Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 201807 AAB

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
107 PM CDT Fri Apr 20 2018

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


.AVIATION...There is plenty of cloud cover across the area this
afternoon with ceilings expected to be VFR through the evening. A
weak warm front is analyzed just to the south of the Rio Grande
with winds slightly shifting from the east to southeast. In the
upper levels a weak disturbance is also moving overhead, so a few
showers will be possible, but would likely not be impactful at the
local aerodromes. Tonight, models indicate MVFR ceilings with a
strengthening low-level jet developing early Saturday morning.
Low ceilings and perhaps slightly obscured visibilities will be
possible through the morning.


.PREV DISCUSSION... /issued 644 AM CDT Fri Apr 20 2018/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...IR satl imagery continues to show plenty of mid level
cld cover moving over the region from west to east ahead of the
500 mb closed low to our west. Meanwhile at the lower levels,
some patchy morning low level cld decks are resulting in some
periodic MVFR ceilings for the RGV airports. As the surface winds
shift around back from the SE later today, this will combine with
the daytime heating to mix out the morning ceilings allowing for
VFR conditions to prevail during the late morning and afternoon
hours. The low level dewpoints will start increasing later today
as the SE winds build. As the low level dewpoints increase expect
the potential for MVFR conditions to increase once again tomorrow
night into early Sat morning.

PREV DISCUSSION... /issued 420 AM CDT Fri Apr 20 2018/

SHORT TERM (Now through Saturday): IR satl imagery and lightning
data shows some patchy conv firing over portions of northeastern
Mexico ahead of a large 500 mb closed low digging across the Desert
SW. The deeper layer moisture and instability that is helping
support this conv will advect up to the north on the east side of
this 500 mb low as it tracks eastwards. This will likely steer this
western conv away from the RGV today. The 500 mb closed low will
continue moving east tonight into Sat eventually moving into the
central Plains States by tomorrow. Because of the northern track
taken by this 500 mb low, most of the better moisture/instability
and upper level divergence will likely remain located too far north
of the RGV to generate much in the way of significant pops in the
short term. However the cold front associated with this closed
low will edge into southern TX later tonight into Sat. This front
may provide the region with enough surface convergence to maintain
some slgt chcs of conv on Sat.

WAA will increase steadily over the region throughout the short term
period allowing the temps to climb through Sat. The NAM and GFS
forecast temps are very close through Sat with the ECMWF coming in a
bit warmer for Sat for highs. Will lean towards a blend of the
NAM/GFS and the warmer ECMWF especially for high temps through Sat.

The PGF ahead of this approaching 500 mb close low will maintain
pretty breezy conditions across the RGV today and Sat as an
associated surface low pressure system develops across the
Southwestern and South Central Plains states. However the gradient
does not appear strong enough to warrant a Wind Advisory at this

LONG TERM (Saturday Night through Thursday): A 500mb low/trough
over the central Plains Saturday night will move eastward over the
ArkLaMiss region by late Sunday. At the surface, the associated weak
cold front will approach and move through deep south Texas Sunday
morning. No rain is expected Saturday night into Sunday morning as
most of the convection with the front should remain north of the
area. Slightly cooler and drier air will filter into the area on
Sunday as surface high pressure builds across the region. Dry
northwest flow aloft and surface high pressure across Texas will
provide subsidence across the CWA through Tuesday. The next 500mb
shortwave trough moves over the Northern Plains Tuesday night and
into the Ohio River valley Wednesday. The latest ECMWF and GFS
differ on the placement and strengthen of this next upper level
system. This will push another weak cold front through central Texas
on Wednesday morning but the front is expected to stall north of the
area Wednesday and Thursday. Low to mid level moisture is expected
to increase across deep south Texas Wednesday and should support a
slight chance of showers and thunderstorms mid to late week. The
ECWMF is more robust with pops than the GFS. Will keep pops limited
Wednesday and Thursday.

MARINE (Now through Saturday): The above mentioned surface low
pressure system associated with the 500 mb closed low moving in from
the west will maintain moderate S-SE low level winds across the
lower TX Bay and Gulf waters. This may push the marine conditions up
into SCEC/marginal SCA conditions briefly along the lower TX
coastline throughout the short term. However will not post any SCAs
at this time.

Saturday Night through Tuesday Night...The pressure gradient will
weaken across the western Gulf Saturday night into Sunday morning as
a weak front moves into the lower Texas coastal waters. Moderate to
strong north winds may support Small craft advisories across the
Gulf waters on Sunday. Winds will diminish Sunday night as high
pressure settles across the western Gulf of Mexico. Light north
winds will prevail across coastal waters Monday then winds will
become east on Tuesday as high pressure moves east.




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