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Area Forecast Discussion (AFD)

Issued by Brownsville/Rio Grande Valley, TX (BRO)

                            
000
FXUS64 KBRO 211117 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
617 AM CDT Wed Aug 21 2019

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

&&

.AVIATION...VFR conditions expected to generally prevail through
the TAF period. Isolated showers will stream northwest from the
Gulf of Mexico at times this morning and additional showers and
isolated thunderstorms may develop across the afternoon seabreeze,
mainly north of the Rio Grande Valley. SE to ESE winds may gust at
times to near 18-20 knots during the afternoon with light winds
returning overnight. 

&&

.PREV DISCUSSION... /issued 423 AM CDT Wed Aug 21 2019/ 

SHORT TERM (Today through Thursday):  Mid level high pressure 
stretched from the Baja coast into the Desert SW continues a slow 
retreat westward off the Pacific coast while the Bermuda High off 
the east coast slides further north and east, allowing a weak 
inverted trough of low pressure to slide northward across the Gulf 
of Mexico and along or near the lower Texas coast. As observed the 
past two days, this should help showers and thunderstorms develop 
across the seabreeze each afternoon. 

The arrival of deeper tropical moisture into the mix today and 
Thursday yields a better chance of showers and thunderstorms in both 
streamer activity off the Gulf during the morning hours and along 
the seabreeze late morning through mid afternoon hours. Have kept 
POPs generally 20 percent today and near 30 percent on Thursday. The 
trend has been to hold off the better rain chances generally each 
model run another 12 to 24 hours, keeping much needed rain mostly 
off the coast, so we tread optimistically, hanging our hat on the 
seabreeze activity to help clean out the dirt collecting in lonely 
rain gauges. 

Temperatures today may approach what was observed yesterday out 
west, with 2-3 degree differences along the mid to lower valley. As 
cloud cover and rain chances increase, forecast highs for Thursday 
drop another degree or two across the mid to lower valley, and still 
above 100 degrees west. Have stuck with triple digit highs for 
McAllen, but feel that may be about the eastern edge of 100s on 
Thursday. 

Will issue a fire danger statement this shift for counties along and 
west of 281/I69C and a discussion will be included below.  

LONG TERM (Thursday Night through Tuesday): The pesky
subtropical high will continue to reside across the eastern Gulf
of Mexico. This high will continue to help increase winds, 
especially during the daylight hours as a thermal low develops 
upstream. Aloft, a mid level weakness will continue to move 
eastward from the Red River Valley this weekend. This may be 
enough to help increase moisture just a bit aloft. With the 
weakness, more moisture, and perhaps a sea breeze, showers and 
thunderstorms will be possible, especially along and east of 
Hwy281. Although rain chances across the middle and upper valley 
are nonzero.

The upcoming weekend and early next week has been trending dryer,
at least in terms of QPF signal. Decided to drop POPs by 10,
however, again the potential for rain is nonzero. The better QPF
signal this weekend and early next week will either be just
offshore or across northern Mexico. With the QPF signal and
inverted mid level trough, didn't go as dry as some of the global
blends. 

Toward the end of the period, globals indicate a cold frontal
boundary surging southward just beyond the scope of this forecast.
If this front does develop and move closer to the area, expect
the lower level pressure gradient to relax. Regardless of 
rainfall, an increase in cloud cover and lower thicknesses suggest
a bit cooler temps this weekend and into early next week. 

MARINE (Today through Thursday): High pressure continues to weaken 
across the Gulf, with a weak mid level trough of low pressure 
sliding north into Thursday, bringing an increased chance of showers 
and thunderstorms across offshore and coastal waters. With a 
weakened pressure gradient along the lower Texas coast and subsiding 
southeasterly swell, expect seas to continue to subside through the 
short term, generally 2 to 3 feet or less. A moderate chop is still 
possible across the bay this afternoon and Thursday with the 
easterly afternoon breeze.

(Thursday Night through Tuesday): Cautionary wording headlines 
will be likely through the upcoming weekend as the stubborn 
subtropical high across the eastern portion of the Gulf as well 
as a thermal low across northern Mexico. Moderate southerly winds 
and elevated seas are expected to continue through early next week
before a cold front tries to move southward by mid to late week. 
Out ahead of this front, expect pressure gradient to relax and 
marine conditions to improve. 

FIRE WEATHER...A slight increase in moisture is expected over the 
next couple of days, unfortunately, humidity values this afternoon 
likely still dip to between 25 to 35 percent or even less across 
western portions of Deep South Texas. With 20 foot winds expected to 
touch 15 mph this afternoon and gust higher, critically dry fuels 
across most of the region, and persistent wildfire activity over the 
past few days across the mid and upper Rio Grande Valley, will go 
ahead an issue another fire danger statement covering all counties 
along the 281/I69C corridor and west. Burning of any kind should be 
postponed. 

&&

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

$$

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HTTP://WEATHER.GOV/RGV

56-Hallman...Aviation