Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 280559 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
1259 AM CDT SAT MAY 28 2016

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

.AVIATION...Satellite images and surface observations indicate
mostly clear skies across most of the CWA late tonight.
Visibilities were near 6sm with mist at KPIL. Expect MVFR
conditions to develop early Saturday morning as low to mid level
moisture increases across northeast Mexico into southwest Texas
late tonight. VFR conditions will prevail after 15Z Saturday as
diurnal heating allows mixing to increase across the area.
&&

.PREV DISCUSSION... /issued 621 PM CDT FRI MAY 27 2016/
DISCUSSION...Updated for latest aviation discussion below.

AVIATION...TSRA debris clouds over central and east-central
portions of the forecast area will rapidly dissipate and move to
the east in the next couple of hours for VFR cigs/vis all areas.
Low clouds will begin to develop after 05Z, mainly east of Hwy
69/281. MVFR cigs will become widespread after 09Z in the same
area. Gusty winds will slowly diminish this evening, generally
remain below 15 kts overnight, then kick back up into the 18 to 26
kt range after 15Z Saturday morning. Will see a mix of MVFR/VFR
cigs through the daylight hours on Saturday, but generally
becoming VFR in the afternoon.

PREV DISCUSSION... /issued 310 PM CDT FRI MAY 27 2016/

SHORT TERM (Tonight through Saturday Night): Drier air aloft has
worked into the area, per current water-vapor imagery, on the
south side of an upper-level low currently spinning over the
Central Plains. Breezy to gusty S-SE winds will persist through
the rest of the afternoon over roughly the eastern half of the CWA
as the pressure gradient remains enhanced between a surface trough
extending from interior Mexico up to the Central Plains low and
surface ridging over the Gulf of Mexico. Winds have remained below
advisory levels, however, and should fall off this evening as the
atmosphere decouples and the gradient gradually decreases. A few
thunderstorms have developed over the higher terrain in Mexico
this afternoon, though it remains to be seen whether they can make
it into the CWA in the drier environment...especially once daytime
heating is lost. Radar trends would seem to favor the southern
counties, if any.

High threat of rip currents along the lower Texas coast will
continue through at least Saturday as mix of wind-driven waves and
longer period swells combine to make surf conditions hazardous for
swimmers. A rip current statement remains in effect.

Heat indices have approached advisory levels of 110-112F in the
McAllen area this afternoon.  Thinking was that dewpoints would mix
a few degrees lower...hence lowering the heat index...but they have
held in the upper 70`s. Conditions should not hold at these levels
much longer, as we are now at the hottest time of day, but this will
need to be monitored again tomorrow.

The weather pattern aloft will feature semi-flat ridging building in
tonight and persisting through Saturday.  Bumped up max temps a few
degrees as a result of increasing heights and more sunshine.
Isolated to scattered thunderstorms possible again on Saturday
with diurnal heating, though severe storms are not expected. By
Saturday night, flow aloft backs slightly to WSW again as next
upper-low progresses into California. This could open the door
again to smaller-scale disturbances in the flow approaching the
area and triggering a few storms, but can`t see a clear timing
signal in the guidance at this time.

Much of short-term forecast was retained in part or blended with
latest model guidance.

LONG TERM (Sunday through Friday): For Sun-Tue, competing forces
will be at work over deep south Texas that will have an effect
mainly on chances of precipitation. Weak upper ridging will
extend northward out of Mexico while weak upper level disturbances
will get ejected out from a broad trough of low pressure over the
Rocky Mountain states and move through the upper flow over us. The
upper disturbances will combine with residual moisture already
over the region for the net result of low end chances of mainly
afternoon/evening showers/thunderstorms generally west of Hwy 77.
Will see partly/mostly cloudy conditions, near to slightly above
normal temperatures, and breezy afternoons all areas.

On Wednesday, the broad upper trough begins to transition into the
central Plains and this will increase lift/moisture across the Rio
Grande Valley as the trough approaches, then crosses, the region
Wednesday night. The GFS/ECMWF both indicate the best chances for
precipitation throughout the entire period during the Wed/Wed
night time frame. Am sure some convective feedback is involved,
but the latest GFS is actually showing the development of an
MCS/major rainfall event over the western third of the forecast
area Wednesday afternoon/evening. However, have not see enough run
to run consistency to bite on this just yet. For now, will
maintain 30-40% chances of precipitation area-wide. Temperatures
may briefly end up somewhat below normal Wed/Wed night, especially
if widespread convection develops.

Notable differences begin to show up between the GFS and ECMWF in
the Thu/Fri time frame with the GFS showing the upper trough
moving across deep south Texas nearly a day ahead of the ECMWF on
Thursday as opposed to the ECMWF which shows the trough passage on
Friday. Either way, will maintain chances of precipitation for
Thu before decreasing chances somewhat for Friday. Temperatures to
remain near normal for the latter portion of the work week.
Afternoons should not be as breezy either as the pressure gradient
weakens somewhat.

MARINE (Now through Saturday night): Strong SSE winds expected
to persist over the Laguna Madre until this evening when
decoupling, along with gradually decreasing PGF, should bring them
down to more moderate levels. SCA for the Laguna is set to expire
at 7pm.

Offshore, seas are running 7-8 feet with south to southeast winds
20G25KT at Buoy 020 this afternoon.  Winds will only gradually
decrease overnight with along with the pressure gradient. Seas also
expected to subside to around 6 feet by early morning. Moderate
southeast winds will prevail across the lower Texas coast on
Saturday with SCEC likely to remain after SCA expires.

Monday through Friday: Somewhat elevated winds/seas will lead to
either Small Craft Advisory or Small Craft Should Exercise Caution
headlines Mon-Wed due to a tight pressure gradient from surface
high pressure over the western Gulf and low pressure over the
central Plains. Winds/seas slowly subside in the Thu/Fri time
frame as the pressure gradient relaxes.
&&

.BRO Watches/Warnings/Advisories...
TX...High Rip Current Risk through this evening for TXZ251-256-257.

GM...Small Craft Advisory until 7 AM CDT this morning for GMZ150-155-
     170-175.
&&

$$

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