Mesoscale Precipitation Discussion 0243
NWS Weather Prediction Center College Park MD
542 PM EDT Wed May 08 2024
Areas affected...North & South Carolina Common Border Region...
Concerning...Heavy rainfall...Flash flooding possible
Valid 082145Z - 090100Z
SUMMARY...Strengthening of MCV and downstream development. Slow
cell motions and mergers with sub-hourly totals over 2" and
localized totals to 2-4" pose possible flash flooding
DISCUSSION...The MCV from this morning's MCS across the TN Valley
translated through the Southern Appalachians but has maintained a
core cluster of thunderstorms that has fed back into its strength,
while also supporting a flanking outflow boundary. Stronger than
forecast local winds across a highly buoyant/unstable environment
across the Piedmont and Coastal Plains of in proximity to the
Carolina's shared border have increased convergence enough to
support downstream convective initiation along the effective warm
advective wing of the circulation near Lumberton, NC. Solid low
70s Tds and modest pooled 850-700mb moisture from broad 15-25kt
southwesterly flow has enhanced local moisture to over 1.5", while
supporting broad MLCAPE values of 2500-3000 J/kg to support this
strong updraft flow; as such flux into the system will support
2"/hr rates. Given the orthogonal intersection, thunderstorms
continue to expand eastward along the mid-level boundary which is
also parallel to deep steering flow while also remaining aligned
with the approaching core of the cluster maintaining the MCV.
Here, directional convergence, adds that just little more flux
convergence for further rainfall efficiency. However, the
limiting factor has been forward speed, so while 1-1.5" fell in
15-30 minutes, the overall totals have limited the overall affect
of flash flooding...but now with downstream development, repeating
may allow for localized 2-4" totals and localized flash flooding
may be possible.
Upstream of the MCV, the effective cold front/flanking line has
laid out NW-SE and remains an effective nearly perpendicular axis
for further isentropic ascent in the wake of the MCV as it passes.
Strength of updrafts are a bit less robust being slightly
elevated over the cold air, but are favorably oriented for
repeating/training. Within this axis spots of 1-3" are possible,
though weaker ascent may limit overall coverage and intensity as
the MCV moves further away and any isallobaric component of the
wind would be reducing.
Gallina
ATTN...WFO...CAE...GSP...ILM...RAH...
ATTN...RFC...SERFC...NWC...
LAT...LON 35237972 34837842 34397788 33927812 33757911
33888006 34418152 34708148 34798059 35118004
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