textproduct: Brownsville/Rio Grande Valley

KEY MESSAGES

Updated at 1233 AM CDT Sun Apr 12 2026

Key Messages:

* Although forecast confidence is low at this time, there is the potential for a high impact strong to severe weather event for Deep South Texas beginning either late Sunday afternoon or early evening and continuing into the late night hours Sunday night.

* The Storm Prediction Center (SPC) includes a Slight (level 2/5) Risk of scattered severe thunderstorms for northwestern portions of Zapata and Jim Hogg counties as well as a Marginal (level 1/5) Risk of isolated severe thunderstorms for the rest of the County Warning Area (CWA).

* Large (1+ inch) to very large (2+ inch) hail and damaging winds (in excess of 60 mph) are possible within the Slight Risk area while large hail and severe wind gusts are possible within the Marginal Risk zone.

* There remains much uncertainty in total rainfall amounts through Sunday night.

* Above average temperatures and mainly dry and breezy conditions resume Monday morning, leading to a moderate risk of rip currents through Sunday afternoon and likely into much of the upcoming week along with Small Craft Exercise Caution marine headlines.

DISCUSSION

Issued at 1021 PM CDT Sat Apr 11 2026

Overnight tonight into tomorrow, a mid/upper level trough moves east- northeastward across northern and central Mexico, becoming negatively-tilted and centered over northeastern Mexico by Sunday evening. CAMs are in agreement that the combination of surface troughing and modest forcing aloft are likely to produce scattered to numerous intermittent showers, and possibly isolated thunderstorms, across Deep South Texas Sunday morning into the afternoon hours as breezy southeasterly winds (gusts up to 20-25 mph) enhance moisture; rain chances increase southward throughout the day to a low to medium (30-50%) chance by tomorrow afternoon across the Northern Ranchlands and areas along/west of I-69 E as PWATs maximize around 1.7-1.9 in., per the HRRR, which is well above the 90th percentile sounding climatology for this time of the year. Sunday afternoon high temperatures are likely to reach into the upper 80s to near 90 F across the Rio Grande Plains and Upper RGV. Tomorrow afternoon, an approaching dryline and the arrival of the trough over northern Mexico are likely to fire up strong to severe convection across most, or parts, of the Sierra Madre, leading to the potential for a high impact strong to severe weather event for our region either late Sunday afternoon or early evening, continuing into the late night hours. At this time, however, confidence remains low due to the great deal of uncertainty in the coverage and intensity of convection Sunday morning and afternoon leading up to the severe threat tomorrow evening.

The latest deterministic runs of the GFS and other reliable short term high resolution models, such as the RRFS, portray isolated to scattered convection of light intensity during the morning and afternoon hours on Sunday, with surface-based CAPE values ranging from around 1,000-3,000 J/Kg by early evening, highest across the Rio Grande Plains and western portions of the Northern Ranchlands and the Upper RGV, where forecast soundings indicate steep low-level lapse rates of 8.0+ deg C/km, DCAPE values nearing 1,000 J/Kg and inverted V signatures, supportive of severe and damaging winds in excess of 60 mph. This would also be a prime opportunity for the deep convection arriving off the Sierra Madre to take further advantage of steep mid-level lapse rates ranging as high as around 7.6 deg C/Km), MUCAPE values up to 2,500 J/Kg as well as supportive EBWD and bulk wind shear to form large (1+ inch) to very large (2+ inch) hail as well as add to the severe wind potential. Therefore, SPC has included the northwestern half of Zapata and extreme northwestern portions of Jim Hogg counties within a Slight (level 2/5) Risk of scattered severe thunderstorms capable of producing large to very large hail and damaging winds. Meanwhile, SPC encompasses the rest of Deep South Texas within a Marginal (level 1/5) Risk of isolated severe thunderstorms, with the primary threats of large hail and damaging wind gusts. As such, the RRFS shows hail- producing convection congealing along a squall line as it crosses over the US border early late Sunday afternoon or early evening, bringing the potential for wind-driven hail further west before gradually losing strength as the convection moves further east across the CWA and diurnally-driven instability reduces.

However, on the flip side, the RAP and the majority of the HREF members portray isolated to scattered light showers in the morning becoming more scattered to numerous in coverage and moderate in intensity by the late afternoon hours, thus reducing afternoon surface diurnal instability, leading to an earlier onset of evening capping. In such a case, convection initiating off the Sierra Madre would significantly weaken before entering Deep South Texas though strong to isolated severe storms could still be possible west of US- 281, with the greatest chances closer to the US-Mexico border stretching from the Rio Grande Plains to the Upper RGV, where these models still prog steep mid-level lapse rates and supportive shear.

Due to the high amount of uncertainty at this time, expected rainfall amounts are also in question. In general, most of the CWA is likely to receive 0.01-0.05 of an inch of rain from daytime convection on Sunday. Yet, if the RRFS comes to fruition, many areas could receive up to 1 inch, or more, from heavy rain accompanying the strong to severe storms. This scenario could bring the potential for minor nuisance flooding of low-lying areas and hydroplaning on roadways. Yet, for the time being, the NBM only progs a 15% chance of rainfall amounts exceeding 1 inch.

Otherwise, the trough pulls out of the region into the late Sunday night hours, reducing chances of rain to 10% or less, possibly by Monday morning, with dry conditions prevailing through most of the rest of the period. A series of troughs and low pressure systems over the Plains are likely to continue to result in a tightened pressure gradient and breezy conditions, with southeasterly winds gusting to 20-30 mph, or higher, each afternoon. Unseasonably warm temperatures continue and a gradual warming trend increases high temperatures to the low/mid 90s across most inland areas by the later parts of the week while overnight lows fall to the lower 70s. The next chance of rain may be next weekend in association with the passage of another upper level trough.

Breezy southeasterly winds maintain a medium risk of rip currents through Sunday afternoon and are likely to continue into the remainder of the forecast.

AVIATION

(06Z TAFS) Issued at 1233 AM CDT Sun Apr 12 2026

Widespread MVFR stratus and light to moderate southeast winds prevail across Deep South Texas early this morning. Brief periods of IFR ceilings will be possible around sunrise. Otherwise, mainly MVFR ceilings will continue for the next 24 hours. Light southeast winds around 10 knots overnight will increase and become gusty later this morning into the afternoon. Some gusts between 25 to 30 knots will be possible in the afternoon. There is low to medium (20 to 40%) chance of showers and/or thunderstorms by the afternoon, especially west and north of the aerodromes. Will continue to mention a PROB30 for MVFR conditions in convection between 18-20Z for MFE.

MARINE

Issued at 1021 PM CDT Sat Apr 11 2026

Moderate to fresh southeasterly winds and moderate seas are likely to continue throughout the period as a pressure gradient remains tightened across the Lower Texas coastal waters. Small Craft Exercise Caution conditions are possible each afternoon and evening across the Laguna Madre and nearshore Gulf Waters. Chances of rain increase throughout the morning and afternoon hours on Sunday to a low (30%) chance by the evening, with showers and thunderstorms possible through the early nighttime hours. There is a low chance for isolated strong to severe thunderstorms, bringing the possibility of hail and strong winds. Mainly dry conditions return Monday morning.

PRELIMINARY POINT TEMPS/POPS

BROWNSVILLE 84 73 86 73 / 10 10 0 0 HARLINGEN 86 70 88 70 / 20 20 0 0 MCALLEN 89 74 91 74 / 30 20 10 0 RIO GRANDE CITY 89 72 91 73 / 30 30 10 0 SOUTH PADRE ISLAND 79 74 79 73 / 10 10 0 0 BAYVIEW/PORT ISABEL 84 71 85 71 / 10 10 0 0

BRO WATCHES/WARNINGS/ADVISORIES

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