Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 171144 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
544 AM CST Fri Feb 17 2017

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

&&

.AVIATION...Current radar indicates that shield of more widespread
rain/showers has moved off to the NE and offshore, with only
isolated light showers remaining in the mid-Lower RGV. This
activity should end over the next couple of hours as drier air
aloft moves in from the west. Going with CIGs a little higher than
guidance later this morning (remaining VFR) as even the light rain
earlier was elevated in nature. Winds will back to S-SW for a time
this afternoon, due to weak low pressure moving north along the
Lower/Middle Texas coast. Winds quickly turn back onshore this
evening. Shallow moist layer at the surface will become trapped by
subsiding air aloft overnight, which is expected to lead to
formation of IFR ceilings after midnight. Visibility may also drop
to IFR at times in fog/mist, but with winds forecast to stay up
around 7-9KT, not anticipating dense or LIFR fog formation at this
time.

&&

.PREV DISCUSSION... /issued 415 AM CST Fri Feb 17 2017/

SHORT TERM (Now through Saturday): Scattered light showers, with
a few pockets of more moderate activity, that are currently
indicated on radar, may be as much as we are going to get in the
rainfall department, at least for land areas. RAP/HRRR pretty much
winding down the precip by 12-13Z, except for a few lingering
showers near the coast. This idea is supported by IR satellite
trends as well. GFS also has best RH offshore by 15Z. Had already
trimmed back PoP`s to silent levels after 18Z, but this may need
to be moved up further.

Once the mid-level trough axis moves through around mid-day,
drier air aloft moves in, with a fair amount of sunshine expected
for most areas this afternoon. High temperatures will generally
reach the low-mid 80s, except along the coast where mid-70s will
be the rule. Overnight, NW flow aloft on the front side of a ridge
takes hold. Winds quickly back to southeasterly this evening,
after a brief bout westerly winds on Friday afternoon. Surface
dewpoints rebound to the 60s over roughly the SE half of the CWA.
Subsidence aloft will trap this shallow moisture near the surface,
so expecting some patchy fog to form. At this time, don`t think
it will become dense, though, as southerly winds stay up in the
7-10mph range.

Saturday will be a very warm and muggy day for mid-February as
the axis of a short-wave ridge aloft passes overhead around mid-
day. Warm-air advection on south winds at 850mb bring temps at
that level up to 18-19C. Afternoon highs will range from the mid-
upper 80s at BRO to the mid-90s in portions of the Upper Valley.
HRL likely to approach its record high for the date of 89F. Might
need to keep an eye on fire weather concerns for Starr/Zapata/Jim
Hogg counties, as RH`s fall below 30% for a few hours during the
afternoon with 10- 15mph winds at 20-ft. level.

LONG TERM (Saturday night through Thursday): A mid level short
wave ridge will be moving east over the area Saturday night.
Farther to the west, a deep, slightly negatively tilted mid level
short wave trough will pivot about a point roughly above Nevada,
with the axis extending south into Northwest Mexico. This feature
will be the one of interest for the long term. Already Sat night,
upper diffluence ahead of the trough will support a few showers
moving out of North Central Mexico into Central Texas. At the
surface, Gulf moisture will be pulled north over deep South Texas,
and a few showers may develop on Sunday. High temperatures Sunday
will be warm, in the middle to upper 80s, well above normal. Some
of the trough energy will break away over the Southern Plains
while the base of the trough keeps translating east Sunday night
and will actually form into a low overhead Monday night. The best
rain chances will be Sunday night into Mon, however, as PVA ahead
of the trough supports and enhances a cold front moving through
mid day Monday. Still, forecast QPF amounts are rather paltry,
with only about a half an inch of rain progged from Sunday night
through Monday, with the best upper dynamics north of the area.
The rain will affect the Upper Valley most Sunday night, with the
concentration shifting east with the front through Monday. Despite
the low rain amounts, the chance for rain for the RGV will be
fairly robust, with a 50 to 60 percent chance over land Sunday
night, and slightly less on Monday as the focus shifts offshore.
Isolated thunder will be possible. High temperatures Monday will
still make it into the 80s before a lid is placed on them by the
arrival of the new air mass in the late mrng to afternoon. The
trough will clear the area Monday night with weak ridging building
in afterward. Temperatures will be more moderate Mon night
through mid week, though still above normal, as high pressure
spreads over the area. High temperatures will then be in the lower
to mid 80s with overnight lows mainly in the 50s.

MARINE:

Now through Saturday: Current observation at Buoy 020 shows ESE
winds at 12-14KT with seas of less than 2 ft. Only isolated light
showers are occurring over the Gulf waters at this time, with
more scattered activity over the northern Laguna Madre. Still
expecting some additional development of moderate showers,
including a few thunderstorms, for the Gulf waters from 20-60nm
offshore through early this afternoon. Otherwise, light to
moderate S-SE winds will prevail through the short-term, with seas
of generally 2-4 ft.

Saturday night through Tuesday night: Moderate southeast winds
and seas will prevail at the outset of the long term as high
pressure across the Gulf interacts with lower pressure over
Central Mexico, ahead of an advancing mid level trough located
farther to the west. Southeast to south winds may increase
slightly Sat night through Monday ahead of an approaching cold
front, and small craft should exercise caution to low end small
craft advisory conditions will be possible. A cold front will push
through on Monday, shifting winds to fresh northwest or north for
the day, and possible small craft should exercise caution to low
end small craft advisory conditions. High pressure will spread
over the area in the wake of the front, and winds will slowly
weaken Mon night into Tuesday. Showers and possibly thunderstorms
Sunday night into Mon will create hazardous conditions for
mariners.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...None.
&&

$$

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53-Schroeder/54



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