833
AWUS01 KWNH 281701
FFGMPD
LAZ000-TXZ000-282200-

Mesoscale Precipitation Discussion 0337
NWS Weather Prediction Center College Park MD
100 PM EDT Tue May 28 2024

Areas affected...Eastern hill country of Texas through Southwest
Louisiana

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

Valid 281700Z - 282200Z

Summary...Clusters of thunderstorms moving across eastern Texas
will drop towards the Gulf Coast while expanding/intensifying
through the afternoon. Rainfall rates could reach 2-4"/hr at
times, resulting in 3-4" of rainfall with locally higher amounts.
Flash flooding is possible.

Discussion...The GOES-E visible satellite imagery this morning
shows a complex evolution of convection and associated outflow
boundaries dropping across eastern Texas. These clusters of
thunderstorms have persisted since this morning, and are moving
along a southward advancing cold front analyzed by WPC and ahead
of a shortwave noted in WV imagery. The regional radar mosaic
indicates two distinct clusters with accompanying outflows, with
the trailing cluster just southeast of Dallas accompanied by an
MCV noted in the local radar. As these clusters continue to move
south, they will encounter extreme thermodynamics characterized by
SBCAPE which has rapidly destabilized in clearings to above 6000
J/kg and a plume of PWs around 1.5-1.7 inches. Although PWs are
currently only around the 75th percentile due to dry mid-level air
noted in regional 12Z U/A soundings, 850mb dew point temperatures
above +20C are at daily record, and as low-level flow off the Gulf
persists from the SE, it is likely PWs will surge to 1.8-2.0
inches by this evening.

850mb inflow is progged to remain modest today at just 10-15 kts
during the aftn, but this will be sufficient to persist the
extremely favorable environment for heavy rain. Acting into these
robust thermodynamics, ascent will increase through convergence
along the outflow and deep layer synoptic lift through PVA and RRQ
diffluence aloft. Together, this will support an expansion and
intensification of thunderstorms, with organization in one or
multiple MCS likely thanks to bulk shear of 25-40 kts. This will
allow rain rates to climb to above 2"/hr as reflected by HREF
neighborhood exceedance probabilities reaching 40%, with brief
4"/hr rates possible as suggested by HRRR 15-min rainfall
exceeding 1" in places.

The CAMs are in generally good agreement in this evolution, and
the challenge becomes the speed at which thunderstorms will
traverse southeast. With the extreme CAPE and DCAPE (1200+ J/kg),
this suggests clusters may continue to forward propagate rapidly
and shift offshore, which is supported by SE oriented Corfidi
vectors reaching 20-30 kts, minimizing the duration of heavy
rainfall. However, there is some potential for storms to slow as
they interact with the Gulf breeze/onshore flow, allowing
propagation vectors to collapse and back sufficiently to enhance
rainfall duration. Should this occur, total rainfall could exceed
5", but is otherwise forecast to be generally 3-4" as shown by
HREF 3"/6hrs exceedance probabilities of 40-60%.

This area remains extremely vulnerable with 40cm soil moisture
above the 90th% in some areas, and 0-10cm RSM above 60%,
especially from the Heart of Texas through the southern Piney
Woods region. Although soil moisture dries towards the coast,
these intense rain rates moving over any urban areas, especially
if storms can slow, would still likely result in rapid runoff, and
thus flash flooding is possible through the evening across much of
this area.


Weiss

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

ATTN...WFO...CRP...EWX...FWD...HGX...LCH...LIX...SHV...

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

LAT...LON   31879593 31799399 31169222 30449130 29989126
            29579177 29639312 29549399 29279461 28929537
            28919663 28869761 28999802 29679803 30919745