Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 072334 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
634 PM CDT Fri May 7 2021

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


.AVIATION...Surface observations and satellite imagery show a
scattered Cu field across the Rio Grande Valley with moderate east
to southeasterly winds this evening. Winds are expected to remain
moderate overnight and pick up Saturday morning with the
tightening pressure gradient. MVFR ceilings will develop before
or around midnight, but VFR conditions will return Saturday


.PREV DISCUSSION... /issued 311 PM CDT Fri May 7 2021/

SHORT TERM (Now through Saturday Night): The two main issues for
the RGV over the short term period will wind and heat. A pretty
significant 500 mb trough axis will dig into the western third of
the country through Sat Night. This trough is expected to close off
over the northern Rockies later tonight into Sat. As this
trough/closed low pushes eastward, 500 mb ridging will in turn build
over the RGV warming temps up steadily this weekend. In addition, as
the trough moves east, a pretty strong surface low pressure system
will develop near  the TX/OK Panhandle region on Sat. This surface
low pressure area will start tightening up the PGF over the RGV
boosting up the surface winds from the S-SE with the strongest winds
likely affecting the easternmost counties. At this point the surface
winds will not likely reach Wind Advisory criteria for tomorrow

The strengthening southerly low level flow in the short term will
start increasing the low level moisture values a bit. Accordingly,
an isold marine layer shower can`t be ruled out. So will mention
some silent pops near the lower TX coastline on Sat.

The short term model temp guidance is in pretty good agreement for
overall trends through Sat Night. So will opt for a model blend
throughout this period.

The strengthening low level wind flow will likely limit any fog
formation tonight.

LONG TERM (Sunday through Friday): The main focus points in the
long-term period continue to be hot, dry, and windy conditions on
Sunday and Monday, with a Wind Advisory possible for central and
eastern parts of the CWFA on Sunday. A significantly wetter
weather pattern will occur beginning on Tuesday as a mid-level
disturbance digs over the Rockies, increasing cloud cover and
precipitation chances, especially on Wednesday and Thursday. A
cold front is forecast to move through sometime late Wednesday
night or Thursday morning.

Strong surface low pressure across the Plains will progressively
move eastward into the Midwest/Ohio Valley regions during the day
on Sunday. As a result, a strong pressure gradient will develop
across Deep South Texas, especially along the coast. Guidance
continues to show sustained wind speeds between 25 and 30 mph
beginning mid-late morning, mainly across coastal counties, with
gusts approaching 40 mph in the afternoon. A Wind Advisory is
looking more and more likely for Sunday for areas east of
US-281/I-69C. With strong low-level WAA in place, high
temperatures will climb into the 90s and triple digits for most
locations, hottest across the upper-RGV and Zapata County. Sunday
night will be very warm and humid with lows generally in the mid-
upper 70s. Similar conditions will transpire on Monday, though the
pressure gradient will be slightly more relaxed, helping keep
winds below Wind Advisory criteria, though this can change over
the next couple of days.

Although exact details are still pending, consensus in the models
suggest a wetter pattern will develop starting on Tuesday. Mid-
level flow will back out of the southwest as a potent trough
positions itself over the Rockies. A series of shortwave troughs
embedded in the main flow will cause showers and thunderstorms to
develop in across central Texas starting Monday night. PoPs will
gradually shift southward increase from the northwest during the
day on Tuesday. Deterministic models continue to show precipitable
water values jump above 2 inches Tuesday night, with the GFS
suggesting a cluster of strong thunderstorms, or an MCS,
developing across south-central Texas and pushing south through
the region overnight Tuesday into Wednesday morning. If this
verifies, heavy rainfall, with pockets of very heavy rainfall, can
be expected. Showers and thunderstorm chances will continue
through the day on Wednesday and possibly through Thursday,
although forecast certainty is fairly low beyond Wednesday.

Finally, a weak/modest cold front will push through Deep South
Texas late Wednesday night or by Thursday morning, then stalling
just south of the Rio Grande. Its arrival from the 12z runs are
about 6 to 12 hours later than yesterday`s 12z model runs. Still
lots of uncertainty of timing and strength of the cold front, but
its presence should keep PoPs in the forecast through Friday as it
stays in the vicinity of Deep South Texas. Temperatures will drop
near or even below seasonal average both on Thursday and Friday.

MARINE (Now through Saturday Night): As the PGF strengthens over
the region, the marine surface winds may increase up close to
marginal SCA levels mainly for the Bay waters during the day Sat.
The lower TX Gulf waters may be a little slower to respond to the
tightening PGF, but could push up near SCA levels Sat Night. The
SSTs are still in the mid to upper 70s and this could inhibit the
downward mixing of the low level southerly winds.

Sunday through Wednesday: Strong southerly flow will be
well established on Sunday and into Monday morning. Small Craft
Advisories will likely be needed for the Gulf waters and possibly
the bay through the day on Sunday into Sunday night. SCEC
conditions will then prevail through Monday as moderate to strong
winds and slightly adverse seas persist. The pressure gradient
will gradually become weaker on Tuesday and Wednesday as a cold
front moves into Central Texas. However, SCEC conditions are still
possible across the Gulf waters.


BAYVIEW/PORT ISABEL  73  84  75  90 /  10  10   0   0
BROWNSVILLE          74  90  77  91 /  10  10   0   0
HARLINGEN            72  91  75  93 /  10  10   0   0
MCALLEN              72  93  77  97 /  10  10   0   0
RIO GRANDE CITY      71  98  75 104 /  10  10   0   0
SOUTH PADRE ISLAND   75  80  76  82 /  10  10   0   0




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