Val Verde County TX Supercells
of 29 April 2006

All images and text
© copyright Gene Moore

Val Verde is a large county is west of San Antonio, Texas with steep rugged terrain, few road and few towns. During years when the jet stream dips south across Baja and the Gulf of California and winds flow easterly up the Rio Grande toward Del Rio, this county is prone to supercell thunderstorms. On this day two supercells with tornado warnings formed early in the afternoon then the atmosphere reloaded and two more supercells formed late in the day. All four supercells had Doppler radar rotation signatures for mesocyclones and possible tornadoes, but in the sparsely populated county there is little change for the National Weather Service to verify these warning, unless a tornado is seen near a town or highway. For me, the first set of storms were not so photogenic and I saw none of the reported tornadoes . The second set of supercells that developed late in the day put on quite a show and lasted well into the night with severe and tornado warnings.

At first glance this may look like a forming shelf cloud, but it's an inflow band that sweeps southeast into a wall cloud. There were two inflow bands on this storm when I first saw it to the west. Both converged into a low wall cloud structure.

Where the two inflow bands meet is a low wall cloud. Behind the wall cloud in a clear (RFD) slot is what appeared to be a tornado. Lumps were moving up the angled front slope when this shot was taken. I was only able to see it briefly before it was engulfed in heavy rain and low scud clouds. They are seen in the band on the left side of the image.

Wide angle shot of the south supercell that is moving along the outflow boundary (OFB) from the previous storms. Note the inflow cloud on the left side of the image. It is hidden behind the low cumulus and scud clouds in the foreground, but it's a horn of plenty shaped cloud flowing warm moist air into the storm from the southeast.

A vertical shot of the approaching supercell with tall cumulus towers shooting up to the anvil level.

At this time the vertical motion into the rotating base of the supercell was outrageous, The cloud material was condensing on or near the ground and lifting a couple thousand feet into the circular cloud base. Violent motions could be seen throughout the structure at this time.

Another shot of the rotating cloud as it came very close to my position. This was one of the last shots I took before letting the storm pass just to my north. What causes the cloud material to form so close to the ground in an intense supercell like this. First, the vertical pressure gradients in the mesocyclone aloft increase the vertical winds in the updraft. Air at the surface is rapidly, sometime violently lifted into the cloud to replace the ascending air. This creates low pressure at the surface, hence the name "meso" cyclone, although many are not this dramatic. Also, when air with moisture is lifted is condenses and forms a cloud. Some the air being lifted in this case is (1) coming out of the down draft rain area to the northeast and is cool and moist (2) there is large hail with this storm so the air being lifted is colder not only from falling hail but most likely hail lying on the ground.

As the rotating wall cloud approached a column of condensation spun up on the front side of the feature. It rapidly moved from left to right across the wall cloud. It is a rotating vertical column with laminar walls that extends from the ground to the cloud base....quite possibly a brief tornado buried within the circulation. The dark notch in the image is a scud cloud in the foreground blocking part of the feature.

After the storm passed highway 277 I remained in pursuit traveling northeast through Carta Valley toward Rock Springs on highway 377. This is a wide angle shot after sunset. I followed the storm until it crossed I-10. At that time the lead storm of the two had a tornado warning, but both cells were very close.

The supercell roars off in the waning evening light. It will prompt tornado warnings as both cells near I-10 about an hour later.