Mesoscale Precipitation Discussion 0822...Corrected
NWS Weather Prediction Center College Park MD
416 AM EDT Tue Sep 11 2018

Corrected for Category of Flash Flooding should have been Likely

Areas affected...Deep South Texas...

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

Valid 110807Z - 111200Z

SUMMARY...Additional heavy rainfall over staturated soils likely
to continue flash flooding condtions.  Increasing storms leading
to possible flash flooding from San Antonio Bay to Baffin Bay.

DISCUSSION...GOES-16 WV suite depicts exiting trof over Eastern TX
but also a digging compact wave near the Big Bend region with a
well defined trof extending south, providing favorable DPVA/height
falls for lower level strengthening.  Closer to the surface, an
MCV with reinforcing mesolows responding to strong latent heat
release near convective cores over E Starr/Hidalgo and a second
one entering Jim Hogg is slowly drifting toward the east due to
these mesolows and so stronger SSWly flow is rotating around
sparking strong convergence band of thunderstorms with IR tops
cooling to -70C crossing the Rio Grande.  These cells are fed by
highly unstable Gulf air where SBCAPEs are over 2500 J/kg with sfc
TDs in the upper 70s.  Currently, the training between the
mesolows is producing high QPE that suggests OU Flash unit stream
flows in Hildalgo/ and SW Brooks county over 600 to 1000 cfs/sm,
and FFG/QPE ratios over 100-200% suggesting flooding/flash
flooding is occurring.

Due to the isallobaric component and approaching mid-level height
falls, the western Gulf LLJ is starting to enhance with SSEly 20kt
sfc flow surging north toward the frontal zone that remains along
the coast and connects to the MCV.  As such strengthening
convergence/isentropic ascent is spurring on additional convection
along the front.  This may pose a short term burst of 2-3" of rain
in about 1-2 hours posing flash flooding risk before shifting
offshore in the 10-11z time frame.  With reduction of inflow from
the Gulf, the MCV/surface convergence should shift eastward toward
the coast and slowly reduce flash flooding risk. 

Gallina

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

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

LAT...LON   28049715 28019689 27639709 27269724 26869720
            26469709 26139705 25869718 25819742 25929782
            25979801 26079840 26189860 26229868 26509880
            27079879 27499832 27869768