Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 172104

Area Forecast Discussion
National Weather Service Brownsville TX
304 PM CST Sun Dec 17 2017

.SHORT TERM (Now through Monday Night): Overcast skies continue
to blanket most of Deep South Texas with a few peaks of sunshine
along the coastal counties. This is allowing temperatures to rise
into the mid 60s this afternoon with cities out west struggling to
reach the 50s. This is in part due to weak surface troughing
along the coast, which models develop into an area of low pressure
late into the short term period. The BRO 12Z sounding showed a
strong inversion just off the surface, which will continue through
tonight and Monday with moderate S/SSW winds bringing warm, moist
air overhead. Low clouds with areas of fog are expected again
tonight as soils also remain moist. A few patches of dense fog
will be possible, especially from Harlingen through the mid Valley
and northern Ranchlands of Jim Hogg and Brooks counties.

On Monday, models develop a warm front along the coastal low and
moves it north of our area, bringing southerly flow back at the
surface. Abundant moisture will allow the possibility of showers and
thunderstorms with the best chance being along and east of Highway
281 and over the marine areas. Increasing surface temperatures and
an approaching mid-level trough will increase instability, so have
kept thunder in the forecast starting Monday afternoon. Temperatures
will rise back to normal in the mid 70s with WAA behind the front.

Monday night into Tuesday the mid-level trough moves into West Texas
with most of the best upper level support keeping rain chances in
the northern counties overnight. Low temperatures will only fall
into the mid 60s overnight as surface dew points will have

.LONG TERM (Tuesday through Sunday): 500mb shortwave trough across
west Texas and northern Mexico Tuesday will move eastward across
the south-central United States Tues night into Wednesday. At the
surface...a frontal wave will develop across northeast Mexico and
south Texas Tuesday providing convection...mainly
elevated...northeast of the CWA. As the surface low lifts
northeast across east TX Tuesday...a weak cold front will move
through deep south TX Tues night providing a slight chance of
showers...mainly across the coastal sections...across the area.
Surface high pressure will build into south TX Wednesday before
shifting eastward Thursday. Expect stronger warm air advection
across the Rio Grande valley Thursday into Friday than Tuesday and
rain chances will return Friday and continue through early
Saturday before a 500mb trough across the southwest U.S. and
northern Mexico Friday moves eastward bringing a stronger cold
front through south TX late Fri night into early Sat morning. A
weak coastal trough is progged to develop offshore the lower TX
coast Saturday and move northward Sunday. This will continue to
provide a slight chance of rain across the coastal sections of the
CWA through the weekend.

.MARINE (Now through Monday night): The main concern will be the low
possibility of patchy marine fog early Monday morning over the Bay
and extreme nearshore Gulf waters. Water temperatures remain in the
low 60s with dew points expected to increase into the mid 60s with
weak onshore flow. Otherwise, light winds and lows seas will
continue across the coastal waters. A weak coastal low will develop
and move northward, shifting winds back to the southeast late in the
period. Showers and thunderstorms will also be possible as a mid-
level trough moves into West Texas and a warm front develops along
the lower Texas coast.

Tuesday through Friday...Moderate southeast winds will prevail
across the coastal waters Tuesday with surface low pressure across
northeast Mexico. Winds will shift to the north and northeast
Wednesday as a weak cold front moves through the lower Texas
coast. Light to moderate northeast winds Wednesday will veer to
the southeast Thursday as surface high pressure across south TX
moves eastward and low pressure develops on the lee side of the
Rockies. Light to moderate southeast winds Thursday will increase
Thurs night as the pressure gradient increases across the western
Gulf of Mexico. Winds should diminish slightly and veer to the
south Friday before a stronger cold front moves through the
coastal waters Fri night. Small craft advisories will likely be
needed in the wake of the front Fri night.

BAYVIEW/PORT ISABEL  62  75  67  79 /  20  30  20  20
BROWNSVILLE          61  75  68  81 /  20  30  20  20
HARLINGEN            59  74  66  81 /  20  30  20  20
MCALLEN              60  74  66  80 /  20  30  20  20
RIO GRANDE CITY      57  72  63  78 /  20  20  30  20
SOUTH PADRE ISLAND   65  74  71  76 /  20  30  20  20



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