Texas Tech University

In the Field

TTU atmospheric scientist Chris Weiss surrounded by StickNets

Atmospheric scientist Chris Weiss sits surrounded by StickNets, some of the scientific instruments he'll deploy ahead of the next storm. They'll collect data critical to improving weather forecasts.

Chris Weiss Works to Save Lives
By Researching Killer Tornadoes

Written by Toni Salama

Despite their destructive and deadly power, tornadoes are elusive things. They're a strangely delicate convergence of elements seen and unseen. Scarcely formed, they writhe, wrestle against everything, even their own existence. Then, just like that, they're gone. Some 1,300 of them swirl above the United States each year.

If anyone can get a handle on them, it's atmospheric scientist Chris Weiss. Since joining the Department of Geosciences' Atmospheric Science Group in 2004, the professor has been at the forefront of several major tornado research projects funded by the National Science Foundation (NSF) and the National Oceanic and Atmospheric Administration (NOAA)—totaling $4 million thus far.

Between 2004 and 2018, tornadoes caused the deaths of 1,217 people in the United States. Weiss doesn't like that one bit. The goal of his research is to improve the accuracy of tornado predictions and increase warning times so people can get out of harm's way.

That means Weiss has a lot of ground to cover. And a lot of sky. In addition to his teaching duties, his field work covers the better part of some 830,000 square miles of Texas, Oklahoma, Colorado, Kansas, Nebraska, Wyoming, Mississippi, Alabama and Tennessee to collect observational measurements. Before every field trip, he and his colleagues invest months in collaboration, making phone calls, running numerical calculations, planning strategy. All so that when they get to where they're going, they can deploy their instruments with the best likelihood of obtaining the most crucial data.

Killer Tornadoes of the Southeast

It's mid-December 2018, and Weiss has just driven 16 hours back from Alabama where he has been placing StickNets, the 7-foot-tall surveyor tripods equipped to measure wind speed and direction, barometric pressure, relative humidity and temperature. He finishes a phone call with another atmospheric scientist at Colorado State University and meets briefly in his office with a graduate student. In an hour or so, he'll start grading finals, but for now he welcomes a pause to talk about his field work, starting with America's deadliest tornado outbreak in recent years.

"Typically the climatology says that the Southeast United States doesn't have as many big tornadoes as what we have here in the Plains states," Weiss begins. "But there's a disproportionate loss of life for the tornadoes that do occur."

TTU atmospheric scientist Chris Weiss deploys a StickNetIn Mississippi, Alabama and Tennessee, the tornadoes that struck in April 2011 took the lives of 311 people, almost 75 percent of the death toll of 419 caused by tornadoes in those states for the entire year, according to figures from NOAA.

"After that event occurred, Congress a few years later decided that they were going to support this specific mission to look at tornadoes in the Southeast," he says.

The mission is known as VORTEX-SE, short for Verification for the Origins of Rotations in Tornadoes Experiment—Southeast, and is funded by NOAA.

"We are in our fourth year of VORTEX-SE. We were in the field in 2016 and 2017, March and April each year," he says. Then, rather than go out during spring 2018, NOAA decided to extend the observation period by deploying the StickNets in December 2018 and retrieve them by the end of April in 2019.

"It's a broad climatology, and we know that tornadoes can occur anywhere from the late fall through the early spring. A lot of tornadoes have occurred in December and January. So we're actually out there now, and instead of covering two months we're out there for five months."

With the 2011 deaths a still-recent memory, Alabama property owners welcome Weiss to their farmsteads, where he installs StickNets in a "mesonet," a network whose scale generally covers an area larger than an individual storm, but smaller than an entire storm system.

"We've set up 24 of these StickNet stations, and I have 24 individual relationships with certain landowners out there who have graciously agreed to allow us to plant our instruments on their property," he says. "And in some places it's tough because if you've ever been to Central Alabama, especially, it's really wooded out there."

Trying to place the StickNets in what Weiss calls exposed locations—where there's no interference from trees, hills or buildings—is more of a challenge that placing the same instruments in the Plains. "It's not quite as easy as, say, Lubbock, where you can pretty much put it down on a street corner and be fine," he says. "But everyone out there is really great, and they're interested in what we're doing."

In this current VORTEX-SE study, the temperature measurements will provide, arguably, the most important data for what Weiss's research team is trying to accomplish. Many theories on tornado development focus on the change in air temperature right near the storm, he says. "That's something we've seen in a lot of numerical simulations and are really trying to get a handle on with real-time observations. We want to know whether these changes in air temperature actually do exist and whether we can discriminate tornadic and non-tornadic storms using that as a criterion."

Deadly by Night

In addition to the visibility problems caused by trees and hills, the Southeast has other challenges that make its tornadoes deadlier than those on the Plains.

"Many of the tornadoes tend to happen at night, and that's quite a bit different from what we typically see in the Plains. We do have nocturnal tornadoes here, of course, but our climatology really peaks out in that late afternoon," Weiss explains. "There's a disproportional amount of nocturnal tornadoes in the Southeast, and of course some people are unable to get those warnings. A lot of people don't have weather radios, for instance, and some of the cities out there don't even have sirens."

In 2011, the Southeast experienced an unusual number of tornadoes that developed from supercells—storm formations more typical on the Plains, Weiss says. "But there's a very specific type of storm in the Southeast called the quasilinear convective system, or QLCS." Weiss describes these storms as big squall lines that sometimes develop wavy inflections rather than a solid line; it's in those inflections that tornadoes tend to develop. And they're harder to predict.

"So that's one specific thing we're trying to understand better are these quasilinear convective systems that produce a good chunk of the tornadoes that occur in the Southeast, and those often happen at night," he says.

Weiss remembers a particular time when all the elements of a Southeast storm were working against him: "We were out there trying to run a project that was a lot like research we did in the Plains in 2016 and 2017, when we were actually tracking these storms and trying to plant instruments out in front of them. And we had some success with it. But these aspects that I've been talking about—I mean, there were tornado warnings, the sky was black, and I couldn't see any storm structure because there was a big hill and lots of trees in the way."

His experience mirrored that of many a Southeast resident: "You can't depend on your senses to know there's a problem or see what's coming."

Warning Fatigue

While meteorology plays an essential role in the deadliness of Southeast tornadoes, human factors also are at work. "There's some basic science here in understanding how the tornadoes operate, but there's the applied element." Weiss says. "Once we learn, for example, the air temperature variation aspect, what we can do with that is to help improve our lead time on our warnings and especially reduce our false alarms on warnings."

Weiss says that the average false alarm on a tornado warning is somewhere around 75 percent. "And if people constantly get those warnings and nothing happens, then this whole notion of warning fatigue comes up." At some point, people just don't heed the warnings anymore. "From the 2011 event, for instance, they had about six days of warning, from the first time that we thought there was a potential for an outbreak," Weiss says, "and you still had over 300 people die. So, obviously, it's not just all about the meteorology and the predictability of the event; it's the communication with the public and assessing how people respond to that."

VORTEX on the Plains

Before VORTEX-SE, Weiss worked on VORTEX-2, a NOAA funded research grant that deployed in 2009 and 2010 (the original VORTEX project was in 1994-95) and covered the "tornado alley" states of Kansas, Oklahoma and Texas, plus the plains of Nebraska and Wyoming. It was his first major grant project at Texas Tech and one that showcased Texas Tech's tornado field research on the national stage. "NBC was out there. The Weather Channel was out there following us," he says. "So we'd have almost daily coverage of the work we were doing out in the field, which was good for all parties involved, I think."

From that field work, Weiss has vivid memories of one particular tornado. "It came out of the rangelands of Wyoming, and it actually was very hard to observe because it was away from the paved road network by quite a distance," he says of the 2009 event. "There were a number of cattle roads that were blocking our access to the storm." Weiss took stock of the situation and decided conditions were too risky to pursue the tornado more aggressively; and by the time the storm made it to their location, the tornado had dissipated. Weiss's first priority is safety, and he steers his team away from unpaved surfaces if there's any likelihood they could get trapped on muddy trails.

Studying the Supercells

As Weiss takes stock of his research, he begins to talk about a different project that's just now wrapping up—this one funded by the National Science Foundation (NSF)—called the National Robotics Initiative (NRI). He describes it as a large collaboration among Texas Tech, the University of Colorado and the University of Nebraska, and the first grant to truly address the potential utility of unmanned aircraft in the study of severe storms.

TTU's Ka-band mobile Doppler radar

The three-year project is a lesson in preparation. The team didn't go into the field—the vast expanse of the Plains—until spring 2018. Weiss says they obtained their best combined data set in South Dakota.

"The first two years were spent developing the concept of combined mobile radar, unmanned aircraft and surface thermodynamic measurements, integrating all three of those things together to get a holistic picture of what these severe storms look like both at the ground level and also aloft," Weiss explains. "And then the third year, which was this past spring, we actually carried out a field exercise where we combined all those elements."

Texas Tech operated the mobile Doppler radar; the University of Colorado contributed the unmanned aircraft; and the University of Nebraska took the surface thermodynamics—temperature, humidity, pressure and wind.

Right now, the team is analyzing the data obtained. But despite their best laid plans, the field work didn't exactly go off without a hitch. "The aircraft in particular had some struggles trying to literally get off the ground. We had some launching problems," Weiss says. "But we did have one really good case where we did integrate the three elements together in an effective manner."

Next on the Horizon

A new project just received funding from the NSF in summer 2018. Dubbed TORUS—short for Targeted Observation by Radars and Unmanned Aircraft Systems of Supercells—the study will deploy into the field in mid-May of 2019 and run for a month. Field work will concentrate in the Plains states and be conducted again over the same time period in 2020, yielding two months of data in total.

"Actually I just had a conference call on that yesterday to talk about all sorts of logistics. So we are in the planning stages for that project right now," Weiss says. "And this project has a lot of the same players as NRI; the University of Colorado and the University of Nebraska are working on this project, too, and pretty much have the same roles."

In addition, TORUS will include the research participation of scientists from the National Severe Storms Laboratory, who will bring instruments to the field as well. The project also will benefit from manned aircraft. "That's one key addition over what we had in the NRI project," Weiss says. "The manned aircraft will be flying about 5,000 feet up or so. That's the P-3 aircraft, and that's been used in a lot of research projects through the years. It has a radar on board so it can make measurements of the storm aloft."

Using Radar High & Low

There's a tradeoff that takes place when using radar that Weiss describes this way: "The Texas Tech Ka-band radars at the ground are at a higher frequency, which allows us to get a more resolute depiction of the storm. The tradeoff is that we can't see as far into the storm. So the aircraft balances that out nicely because it is the exact opposite. The aircraft can get a picture of the entirety of the storm—it can see farther into it—but the resolution is worse. So we marry those two concepts together to get that holistic picture of the storm's structure."

Weiss says that weather research radars are looking for very specific portions of the storm. "We're looking for processes that are occurring that we think are relevant to the development of tornadoes," he says. "So we're out there with a game plan. We're looking for very specific types of features."

Given the elusive nature of storms in general and the formation of tornadoes in particular, it's not always easy to deploy radar and other instruments at the optimum altitude, the optimum depth into the formation and at the optimum time.

"There are features that we often see in numerical simulations, but we don't know if they actually exist in real life," Weiss explains. "So a lot of the work that we do here at Texas Tech is to take the theory and idealized numerical simulations and then go out there and verify, confirm that these features are present in reality."

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The Big Take-Aways:
Weiss' Research Thus Far

As an atmospheric scientist at Texas Tech, Chris Weiss says his field research is as much about testing numerical theories as it is about measuring the storms themselves. Here are some of the finding Weiss's research has produced.

1. Proving That Air Temperature Changes Before Tornadoes

During the VORTEX-SE study, Weiss's research team obtained important samples from several quasilinear convective storm systems (QLCS) unique to the Southeast United States. On April 30, 2017, a QLCS moved through an area where Weiss's StickNets were deployed. The thermodynamic instruments were able to detect that part of the storm line was tornadic while another part of it wasn't, and take samples of both conditions. "We found some fairly striking differences in how air temperature changes," Weiss says. "We found air temperature does tend to change more quickly on the tornadic part, which is something that has been theorized to be true in a lot of the numerical work, but it's not something that's really been observed directly until now. We're really excited about this, and it's probably one of our biggest findings so far." Jessica McDonald, one of Weiss's master's students, presented this research at the American Meteorological Society's 29th Conference on Severe Local Storms held Oct. 22-26, 2018, in Stowe, Vt.

2. Characterizing Cold Pools

Tied in to temperature changes is something called a "cold pool." When a thunderstorm comes in, the air gets really cold because a lot of the rainfall evaporates on the way down and cools the air—that's a cold pool, and cold pools are important for tornado formation. While atmospheric scientists have a grasp on cold pools in the Plains, an exhaustive analysis of cold pools in the Southeast has yet to be done. Weiss is working now to understand those dynamics—and running into a Goldilocks principle. "It seems like you have to have some of that cold air to get the tornado. But if it's too cold then it doesn't work out because the air is too heavy to rise up in the storm," Weiss explains. "So the bottom line is, it's important to understand the intensity of that cold pool, what causes that." Weiss's earliest research findings indicate that Southeast storms can produce some pretty stout cold pools. "We're in the process of trying to understand why that is. So for VORTEX-SE in terms of results, that's been one of the big areas, the cold pool analysis."

3. Running Ensemble Sensitivity Analysis

The National Robotics Initiative, just in from the field, and the upcoming TORUS project both use multiple instruments working together—the ensemble—to obtain real-time measurements. Just as a musical performance needs many practice sessions and a conductor, an atmospheric testing ensemble needs planning and orchestration. Weiss says this begins with proof of concept, showing that the individual components of radar aloft in aircraft, mobile radar on the ground, and surface thermodynamic measurements can all measure data that can be integrated. Planning becomes an enormous task. "It's very difficult to get all these assets in the right spot at the right time. If your forecasting is good and your road network is good and you have plenty of visibility, if you can get all that in place, by golly, you want to have a good plan of attack for where you can get the most bang for your buck with observations," Weiss says. That's why he's doing his homework ahead of time using a research technique called ensemble sensitivity analysis. In this, researchers start with a numerical simulation of a storm event and perturb the initial state just a bit. For example, they might choose to perturb the temperature up or down, or the wind a little faster or slower. "Then we let the model take that and let it go forward in time and see how those tiny little differences grow into much bigger differences later on," Weiss says. With that, they can associate a specific outcome at the end of a timeline with what was perturbed initially. "So if you consider that perturbing as just uncertainty in what that temperature actually is, for instance, then I can send an aircraft to that spot to take that measurement and get a more accurate forecast of the end result." Ensemble sensitivity analysis has been in use for a few years. "But we're just now starting to apply it to the storm scale. That's one of the big things we're doing in my group right now."

4. Understanding the Structure of Tornadoes

Of all the work that Weiss does, the most difficult is attempting to profile the structure of individual tornadoes. "You have to have a lot of things go right in terms of the forecasting, the road network, and of course the radar has to be in the correct position to see what it needs to see," Weiss explains. "We have to be in a position where we can see the debris cloud at the surface, and if you don't see that then you probably have something that is obstructing your view of the horizon." Sometimes storms don't produce tornadoes. Sometimes storms come at night, when Weiss says it's just too dangerous to work. Sometimes they blow the forecast and end up in the wrong state. And this type of field research, the travel, the equipment, costs money. Weiss currently has no large funding to study the structure of tornadoes. But he says that some of the better cases he's profiled came in 2012 and 2013 when his group specifically was looking at tornado structures using Texas Tech's two Ka-band mobile Doppler radars. These radars show fine scales of motion, measured in meters, at a range of 3 or 4 miles, and can profile a tornado event in both horizontal and vertical terms. "The vertical is really important because the near-surface layer is essential for understanding the destruction, because that's where the buildings and the people are," Weiss says. Perhaps even more important is that the key to how the tornado forms and maintains itself may be found in the vertical radar data. "Those details are sometimes in the lowest, maybe, 50 meters, 20 meters above the ground," Weiss says. "So you have to have the kind of pencil-like beam that can get you that depiction. And we've had success with this."

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Valuing the National Wind Institute

Weiss says that Texas Tech's National Wind Institute is critical for the work he does. It's a consortium of different departments across campus—atmospheric sciences, mechanical engineering, civil engineering, architecture—with the common goal of understanding wind events of all kinds, how they are formed and how they affect structures and populations. It helps provide a lot of the support for the technicians, facilities and equipment Weiss works with.

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This article originally was published, in abbreviated form, in Arts & Sciences magazine, Spring 2019 edition.

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