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January-February 2010

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VORTEX2: Inside the Biggest Tornado Chase in History

It was day 26 of the largest tornado research project in history, and the Verification of the Origins of Rotation in Tornadoes Experiment 2009–2010, otherwise known as VORTEX2, had yet to see a tornado. Weary team members crammed into a small hotel meeting room to learn where they were headed, just as they had done every morning for almost a month. Day after day they geared up, learned the target, drove cross-country—sometimes covering hundreds of miles and several states in one day—to watch, wait, deploy, and intercept everything but a tornadic supercell.

They had spent weeks honing their deployment strategies on various types of storms: weak supercells, multicell storms, and one they called “cumulonimbus junkus” in disgust. They were now closing in on the final week of operations.

“The very real possibility that we might not even see one tornado was on everyone's mind,” reflected VORTEX2 Steering Committee member Don Burgess, a retired researcher from NOAA NSSL working part-time for the University of Oklahoma. NOAA Storm Prediction Center (SPC) records confirmed the quiet weather pattern. SPC had issued the fewest severe weather watches during May 2009 since 1992.

Caption: The shared Mobile Atmospheric Research and Teaching radar heads toward the Texas Caprock in the panhandle.

Caption: (L to R) Chris Weiss (TTU), Josh Wurman (CSWR), Yvette Richardson (PSU), David Dowell (NCAR), Howie Bluestine (OU), and Lou Wicker (NSSL).

VORTEX in History

The original VORTEX project was conducted in the central and southern plains in 1994–1995. It was designed to address research questions relating to tornadogenesis and tornado dynamics. However, like 2009, researchers struggled the first year, as an incredibly quiet year for tornadoes prevented them from collecting much data. Only three tornadic supercells were intercepted, and one problem after another prevented data collection on the tornadoes. In 1995 their luck changed, and scientists scored big by documenting the near-ground weather conditions close to several tornadoes. Building on the progress made with VORTEX, VORTEX2 was planned to answer more specific questions.

Researchers began planning VORTEX2 nearly a decade ago, with funding provided by the National Science Foundation (NSF) and the National Oceanic and Atmospheric Administration (NOAA). Scientists and support personnel gathered from across the globe, coordinating, driving, operating, or deploying 10 mobile radars, 14 vehicles with instruments attached, and dozens more outfitted to deploy devices in the field. Their goal was to measure and document all parts of a supercell thunderstorm using the largest collection of cutting-edge weather equipment ever assembled. Researchers hoped to answer important questions about these cyclonic storms. Why do some supercells produce tornadoes and others do not? How exactly do tornadoes form? Are there clues that will help us predict when a tornado will form, how long it will last, and how strong it will be? What specific characteristics of the storm can we measure that will help reduce the false alarm rates of our warnings? How can we increase lead-times so that hospitals, schools, and other large groups of people have more time to get to safety?

The V2 Armada

VORTEX2 had dozens more instruments than the original VORTEX, making a much bigger impression as the caravan rolled through the rural Great Plains. Researchers had carefully choreographed deployment strategies for different types of storms, and each vehicle and instrument had a specific mission. Though individual teams were in charge of positioning and deployment of their instruments, the VORTEX2 Field Command vehicle provided guidance on target storm locations and projections of movement. Field Coordinators worked to organize and communicate storm intercept activities in real-time to all teams, maximizing data collection opportunities while keeping safety a top priority. The entire project was backed up by the VORTEX Operations Center (VOC) at the National Weather Center in Norman, Oklahoma. The VOC provided forecasting and logistical support.

Ten mobile Doppler radars with varying levels of sensitivity were the anchors of the project. University of Oklahoma (OU) and NOAA National Severe Storms Laboratory (NSSL) teams operated 2 C-band radars, the largest and most cumbersome vehicles in the armada. Their mission was to scan the storm from a distance. The 6 X-band radars in the fleet were sensitive enough to detect smaller particles, including cloud droplets, and would be used by NSSL, the Center for Severe Weather Research (CSWR), and the University of Massachusetts(U-Mass) to distinguish tornado debris clouds from precipitation in the mesocyclone region during tornadogenesis. Two even more sensitive radars run by teams from Texas Tech University (TTU), OU, and U-Mass were assigned to scan the features in and around the tornado.

For collecting data inside the storm, Penn State, NSSL, and the University of Michigan teams operated 12 mobile mesonets, or probes (minivans outfitted with racks of surface weather instruments). They had the task of taking measurements of temperature, pressure, humidity, and winds as they drove transects through the storm. StickNets, or 2.5-meter-tall meteorological observing stations, were set up by TTU to measure the environment as the storm and tornado passed by. And tornado pods, or 1-meter towers of instruments, were deployed by CSWR in the path of the tornado to measure the core flow, while disdrometers, or particle probes, were positioned by the Universities of Colorado and Illinois to measure the size of raindrops, searching for tornado indicators in the gradient between light and heavy rain.

Another key element was weather balloons, handled by North Carolina State University, SUNY Oswego (State University of New York at Oswego), and the National Center for Atmospheric Research crews. The balloons were designed to be launched both ahead of storms to give scientists a picture of the prestorm environment, as well as after the storms formed to measure the vertical structures of temperature, humidity, and winds near the thunderstorms.

Meanwhile, high-resolution imagery of the wall cloud, tornado, debris, and damage were to be collected by photogrammetry teams from Environment Canada, NCAR (National Center for Atmospheric Research), Lyndon State, and the NOAA National Weather Service Warning Decision Training Branch. Researchers planned to perform a frame-by-frame analysis of clouds or debris to determine the speed of winds swirling around a tornado.

The media rounded out the caravan of VORTEX2. The project provided a great opportunity to involve the public in weather science. The Weather Channel (TWC) committed to follow VORTEX2 from beginning to end—telling the story of the research and process day by day, on every level as it unfolded. It had its own small armada of producers, freelancers, cameramen, technicians, and even a satellite truck. NSSL offered seats to reporters and photographers in a “media vehicle,” which was an attempt to minimize the number of extra vehicles in the field. The riders could then be embedded in research vehicles for a close-up experience. Blogs, Facebook, and Twitter updates were all part of the effort.

June 5, 2009: Tornado!

June 5 started out like any other day for VORTEX2. The team gathered in a small hotel meeting room in Sterling, Colorado, for the morning weather briefing. Don Burgess, Mission Scientist of the day, announced the target area was on the fringes of the VORTEX2 domain—southeast Wyoming. Burgess made the call to “play the upslope,” which meant to capitalize on winds getting lift from the ridges and bluffs of the western high plains. The armada packed up its luggage and gear and began to snake its way to the northeast toward Kimball, Nebraska, the first staging site.

Three prestorm balloons were launched, and soundings indicated sufficient shear and moisture. The storm was declared the “target” at 4:00 p.m., as it took on tornadic characteristics. All teams deployed to their assigned locations ahead of the storm. NSSL Media Vehicle Driver John Oakland began taking video of the supercell. Voices crackled on the radio as radar operators reported their latitude and longitude at the point of deployment. Oakland panned west towards the storm, capturing the sun silhouetting the supercell and outlining a wall cloud hanging beneath. The sky grew darker as the storm moved towards the armada.

“The entire base of the thunderstorm seemed to be turning and descending towards the ground,” said Oakland.

“There we go, we have a tornado!” reported Mike Bettes live from The Weather Channel, giving the entire nation the opportunity to share in the first VORTEX2 victory. The teams deploying instruments on the ground moved quickly to set up an array of instruments ahead of the tornado. The tornado was now on the ground and moving across the plains with a curtain of light rain circling it. As hail started to fall, crews had to undeploy some of the radars to avoid subjecting them to damage.

Bettes described the scene live on the TWC broadcast: “It looks like it is now tilting—the top portion of the tornado looks to be tilted toward us. You can look right inside the tornado! It almost looks like an outer funnel and inner funnel!”

VORTEX2 teams along with those watching The Weather Channel were amazed as they witnessed the funnel narrowing into a rope, then twisting and turning into a thin wisp of vapor. And then it was gone.

The day that started like every other day ended with a perfect deployment on a supercell thunderstorm that produced a tornado. VORTEX2 collected almost an hour of data on the storm, beginning 20 minutes before the tornado formed until it faded away.

“That one dataset was worth all the heartache,” said Tanya Brown, a Texas Tech University team member.

All 10 radars scanned the tornado, producing classic images of rotation. Mobile mesonets reported excellent sampling of the mesocyclone and rear flank downdraft region within the areas scanned by mobile radars just prior to and during tornado formation. Sixteen balloon soundings were made during the storm-scale deployment. StickNet teams performed a 2-array deployment and sampled the updraft, forward, and rear flanks of the mature tornadic supercell as it crossed the western array. All 12 tornado pods and 4 disdrometers were deployed successfully. As a result, the LaGrange, Wyoming, tornado is now the most intensely examined tornado in history.

The successful research was not without its price. Damage to the VORTEX2 fleet was being reported as operations ended. Probe 1, a mobile mesonet, had a shattered windshield from hail.

“This was unusually relentless,” said Steering Committee Member and Penn State Professor Paul Markowski, who was in Probe 1. “Basically 20 minutes of baseball-sized hail mixed with smaller sizes.”

The next day, the National Weather Service Forecast Office (NWSFO) in Cheyenne, Wyoming, gave the tornado a rating of EF1 on the Enhanced Fujita (EF) Scale. However, the storm assessment team documented power poles snapped off near the ground along the path of the tornado, caused by an estimated wind speed of 118 mph. VORTEX2 teams shared their wind measurements with the NWS, showing that the winds at 10 feet above the ground were about 130 mph. The fastest winds recorded below 328 feet were 143 to 148 mph. The NWSFO subsequently revised its rating of the tornado to EF2 with this new information.

In Retrospect

2009 was a historically low tornado year in the VORTEX2 domain. The 1 tornado intercept was well below the VORTEX2 goal of 5. However, researchers remained encouraged as they worked toward understanding why some supercells produced tornadoes and others did not.

“We made atmospheric lemonade from atmospheric lemons,” said Paul Markowski of Penn State University. Three supercells very close to producing tornadoes were documented during operations and offer valuable “null” cases.

Burgess added, “We got some very interesting data sets on weather types other than supercells—dry microbursts, squall lines, bow echoes, quasi- linear convective systems, ‘ordinary cells'—I learned more about each of these.”

Overall, the VORTEX2 armada traveled over 11,000 miles through 9 states during 2009 operations. Researchers collected data on 11 supercells, including the Wyoming tornadic supercell. The data collected will be studied for years to come. Early attention is being focused on the evolution of the rear-flank downdraft and its apparent role in aiding the development of low-level mesocyclones and tornadoes, or in causing strong surges that diminish the likelihood of tornadogenesis. VORTEX2 researchers met in November to discuss 2009 operations and plan for spring 2010 operations, which are tentatively scheduled for May 1-June 15.

But for many of the researchers who participated in the project, it was not only the science, but the spirit of what they were doing, that will be remembered. VORTEX2 Steering Committee member Howie Bluestein, a Professor at OU, commented, “It wasn't just ‘I' watching a tornado, or just our radars, or my graduate students out there. It's dozens and dozens of people all focused on that one tornado. That was amazing.”

SUSAN COBB was a VORTEX2 participant and is a meteorologist and science writer for the NOAA National Severe Storms Laboratory.

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