Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 100531 AAB
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
1131 PM CST Mon Jan 9 2017

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

&&

.AVIATION...No appreciable change to the forecast which is
mainly an extension of the current package.  Only changes made were
to remove mention of even the FEW overnight clouds as satellite
continues to show clear skies and see no significant low level
moisture to bring even the typical cumulus fractus back to at least
the Lower Valley airports.

No changes to the forecast for Tuesday as wind machine will crank up
under mostly sunny skies with only scattered MVFR to VFR (afternoon)
cumulus.  Kept speeds the same with sustained above 20 knots and
gusts just shy of 35 knots in the Lower Valley.

By evening, winds will lay down a bit but still remain above 10
knots for the most part.  Skies will likely remain clear for the
first half of the night as dry air remains entrenched.

&&

.PREV DISCUSSION... /issued 614 PM CST Mon Jan 9 2017/

DISCUSSION...Updated for latest /00Z/ aviation discussion below.

AVIATION...Mainly a wind forecast for the next 24 hours.
Satellite images show nothing more than passing few cumulus near
the coast and clear skies inland. With dewpoints still on a
gradual recovery overnight and very dry air mass that starts just
off the deck expect nothing more than few MVFR clouds scooting by
in the 30 to 35 knot low level jet for all sites. Surface winds
will dip below 15 knots but probably not much below 10 knots which
will preclude any mentionable fog or haze. Took a gander at adding
a low level wind shear but 30 knot difference criteria within
2000 feet AGL will not be met...closer to 20 to 25 knot
difference.

For Tuesday, the low level jet, which surges close to 40 knots,
will quickly mix down by mid to late morning. This will favor the
usual suspects with the strongest winds (Brownsville and
Harlingen) and ramped up sustained speeds to greater than 20 knots
with gusts over 30 knots. Plenty of sunshine with dry air flooding
the lower levels so expect little more than scattered MVFR cumulus
raising quickly to VFR by late morning. Slightly lower winds for
the mid Valley where the low level jet will mix out a bit. Wind
direction will tend to be from the due south vs. the southeast
which may also help with the speeds, and would not be surprised to
see a gust or two up to 35 knots.
52/BSG

PREV DISCUSSION... /issued 401 PM CST Mon Jan 9 2017/

SHORT TERM (Tonight through Tuesday Night):Pressure gradient finally
becoming established as the bubble ridge that was analyzed along
the coastal bend this morning becomes absorbed by the larger
synoptic flow extending from the Mid-Atlantic into the Western Gulf.
Southerly low level jet to strengthen through Tuesday night with 925-
850mb winds showing upwards to 40knots. Model guidance continues to
show partial mixing of these winds to the surface Tuesday, mainly in
the wind machine zone along and in between I-69E and 69C in the Mid
and Lower RGV, with peak winds just below wind advisory levels
(sustained 30+mph). In any case, windy and warm conditions on tap
with the cold air from the weekend a distant memory. Temperatures
will be warmer still overnight finally going staying above normal
with fair skies but still a coolish breeze.  Temperatures surge 10-
15 degrees above normal Tuesday with all areas well into the 80s
with exception to the coastal strip. Will be monitoring for marine
fog development tonight and through the period as the warm south
winds flow over the cooler shelf waters.

At this time the forecast maintains patchy fog along the coastal
strip overnight and early Tuesday however the developing stronger
southeast wind may push some of this potential fog inland possibly
impacting Eastern Cameron county more then anyone else i.e.,
Brownsville Airport. Probabilities remain low for sea fog but as the
moist southerly flow becomes more established later tomorrow and
tomorrow night there will be a better chance of sea fog.

LONG TERM (Wednesday through Monday): Big issue for the period
remains the timing/location of the upper trough this weekend and
the associated front. Flow remains fairly zonal through Wednesday.
Progressing through the remainder of the week an upper trough
over the Pacific NW amplifies as it digs southeast across the
western states, desert SW, and Mexico and an upper level ridge
builds across the southeastern states and the Gulf of Mexico.

Above normal to near record temperatures continue through the
remainder of the work week and into first half of the weekend as
southerly winds bring in warmer air with highs well into the 80s
each day. 850 temps of 16 to 18C coupled with breezy southerly
flow could lead to max temps on Wednesday and Thursday well into
the 80s, with upper 80s likely across the mid to upper Valley.
Overnight lows remain on the warm side as well with lows in the
lower 70s not out of the question. Breezy to windy southerly winds
expected Wednesday through Saturday, with the strongest winds
occurring Wednesday and Thursday. 925 mb winds show 35 to 40 knots
on Wednesday and 25 to 35 knots on Thursday. Depending on mixing
of winds, currently forecast winds may be on the low side and may
need to be increased in subsequent forecast package.

As we move later into the period, differences in model guidance
become apparent, with the ECWMF moving the trough slower and
further south into Mexico, while the GFS is more progressive and
keeps the trough a little further north. Have opted to lean
towards the slower progression. Due to the slower trek of the
trough, have lowered pops a bit for the weekend, keeping
everything in the slight chance to chance realm. A cold front will
move across the region late in the period, with an approximate
frontal passage on Monday. Cooler temps and increased cloud cover
wrap up the period.

Maintained the mention of marine fog through Thursday morning due
to the returning warm southeasterly flow moving across the cooler
bay and nearshore Gulf waters.

MARINE (Now through Tuesday Night):Southeast to south winds to
steadily increase as high pressure becomes established over the Gulf
Of Mexico.  Winds to approach but not quite reach small craft
advisory levels with cooler Laguna and gulf waters not allowing for
maximum mixing of stronger winds to the surface. Exercise caution
levels are more likely for Tuesday with some winds and seas possibly
exceeding thresholds Tuesday night across the open Gulf waters as
the pressure gradient strengthens another notch. Higher dewpoint air
to spread over the cooler waters the next several days possibly
initializing the development of sea fog. Will be monitor for dense
fog formation For Tuesday night.

(Wednesday through Friday): Pressure gradient remains rather
strong for much of the period as high pressure over the Gulf of
Mexico interacts with areas of low pressure moving across the
central Plains. Adverse marine conditions may develop across the
Laguna Madre and the Gulf of Mexico waters as winds increase and
seas build, with SCEC to SCA conditions possible. Fog may be an
issue through Thursday as warm southerly winds move over the
colder nearshore and Laguna waters.

&&

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

$$

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52



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