Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 240718 AAC

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
118 AM CST Sat Feb 24 2018

.DISCUSSION...Added some pops with isolated thunder out west with
one strong thunderstorm moving through Starr county and showers
spreading into Zapata and Jim Hogg. Fog is only noted in the near
shore waters and web cams are indicated very low visibilities so
upgraded the MWS to a dense fog advisory (only for the nearshore
waters) until 10 am. Increased cloud cover for the rest of the
zones tonight and began to clear them Saturday am.


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


.MARINE...Dense fog has formed over the nearshore Gulf waters
warranting a Dense fog advisory until 10am Saturday.


.PREV DISCUSSION... /issued 1151 PM CST Fri Feb 23 2018/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Broken to overcast low ceilings are expected tonight
under the prevailing surface inversion and persistent Low Level
Jet. IFR to MVFR ceilings are likely with the inversion setting
up at around 1000 feet. The LLJ is forecast to intensify tonight
strengthening to around 40-50 knots with gusty conditions
overnight. Winds to mix to the surface as the cap weakens
Saturday morning winds breaking up the low overcast with VFR
developing and strong SE surface winds sustained at 20-25kts and
gusts between 30 and 40 knots.

PREV DISCUSSION... /issued 516 PM CST Fri Feb 23 2018/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Broken to overcast low ceilings expected tonight
under the prevailing cap. MVFR ceilings will be likely with the
more aggressive NAM taking it down into IFR territory. Some fog
will redevelop, but persistent stronger winds should hinder the
denser variety. A low level jet will persist through Saturday
morning, and a bit longer along the coast, as Gulf high pressure
interacts with deepening low pressure over the southern Plains.
South southeast winds will be breezy to windy by mid Saturday
morning to early afternoon, especially at HRL. Moderate to breezy
winds will then continue into Saturday evening.

PREV DISCUSSION... /issued 310 PM CST Fri Feb 23 2018/

SHORT TERM (Now through Saturday night): Skies continue to clear
across the western portions of the CWA and winds have increased
across eastern portions where diurnal heating has allowed mixing to
increase. The pressure gradient will be strong across the lower TX coast
tonight into Saturday and believe this will inhibit fog development
across most of the Rio Grande Valley tonight into Sat morning but
some patchy fog may develop across extreme western portions of
the CWA Sat morning. May need a Wind Advisory for the coastal
counties Saturday as a strong low level jet across the lower TX
coast will mix down with diurnal heating late Sat morning. Breezy
to windy will prevail across the Rio Grande valley Saturday before
a weak cold front moves into the northern ranchlands Sat night.
Winds will diminish Sat night with scattered showers and isolated
thunderstorms developing along the front late Sat night. Patchy
fog will likely develop across portions of the Rio Grande valley
late Sat night as well.

LONG TERM (Sunday through Friday): A cold front will be moving
through the northern areas of the CWA at the beginning of the long
term period early Sunday. Models continue to bring it through Deep
South Texas late in the afternoon with increasing shower and
thunderstorm chances Sunday into early Monday. Timing of the FROPA
will be important and if it moves through around peak heating,
a few stronger storms will be a possibility. As of now, have kept
temperatures rising to near 80 in the lower Rio Grande Valley and
possibly several degrees higher around Brownsville or Harlingen.
12Z model soundings for Sunday afternoon show a moist and veering
profile with 0-6km shear increasing to 40 to 50 kts along with
CAPE values of 1200 to 1500 J/kg, which may be enough for some
hail and strong winds.

As we go into early next week, coastal surface troughing will
continue to provide a decent chance of rain showers across the
eastern half of the area, including the coastal and marine zones.
Temperatures will also range from the upper 60s to low 70s with
possibly a higher warm-up out west with fewer clouds and showers
expected. Southeast flow will return as the surface high shifts
eastward and the next storm system develops in the Plains.
Temperatures will rebound quickly Tuesday and Wednesday with winds
possibly exceeding Wind Advisory criteria on Wednesday as the
pressure gradient strengthens. The next cold front will move
through some time late Wednesday into Thursday, but model
solutions diverge at this point. Went with more of a blend with
the initial passage, but used the GFS for surface winds, which
seem more realistic on Thursday when the better push of higher
pressure comes. Towards the very end of the long term period, a
coastal trough may develop post-front and bring another shot of
cooler, wetter conditions for next weekend.

MARINE (Now through Saturday night): Seas were 4 feet with
south to southeast winds near 12 knots offshore the lower Texas
coast this afternoon. Moderate to strong southeast winds will
prevail across the coastal waters tonight as low pressure across
northwest Texas and surface high pressure across the eastern Gulf
of Mexico provides a strong pressure gradient across the lower TX
coast. Will continue to word SCEC for the far offshore waters. The
pressure gradient will remain strong across the western Gulf
Saturday and moderate to strong south winds will prevail across
the lower TX coast. A weak cold front will approach the coastal
bend Sat night and winds will diminish as the pressure gradient
weakens across the western Gulf.

Marine fog will redevelop across the Laguna Madre and the nearshore
waters tonight and Sat night as warm air moves across the cooler
water temperatures. Some locally dense fog may develop across the
lower TX coast reducing visibilities to less than a nautical mile.

Sunday through Friday: Light southeast flow will continue ahead of
the next cold front on Sunday evening, which will shift winds back
to the north and northeast into Monday. Shower and thunderstorm
chances will increase ahead of the front with a few stronger
wind gusts possible Sunday night. A coastal trough will provide
light rain chances through Monday with east to southeast flow
returning Tuesday. Southeast flow will increase as the next storm
system in the Plains strengthens through mid-week with Small Craft
Advisories possible. Another cold front will move through
sometime Wednesday night into Thursday.


GM...Dense Fog Advisory until 10 AM CST this morning for GMZ150-155.



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