-- Discussion containing changed information from previous version are highlighted. --
948
FXUS64 KBRO 230000 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
700 PM CDT Wed May 22 2024

...New AVIATION...

.SHORT TERM...
(Tonight through Thursday night)
Issued at 225 PM CDT Wed May 22 2024

Key Messages:

- A Heat Advisory is in effect for most of Deep South Texas
  through 7 PM this evening due to heat indices up to 115 degrees.

- There are low rain chances (20% or less) across the Rio Grande
  Plains late this evening.

- Triple-digit temperatures and heat index values will be an issue
  once again tomorrow afternoon.

Mid/upper level ridging will continue to influence mostly rain-
free conditions through the short term period across Deep South
Texas, but there will be a low potential (20% or less) for an
isolated shower or decaying thunderstorm as convection develops
off of the Sierra Madre mountains in Mexico late this afternoon
and evening. There is a greater chance that any convection that
does develop will weaken and dissipate by the time it reaches the
Rio Grande River. If anything, cloud cover associated with any
activity will provide some relief from the oppressive heat late
this evening for portions of the Mid/Upper RGV and Rio Grande
Plains. Low stratus clouds will develop once again, aided by
persistent low level southerly to southeasterly flow. This will
maintain mild and humid conditions across the region, with low
temperatures only falling into the upper 70s across the Northern
Ranchlands to low 80s across the Rio Grande Valley.

Thursday will once again feature well above normal temperatures,
with most areas along and west of I-69 observing a high
temperature of at least 100 degrees. In combination with the
presence of higher dew points, heat index values will range from
100 to 115 degrees during the afternoon hours. A Heat Advisory
will likely be needed for most of Deep South Texas once again. If
spending an extended period of time outdoors, ensure you are
staying hydrated, taking frequent breaks in the shade or indoors,
and wearing light-colored, loose-fitting clothing to prevent any
heat-related illnesses. Another mild and humid night with lows
mostly in the upper 70s across the Northern Ranchlands and low 80s
in the Rio Grande Valley is expected Thursday night.

&&

.LONG TERM...
(Friday through next Wednesday)
Issued at 225 PM CDT Wed May 22 2024

Dangerous heat will continue to be the main story in the extended
forecast period, especially during the Memorial Day Weekend.
Prolonged subsidence and southerly low level flow will maintain a
warming trend through Sunday and Monday.  Sunday appears to be the
peak of the heat as the 850 temps peak at 28-30.5 Celsius across our
CWA.  A great indicator of this exceptional heat is the fact that
the NAEFS 850 temperatures during the Fri-Mon timeframe were
forecast to be 2-4 standard deviations above normal across our CWA.
This will translate into record-breaking temperatures (or close to
it), especially during the holiday weekend for portions of the CWA.
Little to no relief is expected at night given the moderate gradient
helping to keep overnight lows in the upper 70s to lower 80s for
most of the area.  The NWS HeatRisk product continues to indicate
most of the CWA in the Extreme category for Fri-Mon.

Meanwhile, the combination of this intense heat and surface
dewpoints generally in the mid 70s and higher for most areas,
especially east of I-69C will translate into heat indices 111-118 on
Fri...112-120 on Sat and 114-122 on Sun and Mon.  A widespread heat
advisory is likely on Fri.  An excessive heat warning will likely be
warranted for portions of the Northern Ranchlands and Mid/Upper
Valley on Sat. By Sun and Mon, most of the CWA except for Zapata and
Jim Hogg counties will likely need an excessive heat warning. Zapata
and Jim Hogg counties will have lower heat indices as these areas
will be west of the dryline feature that will be developing each day.

By Mon night, the synoptic pattern does begin to change as the broad
mid/upper ridge axis anchored across Mexico begins to weaken just a
bit and as a cold front approaches Central and Southeast TX.  Most
of the convective activity associated with this front and associated
shortwave energy will remain north of the CWA. However, isolated
convection will be possible across the ranchlands before weakening.
Slightly better rain chances will occur on Tue and Wed as the wind
flow becomes backed which will help to weaken the cap and draw in
deeper moisture. Also, there will be several shortwaves that will
affect the CWA and enhance rain chances for the Tue-Wed timeframe.
For now, will only go with slight chance POPs for Tue and Wed given
the long timeframe involved.  However would not be surprised to see
these POPs increase, especially for the ranchlands, as we get closer
in time to this timeframe. Given the backed winds and higher
moisture, there will be a break in the very hot conditions for the
Tue-Wed timeframe. Temperatures will still be above normal on Tue
and Wed but not be nearly as high as during the first part of the
forecast period.

&&

.AVIATION...
-- Changed Discussion --
(00Z TAFS)
Issued at 648 PM CDT Wed May 22 2024

MVFR at KMFE and KHRL due to ceilings. SCT to BKN low clouds are
in the area with ongoing strong southeast winds. Ceilings should
thicken and lower to MVFR across the board later this evening.
Clouds will scatter out Thursday by mid-day, yielding VFR
conditions, with another day of fresh to strong southeast winds.
-- End Changed Discussion --

&&

.MARINE...
Issued at 225 PM CDT Wed May 22 2024

Tonight through Thursday night...An enhanced pressure gradient
will result in moderate to breezy winds and moderate seas through
tomorrow night along the Laguna Madre and Gulf waters. Small Craft
Exercise Caution will prevail through the period, although a brief
Small Craft Advisory may be necessary along the Laguna Madre and
nearshore Gulf waters due to breezy winds Thursday afternoon.

Friday through next Wednesday...A persistent moderate to
occasionally strong pressure and thermal gradient will maintain at
least widespread caution conditions through Sunday across the
coastal waters. In fact, marginal small craft advisory conditions
will even be possible for the Laguna Madre for Saturday and Sunday.
The gradient will slowly weaken by Monday and continue that trend
into Tuesday and Wednesday with the approach of the front across
Central and Southeast TX.

&&

.PRELIMINARY POINT TEMPS/POPS...
-- Changed Discussion --
BROWNSVILLE             96  81  97  82 /  10   0   0   0
HARLINGEN               99  78  98  79 /   0   0   0   0
MCALLEN                101  81 100  81 /   0   0   0   0
RIO GRANDE CITY        104  80 103  79 /  10  20   0   0
SOUTH PADRE ISLAND      89  82  87  82 /   0   0   0   0
BAYVIEW/PORT ISABEL     94  81  93  80 /   0   0   0   0
-- End Changed Discussion --

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...Heat Advisory until 7 PM CDT this evening for TXZ248>255-351-
     353>355.

GM...None.
&&

$$

SHORT TERM...54-BHM
LONG TERM....60-BE
AVIATION...54-BHM