Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 141735 AAB
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1235 PM CDT Thu Mar 14 2024

...New AVIATION...

.SHORT TERM...
(Today through Friday)
Issued at 348 AM CDT Thu Mar 14 2024

Another warm to very warm day with increased humidity levels is
on tap for today. While high pressure influences will keep the
area dry for today, a weak shortwave trough/low pressure system
just to our west will support continued south-southeasterly winds
and thus an onshore flow pattern. This onshore flow pattern will
result in continued marine layer influences from the Gulf of
Mexico, which ultimately will result in continued low level clouds
streaming in from south-southeast to north-northwest of the the
area today, especially the coastal areas. An amplified H500
pattern in place with anomalously strong ridging over the
northeast PAC into western Canada and a resultant anomalously
strong downstream closed low over the Desert Southwest will result
in a southwest semi-zonal flow aloft pattern over the area in
which mid to higher level clouds will track from. All said, expect
for clouds to be in play, particularly along the coastal areas
and at night. Strong March sun angle could aid in some clearing
during the day today especially areas further inland.

MSAS/LAPS surface analysis continue to depict a tight pressure
gradient over the area with the aforementioned weak surface
tough/low to our west and a departing surface high to our east.
That said, it will be another breezy day again with south-
southeast winds 15-25 mph with gusts 30-40 mph. There could be an
instance or two where winds top 40 mph due to the "Valley Wind
Machine" effects (local topographic and climate effects), but
overall will stay below Wind Advisory Criteria. Temperatures will
continue to run warmer than normal with daytime highs once again
progged to top out in the upper 80s to mid/upper 90s across Deep
South Texas with the cooler values east and the warmest values
west. A bit cooler near the immediate coast and along South Padre
Island (SPI) where highs are expected to top out in the mid 70s to
mid 80s with the coolest values over SPI.

For tonight, winds are expected to subside with the core of the
low level jet to our east and amid decreasing mixing heights.
Clouds will once again be in play (thickest along the coast and
over SPI) with continued marine layer influences from the south-
southeast winds. A quiet, warm, and muggy night overall. There
could be some mist around with narrow dewpoint depressions
(similar overnight lows and dewpoint temperatures in the upper
60s to lower 70s).

Friday will feature another warm to very warm and humid day with
daytime highs climbing into the upper 80s to mid 90s across Deep
South Texas. Once again, with the southeast winds off the cooler
Gulf Waters, temperatures will be cooler along the immediate
coast and over SPI. Winds will be lighter on Friday compared to
Thursday.

&&

.LONG TERM...
(Friday night through Wednesday)
Issued at 348 AM CDT Thu Mar 14 2024

*Key Messages

-Above normal temperatures Friday followed by a cooling trend
 through Tuesday.

-Unsettled weather will sandwich a cold frontal passage Sunday
 morning. The entire period should bring some rain, initially
 favoring the Brush Country and Upper Valley this weekend, but
 spreading across the region early next week.

Most of the long term will be dominated by unsettled weather. One
really has to wait until the end of or just beyond the long term
for a pattern change. That said, I used the NBM to populate the
current forecast package. The overall synoptic pattern will evolve
similarly to the previous package, with expected variances in
some of the details such as rain amounts. SPC shows general
tstorms across the northern tier for Friday, with coverage
spreading to the whole CWA on Saturday, including a marginal risk
for severe weather across the northwest corner of the CWA
including portions of the RGV Plains, Upper Valley and Jim Hogg
Ranchlands. The SPC marginal risk area corresponds roughly to the
WPC excessive rainfall marginal risk area for Saturday.

Starting with Friday night, there will be a Rex Block over the
West Coast. The center of the cutoff low will be over Southern
California and will influence the mid-level flow over Texas. The
mid-level flow will be from the Southwest, with shortwaves apt to
move through the flow and support unsettled weather locally. The
block will start to evolve Saturday night. The cutoff low will
shift east to over the Desert Southwest, starting a slow period of
weakening, and will not move much through the weekend or even
early next week.

At the surface Friday night, a surge of Canadian air will be
moving south over the Plains and even into Texas. The front may
make it far enough south and couple with an upper disturbance to
bring some convection to the RGV Plains. This will be the focus of
the initial rainfall through Saturday.

As it turns out, another large scale cyclonic circulation south of
Baffin Bay will help pull more high pressure south from Canada
and over the Plains over the weekend. This will bring an initially
push to the Lower RGV Sunday morning, and winds will back to east
and northeast. Once the front is through, more widespread rain
will emerge. Incoming high pressure will spread over the region
through mid next week. Since the cutoff low to the west will still
be anchoring southwest flow aloft, an overrunning scenario will
develop, supporting cloudy, cool, and rainy weather.

While the rain axis may almost push south Monday night, it will
move back north as a warm front to keep rain chances alive into
Tuesday and Wednesday. In terms of rain amounts, deterministic
guidance does not portray a large accumulation. Maybe an inch or
two at best. There could be very localized heavier amounts.
Tuesday and Wednesday could yield an inch or two as the front
moves back north. Due to the combination of clouds, rain and
incoming cooler air from the north, temps will trend lower through
the period, with highs bottoming out five to ten degrees below
normal on Tuesday. Lows will be less impacted and will trend
closer to normal through the long term.

Finally...with the longer-fetch and stronger northeast flow
Monday through at least Tuesday, beach equipment managers may need
to consider moving items behind the dunes for potential run-up,
especially at high tide. Otherwise...higher surf and stronger rips
will develop by Monday and continue through Wednesday.

&&

.AVIATION...
(18Z TAFS)
Issued at 1229 PM CDT Thu Mar 14 2024

Mostly MVFR conditions persist at the TAF sites and are expected
to remain the primary condition through the TAF period. However,
it is possible that during the night that cloud ceiling could
lower even further to IFR conditions. However that is not expected
to last too long, before going back to MVFR. Gusty southeasterly
winds are expected to continue through the afternoon, before
weakening during the evening hours.

&&

.MARINE...
Issued at 348 AM CDT Thu Mar 14 2024

Today through Friday...A Small Craft Advisory is in effect for
the Laguna Madre and the Near Shore Waters of the Gulf from 11 AM
CDT this morning to 7 PM CDT this evening. A Small Craft Exercise
Caution (SCEC) is in effect for the offshore waters. A mid-level
shortwave moving overhead this morning will kick of a weak surface
low along the Sierra Madre Mountains. This will again tighten
pressure gradients today resulting in southeast winds increasing
15- 25 kts with gusts up to 30 kts over the Laguna Madre and Near
Shore Gulf Waters. Winds are expected to subside tonight into
Friday giving way to more favorable marine conditions.

Friday night through Monday night...Light to moderate east to
southeast winds and moderate seas will prevail through Sunday.
Winds will shift to east and then northeast Sunday morning with
the passage of a cold front. Winds and seas will steadily
increase as high pressure builds over the area, with winds
becoming fresh Sunday night into Monday, meeting small craft
should exercise caution conditions. Seas will also build. Small
craft advisory conditions will be possible by Monday. The weather
in general will turn more unsettled during the period, with
convective marine hazard threats increasing. Cloud to water
lightning and strong, gusty winds may occur in and near
thunderstorms.

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             85  73  85  71 /  10  10  10  10
HARLINGEN               88  70  89  68 /  10  10  10  10
MCALLEN                 93  73  91  71 /   0  10  10  20
RIO GRANDE CITY         97  71  93  69 /   0  10  10  30
SOUTH PADRE ISLAND      76  69  74  69 /  10  10  10  10
BAYVIEW/PORT ISABEL     84  70  82  68 /  10  10  10  10

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...Small Craft Advisory until 7 PM CDT this evening for GMZ130-132-
     135-150-155.

&&

$$

SHORT TERM...54-BHM
LONG TERM....23-Evbuoma
AVIATION...64-Katz


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