458 
FXUS64 KBRO 182313 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
613 PM CDT Sun Jul 18 2021

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

&&

.AVIATION...VFR conditions prevail for each of the TAF sites
through the period. Light to moderate southeast winds will also
prevail for the next few hours, going nearly calm overnight, and
will pick back up again later Monday morning. Some widely
scattered showers may occur again on Monday, but coverage is
expected to be sparse enough to preclude any mention of showers
in this TAF package. 

&&

.PREV DISCUSSION... /issued 308 PM CDT Sun Jul 18 2021/ 

SHORT TERM (Now through Monday Night): The mid level ridge will 
gradually edge westward over the Four Corners region through the 
short term while a trough over the eastern CONUS stretches and 
extends southwestward over the Southeast CONUS and into Texas by 
Monday night. At the surface, high pressure off the East Coast 
extending across the Gulf of Mexico will allow light to moderate 
southeast winds to persist through the period. Even while under a 
weak ridging pattern, these persistent onshore winds will keep low
level moisture high and will allow for a slight chance for some 
isolated showers and an occasional thunderstorm to develop through
this evening and again tomorrow, so have kept slight chance PoPs 
for mostly the daytime hours overland...along with isolated 
nocturnal showers/thunderstorms over the Gulf waters. With this 
said, most areas will remain dry because these 
showers/thunderstorms are expected to be isolated and brief with 
no solid upper level support. 

Temperatures will be near climatological normal or even a few 
degrees below through the short term. Heat indices will likely top 
out in the 100 to 110 degree range this afternoon and Monday 
afternoon across the entire area, and while this will feel hot, no 
Heat Advisories are expected to be needed at this time. 

LONG TERM (Tuesday through Sunday): Global forecast models
continue to prog unsettled weather to develop across portions of
south Texas Tuesday through Thursday as an elongated 500mb trough
across the southeast United States extending into east Texas
brings a weak cold front into central Texas Tuesday before
stalling. A surface trough is expected to develop across the Texas
coast Wednesday as a shear axis develops in the wake of the
elongated upper level trough across south Texas. The 12Z GFS 
progs strong convection developing across the upper portions of 
the Rio Grande Valley Tues night so will confine rain chances to
the northern and western portions of the CWA Tuesday before
expanding rain chances elsewhere Tues night. An MCV is likely to
develop with the thunderstorm complex Tues night and this will
provide a good chance of rain across deep south Texas Wednesday
with abundant low to mid level moisture across the area. The 500mb 
shear axis across south Texas will lift slowly northward Thursday
and this will continue to provide unsettled weather across deep 
south Texas Thursday with PWAT anomaly values remaining above 
normal across the area. Rain chances will finally diminish Thurs 
night into Friday as the 500mb ridge across the eastern Gulf of 
Mexico nudges westward into the western Gulf Friday and drier air 
finally filters into the coastal sections of deep south Texas 
through the rest of the week into the weekend with the increase in
subsidence. The increase in cloud cover and rain chances will 
provide below normal temperatures for highs Tuesday through 
Thursday before returning to near normal through the rest of the 
forecast period.

MARINE (Now through Monday night): Generally favorable marine
conditions are expected through mid week with wave heights in the
1 to 3 or 2 to 4 foot range and light to moderate southeasterly 
winds expected. However, brief isolated showers and thunderstorms 
will be possible over the waters with heavy rain and occasional 
cloud to water lightning possible with this activity. 

Tuesday through Friday...Light southerly winds will prevail across
the lower Texas coastal waters Tuesday with weak low pressure
across Louisiana. The pressure gradient will remain weak across
the western Gulf of Mexico Wednesday before increasing slightly 
on Thursday with high pressure across the eastern Gulf of Mexico 
and low pressure across northeast Mexico. Light to moderate south 
to southeast winds will prevail across the coastal waters Thursday
before increasing on Friday as the pressure gradient continues to
increase across the western Gulf of Mexico. Moderate south to
southeast will prevail across the coastal waters Friday with SCEC
conditions possible across the offshore waters Fri night.

&&

.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  78  90  77  91 /  10  10   0  10 
BROWNSVILLE          78  93  78  94 /  10  10   0  10 
HARLINGEN            76  93  76  94 /  10  20   0  10 
MCALLEN              77  96  77  96 /  10  20   0  20 
RIO GRANDE CITY      76  99  76 100 /  20  10   0  20 
SOUTH PADRE ISLAND   80  85  80  86 /  10  10   0  10 

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...None.
&&

$$

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55-Adams/Aviation