Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 160530 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
1130 PM CST Sun Jan 15 2017

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

.AVIATION...Skies will remain mostly clear over the next few hours.
However...do expect there to be areas of low clouds moving in and
out across the region overnight from the occasional streamer showers
off shore. A strong 40 kt low level jet just off the surface between
1 to 2 kft may generate LLWS overnight. However...surface winds will
still remain in the 12 to 15 kt range with some higher gusts. The
winds will lessen on Monday as weak surface low develops over across
western portions of the region and clouds will increase as moisture
is wrapped into the area.
&&

.PREV DISCUSSION... /issued 1030 PM CST Sun Jan 15 2017/

DISCUSSION...Made a few minor adjustments to the forecast tonight
mainly to account for cloud cover...or the lack thereof. Overall
forecast trends are on track. The strong storm system across
north-central Texas will continue to move away into Oklahoma by
the morning. Meanwhile...a sfc low pressure system will develop
over the Rio Grande Plains...with winds eventually lessening and
some rainfall chances expected for the Northern Ranchlands on
Monday.

PREV DISCUSSION... /issued 603 PM CST Sun Jan 15 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...The afternoon CU field is quickly dissipating late
this afternoon and do expect any isolated MVFR cigs to lift.
Meanwhile...winds will begin to subside after sunset however
a strong 35 to 40 kt just is about 2 to 3 kft above the surface.
Depending on how the winds die off this evening and overnight...LLWS
may need to be added in a subsequent TAF package. However...winds
will still likely remain elevated overnight. The winds will
lessen on Monday as weak surface low develops over across western
portions of the region.

PREV DISCUSSION... /issued 339 PM CST Sun Jan 15 2017/

SHORT TERM (Tonight through Monday Night): WV imagery shows the
center of the H5 low moving into Far West Texas currently, with
strong dry slot moving ahead of it into South Texas. This has held
down the cloud cover today, which helped to mix more of the low
level jet down to the surface, bringing a breezy day to the
coastal regions. Cloud cover will remain limited overnight, so
some mixing to the sfc of llvl winds will continue with winds of
10 to 15 mph through about sunrise. Around sunrise, the main
surface reflection low will be moving across Oklahoma, with a cold
front extending back across central and southern Texas. a
secondary area of low pressure will be forming right across the
western LRGV at that time. This will funnel the winds more from
the south along the coast. Breezes will still continue for the
coastal areas at 15 to 20mph, but areas along and west of US 281
will see nearly calm winds, with some westerly to northwesterly
component possible late in the afternoon. The western valley will
see temperatures again into the 80s, with some concern that drier
air from aloft may push temps upwards another category. The
coastal counties will remain in the more humid airmass, with
isolated to widely scattered showers developing ahead of the sfc
trough and quickly lifting northward into the main storm system.
For Monday night, with the trough still lingering in the vicinity,
moisture will continue to feed northward. The next H5 low will be
rounding the corner in northwest Mexico, putting our area in
increasing diffluence. Add in a small vort impulse, and you get
widely scattered thundershowers, mainly after midnight across the
northern ranchlands.

LONG TERM (Tuesday through Sunday): A slow moving but strong 500
mb trough/closed low will steadily approach south TX on Tues and
Wed eventually moving through the RGV on Thurs. Following this
500 mb trough passage another couple of troughs will move over the
central and northern portions of TX from next Fri through Sun. The
first of these troughs will push a weak cold front into the
RGV/Deep South TX region on Wed. This front is expected to lift
back up north slowly as a stationary front which will limit any
serious CAA associated with the front. The approach of the 500 mb
trough axis over the RGV on Tues and Wed will have pretty decent
deep layer moisture and some instability to fire up some potential
t-storms early in the longer range period. Enough instability may
be able to interact with the trough axis to maintain some
marginal threat for isold stg/svr conv mainly near the lower and
mid TX coastline on Tues and Tues Night. Much drier and more
stable conditions will prevail over the region from late Thurs
into the weekend as the 500 mb trough axis clears the region
allowing more stable mid level ridging to build over the area.
One of the 500 mb troughs passing the region next weekend will
drive a fairly dry cold front through the area late Sat/early Sun
allowing some cooler air to enter the RGV.

Overall the longer range model guidance is in decent agreement in
the overall handling of the 500 mb pattern through Day 7 for the
RGV. However the GFS reflects stronger CAA for most of the longer
range period versus the ECMWF. Considering that the ECMWF appears
to be handling this overall warmer winter pattern over the last
several weeks/months that has resulted in near record or record
breaking high temps in the RGV...I tend to favor the warming ECMWF
numbers for temps. There are also some fairly big differences
showing up for pops from both the GFS and the ECMWF. So have
opted for a general model blend here as I don`t really have a
model preference for the conv chcs. Overall forecast confidence
in the longer range period is above average today.

MARINE: (Now through Monday night): Small craft advisories are being
hoisted for the Laguna Madre as winds have ramped up further than
forecast, reaching 20 knots. Once daytime heating is over,
decoupling should allow surface winds to decrease to 10 to 15 knots
for the Laguna through the night. Nocturnal mixing offshore will
begin to increase tonight, with marine area reaching near advisory
criteria. A surface trough will be developing inland tomorrow, which
will lower the pressure gradient across the marine zones. This will
keep winds lower than today, only reaching around 15 knots. Stronger
winds today and tonight, along with the long fetch, will push seas
near 7 feet tonight before lowering later Monday night.

Tuesday through Friday Night...No real strong cold frontal
passages are expected across the RGV area throughout this upcoming
week. This will allow weak to moderate surface ridging to maintain
decent south to southeasterly surface winds throughout the long
term period which will keep the marine conditions generally below
SCEC/SCA levels through Fri Night. However the cold frontal
passage next weekend will allow much stronger W-NW surface winds
to blow over the marine locations potentially resulting in SCA
conditions.
&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...Small Craft Advisory until 6 AM CST Monday for GMZ150-155-170-
     175.
&&

$$

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HTTP://WEATHER.GOV/RGV



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