textproduct: Brownsville/Rio Grande Valley

KEY MESSAGES

Updated at 211 PM CST Sat Mar 7 2026

Key Messages:

* Much needed rainfall in the form of showers and thunderstorms will increase later this evening/tonight and persist into Sunday; greatest coverage and chances west of IH-69C and over the Northern Ranchlands.

* The Storm Prediction Center (SPC) has maintained the northwestern section of Zapata County under a Slight (Level 2 of 5) Risk for severe thunderstorms, and the Northern Ranchlands and Starr County under a Marginal (Level 1 of 5) for severe thunderstorms. Large hail and damaging winds will be the primary threats.

* The Weather Prediction Center (WPC) has designated all of Zapata and Jim Hogg counties and the western half of Brooks and Starr counties under a Marginal Risk (Level 1 of 4) for Excessive Rainfall for tonight in their latest Excessive Rainfall Outlook (ERO).

* An enhanced pressure gradient ahead of a cool front could result in windy conditions on Tuesday; southerly winds 20-30 mph with gusts topping 40+ mph is possible and a WIND ADVISORY may be needed.

* FIRE WEATHER concerns could increase behind the cool front in the Wednesday through Saturday timeframe as relative humidity (RH) values drop; trends need to be monitored.

* Moderate to at times strong winds will maintain mainly moderate to adverse seas through next week. A Small Craft Advisory (SCA) may be needed at some point.

DISCUSSION

Issued at 211 PM CST Sat Mar 7 2026

Unseasonably warm and at times breezy conditions under a southwest flow aloft regime will persist across Deep South Texas and the Rio Grande Valley through the forecast period or through next week. While mainly dry/rain-free conditions will persist, the prospects for some much-needed rainfall in the form of showers and thunderstorms are expected to increase later this evening/tonight with additional opportunities possible during the early to middle parts of next week. We'll start off this discussion talking about the most immediate weather threats/concerns across the region through tonight and that is 1) the continued windy conditions through this evening and 2) the potential for showers and thunderstorms developing later this evening/tonight, some of which could become strong to severe in addition to producing heavy rainfall.

As of this update, the latest GOES-19 visible satellite imagery depicts a BKN deck of strato-cumulus clouds overhead with the leading edge of clearing beginning to take place far west over Zapata and Starr counties. As clearing continues to translate eastward, expect for cloud coverage and heights to improve slightly from this morning for a brief period this afternoon, before cloud coverage increases and lowers in elevation once again later this evening/tonight. An enhanced pressure gradient, driven by a weak low/shortwave trough to our west over the Sierra Madre and high pressure over the Gulf Waters, a low level jet (LLJ) overhead (though not as strong as yesterday) with max speeds between 20-30 kts, combined with local topographical effects has maintained the "Valley Wind Machine" over the region today with southerly winds gusting as high as 30-35 mph. Expect for these winds to persist through this afternoon before waning some later this evening after sunset as mixing heights decrease and the LLJ shifts east over the Gulf Waters.

Attention shifts towards the increased prospects some much needed rainfall in the form of showers and thunderstorms later this evening/tonight across Deep South Texas and the Rio Grande Valley. A broad and strengthening sub-550 mb low pressure system near or just off the Baja Peninsula has activated the southern branch jet or sub-tropical jetstream (STJ) in what is a split-flow regime over the Lower 48. Global deterministic models and hi-res CAMs continue to depict showers and thunderstorms developing later this evening/tonight. Sfc-based initiation is expected to begin anywhere from the Sierra Madre to our western areas (i.i along and west of IH-69C) between the hours of 6-9 PM CST. A southeastward advancing cool front that is expected to stall just to our north in the Corpus Christi area coupled with several mid- upper shortwaves/energies tracking along the sub-tropical jet overhead, and diffluence aloft will be amongst the mechanisms to trigger the development of showers and thunderstorms during this 6-9 PM CST period.

Given the more favorable atmospheric conditions, and recent model trends/observations, the probability, placement, coverage, and severity of storms will be greatest along and west of IH-69C and over the Northern Ranchlands. Mid-Lower Valley and areas near/along the coast will be less. The greatest uncertainty will be the downstream momentum from storms further upstream making it further east (i.e. east of IH-69C). Capping will be a limiting factor east of IH-69C as well. That said, for tonight, we have categorical PoPs along and west of IH-69C and over the Northern Ranchlands. Low-medium (20-50%) chances east of IH-69C and much of Kenedy County.

As far as severe weather, SBCAPE values between 1,000-2,000 J/kg and MLCAPE values between 500-1,000 J/kg are amongst some of the items that would support the risk for thunderstorms reaching strong to severe limits. Once again, the best coverage and chances for showers and strong to severe storms will be west and north. That's where the 0-6km bulk shear values and Showalter values are higher, and overall the jet dynamics are also better. Capping further to the east- southeast may limit coverage and severity here in the mid-lower valley towards the coast. That said, the Storm Prediction Center (SPC) has maintained the northwestern section of Zapata County under a Slight Risk (Level 2 of 5) for severe thunderstorms, the Northern Ranchlands and Starr County under a Marginal Risk (Level 1 of 5) for severe thunderstorms and the Rio Grande Valley under a general risk for thunderstorms through tonight in it's latest SWODY1. Large hail and damaging winds remain the primary threats.

Despite the long-term drought that's been in place, these storms will be capable of producing heavy rainfall which can result in localized flooding, courtesy of an increased influx of atmospheric moisture content with precipitable water (PWAT) values ranging between 1.5-1.8 inches. Any flooding that take place will largely be in situations where storms are slow moving and tracking over the same areas. The Weather Prediction Center (WPC) has designated Zapata and the western half of Jim Hogg and Starr counties under a Marginal Risk (Level 1 of 4) for Excessive Rainfall for tonight in their latest Excessive Rainfall Outlook (ERO).

Despite the threat for excessive rainfall/flooding, the rain will be seen as beneficial. It's been nearly 3 months (since mid- December) in which we've seen rain of 0.25 inches or more across the region. Before mid-December dating back to last October, rainfall has been far and few in between. This dry spell that we've been in has been quite remarkable. The latest drought information from the U.S. Drought Monitor shows drought conditions deepening and expanding across Deep South Texas and the Rio Grande Valley with 71% of our county warning area (CWA) now under a D3 (Extreme Drought) to a D4 (Exceptional Drought), with Exceptional Drought encompassing all of Jim Hogg, most of Brooks, eastern Zapata, and far northern Starr counties. So, the bulk of the rain that's to come will be falling across areas that need it the most.

According to some models, it's possible that showers and storms will continue through the overnight tonight into Sunday morning spreading eastward across the remainder of the area including mid- lower valley with the potential for additional development during the day. For Sunday, we have categorical chances for much of Deep South Texas. Medium (40-50%) chances for Cameron County, central/eastern Willacy County, and southeastern Kenedy County, the barrier island, and Gulf Waters. Any storms that develop Sunday afternoon through Sunday evening are not expected to become severe at this time. For Sunday evening/night, we have low- medium (20-50%) chances for much of the region (lowest east). Categorical chances for Zapata and the western half of Jim Hogg and Starr counties.

A reprieve from any rain takes place Monday through Tuesday. On Tuesday, an enhanced pressure gradient ahead of an approaching cold front will result in the return of windy conditions. South-southeast winds 20-30 mph could gusts as high as 40-45 mph and a WIND ADVISORY may be needed on Tuesday. Will continue to monitor these trends. During this timeframe (early to mid next week), forecast models and ensembles continue to advertise a formidable low pressure system near or just off the coast of the Baja Peninsula translating eastward across northern Mexico into Texas. As the parent energy moves over Texas with additional impulses tracking overhead, there could be additional chances for showers and thunderstorms early to mid next week that we have to keep an eye on. The best chances will be placed further to our north across central Texas due to stronger forcing and jet dynamics. Currently, we have low-medium (20-40%) chances. Greatest over the Northern Ranchlands and west of IH-69C. A cold front will be associated with this low pressure system and is progged to push through Deep South Texas in the Wednesday-Thursday timeframe. Fire weather concerns may increase and need to be monitored Wednesday through Saturday behind the cool frontal passage due to lower relative humidity (RH) values.

Temperature anomalies through next week will remain above average with positive geopotential heights and a southwest flow aloft regime in place. High temperatures will run in the upper 80s to 90s most days with overnight lows in the 60s/70s. The exception will be on Sunday due to the combination of clouds, a rain-cooled atmosphere and maybe additional chance for showers and storms. Highs on Sunday are expected to top out in the upper 70s northwest (i.e. Zapata County) to the mid-upper 80s along mid to lower valley. Highs will also be lower, but still above average on Thursday and Friday behind the cool fropa. Highs on Thursday and Friday will top out in the 80s most places with overnight lows mainly in the 50s.

AVIATION

(18Z TAFS) Issued at 211 PM CST Sat Mar 7 2026

Through 18z Sunday....Main weather concerns to aviation operations for the local terminals through the 18z TAF period will be the strong southerly winds through this evening, the re-emergence of MVFR to IFR cigs later this evening/tonight, and the chance for showers and thunderstorms late tonight into Sunday.

As of 11:50 AM CST, GOES-19 visible satellite imagery and sfc observations depicted a BKN strato-cumulus deck of low VFR to high MVFR clouds over the region with ceilings ranging between 2,500- 3,500 feet AGL and unrestricted visibilities. Over the next 6-9 hours, expect for cloud coverage and heights to improve slightly with a brief period of VFR cigs developing this afternoon, before cloud coverage begins to increase and lower in elevation later this evening/tonight. Later this evening/tonight, MVFR-IFR cigs are expected to develop.

Additionally, showers and thunderstorms are possible late tonight into Sunday in response to a slowing or stalled out cold front to our north and mid-upper level shortwaves/energies tracking overhead. While the best chances, coverage, and severity of storms are favored west of IH-69C, there is a low-medium (20-50%) chance for areas east including all of the terminals tonight into Sunday. Capping or elevated convective inhibition (CIN) values is a limiting factor for areas east, including the terminals for tonight.

Have introduced Prob30 groups for shower and thunderstorm potential for the terminals from 06z-18z/Sunday. Any showers or storms that move over the terminals will have the capabilities of reducing cigs/vsbys into the IFR-LIFR range with winds briefly becoming variable with speeds up to or greater than 35 kts. Otherwise, expect for dry/rain-free conditons to prevail through tonight with MVFR- IFR cigs around.

The other concern will be the windy conditions through this evening into tonight. Courtesy of moderate to strong low level jet (LLJ) support just above the sfc, southerly winds 15-20 kts gusting 25-30 kts or so will persist through today before waning later this evening/tonight with speeds between 5-10 kts. During the day on Sunday, southerly winds 5-12 kts will persist.

MARINE

Issued at 211 PM CST Sat Mar 7 2026

Moderate to at times strong southerly winds from an enhanced pressure gradient will maintain moderate to adverse seas (i.e. Small Craft Exercise Caution) through next week. A brief period of Small Craft Advisory (SCA) conditions can't be ruled out through next week. Low to medium shower and thunderstorm chances return this weekend and maybe again next week.

PRELIMINARY POINT TEMPS/POPS

BROWNSVILLE 72 86 71 86 / 20 40 20 10 HARLINGEN 69 87 68 90 / 30 50 20 10 MCALLEN 74 89 70 93 / 50 70 40 10 RIO GRANDE CITY 68 82 65 93 / 80 80 60 10 SOUTH PADRE ISLAND 72 78 72 79 / 20 30 20 10 BAYVIEW/PORT ISABEL 70 84 69 86 / 20 40 20 10

BRO WATCHES/WARNINGS/ADVISORIES

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