Severe Thunderstorm Warning 45, NWS Brownsville, TX

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
641 PM CDT Tue May 6 2025

...New AVIATION...

.SHORT TERM...
(Tonight through Wednesday night)
Issued at 254 PM CDT Tue May 6 2025

The area remains in a marginal risk for severe weather tonight with
CAMS suggesting that the Upper Valley and Ranchlands may get brushed
by a few transiting storms. A cold front analyzed over the RG
Plains may provide a surface based trigger under destabilized mid
level flow. Farther toward the southeast (Lower Valley), the
sounding shows a capped environment, though plenty of available
energy exists in the mid levels. For now, convection over South
Central Texas has behaved, but we will monitor for development
later this evening and overnight. With the models appearing to
stall out the front short of the CWA, another round of convection
will be possible Wednesday afternoon, initiating just north of the
CWA and moving east. We could see some of those storms get better
organized and push south later Wednesday. For now, the RGV Plains
and Ranchlands are in a day two marginal outlook area. Lows in
the mid 70s, highs in the mid 90s. A high rip risk will continue
tonight through Wednesday but may lower to moderate Wednesday
night.

&&

.LONG TERM...
(Thursday through next Tuesday)
Issued at 254 PM CDT Tue May 6 2025

Key Messages:

* Medium to likely (40-70%) chance of showers and thunderstorms
  throughout Thursday and Thursday night.

* Storm Prediction Center (SPC) has placed all of Deep South Texas
  and the Rio Grande Valley within a general risk for thunderstorms
  on Thursday.

* Although confidence is low, there is a possibility for strong
  and/or severe thunderstorms Thursday and/or Thursday night. In
  this scenario, main threats would be strong wind gusts, hail,
  cloud to ground lightning and heavy rain.

The long term starts off wet with a frontal boundary draped across
the area, generating a medium to likely (40-70%) chance of showers
and thunderstorms across all of Deep South Texas throughout Thursday
and Thursday night, with the highest chances across the Rio Grande
Valley. Flow aloft will be mostly zonal, but with a slight
southwesterly component ahead of a shortwave trough moving eastward
through northern Mexico toward southern Texas. SPC has placed Deep
South Texas and the Rio Grande Valley within a general risk for
thunderstorms on Thursday. Although confidence is low at this time,
there is a chance of strong, perhaps severe, thunderstorms on
Thursday and/or Thursday night as the mid-level impulse moves
eastward. The GFS and NAM are in rough agreement of this scenario
playing out Thursday evening into Thursday night, but there remains
disagreement amongst models as a whole in the southward extent,
timing and strength of the convection. That being said, there
remains the potential for strong gusts, hail, cloud to ground
lightning and heavy rain. Either way, the consensus is higher that
by Friday morning, the shortwave will be offshore and northerly
winds in its wake will drive the front southward, bringing
probabilities of showers and thunderstorms from a low to medium (20-
40%) chance Friday morning to less than a 15% chance going into
Friday afternoon. Between Thursday morning and early Friday
afternoon, our forecast calls anywhere from three quarters to half
an inch of rain across the County Warning Area (CWA). Yet, higher
percentile NBM guidance indicates that there is the potential of
some locations receiving 1-2 inches within heavier downpours.

Following, flow at mid/upper levels gradually becomes northwesterly
as ridging builds across Deep South Texas, resulting in dry
conditions for the remainder of the long term. High pressure is
expected to maintain control across the Southern Plains with
northerly to northeasterly winds into Sunday, becoming southeasterly
to southerly for Monday and Tuesday as the high moves into the Gulf.

Highs in the 80s are expected Thursday through Sunday and slightly
below average beginning Friday. Return flow will warm temperatures
from upper 80s to low 90s on Monday to mostly 90s on Tuesday with
Rio Grande Plains possibly hitting upper 90s. Lows in the 60s and
70s Thursday night drop to mainly 60s Friday night through Sunday
night before warming back to 60s Monday night. A few locations in
the Northern Ranchlands may minimize in the upper 50s Sunday night
as temperatures could be 10 degrees, or cooler, below average.

&&

.AVIATION...
(00Z TAFS)
Issued at 637 PM CDT Tue May 6 2025

A mix of VFR and MVFR ceilings prevail at the local aerodromes
early this evening with low clouds and moderate southeast winds.
MVFR ceilings are expected to develop at all terminals later this
evening. Convection developing upstream later this evening and
overnight with a few showers or rumbles possibly nearing the TAF
sites from the northwest or west in the pre dawn hours. Confidence
right now is low for early Wednesday morning flight impacts from
convection, but confidence is higher (moderate or better) for
continuing MVFR ceilings due to low clouds and/or patchy fog. VFR
conditions are expected to return in Wednesday afternoon.

&&

.MARINE...
Issued at 254 PM CDT Tue May 6 2025

Tonight through Wednesday night...Winds should ease up this evening
and we plan to let the small craft advisory expire at 6 PM in favor
of exercise caution conditions tonight. Winds will weaken through
Wednesday before shifting/backing toward the east ahead of a
potential cold front. On and off isolated to scattered convection
will be possible through Wednesday night.

Thursday through Tuesday...Gentle to moderate northerly to
northeasterly winds and moderate (3- 5 feet) seas are expected
Thursday into Sunday. There is a moderate to likely (50-80%)
chance of showers and thunderstorms throughout Thursday and
Thursday night. A few storms may be strong and/or severe with the
potential for strong wind gusts, hail, cloud to ground lightning
and heavy rain. Chances of showers and thunderstorms diminish
throughout Friday morning and remain mostly dry for the rest of
the period. Gentle to moderate winds turn southeasterly to
southerly on Monday into Tuesday along with slight (1-2 feet)
seas.

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             77  92  77  85 /  20  20  20  70
HARLINGEN               75  92  73  87 /  30  20  20  70
MCALLEN                 78  96  77  89 /  30  20  20  70
RIO GRANDE CITY         75  95  74  88 /  40  10  30  70
SOUTH PADRE ISLAND      78  84  76  82 /  20  20  20  70
BAYVIEW/PORT ISABEL     76  89  74  84 /  20  20  20  70

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...High Rip Current Risk through Wednesday evening for TXZ451-454-
     455.

GM...None.
&&

SHORT TERM...54-BHM
LONG TERM....65-Irish
AVIATION...63-KC