Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 181712 AAB
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1112 AM CST Thu Jan 18 2018

.DISCUSSION...Latest observations and radar returns showing
drizzle and light rain beginning to develop and reach the surface.
Strong upper low over the Big Bend area of Texas is beginning to
aide in lift of moisture over the region and combine with the
strengthening of the coastal trough located just east of the
lower Texas coast. Surface dew point are rising but evaporating
cooling is taking place allow for temperatures to fall a few
degrees as the precipitation begins to fall. Will go ahead and
lower Max Temps for the afternoon with most areas remain in the
30s or only touching 40-41 for a few hours this afternoon.


&&

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

&&

.AVIATION...Aviation weather will continue to deteriorate today
and tonight as a strong upper low approaches from the west. Lower
end MVFR to fall to IFR this afternoon especially as drizzle and
light rain develop. IFR conditions are likely tonight and Friday
morning with periods of lower visibility during rain, drizzle and
fog. Some models suggest showers or thunderstorms developing
Friday morning and early afternoon but confidence is low at this
time to mention thunder in the 18Z TAF package.

&&

.PREV DISCUSSION... /issued 614 AM CST Thu Jan 18 2018/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...A strong and broad 500 mb closed low moving in from
the west in combination with a surface trough of low pressure
near the lower TX coastline will result in steadily degrading
aviation conditions today for the lower RGV airports. Surface obs
from all three RGV airports show that ceilings have fallen down to
MVFR levels this morning. The pcpn chances will increase due to
the influence of both the surface and 500 mb systems over the next
24 hours which will result in the ceilings and vsbys falling into
IFR/LIFR teritory later in the TAF forecast period.

PREV DISCUSSION... /issued 441 AM CST Thu Jan 18 2018/

SHORT TERM (Now through Friday): Surface obs from around the region
show that temps from all of the region remain just above freezing in
the mid 30s. Some areas of near freezing temps will still be
possible over the next several hours before sunrise as weak CAA
continues at the surface. So will maintain the freeze warning in
place over most of the region through 10 am with the main threat now
likely shifting to the northern ranchlands. `

Surface obs near the coastline show that a fairly brisk northerly
wind is lingering there which will combine with the low morning
temps to allow the wind chil values to bottom out once more today
mainly near the coastline.

KBRO radar has been detecting some very light echoes over the lower
RGV this morning with none of the surface obs verifying that pcpn
has not been reaching the ground. Expect the pcpn to start gradually
spreading out across Deep South TX and the RGV throughout today and
tonight as a 500 mb trough digs across southern TX and northeastern
Mex from the west and surface troffing develops and hangs near the
lower TX coast. The short term model guidance is in pretty good
agreement in ramping up the pops throughout tonight and Fri and will
go with a three way blend of the model pops through this short term
period.

The cold airmass should start moderating steadily as the CAA weakens
finally over the region and the winds shift around the a milder NE
direction on Fri. Both the GFS and ECMWF models pick up on this
trend and push the highs today and Friday back up into the 40s/50s
today and Friday. The NAM is the coldest of the three short term
model sets and hold the highs in the low 40s today and tomorrow.
This looks a bit too cool considering the shift in the
overall pattern so will go closer to a blend of the GFS and ECMWF.

Overall confidence in the short term temps and pops is above
average.

LONG TERM (Friday Night through Wednesday): Drier air spreads
across deep south Texas Friday night as the mid to upper level
trough axis moves east of the region and the coastal trough weakens.
Very light winds and warm air advection begins above the surface,
may support some dense fog late Friday night into mid morning
Saturday. However, due to some uncertainties, will not mention in
the grids at this time.

Surface high pressure moves east on Saturday allowing southerly flow
to return across the area. Above normal temperatures are expected
across the region through most of the weekend. High temperatures
Saturday will be in the 70s with a mix of sun and clouds. Saturday
night will be mild with low temperatures Saturday night mainly in
the 60s. Sunday will be breezy, especially near the coast, as the
pressure gradient strengthens. Sunday will be warm and breezy with
highs mainly be in the 80s. The next cold front arrives Sunday night
bringing cooler and drier air behind it. The latest GFS remains
slightly faster than the ECMWF, so will leave the midnight frontal
passage timing for now. Some showers are possible, especially
across the coastal waters Sunday afternoon into Sunday night. Near
normal temperatures are expected early next week.

MARINE: (Now through Friday): The PGF across the marine locations
have weakened enough to allow the Gulf swells to finally drop down
below SCA levels. However as the surface troffing forms up near the
coastline through Fri, do not expect great boating conditions to
return any time soon to the lower RGV waters. Conditions across the
Bay and Gulf waters may remain close to the SCEC territory
maintaining fairly choppy bay conditions and elevated Gulf swells.

Friday Night through Monday Night: Southeast flow returns Friday
night through Sunday and the long fetch will bring wave heights up
to Small Craft Advisory levels potentially. Marine conditions will
improve briefly Sunday evening as the gradient relaxes ahead of the
approaching cold front. The cold front will move through the lower
Texas coastal waters late Sunday with Small Craft Advisory
conditions possible behind the front into Monday.

&&

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

$$

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