Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 081202 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
602 AM CST Thu Dec 8 2016

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

&&

.AVIATION...Poor flying weather to persist for the next 12-18
hours with IFR and intermittent LIFR ceilings. Gusty northerly
winds have already arrived at the RGV terminals and sustained
winds will continue to increase through early afternoon. Strongest
winds expected nearer the coast at BRO and HRL with guidance
hitting HRL a little harder...near AWW criterion for gusts, so
will have to monitor. Winds slow to decrease this evening as
pressure gradient remains tight. NW winds around 15 knots should
predominate after midnight with ceilings advertised to rise to
MVFR, which makes sense with the much lower dewpoints that will be
in place by then.


&&

.PREV DISCUSSION... /issued 431 AM CST Thu Dec 8 2016/

SHORT TERM (Today through Friday):(Now through Friday):  Cold front has finally pushed
southward through the remainder of the CWA (Lower Valley) in the
hours since midnight and northerly pressure surge continues. Lifting
associated with the front has produced isolated to widely scattered
light showers early this morning with more moderate showers noted
right along the boundary...south of BRO and offshore.  High
temperatures for today have likely already been realized, and strong
cold-air advection behind the front will yield falling temperatures
through the day for all locations.  Temps should fall into the upper
40`s to near 50F for the mid-Lower RGV by nightfall.  Strong
northerly winds will also develop...especially along the
coast...this morning.  Wind Advisory for the coastal counties looks
to be in good shape, though onset may be an hour or two later .
than 6am.  Will not make any changes to it at this time.

Not much upper support to speak of for today.  There is a weak H5
disturbance now moving into Chihuahua state which is progged to
shear out over central TX this afternoon, but it looks to have
little impact.  Model time-height sections do show decent omega
through most of today, though, with the warmer H7 SW flow riding up
over the shallow cold airmass.  Still expect precip to be mostly of
the light rain/drizzle variety once the initial showers in the
vicinity of the front progress southeastward out of the area.  So
looks like a fairly high PoP (which were raised 10-15% for
today)/low QPF, which is typical of these situations.

Winds now look a bit slower to diminish Thursday night, especially
over the E half of the CWA, but temperatures will continue to fall.
Inherited min temps for tonight looked reasonable so did not alter:
Upper 30`s north to low 40`s near Brownsville.  Precip chances also
taper off from NW to SE, especially after midnight, as drier air at
the surface continues to pour in.  Latest grids indicate wind chill
values touching 30 for an hour or two in isolated spots Friday
morning. Not confident enough yet that this will meet Wind Chill
Advisory criteria. An SPS may suffice, but will let day shift
evaluate.

Friday looks a bit colder in the guidance, so have trimmed 2-3
degrees from afternoon high temps.  A little moisture tries to hang
on near the coast in association with some troughing.  Quite a raw,
chilly day overall.

LONG TERM (Friday Night through Wednesday):Models start out in good
agreement the first 4-5 days of the long term then diverge in
complete opposite directions making the latter half of forecast
package very challenging and placing a very low confidence in the
final outcome the middle portions of next week.

Mid level flow to take on a zonal flow which will allow for a
warming trend to commence the latter half of the weekend. The
cold surface ridge settles over the Mid-Atlantic states Saturday
and Sunday allowing winds to return to the southeast. Weak coastal
trough lingers on Saturday maintaining at least a small chance of
rain across the coastal counties. Clouds may linger and be tough
to mix out keeping temperatures on the cool side but at least a 10
warm up over Friday. Sunday will be even warmer as the southerly
flow becomes more establish and all the arctic modifies. As we
move into early next week the mid level zonal flow will be
dominate with the polar jet retreating north of the U.S./Canadian
border. GFS has backed off on the weak front Monday with south
winds and above normal temperatures prevailing. EC also on board
keeping any hint of a front north of the RGV. Big differences
start showing their ugly head Tuesday and Wednesday as the GFS is
becoming an outlier showing another intense arctic high pressure
ridge moving into the heart of the country. GFS is trending with a
more amplified 500mb trough over the Northern Plains and Great
Lakes while the European continues with a more general zonal flow.
This results in the GFS`s arctic front staying well north of the
RGV. At this time there is a 30 degree difference showing up in
the guidance for next Wednesday`s highs. After much collaboration
with neighboring WFO`s a blend of the models was agreed upon
bringing in a weaker front next Wednesday. Without saying the
latter portion of the forecast has low confidence written all over
it and one should expect several changes until the model come into
better agreement.

Thanks to CRP and other WFO across Texas for much needed
collaboration.

MARINE:(Now through Friday):  Strong northerly winds have arrived
at Buoy 020 with NNE winds of 25G29KT as of 350am.  Seas have jumped
up to about 6 ft. as well.  Winds continue to increase this morning.
Gale Warning begins for the coastal waters at 6am and continues
through midnight on the Laguna Madre and 6am Friday for the offshore
waters. Even after some downward adjustment to the wave guidance,
still looking for seas rapidly building to 10-12 ft. over much of
the Gulf waters by mid-day today and perhaps as high as 14 ft. this
evening. Seas only slowly subside to 8-10 ft. by late in the day on
Friday. Small Craft Advisories will almost certainly be needed after
the period of the Gale Warning on through the end of the short-term
period.

Friday night through Monday...marine conditions continue slowly
improve as strong polar surface ridge moves east. Winds will trend
northeast to east Friday night/Saturday and back to the southeast
Sunday. Still SCA conditions are likely to linger (for at least
the seas) into Saturday morning with much improved conditions
Sunday and especially Monday.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...Wind Advisory until midnight CST tonight for TXZ251-256-257.

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

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

&&

$$

This product is also available on the web at:
HTTP://WEATHER.GOV/RGV

53-Schroeder...Aviation/Short-term
59...Long-term


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