Tornadoes in the Southeast May Be Influenced by Mountainous Terrain; VORTEX-SE Project Investigating This Spring

Chris Dolce
Published: March 20,2017
Scientists this spring will gather more details on evidence that suggests tornadoes are influenced by terrain in parts of the southeastern U.S.
The study is a part of the VORTEX-Southeast project that started last year and brings together meteorologists, researchers and social scientists for tornado-related research in the Southeast.
(MORE: Tornado Central)
Of particular interest for this investigation is a mountainous area of northern Alabama, where it's thought that the local environment has aided in tornado development in past events. Scientists are specifically focused on an area that includes Sand and Lookout mountains and the Wills and Tennessee Valleys, according to the University of Alabama-Huntsville (UAH).

The darker red lines in the blue-shaded area are tornadoes located in the vicinity of Sand Mountain in northeast Alabama Sept. 2006-Dec. 2015.
(University of Alabama-Huntsville)

Research has already been done on this topic, including a paper by UAH scientists Anthony W. Lyza and Kevin R. Knupp that said terrain appears to have played a significant role in several tornado events in the past decade. Among those are three violent tornadoes during the April 27, 2011, Superoutbreak, including near Pisgah, Alabama (EF4), Ohatchee, Alabama (EF4), and Rainsville, Alabama (EF5), along with EF1 tornadoes in the Huntsville, Alabama, area April 11, 2013.

Severe tree damage with mountains in the background from an EF4 tornado that moved along a path from Argo to Shoal Creek, Ohatchee and Forney, Alabama, on April 27, 2011.

(RECAP: 2011 Superoutbreak)
Lyza and Knupp said in their study that they have identified "repeated behaviors of tornadoes in the presence of significant terrain." This includes tornadoes strengthening/weakening at certain points on their path as they encounter upslopes/downslopes of hills and mountains or interact with plateaus. There is also evidence of slight track deviations to follow valleys or the edge of a plateau.
"With Sand Mountain, we have strong evidence that something physical is going on up there," said Lyza in a release from UAH last October. "We looked at the start points for all the tornadoes that affected that area over the past 10 years. There were 49 tornadoes total, and of those 32 formed on top of Sand Mountain."
Interestingly, half the 32 tornadoes in that 10-year period formed in the same general area near Sand Mountain.
"Sand Mountain is generally about 15 miles wide. But if you look at the start points where tornadoes touched down, 16 of those 32 formed within three miles of the northwestern edge. That's not a huge sample size, but it's enough to make you question the possible physical processes that might impact those storm systems as they move atop that plateau," Lyza added.
For two months this spring, scientists with VORTEX-SE will work to gather more information on the effects of terrain on storms in the Sand Mountain area.
(MORE: Tornado Extremes)
The team will use five mobile Doppler Radars, profilers and mobile atmospheric sounding systems to gather more information on localized weather conditions. Data collected during the investigations will then be used in high-resolution computer model simulations.
"These data will allow us to gain new understanding of how terrain features can create conditions conducive for enhancing tornadic storms," VORTEX-SE said on its website.
Interestingly, severe storms are not needed to gather data. Winds out of the south with rain or even insects for the mobile Doppler Radar systems to detect will provide useful data, according to the UAH release.
This is the third VORTEX project since the mid-1990s. The other VORTEX projects were focused on the Plains states, most recently VORTEX 2 in the spring of 2009 and 2010.

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