The outbreak was caused by an upper-level
shortwave trough that moved northeastward from
Mexico into the
Southern Plains states during the nighttime the morning of May 15. The
Storm Prediction Center (SPC) in
Norman, Oklahoma, a division of the
National Weather Service, initially issued a slight risk of severe thunderstorms early that morning over northwestern
Texas, for a threat of large hail and damaging winds. A
low-pressure area associated with the trough moved over
Oklahoma that day, producing light to moderate rainfall and non-severe thunderstorms across that state into parts of
North Texas. Later forecasts expanded the slight risk further into northern and
Central Texas, and later into far southern Oklahoma, and indicated an enhanced risk of a few isolated tornadoes in
North Texas. The atmosphere began to destabilize due to a decrease in cloud cover over western and central Texas; the sunshine and heating, combined with sufficient
wind shear and abundant low-level moisture, combined to produce a very unstable air mass. The SPC issued a
severe thunderstorm watch from southern Oklahoma to central Texas that afternoon around 3:00 p.m. CDT.
Supercells broke out in parts of northwestern Texas during the late afternoon hours, one of which developed the first tornado of the day at 5:38 p.m., near
Belcherville in
Montague County. A second tornado spawned by the same storm, rated as an EF1, touched down near Lake Amon G. Carter, damaging four homes and destroying one. As forecasters realized that conditions now favored tornadic activity, the SPC issued a
tornado watch from far southern Oklahoma into central Texas at 6 p.m. CDT, replacing parts of the original severe thunderstorm watch. The supercell that produced the Granbury tornado later spawned a very large EF3 tornado that hit the
Fort Worth suburb of
Cleburne in
Johnson County around 9:30 p.m. CDT, producing its most significant damage just east of
Lake Pat Cleburne. The last twister of the outbreak touched down at 12:19 a.m., producing EF1 damage in the
Ellis County town of
Ennis, Texas, south-southeast of
Dallas. The system continued to spin up tornadoes on May 16 and 17, though not of the same severity as the storms that occurred on the 15th, each causing only minor to moderate damage of EF0 and EF1 intensity. Four additional tornadoes occurred near the
Shreveport metropolitan area on May 16, two of which touched down near
Waskom, Texas, and two in
Caddo Parish near the towns of
Greenwood and
Stonewall, Louisiana. Two short-lived tornadoes touched down in
Limestone County, Alabama on May 17, causing scattered damage to trees, roofs and a barn. == Confirmed tornadoes ==