National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS64 KBRO 092046
AFDBRO

Area Forecast Discussion
National Weather Service Brownsville TX
346 PM CDT Tue Apr 9 2024

...New SHORT TERM, LONG TERM, MARINE, FIRE WEATHER...

.SHORT TERM...
(Tonight through Wednesday night)
Issued at 343 PM CDT Tue Apr 9 2024

Key Messages:

* Red Flag Warning for Critical Fire Weather Conditions in effect
  for Zapata, Starr, Jim Hogg, Hidalgo, Inland Kenedy, Inland
  Willacy, and Inland Cameron Counties from Noon PM CDT to 9 PM CDT
  on Wednesday

* Wind Advisory issued for all of Deep South Texas from 9 AM CDT to
  9 PM CDT Wednesday

* Isolated to scattered strong to severe thunderstorms are expected
  tonight; Slight Risk (Level 2 of 5) for northern Zapata, northern
  Jim Hogg, and northern Brooks Counties; Marginal Risk (Level 1 of
  5) for much of the area outside of the mid and lower Rio Grande
  Valley and the coastal areas

Active weather with multiple hazards through the short term forecast
period. This discussion will be broken down into three phases.

FIRST: Shower and Thunderstorm Risk This Evening into Tonight:

Several hi-res CAM guidances continue to advertise a cluster of
showers and thunderstorms developing along/ahead of a cold frontal
boundary late this evening and tonight. These showers and storms
will be associated with a shortwave that will be tracking overhead.
The greatest uncertainty at this time continues to be the southward
and eastward extent of the shower and thunderstorm coverage and the
severity/strength of it. Right now, the greatest confidence/coverage
for convection continues to be over our northwestern sections of out
local forecast area.

After collaboration with SPC and CRP, a Slight Risk (Level 2 out of
5) encompasses parts of Zapata, Jim Hogg, and Brooks Counties, a
Marginal Risk (Level 1 out of 5) encompasses much of the area
outside of the mid to lower Rio Grande Valley and coast areas which
remains under a General Outlook for thunderstorms tonight. The
main threats include large hail and damaging winds.

SECOND: Strengthening northwest winds behind the cold front on
Wednesday:

The cold front is expected to move over the area late tonight into
Wednesday morning. After the passage of the cold front, winds are
expected to shift out of the northwest and strengthen. Forecast
models are indicating a pretty strong isollabaric couplet associated
with the cold front with heights rising quickly behind the fropa.
Additionally, low level jet (LLJ) winds at 850 mb are expected to
increase out of the northwest Wednesday morning into Wednesday
afternoon with values sampled between 40-50 kts. As mixing heights
rise through the morning and into the afternoon hours, surface winds
will increase 20-30 mph with gusts as high as 40-45 mph. Given the
situation and after collaboration with CRP, have opted to go with a
Wind Advisory for all of Deep South Texas from 9 AM CDT to 9 PM CDT
on Wednesday.

THIRD: Elevated to Critical Fire Weather Conditions on Wednesday:

Finally, there is a wildfire danger threat on Wednesday. Behind the
cold front, much drier air is expected to advect into the region.
Wednesday morning into Wednesday afternoon, minimum relative
humidity (RH) values are expected to drop to between 15-25% with the
lowest amounts over our western sections. The combination of low RH
values, strong northwest winds, and drying fuels will result in
elevated to critical fire weather concerns on Wednesday. That said,
a Red Flag Warning is in effect for the entire area outside of
coastal and island Kenedy, Willacy, and Cameron Counties from Noon
PM CDT to 9 PM CDT on Wednesday. A Fire Danger Statement is in
effect for Coastal and Island Kenedy, Willacy, and Cameron Counties.


&&

.LONG TERM...
(Thursday through next Tuesday)
Issued at 343 PM CDT Tue Apr 9 2024

Rather pleasant conditions start to take hold at on Thursday to start
of the long term forecast period with winds still out of the north.
As the mid-level trough moves off to the northeast a mid-level ridge
will start to take hold aloft, while surface high pressure build
over Deep South Texas and the Rio Grande Valley. Winds will then
veer back to the southeast by late Thursday into Friday. The onshore
flow will then continue to prevail for the rest of the long term
forecast period, which will aid with temperatures warming up. The
mid-level ridge is expected to hold through most of the long term
forecast. However, on the surface, the high pressure will continue
to move off towards the east with the center of the high pressure
over Southern Georgia/Northern Florida by late Saturday into Sunday.

As for the temperatures, the low temperatures will start off pretty
chilly on Thursday night in the 50s thanks to the clear skies
allowing for plenty of radiative cooling to take place. During the
duration of the long term forecast period, the low temperatures will
warm up quite a bit thanks to the onshore flow brining more warm air
so that by the end of the long term forecast period, the low
temperatures will be in the lower 70s for all of Deep South Texas
and the Rio Grande Valley. On the other hand, the high temperatures
will start out in the 80s on Thursday and gradually warm up through
the long term forecast period as well eventually getting into mostly
90s for the region. Areas along the coast, the temperatures are
expected to be in the upper 80s. In addition, parts of Zapata and
Starr counties could even tip toe into the triple digits on Tuesday
if this forecast pattern holds. Cloudy skies are also possible on
Tuesday so might actually keep some of the high temperatures from
getting so hot.

&&

.AVIATION...
(18Z TAFS)
Issued at 108 PM CDT Tue Apr 9 2024

Main weather concerns to aviation operations for the BRO terminals
through the 18z TAF cycle includes:

* MVFR cigs developing this evening into tonight

* Wind shift overnight from the south-southeast to northwest along
  with the non-zero probability of thunderstorms

* Low level wind shear (LLWS) potential overnight tonight into
  Wednesday morning following the cold fropa

As of this update, VFR to MVFR conditions were taking place at the
terminals with ceilings between 2,000-4,000 feet AGL with some haze
(hz). VFR to MVFR conditons will persist through the remainder of
this afternoon with the help of gusty surface winds.

Later on this evening, forecast models are hinting at the potential
for MVFR cigs developing once again ahead of a cold frontal
boundary. Later on tonight, attention shifts to the potential for
showers and thunderstorms associated with the approaching cold
front. Right now, there is a low to medium chance for showers and
thunderstorms developing late tonight over the Lower Rio Grande
valley that includes the TAF sites. That said, given the low-medium
risk and non-zero probability, have maintained Prob30 groups in the
TAFs to reflect this potential between the hours of 06z-10z.
Clouds/ceilings are expected to improve back to VFR levels as
drier air and strengthening winds out of the northwest develop on
Wednesday.

The other concern will be the winds later tonight into Wednesday and
with that the risk for low level wind shear (LLWS). Winds this
afternoon will continue out of the south-southeast 10-15 kts with
gusts up to 30 kts. These winds will weaken this evening. A wind
shift will take place later tonight amid the passage of the cold
front and/or outflow boundary from thunderstorm activity to our
northwest. Winds out of the south will shift out of the northwest
between 10-15 kts. Overnight tonight (towards daybreak) and into
Wednesday morning roughly between 09z-16z Wednesday, there is the
potential for LLWS to develop as deterministic models and BUFKIT
soundings indicate winds 2,000 feet aloft and at the surface
decoupling with winds 2,000 feet AGL increasing up to 40-45 kts. Have
highlighted this threat in the TAFs as well. Towards the very end of
the 18z TAF period, surface winds will begin to increase and catch
up to the winds aloft.

&&

.MARINE...
Issued at 343 PM CDT Tue Apr 9 2024

Tonight through Wednesday night...Small Craft Exercise Caution
(SCEC) remains in place across the Laguna Madre and nearshore (0-20
nm) Gulf Waters this afternoon due to strong winds mixing down to
the surface from a departing low level jet (LLJ) overhead. A Small
Craft Advisory (SCA) continues to remain in effect for the offshore
Gulf Waters (20-60 nm) till 7 AM CDT Wednesday. Throughout the
evening, an advancing cold front will push the LLJ northeastward and
southeasterly surface winds will diminish to light, especially
closer to the coast. Late tonight, a pre-frontal trough will reach
the coastlines and shift winds from the southwest. Additionally, as
the front advances closer, the chance of thunderstorms will increase
waste tonight from northwest to southeast, leading up to the predawn
hours with the best chances of thunderstorms for the northern marine
zones. This will shift winds from from the west-northwest and
enhance anticipates as the front passes through. Following, fresh-to-
strong northwesterly winds will pick back up and seas will build as
another LLJ strengthens in the wake of the cold front close to the
coast. Tomorrow night, winds will increase again over the coastal
waters as a pressure gradient tightens between the departing trough
to the east and the building high pressure from the west. Additional
and, or, SCEC and SCA advisories may be needed.

Thursday through Next Tuesday...Slightly adverse marine conditions
to start out on Thursday, but will quickly improve during the day
and become favorable as the winds veer towards the southeast. Once
the onshore flow gets going, moderate winds and seas are expected to
persist through next Tuesday with generally favorable conditions.
The only concerns come with some brief periods of slightly elevated
winds that could result in Small Craft Exercise Caution conditions
during the weekend and Monday.

&&

.FIRE WEATHER...
Issued at 343 PM CDT Tue Apr 9 2024

.Fire Weather...As a strong front works through Deep South Texas
Wednesday morning, expect relative humidity values to drop to
between 15 and 25 percent, while 20 foot winds ramp up to 20 to 25
mph. A Red Flag Warning is in effect for the entire area outside of
Coastal and Island Kenedy, Willacy, and Cameron Counties from Noon
PM CDT to 9 PM CDT Wednesday.

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             68  85  61  84 /  30   0   0   0
HARLINGEN               64  85  56  85 /  30   0   0   0
MCALLEN                 66  87  59  87 /  30   0   0   0
RIO GRANDE CITY         63  86  56  87 /  30   0   0   0
SOUTH PADRE ISLAND      69  79  66  76 /  20   0   0   0
BAYVIEW/PORT ISABEL     66  84  60  81 /  30   0   0   0

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...Wind Advisory from 9 AM to 9 PM CDT Wednesday for TXZ248>255-351-
     353>355-451-454-455.

     Red Flag Warning from noon to 9 PM CDT Wednesday for TXZ248>255-
     353.

     High Rip Current Risk through Wednesday evening for TXZ451-454-
     455.

GM...Small Craft Advisory until 7 AM CDT Wednesday for GMZ170-175.

&&

$$

SHORT TERM...23-Evbuoma
LONG TERM....64-Katz
AVIATION...23-Evbuoma