textproduct: Brownsville/Rio Grande Valley

KEY MESSAGES

Updated at 1037 PM CDT Wed May 6 2026

Key Messages:

* Although the risk is conditional at this point, the Storm Prediction Center (SPC) has introduced a Marginal Risk (Level 1/5) of isolated severe thunderstorms late tonight along/west of US-281, with the primary threats being large (1+ inch hail) and damaging winds (in excess of 60 mph).

* The Weather Prediction Center (WPC) maintains a Marginal Risk (Level 1/4) of isolated flash flooding along/west of US-281 on Thursday and across the Northern Ranchlands and northern half of Zapata County on Friday.

* A medium risk of rip currents continues through Thursday afternoon.

* Minor to Moderate Heat Risks (Levels 1/4 and 2/4) continue Thursday through Sunday as afternoon heat indices range from 95-105 F, followed by a Minor Heat Risk Monday through next Wednesday behind a weak cold front Sunday night.

DISCUSSION

Issued at 1037 PM CDT Wed May 6 2026

At the time of this writing, 7:18 PM, a very unstable and warm airmass continues over Deep South Texas, with surface based CAPE values ranging from near 4,000-5,000+ J/kg and a cap beginning to form across the Lower Texas coastal counties, the RGV and the Rio Grande Plains. A surface high pressure building over the Central and Southern Plains in wake of a departing mid/upper level trough has already pushed a cold front southward through San Antonio and is expected to begin moving into our region late tonight into Thursday morning. The latest runs of the RAP and the HRRR, which are capturing a relatively accurate depiction of the atmosphere across the region and upstream, are indicating that frontal lift and forcing aloft will aid in the development of showers and thunderstorms over the Sierra Madre as the front arrives to the Northern Ranchlands. In the meantime, a capping inversion is anticipated to spread across the CWA along with a weakening steering 700 mb flow, thus likely keeping the strongest convection west and southwest of the US-Mexico border as storms slow forward movement and weaken when arriving to the cap, leaving the possibility of showers and sub-severe thunderstorms across mainly the Upper RGV, Rio Grande Plains and the Northern Ranchlands. However, should shear and winds aloft remain elevated and the front move faster, MUCAPE values of around 2,000-3,500+ J/kg, mid- level lapse rates nearing 7-8+ C/km and 2,000-3000+ J/kg surface- based CAPE could lead to isolated strong to severe thunderstorms along/west of US-281, where capping could be breached in a few areas. In this conditional scenario, isolated large (1"+) hail and damaging winds in excess of 60 mph would be possible. Therefore, SPC has included all of Zapata, Jim Hogg, Brooks and the northwestern half of Brooks counties within a Marginal Risk of isolated thunderstorms.

Whether or not this event materializes could further play a role on showers and potential thunderstorm development during the day Thursday and/or Thursday night as embedded disturbances within southwesterly flow aloft ahead of an upper level low could lead to upper level divergence and additional convection. Currently, we anticipate chances of rain to gradually increase from a low to medium (20-50%) chance of rain on Thursday and Thursday night to as much as a medium to likely (40-70%) chance Friday night, when a 700 mb trough moves through. Although mid-level moisture may be borderline too dry, lower level relative humidity of 80-90%+ is likely during this timeframe. Therefore, training of showers could lead to a risk of isolated flash flooding, though minor nuisance flooding and hydroplaning are the bigger concerns, especially if heavy rain develops quickly or rain continues over areas for a prolonged period of time. As such, WPC highlights a Marginal Risk of isolated flash flooding for most areas along/west of US-281 on Thursday and the Northern Ranchlands and northern Zapata County on Friday. The risk of any additional round of isolated to severe thunderstorms is still up in the air, though the GFS still inconsistently advertises a low risk near the Rio Grande Plains and the Northern Ranchlands Thursday night. Either way, by Saturday morning, areas along/west of I-69 E could receive 0.3-0.7 of an inch of rain, with some areas in the Rio Grande Plains receiving up to an inch of rain. The latest NBM probabilitistic guidance suggests a 20-30% chance of the entire region receiving at least 1 inch of rain and a 30-40% chance for some areas along/west of US-281. This is a downward trend in comparison to this afternoon. Finally, there is a low to medium (20-40%) chance of rain on Saturday before diminishing as the trough pulls out of the region.

Temperatures in the 80s on Thursday rise to the upper 80s/lower 90s on Friday and Saturday, then warming to widespread 90s on Sunday as southeasterly winds return. Minor to Moderate Heat Risks are anticipated through Sunday as afternoon heat indices generally range 95-105 F. Embedded mid-level disturbances within ridging over the western US and building surface high over the Plains push a weak cold front into Deep South Texas Sunday night or Monday morning, cooling temperatures back to the 80s/90s into the middle of next week. Drier air behind the front could keep a Minor Heat Risk Monday into next Wednesday.

A medium risk of rip currents continues through Thursday afternoon.

AVIATION

(00Z TAFS) Issued at 700 PM CDT Wed May 6 2026

MVFR ceilings are anticipated to develop over all terminals tonight around or shortly after sunset, becoming IFR at KHRL and KBRO possibly by 06Z. Hourly convective guidance is beginning to change to show a signal for some showers and thunderstorms developing overnight, with the better chances for KMFE. Have left out of the TAFs for the time being but expect to make some adjustments for the 06Z TAFs should expectations grow and/or remain consistent. Cold front moves through late tonight, shifting winds out of the northeast into tomorrow. Ceilings gradually improve to MVFR by late morning and VFR by the afternoon. PROB30s are also possible tomorrow morning if not late tonight.

MARINE

Issued at 1037 PM CDT Wed May 6 2026

Gentle southeasterly winds and slight to moderate (2-4 ft) seas early tonight increase to moderate to fresh northeasterly winds and moderate (3-5 ft) seas, with SCEC headlines possible, late tonight with the arrival of a cold front, persisting into Thursday night. Gentle to moderate southeasterly winds resume on Friday along with moderate (3-5 ft) seas. Moderate northeasterly winds and moderate seas are likely again behind a weak cold front Sunday night or Monday morning, returning back to gentle to moderate southeasterly winds by the middle of next week. A low to medium (20-40%) chance of rain continues through Saturday.

PRELIMINARY POINT TEMPS/POPS

BROWNSVILLE 79 86 78 90 / 0 20 40 30 HARLINGEN 77 83 75 91 / 0 30 50 40 MCALLEN 78 84 75 92 / 10 40 60 40 RIO GRANDE CITY 77 85 73 90 / 10 40 60 30 SOUTH PADRE ISLAND 78 80 78 84 / 0 20 40 30 BAYVIEW/PORT ISABEL 78 82 77 89 / 0 20 50 30

BRO WATCHES/WARNINGS/ADVISORIES

TX...None. GM...None.