Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 201801

Area Forecast Discussion
National Weather Service BROWNSVILLE TX
101 PM CDT WED JUL 20 2016

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


.AVIATION...Local sea breeze front is located generally between
KBRO and KHRL and continuing to advance inland along with a
scattered CU field and some isolated SHRA. Convection is not as
widespread this afternoon due to some drier air aloft and have
kept VC wording in the TAFs for now. The potential for increased
convective activity will be noted on Thursday as a weak
disturbance and a better shot of moisture moves northwest into the
region. Exact timing and coverage is uncertain and have gone with
VC wording again. Otherwise...VFR conditions will prevail...with
gusty easterly winds in the afternoons...become VRB overnight.


.PREV DISCUSSION... /issued 639 AM CDT WED JUL 20 2016/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...VFR expected to prevail next 24 hours but some periods
where showers or perhaps even a thunderstorm (low confidence)
could affect the terminals. Adjusted timing of arrival of shower
activity pushing inland from the Gulf at this time based on
radar/satellite trends and latest HRRR guidance. Confidence still
not high enough to word more strongly than VCSH, though. Drier air
aloft pushes in from east to west through the course of the
afternoon with E breezes gusting up to 20-22KT. Most of the night
should be quiet with light winds and clear skies. By late tonight
(after 09Z Thursday), another slug of mid-level moisture is
progged to arrive along coastal areas. Since this is at the tail-
end of the TAF period and most effects will be after 12Z, will
only go with a few hours of VCSH at BRO for now.

PREV DISCUSSION... /issued 402 AM CDT WED JUL 20 2016/

SHORT TERM:(Now through Thursday): Still a couple of showers
(with just a handful of lightning strikes) around over the Gulf
waters and coastal counties as of this writing, though overall
coverage has waned considerably over the past couple of hours. In
the bigger picture, massive 500-mb high centered over OK continues
to dominate the weather over the central CONUS. Deep South Texas
is experiencing deep easterly flow on the south side of the high.
After a surge of moisture on Tuesday (which seemed to
"underperform" somewhat in terms of convective activity), drier
air upstream per water-vapor satellite imagery can be seen
approaching the CWA at this time. Atmospheric column will continue
to dry through the day (especially after 18Z), with 2.02" of
precipitable water observed on last night`s 00Z BRO sounding
progged to fall to around 1.5" by late this afternoon. Enough
moisture should hang around long enough, though, for some coastal
showers this morning...progressing inland into the afternoon with
the easterly flow enhancing the sea-breeze. Inherited PoP`s
capture the situation well so no changes made there for the first
half of the short-term period.

Hot temperatures will continue today, running a couple degrees above
normal.  Went ahead and trimmed McAllen`s forecast high down to 99
degrees, owing to MOS guidance and a hint of slightly lower 1000-
500mb thicknesses today vs. yesterday (when MFE hit 100 degrees) in
NAM output. Current string of 100-degrees highs there stands at 21,
so we shall see.  Heat indices once again expected to top out in the
104-109 degree range for the Lower/Mid Valley and portions of the
northern ranchlands.

By late Wednesday night, the next weak inverted mid-level wave
approaches with another corresponding increase in moisture.  PW
rises to about 2.0", at least across the southern tier of counties
closer to the mid-level vorticity center.  Superblend PoP`s seemed a
bit overdone for Thursday, so knocked them down 5-10% over the SE
half of the CWA and southern coastal waters during the morning
hours, but this still leaves scattered coverage.  Went with more of
a sea-breeze enhancement type pattern for Thursday afternoon`s
PoP`s. Max temps come down another degree or two, especially across
the Lower/Mid Valley, due to increased cloud cover and scattered
precip. Afternoon heat indices still hold in the 100-105 range.

LONG TERM (Thursday Night through Tuesday):With Mid-Summer
approaching there will be no let up in the heat with only limited
chances of stray convection forming along the daily sea breeze.
Latest model trends remain in good agreement with the dominate
ridge becoming elongated across the southern half of the Conus as
a stronger mid level trough moves across the U.S./Canadian border.
Two high pressure centers develop with one settling over the Desert
SW and the other becoming anchored across the Tennessee Valley and
Southeast Coast. This will place Texas in an ever so slight mid
level weak area of low pressure and the subsidence from the ridge
looks to weaken. Average to below average moisture values and
only the sea breeze and heating to act as lifting mechanisms rain
chances will be low which corresponds well with climatological
normals for mid to late July. Model pop guidance is also coming
in on the low side through the week with a slight uptick at the
end of the period as the subsidence from the ridge wanes. Daily
temperatures will not see much variation near to slightly above
highs and lows persisting. Looking beyond the long term models are
keying on a stronger inverted trough traversing the Northern Gulf
and approaching the Texas coast by midweek. This may enhance the
rainfall chances if this system does develop and move our way.

MARINE: Persistent easterly fetch below the elongated surface
ridge from southeast Texas through Georgia has begun to build
swell into the 2-3 ft. range at Buoy 020 as of 3am CDT/08 UTC.
Generally light easterly winds will dominate in the short-term,
contributing modestly to total seas of about 4 ft. over the Gulf
waters today, subsiding to closer to 3 ft. nearer the shore on
Thursday. No marine headlines expected.

Thursday night through Sunday...Little change over the coastal
waters is expected this week. Broad high pressure persisting across
Northern Gulf to interact with lower pressure over the Bay of
Campeche. This will maintain a light to moderate east to southeast
wind and a slight sea much of the period. A spotty shower or
thunderstorm may move across the Lower Texas Coastal waters at
anytime. No advisories or exercise caution wording anticpated
through the weekend.


.BRO Watches/Warnings/Advisories...


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