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Area Forecast Discussion (AFD)

Issued by Brownsville/Rio Grande Valley, TX (BRO)

FXUS64 KBRO 170004 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
704 PM CDT Sun Jun 16 2019

...00z Aviation Update...

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


.AVIATION...VFR conditions will prevail again through this TAF
cycle. The only exception to this rule may be a brief period of
MVFR for MFE overnight. Spotty showers are still possible for the
coastal terminals. Can't rule out a stray thunderstorm during the
daylight hours on Monday. VCTS will be used given the low 
confidence and likely isolated nature of convection. 


.PREV DISCUSSION... /issued 248 PM CDT Sun Jun 16 2019/ 

SHORT TERM (Now through Monday Night): The moderate southerly 
flow between a mid-level low pressure trough over North Texas and 
high pressure extending across the Gulf of Mexico will continue to
feed a steady supply of low level moisture tonight through 
Monday. Very isolated showers once again popped up over the Lower
Texas coastal waters with a few working their way inland over the
Lower Valley but no substantial rainfall occurred with these 
brief showers. Synoptic pattern remains persistent through Monday 
before the trough exits far enough to the east and 500mb ridge 
begins to build into Monday night. 

Deterministic models, except the ECMWF, remain persistent 
indicating very low chances of rain with near normal highs Monday 
and above normal ovenight lows tonight and Monday night with the 
southerly winds diminishing slightly. The presence of the streamer
showers the last few days keeps a slim chance over the Coastal 
waters and the lower Valley for tonight and Monday morning. One 
issue to keep an eye on is that the Convective Allowing Models 
(CAMs) continue to indicate a cluster of thunderstorms developing 
over Central Texas tonight. Matter of fact, SPC has an Slight to 
Enhanced Risk of severe thunderstorms over much of Central and SC 
Texas with a marginal risk just north of Deep South Texas. These 
CAM models suggest the thunderstorm complex to move southeast off 
the Middle Texas coast before or after sunrise Monday remaining 
north of our CWA. Also, some models show convection developing 
over the Sierra Madre and moving east into the Western Ranchlands.
However, most models suggest outflow boundaries from both areas 
of potential thunderstorms moving through Deep South Texas and 
even the RGV which might act as a trigger for additional showers 
or thunderstorm very late tonight and/or through the day Monday. 
With this mentioned and with probability of rain not zero will be 
adding in 20-30 percent for much of the areas prior to sunrise for
the potential early arrival and Monday. Can not rule out one or 
two thunderstorms, if they develop, producing strong gusty winds 
and the potential for some hail and brief heavy downpours.

LONG TERM (Tuesday through Sunday): Hot and humid weather with 
above average temperatures will prevail as a 500 mb ridge builds 
over northern Mexico. Surface high pressure across the Gulf of 
Mexico will result in onshore breezes and limited moisture moving up 
from the south. Rain chances will remain limited across deep South 
Texas and the RGV through late next week. Southeast to south winds 
will strengthen a bit Wednesday through Sunday as a series of 
surface low pressure systems develop and move across the Plains, 
producing a tighter gradient. Breezy to windy conditions will be 
possible across the area by late in the week. Afternoon high 
temperatures will range from near 90 at the immediate coast, to 
several degrees above the century mark. Heat index values of 105 to 
110 degrees will be quite typical each afternoon, with peak values 
from 111 to 115 degrees for a few hours. A few readings will even 
hit 116 degrees or better toward late in the week and into next 
weekend. Heat advisory conditions will be common. The ridge will 
shift slightly east Friday through Sunday as deeper troughing 
develops over the western United States. This may provide an opening 
for a few showers to move up the coast, and for convection to 
develop over the Sierra Madre Oriental range Saturday night. With a 
general consensus among the models this run, used a blend as a basis 
for the forecast with above average confidence.

Now through Monday Night: Moderate to fresh southeast winds
continue over the Lower Texas coast with high pressure extending
over the Gulf interacting with a low pressure trough crossing
Northern Texas and Oklahoma. The pressure gradient gradually
relaxes later tonight and more so Monday as the low pressure
trough moves northeast. SCEC conditions persist the remainder of
today and tonight before improving Monday. An isolated streamer
shower from the south moving north is possible through Monday with
an outside chance of stronger thunderstorms moving into the
northern coastal water Monday morning with the potential 
thunderstorm complex developing over South Central Texas. 

Tuesday through Friday night: High pressure will remain ensconced
across much of the Gulf in the long term. Transient low pressure 
systems in the Plains will tend to tighten the gradient for the 
second half of the week. Moderate southeast to south winds and 
moderate seas will prevail Tuesday through Wednesday, but both 
will increase Wednesday night through Friday night. Winds will 
increase to 15 to 20 knots, meaning small craft should exercise 
caution. Wave heights will also trend upward, with low end small 
craft advisory conditions possible on the Gulf waters, mainly the 
offshore waters, from Thursday night through Friday night.




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