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Chase Day - March 21, 2005
Paris, Texas Tornado Intercept
by Martin Lisius
This was an unusual chase in several ways. First, there was a significant imbalance between the CAPE (Convective Available Potential Energy) and SRH (Storm Relative Helecity) values over my Northeast Texas target area. At mid-afternoon, analysis depicted modest CAPE of 1000 and strong 0-1 km values well above 300, especially over far Northeast Texas.
A north-south dryline had developed over Dallas-Ft. Worth beneath the northeast edge of an approaching 100 kt 250 mb jet, and 40 kt southwesterly 500 mb flow. Both upper-level features displayed a cyclonic curve and negative tilt.
The Storm Prediction Center posted a moderate risk with potential for significant tornadoes over East Texas and parts of Southeast Oklahoma.
The first storm to initiate in the area developed in the early afternoon, near Lake Lavon. That's where I picked it up. Soon after, more storms formed to the south, just east of Dallas.
I tracked the original cell (northern storm) to near Greenville and compared it with the storm about 20 miles to my southwest. The northern storm featured a dark base, but had a short, leaned over look. The storm to the southwest was taller, but slightly softer.
I stayed between the two cells until I reached Commerce. At this point, I noticed the northern storm had grown taller, with a darker and lower base. I decided to make it my intercept and met it just west of Pecan Gap in Delta County. It had become a very respectable supercell with a bowl-shaped base and a reasonably hard cumuli structure above.
I stayed on the southern edge of the storm base as I tracked it northeast to Roxton. By this time, the storm was spinning like a top and small funnels were dancing beneath a wall cloud. The motion was rapid and had a "pre-tornado" look. But, before one could drop, the low-level circulation unraveled. This storm had a pulsing, up and down history already. It improved a little over a long period of time, pulse by pulse. I felt that a tornado might finally develop once the circulation tightened again. That happened as the storm passed just south of Paris.
I was on the southeast edge of the low-level rotation about 6 miles south of Paris when a low "bowl" formed beneath the storm base, followed by a funnel, and then a tornado. The light was high contrast making the slender, snake-like tornado almost black. A translucent tube formed within the vortex and a dust-debris whirl kicked up. A funnel bounced up and down as the tornado tracked to my north and then northeast. Touch down by my watch was 6:04 PM with termination at about 6:12 PM. Looking closely at the HD video I shot, I noticed a possible pause in ground circulation for almost a minute, so it could have been two tornadoes that I saw. I'll just count it as one for now.
As I recall, the Paris surface observation at 6:00 PM showed east winds with a temperature/dewpoint of only 63/57. It was probably the "coolest" tornado I've ever seen. I'm not sure if the tornado was a result a local boundary interaction, or a gradual increase in shear as it tracked northeast across a tight SRH gradient between DFW and Paris.
I saw just a few storm chasers during the chase, but many "citizen chasers" as I approached Delta and Lamar Counties. Neither watch or warning existed at the time they began to appear. There was rapid, almost surreal motion beneath the base then, so I suspect that got them outside.
For most of the time, the storm looked weak and disorganized on radar. It was more impressive with the naked eye, especially at the lower levels.
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