textproduct: Brownsville/Rio Grande Valley

KEY MESSAGES

Updated at 212 PM CDT Sat Apr 4 2026

Key Messages:

* Cold front passes through Deep South Texas from northwest to southeast from late this afternoon/early this evening into the early/mid morning hours tomorrow, bringing showers and thunderstorms continuing through tomorrow night.

* The Storm Prediction Center (SPC) has highlighted a Marginal Risk (Level 1/5) of isolated severe thunderstorms along/west of US-281, with the primary concerns being large hail and damaging winds.

* The Weather Prediction Center (WPC) includes all of our County Warning Area (CWA) within a Marginal Risk (Level 1/4) of isolated flash flooding for tonight and tomorrow.

* 1 to 3 inches of rain are likely tonight through Sunday night, with the highest chances across the Rio Grande Plains and Upper RGV, where rainfall totals may exceed 3 inches.

* A medium risk of rip currents continues through tomorrow afternoon and marine/coastal conditions are likely to become adverse tomorrow and into the beginning parts of next week.

DISCUSSION

Issued at 212 PM CDT Sat Apr 4 2026

The main driver of the impending unsettled weather is a cut-off low and potent surface low pressure system moving eastward across the Upper Midwest, extending a cold front southwestward, moving into South Texas throughout this afternoon. Ahead of the front, lower level southeasterly flow maintains moisture and warm air advection into the region today, with temperatures maximizing in the mid/upper 90s, which adds to the instability across the CWA, with SBCAPE values ranging from around 1,000-2,500+ J/Kg into the early evening hours, per the RAP. Meanwhile, instability aloft enhances ahead of a mid-level disturbance approaching from the west, increasing MUCAPE to upwards of 1,000 J/Kg, likely surpassing 2,000 J/Kg along/west of US-281, where thermodynamic profiles further suggest mid-level lapse rates of 6.5 deg C/Km and inverted Vs despite weaker shear; as the front arrives into the northern and western portions of the CWA later this afternoon or early evening, moisture pooling combines with instability and enhancing frontal lift to result in scattered to numerous showers and thunderstorms. In consideration of the convective parameters discussed above, CAMs continue to suggest a growing likelihood of embedded isolated strong to severe thunderstorms this evening and into the early nighttime hours tonight along and west of US-281, where SPC has included a Marginal Risk (level 1/5) for isolated large hail and damaging wind gusts in excess of 60 mph. The severe risk is likely to steadily drop off through the overnight hours as instability and mid-level lapse rates decrease. If the front arrives earlier and/or pushes through faster within this time frame, the chance of severe thunderstorms could be maximized whereas a later and slower arrival could delay and/or minimize severe potential. CAMs still indicate a lower chance of embedded isolated strong storms, with the potential for small hail and stronger gusts, east of US-281 and into Lower RGV into the late night and early morning hours tomorrow.

Along with the potential for strong to severe thunderstorms is the expected heavy rain spreading east-southeastward across the remainder of Deep South Texas overnight tonight as rain chances increase to as much as a medium to likely (60-80%) chance late tonight through most of Sunday night. WPC includes all of our region within a Marginal Risk (level 1/4) for isolated flash flooding for tonight and tomorrow; CAMs are in agreement with the most torrential rainfall shifting from northwest to southeast from late this afternoon or early evening into tomorrow morning ahead of and along the frontal boundary, with the most prolific rainfall rates occurring further west. Yet, as the mid-level disturbance passes through late tonight and into tomorrow, further rounds and/or training of moderate to heavy rainfall is likely. Further west, the sudden onset of heavy rain and rapid runoff draws attention to a more critical risk of flask flooding, particularly in the hillier regions of Zapata and Starr County, which was impacted severely by flooding rains last month. Further east and across the more flat and populated areas, the greater concern is for hydroplaning and minor nuisance flooding of low-lying areas along with isolated instances of flash flooding. By Monday morning, most of the region is likely to have received near at least 1 inch of rain, with 2-3 inches across western portions of the Northern Ranchlands, the Rio Grande Plains and Upper RGV. At this time, the NBM still indicates a 30-40% chance of at least 2 inches of rain along/east of US-281 and a 40-70% chance further west, highest across western portions of the Northern Ranchlands, Rio Grande Plains and the Upper RGV, where there is a 15-30% chance of totals surpassing 3 inches by Monday morning.

Following, chances of rain gradually decrease across much of Deep South Texas on Monday, though coastal troughing and additional weaker mid-level disturbances could keep a low (15-30%) chance of rain across portions of the RGV and near/along the immediate coastline into Wednesday. Additional shortwaves aloft may bring further low (15-30%) chances of rain across the region into the later parts of next week as well, though confidence is low to medium at this time. Temperatures gradually increase from the 60s/70s tomorrow and Monday back to the 80s by Wednesday as clouds decrease and southeasterly winds return. Overnight lows also warm from the 50s tomorrow night and Monday night back to the 60s by Wednesday night.

A medium risk of rip currents continues through tomorrow afternoon and coastal conditions are likely to become adverse tomorrow and into the beginning parts of next week.

AVIATION

(18Z TAFS) Issued at 1236 PM CDT Sat Apr 4 2026

VFR conditions with scattered high clouds and breezy south- southeasterly winds of around 10-15 knots, are expected to continue through late this afternoon, with gusts up to 20-25 knots, occasionally higher, likely. Later this afternoon or this evening, showers and thunderstorms develop ahead of and along a cold front, expected to pass through all terminals and shift winds out of the north to northeast by mid-morning tomorrow, noted in the PROB 30s. As the convection arrives, there is the potential for isolated strong to severe thunderstorms, bringing a low chance of large hail and very strong wind gusts in excess of 55 knots, with the greatest probability being at KMFE during the evening to early nighttime hours. Overnight, convection spreads east to KHRL and then KBRO, where there remains the potential for moderate to strong wind gusts and possibly small hail. Along with these risks is the likelihood for MVFR or IFR ceilings, or lower, as the convection moves through with not much recovery following into the daytime tomorrow.

MARINE

Issued at 212 PM CDT Sat Apr 4 2026

Moderate easterly to southeasterly winds and moderate (3-4 ft) seas continue into the early nighttime hours, when a cold front arrives, passing through into the morning hours tomorrow, bringing fresh to strong northerly to northeasterly winds and moderate (6-7 ft) seas, persisting into Monday; a Small Craft Advisory goes into effect for all Lower Texas coastal waters from 7 AM Sunday until 1 PM Monday afternoon. Winds gradually ease throughout the remainder of Monday afternoon with gentle to moderate northeasterly winds becoming easterly on Wednesday and southeasterly on Thursday. Small Craft Exercise Caution conditions are possible again later next week as a pressure gradient tightens and results in moderate to fresh southeasterly winds and moderate seas.

As the front arrives tonight, there is the possibility of isolated strong thunderstorms into tomorrow morning, with the potential for small hail and stronger wind gusts as chances of rain increase to as much as a medium to likely (60-80%) chance tomorrow. Following, a low (15-30%) chance of rain lingers into much of next week as a result of warm advection showers and additional disturbances aloft.

PRELIMINARY POINT TEMPS/POPS

BROWNSVILLE 70 76 59 69 / 70 90 90 60 HARLINGEN 64 74 55 71 / 70 90 80 50 MCALLEN 66 72 59 70 / 80 90 80 40 RIO GRANDE CITY 60 68 55 66 / 90 90 80 40 SOUTH PADRE ISLAND 71 75 64 70 / 70 90 90 70 BAYVIEW/PORT ISABEL 67 77 59 71 / 70 90 90 60

BRO WATCHES/WARNINGS/ADVISORIES

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