CELL MERGER & SAN ANGELO SUPER MESO


 On the evening of Friday, June 12, 1998, I was watching a few storms in North Texas when I observed a very interesting event. Two thunderstorm cells actually merged just NE of Abilene. I was absolutely amazed watching the storm mutate into one HUGE cell that went severe producing golf ball size hail and some damaging winds.  When conditions are favorable, cell mergers result in intense supercells producing tornadoes and violent weather. This evening, the conditions were not favorable and the storm quickly died out as it moved into a more stable airmass. Still, a very impressive event.
(image courtesy of American Weather Concepts)
 

 
On May, 26, 1998, one of the most amazing mesos and hook echos I have ever seen occurred. I just wish that I was able to chase it!  For over three hours, this thing remained virtually stationary over Tom Green county and near or over San Angelo. It produced quite abit of severe damage. It was reported that hail up to baseball sized hail pummeled the same areas for a couple of hours including parts of San Angelo. Wind damage was extensive along with a couple of brief tornados, lots of funnel clouds and rotating wall clouds. Tom Green county was under a constant tornado warning for over 3 hours! For much of that 3 hours, the rotating wall clouds were primarily over or within only a few miles of San Angelo itself.

What is even more amazing is that conditions were not favorable for tornadoes this day. The wind profiles were very weak and general storm motion was only 10-15 mph.  However, the airmass was extremely unstable with CAPE near 6000 with excellent convergence along an outflow boundary from storms the previous day (very similar to the Jarrell event). There was also a good little shortwave that popped out of Mexico across the border enhancing the storm along with excellent daytime heating and a cap strong enough to bottle up all of the energy until about 5:00pm.  Then, this storm just exploded.  In fact, the rotation went well into the atmosphere as this storm produced a vorticity lobe in the mid levels that transversed NE producing other severe storms in N. Texas that night. This Vorticity lobe remained in the Ark-la-tex region for several days producing storms each day, although not nearly as violent. The rotation of this vorticity lobe was very evident on satellite and radar loops. These types of vorticity lobes are more technically referred to as "convectively induced vorticity lobes".

This entire storm could easily be seen rotating on the radar loops (which I was unable to save a copy of) with other cells around it moving NE while this one remained stationary, spinning like a top in place. These two images from different radar sites are 30 minutes apart and the  storm hasn't budged. Absolutely incredible!!  What is really going on here is that the new updrafts kept forming in the same place while the old downdrafts and precip was being blown away to the NE from the upper level winds...just like a chimney. This storm achieved a perfect balance of inflow and RFD/outflow. (notice the long, well defined outflow boundary in the first radar frame)
 
 
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(courtesy of Intellicast)                                         (courtesy of KTAB-TV in Abilene)