August 4th 2008 Tornado and High Wind Event

On the evening of Monday August 4 2008 a total of 5 tornadoes were confirmed by the National Weather Service. Below is a list of the tornadoes, where they hit, and how strong they were on the Enhanced Fujita (EF) scale.

* Griffith, IN, rated EF2
* Bloomingdale, IL, rated EF1
* Bolingbrook, IL, rated EF1
* Orland Park, IL, rated EF0
* Boswell, IN, rated EF0

The stage was set for a severe weather outbreak Monday. With a strong southerly flow out of the south, the mercury climbed into the 90s ranging from 90-95 degrees across Northern Illinois and Northwest Indiana. Combine that with dewpoints in the upper 60s/lower 70s and heat indices were ranging from 100-105. In fact some areas just to the south and west of Chicago were prompted heat advisories till 8pm CDT Monday evening. In addition, the atmosphere was very unstable as was confirmed by several severe weather indexes. With so much potential energy in the atmosphere, all needed was a lifting mechanism.

Around 6pm CDT that evening, thunderstorms started to form in far Northwest Illinois. This cluster of thunderstorms that effected us on Monday is described by many as a Multiple Convective System or MCS. This basically is a continuous line of long lived thunderstorms that can span many miles for several hours. This is characterized by upper level winds that orient themselves in a northwest flow pattern and allow waves of energy (disturbances) to travel the region. Once the storms reached Winnebago and Ogle counties, the line of storms started forming a bow shape (Bow Echo) to it. This signifies that there are strong winds developing from the storms. In addition with these storms was the presence of a low level circulation. These circulations are generally near the leading edge of a line of storms but north of the bow apex. They help to produce brief spin ups or non major tornadoes (anywhere from an EF0 to an EF2). The first image above is a radar image at 745 PM of the Mesoscale Convective System which was in its mature bow echo stage as it moved through Cook, Dupage, and Will counties. The second one is a radar Image at 758 PM displaying the very strong winds associated with the Bow Echo. Cool colors (green) represent inbound winds toward the radar and hot colors (red) represent winds away from the radar. Note the dark blue and purple colors in Kane county. Radar indicated possible winds near 90 MPH across this location at this time.

Now also to mention was the frequency of lightning as we reported over tens of thousand lightning strikes that evening. I have a video showing the spectacular display.