Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 052353 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
553 PM CST Thu Dec 5 2019

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

&&

.AVIATION... Expect VFR conditions to prevail across the area
this evening. Winds will likely go light and variable overnight
ahead of an approaching front. The high dewpoints and light winds
will combine to set the stage once again for another fog event for
much of the region. This will likely result in another round of
IFR/VLIFR conditions for the RGV airports. The best opportunity of
the densest fog is expected between 09-15Z Friday. MVFR/VFR
conditions should then return to the region by 18Z Friday as the
daytime heating and dry air advection increases after the frontal
passage.

&&

.PREV DISCUSSION... /issued 255 PM CST Thu Dec 5 2019/

..Another Foggy Start Expected on Friday...

SHORT TERM (Tonight through Friday Night): Broad 500 mb ridging will
maintain pretty warm temperature pattern over the RGV for tonight. A
strong 500 mb short wave will then move over the broad ridging
moving into the southern Plains States late tonight into Fri. This
will usher through a fairly weak cold front through the RGV early
Fri. The surface flow will likely go light and variable overnight
ahead of this approaching front. This will combine with the
increasing surface dewpoints to set the stage for another fog event
for much of the region. The GFSLAMP, MAV, MET and SREF guidance all
indicate some potential for additional fog late tonight through
early Friday morning. The short range model sets also indicate a
strong signal for the potential for dense fog during the pre-dawn
hours and past sunset due to the light and variable surface wind
flow and dewpoints expected to reach into the mid 60s by sunrise
Fri. So Dense Fog Advisories will once again be a possibility late
tonight and early Fri morning.

Any fog that forms overnight will quickly dissipate later in the
morning Fri as the surface flow shifts around from the N-NW and
drier air filters into the region. The combination of the clearing
skies and abundant sunshine should allow the temps to warm up nicely
tomorrow afternoon with low 80s possible once again. This drier air
in addition to the weak CAA spreading over the region Fri Night
should lower down temps quite a bit. The short range MET/MAV and
ECMWF temps look reasonable and will stick close to a blend of these
through Fri Night.

The influx of drier air tomorrow afternoon and tomorrow night will
seriously reduce the fog potential for the RGV.

Since overall deep layer moisture advection is pretty limited with
the upcoming fropa, will not include any serious pops for the RGV
through Fri Night.

LONG TERM (Saturday through Thursday): The upcoming weekend looks
great with generally dry WNW flow across the region. At the
surface, as high pressure moves east of the Mississippi River
early Sunday, low level flow will transition to a more south
easterly direction helping initiate a gradual warming/moistening
trend across the region into early next week.

By early Monday, a deepening wave across the western states will
begin to slide eastward. Given the magnitude of the wave, expect
this upcoming frontal boundary to be a little stronger than the
previous front. Out ahead of the front on Monday, expect breezy
conditions to take shape, especially across the lower and mid RGV.
The front should push through the region during the day on
Tuesday.

Globals are not in agreement with some variables from Tuesday
onward. First, the GFS blasts the front through the region with
only rain chances along or east of the Lower TX Coastline. The
ECMWF is much wetter with QPF showing up as far inland as Nuevo
Leon. Kept POPs limited for this time until better agreement takes
shape. POPs areawide do increase some going from mid to late week
as the Globals do show a coastal trough developing. With expected
abundant cloud cover and POPs due to isentropic upglide mid to
late week, temperature confidence beyond Wednesday is below
average. For the sake of continuity, didn`t change much since the
last package, however, if trends continue with the coastal
troughing, temperatures will probably be lower than currently
progged.

MARINE (Tonight through Friday Night): The light wind regime and
elevated dewpoint values ahead of the next cold front will allow for
some patchy marine fog especially across the Laguna Madre late
tonight into tomorrow morning. However, will not include any
mention of dense marine fog at this time since this is mainly a
radiational event for the inland areas. Otherwise light surface
winds will maintain fairly low seas for both the Bay and Gulf
waters through Fri Night. So no SCA conditions expected through
Fri Night.

(Saturday through Thursday): Marine conditions will be improving
as the long term starts. Favorable marine conditions are then
anticipated through the weekend before quickly declining on Monday
as winds and seas approach SCA thresholds ahead of the next cold
frontal boundary. Just prior to the front, winds and seas will
subside a bit as pressure gradient relaxes, however, this will be
only temporary as winds and seas behind the front begin to exceed
SCA thresholds once again. In fact, winds late Tuesday and early
Wednesday may gust up to Gale force at times.

Confidence decreases slightly beyond midweek with subtle
differences in forecast guidance. For the moment, it appears a
coastal trough will develop keeping winds and seas elevated. In
fact, a prolonged SCA may be possible from Tuesday through as late
as Friday depending on how quickly the trough departs/weakens.

&&

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

$$

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

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