Update AFD Area Forecast Discussion — Sat Apr 4, 2026 7:36 PM

AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
627 PM CDT Sat Apr 4 2026

...New AVIATION...

.KEY MESSAGES...
Updated at 620 PM CDT Sat Apr 4 2026

Key Messages:

 * Cold front passes through Deep South Texas from northwest to
   southeast from late this afternoon/early this evening into the
   early/mid morning hours tomorrow, bringing showers and
   thunderstorms continuing through tomorrow night.

 * The Storm Prediction Center (SPC) has highlighted a Marginal
   Risk (Level 1/5) of isolated severe thunderstorms along/west
   of US-281, with the primary concerns being large hail and
   damaging winds.

 * The Weather Prediction Center (WPC) includes all of our County
   Warning Area (CWA) within a Marginal Risk (Level 1/4) of
   isolated flash flooding for tonight and tomorrow.

 * 1 to 3 inches of rain are likely tonight through Sunday night,
   with the highest chances across the Rio Grande Plains and
   Upper RGV, where rainfall totals may exceed 3 inches.

 * A medium risk of rip currents continues through tomorrow
   afternoon and marine/coastal conditions are likely to become
   adverse tomorrow and into the beginning parts of next week.

&&

.DISCUSSION...
Issued at 212 PM CDT Sat Apr 4 2026

The main driver of the impending unsettled weather is a cut-off low
and potent surface low pressure system moving eastward across the
Upper Midwest, extending a cold front southwestward, moving into
South Texas throughout this afternoon. Ahead of the front, lower
level southeasterly flow maintains moisture and warm air advection
into the region today, with temperatures maximizing in the
mid/upper 90s, which adds to the instability across the CWA, with
SBCAPE values ranging from around 1,000-2,500+ J/Kg into the early
evening hours, per the RAP. Meanwhile, instability aloft enhances
ahead of a mid-level disturbance approaching from the west,
increasing MUCAPE to upwards of 1,000 J/Kg, likely surpassing
2,000 J/Kg along/west of US-281, where thermodynamic profiles
further suggest mid-level lapse rates of 6.5 deg C/Km and inverted
Vs despite weaker shear; as the front arrives into the northern
and western portions of the CWA later this afternoon or early
evening, moisture pooling combines with instability and enhancing
frontal lift to result in scattered to numerous showers and
thunderstorms. In consideration of the convective parameters
discussed above, CAMs continue to suggest a growing likelihood of
embedded isolated strong to severe thunderstorms this evening and
into the early nighttime hours tonight along and west of US-281,
where SPC has included a Marginal Risk (level 1/5) for isolated
large hail and damaging wind gusts in excess of 60 mph. The severe
risk is likely to steadily drop off through the overnight hours
as instability and mid-level lapse rates decrease. If the front
arrives earlier and/or pushes through faster within this time
frame, the chance of severe thunderstorms could be maximized
whereas a later and slower arrival could delay and/or minimize
severe potential. CAMs still indicate a lower chance of embedded
isolated strong storms, with the potential for small hail and
stronger gusts, east of US-281 and into Lower RGV into the late
night and early morning hours tomorrow.

Along with the potential for strong to severe thunderstorms is the
expected heavy rain spreading east-southeastward across the
remainder of Deep South Texas overnight tonight as rain chances
increase to as much as a medium to likely (60-80%) chance late
tonight through most of Sunday night. WPC includes all of our region
within a Marginal Risk (level 1/4) for isolated flash flooding for
tonight and tomorrow; CAMs are in agreement with the most torrential
rainfall shifting from northwest to southeast from late this
afternoon or early evening into tomorrow morning ahead of and along
the frontal boundary, with the most prolific rainfall rates
occurring further west. Yet, as the mid-level disturbance passes
through late tonight and into tomorrow, further rounds and/or
training of moderate to heavy rainfall is likely. Further west,
the sudden onset of heavy rain and rapid runoff draws attention to
a more critical risk of flask flooding, particularly in the
hillier regions of Zapata and Starr County, which was impacted
severely by flooding rains last month. Further east and across the
more flat and populated areas, the greater concern is for
hydroplaning and minor nuisance flooding of low-lying areas along
with isolated instances of flash flooding. By Monday morning, most
of the region is likely to have received near at least 1 inch of
rain, with 2-3 inches across western portions of the Northern
Ranchlands, the Rio Grande Plains and Upper RGV. At this time, the
NBM still indicates a 30-40% chance of at least 2 inches of rain
along/east of US-281 and a 40-70% chance further west, highest
across western portions of the Northern Ranchlands, Rio Grande
Plains and the Upper RGV, where there is a 15-30% chance of totals
surpassing 3 inches by Monday morning.

Following, chances of rain gradually decrease across much of Deep
South Texas on Monday, though coastal troughing and additional
weaker mid-level disturbances could keep a low (15-30%) chance of
rain across portions of the RGV and near/along the immediate
coastline into Wednesday. Additional shortwaves aloft may bring
further low (15-30%) chances of rain across the region into the
later parts of next week as well, though confidence is low to medium
at this time. Temperatures gradually increase from the 60s/70s
tomorrow and Monday back to the 80s by Wednesday as clouds decrease
and southeasterly winds return. Overnight lows also warm from the
50s tomorrow night and Monday night back to the 60s by Wednesday
night.

A medium risk of rip currents continues through tomorrow afternoon
and coastal conditions are likely to become adverse tomorrow and
into the beginning parts of next week.

&&

.AVIATION...
(00Z TAFS)
Issued at 620 PM CDT Sat Apr 4 2026

An approaching cold front will likely bring showers and
thunderstorms to the area, resulting in MVFR to IFR conditions
developing overnight and lingering through the remainder of the
forecast. Brief LIFR conditions may be possible if a strong
thunderstorm moves over the airfield.

Southeasterly winds are forecast to shift to the north overnight
with the frontal passage, with wind speeds and gusts increasing
Sunday afternoon.

&&

.MARINE...
Issued at 212 PM CDT Sat Apr 4 2026

Moderate easterly to southeasterly winds and moderate (3-4 ft) seas
continue into the early nighttime hours, when a cold front arrives,
passing through into the morning hours tomorrow, bringing fresh to
strong northerly to northeasterly winds and moderate (6-7 ft) seas,
persisting into Monday; a Small Craft Advisory goes into effect
for all Lower Texas coastal waters from 7 AM Sunday until 1 PM
Monday afternoon. Winds gradually ease throughout the remainder of
Monday afternoon with gentle to moderate northeasterly winds
becoming easterly on Wednesday and southeasterly on Thursday.
Small Craft Exercise Caution conditions are possible again later
next week as a pressure gradient tightens and results in moderate
to fresh southeasterly winds and moderate seas.

As the front arrives tonight, there is the possibility of isolated
strong thunderstorms into tomorrow morning, with the potential for
small hail and stronger wind gusts as chances of rain increase to as
much as a medium to likely (60-80%) chance tomorrow. Following, a
low (15-30%) chance of rain lingers into much of next week as a
result of warm advection showers and additional disturbances
aloft.

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             89  70  76  59 /  10  70  90  90
HARLINGEN               91  64  74  55 /  10  70  90  80
MCALLEN                 95  66  72  59 /  40  80  90  80
RIO GRANDE CITY         94  60  68  55 /  50  90  90  80
SOUTH PADRE ISLAND      80  71  75  64 /  10  70  90  90
BAYVIEW/PORT ISABEL     87  67  77  59 /   0  70  90  90

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...Small Craft Advisory from 7 AM Sunday to 1 PM CDT Monday for
     GMZ130-132-135-150-155-170-175.

&&

$$