Mesoscale Precipitation Discussion 0666
NWS Weather Prediction Center College Park MD
417 AM EDT Sun Jul 13 2025

Areas affected...Central Texas...

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

Valid 130815Z - 131415Z

SUMMARY...Potential for significant flash flooding likely to
continue.  Additional 3-6" totals may overlap with ongoing
flooding areas but will result in overall areal expansion of
additional flash flooding through day break.

DISCUSSION...GOES-E WV suite shows a strong/compact center of base
of long wave vorticity center over north-central to northeastern
OK.  A smaller scale shortwave that was noted earlier this evening
has sheared/elongated and expanded the positive tilt trough all
the through the Lower Pecos River Valley into northern Coahuila. 
This setup has maintained a surface low along the Rio Grande near
KDRT with a surface trof that extends northeast through the
southern Hill Country; while the main surface low along the front
continues to sag south toward KBKD in Northwest TX, increasing
surface to low level response.   Additionally, this surface trough
has a 5-7 degree Td gradient along it separating moist air, from
very moist air with Tds into the mid-70s. Broad orthogonal surface
to 700mb has been strongly convergent along the boundary for
clusters of elevated storms to develop with increasing moisture
flux supporting deep warm cloud processes and efficient rainfall
production. Combine this with the elongation of the trof helping
to expand the entrance to the northern stream jet across N TX into
OK maximizing divergence aloft to help maintain the outflow.

The slightly increased confluent flow through the Colorado River
Valley nearer the frontal wave, has rapidly matured the convection
into a smaller MCS with a solid bowing segment along the upstream
edge.  Total PWat values in this confluent region have remained
elevated compared to further west with totals over 2" approaching
2.25".  Given strength of convergence, occasional rates of up to
4" have be estimated with solid 2-3" totals observed across
Lampasas county.  500-1000mb thickness and VWP suggest propagation
vectors will shift from south to more west-southwest counter to
the deeper layer steering flow, allowing for some
training/repeating convective cores.  Given high likelihood of
broader 2-3"/hr rates (with smaller isolated 4" rates), 
additional 3-6" are probable but a localized maximum of 8" can not
be fully ruled out. 

Further west, strengthening LLJ across the southern Hill Country
into the Concho Valley has seen a maturing cluster centered near
Schleicher county.  Slightly reduced deeper layer moisture may
support increased cold pool generation and orientation along the
southeastern flank of the MCV/developing 500mb wave, cell motions
toward the south and potentially eastward into the cluster is
possible and similar 3-6" totals are growing more likely as well.
Concern for this cluster to shift eastward and merge with more
mature complex could present a worse case evolution, for increased
duration to push those isolated additional 8" totals through 15z. 
Regardless, areal coverage of intense rainfall to induce flash
flooding is likely and given placement to the  Hill Country, a few
locations of significant flash flooding becoming increasing
possible. 

Gallina

ATTN...WFO...EWX...FWD...SJT...

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

LAT...LON   32639846 32519758 32189690 31659657 31069670
            30699714 30389772 29729936 29630074 30280123
            31120092 31850015 32279948