Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 090533 AAB

Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
1133 PM CST Thu Dec 8 2016

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


.AVIATION...Little change to the previous forecast package as
conditions remain fairly status quo in terms of ceiling and wind
trends overnight and into Friday evening. 00Z GFS soundings match
prior 12Z and 18Z runs regarding persistent low MVFR ceilings and
mainly VFR visibility despite a few more pockets of light rain.
Drizzle could touch visibility down to 3-4 statute miles between 3
AM and 8 AM Friday for Brownsville but for now left out.

Otherwise, wind forecast is just a continuation of the prior package
with only change a slight increase for the midnight through 6 AM
sustained and gust values, just a knot or two above the prior
forecast (19 gust 29 knots near the coast, for example) with
continued nuisance gustiness through Friday before speeds drop below
10 knots everywhere Friday evening.  Added a TEMPO IFR ceiling
toward midnight Friday night based on near 100 percent RH near/just
above the surface and temperatures steady, also shown by sinking
inversion to below 1000 feet.


.PREV DISCUSSION... /issued 637 PM CST Thu Dec 8 2016/

DISCUSSION...Made a few tweaks for hourly temperature and
dewpoint for tonight through Friday night based on current
temperatures which were some 4 to 8 degrees lower than the values
depicted for 6 pm through 9 pm particularly near the coast where
northwest winds have brought the chill to Port Isabel and South
Padre. Also adjusted dew points downward particularly along/west
of US 77/IH 69E where drier air now oozing into the Rio Grande
Plains and South Texas Brush Country should bring values down into
the 20s and 30s by daybreak and on into Friday. These same
lowering dew points should allow ceilings to rise a little as
well...closer to 2500-3000 feet especially north of the Valley.
Data have been published and should be available on shortly (click on the map below the graphics or
select your ZIP code in the upper left corner).

AVIATION...watching pockets of light rain/drizzle this evening
which in a few areas have dropped visibility to MVFR levels (4
Statute Miles). Pockets of vertical motion below 700 mb continue
through the night and perhaps into midday Friday for the Lower
Valley terminals (Brownsville and Harlingen) which will keep drops
or drizzle continuing off and on. Not too sold on reduced
visibility especially as drier near surface air eases south, so
after 06Z kept visibility restrictions out of the forecast.

Otherwise, mainly a wind and ceiling forecast, each which are
fairly straightforward. Strong gusty winds near or above 20 knots
will prevail through midnight, with only a slow decrease through
early to mid morning Friday before a steady decrease below 15
knots during the afternoon. Ceilings based on guidance and model
cross sections/soundings keep values solidly in low MVFR-land
right through the period. McAllen could break above 2000 feet by
late afternoon with lower surface dewpoints allowing slightly
higher mixing, but confidence not high enough to raise just yet.

PREV DISCUSSION... /issued 316 PM CST Thu Dec 8 2016/

SHORT TERM (Tonight through Friday Night):Surface high pressure
across the central United States this afternoon continues to bring
shallow cold air into central and south Texas. The pressure gradient
continues to increase across the lower TX coast this afternoon with
wind advisory conditions across the coastal sections of the CWA and
borderline conditions inland. Main concern tonight is the winds and
temperatures...especially across portions of the lower Rio Grande
valley late tonight into early Friday the combination
of strong cold air advection and strong northerly winds will provide
wind chill values in the upper 20s to near 30 across portions of
Cameron and Willacy counties. Have issued a wind chill advisory for
Cameron and Willacy counties as a result. Will continue wind
advisory for the coastal sections of Cameron...Willacy and Kenedy
counties through this evening. Warm and moist air aloft continues to
move across the shallow cold air at the surface and this will
continue tonight into Friday before winds aloft veer to the
northwest Friday night. Light rain/drizzle will continue to develop
across the CWA tonight before diminishing across western portions of
the CWA Friday. A slight chance of rain will linger across the
coastal sections Fri night. Will lean towards the MET MOS for
temperatures tonight through Friday night.

LONG TERM (Saturday through Thursday):Lingering coastal showers
will continue through the first part of the weekend as surface
troughing develops in the wake of the arctic front that has
already pushed through the region. The warm onshore flow will run
up over the shallow airmass in place over the RGV...allowing for a
more of a light rain or drizzle set up. Temperature will moderate
on Saturday...however the better warm up will begin on Sunday.

This will occur as the pattern shifts late Saturday and into
early Sunday with the high pressure system over the Texas getting
pushed of to the east as the next storm system exits the Rockies.
Southerly flow will deepen and allow the air mass to modify. Temps
will warm into the low 70s to lower 80s...with precip ending.

For the work week ahead...generally quiet weather and tempeatures
returning to near or even a bit above normal. Long term models
continue to struggle with expected frontal passages...with the
GFS being the most aggressive with their movement. Meanwhile...the
ECMWF has been more reserved in keeping any cold front north of
the region. Given this uncertainty...have not made any alterations
from the previous forecasts.

Tonight through Friday night: Seas were near 14 feet with north
to northeast winds near 29 knots with gusts to near 37 knots at
buoy020 this afternoon. Strong to very strong north winds will
prevail across the coastal waters tonight as strong surface high
pressure building into the state provides a strong pressure
gradient across the lower Texas coast. Will continue Gale warnings
for the Laguna Madre through this evening and for the offshore
waters through early Friday morning. Winds will gradually diminish
across the coastal waters Friday as the pressure gradient begins
to weaken slightly. Moderate to strong north winds will prevail
across the western Gulf of Mexico Friday and continue to diminish
Friday night. Small craft advisories will likely be needed for all
of the coastal waters Friday and for the offshore waters Friday

Saturday through Tuesday: Marine conditions will be improving
through the weekend as the surface pressure gradient weakens
somewhat and winds lessen through the day. However...seas will
take some to relax...with wave heights still in the 5 to 7 feet
range through the day Saturday. SCAs may be need for the offshore
waters Saturday. Light to moderate winds and moderate seas will
return for Sunday and into the first part of the new week.


TX...Wind Advisory until midnight CST tonight for TXZ251-256-257.

     Wind Chill Advisory from 3 AM to 9 AM CST Friday for TXZ254-255.

GM...Gale Warning until midnight CST tonight for GMZ130-132-135.

     Gale Warning until 6 AM CST Friday for GMZ150-155-170-175.



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