Click any image to display full-size
Photo of Shelf Cloud in Aransas County - Courtesy of Texas General Land Office

A line of severe thunderstorms produced large hail, damaging winds, and very heavy rainfall as they moved across South Texas Tuesday morning. The storms developed as a cluster of towering cumulus clouds in Mexico around 9am, that strengthened into a line of thunderstorms as they crossed into Webb County.

At 9:41 AM CST, the storms became severe as they moved east into Duval County when the first hail report came in: pea sized hail. Nexrad Doppler radar survelience well into the core of this storm revealed large hail suspended at high altitudes in the storms, roughtly between 20,000 and 30,000 feet, therefore larger hail stones were likely, but none had been reported at the time. Minutes later, the storms produced wind damage in the town of Rios in eastern Duval county before crossing into Jim Wells County.

The storms continued to increase in intensity as they moved into a more unstable environment near the middle coast. Hail as large as quarters pounded communities in Nueces County from Agua Dulce to Corpus Christi. Strong winds in excess of 60 mph ripped the roof off San Pedro middle school in Robstown, 10 miles west of Corpus Christi. The Nexrad Doppler radar revealed a bow like signature as it moved across the Robstown area which indicated the potential for strong damaging winds.

Another hailstorm developed over Refugio County before moving east into Aransas County near the Aransas Wildlife Refuge. Weather spotters reported quarter sized hail along highway 35 in Aransas and Refugio Counties. Geese were observed to fall from the sky as a result of the large hail. Many people described the landscape as a winter wonderland because the ground was littered in hail. Click this link to see a short video of the hailstorm.

In addition to the wind and hail, tremendous rains fell in a very short time. NWS automated observations measured nearly one inch of rain in ten minutes. The heavy rains produced minor stream flooding across Nueces county where as much as 2 inches of precipitation had fallen.

Photo of Damage to San Pedro Middle School in Robstown - Taken by Jason Dunn (NWS)

Why Did it Happen?

The severe weather event developed as a result of a strong upper level disturbance and an associated Pacific cold front moving across South Texas from Mexico. Warm moist air near the surface was over run by cold air aloft, creating an unstable environment. Temperatures at 25,000 feet were measured as cold as -20 Celcius, cold enough to support large hail. In addition, a strong upper level jet stream was in place to enhance the lift in the atmosphere, enough to produce severe thunderstorms.