Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 161134 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
634 AM CDT Sat Sep 16 2017

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

&&

.AVIATION...Mostly clear skies and light winds prevail across
deep south Texas this morning. VFR conditions will continue
through the next 24 hours with high pressure in control. Light
southeast winds will become gusty later this morning into the
afternoon. Partly cloudy skies and light winds expected to return
by late this evening.

&&

.PREV DISCUSSION... /issued 421 AM CDT Sat Sep 16 2017/

SHORT TERM (Now through Sunday): 500-mb ridge over northeast
Mexico and south Texas this morning will continue to provide
subsidence across deep south Texas for today. Rain-free conditions
and near to above normal temperatures will continue across the
CWA today due to the rather dry atmosphere. Patchy fog will be
possible across the northern ranchlands around sunrise this
morning. The mid level ridge will gradually move eastward over the
Gulf of Mexico through the weekend. This will allow low to mid
level moisture to increase across the western Gulf of Mexico and
northeast Mexico tonight and Sunday. Isolated showers expected to
develop across the coastal waters late tonight into early Sunday
morning. Precipitable water values increase to near 2.30 inches,
mainly across the Rio Grande Valley, Sunday afternoon. Isolated to
scattered showers will be possible across deep south Texas on
Sunday. Will lean towards a blend of the MAV/MET and ECMWF for
pops on the Sunday.

LONG TERM (Sunday Night through Friday): Model guidance continues
to gradually back away from any really significant tropical
moisture influx(es) next week. Overall, the period will be
dominated by high pressure at mid-levels of the troposphere.
Exceptions to this would appear to be on Monday and perhaps
Thursday.

Continuing from the short-term...Sunday night, light S/SW flow at
mid-levels between the western Gulf high and Norma (forecast to
linger near the tip of Baja California) keeps decent amounts of
column moisture flowing into the CWA, especially offshore and
along the coast. This continues through much of the day on
Monday, though by late in the day the mid-level high is centered
back roughly over BRO. Should be enough moisture to overcome the
cap, though, so low-end chance PoP`s with some thunder look like a
good bet for much of the CWA. Will have to rely on sea-breeze/diurnal
effects for forcing.

For Tuesday and Wednesday, upper high center stays nearby, with
subsidence capping off the sounding and gradually drying the
atmosphere further. Have kept PoP`s silent through this period,
except for far offshore. A few factors may come into play for a
modest bump in precip chances on Thursday. Both GFS and ECMWF
indicate a jet max/shortwave trough moving through central TX
(possibly some energy splitting off from Norma), which briefly
returns S/SW flow aloft to the local area. MOS guidance remains
rather paltry, though, so just broad-brushing 20% chances for now
on Thursday. Moving into Friday, 500-mb high builds back over the
area once again. Moisture progged to remain below H85 with some
very dry air aloft, so rain chances very slim to none.

Max and min temperatures don`t appear to be changing very much
through the work week. High temps run about 2-5 degrees above
climo for this time of year, with portions of the Upper Valley
touching 100+ degrees each day. (For reference, average high at
BRO is down to 90F, starting today.) Superblend seemed to be a
good fit and so leaned on it for temps. Warm and muggy nights
continue as well, with morning lows in the mid-upper 70s.

MARINE (Now through Sunday):  Favorable marine conditions expected
along the lower Texas coast today through Sunday. High pressure
across the northeast Gulf of Mexico will maintain light to moderate
east to southeast winds and low seas across the coastal waters
through the period.

Sunday Night through Thursday: Light to moderate SE winds will be
the rule through Monday night. Gradient tightens beginning on
Tuesday as pressures fall in the southern Plains. This will lead
to periods of Small Craft Exercise Caution (SCEC) conditions
through Thursday, though it does not appear that advisories will
be needed. SCEC will be more likely on the Laguna Madre during
the day and on the Gulf waters at night. Low seas initially
gradually build to more moderate levels of 3-4 ft. by Thursday.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...None.
&&

$$

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