Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 181138 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
638 AM CDT Thu May 18 2017

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


.AVIATION...Low clouds with MVFR cigs between 1800 to 2200 ft
continue to drift across the Lower to Mid Valley early this
morning. Conditions will continue to slowly improve through the
late morning as stronger winds develop and mixing occurs. There
should be a period of VFR conditions this afternoon and early
evening before cigs deteriorate once to MVFR once again.
Meanwhile, southeast winds will be gusty through the late morning
and afternoon as the pressure gradient remain tight across the


.PREV DISCUSSION... /issued 422 AM CDT Thu May 18 2017/

SHORT TERM (Now through Friday): Deep South Texas is currently
sitting between mid-level high pressure ridging to the south and
east, and a large cut-off low slowly moving across the Central
Rockies. Moisture continues to stream in between the two systems
as well, with pockets of upper level moisture noted on water vapor
imagery. However, the mid levels remain rather dry as noted on
the 00Z sounding. Meanwhile, persistent low level flow from the
south and southeast as increased dewpoints well into the lower to
upper 70s this morning. This moisture has remained trapped under
the 825mb inversion, keeping cloud cover across much of the

Heading through the today, these low clouds will stick around
through the better part of the morning and even early afternoon.
Meanwhile, the strong low pressure system will slowly push east and
surface low pressure system is expected to develop across the
Panhandles Region is response. With high pressure sitting over the
Gulf, the pressure gradient will strengthen today with SSE winds
increasing. As such, it will be a breezy to gusty day across much of
the coastal counties and, to a lesser degree, farther inland towards
McAllen. There will likely be some occasional gusts over 30
MPH...especially near and along the I-69E corridor...however, winds
should remain below advisory criteria given the low level jet does
not appear to be significantly strong. However, turbulent mixing
from the winds will allow the drier mid level air to mix down and
cause breaks in the clouds today with some sunnier conditions noted
mainly across the Mid Valley and Western Ranchlands.

Breezy conditions will continue tonight and into Friday, although the
low pressure system across the Rockies will move more north into the
Central Plains as high pressure ridging become slightly stronger
across the Eastern Gulf. The pressure gradient will weaken as a
result and winds should begin to weaken through the day Friday.

As far as temperatures go, lows temps will continue to run several
degrees above normal low given how warm dewpoints are. High will be
a few degrees above the norm. Heat index values will feel rather
warm especially across along the I-69C corridor near McAllen and
west towards Zapata. Values could reach between 105-109 degrees.
Meanwhile, closer to the coast heat indices will be near 100 to 105

LONG TERM (Friday Night through Wednesday):Latest model package
remains in decent agreement with the mid/upper air pattern
through the majority of the long term. Broad long wave trough sets
up shop nearly coast to coast with the sub-tropical ridge
building across Mexico and the Western Gulf resembling an early
Summer pattern. At the surface...a couple of cold front moves
south into Texas but do not show much promise of making it
completely through Deep South Texas with the mid level flow
becoming parallel (west) either side of the frontal boundaries.
However the close proximity of the initial front (Sunday/Monday),
weakens the pressure gradient with a backing (east) wind, while
moisture increases and deepens through the layer favoring an
unsettled period Sunday through possibly Wednesday. Model guidance
still favor Sunday and Monday with the best chances of rain with
some uncertainty Tuesday and Wednesday. Highest Precipitable
water, weak to no cap in place and the a light easterly flow
favors a potential sea breeze to enhance Sunday and Mondays
convection. As we move into Tuesday and Wednesday some timing and
moisture differences between the GFS and ECMWF Tuesday and
Wednesday work their way into mix with uncertainty of which models
is correct so will trend with broad brush slight chances until
there is better agreement.

Model guidance temperatures look within reason and trend close if
not right within a degree or two of average with the wetter
Summer like pattern. Highs to tapper off into the upper 80s to
lower-mid 90s, lower on Sunday and Monday with higher chance of
rain, while lows also trend lower with the lighter anticipated

MARINE:(Now through Friday): Current conditions at Buoy 42020 at 3
AM show SSE winds of 15 knots with gusts to 18 knots and seas at 6
feet. However, winds and seas have generally remained elevated
through the overnight hours with seas occasionally reporting in
around 7 feet. Meanwhile, the surface pressure gradient will
strengthen today as high pressure over the Eastern Gulf interacts
will low pressure developing across the Panhandles region. Winds
will increase by mid to late morning with seas building even more in
response this afternoon. Given this, and the already lingering
higher swells, have added all of the Gulf Waters from 0 to 60 NM to
the Small Craft Advisory that was already out and have extended it
through at least Friday morning. However, this may need to be
extended depending on lingering swells and winds. Meanwhile, the
winds will increase across the Laguna Madre later this morning and
through the afternoon with a Small Craft Advisory for winds being
issued. The winds across the bay will decrease to night. The
pressure gradient will lessen somewhat on Friday.

Friday Night through Monday...The overall pressure gradient is
expected to weaken through the period as broad mid level high
pressure builds over the Western Gulf and a frontal boundary moves
into Southcentral Texas Sunday and Monday. Residual southeast
winds and seas Friday night and Saturday could maintain small
craft advisories conditions. Winds then trend more easterly and
weaken with seas slowly responding Sunday and Monday.


GM...Small Craft Advisory for winds from 10 AM this morning to 8 PM
     CDT this evening for GMZ130-132-135.

     Small Craft Advisory until 7 AM CDT Friday for GMZ150-155-170-



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