May 25, 1999      W.Texas Caprock Supercells

As with most chases in late May in W Texas, supercells are nearly a sure bet ,and
there is always the real threat for tornadoes. The Storm Prediction Center focused
the severe storm outlook on W Texas, and more specifically the Panhandle and
S.Plains/Caprock area. A moderate risk was outlooked and the tornado potential
was listed as fairly high(climatology suggests this too). I planned to chase today
with Kathryn Ray and Pat Mc Mahon. A surface low was expected to develop by
afternoon northwest of Lubbock TX. Intense warm advection and a very sharp
warm frontal boundary were expected to contribute to the severe storm threat by
late afternoon. What made the tornado threat so high was that the low and mid
level jets crossed over the Texas Panhandle/South Plains in an area of strong
convergence at the surface and diffluence/divergence aloft. This would tend to
cause the supercells to sustain for long periods of time, but would also favor the
splitting of supercells, particularly nw of Lubbock and sw of Amarillo. With this in
mind, I prepared the night before to chase, and studied the forecast models very
closely to see where the primary target zone would set up.

My original target zone was in and around the Lubbock area. The moisture was
deeper there, and it appeared on the forecast models that the warm front/dry line
intersection was going to be in that vicinity by late afternoon. The cap today was
strong enough to restrain storm development at least until mid afternoon. Forecast
models were indicating very unstable air was going to be in place over W Texas
so initial development would be explosive (CAPEs were in excess of 4000 j-kg).
My optimism was quite high today, now it was time to see if potential would be
actual. We left Tulsa around 9am and prepared for the 6 hour drive to Lubbock.
Most people do not realize that storm chasing is almost 90% driving to get into
place at times, and !0% of actual chasing. Long days, poor eating habits, and
limited sleep are just a few things that make chasing hard on the body. Today
was going to be a long haul chase so we split up driving into shifts. For much of
the drive to Lubbock, I called up weather data trying to verify my target zone. The
further we went, the more I was leaning to initial development up on the Caprock.
the Caprock is the elevated plains of W Texas that is more or less aligned with
I-27. Our drive was looking like it was going to be a little further than originally
planned on. The severe storm threat was starting to become more focused in the
area between Clovis NM and Lubbock. Already, there were clusters of convective
towers organizing all over W Texas and extreme E New Mexico. My opinions of
this were mixed as this was happening well before peak heating!!

By the time we reached Haskell TX, the day's first storms were just starting to pop.
One cluster of storms initially formed along the dry line near Clovis. Another area,
much closer to us, was developing near Crosbyton TX along the warm front in an
area of extreme instability(already!). We decided to head west on U.S. 380 to get
in position to intercept the developing storm near Crosbyton. We passed through
areas that would see tornadoes later in the day in route to Crosby Co.. The whole
chase plan was now changing not by design! We reached the town of Spur and
headed northwest to get ahead of the storm that was developing near White River
Lake in Crosby Co. I was not too sure we were going to be able to reach the storm
before the circulation produced a tornado. The supercell was developing very
quickly but also remained fairly small on radar. The circulation was increasing quickly as it slowly moved to the east-southeast. A severe t-storm warning was
eventually issued by the NWS Lubbock for the storm. Large hail up to golfball
sized was expected to pound parts of S/E Crosby Co.. We could see the small
but well structured supercell to our northwest about 25 miles. Radar indicated the
rotation was becoming very compact and intense, so a tornado warning was soon
to be posted!!

The severe t-storm warning was upgraded to a tornado warning for Crosby Co.
as we headed northwest on FM 783. A developing tornado was located just to the
west of White River Lake. We still had a pretty good distance to close on the storm
before we would be able to see any cloud base features. We continued on and
eventually started to see the wall cloud about 12 miles to our northwest. Rapid
cloud transformations were happening around the wall cloud, so rotation had to
be very intense. We watched the wall cloud as we tracked nothwest across far
W.Dickens Co.. Brian Stertz called me from Tulsa telling me to keep an eye on
radar as there was a intensifying supercell to the northwest of Plainview too at
this time. He indicated that the storm looked as though it may split soon so he
told us to watch out for that right mover. We kept an eye on the storm that we were
closing in on, as well as watched radar for the storm Brian called us about. Our
storm was much smaller than that storm on radar, and it appeared as though the
storm closest to us was shrinking. We had to make the critical decision to either
stay with the Crosby Co. storm or blast northwest to Plainview and intercept the
right mover. Eventually, storm structure indicated that the Crosby Co. storm was
on the wane. We picked up the pace and headed for Plainview. Brian called us
back and told us the storm did split and there were now 2 very strong rotations
on radar. The left moving circulation was moving n-ne near Dimmitt (Castro Co.).
The larger circulation with the right moving cell was near the town of Hart, also
in Castro Co.. The storm was heading for Edmonson and eventually Plainview!
Tornado warnings were promptly issued for both circulations. We were still way
out of position and now had a very long haul to catch these!!

Radar indicated very strong circulations as the storms went their separate ways.
Oddly enough, the left moving supercell produced the first tornado near the town
of Easter TX in Castro Co.. The right moving supercell grew even larger when it
crossed into Hale Co.; hail up to softball sized was indicated with the storm. As
with most right movers, the circulations often end up on the south-southeast side
of the supercell. We were near the town of Petersburg, and the storm had turned even more right and was going to pass just west of Plainview. A very large hook
echo was on radar and circulation was almost a sure bet that a tornado was soon
imminent. The circulation just missed the town of Halfway which is about 10-12
miles west of Plainview, but the large hailcore did not. Radio reports of extreme
hail damage was reported in Halfway. Some of the hailstones were reported to
be as large as grapefruits. We were trying to plot an intercept point for the storm,
but the erratic nature of the supercell's track made this very difficult. The threat
from the huge hailcore did not make this any easier!! We wanted to get ahead of the storm but remain far enough from the hail. We decided to head over to I-27
and head north. Radar was showing that the circulation was becoming wrapped
in heavy rain/hail as it narrowly missed Plainview. Very strong outflow winds of
up to 70 mph were blasting the west sections of Plainview. The usual rule still
applies....the larger the hailcore, the more intense the outflow. This storm was no
exception!!

We pulled over about 2-3 miles south of where radar indicated strong rotation.
The circulation was apparent in the cloud motions, but the lower levels were more
or less obscured by the heavy rain/hail. A pronounced gust front was surging to
our location from the Plainview area, but radar indicated very strong rotation was
continuing just to our north. The supercell then tracked to the southeast more, and
was now heading for the Lockney/Floydada area. Tornado warnings were very
quickly issued for N/W Floyd Co.. One thing for certain, this supercell was hard to
chase-very erratic circulation patterns and frequent track deviations!! The main
circulation was now deeply embedded in the intense core and radar indicated an
"eye" like appearance where the possible tornado was detected. We attempted to
chase this storm but without any success. It was too much of an HP supercell to
see any discernable features.

The Floyd Co. supercell gusted out completely as it passed between Floydada
and Dougherty. An earlier outflow surge near Plainview had completely stabilized
much of the area around Plainview, in fact, the outflow blasted out all the way to
the New Mexico border. Other supercells exploded with great intensity along and
just north of these outflow boundaries. The number of these supercells was so overwhelming that it was difficult to single out a strongest storm. All had rotation
and all had small/moderate hooks on radar. We decided to follow an intensifying
supercell in Crosby Co.(once again!). Radar indicated strong circulation and it
was taking on the classic look on radar. We headed back south on FM 28 from
the Dougherty area. We could see the storm to our south-southeast and it looked
small as the earlier storm in Crosby Co.. Other supercells popped up all over the
area east of Lubbock. One such supercell grabbed our attention long enough
that we missed the tornado that was reported near White River Lake. We followed
much the same route we took earlier in order to catch up to the supercell. By the
time we reached the supercell, the circulation had weakened some. Rotation was
still quite visible but the tornado had lifted. Several small funnels/appendages
lowered under the wall cloud, but no tornadoes were seen as it moved across
the barren country in SE Crosby Co.. We turned our attention to another supercell
that was closer to us and right on the edge of the Caprock.

We kept with the rotating supercell and wall cloud as it crssed into W. Dickens Co.
to the west of Spur. Sunset was approaching quickly by now so our best hope
was for lightning pictures and some beautiful cb shots as the setting sun brightly
illuminated the higher portions of the cloud, while the dark base provided an
awesome contrast. While we were watching the Dickens Co. supercell, a new lp
supercell (very small) formed to our immediate south. This storm formed along
the outflow from the Dickens Co. supercell. This storm was highly striated and
had a very striking appearance from our location. The core was quite small but
definitely intensifying. Numerous other supercells continued on to our southeast
near Aspermont and Abilene TX. We finished off our chase and watched the lp
storm drift slowly off to the southeast into Kent Co.. A nice peaceful ending of the
chase!!