Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 241125 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
621 AM CDT Sat Mar 24 2018

.DISCUSSION...Updated for latest aviation discussion below.


.AVIATION...Breezy south winds and MVFR ceilings prevail across
deep south Texas this morning. Recent BRO sounding data indicated
winds of 35 knots at 1000 feet and 42 knots at 2000 feet. Some of
these stronger winds are expected to mix down to near the surface
later this morning into the afternoon. Windy conditions expected to
develop after 14z, with BRO/HRL airports reaching gusts of 35 knots
in the afternoon. VFR conditions expected to develop by mid morning
Saturday as winds increase and low level clouds lift. South winds
should begin to lower after 01z Sunday with the loss of daytime
heating but the winds should remain around 15 knots this evening and


.PREV DISCUSSION... /issued 452 AM CDT Sat Mar 24 2018/

SHORT TERM (Now through Sunday):  Wind will be the main concern in
this portion of the forecast. A tight surface pressure gradient
will be maintained across deep south Texas with broad high
pressure over the Gulf of Mexico interacting with lower pressure
over northern Mexico and the central United States. Model guidance
suggests that wind speeds should reach wind advisory criteria for
today. The Harlingen international airport ASOS recently recorded
a wind gust of 36 mph. The latest Brownsville VAD wind profile
indicates south winds of 35 knots at 1000 feet and 55 knots
between 2000 to 3000 feet. Some of these stronger winds are
expected to mix down to near the surface later this morning into
the afternoon. For these reasons, have decided to issue a Wind
Advisory from 10 am this morning through 7 pm this evening for
Cameron, Willacy, and Kenedy Counties.

Otherwise, a 500 mb ridge of high pressure overhead will produce dry
weather during the forecast period, with a persistent onshore
flow generating well above normal daytime high and overnight low
temperatures. High temperatures today will range from the low to
mid 80s near the coast to the 90s inland. Breezy to windy south
winds will develop later this morning into the afternoon with a
mix of sun and clouds. Temperatures tonight will be mild with lows
generally in the low 70s with some increasing clouds. Winds will
diminish tonight as the winds decouple with the loss of diurnal
heating. High temperatures Sunday will be back in the 80s near the
coast to the 90s inland under partly cloudy skies. Sunday will be
breezy, especially near the coast, as the pressure gradient
pressure strengthens.

LONG TERM (Sunday Night through Friday): Very little change to
the Sunday night through Tuesday portion of the forecast.
Initially quasi-zonal flow at jet-stream level gradually backs to
more southwesterly by Tuesday as western CONUS trough digs into
the Desert Southwest and then translates inland. Column RH`s stay
low due to very dry air in roughly the 850-600mb layer, so no
mentionable chance of precipitation in this period. Model guidance
for temps has been pretty stable, so only made tweaks here and
there. Pressure gradient remains tightened with a lee cyclone
emerging into the Central Plains Monday. Breezy to windy
conditions continue, especially for the three coastal counties,
where a Wind Advisory may be required. Well-above normal
temperatures also continue, ranging from the upper 80s-near 90F
for the Lower RGV to the upper 90s for the Falcon Lake vicinity in
Starr County.

Slight chances of precip enter the forecast Tuesday night, at
least if the GFS is to be believed. It shows a possible short-wave
in the SW H5 flow inducing some surface troughing near the NW CWA,
as well as better moisture pooling ahead of the next cold front
vs. the ECMWF. Speaking of that front, models are moving up the
timing somewhat, with the GFS now moving the front through during
the daytime on Wednesday, whereas the ECMWF holds off until
Wednesday night. WPC favoring the somewhat slower movement of the
front (due to slower progression aloft), so obviously still some
uncertainty here. Relied on a blend of existing forecast/NBM/WPC
guidance for temps from Wednesday onward.  Wednesday temps should
still be on the warm side, of course depending on ultimate timing

Both models hitting PoP`s hardest in Wednesday night timeframe, as
column moisture deepens and main vort max swings through Central
Texas after "bottoming out" over Chihuahua during the day on
Wednesday. Raised broad-brushed PoP`s to 40% and will include
thunder mention, in alignment with MOS guidance numbers and
proximity of the jet stream. A much drier airmass is progged to
sweep in Thursday, along with only modest cooling of 5-10
degrees. Progged RH`s fall to 20-30% west of Hwy. 281/I-69C.
20-ft. winds are forecast to be below 10mph, but may have to watch
fire weather concerns if post-frontal winds are stronger or more
persistent than currently progged.

For Friday into Saturday, upper ridging builds upstream with very
dry atmospheric column resulting in nil rain chances. NE surface
winds on Friday should make for a fairly pleasant day, with temps
nudging back up toward the mid-80s for much of the area on

MARINE (Now through Sunday):  Buoy 42020 reported south-southeast
winds around 21 knots gusting to around 27 knots with seas slightly
over 6.6 feet with a period of 7 seconds at 0330 CDT/0830 UTC. Buoy
42045 (TABS K) reported southeast winds around 16 knots gusting to
around 19 knots at 02 CDT/07 UTC. High pressure over the northeast
Gulf of Mexico will interact with low pressure across west Texas
through the forecast period. Strong winds and rough seas are
forecast for the lower Texas coastal waters for much of the forecast
period. A Small Craft Advisory is now effect for the Laguna Madre
through 7 pm this evening. Also, have extended the Small Craft
Advisory for the Gulf waters through 10 am as winds and seas are
marginally verifying at this time and may slightly improve by
this afternoon.

Sunday Night through Thursday: Adverse marine conditions are
expected through much or all of the long-term, with Small Craft
Advisories (SCA`s) and Exercise Caution (SCEC) likely. Pressure
gradient remains enhanced Monday as a surface cyclone in the lee
of the Rockies interacts with higher pressure over the NE Gulf.
SCA-level winds likely for all of the waters Monday afternoon,
with Gulf seas building to 6+ feet. Seas then build further, to
around 8 ft., Monday night and possibly persist at this level
until Wednesday. Winds relax somewhat Wednesday, as the gradient
weakens ahead of a cold front, but seas stay agitated. Some
uncertainty on the timing of this front, but winds should shift
northerly and increase again by later Wednesday night.


TX...Wind Advisory from 10 AM this morning to 7 PM CDT this evening
     for TXZ251-254>257.

GM...Small Craft Advisory for winds until 7 PM CDT this evening for

     Small Craft Advisory until 10 AM CDT this morning for GMZ150-155-



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