Area Forecast Discussion
Issued by NWS Brownsville, TX

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000
FXUS64 KBRO 150839
AFDBRO

Area Forecast Discussion
National Weather Service Brownsville TX
339 AM CDT Fri Mar 15 2024

...New SHORT TERM, LONG TERM, MARINE...

.SHORT TERM...
(Today through Saturday)
Issued at 337 AM CDT Fri Mar 15 2024

Amplified large scale H500 pattern aloft featuring an anomalously
strong upper ridge over the northeastern PAC into western Canada and
an anomalously strong closed H500 low over the Southwest U.S. is
driving an active southwest flow aloft sub-tropical jet over Texas.
Computer models continue to depict several mid-upper level
perturbations/energies tracking along this jet through Saturday and
even beyond. Despite the favorable synoptic setup, our local
forecast area is capped. According to the latest 00z KBRO sounding,
there exist a capping inversion from about 930-850 mb. This despite
CAPE values in excess of 2,000 J/kg, steep mid level lapse rates
between 7-8C/km, and showalter values suggesting a moderate to very
unstable atmosphere.

That said, the short term forecast period will feature warm to very
warm and humid conditions with mainly dry weather and/or many dry
hours. However, can`t rule out the possibility of an isolated
thunderstorm or two through Saturday as once again several
shortwaves track along an active southwest flow aloft sub-tropical
jet.

Right now, the best chances for any showers or thunderstorms is
across our northwestern sections (i.e. Zapata, Jim Hogg, Brooks) and
areas north over Corpus Christi`s and San Antonio`s area. That`s
where the best forcing lies with 0-6km bulk shear values north of 50
kts and strong er surface convergence due to the closer proximity to
a southward advancing cold front.

Today will be similar to the past couple of days. Warm to very warm
and humid with daytime high temperatures ranging between the
mid/upper 80s (inland east) to mid 90s west. The immediate coastal
areas and South padre Island will be cooler due to continued onshore
flow out of the south-southeast. Highs in these areas will top out
in the mid 70s to lower 80s. Again, much of the day will be dry,
however can`t rule out the possibility of an isolated thunderstorm
or two given the shortwaves riding overhead. The lack of a lifting
mechanism, a capped environment, and the strength of the shortwaves
could be limiting factors.

Tonight, a mainly warm and muggy night can be expected. Additional
shortwaves could help to set off some thunderstorms. The best
chances at this time is across our northwestern half of the area
where once again shortwaves will be stronger and the better forcing
exist. Overnight lows are expected to be in the upper 60s to lower
70s.

Saturday will be a warm day, not as warm as previous days. There
will be another chance for an isolated thunderstorm as additional
shortwaves pass through and the aforementioned cold front sags
further to the south. Highs are expected to be in the 80s (70s over
the Island).

&&

.LONG TERM...
(Saturday night through Thursday)
Issued at 337 AM CDT Fri Mar 15 2024

A cut-off low across the Desert Southwest and ridge across the
Pacific Northwest at 500mb hold in a Rex Block pattern into mid-
week, before the mid-level low finally wins out, trekking eastward
into the Southern Plains by the end of the week. This will
maintain a relatively active mid-level pattern across Deep South
Texas through the long term period, with a series of disturbances
every 18 hours or so, holding southwest to nearly zonal mid-level
flow in between each shortwave. At the surface, a cold front
arrives into the Rio Grande Valley by late Sunday morning, with a
reinforcing surge of high pressure and cold air advection Monday
keeping temperatures below normal. CAA continues into early
Tuesday before winds turn easterly. Southeasterly onshore flow
returns Wednesday kicking highs back toward normal and a warm
front with weak surface low works northward on Thursday across
Deep South Texas, cementing above normal temperatures once again.

Overall, the long term period looks to bring beneficial rainfall
to the CWA, with the best POPs toward the brush country and Rio
Grande basin. Hopefully this parks some much needed rainfall over
the reservoirs, once again nearing historical lows. PWAT values
through the period persistently nudge above the 90th percentile
(1.4 inches) for mid to late March, to near 1.6 to 1.8 inches
nearly every day.

Of course, the concern with this active pattern would be for any
isolated severe weather Saturday night, Sunday night, and mid
week, especially storms with large hail, running off the Mexican
plateau toward the borders of Zapata, Starr, and Hidalgo counties.
Isolated severe storms near the border can become quite common by
mid to late March. SPC has most of the brush country, ranchlands,
and upper RGV in a Marginal Risk for severe weather Saturday
night. Overrunning showers or isolated thunderstorms are possible
Monday into Tuesday. Current QPF forecasts are ranging from one
half inch to around one inch total into Thursday, but with plenty
of available moisture and multiple chances for convection, a few
locations may top 2-3 inches for the week if they can catch a
couple of storms.

&&

.AVIATION...
(06Z TAFS)
Issued at 1238 AM CDT Fri Mar 15 2024

Through 06z Saturday.....MVFR conditions with maybe some instances
of IFR conditions due to ceilings are possible through the overnight
hours. MVFR visibilities are also possible due to haze. During the
day on Friday, mainly MVFR conditions are expected to continue.

Winds will continue out of the southeast 5-15 kts through the 06z
TAF cycle. Winds could gust up to 20 kts during the afternoon hours
on Friday.

&&

.MARINE...
Issued at 337 AM CDT Fri Mar 15 2024

Today through Saturday...Light to moderate winds will result in
light to moderate seas and overall a return to favorable marine
conditions. Will have to continue to monitor the threat of an
isolated shower or thunderstorm through Saturday despite the return
to more favorable marine conditions.

Saturday Night through Thursday...A cold front arrives Sunday
morning with northerly winds increasing by Monday, before
diminishing and turning easterly Tuesday to southeasterly
Wednesday and Thursday. Small Craft Caution to Small Craft
Advisory conditions are likely Monday into Tuesday. There is a
chance of showers and thunderstorms Saturday night through
Thursday.

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             85  72  85  70 /  10  10  10  20
HARLINGEN               89  70  86  68 /  20  10  10  30
MCALLEN                 92  73  88  70 /  20  10  20  30
RIO GRANDE CITY         92  71  88  68 /  10  30  30  40
SOUTH PADRE ISLAND      76  69  75  68 /  10  10   0  20
BAYVIEW/PORT ISABEL     82  69  81  67 /  10  10  10  20

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...None.
&&

$$

SHORT TERM...23-Evbuoma
LONG TERM....56-Hallman
AVIATION...23-Evbuoma


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