365
AWUS01 KWNH 200539
FFGMPD
TXZ000-200900-

Mesoscale Precipitation Discussion 0471
NWS Weather Prediction Center College Park MD
139 AM EDT Thu Jun 20 2024

Areas affected...South Texas...

Concerning...Heavy rainfall...Flash flooding possible

Valid 200340Z - 200900Z

SUMMARY...Outer band of T.S Alberto may train across sensitive
areas with additional spots of 2-4" possible resulting in
potential reaggravation of flash flooding across S TX.

DISCUSSION...Regional RADAR mosaic depicts a subtle
shortwave/mid-level vorticity center moving eastward into the Rio
Grande Valley near Laredo, Texas.  This feature appears to be at
the north-northwest edge of the inverted low to mid-level trough
of the outer circulation of T.S. Alberto.  Aloft, the feature is
enhanced by upper-level evacuation support at the diffluent
portion of the 3H jet that becomes further defined by the
transverse banding in the arched cirrus pattern across central to
northwest TX.  This feature continues to influence low level
confluence into a trailing surface to boundary layer outer band
across South Texas from the wave across from Duval to Neuces and
back out across the western Gulf.  Ample deep layer moisture to
2.75" and unstable air mass off the coast into the western Gulf
with 3000-3500 J/kg of SBCAPE will continue to support efficient
rainfall production for thunderstorms that can develop.

Maintaining convergence will be the biggest uncertainty for
maintaining the band, but given the northern influence of low
level flow backing subtly, along with fairly solid consistency in
hi-res CAMs and RAP forecasts.  Cells are likely to be maintained
even as winds decrease about 5-10kts over the next few hours
through the 925-850mb layer.  Frictional convergence is likely to
be the best factor for thunderstorm redevelopment and given it is
fairly orthogonal to the coast (enhanced by local effects near
bays/islets/peninsulas) the risk for retaining the band seems
highly likely, though may waver/vary north-south through time to
likely limit any particular area receiving 2-3"/hr rates for long
periods.  As such, streaks within the band of 2-3" are likely,
with some spots of 4" remaining possible.  Given area has become
saturated, especially near Corpus Christi area where FFG values
are below .5" at all time periods, ongoing flooding is likely to
continue through early morning hours. However, for the bulk of the
area of concern, flash flooding is considered possible.

Gallina

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...CRP...

ATTN...RFC...WGRFC...NWC...

LAT...LON   28389835 28269756 28279684 28069681 27829703
            27529721 27339740 27389856 27479909 27889952
            28359907