The leading edge of a slow moving upper level disturbance across the southwest U.S. induced thunderstorms across the Sierra Madre Oriental during the early morning hours of May 8th. These storms moved into the Rio Grande Plains toward noon, then linked up with additional lift from an approaching wind shift line drifting south from the South Texas Plains. Feeding on a very unstable atmosphere  - cold and dry air well above the earth���s surface - initial storms would slam Zapata County during lunchtime with damaging wind, large hail, flooding rain, and frequent lightning. As the afternoon progressed, increasing contrast between cooler air across the South Texas Plains (60s and 70s) with the last of the early May heat in the Rio Grande Valley (90s) set the stage for additional storms with damaging winds and flooding rain in Zapata, and culminated with a monster supercell thunderstorm which cruised from southwest Brooks County through Raymondville before weakening.
This impressive supercell storm dominated the episode, and produced a measured instantaneous wind gust over 100 mph in rural Hidalgo County. Fortunately for the populated middle Valley, where more than 700,000 persons are at risk, this cell slid through northern Hidalgo County north of the SR 186 and U.S. 281 interchange, and accelerated through the Lower Rio Grande Valley National Wildlife Refuge northeast of Linn and San Manuel before reaching Raymondville (Willacy County). The cell quickly weakened by the end of dinner hour (6 to 7 PM CDT) before reaching the Laguna Madre and Gulf of Mexico.

Hail in ZAPATA, TEXAS
From 08-MAY-12 14:20:00 to 08-MAY-12 14:25:00 (CST-6)
Location: ZAPATA ARPT
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public reported quarter size hail at the intersection of Lincoln and 5th Street.

Thunderstorm Wind in ZAPATA, TEXAS
From 08-MAY-12 11:00:00 to 08-MAY-12 11:00:00 (CST-6)
Location: SAN YGNACIO
Magnitude: 56.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Zapata County emergency manager reported thunderstorm wind gusts of 60 to 65 mph occurred in San Ygnacio. Three to four homes were reported to have roof damage and one mobile home was destroyed.

Thunderstorm Wind in ZAPATA, TEXAS
From 08-MAY-12 11:35:00 to 08-MAY-12 11:35:00 (CST-6)
Location: ZAPATA ARPT
Magnitude: 54.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

AWOS at Zapata reported a 62 mph thunderstorm wind gust.

Heavy Rain in HIDALGO, TEXAS
From 08-MAY-12 15:55:00 to 08-MAY-12 16:25:00 (CST-6)
Location: LINN
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

The Hidalgo County Precinct #4 Constable recorded 4 to 4.5 inches of rainfall across his ranch to the northwest of U.S. Highway 281, approximately 6 miles north of Linn.  High standing water of unknown depth was reported on unpaved roads and in some of the fields.

Flash Flood in ZAPATA, TEXAS
From 08-MAY-12 14:30:00 to 08-MAY-12 14:45:00 (CST-6)
Location: ZAPATA ARPT
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Street flooding with briefly up to 3 feet of moving water near the intersection of Irene and US 83.  Photos also showed urban type flooding at a local park in the city of Zapata, with an estimated 1 foot of water depth.

Thunderstorm Wind in HIDALGO, TEXAS
From 08-MAY-12 16:06:00 to 08-MAY-12 16:12:00 (CST-6)
Location: LINN
Magnitude: 89.00 MG
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Law Enforcement

A semi trailer was blown over on US 281, 6 miles north of TX HWY 186. Driver of semi was injured. Driver stated that he had pulled onto the shoulder due to blinding rain and pelting hail and soon after, the downburst moved the trailer onto the dirt shoulder and then turned over. The trailer was carrying 5 tons of cargo (vacuum cleaners) and at least 200 gallons of diesel, which had to be removed from the scene.
The Precinct Constable, who lives about a mile southwest of the trailer incident, reported numerous asphalt shingles pulled from the northwest facing roof, and one window was blown out. Numerous mesquite trees were snapped or had large healthy limbs broken and healthy ebony and oak trees were also damaged on the ranch. Heavy cable was torn out of a telephone tower (0.2 miles SE of the ranch house) at an estimated height of 200 feet above the ground.
A peak instantaneous wind gust of 102 mph was recorded at a 10 meter temporary wind platform as the microburst surged through.  The same platform recorded 35 minutes of wind gusts to 50 mph or higher; the platform was less than one half mile from the Constable's house.

Thunderstorm Wind in WILLACY, TEXAS
From 08-MAY-12 17:05:00 to 08-MAY-12 17:05:00 (CST-6)
Location: RAYMONDVILLE
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Emergency manager reported winds from 50 to 60 mph in Raymondville.

Thunderstorm Wind in ZAPATA, TEXAS
From 08-MAY-12 14:25:00 to 08-MAY-12 14:26:00 (CST-6)
Location: ZAPATA ARPT
Magnitude: 56.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public reported estimated wind gust of 60 to 65 mph at Lincoln and 5th Street.