Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 221044

Area Forecast Discussion
National Weather Service Brownsville TX
544 AM CDT Mon May 22 2017

.DISCUSSION...Showers developing along a possible boundary from
last nights convection from near Rio Grande Valley to McAllen
expected to spread north through Mid and Upper Valley. Warm air
advection with southerly flow increasing with a disturbance moving
off the coastal bend north of Corpus Christi will increase the
convergence factor along these boundaries with showers and a
possible thunderstorm increasing between 69C and 69E the next few
hours. Updated the pop forecast to reflect this developing


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


.AVIATION...MVFR conditions at the 3 TAF sites to dissipate
through the morning as daytime mixing mixes out the lower clouds.
Mostly cloudy VFR conditions are expected to persist most of the
day with MVFR conditions returning tonight. Showers are developing
this morning and may increase in areal coverage through 15Z. An
isolated thunderstorms is also possible but probabilities are too
low mention the TAFs at this time. Better chances for thunderstorms
will be along the Northeast coast of deep south Texas this
morning with isolated convection popping up through the afternoon
with daytime heating combining with the abundant moisture and
boundaries hanging around from last night thunderstorms.


.PREV DISCUSSION... /issued 423 AM CDT Mon May 22 2017/

SHORT TERM (Today through Tuesday): A quasi-stationary front
remains along the Coastal Bend extending into the Northern and
Western Ranchlands. Disturbances are passing to the north and south
of the Rio Grande Valley leaving the CWA temporarily rain free in a
weak area of subsidence.  The atmosphere will become re-energized
with isolated to scattered showers/tstms this afternoon as daytime
heating combines with the abundant moisture and left over boundaries
from last evenings/night convection. Not expecting organized
convection today with the boundary across the north retreating
northward just a bit today and an absence of significant energy in
the mid level flow. This may change later tonight and especially
Tuesday as a series of upper level disturbances over the
Rockies/Central Plains moves southward through Texas in association
with the vigorous upper trough strengthening over the Midwest and
Central Plains. This will invigorate the stationary front pushing it
southward combining with a destabilizing atmosphere and
strengthening upper support with increasing divergence aloft as an
upper jet max approaches Tuesday. SPC has all of Deep South Texas
under a slight risk of Severe thunderstorms with the best chances
occurring later Tuesday into Tuesday night as instability peaks with
ML CAPE exceeding 2500 j/kg, LI at -9 and steepening lapses rates.
Hail will be the biggest threat early on with the threat of damaging
wind if the storms organize into an MCS.

Outside of the potential convection...Mostly cloudy conditions along
with hot and humid conditions. Highs still exceeding 90 degrees in
the Rio Grande Valley with mid to upper 80s across the Northern
Ranchlands. Heat indices continue to range 100-106 with dewpoints
remaining well above normal in the mid to upper 70s. Overnight lows
tonight will be stifling only falling into the mid 70s to near 80

LONG TERM (Tuesday Night through Sunday): The main issues in
the long term will the the potential for severe thunderstorms
Tuesday night and building heat late in the week and into the
weekend. The forecast period begins with the broad mid and upper
level trough over the central and eastern portions of the United
States Tuesday night. At the surface...a weak cold front will move
across Deep South Texas and the Rio Grande Valley Tuesday night.
Abundant moisture, precipitable water values exceeding 2 inches,
pooling across the area Tuesday night combined with a weak cold
front and an unstable atmosphere will provide a chance of showers
and thunderstorms Tuesday night. Some convection across the area
may be ongoing from Tuesday afternoon. The Storm Prediction Center
has all of the Deep South Texas in a slight risk of severe
thunderstorms with large hail and damaging winds the main threats.
Also, the slow movement of some thunderstorms could produce
isolated flash flooding.

The weak cold front is expected to move south of the CWA by sunrise
Wednesday. Rain chances will quickly end Wednesday morning as drier
air filers into the region in the wake of the front. Temperatures
will at least be near normal Wednesday before returning to above
normal through the rest of the week and into the weekend as a
subtropical ridge develops across northern Mexico Friday.

MARINE: (Now through Tuesday): Conditions at Buoy 42020 at 3 am show
southeast winds around 15 knots and seas around 3 feet.  Light to
moderate southeast winds and slight to moderate seas continue today,
tonight and Tuesday with weak high pressure extending across the
Gulf and a stationary front along the Coastal Bend. The front
becomes gets a boost of energy from an upper level trough and moves
through the coastal waters Tuesday night.

Tuesday Night through Friday Night...A weak cold front will move
through the Lower Texas coastal waters late Tuesday night allowing
winds to shift to the north to northeast and increase. Moderate
north to northeast winds will prevail on Wednesday as surface high
pressure builds across the northwest Gulf of Mexico. Winds will
gradually turn to the southeast by Wednesday night as high pressure
moves east across the Central Gulf. The pressure gradient will begin
to tighten across the lower Texas coast on Thursday resulting in
southeast winds increasing across the coastal waters. Moderate to
strong southeast winds will should support SCEC to low-end SCA
conditions across portions of the coastal waters Thursday and


BAYVIEW/PORT ISABEL  90  78  90  72 /  20  30  30  40
BROWNSVILLE          94  78  93  73 /  30  20  30  40
HARLINGEN            94  76  94  70 /  30  20  30  40
MCALLEN              96  78  97  71 /  40  20  20  50
RIO GRANDE CITY      93  75  97  70 /  30  20  20  50
SOUTH PADRE ISLAND   84  79  83  74 /  20  30  30  40




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