Graphic for MPD #0104
Mesoscale Precipitation Discussion 0104
NWS Weather Prediction Center College Park MD
254 AM EDT Sat Mar 16 2024

Areas affected...Deep South Texas...

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

Valid 160700Z - 161200Z

SUMMARY...Strong moisture flux into mature complex along front
should maintain efficient rainfall production with 2-3"/hr rates
through late overnight period.  Muddled steering flow may allow
for some slow cells motions and localized totals over 4" and
result in possible flash flooding through daybreak.

DISCUSSION...Goes-E 10.3um EIR depicts a mature convective complex
across Deep South Texas with overshooting tops to -70C indicative
of solid unstable inflow.  06z surface fronts continues to slowly
sag southward from near VCT to CRP to BKS and ZPY providing a
solid moisture convergence boundary and now as low level flow
continues to veer, is also generally confluent but becoming
increasingly orthogonal to the boundary providing continued
isentropic ascent even as low levels may be starting to
stabilize/cap.  RAP analysis and GOES AMVs suggest weak upper
level flow is favorably oriented toward weak outflow jet to the
northeast and satellite imagery denotes that fact with some
transverse banding filaments noted along the far
fringes...however, this favorable region appears to be lifting
away.  As such, a delicate balance appears to remain in place with
mid-level steering also starting to veer and support northeasterly
motion to internal updrafts with the complex as well.   However,
solid inflow suggests southeastward propagation and so, the
complex is expected to continue to be slow moving along the
frontal zone.

Total moisture values have ticked up to near 2" through depth, but
surface to boundary layer values per CIRA LPW continue to rise
being well over 1" below 850mb and Tds into the mid 70s.  While
winds are in the 15-20kt range, there remains solid
confluence/convergence to the boundary to allow for enhanced
moisture flux for continued efficient rainfall production;
generally between 2-3"/hr though HRRR 15-minute totals of
1.5-1.75" have been forecast.   As noted earlier, overall slow
cell motions appear to be allowing for increased localized totals
with spots of 4, perhaps 5" plausible within the next few hours.
While FFG values are high/soils dry, few soil conditions can
infiltrate this amount in short-time, so much could run off and
induce localized flash flooding concerns.  

Uncertainty remains with stronger isentropic ascent along the
upstream portion of the frontal zone and the Sierra Madre.  Given
veering steering, this may present back-building and then repeat
cell tracks across S Zapata, Starr county and then downstream with
areas that may have already seen 2-4" locally.  If this were to
manifest spots over 6" are possible and flash flooding would
clearly be more likely, but as for now; there are mixed signals
that this will occur.

Gallina

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

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

LAT...LON   28589703 28319646 27829705 27499720 27059732
            26709730 26439769 26099828 26379907 26699933
            27319954 27449866 27939785
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Last Updated: 254 AM EDT Sat Mar 16 2024