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Chase Day: April 24, 2006
Thornberry, Texas Tornado Intercept
By Martin Lisius

Monday April 24, 2006 looked like just another chase day for me when I left Arlington for my Altus, Oklahoma target.  There was a dryline stretching roughly north-south across northwest Texas and western Oklahoma, and 35-45 kt southwesterly winds at 500 mb blowing above.  The tornado potential, in my estimate, was moderate.  I was cautiously optimistic.

When I arrived at Oklaunion, Texas around 3:00 PM CDT, I could see short towering cumulus to my immediate northwest.  Moisture was obviously converging there, so I stopped, watched and waited.  I was sweating in the 95/61 air (next to a pile of red dirt) as the towers slowly improved, growing taller.  Eventually, one tower exploded upward right in front of me.  I drove north to Davidson, Oklahoma and then east on US 70 to stay in front of the storm which was now severe.  It was easy to stay along the eastern edge of the updraft for the next several hours since the storm was following the highway.  Several cell splits occurred during this time.  Nothing was too impressive about the storm except that it did have a nice, dark rain-free base and was isolated from any other significant convection.  I figured that it would improve once it reached I-44 where stations were reporting upper 60 dewpoints and low-level winds were better.

Just before reaching I-44, the storm suddenly moved right, or east-southeast, just after another split with the former moving northeast.

The storm quickly intensified and I moved south, across the Red River, to stay ahead of it.  I managed to reach the eastern edge of the storm base again at Adams Road, just north-northwest of Thornberry, Texas.  The sun had set and I figured I would stay with it until dark, just in case. 

"Just in case" began to materialize moments later when I noticed a lowering to my west-northwest with rapid "tornadic" rotation.  I looked down and noticed a whirl of dust kicking up at 8:21 PM.  At that time, I called 911 and reported the tornado.  The dust appeared to be just over the Red River about 4 miles northwest of Thornberry.  The lowering/whirl lasted for several minutes followed by a funnel/whirl and then condensation joining the whirl forming a slender cone to the ground.  About this time, I could hear the EBS tone on NOAA Weather Radio and the issuance of a tornado warning.  As the tornado drifted east-northeast, it grew larger and eventually became a thick stovepipe as it moved into a moderately dense rain shaft to my north-northwest.  The rain and the growing darkness made the tornado a ghost-like feature.  At about 8:41 PM, the tornado either dissipated or became invisible.  From my angle, it appeared that the tornado had crossed the Red River into Clay County, Texas by this time.  It was just close enough to my position for me to hear the usual waterfall-like steady roar of air.

I drove south, away from the storm, and photographed forked lightning emanating from the top of the updraft, just below the anvil.

For most of its life, this storm was an ordinary supercell.  It did not become extraordinary until it moved right and into a 5000 SB CAPE bulls eye (per the 6:00 PM SPC mesoanalysis).  For this reason, the tornado that eventually developed over rural terrain was a nice surprise.

See this footage at www.stormstock.com