textproduct: Brownsville/Rio Grande Valley

KEY MESSAGES

Updated at 1004 PM CST Sun Jan 4 2026

- Patchy to areas of fog, locally dense, is likely for most of Deep South Texas late tonight through sunrise Monday morning. A Special Weather Statement (SPS) or Dense Fog Advisory may be issued overnight.

- Patchy fog is expected each night/early morning.

- Breezy conditions are likely each afternoon/early evening Monday through Thursday, mainly along and east of US 281/I-69 C, with gusts up to 25-30 mph possible.

- Unseasonably warm temperatures continue into Thursday, with near record to record-breaking afternoon highs in the mid/upper 80s likely.

- A weak cold front Thursday night or Friday is possible.

DISCUSSION

Issued at 1004 PM CST Sun Jan 4 2026

Before getting into the meat of the forecast, would like to discuss the potential for fog tonight as mainly clear skies and light to calm onshore winds continue. While short range hi resolution models are fairly consistent that the majority of Deep South Texas and the Rio Grande Valley will likely see at least patchy fog, there is growing confidence that areas of fog, locally dense (visibilities reduced to a quarter mile or less), could develop across the northern ranchlands and northern portions of the Middle/Lower RGV late tonight through sunrise Monday morning. The probabilities of dense fog in these areas still diverge greatly as SREF holds a 70% chance while HREF only yields a 30% chance. Either way, an SPS or Dense Fog Advisory may be issued if observations and guidance indicate more widespread fog developing. Additionally, patchy fog remains possible each night/early morning throughout the remainder of the forecast.

Tonight, a mid/upper level high pressure shifts southeastward offshore northeastern Mexico, approaching and lingering near the Yucatan Peninsula through midweek, maintaining zonal to west- southwesterly flow and subsidence aloft over Deep South Texas through Wednesday, continuing to result in dry conditions (PoPs less than 10%) through Friday. In the meantime, at the surface, high pressure in control over the Gulf shifts winds from southeasterly tonight to south-southesterly Monday into Thursday. Persistent troughing over the Sierra Madre ahead of mid-level shortwave continues into Thursday as well, leading to a tightening pressure gradient, causing for breezy conditions in the afternoon/early evening hours each day mainly along and east of US 281/I-69 C, where gusts up to 20-25 mph are possible, potentially up to 30 mph on Wednesday. As the shortwave lifts northeastward over western and central Texas on Thursday and the parent trough deepens over the Desert Southwest Thursday night, a weak and dry cold front is expected to move through the region either late Thursday night or during the day on Friday, shifting winds out of the north. The deepening trough passes north of the CWA Friday night and a building surface high over the Southern Plains could send a surge of high pressure or secondary cold front through Friday night or Saturday morning. Chances of rain may increase to a low (15-20%) chance along the coast Saturday into Sunday as northerly to northeasterly winds continue.

A slightly "cooler" airmass (in comparison to last week) and efficient radiational cooling under mainly clear skies tonight is likely to allow for Monday morning lows to reach the upper 50s across the northern ranchlands and 60s for the RGV, which is still nearly 10 degrees above average. As enhanced lower level southeasterly southerly warm air advection returns Monday and persists into Thursday, overnight lows are expected to fall into mainly the 60s while afternoon highs rise into the mid/upper 80s, which is near 15 degrees, or even warmer, above normal. That said, near record to record- breaking highs are likely Monday through Thursday. Behind the front, temperatures could finally fall to near average, most notably by Saturday morning.

AVIATION

(06Z TAFS) Issued at 1004 PM CST Sun Jan 4 2026

Overnight, winds turn south-southeasterly, becoming light or calm. Mainly clear skies and elevated humidity are expected to develop low stratus and/or patchy fog, reducing visibility to 5 SM, or lower, at KHRL and KMFE as well as LIFR/IFR/MVFR ceilings by perhaps 10/11 Z, continuing until perhaps 13/14 Z Monday. Ceilings may only reduce to MVFR at KBRO. Conditions should improve to VFR at all terminals in the morning as southeasterly winds become breezy by the afternoon hours, around 10-15 knots, gusting to 20-25 knots, remaining breezy into the early nighttime hours Monday night.

MARINE

Issued at 1004 PM CST Sun Jan 4 2026

Gentle to moderate easterly winds and slight (1-2 feet) seas shift to southerly by Monday morning, enhancing to mostly moderate with slight to moderate (2-3 feet) seas by Monday evening, continuing through Wednesday morning. Small Craft Exercise Caution (SCEC), possibly even Small Craft Advisories headlines, are anticipated Wednesday afternoon into Thursday as a locally enhanced pressure gradient tightens, leading to moderate to fresh southerly winds and moderate (3-5 feet) seas. Winds diminish briefly Thursday evening, shift out of the north Thursday night or Friday as a weak cold front passes through, with moderate seas continuing. A secondary cold front or surge of high pressure may re-enhance winds and seas Friday night into Sunday. Chances of rain increase to a low to medium (20-40%) chance over the weekend.

PRELIMINARY POINT TEMPS/POPS

BROWNSVILLE 63 83 67 84 / 0 0 0 0 HARLINGEN 60 84 64 86 / 0 0 0 0 MCALLEN 63 86 66 88 / 0 0 0 0 RIO GRANDE CITY 60 87 62 86 / 0 0 0 0 SOUTH PADRE ISLAND 67 76 69 77 / 0 0 0 0 BAYVIEW/PORT ISABEL 62 81 66 83 / 0 0 0 0

BRO WATCHES/WARNINGS/ADVISORIES

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