Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 240749 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
249 AM CDT Sun Sep 24 2017

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


.AVIATION...KBRO radar shows some patchy marine showers trying to
edge in along the coastline from the Gulf of Mex. Accordingly will
include a mention of vcsh for the BRO and HRL areas for the first
few hours of the current TAF set. The 00z BRO sounding shows that
the atms CAPES and PWAT values over the RGV have not changed much
over the previous 24 hours. So expect daytime heating and the
local sea breeze effects to fire off some isold/sct conv during
the afternoon and early evening hours. This activity will likely
be isold enough to limit the aviation impacts to the local
airports. Will go with overall VFR conditions of the RGV aiports
with some brief reductions to MVFR levels due to lowered ceilings.


.PREV DISCUSSION... /issued 639 PM CDT Sat Sep 23 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Tranquil conditions are expected through the overnight
hours as winds diminish to light levels and a few clouds develop.
Tomorrow, VFR is expected to continue with moderate winds and
scattered cloudiness. Convection is expected to be isolated and
has been kept out of the TAFs. However, it may need to be included
in the next TAF issuance if scattered showers and thunderstorms
are anticipated.

PREV DISCUSSION... /issued 252 PM CDT Sat Sep 23 2017/

SHORT TERM (Now through Sunday night): Well-amplified ridge over
the Midwest will slowly move eastward as a deep trough over the
western half of the U.S. slowly nudges eastward. A mid-level low
over the northern Gulf will remain to our east, leaving weak flow
overhead of Deep South Texas. There still isn`t a lot of upper
level support for more widespread rain chances, rather most of the
convection will be seabreeze-driven. RH values of 60 to 80% in
the low levels along with precipitable water measured from the 12Z
sounding of near 2.10" will allow for locally heavy downpours
again this afternoon and tonight with any thunderstorms that form.
Activity should decrease to mainly the marine areas overnight
with isolated convection again on Sunday. Temperatures continue to
run above normal and several degrees above model guidance, so
have kept high temperatures in the mid to upper 90s for most
areas. If convection doesn`t manage to develop, wouldn`t be
surprised to hit 100F a couple more times in the Mid Valley.

LONG TERM (Monday through Saturday):Main challenge during the
long term continues be the chance for showers and thunderstorms
and the potential for heavy rainfall. Latest model suite remain in
fair agreement with the synoptic pattern and moisture profiles.

South Texas continues to lie between a large scale trough in the
west and a mid level ridge over the Gulf extending into the
Tennessee and Ohio Valleys. Southwest flow aloft, associated with
the western trough and a persistent moist southeast surface flow
will allow for a deepening of tropical moisture. This lead to
scattered and possibly numerous showers and thunderstorms Tuesday-
Thursday with the western zones initially seeing higher pops
(initially Tue-Wed), with a closer proximity to the upper trough
but all areas are expected to see a good chance of rain in this
pattern. GFS remains the most robust on rain chances, especially
in the Lower Valley where a coastal trough may develop, but all
models continue to trend upward through mid week. Next issue is a
frontal boundary expected to work its way into the area Thursday
and Friday. This front will likely act as a focus for areas of
potentially heavy rainfall especially with forecast pwats still
advertising values of 2-2.5 inches. Seven day qpf values with the
bulk falling during days 3-5 are ranging 0.5-1 inches in the east
and 1-2 inches in the west and this could easily jump up a few
inches if the upper trough trend slightly more eastward keeping
the mid level trough over the Central Gulf. In any case, this
looks like our best chance for widespread rain this Summer.

Both the GFS and ECMWF are in fairly good agreement with the front
oozing it through the CWA Thursday night into Friday with drier
air slowly filtering into the northern counties Saturday and
South of the River next Sunday.

As for the rain chances and clouds increase
temperatures to moderate near to slighlty below normal with
exception to the overnight lows which are likely to remain above
normal. Model guidance shows temperatures to drop 5-8 degrees below
seasonal averages next weekend in wake of the front.

MARINE:(Now through Sunday night): Marine conditions remain similar
to the past several days as surface high pressure remains over the
northeast Gulf with not much of a pressure gradient. Winds will
range from 10 to 15 knots out of the E/SE with seas at 2 to 4 feet.
Showers and thunderstorms will be possible through the short term
with a few gustier winds and higher seas near thunderstorms.

Monday through Thursday...Coastal waters to remain tranquil
with light to moderate southeast flow and low to moderate seas.
southeast winds Monday and Tuesday back more to the east Wednesday
and possibly turn east-northeast Thursday as a cold front works its
way south close to the Lower Texas coast. Showers and some
thunderstorms to increase in coverage through the week with locally
higher wind and seas. The front is forecast to move through the
coastal waters some time Friday.




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