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Area Forecast Discussion (AFD)

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

FXUS64 KBRO 211654 AAB

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1154 AM CDT Thu Mar 21 2019

...18z Aviation Update...

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


.AVIATION...VFR conditions expected through this forecast cycle.
Clear skies this afternoon will give way to increasing clouds this
evening and overnight. That said, ceilings should remain
relatively high. Winds this afternoon will be transitioning to a
more easterly and eventually southeasterly direction with time. 
Shortly after sunrise Friday morning, surface winds are expected 
to increase out of the southeast with some gusts nearing 20 knots
by the end of this TAF cycle. 


.PREV DISCUSSION... /issued 631 AM CDT Thu Mar 21 2019/ 

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...A weak front will wash out just north of the Rio
Grande Valley today. As broader high pressure settles over Texas 
and nudges toward the western Gulf over the next 24 hours, drier 
air will move in near the surface, and winds will veer to the SE.
Skies to remain VFR.

PREV DISCUSSION... /issued 418 AM CDT Thu Mar 21 2019/ 

SHORT TERM (Now through Friday): Relatively uneventful weather 
is expected in the short-term, particularly when contrasted with 
recent days. Last of the spotty light rain, mainly over 
Starr/Hidalgo/Willacy continues to fade away, and should be 
completely gone by daybreak. For Thursday, H5 ridge axis will be 
nearby as surface high drifts from central Texas toward the NW 
Gulf of Mexico. Model time-height sections indicate that RH will 
continue to become more shallow as the day goes on, especially at 
mid-upper levels, due to influence of the ridging. Most areas 
should see some sun at some point today, though clouds are 
expected to hang on longer further west. Afternoon high temps 
should range from near 70F at the coast to the mid-70s elsewhere, 
which is still 5-7 degrees below normal, as winds don't really 
veer around to SE until around sunset.

Seasonal temps expected overnight (upper 50s-low 60s) beneath partly 
cloudy skies and light winds.  Not expecting any fog as mixed-layer 
dewpoints will have fallen to the low-mid 50s Thursday afternoon. 
Both NAM and GFS suggesting that short-wave disturbances may move 
off of the Mexican plateau, but not expecting them to hold together 
and reach the western counties at this point.

For Friday, another nice day in store, though SE winds increase to 
near 15mph in the afternoon.  Column RH starts creeping back up, 
from west-to-east, ahead of an approaching Pacific front.  Not 
seeing much in the way of forcing (with significant cap aloft), 
though, and MOS PoP's are mostly in the single digits, so have held 
precip chances for Friday daytime to silent levels.  Afternoon high 
temps tack on another couple of degrees with the increasing warm-air 
advection, even with cloud cover on the increase.  Still doesn't 
look like we'll recover to climatological normals yet (80-83F range 
in the Brownsville-McAllen corridor).

LONG TERM (Friday Night through Wednesday): 500mb trough across
the southern Rockies Friday will draw moisture from the western
Gulf of Mexico northward across the west-central portions of the 
state Fri night into Saturday as a Pacific cold front moves across
northwest Texas Saturday morning. The bulk of the instability and
the best rain chances should remain well north of the CWA Fri
night into Saturday but some forecast models indicate the 
potential for convection developing across northeast Mexico Fri
night and moving towards the Rio Grande valley early Sat morning
before collapsing. Assuming showers and thunderstorms develop
across the Mexican plateau and move eastward...forecast model
soundings are not progging strong convection across the area Fri
night into Saturday. With that said...will continue to mention a
chance of showers and thunderstorms late Fri night into Sat
morning as a region of positive vorticity moves across southwest
Texas Fri night in the southwest to west flow aloft. Rain chances
will linger Sat afternoon before low to mid level moisture
decreases across deep south Texas Sat night into Sunday as a more
zonal flow develops across the state in the wake of the upper
trough across the Texas panhandle lifting northward. Warmer
temperatures will develop Sunday and continue into early next week
before a weak cold front moves into the area Mon night into
Tuesday. There are some differences between the global models on
the strength of the front as well as rain chances as the ECMWF is
cooler and wetter than the GFS with a stronger front moving into
the Rio Grande valley Tuesday. Will go with the model blends for
the rest of the forecast period with slightly below normal to
near normal temperatures Tuesday into Wednesday.

MARINE (Now through Friday): Favorable boating conditions are in
store for the next 36 hours. Latest report from Buoy 42020 shows 
light SE winds and 3-4 foot swells still coming in from the east. 
Farther out, Buoy 42002 shows a similar swell. This swell should 
gradually diminish today as fetch is lost, leaving slight seas of 
2-3 ft. in place for Friday. Winds will remain on the light side 
(< 10 knots) until Friday afternoon when southeasterlies pick up a
bit, but still below Small Craft Exercise Caution (SCEC) 

Friday night through Monday...Moderate southeast winds will
prevail across the coastal waters Fri night into Saturday with 
surface low pressure on the lee side of the Rockies and surface
high pressure across the eastern United States extending southward
into the eastern Gulf of Mexico. Light to moderate southeast winds
will prevail across the western Gulf as a weak cold front moves
across northwest Texas. The pressure gradient will weaken across
the lower Texas coast Monday as the front moves across central
Texas. Light southeast winds should prevail across the coastal
waters Monday. 




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