A deadly tornado outbreak occurred in Central Texas during the afternoon and evening of May 27, 1997, in conjunction with a southwestward-moving cluster of supercell thunderstorms. These storms produced 20 tornadoes, mainly along the Interstate 35 corridor from northeast of Waco to north of San Antonio. The strongest tornado was an F5 tornado that leveled parts of Jarrell, killing 27 people and injuring 12 others. Overall, 30 people were killed and 33 others were hospitalized by the severe weather.
Although the atmospheric conditions enabling the event were forecast to be conducive for strong winds and large hail, forecasters did not initially anticipate as much of a risk of strong tornadoes due to the lack of substantial wind shear over the region. Instead, the coalescence of several weather features—including a cold front, a dry line, and a gravity wave—provided locally favorable conditions for rotating thunderstorms and the formation of tornadoes. This peculiar evolution led to the unusual southwestward motion of the storms and the tornadoes they produced.
A tornado watch was first issued at 12:54 p.m. on May 27 for portions of East Texas and western Louisiana; the first tornado touched down at 1:21 p.m. in McLennan County while the final tornado lifted at 8:23 p.m. later that day in Frio County. The 20 tornadoes collectively inflicted at least $126.6 million in damage. The F5 Jarrell tornado was the outbreak's most powerful and deadliest tornado. It destroyed most of the 38-home Double Creek Estates subdivision west of Jarrell where the most extreme damage occurred. Residences were completely dismantled, swept away, and reduced to a concrete slab, while trees in the area were completely shredded and debarked. Fields were scoured to a depth of and asphalt was torn from roads. Due to the tornado's intensity, the debris was often small in size and beyond recognition. There were four other tornadoes rated F3 or higher. One F3 tornado moved across Cedar Park, damaging parts of the business district and numerous homes in nearby neighborhoods. An F4 tornado struck areas near Lake Travis and caused one fatality. In addition to the tornadoes, the storms also produced large hail and strong straight-line winds; Kelly Air Force Base in San Antonio recorded a wind gust.
Meteorological synopsis
Atmospheric setup
The severity of the 1997 Central Texas tornado outbreak was predicated on an unusual spatial and temporal alignment of weather features at highly localized scales. The broader environment was not particularly anomalous for the late springtime over Central and East Texas. Unlike conventional tornado outbreaks in Texas, the 1997 outbreak was not associated with a strong trough of low pressure and strong density gradients in the lower troposphere. Instead, the most prominent weather system over the central U.S. at the time was a distant upper-level low centered over Nebraska imparting little influence on atmospheric conditions over Texas.
Consequently, winds in the mid-levels of the troposphere over Texas on May 27 were weak and westerly, ranging from over North Texas to below over Central and South Texas. Winds closer to the surface were also quiescent; the average storm-relative winds within the lowest of the atmosphere as measured in Del Rio, Texas, prior to the onset of storm development was only . Further aloft at the level of the jet stream, there were two nearby wind speed maxima over northern Mexico and the central Mississippi Valley; this led to strong divergence of air over Texas. Wind shear was negligible within the lowest of the atmosphere contrary to typical tornado outbreaks.
Despite generally meager winds, the atmosphere was nonetheless thermally energetic. The combination of several days of onshore wind flow from the Gulf of Mexico and the persistence of a capping inversion aloft led to an accumulation of moist air over the state. Dew points soon exceeded within the boundary layer, representing ample moisture in the lower levels of the troposphere. Radiosondes launched from Corpus Christi and Fort Worth on the morning of May 27 detected the presence of a robust "elevated mixed layer" of air aloft characterized by steep lapse rates—the change of temperature with height—near the dry adiabatic lapse rate. This contributed to high convective available potential energy (CAPE) exceeding 5,500 J/kg across most of Central and East Texas, denoting a highly unstable atmosphere. In some cases CAPE was as high as 6,500 J/kg. The lack of fronts moving across Texas in the 36 hours before the tornado outbreak allowed this instability to remain and spread across much of the state.