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000
FXUS64 KBRO 170530 AAB
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1230 AM CDT Wed Apr 17 2024

...New AVIATION...

.SHORT TERM...
(Tonight through Wednesday night)
Issued at 326 PM CDT Tue Apr 16 2024

Semi-zonal 500 mb southwest flow aloft regime will remain in place
over the local forecast area to start the short term forecast period
(i.e. through tonight) before becoming more zonal towards the end of
the short term forecast period (i.e. Wednesday-Wednesday night).

Near the surface, the forecast area will remain on the western edge
of a large sfc high pressure system centered well to our east. The
synoptic setup will keep our local CWA under a south-southeast flow
regime. High geopotential heights aloft including a nearby 591
dam heat dome just to our south coupled with continued moisture
and warm air advection (WAA) in place will result in continued
warmer than normal temperatures tonight through Wednesday night.
Clouds will remain in focus through the short term forecast period
with high clouds from the 500 mb pattern moving in from the west
(Mexico) and lower layer (marine induced) clouds coming in from
the south- southeast. These clouds with the help of low level
moisture will help to keep tonight and Wednesday night warm and
muggy with overnight low temperatures in the lower 70s with
similar dewpoint values. Elevated winds at night should help to
prevent the development of any widespread fog.

During the day on Wednesday, there could be enough mixing and winds
where clouds break up especially during the afternoon hours. Am
going for a very warm and humid day with highs in the upper 80s to
mid 90s over Deep South Texas and dewpoints in the lower 70s.

Wednesday evening/night deterministic forecast models and ensembles
are indicating the development of thunderstorms well to our west
over the plateau of the Sierra Oriental Madre mountains of Mexico in
a very unstable airmass according to the latest Showalter values
with steep mid-level lapse rates of 8 C/km, and MUCAPE values
between 1,000-2,000 J/kg. With little (weak) flow aloft, these
storms are expected to remain rather stationary and are expected to
stay well to our west outside of our CWA. That said, not expecting
any convective activity over the area at this time for Wednesday
evening/night.

&&

.LONG TERM...
(Thursday through next Tuesday)
Issued at 326 PM CDT Tue Apr 16 2024

The long term begins Thursday morning with a shortwave trough at mid
to upper levels moving eastward across northern central Mexico,
placing the County Warning Area (CWA) within a troughing pattern. At
the surface, convergence associated with an area of low pressure on
the lee side of the Sierra Madre may initiate some showers and
thunderstorms Thursday evening, across the higher terrain in Mexico,
some of which may crossover into the RGV Plains and upper RGV. The
Storm Prediction Center (SPC) places the CWA within a general
outlook for thunderstorms to account for any possibility of
thunderstorms increasing in coverage as they move eastward. However,
SPC also notes that there will be a lack of low level shear needed
to allow for updrafts to bring thunderstorms to severe limits across
the region. Still, cannot rule out a chance of a severe thunderstorm
popping up, or moving into, the northwestern CWA since SPC places a
marginal risk of severe thunderstorms within National Weather
Service Corpus Christi`s CWA.

As the trough passes, dryer air will work into the region, via a 500
mb ridge, thus keeping chances of showers and thunderstorms low on
Friday and allowing for temperatures to keep soaring well into the
90s for much of the CWA with 80s closer to the coast for Thursday
and Friday.

A more decent shot at thunderstorms is over the weekend as another
trough crosses over Southern California. As it progresses eastward,
similar to the previous trough, upper level shearing from the
subtropical jet stream will modify the trough`s structure and
overall weaken the upper level winds flowing around the trough`s
base. Nevertheless, a cold front, generated from an expanding area
of surface high pressure over the Central Plains, will advance
through Texas beginning on Friday. As the front approaches closer,
a tightening pressure gradient between the lowering pressure over
the Sierra Madre and the high pressure over the northeastern Gulf
of Mexico, will enhance the southeasterly onshore flow, which
will also increase mid-level moisture needed to generate
thunderstorms and heavy rain. Saturday night, as the cold front
arrives into the RGV Plains and continues southeastward, the
boundary will act as a lifting mechanism of the deep moisture
gradient over Deep South Texas and initiate thunderstorms with
ongoing showers lasting through Sunday.

At this time, the SPC deems the possibility of severe thunderstorms
to be too low to initialize a convective severe weather outlook,
indicating that upper level winds will be too weak to provide enough
speed divergence needed for thunderstorms to reach severe criteria.
However, the National Blended Model (NBM) indicates at least 0.5
inches to 0.75 inches of rain in addition to other model guidance
suggesting 1.00 inches to 2.00 inches of rain across parts of the
CWA.

Temperature-wise, temps ahead of the cold front will be slightly
above average for Saturday, though slightly cooler than Thursday and
Friday, due to increased moisture and clouds. Sunday, temperatures
will fall to below average as overcast skies prevail with the
showers and thunderstorms. On Monday, northeast winds and drier air
will work into the entire CWA and and dissipate clouds from north to
south and cooler air will further cool off the surface to more below
average. Temperatures will rebound on Monday and become more
seasonable Tuesday while remaining dry.

&&

.AVIATION...
(06Z TAFS)
Issued at 1225 AM CDT Wed Apr 17 2024

MVFR conditions exist at all sites now due to lowered ceilings.
MVFR due to lowered ceilings will dominate today, Wednesday, but a
few breaks could develop in the afternoon with moderate to breezy
southeast winds mixing out the boundary layer.

&&

.MARINE...
Issued at 326 PM CDT Tue Apr 16 2024

Tonight through Wednesday night...A High Risk for Rip Currents
will remain in effect for the beaches through Wednesday morning.
Afterwards, a moderate risk for rip currents will exist. A Small
Craft Exercise Caution is necessary for the Laguna Madre through
the rest of today and for the Gulf Waters through tonight.
Afterwards, more favorable marine conditions will take shape with
light to moderate winds and seas.

Thursday through Tuesday...Overall, gentle to moderate southeasterly
winds will continue through much of the period. Friday and Saturday,
moderate to fresh winds are possible over the Laguna Madre and close
to the coast, creating Small Craft Exercise Caution (SCEC) with
winds shifting from the east ahead of an advancing cold front.
Saturday night, chances of showers and thunderstorms increase thus
also increasing chances of gusty winds from thunderstorms and heavy
rain and leading to more adverse marine conditions and continuing
through Sunday. Moderate to fresh northeast winds on Monday turn
easterly on Tuesday.

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             88  74  88  74 /  10   0   0   0
HARLINGEN               91  71  91  71 /  10   0   0   0
MCALLEN                 94  74  93  74 /  10  10   0   0
RIO GRANDE CITY         96  74  95  73 /   0  20   0   0
SOUTH PADRE ISLAND      79  73  79  73 /  10   0   0   0
BAYVIEW/PORT ISABEL     86  72  85  72 /  10   0   0   0

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...High Rip Current Risk until 7 AM CDT this morning for TXZ451-454-
     455.

GM...None.
&&

$$

SHORT TERM...54-BHM
LONG TERM....63-KC
AVIATION...54-BHM