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Twister Chasers - Notes from the Field


 

It’s muggy outside, even for late April in North Texas. Juicy air from the Gulf of Mexico pumps across the state with an incessant southerly breeze.


All afternoon, my teenage son and I have been working the land on our small Fannin County farm. He’s been riding the tractor for the past hour, plowing through the black dirt to prepare a one-acre plot for his cotton patch.


I’ve been keeping one eye on him and another on the sky. Gradually, the clear blue skies yield to puffy white clouds that pile higher, then grow darker. I glance back at Ryan and see he’s finishing his work.


Looking northward, I see an ominous cloud just beyond our property. My eyes widen as it drops an appendage. Though partly obscured by a line of timber, the telltale haze of dirt around its mid-core means only one thing.


TORNADO.


Twister Chasers - A Hackberry Farm Photo School Blog
Fannin County, Texas tornado churning up dirt.


Twister Chasers - A Hackberry Farm Photo School Blog
Tornado emerging from a supercell thunderstorm.



We jump into the pickup and head toward the storm. Yes, toward the storm.


For three years, I’ve crisscrossed the Texas and Oklahoma plains in search of tornadoes, spending time with the pros to learn the ropes of storm chasing. These people work diligently to keep us safe when Mother Nature’s at her worst.


Tornadoes move in a mostly predictable and linear fashion. I can tell that this one is far enough from us to safely pursue, so we drive northward to a hilltop for a better view.


From this vantage point, we watch the supercell thunderstorm march eastward across a wedge of Fannin County ground that sits between the Red River and Bois d’Arc Creek. In the storm’s southeastern quadrant, a giant, whirling twister forms deep in the cloud’s bowels and stretches earthward, where it churns up dirt, immense oak trees and, sadly, a few homes. Where the tip meets the earth, winds grind around a hyper-local low-pressure system at more than 150 miles per hour and speed inward toward the funnel’s core. The destruction is swift.


Within 15 minutes of the tornado’s formation, it ropes out and disappears. Before the mother storm dissipates completely, she lays down two more short-lived tornadoes. Then, like a meteorological phantom, she’s gone. 



Twister Chasers - A Hackberry Farm Photo School Blog
A new funnel cloud cycling from a rotating thunderstorm.


STORM ANATOMY 101 


Thunderstorms — despite their dreaded progeny — are essential rain generators for the state. Texans receive much of their annual rainfall from storms that, under ideal conditions, form and dissipate in just a few hours. With topography that’s wedged between the mountains to the west and the Gulf of Mexico to the south, much of Texas serves as the field of play for a pushing-and-shoving match between air masses that develop over the state each spring and, to a lesser degree, in the fall.


In the spring, as the weather warms and the conditions ripen, air masses compete in a huge clash of forces. Warm, moist air flows inland from the Gulf of Mexico, while hot, dry air spills in over the mountain West and flows over this shallow moist air mass across the Texas plains. Along the line of demarcation where the two air masses meet, a dryline typically forms. A few miles above in colder air, the jet stream roars with strong winds.


Along that dryline, the collision forces some moist, unstable air upward. As the sun warms the Earth, like the stove heating a pot of water about to boil, thermals rise upwards as the atmosphere becomes more unstable. First, shallow thermals create puffy white clouds, but as the day wears on, the tops of the clouds grow higher and higher.


Under normal conditions, jet stream winds aloft speed across slower winds at the surface and create wind shear. One of the elemental building blocks of a thunderstorm, this wind shear is associated with an invisible shaft of horizontally rotating air like a water wheel caught in a stream.


Those rising thermals along the dryline begin to push the horizontal column of air upward within the growing thunderstorm updraft. The spinning column of air tips from horizontal to vertical, and rotation begins. A supercell thunderstorm is formed.


Supercells are immense, single-updraft storms that can contain weather’s most notorious villains: hail, inundating rains, wind, microbursts and — baddest of them all — tornadoes. The thermal updraft feeds the storm’s voracious appetite with moisture and warmth, building upward motion to nearly 90 miles per hour.


Twister Chasers - A Hackberry Farm Photo School Blog
The immense scale of a thunderstorm. A growing supercell next to Guadalupe Mountain - Texas' highest peak at 8,751 feet above sea level.

Thunderstorms essentially work like a heat pump. They pull large masses of warm air from the ground and cool it. The cool air descends back to the ground with rain or hail and accompanying theatrics from the storm. A thunderstorm can pack a meteorological wallop. 


MEET THE SUPERCELL 


When mature, a storm's precipitation area can grow as large as 900 square miles at the base and more than 60,000 feet tall. How big is that? That’s bigger than Houston and twice as tall as Mount Everest. Whoa.


This immense, floating structure twists vertically as the powerful drafts push the column of air skyward. As the updrafts intensify, the column of air twists tighter and smaller. Imagine a figure skater spinning with arms outstretched. As they pull in their arms, the total diameter decreases and the spin speed increases. That’s what happens to the spinning updraft in the thunderstorm.


The lowering of the cloud base, called a wall cloud, is cylindrical and may begin to rotate before a tornado. This is often a precursor to a tornado, so storm-chaser confirmation of a rotating wall cloud (along with radar rotation signatures) often triggers a tornado warning.



Twister Chasers - A Hackberry Farm Photo School Blog
A supercell thunderstorm with a wall cloud forming.


Under certain conditions, intense rotation may develop within the wall cloud, leading to the formation of a funnel cloud. If this rotation is apparent at the ground, it is classified as a tornado.


According to the National Oceanic and Atmospheric Administration, each year (on average) more than 150 tornadoes touch down on Texas soil. At about 12 percent of the national total, we get a lot more than our share of the action.


While most tornadoes are small spins that last just a brief time, others grow into monsters that pose a threat to life and property wherever they drop. 


EYES IN THE FIELD 


“Be here at 4:30 and we’ll head out,” storm chaser Bryan Leeper tells me. “I’ve been watching the conditions — it looks like today could be a good one.”


Bryan works for the Texas Department of Transportation, but he’s also a frontline storm chaser for Amarillo’s Channel 7 television weather team, their eye in the field whenever storms develop in the Panhandle. Bryan and others like him corroborate radar data for the team at the studio, an invaluable service to improve forecasting and reporting accuracy. Radar products are increasingly advanced, but they still can’t detect all the granularities of a fast-changing storm.


Twister Chasers - A Hackberry Farm Photo School Blog
Storm chaser Bryan Leeper.

Bryan and I head west from his hometown of Lakeview toward Briscoe County, where a line of thunderstorms is growing along the dryline. The late afternoon heat comes with a high dew point that imbues the air with moisture. Instability — caused when colder air from an upper-atmosphere disturbance lies above this warm, moist surface air — sets the stage for an active evening of severe weather.


“Look at the radar and tell me what you see,” Bryan says, turning his pickup to head toward the darkening sky. I’m excited at the prospect of using my National Weather Service storm training, an approved course that teaches amateur meteorologists about the nuances of severe weather and how to interpret radar data.


The cab of Bryan’s truck sports an assortment of technological gadgets designed to hunt and document storms. A dash-mounted cellphone camera livestreams video back to the station. Bryan’s talking to the team via telephone and watching the radar on an iPad mounted to the console. On the screen, I see storms popping up along the dryline that stretches from southwest to northeast. Every time the radar refreshes, we see the storms grow and intensify. Each one is unique.


Twister Chasers - A Hackberry Farm Photo School Blog
A myriad of technology helps storm chasers be accurate and safe.

We see a classic “hook” echo signature forming on one of the storms near Silverton, a telltale sign that it has the rotational elements that may spawn a tornado. We head southwest, hoping to parallel the storm and get a glimpse of any severe weather it may produce. When we’re within 15 miles, the storm matures and begins to wane.


Another storm is brewing north of Clarendon, so we head in that direction. Chasing storms is a roll of the dice. By the time, we get to the Clarendon storm, it cycles out as well.


MAKING A COMEBACK 


By 7 p.m., the storms wax and wane in intensity up and down the dryline. Some are severe, and a few spark tornado warnings, but they’re too far away to chase.


Wait a minute, the Silverton storm is showing signs of regeneration. A reorganized updraft is feeding fresh fuel into the storm.


Storms sometimes collapse, sending a stream of cool air downward. This outflow can cut off the warm inflow to other storms and diminish them as well.


We turn southeast to try to get in front of the Silverton storm, which is intensifying rapidly.


“Pop onto the other radar screen and see what the other chasers are doing,” Bryan says.



Twister Chasers - A Hackberry Farm Photo School Blog
Thunderbolts light up the sky from a powerful thunderstorm.


When I open the app, I’m mesmerized by the red dots that show the location of chasers logged on to the crowdsourcing network. From the movement of the dots, other chasers seem to think the Silverton storm is hot again. More eyes on the storm mean better documentation and confirmation of radar data, always improving the science of storms.


From Clarendon, we drive 45 miles to Estelline. From Estelline, we head toward Turkey. The radar signature of the behemoth continues to grow; a bump on the storm’s southeast corner soon turns to a full-blown hook. While not tornado-warned yet, Bryan thinks it will be.


Bryan and I pull off the road near two storm-chasing vehicles. One last look at the radar shows the storm’s core headed toward us. I can hear the roar of the monster supercell as it dumps rain and hail.


Rain is a product of supersaturation in the storm. The cloud becomes so saturated with moisture that it eventually falls to the ground. Hail, on the other hand, is a direct byproduct of the strength of the storm.



Twister Chasers - A Hackberry Farm Photo School Blog
A motherrship supercell thunderstorm roating over the Texas Rolling Plains.


A cloud's droplets grow in rapidly rising updrafts, where high-in-the-atmosphere subfreezing temperatures lead to a mixture of supercooled water and ice crystals. If conditions are right, water can continually freeze onto the ice, forming hailstones. Stronger updrafts can support larger hailstones, as they continually collect more supercooled water that freezes on their surface. In the Panhandle, for instance, intense updrafts in supercells can support hail as large as grapefruit.


THE BIG ONE? 


To our west, the big Silverton storm is creeping at 20 miles per hour across the broken badlands where the Rolling Plains abut the Caprock Escarpment. The hail and heavy rain are to our northwest; in the storm’s southeastern quadrant, a rain-free base appears. Predictably, that’s where the tornado may also appear. As we watch, the wall cloud descends.


Bryan calls into Channel 7 and reports what he’s seeing. The ground spotter has confirmed what the radar is indicating: this storm may produce a tornado. The radio blares with the warning sound of a severe weather event.


The massive wall cloud slides just to our north. Estelline, a tiny town on the south bank of the Red River, may be in trouble.


Twister Chasers - A Hackberry Farm Photo School Blog
A rotating wall cloud means that a tornado could be imminent,

Bryan and I stay just south of the storm, paralleling the storm’s path. We slip past it and turn so we can position ourselves outside Estelline.


The storm is full of rain and hail when it catches up to us. Underneath it, the darkest daytime I’ve ever experienced feels ominous.


A half-mile away, the wall cloud descends nearly to the ground. A tense moment passes. By now, a dozen storm spotters are on the scene, watching the storm with anticipation.


Fortunately for the people of Estelline, the wall cloud doesn’t drop a tornado. Within 15 minutes, the storm wanes and cycles out. The afternoon heating has dissipated, so we know the storm is gone for good.


As fast as that line of storms popped up on the radar, the whole severe weather event is over. Overall, no loss of life and only minimal impact on livestock and property, we learn later. Bryan and the other eyes in the field helped relay accurate data for the early warning needed to keep people safe.


There may be no rest for the weary, however. Forecast models show that tomorrow, conditions are good for another outbreak. Bryan and the others wouldn’t miss it for anything.



Twister Chasers - A Hackberry Farm Photo School Blog
Mammatus clouds lit by a setting sun.

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