Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 131137 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
537 AM CST Sat Jan 13 2018

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


.AVIATION...Light winds and clear skies prevail across deep south
Texas this morning. Winds will increase to 10 to 15 knots
late this morning into the afternoon as another weak northerly
surge arrives. Winds are expected to become light this evening and
overnight. Skies will remain clear through the next 24 hours.


.PREV DISCUSSION... /issued 438 AM CST Sat Jan 13 2018/

SHORT TERM (Now through Sunday): Reinforcing surface high
pressure will build into deep south Texas today. Temperatures will
be cooler than normal, running 5 to 10 degrees below normal
through Sunday. High temperatures today will be in the upper 50s
to the mid 60s under sunny skies. Moderate north to northeast
winds will be possible this afternoon. Otherwise, light winds are
expected through the period. Low temperatures tonight will be in
the 30s and 40s with mostly clear skies. Temperatures Sunday will
be a few degrees warmer than today, with high temperatures in the

LONG TERM (Sunday Night through Friday): Fairly quiet weather to
begin and end the long-term period, with much cloudier, cooler,
and occasionally rainy conditions during the middle part of the
work week (Tuesday through Thursday). 00Z runs of GFS and ECMWF in
pretty decent agreement on larger-scale features but differ on
the strength of incoming cold-air mass behind a frontal passage on
Tuesday. This also has implications for how long a subsequent
coastal trough will persist.

First, the easy part: For Sunday night into Monday, initially
modest NW flow aloft flattens as troughing drops into the Central
Plains. SE surface winds coupled with partial sunshine should
allow afternoon temps to reach the low-mid 70s, or a few degrees
above normal for mid-January. Might see some patchy fog after
midnight Monday night, as winds begin to back and slacken ahead of
the approaching cold front.

Front should move through the CWA during the daytime hours on
Tuesday, with some differences in timing noted: GFS has the
boundary across south-central TX at 12Z Tue, with the ECMWF
already pushing it into the northern tier counties. 00Z NAM
timing agrees more with the GFS, though that is at the very end of
its run. A chance of showers, mainly light, will accompany the
front. Significant differences in high temps for Tuesday, due to
the difference in arrival timing and strength of the cold air
behind the front, with the GFS 10-15 degrees warmer than the ECM.
Weighed the ECM heavier, given that the GFS has been too warm
several times now this winter with cold surges. Hopefully the NAM
will provide more clarity once its run extends out far enough in

Drier air filters in Tuesday night, though pockets of light
rain/drizzle likely to persist near the coast as a surface trough
sets up offshore just south of the area. Continued cold-air
advection will yield a cold night, with temps progged in the 30s F
over all land areas. Temps across the northern and western
ranchlands may dip to near freezing for several hours, so will
have to monitor this period for a freeze watch. Wind chill values
are also expected to be near advisory criteria Tuesday night/early
Wednesday. Threat of any frozen precip across the north still
looks quite low. Even with the cold surface temps, prog
thicknesses do not support it. PoP`s will be decreasing quickly as
well with drier air moving in.

Wednesday should be cloudy and chilly, along with some
drizzle/light rain along the coast, with temps struggling to reach
the low 50s even at BRO. Wednesday night into Thursday, an upper
low will move from the Plains toward the ArkLaTex region, finally
inducing the coastal low/trough to move northward along the Texas
coast. This will spread some mentionable rain chances back further
inland, with temps beginning to recover into the mid-50s to low
60s by Thursday afternoon.

Short-wave ridging aloft takes hold on Friday, with temps climbing
back to within a few degrees of normal. Right now, Saturday looks
to be warm and breezy, as flow becomes more zonal aloft and S/SE
surface flow picks up ahead of the next possible (weak) front,
which is due in Saturday night or Sunday.

MARINE (Now through Sunday):  A surge of high pressure will build
into the western Gulf waters today. Moderate northeast winds and
moderate seas are expected for today. Small craft should exercise
caution on the Gulf waters 20 to 60 NM east of Padre Island due to
elevated winds and seas. Marine conditions improve tonight and
Sunday as high pressure spreads out then moves east. Light to
moderate onshore flow and low to moderate seas will prevail tonight
and Sunday.

Sunday Night through Thursday: Relatively benign marine conditions
through Monday with moderate SE winds and seas generally 3-4 ft.
Winds begin to back on Monday night ahead of the next strong cold
front which will move through the coastal waters Tuesday morning.
North winds quickly increase to near 25 knots behind the front,
necessitating Small Craft Advisories as seas build to 7-8 ft. on
the Gulf by early Wednesday. A few gusts to gale-force can`t be
ruled out immediately behind the front, mainly for the 20-60nm
offshore waters. Coastal troughing will keep winds elevated
through much of Wednesday, with seas remaining agitated as well.
SCA conditions likely to continue on the Gulf through much of




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