August 18th 2015 Tornado Warned Supercell Romeoville Illinois

Jan 07, 2016

Summary:

Tracked first set of storms noting supercell structures before abandoning for better development further east towards home. Got on Supercell that almost produced tornado near the NWS Chicago office in Romeoville, IL

Stats:

Tornadoes: 0
Hail: o.00
Wind: n/a

The Forecast:

Slow moving upper level system bringing cold front across IL warm sector where up to 2000 CAPE was located. Backed surface flow meant storms stood a chance of rotating, but lack of surface flow and generally weak speed shear meant storm mode would likely be sloppy. Targeted areas further west where destabilization was forecast to first take place.

Detailed Account:

This day held marginal, yet semi local potential so it seemed foolish to pass up. I was able to re arrange my work schedule to be able to chase. I met up with Danny Neal and Ricky Castro from the NWS (who was down to chase) and after monitoring things a bit we decided to head west where the highest instability and initiation were likely to occur. An outflow boundary across eastern IL captured our attention as well but we wanted to play the odds.

Storms began to fire southwest of Galesburg and we quickly moved to intercept. Arriving on the first storm we noted a sloppy looking wall cloud but some intense CG lightning as the storm appeared to be strengthening.
IL Storm

We were hard pressed to find any real organized rotation, but kept with the storm. Other storms were going up nearby and the overall evolution of things appeared to be sloppy. While re-positioning on the storm near Gilson we noted an interesting looking feature that resembled a needle tornado.  There appeared to be more rising motion than rotation and we dismissed the feature but it will still interesting.
scud

Other chasers in the area captured the feature as well, with what looked like could have been some sort of ground activity, but after some debate it was deemed too inconclusive to label it a tornado, especially without any real damage to associate it with.  I theorized the storm interacted with a boundary that was in the area and briefly ingested some jucier air. Still, its important to document everything because you never know sometimes! The storm, however, began disorganizing at this point. To our dismay, a couple mini supercells went up near I-55 in the Pontiac area and put down some photogenic rope tornadoes. We made a dash to catch the storms but they fell apart as we arrived.

Turning north and heading for home, some new storms went up in the far outreaches of the Chicago metro area. Some of these were gaining tornado warnings based on reported wall clouds/funnels and possible touchdowns. We got on one particular beefy looking cell near Channahon and tracked it into nearby Morris, where it began displaying tiered mesocylone structure.
DSC_9190

The storm organized further as we tracked it into the Joliet area, home turf…and not an easy place due to heavy traffic and numerous stop lights. The storm really began to organize and displayed a classic rotation signature on radar, prompting the NWS to issue a tornado warning. Heading north on Weber Road (an area I frequent very often) the supercell displayed classic structure. A big RFD clear slot surged through as I battled traffic to get to an area we all knew had a better view.
20150818181401(1)

I began thinking the storm would seriously produce at this point, and when we got a clearer view we were greeted by a large, rotating wall cloud.
WeberRd

The storm was about to pass directly over the NWS Chicago office, and we pulled over to watch it. The rotation tightened up briefly to almost a nub funnel.
WeberRd2

Soon after though it began to disorganize, and fell apart. We noticed there was a complete lack of surface flow…again. This likely once again spared the area a bigger tornado threat. Unfortunately east of this area, tracking storms is difficult as there are several river/canal valleys to work around in addition to thick metro traffic. We kept behind the storm for a bit before letting it go as moved deeper into the metro area. Now a squall line had formed behind this cell with embedded QLCS circulations. A couple more tornado warnings were issued as they passed just to our north, doing damage.

After grabbing some Wendy’s we arrived back at Danny’s place to end the day.

Conclusion:

For what looked to be a marginal day, it certainly turned out to be more active than we thought. Missing those photogenic tornadoes by I-55 stung, but getting on that tornadic beast of a supercell in our backyards really made the day intense. The area got lucky, that thing was very close to dropping a tornado. Once again an off season local chase keeps the season going…what a busy year.

Map:
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Storm Reports:

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