A very unstable airmass was in place over South Texas by mid afternoon, with a surface low pressure trough just to the north of the area providing a focus for thunderstorms to develop. By 3 PM, a supercell thunderstorm formed along this boundary, and moved south. With breezy southeast winds feeding moisture to the storm, the supercell continued to intensify as it moved into more moist and unstable air. Strong rotation within the storm resulted in large hail, with quarter to golf-ball sized hail reported. Two tornadoes formed from this supercell; one that affected the southeast side of Alice, Texas, and one that affected locations in and south of Premont, Texas. As daytime heating ended, the storm slowly weakened as it moved south of Jim Wells and Kleberg Counties.
The radar loop from Tuesday afternoon shows an unusual, southward-moving supercell. The loop begins around 3pm with a storm developing over Atascosa County, then moving south and merging with weaker storms over Live Oak County. The storm then intensifies rapidly, developing a well-defined inflow notch and circulation. This circulation peaks over the east side of Alice, producing an EF1 tornado, then quickly collapses. The storm reintensifies after another cell merger further south in Jim Wells county, and produces another tornado in and south of Premont, Texas near the end of the loop.
Here are maps showing the path of the two tornadoes. Teal coloring indicates EF0 damage, and green coloring indicates EF1 damage. Circles outside the tornado paths indicate non-tornadic damage reports.
Here's the sounding taken in the middle of the event. Note the deep surface-based moist layer, strongly backed winds, and pronounced dry slot aloft.
Surface observations show a warm, humid airmass across South Texas, with strong Gulf inflow into a low pressure trough inland from the Coastal Bend.
Maps showing the state of the upper atmosphere are shown below.
Follow us on Twitter
Follow us on Facebook
Follow us on YouTube
CRP RSS Feed