Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 180040 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
640 PM CST Fri Feb 17 2017

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


.AVIATION...After a dry and warm start to the evening...a light south
to southeast wind will kick in later tonight and tomorrow morning
allowing the low level dewpoints to start increasing. This will
increase the potential for some reduced vsbys/ceilings around the
mid portion of the current TAF issuance. The GFS/GFS LAMP guidance
is the most aggressive with reducing the vsbys/ceilings down to
LIFR levels. The NAM guidance is not quite as aggressive but still
reflects ceilings dropping down to LIFR levels later tonight while
keeping the vsbys up. Will bring in IFR/LIFR conditions for the HRL
and BRO airports later tonight through early Sat morning leaning
closer to the GFS/GFS LAMP solution. A little lower dewpoints move
into the MFE area throughout the next 24 hours and this maintains
a little better conditions there. However will include some
mention of IFR ceilings mainly due to low status. MVFR/VFR
conditions will then return during the latter half of the current
TAF period as daytime heating and low level mixing increases.


.PREV DISCUSSION... /issued 258 PM CST Fri Feb 17 2017/

SHORT TERM (Tonight through Saturday Night): Subsidence prevails across
Deep South Texas this afternoon in the wake of the upper level
trough axis. South to southwest surface winds will continue across
area through the rest of the afternoon before winds quickly back to
the southeast this evening. Shallow moist layer at the surface will
become trapped by subsiding air aloft overnight, which will lead to
increasing low clouds after midnight. Surface dewpoints will recover
to the 60s across the eastern half of the CWA which should support
the development of patchy fog. Dense fog is not expected as winds
should remain around 10 mph overnight. Low temperatures will range
from the upper 50s across the west to the mid 60s near the coast.

A 500mb shortwave ridge will pass overhead on Saturday resulting in
very warm temperatures across the region. High temperatures Saturday
will range from the mid-upper 80s near the coast to the mid-90s
across the west. There is also a fire weather concern for the
western portions of Deep South Texas Saturday afternoon,
especially for Starr/Zapata/Jim Hogg counties, as relative
humidity values fall below 30 percent for a few hours with 20 feet
winds at 10-15 mph. Low level moisture continues to increase
Saturday night with dewpoints in climbing into the mid to upper
60s across the entire area. Low temperatures Saturday night will
range from the upper 60s across the west to the lower 70s near the
coat under mostly cloudy skies.

LONG TERM (Sunday through Friday): 500mb trough across the
southwest United States and northwest Mexico Sunday will move
across west Texas and northeast Mexico Monday. Low to mid level
moisture is progged to increase across south TX Sunday into Sun
night with convection developing across east TX Sun afternoon and
building back towards the southwest Sun evening. The global models
differ on the amount of moisture with the ECMWF considerably
wetter than the GFS Sun night into Monday. In
addition...conditional instability will be high across the CWA
Sun afternoon through early Monday as CAPEs will be high with
temperatures well above normal Sunday. The limiting factor will be
the low level inversion which will provide a cap on convection
developing across the area. If this cap erodes...then the
potential for severe thunderstorms exists as highlighted by the
latest day 3 SPC outlook. Confidence is low on widespread severe
weather developing across the area Sunday night through early
Monday but cannot rule out isolated strong to severe storms
producing hail/damaging winds. The upper level trough will move
into the western Gulf of Mexico Monday night into Tuesday before
a cutoff low across the northwest Gulf Tuesday. Rain chances will
quickly diminish from west to east Mon afternoon as subsidence
increases across southwest TX. Rain chances will linger across the
coastal sections Mon night as some moisture wraps around the
backside of the 500mb low developing across the northwest Gulf.
500mb ridge across northern Mexico and the 500mb low across the
central Gulf Wednesday will provide subsidence across south TX
through the rest of the week. An onshore flow is expected to
return Thursday before a dry cold front moves through the area
Friday as a 500mb trough across the western U.S. Thursday moves
across the central U.S. Friday.

MARINE (Now through Saturday Night): Buoy 42020 reported south-
southwest winds around 8 knots with seas of 1.6 feet with a period
of 4 seconds at 14 CST/20 UTC. Brownsville radar currently indicates
that most of the convection has pushed well east of the lower Texas
Gulf waters. Light to moderate south to southeast winds with seas of
generally 2 to 4 feet will continue through the forecast period.

Sunday through Wednesday...Moderate to strong southeast winds will
prevail across the coastal waters Sunday before low pressure
develops across the lower TX coast/northeast Mexican coast Sun
night into early Monday. Winds will be light and variable across
the western Gulf of Mexico early Monday as a result before winds
shift to the north and increase in the wake of the low Mon
afternoon. Light to moderate northerly winds should prevail across
the coastal waters Mon night into Tuesday. The pressure gradient
should relax across the lower TX coast Wednesday but will remain
stronger well offshore. Light north winds will prevail across the
Laguna Madre and light to moderate north winds offshore




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