116
AWUS01 KWNH 300241
FFGMPD
TXZ000-300800-

Mesoscale Precipitation Discussion 1403
NWS Weather Prediction Center College Park MD
1040 PM EDT Tue Sep 29 2026

Areas affected...Big Bend of Texas through the western Hill
Country

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

Valid 300239Z - 300800Z

Summary...Showers and thunderstorms lifting out of Mexico will
repeat across portions of Texas near the Big Bend region. These
storms will contain rain rates exceeding 1"/hr at times which may
lead to flash flooding.

Discussion...The GOES-E IR imagery this evening shows an area of
rapidly cooling cloud tops just south of the Texas Big Bend
region. This deepening convection is developing downstream of the
remnants of Polo which are estimated via satellite imagery to be
over the Mexican state of Chihuahua and approaching West Texas.
Impressive moisture convergence is occurring as streams from both
the Gulf and Pacific merge, which has helped to surge PWs to 1.7
to 2.0 inches (1.89" measured at Del Rio on the 00Z RAOB), well
above the 90th percentile for the date. This PW is aligning within
a pool of MUCAPE that has increased to 1500-200 J/kg, supporting
the ongoing convection. Although the regional radar mosaic shows
only weak echoes at this time, the GOES-E GREMLIN radar emulation
appears to be doing a good job matching the area of strongest
IR/lightning, and suggests impressive rainfall just over the
international border lifting northward.

Despite the weak signal in the current reflectivity, the CAMs
indicate that activity lifting towards the Stockton and Edwards
Plateaus will expand, intensify, and train into the overnight
hours. The spatial coverage of this rain may remain modest, but
any storms that develop within the robust thermodynamics will
likely contain heavy rain rates. Additionally, forcing for ascent
may increase in the next few hours as the remnants of Polo shift
northeast, driving 850mb winds to as high as 40 kts, or reaching
2x the mean flow. This could produce additional intensification
which is supported by both HREF and REFS hourly rainfall
probabilities reaching 20-30% for 1 inch as far east as the
western hill country during the next few hours.

Additionally, the approach of the remnants of Polo will drive a
surge in bulk shear values to 30-40 kts, helping to organize cells
into clusters, while at the same time causing Corfidi vectors to
veer more against the mean wind to support training. While neither
the HREF or REFS suggest widespread or considerable FFG exceedance
probabilities (less than 15% chance), this may be a bit underdone,
so there appears to be at least an isolated flash flood risk
developing into the overnight.


Weiss

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

ATTN...WFO...EWX...MAF...SJT...

ATTN...RFC...FWR...NWC...

LAT...LON   31380170 30820059 29880032 29130044 28660119
            28620207 28790311 28790328 29270400 30050403
            30790359 31170276