Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 200112 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
712 PM CST Sun Feb 19 2017

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


.AVIATION...Currently the KBRO radar is showing an area of
convection firing up west of Zapata County moving up to the NNE.
The 00z BRO sounding continues to show a CAPE of 2800 j/kg.
However a fairly strong cap remains in place over the RGV. The
latest HRRR model run looks to be initializing on the ongoing conv
pretty well with this model showing the conv primarily impacting
the northern and western counties through around 09z mainly
staying clear of the lower RGV airports. The HRRR then brings a
more ragged line of conv through the lower RGV during the morning
hours tomorrow. The conv will then end after midmorning tomorrow
as drier and more stable air moves into the region as the 500 trough
axis moves east. So will bring down the ceilings to MVFR/IFR
levels late tonight into early Monday generally in line with the
trends indicated by the HRRR with VFR conditions returning late in
the current TAF period.


.DISCUSSION...Updated for latest marine discussion below.


.MARINE...Surface obs from across the marine locations indicate
that the winds across the bay have dropped down below SCA levels
while Buoy020 is showing stronger SE winds at 20g25kt with swells
near 6 feet this evening. Expect the PGF ahead of the surface low
pressure system to our west to remain stronge enough for the Gulf
waters to maintain hazardous winds and seas through around
midnight tonight. So will post up an SCA for the Gulf waters.


.PREV DISCUSSION... /issued 318 PM CST Sun Feb 19 2017/

..Potential still exists for marginal severe weather threat
across portions of deep south Texas this evening through early
Monday morning...

SHORT TERM (Tonight through Monday Night): Satellite and radar
images indicate showers and isolated thunderstorms continue to
develop across portions of northern Mexico northward across portions
of southwest Texas and the Big Bend region ahead of the 500mb trough
moving eastward across the southwest United States and northwest
Mexico this afternoon. The cap across the area continues to inhibit
convection across the CWA this afternoon but models indicate the cap
will erode across northern and western portions of the CWA late this
afternoon into early this evening. This will allow showers and
thunderstorms...some possibly develop rapidly across
western portions of the ranchlands and extreme western portions of
the Rio Grande valley this evening through tonight before evolving
into a quasi-linear convective system (QLCS) and moving eastward
across the CWA late tonight into early Mon morning. There still is
some uncertainty if the cap along the coastal sections will erode
and what impacts that would have on the potential squall line
reaching the eastern portions of the CWA. Will continue to mention
high pops for tonight into Monday with heavy rainfall/severe wording
for tonight. Per the latest SPC outlook...the main severe threat
appears to be damaging winds but large hail and isolated tornadoes
cannot be ruled out especially is isolated thunderstorms develop
ahead of the main line. The bulk of the rainfall should be north and
east of deep south TX tonight into Monday but heavy rainfall can be
expected with thunderstorms associated with the QLCS.

Drier air will filter into the western portions of the CWA Monday
into Monday night as the flow aloft veers from the south to
southwest and eventually west as a cut-off low develops across
southwest TX and moves across deep south TX Tues night. Rain chances
will diminish from west to east Mon afternoon through Mon evening as
a result.

LONG TERM (Tuesday through Sunday): The forecast begins with a
closed 500mb low over the middle Texas coast Tuesday morning. The
mid level low will eventually move eastward over the western Gulf
of Mexico Tuesday night into Wednesday. Some wrap around moisture
on the backside of the 500mb low will support some isolated
convection along the Lower Texas coast Tuesday. Differences
continue between the GFS/ECMWF with the placement of the mid level
low and the amount of available moisture. Subsidence will prevail
across the region Tuesday night and Wednesday courtesy of
northerly flow aloft and at the surface. Winds become southeast on
Thursday as surface low pressure develops across the Plain
states. A dry cold front is expected to move across Deep South
Texas Friday night. Breezy northeast winds Saturday morning
quickly veer to the southeast Saturday night as surface high
pressure moves east.

Tonight through Monday night: Seas were near 5 feet with south to
southeast winds near 18 knots at buoy020 early this afternoon.
Moderate to strong south to southeast winds will prevail offshore
the lower Texas coast tonight with light to moderate south to
southwest winds across the Laguna Madre before a convective
frontal boundary/weak cold front moves across the coastal waters
late tonight into early Mon morning. Winds and seas will be
considerably stronger and higher as a line of showers and
thunderstorms...likely a squall...moves through the coastal waters
late tonight into early Monday. In the wake of the cold
front...winds will be shifting to the north and northeast in the
wake of low pressure developing along the frontal boundary
offshore the lower TX coast Monday. Light northeast winds will
prevail across the coastal waters Mon night as the weak frontal
system offshore moves farther east into the western Gulf of

Tuesday through Friday: Light to moderate northwest to north winds
will prevail across the Lower Texas Coastal waters through Wednesday
as high pressure spreads over the area. Winds will gradually turn to
the southeast Wednesday night then south on Thursday as high
pressure moves east. Low to Moderate seas expected through the


GM...Small Craft Advisory until midnight CST tonight for GMZ150-155-



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