textproduct: Brownsville/Rio Grande Valley

KEY MESSAGES

Updated at 524 AM CST Sat Dec 13 2025

* Fog, mist, low stratus possible again tonight. * Warmer than normal temperatures and mainly rain-free weather will prevail through next week. * Our next best chance for rain will be on Sunday in response to a cold front; medium (40-60%) chances on Sunday.

* Another chance for showers and storms will be Tuesday night into Wednesday.

* Hazardous marine and coastal conditions are expected to develop on

DISCUSSION

Issued at 1105 PM CST Fri Dec 12 2025

The forecast period for Deep South Texas and the Lower Rio Grande Valley will continue to consist of warmer than normal temps with a couple chances for rain, though there will be many rain-free hours.

Tonight will be similar to last night as far as the potential for fog, mist, and/or low stratus development. However, the thickness and coverage of any fog is not expected to be as great as last night due to slightly wider dewpoint depressions and the potential for some clouds to develop later tonight. The HREF model is indicating a general low-medium (30-60%) chance/risk for fog/mist developing across much of Deep South Texas and the Rio Grande Valley tonight. Otherwise, expect for a quiet night under mostly clear skies and milder than normal temperatures.

As highlighted earlier, much of the forecast period will be dry/rain- free. However, Sunday will feature our next best and widespread chance for showers and maybe a rumble of thunder to develop. Forecast models/ensembles continue to advertise a strong southward advancing cold front approaching the region on Sunday. This cold front is associated with an Arctic 1040-1045 mb sfc high pressure system that will be established over the Midwest U.S. As this happens, the combination of increased sfc convergence and a nearby weak shortwave trough will increase the prospects for showers (maybe an isolated thunder or two) to develop over the region on Sunday. We've maintained medium (40-60%) chances for showers across Deep South Texas on Sunday. Rain chances diminish from north to south as the cold front sweeps through the region and shifts into northeastern Mexico Sunday evening/night.

Tuesday night into Wednesday is another period that we have to monitor for the potential for showers and thunderstorms. During this time period, a return flow out of the south on the backside of a broad sfc high pressure system centered over the Southeastern U.S. will result in increased moisture and warm air advection (WAA). Increased atmospheric moisture content interacting with a nearby shortwave trough or weak frontal boundary will result in increased prospects for showers and thunderstorms Tuesday night into Wednesday. Currently, we only have low grade (20-30%) PoPs along and east of IH-69E. Again, we will continue to monitor these trends in the days ahead.

Through the middle parts of next week, an up, down, up (roller- coaster) temperature pattern will take place. However, late next week into next weekend, the cold and wintry weather across the northern U.S. begins to retreat northward into Canada as flat ridging (low amplitude 500 mb pattern) envelopes a vast majority of the Lower 48, marking a major large scale weather pattern change towards the milder, less wintry side. For us here in Deep South Texas, this means a stabilized, warmer than normal pattern will solidly be in place with less risk of cool frontal passages and less fluctuations in temperatures.

Overall, temps will average out warmer than normal for the balance of the forecast period with daytime highs in the 80s most locations each day except for Sunday through Tuesday. Ahead of the cold front on Sunday, high temperatures will top out in the 70s most places (lower 80s along parts of the RGV). Monday is progged to be the coolest day of the forecast period with daytime highs struggling to make it out of the 60s. Finally, on Tuesday, temperatures will begin to moderate as daytime highs are expected to climb back into the 70s most places. Wednesday through at least next Saturday, above normal temperatures will be driven by a 585-588 mb ridge. Overnight low temperatures will mainly be in the 60s during the forecast period. Sunday night into Monday will be the coolest with overnight lows in the 40s across the Northern Ranchlands and 50s along the RGV. Monday night into Tuesday, overnight lows will be in the 50s most places.

AVIATION

(12Z TAFS) Issued at 524 AM CST Sat Dec 13 2025

LIFR conditions are prevailing at the aerodromes right now, likely the result of MIFG, as observational cameras provided by TXDOT show the fog to be highly localized. After sunrise, VFR will be in place until a re-formation of fog occurs after sunset tonight.

MARINE

Issued at 1105 PM CST Fri Dec 12 2025

Favorable marine conditions with low to moderate winds and seas will persist through Saturday night. On Sunday, marine conditions deteriorate with Small Craft Exercise Caution (SCEC) to Small Craft Advisory (SCA) conditions developing in response the aforementioned cold front. These conditions will persist through Monday/Monday evening before showing some improvements and a return to low to moderate seas and winds. There will be near day- to-day chances for showers and storms over the Gulf Waters tonight through Wednesday.

PRELIMINARY POINT TEMPS/POPS

BROWNSVILLE 83 68 80 58 / 10 10 60 30 HARLINGEN 84 63 77 52 / 10 10 50 20 MCALLEN 85 67 79 53 / 10 10 60 20 RIO GRANDE CITY 84 65 77 51 / 0 10 70 30 SOUTH PADRE ISLAND 76 69 74 61 / 30 10 70 30 BAYVIEW/PORT ISABEL 81 65 77 57 / 20 10 60 20

BRO WATCHES/WARNINGS/ADVISORIES

None.