Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 201721 AAB

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1121 AM CST Mon Nov 20 2017

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


.AVIATION...A few showers may persist over the eastern sections
of the CWA through early afternoon, but a mid level short wave
trough axis is over the CWA and is moving east, pushing the best
upper energy out over the Gulf. Ridging and drier air is upstream,
which will increasingly dominate into tonight and Tuesday. An
elevated inversion remains in place, which will lock in thicker
low clouds through this afternoon, albeit with any ceilings above
3 kft. Skies should scatter out this evening, with possible high
cirrus moving in from upstream. Light southeast winds tonight will
turn to south on Tuesday. Quick dew point recovery in still cool
night time temperatures along with light winds could lead to
patchy ground fog at MFE and HRL near dawn. Otherwise, VFR on tap
for the vast majority of the period.


.PREV DISCUSSION... /issued 521 AM CST Mon Nov 20 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...A weak upper level disturbance will sweep eastward
across the Rio Grande Valley this morning and combine with
increased low level moisture from the Gulf. This will bring BKN-
OVC skies to much of the region with a slight chance of showers
and CIGS dropping into the MVFR category at times from VFR.
Clouds will slowly begin to decrease this afternoon and overnight
as the upper level disturbance passes to the east. Winds will
generally be 10 knots or less through the period.

PREV DISCUSSION... /issued 342 AM CST Mon Nov 20 2017/

SHORT TERM (Today through Tuesday):Shortwave trough aloft to move
west to east across the forecast area mainly during the morning
hours today bringing increasing clouds and onshore flow/low level
moisture. Combination of increased lift and moisture will bring
slight chances of showers with little rainfall to mainly the
southeast quadrant of the region (Hidalgo, Willacy, and Cameron
Counties). Otherwise, will see mostly cloudy conditions for much of
the day across the region except out over the far west where
moisture will be less. Cloud cover will be significant enough to
keep high temperatures limited to near normal values in the
lower/mid 70s most locations this afternoon.

The aforementioned shortwave trough will eject to the east of deep
south TX this afternoon/tonight with clouds slowly diminishing
throughout the atmospheric column and chances of showers ending over
the landmass as a drier northwest flow develops aloft and low level
moisture is shunted eastward over the Gulf. For Tuesday, the low
levels continue to dry further as the flow becomes southwest, then
west, as a dry cold front approaches the area from the north. The
drying low levels and dry northwest flow aloft will result in mostly
sunny to partly cloudy skies for Tuesday with temperatures jumping
up to well above normal values in the lower to mid 80s area-wide,
which will roughly be 6 to 11 degrees above normal.

LONG TERM (Tuesday Night through Sunday):The 00Z Model suite
continues in good agreement and consistency with the mid/upper
level flow as well as the surface features in the next 7 days.
Main challenge is at the very beginning of the long term when a
sharp 500mb shortwave trough dives south along the Texas coast
Tuesday night into the Western Gulf of Mexico Wednesday. Both
GFS/ECMWF indicated sufficient depth of moisture across over the
Eastern third of the of the CWA with decent lift/forcing
associated with the left exit region of 100+ knot jet. Model
guidance continues to advertise fairly high pops Tuesday
night/Wednesday with ECMWF the most aggressive. Latest forecast
will begin to increase pops about 10 percent to the 30-40 percent
range but will keep rain chances mainly confined to the coastal
counties and the coastal waters. Once this system moves into the
Western and Central Gulf, Wednesday night, dry weather is
expected for Thanksgiving and through next weekend.

Cold front late Tuesday night into Wednesday will usher in another
shot of cooler air with temperatures falling below normal for
Wednesday. Deep Layer dry air overspreads the CWA as strong broad
mid level high pressure builds in from the west maintaining cool
nights and mild days Thursday through next weekend. Large diurnal
spread of temperatures is likely with 40s and 50s overnight and
70s and 80s during the day.

MARINE:(Today through Tuesday): Somewhat elevated seas over the
Gulf waters will continue to slowly subside through the day today as
weak surface high pressure builds over the northwest Gulf. Modest
winds/seas to prevail tonight/Tuesday ahead of the next cold front
slated to move across the waters.

Tuesday night through Friday...Adverse marine conditions start
off the long term as a strong cold front pushes through the
coastal waters. Small craft advisories with gusts nearing gale
force are possible Wednesday morning when the tightest pressure
gradient is expected to arrive with a strong mid level jet streak.
Marine conditions to be improving rapidly Thanksgiving day as a
strengthening low pressure system moves into the Central and
Eastern Gulf towards Florida. Excellent to good marine conditions
are expected Friday and next weekend.




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