Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 271759
AFDBRO

Area Forecast Discussion
National Weather Service BROWNSVILLE TX
1259 PM CDT FRI MAY 27 2016

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

&&

.AVIATION...Breezy south-southeasterly winds expected to continue
through the afternoon at the terminals before winds de-couple
after sunset and pressure-gradient force gradually decreases.
Water-vapor channel satellite imagery shows that drier air aloft
continues to move into the area, but low-level moisture remains
in good supply. Per visible and surface ob trends, will keep VFR
CIG`s prevailing through the afternoon at HRL and BRO...though BRO
could occasionally dip back to high-end MVFR through 20Z. Deeper
mixing at MFE should allow for generally unlimited ceilings until
mid-evening. May need to keep an eye on an eye on any
showers/thunderstorms developing in area of surface convergence
over the western counties of the CWA possibly approaching MFE
later this afternoon...but confidence is low due to the drier air
moving in. Winds return to near-breezy levels by mid-morning on
Saturday with CIG`s lifting back to higher-end MVFR (except VFR at
MFE).

&&

.PREV DISCUSSION... /issued 642 AM CDT FRI MAY 27 2016/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Satellite images and surface observations indicate
some low clouds and some high clouds across portions of the CWA
this morning. Ceilings were near 1000ft at KT65 to near 2200ft at
KPIL. Visibilities were near 4sm with mist at KHBV to near 6sm
with haze at KHRL. Expect MVFR conditions to prevail across
portions of the Rio Grande valley and the northern ranchlands this
morning before a surface trough moves through the CWA this
afternoon bringing drier air into the western portions in the wake
of a surface trough. VFR conditions will prevail this afternoon
into this evening as a result.

PREV DISCUSSION... /issued 435 AM CDT FRI MAY 27 2016/
SHORT TERM (Today through Saturday):

Synopsis...500mb low/trough across Colorado/New Mexico extending
into northern Mexico this morning will move eastward today
bringing drier air aloft across portions of western and central
Texas this afternoon. At the surface...surface low pressure across
the Oklahoma/Texas panhandles and a surface trough extending
southward across west Texas this mornign will move eastward this
afternoon.

Today...One of the main impacts will be strong winds across the
coastal sections of the CWA this morning as the MCS across east-
central Texas continues to enhance the tight pressure gradient
across the lower Texas coast. Will hold off on wind advisories for
the coastal sections to see if the stronger winds aloft mix down
with diurnal heating later this morning. Another impact will be the
high threat of rip currents along the lower Texas coast today as a
mix of wind driven waves and long period swells combines to make
surf conditions hazardous for poor swimmers. Will go ahead and issue
a rip current statement as the Memorial Day weekend begins today.
The other possible impact will be isolated to scattered showers and
thunderstorms developing across the eastern portions of the CWA this
afternoon as diurnal heating allows instability to increase. Believe
most of the convection this afternoon will be more to the northeast
of the CWA today but cannot rule out thunderstorms developing along
the surface trough across south central TX this afternoon.

Tonight and Saturday...The high threat of rip currents will continue
along the lower Texas coast tonight and Saturday as strong winds
offshore the lower TX coast continue to provide a mix of wind driven
waves and the persistent fetch continues to provide long period
swells. As far as thunderstorm potential...isolated thunderstorms
cannot be ruled out early this evening but the loss of diurnal
heating should limit convective activity after sunset. The potential
for thunderstorms will increase Saturday...especially across western
portions of the CWA...as westerly winds aloft back to the southwest
in response to a weak shortwave trough moving across southwest
portions of the state Saturday afternoon. Isolated to scattered
showers and thunderstorms are expected across the upper portions of
the Rio Grande valley and northwest ranchlands as diurnal heating
provides higher surface instability across the western portions of
the CWA SAT afternoon.

LONG TERM (Saturday Night through Thursday):  The sultry weather
continues for the remainder of the holiday weekend and right on
through most of next week. This will lock up May as yet another
warmer than average month, the fourth straight of the calendar
year in general across the Valley. As for the sensible weather?
The remainder of the holiday weekend looks to be on the low to no
rain side for most as the 500 mb ridge pokes north once again -
though enough moisture along the Sierra Madre should kick off
isolated to scattered evening thunderstorms which may be able to
ooze east to southeast, perpendicular to the mean flow, to give
some leftovers to the mid and upper Valley from highway 281
westward.

By Tuesday night, both the GFS and ECMWF deterministic runs begin
breaking down slightly the South Texas ridge as weak short waves
eject from the trough along the California coast and push a piece
of the trough into Arizona/New Mexico. This ridge breakdown and
accompanying west southwest flow aloft combined with some increase
in mean column RH should increase the coverage of rain along/east
of the Sierra Madre each late afternoon/evening, with better
opportunity for more organized convection to reach farther into
the Valley with some combination of clusters or perhaps an
organized QLCS and leftover "debris" rain that could impact
everyone mainly during the overnight hours early Wednesday and
again early Thursday. Whether any of that precipitation can
survive past daybreak on those days remains to be seen.

So, for the sensible weather, made only minor adjustments to the
forecast, mainly to reduce/eliminate mentionable rain chances
Sunday through Tuesday over most areas during the late night
through afternoon, as position of upper ridge and continued stiff
south to southeast flow will make it difficult for anything to get
going especially where the most populated areas are. There should
be periods of cirrus as well as pocket of hazy sunshine, so no
clean azure blue skies anytime soon. For the evening/overnight,
leaned on persistence/climatology in such a pattern with keeping
rain chances most mentionable from the mid Valley west through
Memorial Day. For beachgoers, at least a moderate risk/threat for
rip currents into Memorial Day, which may be enough to extend the
rip current statement right through the entire holiday weekend.

For Tuesday, still have a broad area of low rain chances on land
through the nearshore waters, but not sold on that conditions just
yet so left just for consistence.

Persistence in temperatures (low to mid 90s by afternoon and near
80 by daybreak) along with yucky heat index values, still in the
102 to 108 range by afternoon and 85 to 90 overnight, will
dominate through Tuesday.

Tuesday night may see the first instance of more organized storms
that can press a bit farther east across the Valley, but how far
east remains to be seen. Made only minor tweaks to the numbers but
left the idea of 30/40 percent chances intact, continuing into the
daylight hours which would likely be "debris" showers - but kept a
broad brush with thunder mention also for consistency sake.

For Wednesday night and Thursday, the ECMWF and GFS begin to part
ways. The GFS moves the entire upper low into Texas on its way
toward the Mississippi Valley by early Friday, which would push
some relief from the swelter into the region to close the work
week. The ECMWF also lowers the 500 mb heights but closes off the
upper low over central Texas with plenty of deep moisture along
the wind shift line. There`s all kinds of ways this could evolve,
so for now elected to keep the highest rain chances over the
mid/upper Valley with lower chances elsewhere. Potentially heavier
rainfall can`t be ruled out on the whole for this time, which
would get June off to a fast start. Stay tuned!

MARINE: Today through Saturday - Seas were near 7 feet with
south to southeast winds near 31 knots at buoy020 early this
morning. Strong south winds will prevail across the coastal waters
today as surface low pressure across the southern plains continues
to provide a tight pressure gradient across the lower Texas coast
this afternoon. Will go ahead and issue a Small Craft advisory for
the Laguna Madre this morning through the afternoon. Strong
southeast winds will prevail offshore the lower Texas coast
tonight so will go ahead and extend the SCA for the offshore
waters through early Saturday morning. The pressure gradient is
expected to weaken slightly on Saturday. Moderate to strong
southeast winds will prevail across the lower Texas coast as a
result.

Saturday night through Tuesday night: Tended to lean toward the
slightly higher wind values on the GFS, particularly each night,
with fairly tight gradient and 20 to 25 knot winds up to column
through 850 mb or so. marine layer still exists but may be waning
as western Gulf SST now in the lower 80s. Seas which have built to
6 to 7 feet today and will be a factor to start the holiday
weekend will continue to be problematic to close the weekend with
long fetch, and latest Wave Watch model carries 6 feet into
Sunday. Slight improvement with ridging building into Monday and
Tuesday may occur in the seas, but still carry areas of 5 feet on
average and these values may be a hair too low. Bottom line? Not
the easiest time for pleasure craft looking for smooth sailing
along the Lower Texas Gulf waters through the holiday weekend.

&&

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

GM...Small Craft Advisory for winds until 7 PM CDT this evening for
     GMZ130-132-135.

     Small Craft Advisory until 7 AM CDT Saturday for GMZ150-155-170-
     175.

&&

$$

This product is also available on the web at:
HTTP://WEATHER.GOV/RGV

53-SCHROEDER/19



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