textproduct: Brownsville/Rio Grande Valley

KEY MESSAGES

Updated at 539 AM CST Mon Dec 22 2025 * A Special Weather Statement is in effect for all of Deep South Texas and the Rio Grande Valley tonight until 10 AM Monday morning as areas of fog, or patchy, locally dense, fog develop, reducing visibility to 1-3 miles, or less.

* A Marine Dense Fog Advisory is in effect for the Laguna Madre and nearshore (0-20 nm) Gulf Waters from midnight tonight until 11 AM Monday morning.

* There is a low (15-30%) chance of rain Monday and Tuesday afternoon from isolated to scattered showers and thunderstorms, with a potential for brief moderate to heavy rain within the deepest convection.

* Unseasonably warm temperatures continue with highs in the 80s and lows in the 60s, which is 10-15 degrees F above average.

DISCUSSION

Issued at 1032 PM CST Sun Dec 21 2025

The most recent satellite and observations across Deep South Texas this evening indicate a stalled frontal boundary draped across southern Texas, extending southwestward into the Rio Grande Plains and western portions of the northern ranchlands, with southeasterly winds to the south of the boundary and northeasterly to northerly winds to the north. At this time, confidence is medium to high that elevated moisture content, light to calm winds and mainly clear skies will support the development for areas of fog or patchy, locally dense, fog with the greatest chances near the coast. As such, a Special Weather Statement is in effect for all of Deep South Texas and the Rio Grande Valley through 10 AM Monday morning. Pockets of reduced visibility, generally 1 to 3 miles, with locally dense fog to a mile or less are likely. Should model guidance and observations from station data and webcams indicate rapid development of more widespread dense fog, a Dense Fog Advisory may be issued overnight for portions, or all of, the region. Short term high resolution guidance is in fair agreement of the boundary remaining stationary overnight before lifting northward and/or mixing out on Monday as southeasterly winds return from a surface high over the Gulf extending into the region. Additionally, patchy to widespread fog remains possible during the late night and early morning hours each night through this upcoming weekend.

As southeasterly surface flow returns and re-enhances moisture levels across the region on Monday, mid to upper level troughing, extending from central and northeastern Mexico, is likely to provide a source of lift across the region for showers and thunderstorms. Recent runs of the convection allowing models (CAMs) have consistently suggested precipitable water (PWAT) values rising to as much as 1.5-1.7 in., or greater, by late Monday afternoon into Tuesday. A few CAMs advertise isolated to scattered showers and thunderstorms Monday and Tuesday afternoon, bringing the possibility of brief moderate to heavy rain within the deepest convection, especially on Monday. This is fairly consistent with the latest NBM guidance, which suggests a low (15-30%) chance of rain during the peak hours of daytime heating and enhanced diurnal instability on Monday and Tuesday afternoon before falling to less than a 10% chance overnight, with rainfall totals up to an inch possible in the middle and lower RGV. Otherwise, chances of rain decrease Tuesday evening with a less than 10% chance of rain for most of the remainder of the forecast as ridging resumes. The next chance of rain could be the end of next weekend as a cold front may work its way into Deep South Texas, bringing a low (15-30%) chance of rain.

The other focus of the forecast continues to be the unseasonably warm temperatures, with daytime highs in the 80s and overnight lows in the 60s, which is 10-15 degrees above normal. A high temperature of 87 F was recorded in Brownsville today, which broke an old record of 86 F, set in 1921. Additional records could be broken over the next 7 days. A cool-down in temperatures is possible on Sunday in association with a potential cold front.

A low risk of rip currents continues through Monday afternoon.

AVIATION

(12Z TAFS) Issued at 539 AM CST Mon Dec 22 2025

Latest surface observations and satellite imagery indicate LIFR conditions with patchy to areas of fog and very low ceilings. Conditions will gradually improve to VFR later this morning as light southeasterly winds increasing to 5 to 10 knots by the afternoon. Isolated to scattered showers and thunderstorms are possible this afternoon and evening. MVFR conditions expected late in the period as patchy to areas of fog develops and low stratus returns, especially at MFE and HRL.

MARINE

Issued at 1032 PM CST Sun Dec 21 2025

Areas of fog or patchy, locally dense, fog are expected to continue to develop overnight and a Marine Dense Fog Advisory is in effect from midnight tonight until 11 AM Monday morning. Fog remains possible for the late night and early morning hours each night. Otherwise, mostly light to gentle, moderate at times, southeasterly to southerly winds and slight to moderate (2-4 ft) seas continue, becoming moderate winds this upcoming weekend as a slight pressure gradient develops ahead of a possible cold front on Sunday. Aside from a low to medium (20-40%) chance of rain Monday and Tuesday afternoon, probabilities remain less than 10%, with a low to medium (20-40%) chance possible again on Sunday in association with the front.

PRELIMINARY POINT TEMPS/POPS

BROWNSVILLE 83 68 82 66 / 30 20 20 0 HARLINGEN 83 65 83 63 / 20 10 20 0 MCALLEN 84 69 85 67 / 20 10 30 0 RIO GRANDE CITY 84 65 86 64 / 20 10 20 0 SOUTH PADRE ISLAND 76 70 76 68 / 20 20 20 0 BAYVIEW/PORT ISABEL 81 66 80 65 / 20 10 20 0

BRO WATCHES/WARNINGS/ADVISORIES

TX...None. GM...Dense Fog Advisory until 11 AM CST this morning for GMZ130-132- 135-150-155.