Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 132052

Area Forecast Discussion
National Weather Service Brownsville TX
252 PM CST Tue Feb 13 2018

.SHORT TERM (Now through Wednesday Night):  Latest surface analysis
and observations indicate a warm front poised over the Gulf waters
extending southeast of Port Isabel extending northeast into the NC
Gulf. The front is expected to make slow progress northward
overnight and may reach a McAllen to Sarita line by Noon Wednesday.
Models differ on the timing of the warm front with the NAM the
slowest but none the less the front should work its way through the
CWA Wednesday with much warmer temperatures and improving surface
visibilities in its wake. Strong but shallow surface inversion and
very weak isentropic lift and a strong mid level ridge building
overhead, from the east, should result in little chance of rain, but
maintain patches of drizzle and fog overnight/Wed morning and until
the warm front passes to the north.

Visibilities within the fog today have varied greatly at times
but have averaged 1 to 3 miles especially in the Mid and Lower
Valley. NNW winds lower tonight as the warm front approaches with
an increase in dew points increasing the probabilities of dense
fog development. Models continue to differ on how dense it may
become so will defer to the overnight shift to monitor for the
potential of a Dense Fog Advisory. Some breaks in the clouds are
anticipated tomorrow as the front clears the area. Mid level ridge
and the drier air associated with it may provide enough
subsidence for some sun to break through in the afternoon. Shallow
surface moisture and and increasing dew points are likely to
produce another around of marine/advection fog impacting mainly
the coastal region and the lower Valley with lower visibilities of
1/2 to 1 mile at times Wednesday night. Farther inland Southerly
winds may be too high to allow for dense fog so the 2 to 4 miles
looks good for these areas.

Wont see much in the way of temperatures falls tonight and may even
see temperatures rise overnight and for sure in the Lower Valley
around sunrise as the warm front moves into the vicinity.
Temperatures start out in 50s and may end up in the lower 60s by
sunrise. Temperatures to warm up significantly Wednesday with GFS/EC
still on board pushing highs near 80 degrees. Mild and humid
Wednesday night with lows in the 60s.

.LONG TERM (Thursday through Tuesday): More spring-like pattern
shaping up for much of the long-term period with warm and
occasionally breezy conditions predominating, except perhaps over
the weekend when a cold front may penetrate into our area.
Precipitation will be generally scant as well.

On Thursday, an H5 high center is progged to lie over the Western
Gulf, providing dry mid-levels. Combined with low-level southerly
flow, this should make for the warmest day over the coming week,
with afternoon readings in the mid-80s common west of Hwy.
77/I-69C and perhaps some upper 80s out near Falcon Lake/Zapata.
More of the same in store for Friday, as southerly flow is
maintained ahead of an approaching cold front (more on that
below). Temps may stay a degree or two below Thursday`s readings,
with the H5 high being nudged eastward by an upstream trough.

The saga of the weekend front continues, with consistency
within/amongst models still pretty hard to come by. 12Z GFS run
places the boundary just north of the CWA at 00Z Sat, then brings
it through most of the area overnight. 00/12Z ECMWF runs stall it
out over south-central TX. Latest NAM doesn`t quite go out far
enough to provide clarity, though its frontal placement at that
time is in-between the GFS and ECM. Should be noted that GFS
doesn`t bring the H85 front this far south (suggesting a shallow
airmass behind it), and also quickly reverses it northward on
Sunday. Moreover, the surface high behind the boundary never
really makes a southward plunge, instead translating more eastward
from the Plains into the Midwest.

All in all, this suggests the front will hang up and become
stationary somewhere near the northern CWA. WPC is depicting this
scenario also. Due to the uncertainty, went with a consensus blend
of temps and winds for the Friday night-Sunday night period. This
yielded a bit a cooldown for Saturday, but still not much below
climo. PoP/Wx-wise, leaned toward chances light rain and drizzle
over the northern/western CWA and slight chances of showers
further south and east. Precip amounts should stay on the light

Winds should veer back to onshore for all areas as the day goes on
Sunday, with temps still more-or-less near seasonal norms and just
slight chances of rain/showers. Breezy and warm weather returns
for Monday and Tuesday, with high temps again reaching the 80s
away from the coast. Maintained inherited 20% PoP`s for Tuesday,
with some negative-tilt troughing at H25 upstream, a possible H5
shortwave approaching from the west through northern Mexico, and
some moisture beginning to pool ahead of the next front dropping
down the Plains, which could be a player toward the middle-latter
part of next week.


.MARINE (Now through Wednesday Night):  Warm front extending across
the southern outer waters moving slowly northwest and should clear
all areas later Wednesday morning. The Laguna Madre will continue to
see a northerly winds west of the front through this evening and not
until Wednesday morning see winds turn southeast to south. Much of
the same for the gulf waters northeast to east winds north of the
front and southeast winds in wake of the front. Not expected strong
winds but wind and seas may increase near exercise caution levels
later tomorrow as the front passes farther north. Main concern will
continue to be the foggy conditions with marine fog continuing to
produce lower visibilities of 1-3 miles. Some areas are likely to
see some patchy dense fog with visibilities lowering below one mile
and occasionally down to one quarter mile at times especially across
the Laguna Madre and near shore waters.

Thursday through Monday: Generally moderate winds and seas will
prevail, with a few periods of Small Craft Exercise Caution
(SCEC) for winds likely. Waves should be mainly locally wind-
generated as lengthy fetch is unable to organize and produce much
swell. Winds on the Laguna Madre should reach SCEC levels Thursday
afternoon, but appear to remain shy of Small-Craft Advisory
criterion. Winds slacken a bit for Friday as pressure-gradient
weakens ahead of a cold front, which may enter the northern waters
Friday night or Saturday (though with considerable uncertainty).
Another period of SCEC conditions possible north of where the
boundary sets up. The front should lift back northward on Sunday,
with SE winds in the SCEC-range again by Monday afternoon.

Some marine advection fog is also possible for Laguna and near-
shore waters early Thursday morning and again Thursday night-
Friday morning.


BAYVIEW/PORT ISABEL  58  75  64  79 /  20  20   0  10
BROWNSVILLE          58  77  66  81 /  20  20   0  10
HARLINGEN            55  77  64  83 /  20  20   0  10
MCALLEN              55  78  66  85 /  20  20   0  10
RIO GRANDE CITY      55  80  64  87 /  20  20   0  10
SOUTH PADRE ISLAND   61  71  65  74 /  20  20   0  10




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