textproduct: Brownsville/Rio Grande Valley

KEY MESSAGES

Updated at 528 PM CST Thu Dec 18 2025

* Unseasonably warm temperatures including record to near record- breaking temperatures along with mainly dry weather conditions are expected to prevail through next week.

* A cold front will push through the region tonight and will bring temperatures to near seasonable levels on Friday.

* Adverse to hazardous marine conditions are expected to develop tonight into Friday in response to the cold fropa.

DISCUSSION

Issued at 1116 AM CST Thu Dec 18 2025

The contiguous U.S. is in the midst of a significant large-scale weather pattern change. This change in the 500mb pattern will result in widespread, record to near record-setting warmth engulfing a vast majority of the country through Christmas Week. The epicenter of this warmth will be located over the Plains/Midwest with temperature anomalies on the order of +2 to +4 STDEVS (standard deviations) above normal. During this time period, the cold and wintry weather that's plagued the northern 1/3rd of the country over the past few weeks will retreat northward into Canada with the jet stream/active storm track placed near or along the U.S.-Canadian border.

For Deep South Texas and the Rio Grande Valley, an anomalously strong 588 dam heat dome (+1 to +3 STDEVs) is expected to emerge Christmas Week. This will effectively foster a warmer than normal and dry (rain-free) weather pattern through the forecast period or through at least next Friday. Record to near record-breaking temperatures are in the cards for Deep South Texas and the Rio Grande Valley today through at least the early parts of next week (see CLIMATE SECTION for more details).

Outside of a cold front associated with a 1020-1025 mb sfc high pressure system that's expected to sweep through Deep South Texas and the RGV tonight, dropping overnight lows into the 40s and 50s, and daytime high temperatures into the 70s on Friday (near seasonable levels), high temperatures today and then again Saturday through next Friday is progged to be in the 80s with overnight lows mainly in the 60s. These values will be on the order of 10-15F degrees above normal.

AVIATION

(00Z TAFS) Issued at 528 PM CST Thu Dec 18 2025

VFR conditions prevail for the 00Z TAF cycle. A cold front tonight will shift easterly flow to northerly. Winds may become gusty to 20kts following frontal passage between 05-10Z. There is a low chance (less than 30%) of vsby reduction to 4SM or less at HRL and BRO (04-09Z), but confidence is low that temperatures will reach the dewpoint before dry air advects in.

MARINE

Issued at 1116 AM CST Thu Dec 18 2025

Favorable marine conditions are expected to prevail through today. However, a cold front will sweep through Deep South Texas tonight. Small Craft Exercise Caution (SCEC) to Small Craft Advisory (SCA) conditions are expected to develop over the Laguna Madre and the Gulf Waters tonight into Friday. Given the high end SCEC to small end SCA, we decided to issue a Small Craft Advisory from 10 PM CST tonight to 9 AM CST on Friday. Marine conditions are expected to improve later on Friday with low to moderate winds and seas returning Friday evening and prevailing through next week.

CLIMATE

Issued at 1116 AM CST Thu Dec 18 2025

Strong mid-upper level ridging over the region will result unseasonably warm temperatures today and again over this upcoming weekend. Record to near-record breaking high temperatures are expected to take place during this timeframe.

Brownsville Record Highs Thursday, December 18, 2025....86/2024 Saturday, December 20, 2025....88/1889 Sunday, December 21, 2025....86/2017, 1921

Harlingen Record Highs Thursday, December 18, 2025....86/1948, 2012, 2021 Saturday, December 20, 2025....88/2007, 1921 Sunday, December 21, 2025....92/1920

McAllen Record Highs Thursday, December 18, 2025....87/2012, 2002 Saturday, December 20, 2025....89/2007, 1990, 1978 Sunday, December 21, 2025....90/1949, 1948

PRELIMINARY POINT TEMPS/POPS

BROWNSVILLE 61 77 61 83 / 0 0 0 0 HARLINGEN 55 75 56 85 / 0 0 0 0 MCALLEN 56 77 59 86 / 0 0 0 0 RIO GRANDE CITY 51 77 55 86 / 0 0 0 0 SOUTH PADRE ISLAND 66 72 66 76 / 0 0 0 0 BAYVIEW/PORT ISABEL 60 74 59 82 / 0 0 0 0

BRO WATCHES/WARNINGS/ADVISORIES

TX...None. GM...Small Craft Advisory from 10 PM this evening to 9 AM CST Friday for GMZ130-132-135-150-155-170-175.