Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 202325

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
625 PM CDT Mon Mar 20 2017

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

.AVIATION...Satellite images and surface observations indicate
clear skies across the CWA early this evening. 500mb ridge across
northern Mexico and west Texas will continue to provide
subsidence across south TX tonight through Tues afternoon. Expect
VFR conditions to prevail across deep south TX this evening
through early Tues morning as a result.

.PREV DISCUSSION... /issued 257 PM CDT Mon Mar 20 2017/
SHORT TERM (Now through Tuesday night): High presssure at the
surface and aloft will maintain warm and dry conditions across
Deep South Texas through the short- term. A very dry atmosphere is
in place, with the 12Z BRO sounding measuring only 0.62" of
precipitable water (which is in the lowest 10th percentile for
this date). This morning`s flat Cu field has already mixed out.

Breezy southeast winds will gradually diminish after sunset this
evening. Low temperatures tonight will be in the 60s across the area
under mostly clear to partly cloudy skies. Patchy fog will be
possible again across portions of the northern ranchlands. More of
the same in store for Tuesday, with plenty of sunshine and high
temperatures ranging from the mid-80s in Cameron County to the mid-
90s in the vicinity of Falcon Dam.  Tweaked temps down just a bit
vs. inherited for Tuesday, as it appears that they are
"underperforming" just slightly today, even with full sunshine. Soil
moisture remaining from rains of about 10 days ago may be holding
surface heating back just a little...for now, anyway.  Tommorow`s
H85 temps and 1000-500mb thicknesses will be essentially unchanged.
Breezy southeast winds (slightly stronger than today`s) will develop
again on Tuesday due to the tightening pressure gradient courtesy of
pressure falls in west Texas.  Wednesday morning`s lows will again
be in the 60s across the CWA.

LONG TERM (Wednesday through Monday):Pattern change slowly
evolving through the long term period as mid/upper ridge moves
east and flattens as a series of low pressure troughs traverse
west to east across the country. For Deep South Texas and the RGV
model trends and WPC continue to limit rainfall chances and
maintain well above normal temperatures through the period. Main
weather element impacting the CWA looks to be wind and
unseasonably warm temperatures.

Lead low pressure trough moves into the Desert SW Thursday and the
Southern/Central plains Friday. Deep Cyclogenesis takes place
over the Front range and moves into the Southern Plains. This will
turn on the Valley wind machine with winds peaking Thursday/Thu night.
Confidence in Wind advisory conditions remain high for at least
the eastern half or third of the CWA Thursday afternoon. Still
Breezy to windy for the Coastal counties Friday with less wind in
the Mid and Upper Valley with a pre-frontal trough moving into the
region. This trough may be the catalyst for a minor heat spike but
sufficient enough to push temperatures in the low to mid 90s most
locations west of I-69E. Confidence in any rainfall continue to
lower as the frontal boundary associated with the mid/upper trough
will have little moisture to work with. POP Guidance continues
trending lower in the RGV with a small window across the Northern
Ranchlands Friday afternoon or evening when the trailing weak
Pacific front moves into the region. As a result, have trended
along with the model guidance sporting slight chances across the
north with token 10 percent in the Valley.

The next in the series of low pressure trough moves in quickly
behind the departing system Saturday night/Sunday. Again this
system looks to starve for moisture with no deep tap from the
Pacific or Gulf of Mexico. More of the same breezy/windy and
above normal temperatures are anticipated for the weekend and
early next week.

MARINE:(Now through Tuesday night):  Small Craft Exercise Caution
conditions continue this afternoon for the Laguna Madre, with wind
speeds around the bay at 15-20 knots.  Buoy 42020 reported south
winds around 14 knots with gusts near 16 knots and combined seas of
3 feet as of 14 CDT/19 UTC. The pressure gradient will begin to
tighten tonight and Tuesday, which may allow winds to reach SCEC
criteria on the outer Gulf waters at times beginning late tonight.
Seas build to 4 ft. on the outer waters by Tuesday morning, with 3
ft. nearer the shore. SCEC also likely again for the Laguna Madre on
Tuesday afternoon with winds in the 15-20 knot range.

Wednesday through Saturday...One more fair day, Wednesday, before
the pressure gradient begins to strengthen. Strong southeast
winds and building seas are anticipated Thursday through Friday
morning as a deep surface low develops over the Southern Plains.
the adverse conditions will likely prompt small craft advisories
for the Laguna Madre Thursday spreading over the Gulf waters
Thursday evening and Friday. Winds and seas lower Saturday but
remain out of the south as a frontal system weakens rapidly north
of the coastal waters.



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