Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 182350 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
650 PM CDT Thu May 18 2017

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


.AVIATION...Multi-layer cloud decks and breezy southeast winds
prevail across Deep South Texas this evening. A low level
inversion will support MVFR ceilings at all TAF sites by late this
evening as southeast winds become more moderate. Surface high
pressure interacting with lower pressure across west Texas will
will result in a tighter gradient over the area on Friday. Breezy
surface winds should mix out MVFR ceilings by mid to late


.PREV DISCUSSION... /issued 246 PM CDT Thu May 18 2017/

SHORT TERM (Now through Friday Night): High pressure at the
surface and at the 500 mb level will continue to be the dominant
weather features over Deep South Texas and the Rio Grande Valley
during the short term forecast period. Dry weather will continue
across the BRO CWFA courtesy of this weather pattern. A breezy to
windy onshore flow is also likely, helping to keep temperatures at
above normal levels.

LONG TERM (Saturday through Thursday):Upper level trough over the
Plains continues to lift east northeast towards the upper midwest
through the weekend, pushing a weak cold front south across
Texas, while 500 mb ridging nudges north from Mexico. Push with
front remains weak and concur with prior shifts keeping boundary
north of the CWA and washing out. Ahead of the front moisture
will pool and deepen with steady onshore flow, but the best
moisture stays well north of the area. Saturday looks to be
generally rain free across the area, though a few showers and
thunderstorms may move into the northern and western zones
overnight. Latest GFS model guidance brings in a drier day for
Sunday, with slightly drier air moving in from the south
southeast and previously progged impulses in the flow further
north, while the ECM continues to be bullish, moving boundary
further south (which appears unlikely), and having more moisture
in place. Latest model GFS guidance shows lower PWATs Saturday
night into Sunday, down from the 2 inch plus range with
yesterday`s 12Z run to 1.7 to 1.9 inches today, but kept the 1.8
to 2.0 inch range for Monday. Should see some convection across
the area Sunday, with daytime heating, seabreeze, and deepening
moisture. Leaned towards GFS a bit for pops, with the western and
northern counties (where the best moisture resides) more likely to
see rain Sunday and Sunday night. Best chances for the rest of
the area look to be Monday when another surge of moisture moves
across the Valley. Above normal temperatures continue Saturday
with highs well into the 90s across much of the inland areas and
approaching the 100 degree mark across Zapata and Starr counties.
Increased cloud cover and rain chances will bring cooler
temperatures, closer to normal, for Sunday and Monday.

By Tuesday, forecast becomes less clear, with models in
disagreement with timing and location of next shortwave digging in
across the Midwest and Great Lakes region, as well as location and
strength of the midlevel ridge building in by late in the period.
This makes the timing of the next front pushing across Texas
difficult to pin down at this point. ECM brings the front through
Tuesday with not much fanfare and a quick shot of pops Tuesday
afternoon, while the GFS remains on the slower side, pushing the
front though Wednesday and being more optimistic with pops. Given
the uncertainty at this point in time and model disagreement, have
opted to go with a slight chance of pops Tuesday through
Thursday. Above normal temperatures return for Tuesday with a
possible heat spike ahead of the approaching front, but near
normal temperatures return for Wednesday and Thursday.

MARINE (Now through Friday Night): Buoy 42020 reported south-
southeast winds around 18 knots gusting to around 19 knots with seas
slightly over 6 feet with a period of 8 seconds at 13 CDT/18 UTC.
The interaction between high and low pressure will continue to
produce Small Craft Advisory winds and seas along the Lower Texas
Coast through the forecast period.

Saturday through Tuesday: Pressure gradient weakens through the
weekend as a weak front moves into central Texas Saturday and
Sunday. Moderate southeasterly winds and elevated seas may
necessitate the continuance of small craft advisories into
Saturday. Conditions improve going into Sunday as winds diminish
and shift to the east and seas subside, with seas possibly still
in the small craft exercise caution range through Sunday morning
across the far offshore Gulf waters.


GM...Small Craft Advisory for winds until 8 PM CDT this evening for

     Small Craft Advisory until 7 AM CDT Friday for GMZ150-155-170-



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