The combination of a weak diffuse front in the vicinity and the passage of a shortwave led to the development of strong to severe thunderstorms that moved across the ranchlands and brush country. Storms produced periods of large hail, gusty winds, and heavy rainfall.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS BRO wrote it up.
The combination of a weak diffuse front in the vicinity and the passage of a shortwave led to the development of strong to severe thunderstorms that moved across the ranchlands and brush country. Storms produced periods of large hail, gusty winds, and heavy rainfall.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Brownsville, TX wrote its last area forecast discussion before the first event at May 21, 2:04 PM CST, 2 hours 51 minutes earlier.
Area Forecast Discussion...CORRECTED National Weather Service Brownsville TX 304 PM CDT Sun May 21 2017 .SHORT TERM (Now through Monday Night): Weak and diffuse front lingers across the ranchlands today and remains in the general vicinity through Monday providing a focus for shower and thunderstorm development. Convection has been minimal so far today, initially limited to right along the front, however daytime heating, instability, and plenty of moisture in place have resulted in a few showers developing further south across the Rio Grande Valley. Expect convective activity to remain in the isolated realm through mid-afternoon. The remainder of the forecast remains tricky, with slightly higher confidence today. Timing and placement remain difficult as we move into this evening and the overnight hours. Strong to severe thunderstorms are possible once again late this afternoon and overnight as a shortwave moves east across northern Mexico and South Texas, allowing convection to organize and move into the region. Model guidance indicates two possible periods of activity. The first across the western counties with discrete cells the develop over northern Mexico and move into the western counties, in particular Zapata County, from mid-afternoon through early evening. Storms have already fired up over Mexico and are moving into Webb County, so this solution seems reasonable and likely. Went ahead and increased POPs for the western counties between 18z and 00Z. High res model guidance continues to suggest that the second and more substantive round of convective activity, a MCS, will move into the western and northern zones between 23z and 03z and pushing east southeast across Deep South Texas and the Rio Grande Valley in the ensuing hours. Exactly how far east it progresses remains difficult to judge. Raised POPs a tad out west and tapered them going east and southward. Forecast soundings continue to show effective shear of 50 to 60 knots, MLCAPE around 2500 J/kg, as well as steepening lapse rates, and drier air moving into midlevels, which could lead to large hail (especially in discrete cells) and gusty damaging winds with any severe storm that develops. Although SRH is marginal, can't rule out an isolated tornado. The best severe threat remains across the northern and western ranchlands (Zapata, Jim Hogg, and Starr counties), where SPC has upgraded the area to Slight Risk. The remainder of Deep South Texas and the Rio Grande Valley remain in a Moderate Risk. In addition to the threat of severe weather, locally heavy rainfall is possible, especially across the western and northern zones, where moisture has pooled along the front. Areas closer to the front and those that see training storms could see possible totals of 2 to 4 inches. Although, flash flooding concerns are minimal at this time, given the recent dry trend, and flash flood guidance values of 4 to 5 inches an hour, ponding of water on roadways and in low spots is possible. Shower and thunderstorm chances continue through Monday night, but are highly dependent of location of front and any small perturbations in the flow aloft. Convective activity will be more scattered, with isolated strong to severe thunderstorms possible across the northern ranchlands, closer to the front. .LONG TERM (Tuesday through Sunday): The broad 500mb trough across the central and eastern portions of the United States will continue to provide unsettled weather across south Texas Tuesday through early Wednesday before the upper level trough sharpens across the east-central U.S. Wednesday. At the surface...a weak cold front will move through the CWA Tues night into early Wednesday. Low to mid level moisture will remain high across the area Tuesday through early Wednesday and this will provide a chance of showers and thunderstorms Tuesday and Tues night before drier air filers into the area Wednesday in the wake of the front. Temperatures will at least be near normal Wednesday before returning to above normal through the rest of the week into the weekend as a 500mb ridge moves across the central U.S. Thursday in the wake of the 500mb trough moving eastward and the subtropical ridge develops across northern Mexico Friday. A weak 500mb shortwave trough is progged to move across west TX Saturday but rain chances will remain well north of the CWA. && .MARINE (Now through Monday Night): Conditions at Buoy 42020 at 2 PM show east winds around ten knots and seas near four feet. A stationary front draped across South Texas and the northwestern Gulf of Mexico will maintain a fairly weak pressure gradient. Light to moderate east winds this afternoon will become southeast overnight tonight and continue through Monday night. Low to moderate seas expected through the period, with a slight upward trend Monday night, as wave heights build slightly across the far offshore Gulf waters. Isolated to scattered showers and thunderstorms are possible through Monday night. Tuesday through Friday...Light south to southeast winds will prevail across the coastal waters Tuesday with low pressure across northeast Mexico. A weak cold front will move through the coastal waters Tues night allowing winds to shift to the north to northeast and increase Tues night into Wednesday. Moderate north to northeast winds will briefly prevail across the western Gulf of Mexico before high pressure moves eastward allowing winds to veer to the southeast Wed night. The pressure gradient will increase across the lower Texas coast Thursday and winds will increase from the southeast across the coastal waters. Moderate to strong southeast winds should prevail across the lower TX coast Thursday and Friday. SCEC to near SCA conditions will prevail across portions of the coastal waters Thursday and Friday. && .PRELIMINARY POINT TEMPS/POPS... BAYVIEW/PORT ISABEL 79 90 77 90 / 30 20 30 30 BROWNSVILLE 79 92 77 92 / 30 20 20 30 HARLINGEN 76 92 75 94 / 30 30 20 30 MCALLEN 79 95 77 96 / 30 30 20 30 RIO GRANDE CITY 77 93 75 98 / 50 30 20 30 SOUTH PADRE ISLAND 79 82 77 85 / 20 20 30 30 && .BRO WATCHES/WARNINGS/ADVISORIES... TX...None. GM...None. && This product is also available on the web at: HTTP://WEATHER.GOV/RGV 58/61
Hazardous Weather Outlook National Weather Service Brownsville TX 340 PM CDT Sun May 21 2017 TXZ248>257-222100- Zapata-Jim Hogg-Brooks-Kenedy-Starr-Hidalgo-Inland Willacy- Inland Cameron-Coastal Willacy-Coastal Cameron- 340 PM CDT Sun May 21 2017 This Hazardous Weather Outlook is for portions of Deep South Texas. .DAY ONE...Tonight THERE IS A MODERATE RISK OF RIP CURRENTS AT THE BEACHES OF SOUTH PADRE ISLAND AND AT BOCA CHICA BEACH. SCATTERED THUNDERSTORMS...SOME POSSIBLY STRONG TO SEVERE WITH LARGE HAIL...DAMAGING WINDS...AND HEAVY RAIN WITH FLASH FLOODING...ARE EXPECTED. .DAYS TWO THROUGH SEVEN...Monday through Saturday AN ELEVATED RISK OF RIP CURRENTS IS POSSIBLE AT THE LOCAL BEACHES MONDAY THROUGH WEDNESDAY...AND AGAIN FRIDAY AND SATURDAY. SCATTERED THUNDERSTORMS...SOME POSSIBLY STRONG TO SEVERE WITH LARGE HAIL...DAMAGING WINDS...AND HEAVY RAIN WITH FLASH FLOODING ...ARE EXPECTED MONDAY AND TUESDAY. .SPOTTER INFORMATION STATEMENT... ANY OBSERVATIONS OF LARGE HAIL...STRONG WINDS WITH DAMAGE...AND FLASH FLOODING FROM HEAVY RAIN SHOULD BE REPORTED TO LOCAL LAW ENFORCEMENT AND THE NATIONAL WEATHER SERVICE OFFICE IN BROWNSVILLE. GMZ130-132-135-150-155-170-175-222100- Laguna Madre from the Port of Brownsville to the Arroyo Colorado- Laguna Madre from the Arroyo Colorado To 5 NM north of Port Mansfield TX- Laguna Madre from 5 nm north of Port Mansfield to Baffin Bay TX- Coastal waters from Port Mansfield to the Rio Grande out 20 nm- Coastal waters from Baffin Bay to Port Mansfield out 20 nm- Waters from Port Mansfield to the Rio Grande extending from 20 to 60 nm- Waters from Baffin Bay to Port Mansfield extending from 20 to 60 nm- 340 PM CDT Sun May 21 2017 This Hazardous Weather Outlook is for portions of The Gulf of Mexico and The Laguna Madre. .DAY ONE...Tonight NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .DAYS TWO THROUGH SEVEN...Monday through Saturday SMALL CRAFT ADVISORIES MAY BE NEEDED FOR ALL OR PORTIONS OF THE LOWER TEXAS COASTAL WATERS THURSDAY THROUGH SATURDAY. .SPOTTER INFORMATION STATEMENT... SKYWARN SPOTTER ACTIVATION WILL NOT BE NEEDED.
The Corpus Christi radar (KCRP), 203 km away, was scanning. The volume nearest the first event began at 22:55 UTC.
3 hail, 2 flash flood, 2 thunderstorm wind. Local standard time, as filed.
Employee at Pepe's Grocery Store in San Ygnacio relayed customer report of hail the size of golf balls 5 miles NNE of San Ygnacio.
Public reported via social media quarter size hail in the city of Zapata.
Zapata County Sheriff's Office reported Corralitos area arroyo flooded with water and debris over Highway 83 in the vicinity of San Ygnacio. Radar estimated 3 to 4 inches of rain.
Zapata County Sheriff's Office reported the Medina addition arroyo was flooded with water and there was flooding in the city of Zapata. Radar estimated 3 to 4 inches of rainfall.
Media reported portion of roof blown off of house in Fronton. Several trees were blown down as well. Time estimated via radar imagery.
Public reported half dollar size hail in Fronton.
Starr County Sheriff's Office reported utility pole blown down by thunderstorm winds on Lucianos Road in Escobares. Time estimated by radar.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Texas in 2017Every state in 2017This day in weather historyWarnings in Texas, May 2017
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 703977, 703978, 703982, 703983, 703980, 703981, 703985.