Southern Great Plains Site in Path of Tornado

Published: 7 May 2012

Property of several SGP site personnel took a hit during the April 30 tornado. Site operations manager John Schatz shared this photo of damage to and around his barn.
On April 30, at about 10:30 p.m, a tornado touched down in Medford, Oklahoma, northwest of the Central Facility at ARM’s Southern Great Plains site. The storm track moved southeast, passing through several counties and leaving a path of destruction in its wake. In spite of winds in excess of 80 mph and baseball-sized hail, ARM instruments and structures sustained only minor damage. Unfortunately, several SGP staff and farmers in the area were not so fortunate.

“While our facilities really dodged a huge weather bullet, about half of our employees had some degree of property damage from the storm,” said Doug Sisterson, SGP Site Manager for ARM. “And after braving the worst of it in their storm shelters, then helping their neighbors through the night, they still showed up for work the next morning. These people are incredible.”

Compounding the situation, a rainstorm on April 29 dropped nearly 12 inches of rain, flooding many roads throughout the area. As both ARM site staff and neighbors continue to assess damage and get on with recovery, ARM’s new scanning radars provide a detailed glimpse into the eye of the storm.

Precipitation Radars Record Storm Signatures

As annotated by Scott Collis, ARM Precipitation Radar Translator, data from the X-band scanning radars show the storm from two different directions beginning at around 8:30 p.m. local time. Both panels show a single, fixed elevation angle sweep of the radars at 0.5 degrees. The left hand panels show a quantity called the “equivalent reflectivity factor” and is proportional to the rain (or hail!) content of the thunderstorm. The right hand panel shows radial velocity of the rain and hail particles. High positive values (red) indicate movement away from the radar; high negative values (blue) indicate moment towards the radar. Click on image to enlarge.
At the SGP site, a network of scanning X-band (9.5 gigahertz) precipitation radars are situated around ARM’s Central Facility, southeast of Medford. This multi-scale network of close-range fast-scanning radars can observe atmospheric phenomena down to very fine resolutions not available with typical Doppler weather radars.

As the storm moved into the radar domain, the radar closest to Medford went offline as power lines snapped to the ground. However, the other two radars continued to operate, capturing the two key indicators that a tornado is taking place: a hook echo and a Tornado Vortex Signature (TVS). The hook echo is noted by a tightly wound ribbon of reflectivity, while the TVS is visible as a couplet of incoming and outgoing “radial velocities”—indicating rapid rotation where the tornado is spinning up into the parent thunderstorm.

These indicators occurred at the same time as the downdraft at the rear of the storm intensified, feeding 90-plus mph winds into the hook region. As the hook structure rapidly decayed, the winds—though still severe—took on more of a “gust” rather than sustained form. Data from the radars corroborate well with tornado reports from spotters and the National Weather Service, and will be extremely useful as scientists analyze this complicated and unexpected storm development.

Picking up the Pieces

Severe weather is a way of life in the storm belt that is the Great Plains, and the hearty people that live and work there are prepared for the worst. As the storm surged through the various counties, storm cellars throughout the area were put to the test—and, thankfully, served their purpose! Above ground? Well, that’s another thing.

Nearly half of the power poles west of I-35 into the town of Lamont were snapped, and the huge grain bins that served as a landmark for the turns south onto the Billings-Nardin Road were leveled. The big farm on the west side of the Billings-Nardin road reportedly had its barn and grain bins “relocated” to the road, and the Salt Fork River was above the bridge and impassible.

...and after.

In the Medford area, all main power poles were sheared off and laying across the roadways to within 100 feet of the C-band radar at Nardin, and the transformer for the radar was in the ditch. The grain elevator to the north had one of the huge storage bins collapse and tin littered the field up to the radar site, including one small piece inside the fence.

While the radar had several visible dents and one crack on the radome from hail damage, land owners to the south suffered significant damage. Drawing a line from the gain elevator to the homes puts the Nardin radar within 1/2 mile of the center of the damage path, perhaps even closer.

Uprooted trees, smashed barns, and collapsed grain silos tell the story. Photos by SGP staff John Schatz, Site Operations Manager; David Breedlove, Deputy Site Operations Manager; and Chris Martin, Senior Engineering Technician. (Click on images to enlarge.)

The transformer for the C-band radar lays in the ditch.
The C-band radar dome came through with only minor dents.
Nardin grain elevator lies crumpled on the ground.
Dave Breedlove's barn was reduced to scrap lumber.
Dave Breedlove stands by an uprooted tree on his property. And yes, still smiling!