  Six tornadoes touched down in western Missouri.  The most significant tornado touched down in southern DeKalb County, MO.  The tornado was the ground for more than 14 miles and caused F1 and F2 damage.

April 16 - Bullseye on Illinois

Easter Sunday dawned warm and humid across the southern half of the Midwest.  A strong low pressure system was located over southern Iowa, and a warm front extended from the low cutting across central Illinois, southern Indiana, and northeastern Kentucky (Figure 10). The atmosphere was primed for thunderstorm development.  By early afternoon tornado and severe thunderstorm watches covered eastern Missouri, all but extreme southern Illinois, and much of central Indiana.  Storms rapidly developed, and the first tornado touched down in Macon County, IL shortly after 2:30 p.m. About the same time, a three-inch hailstone was reported in downtown Normal, IL (McLean County).  Before the afternoon was over, nine tornadoes were confirmed to have touched down (preliminary count) in Illinois, all in the central part of the state.  The most damaging storms occurred roughly along Interstate 70 in Christian, Coles, Effingham, and Jasper Counties counties, where two supercell thunderstorms were responsible for most of the twisters (Figure 11).  The most damage occurred in Effingham and Jasper Counties, where the tornadoes were rated F2. The storms weakened as they moved into Indiana,  although one tornado did touch down in Parke County. Otherwise, severe weather in Indiana and Kentucky was generally limited to 0.75 inch to 1.00 inch hail.  

The thunderstorms in central and northern Illinois also produced heavy rain, and flash flood warnings were issued for a number of counties in Illinois and later in Indiana as the storms moved east.  As much as four inches of rain fell in some locations from the storms, with the heaviest rain in the southern Chicago suburbs.  Lansing, IL, just south of Chicago, reported 5.10 inches of rain. The rain caused flooded basements, sanitary sewer backups, and forced a number of creeks out of their banks. Water was reported to be up to 10 feet deep in some low-lying areas.  In central Illinois, the heavy rain left water standing in fields, delaying spring planting in many areas.

SDH