Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 291808 AAB
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1208 PM CST Wed Jan 29 2020

...18z Aviation Update...

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

&&

.AVIATION...VFR conditions, with light to moderate north/northwest
to northeast winds, expected to prevail through tonight. Latest
model guidance does indicate low-level clouds (at or slightly
above 1500 ft agl) forming and/or drifting over the region as
early as 09-11z Thursday. Overall confidence is low at this time
on whether MVFR cigs will develop by or before 18z Thursday, but
did include a FEW-SCT deck around 2000 ft agl at all TAF sites
starting around 10z. Wind direction will be quite variable over
the next 24 hours, with winds starting off out of the north or
northwest this afternoon, then veering more easterly by this
evening. Winds are expected to remain light and turn out of the
northeast overnight tonight, into the early morning hours on
Thursday before again veering southeasterly by late morning.

&&

.PREV DISCUSSION... /issued 520 AM CST Wed Jan 29 2020/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...The drier air moving in behind the yesterday`s cold
front continues to spread over the RGV today. This will allow the
VFR conditions to prevail over the upcoming 24 hours even as some
high clouds begin to move in overnight tonight. There are no
aviation hazards expected over the upcoming 24 hours for the RGV.

PREV DISCUSSION... /issued 353 AM CST Wed Jan 29 2020/

SHORT TERM (Now through Thursday): Beautiful weather expected today
across Deep South Texas and the Rio Grande Valley under the
influence of the mid-level ridge and surface high pressure settling
in behind the front. After a chilly start to the day, highs will
reach the low to mid 70s under mostly sunny skies with light
northerly winds. In this very dry airmass, relative humidity values
are expected to drop into the teens out west and into the 20s along
the eastern counties this afternoon, but winds will be light, so
erratic fire behavior and spread will not be a concern at this time.

Heading into Thursday, the mid/upper-level ridge slides off to the
east as the next mid-level trough digs into the southwestern part of
the state and northern Mexico. Ahead of this system, isentropic lift
will be responsible for increasing cloud cover through the day on
Thursday and into the start of the long term period as warm, moist
air from the south overrides the cooler air at the surface. Rain
chances are introduced Thursday afternoon and increase into the
start of the long term period as the trough swings overhead and
isentropic lift continues.

LONG TERM (Thursday Night through Tuesday): Mid-level trough
axis swings east across Deep South Texas Thursday night into
Friday morning. Models develop a weak surface low along a frontal
boundary meandering south of the border, as well as weak low
pressure across the northwestern Gulf of Mexico. This combines
with ongoing isentropic lift to bring our best chance of rain for
the week, with POPs generally 40 to 50 percent, and slightly
higher chances across offshore waters. PWAT values peak to around
1 to 1.2 inches early Thursday night before dropping to 0.75 of
an inch into Friday morning. Have lowered guidance QPF slightly.

High pressure and drier air are expected over the weekend, with
southerly surface flow returning Sunday into Monday as both high
pressure heads east across the Gulf of Mexico and low pressure
develops into the Central Plains. A cut off low develops over the
weekend near Baja California and may aide in some moisture return
across northern Mexico and into South Texas. Feel models may be
overdoing this moisture return slightly. Have left in the slight
chance to isolated POPs Sunday night into Monday across the coast.
Next front arrives Tuesday, with very dry southwesterly flow
aloft. Relative humidity values could dip into the teens across
the western counties, with relatively light northerly 20 foot
winds.

High temperatures generally warm through the long term, starting
below normal into the mid and upper 60s, and gaining a few degrees
each day toward the mid 80s Monday into Tuesday. A couple of
cooler nights are in store across the northern ranchlands Thursday
and Friday night, dipping into the mid 40s. Overnight lows also
begin to rebound warmer slightly each night this weekend into
Tuesday.

MARINE (Now through Thursday): Buoy 42020 reported seas of 6.6
feet with 29 knot north-northwesterly winds gusting to 39 knots as
of 2:20 this morning. Small Craft Advisory conditions are
expected to continue for the Gulf of Mexico coastal waters through
early this afternoon. Winds and seas will then gradually subside
through Thursday as high pressure continues to settle into the
area.

Thursday Night through Tuesday: Favorable seas Thursday night
deteriorate into Friday with increasing northerly flow. There
remains a chance of showers across coastal waters Thursday night
into Friday afternoon. Winds and seas subside on Saturday into
Sunday, with very favorable marine conditions returning. As low
pressure develops across the Central Plains and high pressure
works east across the Gulf of Mexico, expect southerly winds to
increase into Monday, building seas into Tuesday before the
arrival of another cold front. There is another chance of showers
late Sunday through the day on Monday across coastal waters.
Small Craft Advisories may be needed Monday and Tuesday.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...Small Craft Advisory until 3 PM CST this afternoon for GMZ150-
     155-170-175.

&&

$$

This product is also available on the web at:
HTTP://WEATHER.GOV/RGV

Aviation Update...Mejia-67



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