The Llano County Supercells
of 10 March 2000

This early spring chase started in northeastern Mason County of Texas. The wide open terrain provided a beautiful backdrop for storm photography. Two supercells developed on this afternoon producing mesocyclones, very large hail and funnel clouds the did at times make contact with the ground, although no damage tracks were found. Generally due to a strong jet stream pattern in March storms move quickly keeping chasers on the run. On this day the storms moved slowly providing numerous chances for photography until they got into the rugged hill country of southern Llano and Gillespie Counties. One of the storms passed over the town of Castell where a killer F-4 tornado struck last year. I chased that storm, but was pinned down by flooding and large hail. On this day I fared better by giving the second supercell more respect and staying out of the rotating updraft area. Helping me on this chase was Bill Tabor out of nearby Austin.

All images and text © copyright Gene Moore unless otherwise indicated.

developing supercell with inflow   early stage of both supercells

Early stages of the first storm showed signs of setting up a strong easterly inflow jet. Note the beginning stages of a tail cloud on the northeast quadrant of this extensive cumulus updraft. No precipitation was falling at our location, but an audible roar was heard coming from the east. This sound combined with streamers from the anvil led us to believe large hail was already in progress.

 

The coverage of my 17 mm wide angle compresses the scene making both storms look small, but they were covering much of the sky at this time. The closest updraft was sporting a tail cloud extending east. No precipitation was seen under the base of the first cell as in a classic LP (low precipitation) structure. The storm further northwest is developing in a more classic manor with rain falling from the north east quadrant of the storm.


rotating supercell with inflow   developing tornado

LP supercell with an inflow tail cloud. Violent rotation was in progress at this time in southeast portion for the updraft. This was our view looking north and the cloud rotation was above and just left of the road. Note the stacked structure on the eastern side of the concentric updraft. The whole storm was turning. As the area just north of the circulation crossed highway #29 golfball hail forced us under the canopy of a large tree.

 

A rotating rain curtain swings around the back of the circulation as the storm turns from LP to a classic supercell. This configuration would show up on a radar as a "hook echo." Two inch diameter hail was beginning to fall at our location and tennis ball hail was verified to our east. This funnel never became planted on the ground, but whisps of condensation were seen nearing the ground.

funnel approaches highway #29   radar image

The funnel narrows and spins tighter in this image forming a very narrow needle under the base that can be seen shooting to ground in a few of our photographs. The bright backlighting burned out this feature in most of the shots. A second very narrow rope vortex can be seen traveling south through the rain curtain. Some of the condensation from this feature can be seen on the ground and to the right of the funnel. This funnel made Storm Data as a tornado, although we did not see debris at the time.

 

Radar image of second supercell moving into Llano County as first cell weakens. Both storms are shown just to the east of Junction, Texas. The large storm complex to the north may be seen in the background of some of the images. Image courtesy of WeatherTAP.

Second supercell   Large red funnel in setting sun

Supercell number two moving through northern Gillespie County toward the Enchanted Rock State Natural Area. \Note the twin inflow flanks from both the west and the south southeast. The area of intense rotation was at the intersection of these flanks.

 

We chose to avoid driving under the rotating base structure and approached the storm from the west-southwest. This method was slower, but it allowed us to avoid the golfball to tennis ball haid that fell from both storms. The large red funnel appeared rather suddenly from out of the rain as the setting sun cast light under the storm. The rotation of this vortex was very strong producing a laminar glaze on the side of the funnel to reflect the evening sunlight.

second view of funnel  

An excellent synoptic study of this day can be found on Lon Curtis' web page. Radar, synoptic maps and satellite are used to look over the situation. Look about half way down the page. His study concentrates on the nearby Bell County supercell seen in the background of some of my shots, but is quite useful in providing data for this case as well.

After looking northeast to witness this dramatic scene the roads became tree shadowed as they twisted through the park area. This blocked the view funnel as it moved southeast and extended very close to the ground. We later learned this became a tornado as it rain wrapped just to our southeast. The only damage it did was to flatten a bunch of trees in the Enchanted Rock area.

 

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