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The following is an account of a recent stormchasing expedition by Darien native Bill Ozanne. Mr. Ozanne graduated from Darien High School in 1997 and attended the University of Vermont for one year before realizing that he wanted to pursue a career related to his lifelong interest in weather. He subsequently transferred to the University of Utah, graduating in 2002 with a bachelor's degree in meteorology.
BY BILL OZANNE
Henrietta, TX; April 30th: Tornado warnings screamed simultaneously
over the weather band and local radio stations. A dozen other storm chasers had arrived in this north Texas town when
our SUV skidded to a stop in an abandoned lot. After following our storm for over 70 miles we were finally in position,
directly under a supercell thunderstorm.
In February my father handed me an interesting magazine article he read
last fall. I looked at the title and
said, “Let’s do it.” That was exactly
what he was thinking and the trip was unofficially set. The article was about the increasingly trendy
hobby of storm chasing.
After two months of research and mock chasing from home the dates were
firm. We would arrive in Dallas on April
29th for three full days of chasing. This was a small window of time and we needed some luck to be
successful. The fact that I graduated
from the University of Utah with a degree in meteorology was certainly going to help.
On April 30th daylight revealed low clouds with warm, humid
conditions. A quick check on the
internet revealed that all of the ingredients had to come together for a severe
weather day. We headed west to our
target position 50 miles ahead of the dry line in Graham. This left us in a central position, allowing
a quick intercept of any storms that may form in north Texas.
Similar to a cold front, which represents a division between warm and
cold air, the dry line denotes a discontinuity between dry and humid air. During spring the dry line is often found in
the plains with moist air from the Gulf of Mexico to the east and dry air from
the Rocky Mountains to the west. The
daily advance of this boundary can serve as a focusing mechanism for the
formation of supercell thunderstorms. A
particular type of storm that is long-lived and produces more tornados than any
other.
By noon the low clouds burned off,
temperatures were climbing and the dry line was advancing towards our
position. Everything was happening very
rapidly now. Checking radar on a local
library’s computer we saw a storm forming to the southwest. My dad jumped in the driver’s seat while I
rode shotgun to navigate and spot. We
plotted a course out of town to intercept and the chase began.
Halfway to the new target I called
it off noticing something strange was happening outside. Puffy low clouds were growing into large
turrets all around, but higher in the atmosphere strong winds toppled them
before reaching maturity. We pulled off
the highway for a better look. I watched
another tower go up to the north. This
one was different. It stayed together,
growing higher than all the others while expanding its horizontal area.
This was a supercell storm. Its cloud tops reached 50,000 feet. Upper-level winds weren’t destroying this
storm; they were aiding development and setting the entire system into
rotation. We moved ahead of the storm
and stopped to watch it race overhead. The base was lowering and growing darker as cloud tops grew thicker
blocking out more sunlight.
Driving into Henrietta we passed a
television news truck and a van full of guided storm chasers. Winds were racing into the center of the
storm as it sucked in its last gasp of energy. Shades of green mixed in with the blackened sky as a wall cloud lowered
from the storm’s base. The air became
still. Signs of a tornado were
everywhere. Our vehicle became entrained
in heavy rain and small hail.
The tornado never formed. A strong cold front caught our dry line
storm. The supercell merged with a
squall line of gusty winds and large hail. We were close. The cold front,
dry line intersection is one of the sweetest spots for tornados. Earlier, a tornado was spotted a few miles to
the north associated with another supercell. Officially, Henrietta reported dime sized hail. Had the cold front arrived later a tornado
would have been a real possibility.
We followed the leading edge of the
squall line another 20 miles east dodging rain and hail before heading back to
Dallas. Vivid lightning continued well
into the night. Our plan called for
another two days of chasing but we flew home the next morning as forecasts were
for only heavy rain. After a complete
success on my first chase I am looking forward to another chase later this
spring when severe weather returns to the plains.
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