Area Forecast Discussion


271 
FXUS64 KBRO 212052
AFDBRO
Area Forecast Discussion
National Weather Service Brownsville TX
252 PM CST Wed Feb 21 2018
SHORT TERM (Now through Thursday night): Surface cold front is 
currently progressing southward through South Texas. The western 
portion of the front has been accelerated somewhat by convection, 
and currently lies between LRD and APY. Further east, the front 
has yet to reach ALI or CRP. Have made several adjustments to 
temps/wind earlier today based on obs, short-term guidance, and 
collaboration with neighboring office. 12Z runs of NAM and GFS 
actually in better agreement on timing of frontal wind-shift with 
front, but GFS temps are not as cold. NAM seems to be in better 
alignment was observed temps upstream, so have generally gone with
a MET-guidance heavy short-term consensus through Thursday 
evening. Think the NAM has the right idea overall, but still could
be a little too fast bringing the boundary through the Lower 
Valley, which may not reach BRO until ~12Z tomorrow morning.
Temps will be falling quickly behind the front, with some spots 
in Texas falling 30 degrees in a few hours. Won't see quite this 
precipitous of a drop, but still a much cooler feel with temps 
falling into the upper 40s by daybreak over the northern/western 
Ranchlands but still near 60 at BRO (sharp gradient across the 
front). Thursday high temps only recover into the mid-50s to lower
60s. As far as sensible weather goes, scattered to numerous 
showers and isolated thunderstorms are expected along and just 
behind the front. May also see some patchy fog in the mid-Lower 
Valley tonight. Have gradually pulled thunder out of the forecast 
from NW to SE overnight as atmosphere becomes too stable for even 
elevated convection. Transition will be to more light rain/drizzle
as southerly flow rides up over shallow cold airmass. Models 
trending down on measurable PoP's during the day Thursday, with 
little lifting mechanism evident, so have followed suit. Rainfall 
totals will generally be only a few tenths of an inch, though 
brief heavier rains in thunderstorms could also occur.
Thursday night, still some uncertainty as to when more onshore flow 
will re-develop with the boundary lifting back inland/northward as a 
warm front.  NAM had been quick to do this as well, but seems to be 
slowing down.  Went with more of a general model blend Thursday 
night to account for the uncertainty.  If onshore flow resumes, 
temps may actually rise slightly Thursday night into early Friday 
morning.  Kept isolated/scattered PoP's across the northern 
counties, as inherited, to account for the possibility of the 
boundary lifting back northward, which could kick off a few light 
showers.
.LONG TERM (Friday through Wednesday): A stationary H5 Bermuda ridge
will face off with a large scale trough over the West on Friday,
which features smaller scale embedded short waves rotating through
with the flow. One such shortwave will move from the four corners
into the southern high plains on Friday, generating pressure falls
out into the Plains and maintaining a tighter gradient with high
pressure over the Gulf, all supporting a moderate southeast to south
inflow over the CWA on Friday and Saturday. The south inflow on
Saturday will support a rapid recovery in temperatures, with high
temps of 70s to lower 80s on Friday rebounding well into the 80s
and near 90 in spots on Saturday.
A late weekend cold front will move toward south Texas on Saturday,
trailing behind and south of the ejecting Plains short wave. The
front is forecast to push into the area late Saturday to Saturday
night, though with a lack of significant upper support and continued
southwest midlevel flow the front will lack punch. Surface winds
will shift to east or northeast on Sunday, and some energy moving
over in the southwest flow will trigger a few showers and an isolated
tstm initially, with with more of an overrunning pattern setting up
Sunday night into Monday. High pressure will shift east on Tuesday,
with winds veering to southeast and pushing the remnant boundary back
north. Temperatures Sunday through Tuesday will be milder, in other
words slightly cooler, and near normal, but will trend upward again
on Wednesday.
&&
.MARINE:
Now through Thursday night: Gulf seas remain agitated with TABS-K
buoy reporting 6 ft. Have maintained SCEC wording in the CWF and
held off on any SCA's as trend should generally be for swells to
slowly subside overnight. Marine Weather Statement for fog in the
nearshore waters/Laguna remains in effect until 6pm, with on SPI
suggesting it is representative with VIS estimated at 1-3nm, at
least along the immediate coast. Cold front should move into the
coastal waters this evening, replacing moderate SE winds with
moderate NNE winds behind it. Front is expected to stall over the
outer Gulf waters, keeping the pressure gradient fairly weak.
Light-to-moderate onshore flow looks to redevelop later Thursday
night, but some uncertainty as to exactly when. No SCA's expected
through the period unless seas run higher than forecast this 
evening.
Friday through Monday night: High pressure over the Gulf will 
interact with lower pressure to the west to produce moderate 
southeast winds and upper end moderate seas. Periods of small 
craft should exercise caution to low end small craft advisory 
conditions will be possible with Gulf wave heights near seven 
feet. Southeast winds will be slightly stronger on Saturday as the
gradient tightens up ahead of a cold front, and small craft will 
also need to exercise caution on the Laguna Madre. A cold front 
will then approach the waters Saturday night and Sunday, shifting 
winds to east. The front will struggle to push through, but 
moderate northeast winds are forecast to develop Sunday night 
through Monday night. Moderate seas will continue behind the 
front.
&&
.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  60  62  59  79 /  50  20  10  10 
BROWNSVILLE          60  63  60  81 /  40  20  10  10 
HARLINGEN            58  61  59  82 /  40  20  10  10 
MCALLEN              57  60  58  83 /  50  30  10  10 
RIO GRANDE CITY      53  59  58  78 /  50  20  20  10 
SOUTH PADRE ISLAND   62  63  59  73 /  40  20  10  10 
&&
.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...None.
&&
$$
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