Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 110038 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
638 PM CST Sat Dec 10 2016

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

&&

.AVIATION...The 00z BRO sounding shows a pretty saturated airmass
in place this evening with a fairly strong low level inversion
persisting. This is resulting in a mixture of VFR/MVFR conditions
around the RGV early this evening. The latest NAM forecast
soundings maintains the saturated low level inversion in place
over the region through the night which will reduce the ceilings
back down to IFR levels. Some fog has started to form over the
northern and western counties and as the surface winds start to
slacken later tonight expect this fog to progress further south
lowering vsbys for the RGV airports. The low level wind flow
tomorrow will finally shift around from the south which will
increase the WAA and the low level mixing allowing for the
ceilings/vsbys to improve back up to VFR levels.

&&

.PREV DISCUSSION... /issued 250 PM CST Sat Dec 10 2016/

SHORT TERM (Now through Sunday night):  Zonal flow aloft will
dominate Deep South Texas, and indeed, most of the CONUS, through
the short-term period.  After one more cool night, southerly winds
return on Sunday for a quick warm-up.

For the near-term, through 00Z, trimmed back PoP`s per recent radar
trends.  Picking up some light (15 dBZ) echoes near the Lower Valley
and coast...in association with convergence into the coastal
trough...but have yet to see any evidence of this reaching the
ground.  Mid-Lower Valley locations warmed up a few degrees more
than expected today, when the sun shone for a couple hours, as per
previous AFD update.

Forecast trend overall has remained the same, but 12Z runs of NAM
and GFS showing some timing differences with regard to SSE flow
setting up overnight.  Both models show NW winds of past couple of
days finally backing around to light SW this evening, which allows
temps to actually rise a few degrees through the night.  However,
GFS brings the more moist flow back inland around 03-06Z, whereas
the NAM is about 6 hours slower...and shows a more sudden jump in
dewpoints mid-morning on Sunday.  Latest RUC and HRRR lend more
support to the NAM solution, so based on that, and the fact that
it`s capturing current temps/dewpoints better, will lean pretty
heavily on it for the forecast.

With the slower moisture return, have backed off some on fog
potential tonight.  Will still word patchy coverage over most areas,
but delay onset until after 06Z.  Can`t rule out some isolated light
rain overnight along the coast, but all other areas should stay dry.

Moving into Sunday, the spring-like warmup kicks in, especially once
a weak trough aloft passes during the morning, swinging upper winds
to more WNW.  H85 winds turn SW, ahead of a front moving into the TX
Panhandle.  Depth of moisture will trend down from its current 700-
mb level down to 850mb or perhaps even lower. Upshot will be more
sun with temps reaching the low 80s in the mid-Valley with mid-upr
70`s elsewhere.  Dewpoint in Brownsville reaches 70F by late
afternoon, so the muggy feel will return.  Low temps for early
Monday looked good and so were retained...from near 60 NW to near 70
SE.  MOS guidance hitting fog potential pretty hard for late
tomorrow night as well.  Will introduce areas of fog across all land
areas and the Laguna Madre for now.  Dense fog potential would seem
to be better over the NW counties where winds will die off more so
than nearer the coast.

Continued 8 to 10 second swell period with a still brisk east to
northeast onshore flow has continued tidal run-up to the dune line
at high tide this afternoon per webcams on S. Padre Island.  Don`t
see a need to extend the Coastal Flood Statement at this juncture as
water levels (both observed and residual vs. prediction) are running
a bit lower than this time yesterday.  Next high tide will be minor,
and by then winds offshore should have shifted to SE, which should
calm down the swell.

LONG TERM (Monday through Saturday): The lastest GFS/ECMWF are
in better agreement through the forecast period. A nearly zonal
flow aloft will prevail through much of the week. Southerly flow
at the surface will allow moisture to increase across the area and
warming temperatures through mid week. A cold front will move
into central Texas on Monday but will stall well north of the
area. Another cold front will approach Deep South Texas Wednesday
night before stalling near the northern Ranchlands on Thursday. By
late week, a sharp 500 mb short wave trough will dive south
through the Pacific Northwest and lift across the Great Basin.
This will result in mid level flow becoming southwest over the
forecast area.

Above normal temperatures will prevail Monday through Wednesday.
High temperatures each day will be in the 80s with overnight low
temperatures generally be in the 60s. Slight chance of rain will
develop Wednesday night through Thursday night with increasing cloud
cover as a cold front approaches and stalls across area.
Temperatures will recover Friday and Saturday as southeast winds
return and push warm Gulf air back over the area.

MARINE (Now through Sunday):  Conditions at Buoy 020 as of 150pm
CST were reported as E winds of 18G21KT, with seas near 7 ft.
Extended SCA for the outer Gulf Waters only through 9pm.  Winds veer
SE by this evening, but stay at around 16-20 knots.  SCA may need to
be extended, again for the outer waters, into Sunday morning as
latest wave guidance keeps seas right around 7 ft. out there.  SCEC
likely for the nearer-shore waters.  Conditions on the Laguna Madre
should remain relatively favorable with some moderate southerly
breezes by Sunday afternoon.  Seas on the Gulf finally subside to
around 5 ft. by later Sunday night, though moderate S winds may
require SCEC.

Monday through Thursday...Broad surface high pressure across
the Gulf will support light to moderate south to southeast winds and
low to moderate seas through the period. Isolated to scattered
showers are expected across the coastal waters Wednesday night into
Thursday as a front approaches and stalls across the area.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...Small Craft Advisory until 9 PM CST this evening for GMZ170-175.

&&

$$

This product is also available on the web at:
HTTP://WEATHER.GOV/RGV

Short Term...60
Long Term...69
Graphicast/Upper Air...56


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