AWUS01 KWNH 071232
FFGMPD
TXZ000-071800-

Mesoscale Precipitation Discussion 1058
NWS Weather Prediction Center College Park MD
832 AM EDT Sun Sep 07 2025

Areas affected...Western Hill Country & Lower Pecos River Valley
of Texas...

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

Valid 071230Z - 071800Z

SUMMARY...Ongoing flash flooding likely to continue for the
remainder of the morning with very slow moving and surprisingly
efficient rainfall production producing highly focused 2"/hr rates
over sensitive/low FFG terrain.  Additional 3-5" totals resulting
in likely focused flash flooding.  A spot or two of considerable
and/or significant flash flooding is possible.  

DISCUSSION...Regional RADAR mosaic over the last few hours has
seen a slight uptick in convective activity in both strength and
coverage with the scattered observations indicating surprisingly
efficient rainfall production with 2"/hr rates and some localized
2-5"/3hrs reported resulting in localized flash flooding.  The
overall environment is expected to change very little over the
next few hours as cells continue to remain fairly stationary with
small movement.

The overall dynamics has been supportive of the scattered
convective environment, as GOES-E WV shows a very concentric but
broad upper-level ridge across northern Mexico, placing SW TX/Hill
Country into a favorable upper-level divergent pattern at the
entry of a speed max of a jet just east of the 30N100W benchmark. 
Small northeast quadrant diffluence, but also slightly digging
northern stream influence across the Big Country in combination
with approaching northern stream short-wave feature is combining
to allow for solid evacuation of these thunderstorms.  In
addition, the shortwave to providing ascent, has strengthened
surface easteries, though a shallow boundary layer/inversion is
drawing moisture up through the Rio Grande  Valley to the Lower
Pecos (per Sfc-850mb LPW animation) and lifting in northward on
850mb flow per VWP in the region.  Total deep layer moisture is
lower than expected for such an observed efficient cells; the flux
is most likely loading the lower warm cloud portion with the low
to mid-70s Tds for 2"+/hr rates for the highly focused updrafts
that have developed.  

The vertical shear profile (along with the upstream height-falls)
supports a westerly back-building environment counteracting the
steering flow aloft to result in a fairly stationary nature in the
short-term.   As the height-falls/shortwave arrives, a slow
southward motions are likely into the Rio Grande Valley toward
Mexico.  Flux up the Rio Grande is expected to continue to keep
slow but efficient rainfall production likely over the next 4-6
hours.  As such, spotty 3-5" totals are probable and will result
in focused (scattered in coverage) but potentially considerable
flash flooding conditions (as FFG values are naturally low
1-1.5"/hr & 1.5-2.5"/3hrs) in fairly rugged terrain.

Gallina

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

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

LAT...LON   31120201 31120100 30649929 29949871 29149935 
            28850041 29180092 29640153 29870197 30260236 
            30810241 

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