Fairdale, IL EF-4 Case Study

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The Baron Tornado Debris Signature (TDS) Indicator, above, shows debris lofted by a tornado on the ground, approaching Fairdale, Illinois.

On the evening of Thursday, April 9, 2015, an EF-4 long-track tornado was detected by radar, moving through north-central portions of Illinois. The town of Fairdale, Illinois suffered the brunt of the damage from the storm.

Initial touchdown occurred at 6:39pm just northwest of Franklin Grove, Illinois, then traveled on a very straight line to the northeast, passing just south of Lindenwood, and continuing on a straight path through Fairdale. The tornado lifted off the ground northeast of Fairdale at 7:20pm.

This analysis details the timeline of the Fairdale event, and the performance of Baron weather intelligence.

 

6:27 PM

At this time, Baron Safety Net automated alerts for twisting storms were generated, and would have been received in affected locations 12 minutes before touchdown.

In the video, National Weather Service Tornado Warnings appear as red polygons, while automated Baron Safety Net alerts are shown in blue.

 

6:47 PM 

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At 6:47pm, the super cell thunderstorm was west of the town of Rochelle, Illinois. The storm had a defined hook echo, with a low-level shear marker and Baron Shear SCIT in the region of the hook. These tools identify localized wind shear, allowing meteorologists to instantly see areas of greatest concern. There was 104 mph of shear with the storm at this point, with the SCIT arrow is pointing in the direction of Fairdale and near the point where the storm crossed Interstate 39.

 

7:06 PM

By 7:06 pm, the storm was crossing I-39 just to the west of Fairdale. The tornado appears to have been near its strongest at this point. On the 7:06pm reflectivity scan, the storm still had 104 mph of wind shear, with a Baron Tornado Index (BTI) ranking of 4.7.

fairdale_ref_706The reflectivity image also showed a “donut hole” under the low level shear marker, which we often see in with tornado-producing storms.

 

 

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During the same volume scan, the Baron Shear Rate product showed an area of enhanced shear in the location where the tornado was occurring (circled).

 

 

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Dual-polarimetric radar is of extreme value during events like these. Also at 7:06 pm, there is an area of lowered values in the Baron Resampled Correlation Coefficient (CC) data, which is likely associated with debris lofted by the tornado.

 

 

 

These elevated values also triggered a Tornado Debris Signature (TDS) marker, shown at the very top of this page.

 

7:13 PM

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Also generated from dual-pol data, the Baron TDS Swath shows the path of lofted debris in the area of Fairdale, a major indicator of a tornado on the ground.

 

 

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Hail was a threat with this storm, as well. The Baron Hail Swath data clearly defines the path the storm took through north-central Illinois, based on the likelihood of hail falling during this portion of the storm’s lifecycle.

 

 

 

 

 

Lastly, this video shows the progression on Baron shear markers tracking the storm as it moved across the region. The drawn line indicates the actual path of the tornado on the ground.