Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 140559 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1259 AM CDT Mon May 14 2018

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


.AVIATION...Multi-level cloud decks and light southeast winds
prevail across deep south Texas early this morning. Widespread
IFR/MVFR ceilings are expected to develop ovenight as light
southeast winds continue. Ceilings will begin to lift/burn
off/dissipate around mid-morning. Surface winds will generally
remain southeasterly across the entire area through period.


.PREV DISCUSSION... /issued 616 PM CDT Sun May 13 2018/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...GOES-16 satellite imagery was showing daytime-heating
induced cumulus on the decrease across the forecast area with the
approach of sunset. Otherwise, high cirrus associated with
afternoon convection over the Mexican mountains to the west was
slowly overspreading the region. VFR conditions at the beginning
of the TAF period will slowly give way to MVFR CIGS developing
from the coast westward after 03Z this evening. Low clouds look to
develop across the majority of the forecast area overnight leading
to widespread IFR/MVFR CIGS. CIGS will begin to lift/burn
off/dissipate after 15Z Monday morning. Surface winds to generally
remain southeasterly across the entire area through TAF period.
Winds to subside this evening with the loss of daytime heating to
less than 10 knots then rebuild to 12 to 18 knots after 18Z

PREV DISCUSSION... /issued 322 PM CDT Sun May 13 2018/

SHORT TERM (Now through Monday night): South Texas to remain under
the influence of mid level high pressure. The ridge is anchored
over Northern Mexico extending north into S Texas between a mid
level low over the Eastern Gulf and another low/trough over the
Inter-mountain West. Surface moisture has increased over the last
few days but remains in the lowest 5000 feet with a deep
subsidence layer between 850-400mb due to the ridge overhead. Even
with plenty of instability and a weak cap in place, over the RGV,
daytime heating and the afternoon seabreeze is not producing
sufficient lift through the dry layer to allow for convection.
Farther west forecast soundings indicate a slightly stronger cap
with some increase in mid level moisture spilling over from the
mountains of Mexico. Models suggest slightly higher probabilities
of convection developing over portions of the Sierra Madre but
the question remains if any of this potential convection can
overcome the dry air and will the cap weaken enough for a few
cells to cross the river intact? With only the 00Z ECMWF showing
15-20 percent and model blends 10 percent or less over the western
zones, will keep the forecast dry for this package.

Overall, the diurnal weather regime will be favor persistence with
mostly cloudy conditions during the late night and early morning
hours giving way to partly cloudy to partly sunny skies for the
afternoon Monday. Temperatures will continue to be above normal with
70s overnight and 90s during the day while the heat indices
exceeding 100 degrees in most locations Monday afternoon.

LONG TERM (Tuesday through Sunday): Mid-level ridging will be
well in place across the Southern Plains and into Deep South
Texas for much of the coming week. This means hot to very hot
conditions with very low chances of rainfall. Afternoon highs
lately have already been above normal for the middle of May with
models showing the warmest weather from Thursday to Saturday. GFS
and ECMWF show 1000-500 mb thicknesses approaching 580 dam all
the way to the coastal counties for the second half of the week
with 850 mb temperatures ranging from 21 to 23 C. Since MOS
guidance oftentimes has been underforecasting temps, decided to
go several degrees above guidance with highs in the mid to upper
90s in the lower to mid RGV and around 100 F in the upper RGV,
especially from McAllen to Falcon Dam.

Any appreciable moisture will be limited to below 850 mb with
possibly slightly higher along the Rio Grande out west Tuesday
night into Wednesday. Models show the possibility of some
convection developing in the higher terrain of Mexico, but latest
guidance has trended a bit down across the U.S. side, so have kept
PoPs at silent 10 % for now.

MARINE (Now through Monday night): Broad surface high pressure over
the Gulf and mid level ridging anchored over Northern Mexico and
South Texas to maintain fairly tranquil conditions across the Lower
Texas coastal through Monday night. Light to moderate winds and low
seas to prevail the next 24-36 hours.

Tuesday through Friday: Surface high pressure over the northern
Gulf of Mexico will maintain light to moderate southeast winds
through Thursday with low to moderate seas. The pressure gradient
tightens on Friday with winds possibly approaching 20 knots across
the Bay and nearshore Gulf waters. Therefore, Small Craft
Advisories will be possible.




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