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Area Forecast Discussion (AFD)

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

FXUS64 KBRO 230015 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
715 PM CDT Wed May 22 2019

.DISCUSSION...A few minor changes to the forecast grids include 
adjusting cloud cover tonight and tomorrow for a quicker east to 
west spread of the marine stratus layer and raise high 
temperatures for Thursday a few degrees, which mainly affect the 
coastal strip and the Lower and Mid RGV. Heat remains the main
forecast issue with heat indices expected to once again exceed 100
degrees once again Thursday afternoon. 


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


.AVIATION...MVFR cigs to prevail this evening and overnight with
the marine stratus layer advancing westward rather quickly. The
lower cigs continue into Thursday morning before mixing out with a
mix of higher end MVFR to lower end of VFR Thursday afternoon.
Pressure gradient remains moderate to strong with southeast flow
15-20 knots tonight and 20-30 knots Thursday. 


.PREV DISCUSSION... /issued 259 PM CDT Wed May 22 2019/ 

SHORT TERM (Now through Thursday night): The main forecast issue in 
the short term will be heat, with mid 70s to near 80 degrees at 
night, and 90s to near the century mark on Thursday. Heat index 
values will stay in the 80s to lower 90s until late in the 
evening, while values on Thursday afternoon will reach the 102 to 
107 degree range for a few hours in the afternoon for portions of 
deep South Texas and the RGV. The elevated heat index values will 
be supported by dew points well into the 70s for most of the area.

On the large scale, stable mid level ridging over the lower 
Southeast United States extends west into portions of East Texas. 
High pressure over the Gulf will provide continued moist, low 
level southeast flow, along with moderate to breezy southeast 
winds. If anything, downstream mid level ridging will build 
slightly farther west to over the North Central Gulf in the short 
term. The stable conditions will favor haze, as particulate matter
from burning in Mexico continues to move north on the prevailing 
winds. A mix of clouds and sun will prevail on Thursday, though 
the extra morning cloudiness will scatter out to some extent by 
afternoon. Rain chances will remain muted in the short term.

LONG TERM (Friday through Wednesday): Hot and breezy conditions
will be the story in the long term as we finish off the week and
head into the weekend. In the midst of an amplified upper-level 
flow, high pressure will broaden across the Southeastern U.S., 
extending westward into the Western Gulf and across Deep South 
Texas. Models are in fair agreement through much of the long term 
period, therefore, few changes were needed in this forecast 
update. Daily high temperatures will be a few degrees above normal
with elevated dew points, maintaining heat index values of 105 or
greater at times. Model time-heights show very shallow moisture 
with RH values below 25% above 850mb. The only notable chance of a
shower or storms is on Friday with a bit deeper moisture 
available near the coast. Breezy conditions along the coastal 
counties may hinder seabreeze development, so have kept silent 10%
PoP for now.

MARINE (Now through Thursday night): Moderate to strong 
southeast winds and moderate to high seas will persist through the
forecast. A broad and strong surface high pressure area will 
remain anchored in place over the Gulf of Mexico, supporting a 
tighter pressure gradient and the related higher winds and seas. 
Small craft advisory conditions will persist in the short term, 
with wave heights in addition to winds meeting criteria on the 
Gulf, and choppy to rough conditions on the Bay.

Friday through Wednesday: Adverse marine conditions will be
possible each day as a series of surface lows develop and move
through the Central Plains, tightening the pressure gradient
across the Western Gulf. Periodic Small Craft Advisories will
likely be needed for at least hazardous seas. The gradient should
relax a bit early next week, though Small Craft Exercise Caution
conditions can be expected.


GM...Small Craft Advisory for winds until 7 AM CDT Thursday for 

     Small Craft Advisory until 7 AM CDT Thursday for GMZ150-155-170-



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