Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 200457 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1157 PM CDT Sat May 19 2018

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

.AVIATION...MVFR conditions are trying to settle into Deep South
Texas and the Rio Grande Valley as surface winds diminish to light
levels. Tomorrow, full VFR will be in effect with breezy winds
and higher clouds. However, a slip back into MVFR is expected
around sunset Sunday evening.

.PREV DISCUSSION... /issued 826 PM CDT Sat May 19 2018/

DISCUSSION...Updated for latest marine discussion below.

MARINE...Wind observations around the Laguna Madre have already
fallen below 20 knots this evening, so have elected to expire the
Small Craft Advisory for Winds there and the 0-20nm Gulf waters a
bit early. Not thinking that gradient will be strong enough to
support a SCA on the Gulf waters overnight, even with the
nocturnal maximum, though likely to remain solidly in SCEC range.
Latest short-term guidance consistent with this idea, so have
updated winds and seas accordingly. Also reduced PoP`s to below
mentionable levels in the coastal waters overnight. Text products
updated and disseminated.

PREV DISCUSSION... /issued 626 PM CDT Sat May 19 2018/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Surface troughing sagging southward from the Central
Plains toward northern Texas will maintain a moderately tight
pressure gradient over the next 24 hours. Breezy to gusty winds
observed currently at the RGV terminals will subside after sunset
but still remain 10-15KT overnight. MOS guidance and BUFKIT RAP
forecast soundings consistent in returning MVFR ceilings overnight
through late morning on Sunday. VFR should return thereafter, as
CIG`s lift/scatter out with breeziness again developing (though a
bit less than today).

PREV DISCUSSION... /issued 329 PM CDT Sat May 19 2018/

SHORT TERM (Tonight through Sunday Night): The ridge axis aloft ha
finally shifted east as the longwave trough digs across the western
US. This, along with a passing wave around the bottom of the trough,
is inducing low pressure deepening across the northern Panhandle
into SW Kansas. This deepening low has brought our winds upwards
today, generally reaching around 20 knots with some higher gusts.
This has also drawn moisture northward from the Gulf, making for a
slightly less hot, but much more humid day today. This is noted by
heat index values still right around 100 right now. The sfc low
remains steady in Kansas, keeping local gradient tight through the
night. Winds will stay around 15kts overnight, while moisture near
the surface will keep skies partly to mostly cloudy. Most of
tomorrow will be similar to today, with partly to mostly cloudy
skies and breezy southeast winds. Heat index readings will again
reach around 100 during the afternoon, especially right along the
river. The next wave rounds the base of the midlevel trough Sunday
night, and models are still noting convection trying to form on the
mountains in Mexico and sweeping to the northeast. While the chances
for full-fledged thunderstorms crossing the river are not great,
there still may be some leftover showers trying to move northeast,
along with some possible midlevel light rain spreading over the
western counties. Have made some adjustments to the rainfall
forecast, focusing things after midnight Sunday night when showers
might finally arrive.

LONG TERM (Monday through Saturday): Strong 500 mb troffing will
be digging down the West Coast starting Mon while broad 500 mb
troffing will be in place over much of the Gulf of Mex. In between
these two features weak ridging will prevail at the start of the
upcoming work week. Some decent deep layer moisture will be
located over eastern Mex and southern TX at the start of the work
week. This may result in some diurnally driven conv on Mon. Also
the conv potential may be enhanced a bit as a weak 500 mb short
wave moves over the region Mon. As the west coast troffing closes
off and shifts up to the NE, the moisture levels will gradually
diminish heading into the rest of the upcoming week which will
allow the pops to decrease. As the West Coast closed low shifts
northeast the ridging over South TX will build gradually west with
a generally hot and dry atms in place over the RGV into next

The GFS and ECMWF models are in pretty good agreement in the
handling of the overall synoptic pattern over the RGV over the
upcoming week. Will stick with a general blend of the two models
for pops through Day 7 and will go a little on the warmer side of
guidance for high temps as both models seem to be underperforming
in the handling of the high temps.

MARINE (Now through Sunday night): Advisories remain in effect
through this evening for the Laguna Madre and Gulf water south of
20nm as winds continue to breeze northward around 20 knots. The
usual swapping of gusty winds will happen overnight, as the Laguna
winds relax to around 15 knots, but the Gulf waters beyond 20nm see
an increase of winds to around 20 knots. The advisory for the
nearshore gulf will likely be extended, and the farther offshore
waters will be added for the nighttime hours. Winds will again swap
in the morning, with Laguna winds jumping back up to 20 knots.

Monday through Thursday Night: The PGF over the lower TX coastline
will gradually weaken some next week allowing the winds and seas
to remain fairly low. Low to moderate E-SE surface winds will
prevail through next Thurs. No SCA conditions expected at this



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