Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 202319 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
619 PM CDT Fri Oct 20 2017

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


.AVIATION...Model guidance is indicating a weak fog signal for
late tonight, and have incorporated that into the TAFs. HRL saw
lower visibility, a half mile, this morning, and expect the same
early Saturday morning, but it should be low level ground fog.
There will be at least light southeast winds, which should help
prevent more widespread fog until after dawn when temperatures
begin to rise, burning off the ground fog. The morning sounding
corroborated this trend with signs of a surface based radiation
inversion, which will likely repeat Saturday morning. Dew points
have recovered into the lower 70s, and overnight cloud cover will
be mostly thinner, higher based clouds, so the ingredients seem
favorable for fog. Patches of locally dense fog will be possible,
and there may be a few low cloud decks as well for the mid valley.
Fog may again be a player Saturday night into Sunday as winds
decrease a bit more overnight ahead of the Sunday cold front, with
model guidance already hinting at mild visibility restrictions.


.PREV DISCUSSION... /issued 252 PM CDT Fri Oct 20 2017/

SHORT TERM (Now through Saturday Night): Main short term
forecast issue is fog possibility again tonight. Surface moisture
remains ample with dewpoints in the low 70s, and being limited
generally to the lowest 1000 feet or so. Above that is very dry
air capping things off. With expected light southeast flow
continuing tonight, this will provide the proper atmospheric setup
for fog formation across the region. HRL had dense fog around the
airport this morning, and will likely happen again tonight. More
widespread fog will also be expected for the remainder of the
valley mainly around sunrise. Saturday will be similar to today,
with partly cloudy skies. Kept temperatures near consensus for
highs in the low to mid 90s, but not reaching near any daily

LONG TERM (Sunday through Friday): Sunday appears to be the only
active day weather-wise through the long term period. A cold
front is expected to drop south across Central and South-central
Texas by Sunday morning. Models are generally handling the FROPA
well, with it entering the Northern Ranchlands by late morning
Sunday, and moving south through the RGV by the early to mid
afternoon. Long term guidance does differ with POPs however, with
the ECMWF holding on to slightly higher values with the GFS
remaining drier. Have generally kept the same forecast trend as
the previous one, keeping POPs slightly lower. Guidance does
suggest that dry, stable air aloft will move in quickly along or
just lagging behind the front. Do think that this will help
suppress convection overall even though scattered showers and
thunderstorms are possible. Also, the better forcing and dynamics
will stay well north of deep south Texas. Temps will still
generally be warm ahead of the front, before falling.

High pressure will move into the Valley Sunday night into Monday
with dry air continuing to filter in quickly. Winds will continue
to be breezy until the front settle in on Monday. Temps and
dewpoints will also be noticeably cooler. The remainder of the
week should remain dry with a reinforcing high pressure system
expected Tuesday into Wednesday. This system will quickly move
east over the Gulf waters as surface low pressure system and cold
front develops in near the Panhandles region causing an increase
in southerly flow over the region by Thursday. A stonger H5 trough
moving through the Central Plains may drive this next front
towards the RGV by the weekend. Meanwhile, temps through the week
will generally be near or slightly above normal.


Now through Saturday night: Long period swells have begun to
reach the nearshore waters this afternoon, as a long fetch of
easterly winds continue to push swells into the western Gulf.
Swells will remain 4 to 5 feet through tomorrow night, but will
roll with an 8 to 10 second period. Onshore flow will remain light
through the short term.

Sunday through Wednesday Night: A cold front will sweep south
through the Lower Texas Coastal waters on Sunday with strong
surface high pressure building in Sunday night. Showers and
thunderstorms will be possible. Small craft advisories will
likely be needed across the offshore waters Sunday night into
Monday due to increasing north winds and elevated seas. Marine
conditions will improve briefly Monday into Tuesday as high
pressure settles across the area. However, a reinforcing high
pressure system will push into the region late Tuesday into
Wednesday with winds and seas increasing once again with more
advisories possible.




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