Animated loop of 1.4 degree reflectivity indicating rapid updraft development and icing, from Raymondville to Harlingen stretching to Weslaco, May 12, 2012
Loop of 1.4° radar base reflectivity between 404 PM and 545 PM across the Lower Rio Grande Valley on May 12th. Note the rapid development of cells in Cameron County, with others forming rapidly near Weslaco (southeast Hidalgo). South moving boundaries from earlier storms near Raymondville triggered the newer development.
7 PM May 12th, 2012 observed atmospheric profile at Brownsville
Atmospheric profile from Brownsville, posted at 7 PM with initial data sampled closer to 6 PM, soon after hailstorms raced through the Lower Valley. Click for larger version. The combination of dry air aloft, a very steep temperature drop with height, and a trigger in the form of a boundary between much drier and much more humid air near the surface aided rapid updraft formation.
Oh, Yes it Did...
...Hail (Again) in portions of the Rio Grande Valley on May 12th 2012

Recap
A little more than a day after a thunderstorm system brought more severe weather to the Rio Grande Valley, the last vestige of very unstable air held forth mainly along and east of Highway 77. Despite unfavorable upper level conditions, the combination of the unstable air with a trigger in the form of a wind shift/dry line which moved within striking distance of Highway 77 allowed a small but potent cluster of thunderstorms to explosively grow initially in northern Willacy County just before 4 PM CDT. These storms would produce south–moving outflows, which added to the dryline trigger. Additional storms would fire in only a half hour, working on the very unstable atmosphere (above right) to increase updraft speed and develop quarter to half dollar sized hail – at least – between west Harlingen and La Feria and points south between 515 and 545 PM. Once again, there was some damage to vehicles caught in the hail, much containing jagged edges. Many residents caught by surprise by the rapid development moved their vehicles under gas station canopies, car washes, and highway underpasses.

A preliminary storm report follows. Note that some times are estimated after reconciliation with radar, and may not match earlier preliminary reports that can be found online.

PRELIMINARY LOCAL STORM REPORT...SUMMARY 
NATIONAL WEATHER SERVICE BROWNSVILLE TX 
731 PM CDT SAT MAY 12 2012  

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON... 
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
             ..REMARKS..  

0406 PM     HAIL             E RAYMONDVILLE          26.48N  97.78W 
05/12/2012  E0.88 INCH       WILLACY            TX   PUBLIC
            NICKEL SIZE HAIL NEAR RAYMONDVILLE ABOUT 2 MILES EAST
            OF HWY 77  

0425 PM     HAIL             1 N RAYMONDVILLE        26.49N  97.78W 
05/12/2012  E1.00 INCH       WILLACY            TX   PUBLIC
            PUBLIC REPORTED QUARTER SIZE HAIL ON NORTH SIDE OF
            RAYMONDVILLE  

0425 PM     HAIL             7 N RAYMONDVILLE        26.58N  97.78W 
05/12/2012  E1.00 INCH       WILLACY            TX   EMERGENCY MNGR
            EMERGENCY MANAGER REPORTED QUARTER SIZE HAIL NEAR
            YTURRIA  

0434 PM     HAIL             RAYMONDVILLE            26.48N  97.78W 
05/12/2012  M0.88 INCH       WILLACY            TX   BROADCAST MEDIA  
            PUBLIC VIA BROADCAST METEOROLOGIST REPORTED NICKEL SIZE
            HAIL AT THE CORNER OF 1ST AND TAMPICO  

0500 PM     HAIL             RAYMONDVILLE            26.48N  97.78W 
05/12/2012  E1.00 INCH       WILLACY            TX   PUBLIC  
            PUBLIC REPORTED QUARTER SIZE HAIL ON BUS 77 JUST NORTH OF
            RAYMONDVILLE  

0510 PM     HAIL             2 W HARLINGEN           26.20N  97.72W 
05/12/2012  M0.75 INCH       CAMERON            TX   PUBLIC  
            PALM VALLEY RESIDENT REPORTED 5 PALM TREES SET ON FIRE
            BY LIGHTNING.  

0515 PM     HAIL             2 W HARLINGEN           26.20N  97.72W 
05/12/2012  M0.88 INCH       CAMERON            TX   PUBLIC  
            WEST SIDE OF HARLINGEN ALONG HIGHWAY 77 83 REPORTED
            NICKEL SIZE HAIL

0515 PM     HAIL             LA FERIA                26.16N  97.82W 
05/12/2012  E1.00 INCH       CAMERON            TX   PUBLIC  
            PUBLIC REPORTED QUARTER SIZE HAIL NEAR LA FERIA...TIME
            ESTIMATED.             

0520 PM     HAIL             HARLINGEN               26.20N  97.69W 
05/12/2012  M0.75 INCH       CAMERON            TX   PUBLIC  
            PENNY SIZE HAIL AT HARRISON AND HWY 77  

0520 PM     HAIL             HARLINGEN               26.20N  97.69W 
05/12/2012  M0.75 INCH       CAMERON            TX   AMATEUR RADIO  
            PENNY HAIL RELAYED BY HAM OPERATOR FROM GENERAL PUBLIC  

0525 PM     HAIL             3 W HARLINGEN           26.20N  97.73W 
05/12/2012  M1.00 INCH       CAMERON            TX   PUBLIC  
            NICKEL TO QUARTER SIZE HAIL AT ALTAS PALMAS AND HWY 83  

0532 PM     HAIL             2 W HARLINGEN           26.20N  97.72W 
05/12/2012  M1.00 INCH       CAMERON            TX   PUBLIC  
            RELAYED REPORTED FROM SPOUSE OF NWS EMPLOYEE. QUARTER
            SIZE HAIL BROKE CAR WINDSHIELD ALONG HWY 83 WEST SIDE OF   
            HARLINGEN  

0532 PM     HAIL             HARLINGEN               26.20N  97.69W 
05/12/2012  M1.00 INCH       CAMERON            TX   EMERGENCY MNGR  
            CAMERON COUNTY EM HUMBERTO BARRERA REPORTED QUARTER  
            SIZE HAIL AT COUNTY ROAD 800 AND RANGERVILLE RD.    

0540 PM     HAIL             6 SE LA FERIA           26.09N  97.77W 
05/12/2012  M1.00 INCH       CAMERON            TX   TRAINED SPOTTER  
            SKYWARN SPOTTER NEAR REPORTED QUARTER SIZE HAIL NEAR  
            RANGERVILLE. TIME ESTIMATED BY RADAR.
            


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