textproduct: Brownsville/Rio Grande Valley

KEY MESSAGES

Updated at 554 PM CST Sat Dec 13 2025

* A cold front approaches tonight and passes early Sunday, with dense fog expected tonight, a low to medium chance of rain Sunday, and cooler temperatures into Tuesday morning. * Hazardous beach, surf, and marine conditions are expected Sunday into Monday.

* Warmer than normal temperatures return mid next week.

DISCUSSION

Issued at 1234 PM CST Sat Dec 13 2025

A persistent trough of low pressure with a series of winter systems works through the Great Lakes and New England through next week. Closer to home, the next 500mb trough is now expected to drop from Baja Cali down the western coast of Mexico through the week. At the surface, expect a warm day today, with above normal temperatures, and a very humid and potentially foggy night as the next front heads south. A Dense Fog Advisory may be needed, with current probabilities over 60 percent for visibilities to drop below one-half mile between 2 AM and 8 AM.

Have leaned further into the NAM guidance, since it is generally the undisputed model for shallow cold air events, and we may need to nudge temperatures cooler yet for Sunday through Tuesday. Rain chances have trended drier once again, with an earlier arrival of the front, now Sunday morning taking some instability back out of the equation. A weak coastal trough sets up behind the front and continues light rain or drizzle along the coast through early Monday morning.

Beach conditions are expected to deteriorate by Sunday afternoon, with a high risk of life-threatening rip currents, elevated surf, and narrow beaches during high tide Sunday evening.

AVIATION

(00Z TAFS) Issued at 554 PM CST Sat Dec 13 2025

Key Aviation IDSS Messages:

* IFR-VLIFR conditions are possible again tonight due to fog (possibly dense), mist, and/or low stratus.

* Strong cold front arrives Sunday morning from north to south; winds will shift out of the north and become blustery late morning through the afternoon hours. Northerly winds could gusts as high as 25-30 kts.

* Rain showers will be associated with the arrival and passage of the cold front on Sunday.

Over the next 6-9 hours, the main weather concern like the previous couple of nights will be the potential for another round of fog (possibly dense), mist, and low stratus developing. Ahead of an approaching cold front, the environmental conditions this evening/tonight will be very similar to previous nights. That is light winds, mainly clear skies, and copious amounts of low level moisture. Given the persistence in the pattern and expectation of sufficient radiational cooling taking place through this evening, TEMPO groups have been added through tonight at all of the TAF sites to account for the potential for fog/mist/low stratus developing yet again. Any fog or low stratus that develops will have the capabilities of reducing flight categories down to MVFR and eventually IFR-VLIFR levels.

Big changes to the weather pattern is expected to take place over the next 12-18 hours. A strong cold front is expected to push through the region from north to south during the morning hours, resulting in a wind shift out of the north along with the chances for showers beginning mid-late morning and persisting into the afternoon hours. Fog (possibly dense) and low stratus will be ongoing ahead and just behind the cold front. It may take time for the drier air to work its way into the region. That said, it's possible that MVFR-IFR conditions could continue into the afternoon hours.

Overall, expect for flying conditions to deteriorate over the next 6- 9 hours from VFR conditions to MVFR-LIFR conditions (possibly instances of VLIFR conditions) due to fog, mist, and/or low stratus. MVFR-VLIFR conditions are then expected to persist through the remainder of the 00z TAF period with showers possibly accompanying these conditions mid-late morning into the afternoon hours.

South-southeast winds 10-15 kts this evening will weaken and trend towards light and variable to calm tonight. In response to a cold fropa, winds will shift out of the north Sunday morning. An enhanced pressure gradient associated with the cold front will result in northerly winds becoming blustery late morning through the afternoon on Sunday with speeds between 15-20 kts and peak gusts between 25-30 kts. This could impact east-west oriented runways on Sunday.

MARINE

Issued at 1234 PM CST Sat Dec 13 2025

Generally lighter onshore winds will maintain favorable marine conditions into late tonight. A strong cold front approaches Sunday morning, with showers and patchy dense fog late tonight. Northerly winds may gust occasionally to gale force, so will continue to monitor for an upgrade to Gale Warning if gale force wind gusts become more frequent, but have issued a Small Craft Advisory through Sunday night. Conditions begin to improve late Monday, with low to moderate southerly winds and seas through the remainder of the week.

PRELIMINARY POINT TEMPS/POPS

BROWNSVILLE 67 76 54 66 / 10 40 20 10 HARLINGEN 63 76 50 66 / 10 30 10 0 MCALLEN 67 76 51 66 / 0 40 10 0 RIO GRANDE CITY 64 75 50 65 / 0 50 10 0 SOUTH PADRE ISLAND 67 74 58 65 / 10 50 30 10 BAYVIEW/PORT ISABEL 65 75 55 64 / 10 40 20 10

BRO WATCHES/WARNINGS/ADVISORIES

TX...None. GM...Small Craft Advisory from 9 AM Sunday to 6 AM CST Monday for GMZ130-132-135-150-155-170-175.