Area Forecast Discussion
Issued by NWS Brownsville, TX
FXUS64 KBRO 251757 AAA
Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
1257 PM CDT WED MAY 25 2016
.DISCUSSION...Updated for latest aviation discussion below.
.AVIATION...Ridging aloft still holding on but is in the process
of flattening as an upper-level low moves into SoCal. This has
allowed some high clouds to stream in from the E. Pacific. There
is also sufficient low-level moisture to support generally VFR
ceilings through the afternoon...possibly scattering out for a
time in the early evening. Breezy SE winds also expected thru the
Main challenge overnight is timing arrival of showers and possibly
thunderstorms into the terminals ahead of an upper-level impulse.
Short-term guidance in good agreement on this feature developing,
but hard to see it upstream in current satellite imagery. Due to
uncertainty, will just mention VCSH at MFE between 04-10Z and
06-12Z at HRL, though confidence is lower there. BRO could see
IFR CIG`s develop late tonight. Impulse should clear the
terminals by early tomorrow morning with low-end MVFR ceilings
lifting a bit by mid-morning.
.PREV DISCUSSION... /issued 703 AM CDT WED MAY 25 2016/
DISCUSSION...Updated for latest aviation discussion below.
AVIATION...Surface obs indicate MVFR ceilings continue across
the RGV as a shallow moist layer is evident on the 00z BRO
sounding below the 940 mb level. The daytime heating and low
level mixing after sunrise will improve the conditions back to VFR
levels later this morning into this afternoon. Model forecast
soundings show another low level saturated layer reforming again
tonight into early Thurs morning. This will allow for more MVFR
ceilings to return once again from around 03-12z Thurs across the
PREV DISCUSSION... /issued 449 AM CDT WED MAY 25 2016/
SHORT TERM (Today through Thursday): A strong 500 mb closed low
will be moving east out of the SO CAL today and tonight and will
move into the Four Corners area by midday Thurs. The 500 mb ridging
in place over the TX/Mex border region will in turn break down which
will allow a more divergent flow aloft to build in over the RGV
increasing the UVV. Deep layer moisture appears to increase as the
500 mb trough axis moves closer to the region. So expect the conv
potential to increase accordingly. Short term model pop guidance
differs greatly through the short term guidance from the NAM/GFS and
ECMWF. The ECMWF is the wettest of the third model sets with the NAM
coming in the driest with the GFS going more middle of the road.
Will hold the pops in the short term in the chc range closer to the
middle of the road GFS with the better pops concentrated over the
western counties closer to the better dynamics associated with the
500 mb trough.
The 07z Day 1 conv outlook from SPC places the western portions of
the cwa under a marginal risk of severe weather as sufficient CAPE
values/mid level and orographic lift could fuel some isold svr
storms if the cap could be broken later this afternoon and this
evening. Large hail and damaging winds will be the main threat.
Max temps will lower a bit on Thurs due to the increase cld cover
and conv chances. The NAM forecast temps are a bit warmer in
comparison to the GFS and ECMWF numbers and will opt to go closer
to the better consensus demonstrated by the MAV and ECMWF
LONG TERM (Thursday Night through Tuesday): forecast reasoning
remains the same. A pair of deep 500 mb troughs transiting through
the western United States will establish a persistent southwest to
northeast mid-level flow over the BRO CWFA throughout the long
term portion of the forecast. Shortwaves riding within this flow
will initiate convection over the neighboring high terrain of
Mexico and also within Deep South Texas and the Rio Grande Valley.
Isolated to scattered showers and thunderstorms are forecast, and
successive shifts will need to monitor for the potential for
strong to severe thunderstorms, especially due to the already
existing potential for severe weather mentioned in the short term
forecast discussion above.
MARINE (Today through Thursday): The tightening PGF across the
lower TX Bay and Gulf waters due to the influence of the surface
lows developing across the central Plains states will maintain
pretty decent winds across coastline. This will hold the marine
conditions up close to SCEC criteria from Today through Thurs. Some
marginal SCA conditions could briefly develop but will not post an
SCA at this time.
Thursday night through Tuesday: strong winds and rough seas, with
likely Small Craft Advisory, are forecast Thursday night through
Saturday night with surface high pressure over the Gulf of Mexico
interacting with low pressure over the Central Plains and northern
Mexico. More moderate winds and seas, with Small Craft Exercise
caution possible, are anticipated Sunday through Tuesday as the
center of the high pressure system moves closer to the western
Gulf of Mexico and the Lower Texas Coast.
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