Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 261734

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1134 AM CST Sun Feb 26 2017

.DISCUSSION...Updated for latest aviation /18Z/ and marine
discussion below.


.AVIATION...Swath of mainly VFR stratocumulus has overspread the
Valley as expected, with a quick hitting brief showers mainly east
of US 281 barely affecting Brownsville and Harlingen and offering
no significant visibility restrictions as they cruise by. Main
forecast issue this afternoon is the Valley wind machine, which is
achieving nicely so will tease up winds a hair especially for
Harlingen/Brownsville. As for clouds this afternoon, expect fairly
quick erosion at McAllen/Miller and possibly reaching the Lower
Valley terminals toward sunset so will add a TEMPO group to cover.

For tonight, low level southerly jet is just enough to keep winds
near 10 knots and prevent anything more than fuzzy haze at high
MVFR or 6 miles. As for clouds, deep layer drying should allow
enough mix-down for a period of clearing after midnight, though
McAllen may see a redevelopment of low MVFR ceilings late so will
keep mention there.

Monday morning will see lesser wind recovery than today with low
level wind fields decreasing and actually veering southwest toward
18Z. Should be enough low level moisture for scattered to TEMPO
broken MVFR to low VFR cumulus but that`s about it.


Outer waters have been sitting just on the edge of Small Craft
Advisory winds (20 knots with higher gusts) since mid morning.
However, while Buoy 20 is sitting over the line, TABS Buoy K
(42045) is barely gusting to 20 knots as of 11 AM. With diurnal
weakening of the wind field over the relatively "cool" waters
compared to land, expect caution conditions (15 to 20 knots and
gusty) to be predominant with seas somewhere in the 4 to 6 feet
range as they are now. For this reason elected to hold caution
wording, and also remove from the waters closest to the coast
where speeds should be cut even further (i.e. 12 to 17 knots).

For Laguna Madre, teased up the winds a few knots enough to add
Caution to the forecast based on recent gusts over 25 knots at
inland Bayview and Harlingen. Will keep a close eye on whether a 3
to 6 hour advisory will be needed there but for now looks to be
just below. Expect the isolated showers to end by early to mid


.PREV DISCUSSION... /issued 634 AM CST Sun Feb 26 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...IR satl imagery shows widespread low and mid level cld
decks spreading over most of Deep South TX this morning on the
increasing southerly low level flow. This will maintain ceilings
at VFR/MVFR levels throughout much of the upcoming forecast
period. The rebounding surface moisture levels will combine with
the nocturnal low level inversion tomorrow morning to drop the
ceilings down closer to IFR levels for all three airports. KBRO
radar is showing some patchy shower activity early this morning
over Mexico moving north the region. This activity will be too
spotty to be worth a mention in the 12z TAFs.

PREV DISCUSSION... /issued 405 AM CST Sun Feb 26 2017/

SHORT TERM (Today through Monday): The 500 mb flow pattern over the
RGV will remain pretty zonal throughout today and Mon. At the
surface...high pressure will shift steadily east which will allow
the WAA to persist over the region throughout the short term which
will allow the temps to increase through tomorrow allowing the high
temps to rebound into the 80s and 90s. The southerly low level flow
will also allow some better moisture values to increase over the RGV
today and tonight. Some patchy areas of 500 mb PVA will move over
the region from west to east which may interact with the increasing
moisture levels to allow some isold conv to form up today. KBRO
radar is indicating some spotty showers already moving up north from
Mexico. Drier air will then move into the region Sunday as the
better moisture values move up to our north and northeast. The
better sunshine amounts tomorrow due to the drier air will allow the
high temps to reach well above climo for the end of February. The
GFS/NAM and ECMWF pops for today all agree on some slgt chc pops
with single digit pops expected tonight and Monday.

The NAM and ECMWF forecast temps remain on the warmer side versus
the GFS numbers. Considering the recent rounds of record to near
record high temps that have impacted the RGV...will go on the warmer
side of the model temp guidance especially for highs.  Despite the
above normal highs expected Mon...the record highs for
Brownsville...Harlingen and McAllen for Mon may be a bit out of
reach of our current forecast highs.

LONG TERM (Monday Night through Saturday): Temperatures will
remain well above normal through Wednesday as west to southwest flow
aloft and southerly winds at the surface continues. Tuesday will be
the hottest day of the week with high temperatures in the 90s away
from the beaches, some triple digits are possible along the river
across the upper Valley. Low temperatures Monday night and Tuesday
night will generally remain in the 70s. A cold front will move
across Deep South Texas and the Rio Grande Valley on Wednesday.
Descent moisture near the coast should support isolated convection
across the coastal counties with scattered pops over the Gulf waters
with the front. Erratic fire behavior and potential spread is
possible on Wendesday due to the drier air and gusty north winds in
the wake of the frontal passage.

The combination of deeper moisture, southwest flow aloft, and the
development of a coastal trough/surface low will lead to increasing
rain chances starting late Thursday. The best opportunity for rain
appears to be Friday night into Saturday. QPF for ranges near 0.50"
for the event, though 1" is not out of the question as per WPC
latest Day 6-7 guidance. Abundant cloud cover and overrunning rain
will likely keep daytime temperatures below average Friday and near
normal on Saturday. Broad surface high pressure across the Midwest
will produce long east/northeast fetch across the entire Gulf late
in the period. This may produce some tidal overwash/run up toward
the dunes at South Padre Island late next week/weekend.

MARINE (Now through Monday): Buoy020 is reporting a SE wind of
18g21kts with swells around 5 ft. The PGF will maintain the winds
and seas near SCEC levels throughout today. The PGF will then start
to weaken some later tonight into Mon with a moderate S-SE wind

Monday Night through Thursday Night: Moderate south to southeast
winds and occasionally elevated seas will prevail Monday night into
Wednesday morning. Strong northerly winds and building seas will
develop in the wake of a cold front Wednesday afternoon. Periods of
Small Craft Exercise Caution or marginal Small Craft Advisories will
be possible Monday night through Wednesday morning. Small Craft
Advisories will likely be needed by Wednesday night for more
hazardous marine conditions.




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