Area Forecast Discussion
Issued by NWS Brownsville, TX
FXUS64 KBRO 270239 AAB
Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
939 PM CDT TUE JUL 26 2016
.DISCUSSION...Brownsville radar shows isolated convection over
Starr County quickly dissipating. Surface observations and
satellite images indicate thick debris clouds with rain cooled
air across the western portions of Deep South Texas late this
evening. Made a few adjustments to the sky, temperature and
dewpoint grids based on observational trends. Otherwise, no other
changes were made to the current forecast.
.PREV DISCUSSION... /issued 656 PM CDT TUE JUL 26 2016/
DISCUSSION...Updated for latest aviation discussion below.
AVIATION...A weak disturbance over the Northwest Gulf of Mexico
remains nearly stationary with associated convection well west
and north of the Rio Grande Valley airports. Otherwise, a few
passing low cu clouds along with some high level cloudiness
prevail across the Rio Grande Valley this evening. VFR conditions
expected through the next 24 hours. Moderate southeast winds this
evening will gradually become light later this evening and
overnight. Southeast winds will become moderate by late Wednesday
morning with gusts around 20 knots in the afternoon.
PREV DISCUSSION... /issued 304 PM CDT TUE JUL 26 2016/
SHORT TERM (Tonight through Wednesday Night):
Very distinct continuity boundary developing along the north side
of a shear zone associated with a broad areas of mid level low
pressure over Eastern and Southern Texas. The ongoing convection
this afternoon coupled with best moisture and convective
temperatures being reached will maintain low rain chances across
the western half of the CWA. Mid level dry air has and will
continue to filter into the Eastern and Southern areas so will
keep rain chances limited to near zero. Models indicate that the
inverted mid level trough to weaken as it takes on slow westward
drift while mean relative humidity between 925 and 700mb drops
over the next 24 hours. The limited moisture will keep rain
chances at bay with guidance also confirming very low pops for
tonight and Wednesday. Even with best moisture continuing to
reside over the ranch lands the drier mid level air pushes
westward through the day limiting the rain chances there as well.
Unfortunately, the drier mid level air wont allow for our surface
humidity to lower any as surface winds from the south to southeast
will keep the lower layers teaming with higher humidity levels.
This will allow for heat indices to approach 110 degrees in the
Lower Valley tomorrow afternoon for at least a few hours.
Otherwise, with Mid-Summer here to stay for a while temperatures
are expected to remain slightly above normal.
Long Term (Thursday through Tuesday): A strong ridge will remain
positioned over the southwest United States and over the western
North Atlantic, while a weakness in between the respective height
centers will be positioned roughly from northeast Mexico to the mid
Mississippi Valley. The weakness in between the height centers
will allow for mild destabilization of moist air moving up from
the southwest Gulf, thus favoring ongoing isolated convection for
the lower Texas coast and for deep South Texas and the RGV. In a
general sense, this will be manifested by nocturnal streamer
showers and the sea breeze. More challenging will be pinpointing
the specific details of these smaller scale phenomena. A model
consensus does a fair job of reflecting low end mid day pops over
eastern sections and keeping low end pops over the marine areas.
The west Gulf weakness will tend to fill-in late in the week and
into the weekend, with better subsidence helping to suppress already
minimal convection chances. Still, some minor activity over the west
Gulf will be almost unavoidable given the anticyclonic surface
circulation over the Gulf pulling moisture up from the south. The
GFS wants to regenerate a bit of an inverted over the west Gulf by
early next week, as does the ECMWF, which also supports more
palpable PoPs, but strong ridging over the central plains will
resist much northward extension. In general, however, a daily mix of
clouds and sun will be the norm through the long term, with
temperatures running slightly above normal.
Tonight through Wednesday night...A moderate pressure gradient
between broad surface high pressure over the gulf and lower pressure
associated with lee side trough over Northeast Mexico to maintain a
moderate south to southeast wind and a low to moderate sea. Winds
may briefly peak in the exercise caution level over portions of
the Laguna Madre Wednesday afternoon.
Thursday through Sunday...Broad high pressure will reign supreme
across the Gulf, resulting in light to moderate south southeast
winds and low to moderate seas. Isolated showers will be possible
during the period.
.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL 81 96 81 94 / 10 10 10 20
BROWNSVILLE 79 96 79 95 / 10 10 10 20
HARLINGEN 79 100 78 98 / 10 10 0 20
MCALLEN 79 101 79 99 / 10 10 0 20
RIO GRANDE CITY 79 103 79 102 / 20 10 0 10
SOUTH PADRE ISLAND 82 90 82 89 / 10 10 10 10
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