Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 172354 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
654 PM CDT Sat Aug 17 2019

.DISCUSSION...Updated for latest /00z/ aviation and included a fire
weather discussion below.


.AVIATION...Once again...mainly a wind forecast for the next 24
hours. With "Valley Wind Machine" pattern underway, one thing to
keep an eye on is possible brief MVFR ceiling development,
especially around McAllen/Miller Airport, after 06Z and through
just before daybreak. For now, have covered with scattered at
~1800 feet. Otherwise, just a few-scattered MVFR cumulus fractus
elsewhere later tonight, then perhaps a brief period (like today)
of broken low VFR ceilings between 9 AM and noon before conditions
mix out...likely few VFR.

As for winds, mid to late evening diminishing but still at 10
knots in general overall through the wee hours, then a quick
pickup to near 20 knots by late morning with gusts near 30 knots
soon after as pressure gradient maximizes Sunday.


.FIRE WEATHER...Had a spot request for a small wildfire in
southwest Starr County late this afternoon...and the latest
observed dryness conditions (based on 100 hour fuels) were in the
critically dry level with extremely dry just to the east in
southern Hidalgo County. Afternoon humidity fell below 25 percent
nearby at the Falcon Lake Mesowest site, with frequent 20 foot
gusts to 20 mph (though sustained winds were closer to 8 to 10
mph). With a slight increase in wind Sunday afternoon but with
similar RH and forecast critically dry or worse fuel conditions, a
fire danger statement may be needed for areas along/west of I-69C
(western Brooks/Hidalgo through the Rio Grande Plains).


.PREV DISCUSSION... /issued 253 PM CDT Sat Aug 17 2019/

SHORT TERM (Now through Sunday Night): No big changes are
expected in the short term. A Mid level ridge will continue to
provide subsidence over the region through the weekend. At the
surface, broad high pressure across the Gulf of Mexico will
interact with low pressure across northern Mexico. This will
support breezy conditions over the eastern half of the forecast
area for the rest of this afternoon and again on Sunday.
Temperatures currently range from the mid to upper 90s along the
coast to a few degrees above 100 across the western portions. The
combination of hot temperatures and high dewpoints continue to
produce heat indices this afternoon between 106 and 110 degrees.
However, can`t rule out a few hours of heat index values up to 113
degrees over portions of the Rio Grande Valley into the Falcon
Lake region.

A another warm and humid night is expected with winds diminishing
somewhat overnight. Low temperatures tonight will be mainly in the
low 80s under partly cloudy skies. The mid level ridge builds over
Texas on Sunday which will allow for another hot and rain-free day.
High temperatures on Sunday should be a degree or two higher than
today with the 500mb ridge nearly overhead. High temperatures will
range from the mid to upper 90s along the coast to around 105
degrees across the west. Heat index values of 107 to 112 degrees
will be likely across the area on Sunday due to a slight uptick in
moisture. Therefore, a Heat Advisory may be needed for portions of
deep south Texas and the Rio Grande Valley Sunday afternoon.

LONG TERM (Monday through Saturday): 500mb subtropical ridge
across northwest Texas Monday will continue to provide subsidence
across south Texas through Tuesday. Low to mid level moisture is
expected to increase across portions of the western Gulf of Mexico
Wednesday into Thursday as a 500mb low/inverted trough moves across
the southwest Gulf of Mexico Thursday. This will provide a slight
chance to chance of showers and thunderstorms...mainly across the
coastal sections of the CWA...Wednesday into Thursday. At the very
least...the increase in cloud cover will allow high temperatures
to decrease a degree or two providing some relief to the oppressive
heat that has been entrenched across the area. The rest of the
forecast period is dependent on the development of a closed 500mb
low across the northwest Gulf of Mexico Friday. The ECMWF
continues to prog this feature and lifts it northward towards the
upper Texas coast Saturday. If the ECMWF model solution is
correct...subsidence will likely increase across southwest Texas
Friday into Saturday which would limit seabreeze convection
across the Rio Grande valley and northern ranchlands. Will
mention a slight chance of showers and thunderstorms across the
CWA through the rest of the week into the weekend for now as
higher rain chances will likely remain offshore the lower Texas
coast towards the upper Texas coast.

MARINE (Now through Sunday Night): Broad high pressure across
the Gulf will support moderate onshore flow and low to moderate
seas through the period. Winds will gradually decrease this
evening across the bays, however, a slight uptick is expected
across the gulf waters after sunset. Small Craft Exercise Caution
conditions will be likely on the on Laguna Madre and portions of
the Gulf waters on Sunday.

Monday through Thursday...Light to moderate southeast winds will
prevail across the coastal waters with surface high pressure
across the eastern Gulf of Mexico. The pressure gradient will
remain unchanged across the lower Texas coast Tuesday before
weakening on Wednesday. Light to moderate southeast winds will
prevail across the lower Texas coast Tuesday before diminishing
Wednesday. Light southeast winds should prevail across the western
Gulf of Mexico Wednesday into Thursday.




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