Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 271743 AAB

Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
1243 PM CDT Thu Oct 27 2016

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

.AVIATION...Satellite images and surface observations indicate
mostly mid level clouds across the western portions of the CWA
this afternoon. Ceilings were near 4900ft at KHRL to near 6000ft
at KAPY. Expect VFR conditions to prevail the rest of the
afternoon into the evening as the 500mb ridge across northern
Mexico and west Texas continues to provide subsidence across deep
south TX.

.PREV DISCUSSION... /issued 544 AM CDT Thu Oct 27 2016/
DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Prevailing VFR TAFS the next 24 hours. An H5 ridge to
the west will support stability today with light northeast winds.
Winds will taper off tonight, with patchy fog again a possibility
for the mid valley, northern ranchlands and brush country late.
Though not necessarily causing downgraded conditions, increased
convective activity over the west and southwest Gulf tonight may
bring enhanced cloudiness and coastal showers into the area

PREV DISCUSSION... /issued 412 AM CDT Thu Oct 27 2016/

SHORT TERM (Today through Friday):H5 ridging over the Southwest
United States and Northwest Mexico will hold fast or build
slightly east today as a mid level trough axis extending south
into East Texas lifts to the east. High pressure to the northeast
will also extend back into the local area. This will result in
mainly sunny skies today with light winds and above average
temperatures ranging from the mid 80s to near 90 inland, five to
ten degrees above normal.

Mostly clear conditions will occur tonight across deep South Texas
and the RGV, with light, patchy fog possible in the mid valley and
up into the ranchlands and brush country. As convection increases
across the Western and Southwestern Gulf (see below) coastal showers
may move ashore into the lower Valley. Overnight low temps will be
mainly in the mid 60s with a few 70s near the coast. The lows will
be in the five degree warmer than normal range.

The GFS and ECMWF show H7 heights bridging across the North Gulf
today through Friday, with the H5 center over West Texas a little
slower to flatten. The GFS is just a little more definitive in
developing an upper weakness over the Western Caribbean and/or
Southwest Gulf by Friday, but it is evident in both models. The
upshot will be increased instability over the Gulf and enhanced
moisture and convection moving west into the long term period. For
the short term, rain chances will increase over the Gulf Thursday
night, with isolated shower coverage then on tap for the CWA on
Friday. The showers may in fact be sea breeze driven, and therefore
dependent on timing. Forecast precipitable water values will
increase by half an inch to one and a third inches by Friday, not
particularly robust by local standards, but enough to lend credence
to the low end pops in the forecast. Kept high temperatures on
Friday a degree or two less based on enhanced cloudiness, with 85 to
90 degrees over inland areas, still several degrees above normal.

LONG TERM (Friday Night through Wednesday):The persistent 500MB
dome of high pressure that as been dominating the weather pattern
for the last several days will finally begin to flatten and
elongate across the Southern Plains as an inverted trough
approaches the region late on Friday. The feature will bring
increasing moisture level back to the RGV. However...the weakening
ridge centered to the north will still be keeping a rather large
area of dry air and subsidence across the Deep South Texas.
Forecast soundings indicate moisture may not increase as quickly
as expected for Friday night into Saturday and have opted to cut
back on POPs.

There is still good chance at precipiation the
trough/tropical wave aloft continues to advance westward across
the Southern Texas/Northern Mexico Gulf Coast and farther inland
by Sunday into Monday. As this occurs...the ridge over Texas will
skirt along the southern states before reestablishing a dominate
high pressure dome over the Gulf waters. With the RGV between the
two middle level features...and another wave of tropical moisture
moving into the area of ascent...increased chances for showers and
at least some thunderstorms will be possible for early next week.
Additionally...the moisture transport up into the region should be
enhanced by an surface troughing/low pressure in the Bay of
Campeche..which will keep some rain chances in the forecast
through the remainder of the period.

Temperatures will likely still run a bit above average through
the long term...however cloud cover and rainfall should prevent
anything more than only a few degree over the norm.


Today through Friday...The long easterly fetch across the Gulf is
resulting in a significant swell component to wave heights. Light
northeast to east winds will continue on the Gulf during the short
term, but the wave models do not appear to be capturing all of the
swell. Added a ft to the guidance for today, based on a comparison
with measured data at Buoy 42020. Resurgent convective activity over
the Southwest Gulf Thursday will work north along the coast into the
waters of the Lower Texas Coast Thursday night into Friday.

Friday Night though Monday Night...Building seas will continue
through the weekend and into early next week as surface high
pressure over the Northern Gulf/SE CONUS interacts weak surface
troughing over the Western Caribbean Sea and Southwestern Gulf.
A long easterly fetch of light to moderate winds will build
swells from the ENE to ESE through the period...with heights of 4
to 6 feet. However...some higher seas could occur. It is possible
that SCAs may be needed. Inverted mid level troughing will bring
increased convective activity for the marine areas through the
weekend as well.



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