Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 241827 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
1227 PM CST Tue Jan 24 2017

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

.AVIATION...Satellite images and surface observations indicate
clear skies across the CWA early this afternoon. Visibilities were
near 5SM with haze at KHBV. Expect VFR conditions to prevail the
rest of the afternoon into the evening as surface low pressure
across the southern plains continues to provide southerly winds
across the Rio Grande valley and northern ranchlands. MVFR
conditions are expected to develop late tonight into early Wed
morning as low level moisture increases along and ahead of a cold
front moving through the CWA Wed morning. This will allow some low
clouds/fog to develop as winds diminish tonight and clear skies
allow fog to develop.
&&

.PREV DISCUSSION... /issued 540 AM CST Tue Jan 24 2017/
DISCUSSION...Updated for latest aviation discussion below.

AVIATION...12Z BRO raob indicated a southerly low-level jet
maxing out with 37KT at 1,500 ft. With surface winds running at
8-10KT, will carry LLWS at BRO and HRL in the initial prevailing
group until mixed layer develops and distributes the wind speeds
more evenly in the vertical. This mixing, courtesy of strong
daytime heating, will lead to windy conditions by late morning at
BRO and HRL where AWW`s may be needed...with somewhat lesser
winds at MFE. A few cumulus or cirrus clouds may pass by today,
but conditions will stay VFR. Winds decrease after sunset but
remain in the 10-15KT range for much of the night. Models hint at
some MVFR CIG`s developing after 09Z Tuesday (at the tail end of
the TAF period) ahead of an approaching cold front. Will insert a
SCT020 deck for now.

PREV DISCUSSION... /issued 409 AM CST Tue Jan 24 2017/

SHORT TERM:(Now through Wednesday): Short- range model solutions
have been backing off slightly, but still expect southerly winds
to crank up today, especially in the coastal counties, as a
surface low deepens over the Central Plains and tightens the
pressure gradient. Will be issuing a Wind Advisory shortly for
Cameron, Willacy, Hidalgo, and Kenedy counties. A more
southwesterly wind direction at low levels (but above the surface)
will lead to compressional heating, with temperatures hitting
record territory once again; see Climate section. With the higher
winds and low RH`s due to the hot temperatures, there will be fire
weather concerns again today.

Fairly quiet this evening before a dry cold front arrives in the
Northern Ranchlands around sunrise, and then pushes through to the
coast by noontime.  Some decent cooling, but no precip, is expected
with this front.  Temp forecast in the mid-Lower RGV a bit tricky,
depending how much heating occurs before the FROPA, but most areas
should top out in the mid-upper 70s...which is still above normal
for this time of year.  Breezy northerly winds also develop behind
the front, bringing in a drier airmass with fire weather concerns
again in play.

LONG TERM (Wednesday Night through Monday)...The first half of
the longterm starts off dry and mild (near normal) and ends up
wetter and cooler (below normal). Models remain in tandem with
longwave trough becoming established across the country (Wed-Thu)
extending SW from a deep cyclone over Hudson Bay and the Great
Lakes Region to a shortwave trough along the California coast.
The elongated trough begins to split Friday with the western base
of the dropping into NW Mexico eventually becoming a closed low
and tracking every so slowly east. It`s this low that will likely
be the trigger for increasing rain chances beginning as early as
Friday night and continuing into next Tuesday.

Latest forecast remains a blend of the models which show little
change from previous runs. Thursday and Friday will continue to
be dry and relatively mild or near normal. As the low out west
develops moisture begins to increase and another surge of
northerly winds overspread the RGV Saturday as the northeastern
trough begins to deepening and the northern jet stream takes a dip
to the south. Clouds, rain and cooler temperatures are in the
offering next weekend and into early next week as the low tracks
eastward ever so slowly.

MARINE:(Now through Wednesday):  Wind speeds have been trending
upward at Buoy 42020 for the past several hours, with sustained
southerly winds already around 20 knots.  Consequently, a Small
Craft Advisory has been issued for the Gulf waters through 6pm this
evening.  Models are hinting at a relative lull in the offshore
winds this evening, but the SCA may need to be extended if seas
(which are expected to build to 5-7 ft. today) remain elevated.  SCA
for Winds is also in effect for the Laguna Madre from 10am to 4pm
today.  A cold front will move through the coastal waters early in
the day on Wednesday with stronger northerly winds behind it,
necessitating another period of likely SCA`s, especially for the
Gulf waters.

Wednesday night through Saturday...Post cold front northerly winds
and higher seas to linger through Wednesday before surface high
pressure moves east weakening the pressure gradient. Winds veer
northeast gradually diminishing with a slow subsiding of the
seas Thursday and Friday. Another northeast to north surge
Saturday and Sunday with adverse marine conditions developing.

FIRE WEATHER...Moisture gradually returns to the eastern zones today
on increasing southerly winds with 20-ft. speeds around 20mph. Lower
RH`s persist out west, but 20-ft. wind speeds will be lower as
well...closer to 10mph. Still appears unlikely that Red Flag Warning
criteria will be reached today, but will be issuing a Fire Danger
Statement shortly for all counties but Starr, Zapata, and Jim Hogg.
On Wednesday, northerly winds increase behind a dry cold front.
Another Fire Danger Statement or a relatively short duration Red
Flag Warning will probably be needed.  SPC has the entire CWA in its
"Elevated" area in the Fire Weather Outlook valid for Wednesday.

CLIMATE... Near-record high temperatures are forecast today in the
Rio Grande Valley. Daily records for Brownsville, Harlingen, and
McAllen are 86F, 87F, and 89F, respectively.  Forecast high
temperatures are 87F at Brownsville, 88F at Harlingen, and 91F at
McAllen.
&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...Wind Advisory until 5 PM CST this afternoon for TXZ251-253>257.

GM...Small Craft Advisory for winds until 5 PM CST this afternoon for
     GMZ130-132-135.

     Small Craft Advisory until 6 PM CST this evening for GMZ150-155-
     170-175.
&&

$$

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