Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 282339

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
539 PM CST Tue Feb 28 2017

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

.AVIATION...Satellite images and surface observations indicate a
few high clouds across the CWA early this evening. Expect MVFR to
IFR conditions to develop late tonight into early Wed morning as
low level moisture under the 850mb thermal inversion allows low
clouds/patchy fog to develop across portions of the Rio Grande
valley and northern ranchlands.

.PREV DISCUSSION... /issued 251 PM CST Tue Feb 28 2017/
SHORT TERM (Now through Wednesday night): H5 zonal flow continues
across the region during the next 36 hours as H5 ridge across the
Gulf gets squashed by the longwave trough passing to the north.
Onshore flow will continue to pump moisture northward due to a
considerable llvl jet. But the jet and moisture are trapped
underneath a strong capping inversion, which was at around 2000
feet as of this morning`s sounding. So once daytime heating
ceases, low clouds will thicken up across the area, while surface
winds will remain breezy from the southeast around 15kts. With the
cap as close to the surface as it is, the potential for some
cloud formation to get pushed to the surface will result in some
very light fog/haze for the region, especially inland closer to
the approaching front.

The front remain a very weak feature, quickly becoming detached from
the main H% trough sweeping into the Great Lakes region. The initial
wind shift will come through Deep South Texas during the noon hours,
but will bring a light wind shift from the north. Some isolated
shower activity is possible with the front, but again, the capping
inversion will take considerable heating to break, which would take
all of peak heating to accomplish. Have focused any residual PoPs to
the coastal counties and offshore mainly during the afternoon.

Now the main push of drier air and breezes doesn`t arrive until at
sunset or later Wednesday evening. With this delay in the arrival of
the driest air, this will lessen the threat for erratic fire
behavior for the western valley, with only a small threat window
just before sunset.

LONG TERM (Thursday through Tuesday): Strong, 1030 mb high pressure
will settle over East Texas and the Northwest Gulf Wednesday night
and Thursday. Some clearing will occur Wednesday night, but mostly
cloudy skies will prevail Thursday, with the precip band pushed
south of the area. High temperatures Thursday will be in the lower

As high pressure shifts toward the upper Midwest, low level east to
northeast winds will continue into Thursday and Fri., being overrun
by west southwest flow aloft. Winds aloft would have to be a bit
more from the northwest to allow for a rapid and complete clearing.
A weak coastal trough will support nearby low level convergence and
cloudy skies, except for the possibility of some clearing across the
ranchlands and brush country, along with enhanced rain chances
Friday through Sunday. This will also help keep temperatures a
little more reasonable, and closer to normal, than they have been.
Thursday night and Friday should be the coolest days of the period,
with lows in the 50s Thursday night and highs in the 60s and 70s on

A warming trend will ensue Friday night through Tuesday, just as
winds are veering to east and southeast. Moisture will increase, as
will rain chances, as the old front moves back north as a warm
front. Model guidance from the GFS and ECMWF both continue to carry
chance or better 12 hour rain probability on Sat. and Sun. for
Brownsville, Harlingen and McAllen. The GFS and ECMWF both try to
bring a front into Central Texas Tuesday or Wednesday of next week,
almost as a back door affair, but the signal has weakened from
yesterday, and it appears that a moist onshore flow will persist
during the first couple of days after the second weekend in March.

Coastal concerns: The arrival of a cold front late Wednesday will
produce strong north northeast winds Wednesday night into Thursday,
along with offshore wave heights of up to 9 feet. Winds will remain
in an unfavorable northeast direction through Thursday or Friday,
and the formation of a coastal trough will help maintain a tighter
gradient into Saturday, while swells remain elevated. Predicted
tides during this interval are forecast to rise to above one foot
above mean lower low water around each mid afternoon from Thursday
through Sunday. The addition of another foot to foot and a half of
swell water on top of high tides will produce a total tide of two
feet or more, enough to produce overwash on the beaches and minor
coastal flooding.

Now through Wednesday night: Breezy southeast winds will continue
for the region through sunset, with Small Craft Advisories
continuing for the Laguna Madre through 6pm. Winds will decouple
after sunset, but will remain elevated 10 to 15 knots overnight.
Seas will remain steady around 5 feet as the long southeast fetch
continues across the Gulf. Winds will be lighter on Wednesday as a
weak front moves through the region. Winds will shift to the
north in the early afternoon, but will remain 10 knots or less
through sunset. After sunset, the main push of north winds will
arrive, with north winds reaching 20 to 25 knots around midnight.
Small Craft Advisories will be needed at that time, but may vary
as timing of the strongest winds continues to slip in latest model

Thursday through Sunday: Poor marine conditions will prevail in the
wake of the Wednesday cold front. Small craft advisory conditions
will continue into Thursday morning with strong northeast winds and
high seas ongoing. High pressure spreading over the northwest Gulf
and the formation of a coastal trough to the south will keep the
gradient tight and will support fresh onshore winds into Friday and
even Saturday. Seas will remain high through this period. Winds will
weaken and veer on Saturday as high pressure to the north shifts
east, but continued swell may keep seas above small craft advisory
criteria through Sunday.

GM...Small Craft Advisory for winds until 6 PM CST this evening for


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