Mesoscale Precipitation Discussion 1176
NWS Weather Prediction Center College Park MD
1002 PM EST Mon Dec 16 2024

Areas affected...Southern Arkansas...Northwest Mississippi..Adj
portionsOK, TX, LA...

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

Valid 170300Z - 170830Z

SUMMARY...The potential for continued back-building of weakening
but training showers may present a low-end scattered incident or
two of flash flooding through the overnight hours.

DISCUSSION...GOES-E WV suite denotes an elongated trough/stream
intersection extending from northeast Texas across the Delta
Region of the MS River toward the southern Ohio Valley toward the
tail end of the more amplified exiting flow across the Lower Great
Lakes.  GOES-AMVs confirm RAP analysis of this intersection
extends the length of the broad right entrance to the 70-90kt 3H
jet across the TN/OH valley.  A small inflection/wave is highly
divergent across NE TX providing the enhanced ascent pattern noted
with strong cirrus filaments along the northern edge of the
convective clusters across NE TX, AR into N MS/SW TN.  The deep
unidirectional flow extends back to central TX, where moisture is
generally confluent before veering into solid isentropic ascent
toward the upper level jet entrance.  As such, CIRA LPW and RAP
analysis show an enhanced pool of moisture starting to near 1.5"
with the vast majority below 850mb.

Surface analysis shows defined sagging cold front across AR, that
is starting to sharpen, with warm sector southerly flow providing
weak but sufficient surface convergence from 5-10kts.  Strong
convection with some weak QLCS features generally training along
the boundary/deep layer moisture interface are fed upstream by
pool of 1000-1250 J/kg of MUCAPE before diminishing rapidly toward
N MS.  Rates of 1.5-1.7"/hr are probable given moisture/unstable
air and with training profiles may allow for streaks of 2-3"
totals, though eastward along the line will see enhanced
southeastward propagation.  While soil conditions are fairly
dry/generally recepible; they are starting to go a bit dormant and
rates may be sufficient for localized pooling/enchained run-off. 
As such flash flooding is considered possible.  

While upstream convection appears to becoming a bit more fractured
due to slightly weaker flow, the upper-level divergence/outflow
channel is suggestive/supportive of back-building/isentropic
ascent.  Additionally, this mid-level wave is supporting some
shortwave ridging across SW to south-central AR and backing
propagation vectors to be be more northward allowing for greater
potential for training cells through the next 4-5 hours.  Hi-Res
CAMs are inconsistent in the evolution overall convective
activity/coverage...given the weakened upstream convergence, but
ones that do have stronger convergence do depict a higher
potential for training/back-building signal near areas that have
already received the higher rainfall resulting in initial flash
flooding warning.  Confidence is high contingent on the evolution
and so the risk for continued flash flooding across Texarkana
toward the central LA/AR border is also considered possible
through 09z (as signals further diminish through the entire hi-res
CAM suite).

Gallina

ATTN...WFO...JAN...LZK...MEG...SHV...

ATTN...RFC...ABRFC...LMRFC...NWC...

LAT...LON   34649054 34488968 33928946 33409022 33069166
            32919259 32909333 32849406 33109473 33359479
            33799453 33989415 34199346 34409209