Nov 22, 2010
A rare and unusual severe weather outbreak caused tornado and straight-line wind damage in Union Grove, Wisconsin and Loves Park, Illinois on Monday. Severe storms had developed across eastern Iowa and crossed into Illinois during the early afternoon. The storms looked very impressive on radar for a couple of hours, however no warnings were issued. Eventually a persisting thunderstorm near Rockford, Illinois caught the attention of meteorologists as rotation became more evident on radar. A tornado warning was issued with a tornado confirmed on the ground. Loves Park and Caledonia, Illinois suffered moderate tornado damage. Storms continued to move to the northeast into Wisconsin spawning additional tornadoes near Union Grove and Lake Geneva, Wisconsin.
The culprit was a strong late season low pressure system that moved into eastern Iowa and southwest Wisconsin through the early afternoon hours. Moisture was streaming north from the Gulf of Mexico, combined with very strong wind shear and modest instability, these ingredients were enough to produce severe weather.
The tornado that traveled through Union Grove, Wisconsin primarily caused EF-1 damage with winds reaching around 90mph according the National Weather Service Milwaukee/Sullivan. I took these photos east of Union Grove that illustrate trees had been snapped like twigs. There were numerous homes along the tornado path that had their roofs damaged from Union Grove northeast to the village of Franksville. Yellow home insulation was also noted along the 11.5 mile tornado track on the farm fields.
Below are radar images showing the development of mini-supercell thunderstorms across Iowa and Illinois. The first storm to produce a tornado is shown approaching Rockford, Illinois. Initially the storm was weakening as it was entering Rockford, but rapidly strengthened as it moved east near Loves Park, Illinois. The storm then produced a tornado in the Loves Park area causing damage up through Caledonia, IL along a 16.4 mile path. The tornado was rated an EF-2.
This same supercell moved through southeastern Wisconsin and produced another EF-1 tornado in southern Walworth County near the village of Walworth and south of Lake Geneva. Interestingly, the tornado dissipated but a new circulation developed to the northeast in southern Racine County. Shown below you can observe on the radar velocity image the red and green colors come close together. This is called a velocity couplet. What this implies to meteorologists is a very strong and tight rotation within the thunderstorm. The brighter the colors indicates the stronger the winds being detected on the radar. In this instance, the tight velocity couplet moved over the city of Union Grove, Wisconsin which in fact had a tornado on the ground.
Below is amateur footage of the tornado in Loves Park, Illinois. The twister was strong enough to bring down high powered transmission lines. The second video is from a Citgo gas station along interstate 94 and highway 20 in northeast of Union Grove, Wisconsin. The tornado traveled over the station causing minor roof damage.
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