776
AWUS01 KWNH 280038
FFGMPD
TXZ000-280636-

Mesoscale Precipitation Discussion 0090
NWS Weather Prediction Center College Park MD
837 PM EDT Thu Mar 27 2025

Areas affected...south Texas

Concerning...Heavy rainfall...Flash flooding likely

Valid 280036Z - 280636Z

Summary...Locally significant flash flood potential should
continue through 06Z/1am CDT.

Discussion...A very slow-moving cluster of deep, intense
convection continues to make progress across Deep South Texas
while producing multiple hours of 1-3 inch/hr rain rates.  These
rates have falling in populated areas near McAllen and Harlingen,
prompting significant impacts.

Radar mosaic imagery indicates the leading edge of a cold pool
extending from just north of Brownsville west-southwestward along
and just south of the Rio Grande River.  Meanwhile, mesoanalyses
and satellite imagery indicate renewed convective development
across portions of northeastern Mexico associated with a mid-level
shortwave trough centered near 27.3N, 101.4W.  Steep lapse rates
aloft were located just west of the ongoing complex and much of
northern Mexico as well.

While the heavy to extreme rain rates currently being observed
just north of Brownsville may shift offshore over the next couple
hours, the combination of a trailing/lingering outflow boundary
near the Rio Grande and upstream ascent/instability from
aforementioned lapse rates should result in a continued threat of
at least elevated convection over the next 3-6 hours.  The
heaviest rainfall threat will be modulated by the southward shift
of the outflow boundary - should this boundary drift back to the
north into south Texas, a renewed threat for 2+ inch/hr rain rates
could materialize and raise continued, significant flash flood
potential.  At least areas of 1-2 inch/hr rain rates are expected
with deep convection given the upstream instability and lift -
even with elevated convective activity.  Ground conditions are
inundated with significant impacts being reported amid near-zero
FFGs from Harlingen westward to Rio Grande City.  Additional
rainfall will likely exacerbate those impacts.

Cook

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

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

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

LAT...LON   27539856 27469744 26169691 25879768 26469918
            27129935