May 13, 2005
Storm Chase
Northwest Texas
Editor: Putnam E. Reiter
Forecast/Setup -
Risk Area: Moderate Risk
Initial Target Area: Altus, Oklahoma
This one was a sneaker to most people.
There are many reasons, the models, previous convection, and in general how
slow 2005 has been. May 12th was an exciting day in the Texas panhandle, as
about ten tornadoes occurred. Today seemed very similar in setup and
somewhat more favorable due to the boundaries floating around the region.
The region had not seen a strong cold front in over a week and this meant
that deep layer high quality moisture was available. In southern Oklahoma
dewpoints were in the upper 60s and 850mb dewpoints were near 16C.
As noted the day before lots of convection
develop in the Texas panhandle. This convection moved east across Oklahoma
during the night. It provided much needed rainfall for the state. At
sunrise the most active area of convection was in eastern Oklahoma. While
debris clouds covered much of the state, these clouds started to clear by
mid-morning, allowing for strong surface heating. Outflow boundaries from
overnight convection remained across the region with the most notable
boundary near the Red River. The dryline was located in the western part of
the panhandles in the early morning with a cold front in SW KS and northern
Texas panhandle. During the day the dryline was progged to mix eastward to
the edge of the Cap Rock. The outflow boundary was forecasted to move north
into southwest Oklahoma, this boundary actually made it to northern
Oklahoma. Wind fields were progged to remain favorable with 40kt 500mb flow
overlaid on 10-15kt 700mb/850mb flow. Directional shear was decent given
southeasterly surface flow veering to the west at 700mb.
The big unknown was how fast clouds would
clear. Models progged strong instability under full sun. In this case, the
clouds did clear with surface temperatures reaching the low 80s. This
resulted in CAPE values around 3500 J/Kg and LIs to -12. A shortwave trof
moving eastward into the Texas panhandle at early afternoon was expected to
be the trigger for convective development along the various surface
boundaries. The cap was modest, but somewhat weak for mid-May.
By early afternoon SPC issued a tornado
watch for much for southwest Oklahoma into northwest Texas. The first storm
developed north of Paducah, Texas. A while later other storms developed
northward along the dryline on the TX/OK border. Additionally, storms
developed along the convective outflow boundary in northern Oklahoma.
Supercells did develop along the dryline, however only a few storms remained
discrete. The first storm was the one near Paducah and the second one near
Mangum. A few others might have also been initially discrete, but many
converged into larger activity later in the day.
By 8:00pm many of the storms had clustered
and two separate MCS's began. The first one was near Munday, Texas, as
noted by these RADAR images (8:00pm
and
10:17pm).
The second one was located in central Oklahoma. Three brief tornadoes were
reported this afternoon. While not quite what we expected on the tornado
scale, SPC and NWS forecasting were great.
SPC Products: SWO
Day 1
Graphics:
Risk Area
-
Tornado Prob -
Damaging Wind Prob
-
Hail Prob -
Storm Plot
- LSRs
Surface Maps:
Temperature -
Dewpoint
- Wind Speed
- CAPE
- LI
Text Products:
Watches -
Mesoscale Discussions
- Warning Decision Updates
Soundings:
Wichita Falls
Mesoeta 00z Initialization:
Surface Pressure
-
850mb Temperatures
- 850mb
Dewpoints -
850mb Windspeed
- 850mb
Vertical Velocity -
850mb Relative
Humidity -
700mb Wind
- 700mb
Temperatures -
700mb Relative
Humidity -
700mb Vertical
Velocity -
500mb Vertical
Velocity -
500mb Temperature
- 500mb
Vorticity -
500mb Wind
- 500mb
Relative Humidity -
250mb Wind
- 250mb
Relative Humidity
The Chase -
Team 1 - David Underwood, Rob Ferguson, and
Putnam Reiter
Miles Driven - 450
Departure Time - 13:45 CDT
Return Time - 01:00 CDT - 05/14/2005
We left Oklahoma City and headed south on
i-44. We gathered data on the way down, but there wasn't really anything
different than what we had seen earlier. We stopped briefly north of
Chickasha and then continued heading south. We got to Lawton and turned
west towards Altus on Highway 62. We arrived in Altus close to 16:00 and
got fuel. As we headed west out of Altus we got word of a storm in
northwest Texas. Here is where we had to make our first big decision for
this chase. Should we stay in Oklahoma, near Hollis, as it was our initial
target or go to an already good storm. After consulting with several
people, we elected to go after the Paducah storm. West of Altus we took
Highway 34 south. The objective here was to give us a chance to turn around
if another storm went up in Oklahoma.
We got to Highway 6 near El Dorado and
continued south to Quanah. During this part of the trip we got information
on the Paducah storm and could see development to the north. We got some
storm scale features as we drove into Quanah. We drove on through Quanah
heading for Crowell. By this time we got word the storm had started a
southeast movement. Half way between Quanah and Crowell we got a view of
the updraft region of the storm. The time was around 17:15. We saw a wall
cloud, and decided to stop and watch it. We sat there for a little bit and
knowing that the storm was heading southeast we continued on south to
Crowell. We turned west on Highway 70 and drove a few miles outside of
Crowell. Getting a real good view of the updraft area, we pulled over and
watched for a little bit. We watched as the storm went through rear-flank
downdraft (RFD) cycles. As the cycle would begin we'd see the wall cloud
tighten up and then a few minutes later break apart.
The storm was getting close to us and
hearing that 70 vil were located north of us, we decided to get south. We
took a dirt road south a few miles and then jumped back over to Highway 6
south. We turned west of FM 263 for a few miles and watched some more. As
the storm got close to us we turned around and headed back to Highway 6
south. As we turned south we noted precipitation falling just southwest of
the updraft area. This precip core intensified and we noticed a new updraft
area and at one point had two supercells. We drove south on Highway 6 and
pulled over to watch the storm some more. At this point we were a few miles
north of Benjamin. Watching to our north we noticed that the original
supercell was producing a well defined wall cloud and we even got a brief
funnel out of it. Shortly after that the wall cloud broke up during an RFD
cycle. Almost as interesting as the storm were all the chasers.
Reaching Benjamin we turned east on Highway
114. We got about a mile east when we heard a report of a tornado. Looking
around we saw the same suspect areas and I thought the report was coming
from north of Benjamin in a prior area we had been watching. However, the
party reporting the tornado noted it 5 west of Benjamin. Turning around and
heading back west we saw dirt being lifted into the storm on the updraft.
We did not see what we would call a tornado. The storm had 40kt inflow, so
not a surprise to see lots of dirt and maybe some rotation in the dirt.
None of this would lead us to believe that a tornado occurred in the
reported area.
We drove south on Highway 6 to Knox City,
continuing to watch the storm as we went. It was about 19:00 at this point
and the storm continued frequent RFD cycles, each of them disrupting the
updraft region. As we got into Knox City we decided to drive west a few
miles on Highway 143 to near the updraft area. We got just west of the
business end of the storm (updraft area) and stopped for a little bit. The
rotation area firmed up just to our east and then we got caught in the RFD.
The ambient air temperature for the storm's inflow was about 84F (28.8C).
The temperature we measured on the RFD was 68F (20.0C). Research many years
ago (from VORTEx) showed that RFD temperatures more than 3-4C difference
from the inflow temperature may disrupt the updraft region and limit
tornado-genesis. This would certainly explain what we saw during the RFD
cycles.
By 19:30 we really thought there was little
chance of a tornado with the storm. We sat southwest of Knox City for a
little bit watching things. We decided to end the chase and start our way
home. About this time we heard a report of a tornado east of our location.
We didn't see much that would confirm this report, although it is certainly
possible for a brief touchdown to have occurred. We headed back to Knox
City and then up to Benjamin. We turned right on Highway 114 and took it to
Seymour where we turned on to Highway 82 to Wichita Falls and then jumped on
I-44 back to Oklahoma City.
Thanks for the coordination Andy, Jay, and
Ray.
Lessons Learned -
- Not much to comment about here, we had a
really good chase. A little yelling at each other, but that is normal. We
handled storm evolution nicely, which is comforting given that this storm
was a southeast mover. I remember all too well when we got nailed by tennis
ball hail two years ago in the same area.
- Chaser convergence was at an all time
high, most likely due to the slow storm season for Texas and Oklahoma. We
heard questionable tornado reports near Benjamin. Our opinion, being just
east of the reported location, was the chaser saw inflow under the updraft
area. Given that the storm had 40-50kt inflow, dust bowls near the updraft
area were common. We saw a few bad behaviors, like people stopping in the
road and other things. I guess there is little that can be done. The
majority of us followed chaser ethics.
Multimedia -
- Wall Cloud south of Crowell -
1,
2,
3,
4
(The last two the RFD breaks up the wall cloud)
- Picture of the storm, south of Crowell -
1
-
Webcam
- Fredrick
RADAR Loop
Encounters -
Engaged Storm: Crowell, Texas
Tornado: No
Funnel: Yes
Hail (larger than 0.75 inches): Yes - Nickel - Vera, Texas
Wall Cloud: Yes - several
Wind (above 57.4 mph): Most likely, due to inflow but not accurately
rmeasured.
