NWS Lincoln, IL -- SWOP event summary

October 26, 2010

A line of strong thunderstorms swept across central and southeast Illinois during the early morning hours of October 26th, producing wind gusts of 40 to 60 mph.  Scattered wind damage was reported around the area, including numerous downed trees and power lines and minor structural damage.  In addition, semi-trucks were blown over on I-55, I-72, and I-39.

A powerful low pressure system tracking from the Plains into the Upper Midwest was responsible for the thunderstorms.  As this low moved northeastward, it pulled a strong cold front eastward toward Illinois.  A squall line developed along the approaching front across Missouri during the evening of October 25th, then crossed the Mississippi River into west-central Illinois after midnight.  An upper-air weather balloon realeased by National Weather Service Lincoln at midnight showed a weakly unstable environment with plenty of wind energy aloft.  Ground-level winds were measured at 25 mph, but quickly increased to over 70 mph at 3000 ft aloft.  As the thunderstorms moved into this volatile environment, many of them began bringing those stronger winds down to the surface.  A relatively stable layer from the surface up to about 2000 ft prevented widespread wind damage: however, some of the stronger thunderstorm cells were able to bring damaging winds down to the ground.  As a result, scattered areas of wind damage were reported across central and southeast Illinois well after midnight. The storms rapidly pushed eastward into Indiana by around 9 AM on October 26th.

Once the cold front cleared the area, very strong westerly winds developed in response to deepening low pressure over northeast Minnesota.  As of 1 PM October 26th, the minimum central pressure of the low had dropped to 957mb, making it one of the strongest low pressure systems ever observed in the continental U.S., outside of a hurricane.  Wind speeds across central Illinois during he afternoon of the 26th reached 30 to 40 mph, with gusts over 50 mph at times.

Here is a listing of some of the storm reports received from the SWOP network: