Vigorous energy cycling around a seasonally strong upper level disturbance crashing into Texas brought a final round of potent thunderstorms through much of the Rio Grande Valley during the late night hours of May 10th into daybreak on May 11th. Initial severe thunderstorms and isolated tornadoes pummeled the Coastal Bend and South Texas Plains from Corpus Christi to near Laredo during the evening of the 10th. As night progressed, pockets of colder air behind the initial line pushed its west end southward; just before midnight, this end would link up with individual cells moving off the Sierra Madre west of Zapata County and form a separate, smaller line from Jim Hogg to Zapata County. This line quickly intensified and dumped heavy rain, high winds some large hail, and one confirmed tornado. As the line marched from the Ranchlands into the Rio Grande Valley, it weakened a bit; as the remnants neared the coast before daybreak, individual small rotating storms developed and redeveloped in Cameron County, with several reports of funnel clouds and at least one confirmed tornado in San Benito (just after 3 AM) from a few hours prior to until just after daybreak on the 11th.
While minor flooding was reported across some of the hilly terrain of the Rio Grande Plains, rainfall was more welcome in the Lower and Mid Valley, with many locations between San Benito, Harlingen, and McAllen receiving 1 to 2 inches of soaking.  Frequent to excessive lightning strikes knocked out power to portions of the Rio Grande Valley as the intense storms passed; the lightning caused one structure fire in Pharr.

Lightning in HIDALGO, TEXAS
From 11-MAY-12 03:05:00 to 11-MAY-12 03:20:00 (CST-6)
Location: MC ALLEN
Property damage: 15.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Frequent to excessive lightning struck McAllen and Pharr as an individual strong thunderstorm followed the initial line of activity.  The City of McAllen reported 4,200 customers without power during the peak of the storm. Lightning caused a structure fire just east in Pharr and knocked out power to some residents of the city.

Hail in JIM HOGG, TEXAS
From 10-MAY-12 22:25:00 to 10-MAY-12 22:28:00 (CST-6)
Location: RANDADO
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Jim Hogg County Sheriff's Office reported quarter size hail in Randado.

Thunderstorm Wind in ZAPATA, TEXAS
From 10-MAY-12 22:17:00 to 10-MAY-12 22:25:00 (CST-6)
Location: ZAPATA ARPT
Magnitude: 61.00 EG
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter estimated wind gusts of 65 to 70 mph in downtown Zapata at the intersection of 5th and Lincoln Street. Initial report time was 1122 PM CDT; final time range estimated by radar.

Heavy Rain in ZAPATA, TEXAS
From 10-MAY-12 22:15:00 to 10-MAY-12 22:45:00 (CST-6)
Location: ZAPATA
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Heavy rainfall of unknown amount caused minor flooding in the Medina Addition section of the City of Zapata.

Flash Flood in ZAPATA, TEXAS
From 10-MAY-12 22:40:00 to 11-MAY-12 00:30:00 (CST-6)
Location: FALCON RES NORTH
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

The Zapata County Sheriff's Office reported 3 feet of flowing water along U.S. Highway 83 in the vicinity of El Clareno Ranch, about 7 miles south-southeast of the City of Zapata.  The highway was closed from 1140 PM on the 10th until 130 AM on the 11th.  No damage, injuries, or deaths were reported.

Tornado in CAMERON, TEXAS
From 11-MAY-12 02:15:00 to 11-MAY-12 02:16:00 (CST-6)
Location: SAN BENITO MUNI ARPT
Tornado F-scale: EF0
Property damage: 15.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

A mini-supercell thunderstorms dropped a very brief tornado, containing estimated 80 mph winds (high end EF0 on the Fujita Scale) on top of a single family home, causing considerable damage to property at the well built structure.  Damage included:  four sections of cyclone fence bent in different directions around the home; a boat and trailer flipped over, numerous snapped tree limbs in different directions, and other limbs that came from an undetermined tree, barrel-tile roof shingles lifted off, one broken window, and a damaged carport.  Unusual was the singular nature of the damage - striking only this property - with one of the shortest track lengths (a tenth of a mile) one would see on survey.

Hail in ZAPATA, TEXAS
From 10-MAY-12 22:15:00 to 10-MAY-12 22:25:00 (CST-6)
Location: ZAPATA ARPT
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: County Official

Penny to quarter sized hail was reported at two locations in the City of Zapata between 1115 and 1125 PM local daylight time as severe thunderstorms marched across the area.  The first report was an unknown location; the second was at the intersection of 5th Avenue and Lincoln Street.

Lightning in ZAPATA, TEXAS
From 10-MAY-12 22:10:00 to 10-MAY-12 22:20:00 (CST-6)
Location: ZAPATA ARPT
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Frequent to excessive lightning knocked out power to the south half of the City of Zapata during a severe thunderstorm during the late evening of May 10th.

Tornado in JIM HOGG, TEXAS
From 10-MAY-12 22:59:00 to 10-MAY-12 23:59:00 (CST-6)
Location: RANDADO
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Jim Hogg County Sheriff's Office reported tornado briefly touched down at the intersection of Highway 16 and FM 649 in the vicinity of Randado.