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Area Forecast Discussion (AFD)

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

                            
000
FXUS64 KBRO 201742 AAB
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1242 PM CDT Tue Aug 20 2019

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

.AVIATION...Satellite and radar images as well as surface
observations indicate most of the cumulus development across
eastern portions of the CWA with isolated showers developing 
along the seabreeze front across the coastal sections early this 
afternoon. Ceilings were near 6000ft at KEBG. Expect VFR
conditions to prevail across the Rio Grande Valley through the
rest of the afternoon into early this evening as the 500mb
subtropical ridge across northern Mexico extending into the
northern and central portions of Texas continues to provide
subsidence across southwest and deep south Texas. 
&&

.PREV DISCUSSION... /issued 607 AM CDT Tue Aug 20 2019/ 
DISCUSSION...Updated for latest aviation discussion below.

AVIATION...VFR conditions prevail through the TAF period with
very brief MVFR CIGs possible over the next couple of hours and
again overnight tonight, especially across MFE after midnight. Any
reductions in ceiling should be short lived. Breezy southeast
winds return this afternoon, with an easterly turn along and
behind the seabreeze by mid afternoon from east to west across 
the RGV. An isolated shower or thunderstorm along the seabreeze is
possible today, mainly north of the valley. 

PREV DISCUSSION... /issued 341 AM CDT Tue Aug 20 2019/ 

SHORT TERM (Now through Wednesday): High pressure shifts northwest 
through the short term period, allowing the pressure gradient to 
continue to weaken, letting southeasterly winds generally decrease, 
across Deep South Texas into tomorrow. Wind gusts this afternoon 
could still reach 20-25 mph at times, especially across the mid to 
lower Rio Grande Valley. An isolated shower or thunderstorm is 
possible along the seabreeze, mainly across Willacy or Kenedy 
counties this afternoon, otherwise, dry conditions will generally 
persist through tonight. 

The seabreeze may have a better chance of heading further inland 
today and tomorrow, although the lack of moisture today may limit 
development compared to Wednesday with a return of Gulf moisture. 
Have nudged POPs slightly down this afternoon, generally between 15 
to 20 percent, while keeping 20 to 30 percent POPs for Wednesday 
afternoon across areas mainly along and east of 169C.  

With slightly drier air in place today, expect heat indices to stay 
below Heat Advisory criteria, likely ranging from 105 to 109 across 
most locations this afternoon. Temperatures may top off a degree or 
two cooler than yesterday for locations east, with the better chance 
of a break in the heat expected Wednesday due to increased cloud 
cover, stronger seabreeze, and chance of rain. Since 20 foot winds 
have remained slightly elevated out west, will go ahead and issue a 
Rangeland Fire Discussion for elevated fire danger today. Burning of 
any kind across Deep South Texas is strongly discouraged. 

LONG TERM (Wednesday Night through Monday): The long term period 
begins with an inverted trough over deep South Texas giving us a 
little break from the influences of the mid level ridge which was 
pushed further north over the Four Corners region. This weakness 
overhead allows low to mid level moisture to move in, increasing the 
chance for showers and thunderstorms over our Gulf waters and 
possibly the eastern portion of our CWA as well. Increased PoPs and 
cloud cover will allow high temperatures to drop slightly (although 
still likely stay above normal) and bring a little relief from the 
oppressive heat.

On Thursday, models show a 500 mb low in the Bay of Campeche begin 
tracking northward around the northwestern edge of the Gulf through 
Saturday. While this feature is shown on both the ECMWF and GFS, 
discrepancies in its development bring down forecast confidence a 
bit through the rest of the forecast period. With this being said, 
both the GFS and the ECMWF have this feature skirt along the 
northwestern Gulf on Friday and keep the bulk of the low to mid 
level moisture offshore. Beyond Friday, models diverge even more 
with the progression of the aforementioned 500 mb low/tropical wave 
but will still go with rain chances each day due to the mid level 
weakness overhead and lingering moisture. 

Overall, the long term period will be slightly less hot with rain 
chances primarily across the eastern portions of the CWA and over 
the Gulf waters. 

MARINE (Now through Wednesday): High pressure edges northwest 
toward the Desert SW over the next couple of days, weakening the 
pressure gradient across the lower Texas coast. This will allow the 
southeast onshore flow to continue to decrease into Wednesday. 
Afternoon wind gusts may briefly reach 20 knots today across the 
bay, otherwise, marine conditions should be a slight improvement 
from yesterday. Gulf seas continue to subside as wind speeds overall 
decrease through Wednesday, with 2-4 feet expected today, shifting 
further offshore and generally subsiding to 2-3 feet on Wednesday, 
with improving surf conditions along the lower Texas coastal 
shoreline. Southeasterly swell may keep rip current risks elevated 
into Wednesday. 

Wednesday Night through Saturday...Light to moderate southeast 
winds and low seas will prevail through Thursday night. As the 
pressure gradient increases on Friday, the winds and seas become 
moderate through Saturday. Showers and thunderstorms will be 
possible at times across the coastal waters through the period.

FIRE WEATHER...Humidity values are expected to drop today as 
slightly drier air aloft works into the region with sufficient 
mixing, allowing dewpoints out west to dip into the upper 50s. 
Observations across the western and central counties yesterday 
raised fire weather concerns with lower than expected humidity 
values and elevated 20 foot winds during the driest portion of the 
afternoon. With criteria almost being met in the grids on both 
humidity and winds, and critically dry fuels across the region, will 
go ahead and issue a fire danger statement for this afternoon across 
all but the coastal counties across Deep South Texas. Burning of any 
kind is strongly discouraged and should be postponed a day or two. 
&&

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

$$

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