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WPC Met Watch


Mesoscale Precipitation Discussion: #0244 (Issued at 928 PM EDT Wed May 08 2024
) MPD Selection


Graphic for MPD #0244

Mesoscale Precipitation Discussion 0244
NWS Weather Prediction Center College Park MD
928 PM EDT Wed May 08 2024

Areas affected...Tennessee River Valley into Southern

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

Valid 090130Z - 090700Z

SUMMARY...Significant life-threatening flash flooding is currently
ongoing across northern Middle TN; with additional thunderstorms
developing upstream and a narrowing corridor for training
downstream suggesting further expansion of considerable flooding
through the rest of Middle and southeastern TN.

DISCUSSION...01z surface analysis depicts a surface low over south
central MO between TBN and VIH with warm front draped southeast
across W KY into northern TN.  Here, strong convection is
reinforcing the frontal zone across northern TN; steepening the
isentropes in the area.  A secondary convergence zone likely from
this morning's MCS reinforced by differential heating and weak
outflow can be analyzed from NW TN south-southeast to near HSV to
near RMG.  Weak TCU bubbles along this boundary to help denote it.
 VWP along with RAP analysis and short-term forecast show broad
southwesterly 35-40kt LLJ across the MS River Valley intersecting
the boundaries fairly orthoganally to induce stronger vertical
ascent, given the strength and forcing pressing in from the west;
there is limited expected southward sag with time allowing for
additional development in W KY and eventually further upstream out
of MO to once again align with already saturated areas with falsh
flood emergencies across that have seen 3-6". Very moist/unstable
enivornment with 3500-4000 J/kg of MLCAPE and TPW to 1.75" should
support 2-2.5"/hr rates.  So, an additional 3-5" along this swath
is possible, broadening the area of significant life-threatening
flash flooding along and likely south of the axis from
Marshall/Trigg county, KY to Sumner to Cumberland county. 

Elsewhere, the eastern gradient of the LLJ and enhanced moisture
of 1.75" is aiding moisture convergence ascending over the outflow
boundary across N AL.  Supercells continue to develop and track a
bit south of southeast with flanking line/RFD trying to reinforce
the outflow boundary. Given upstream LLJ will continue to
strengthen, isentropic ascent should support
back-building/regeneration upstream and allow for additional
training with 2"/hr rates likely to be the norm.  As such, this
should be another axis of 4-6"+ probably a bit south of this
morning's heavy rainfall. The HRRR has been persistent with this
evolution  and provides some confidence, though trends suggest it
may be a bit too far south, but storm scale interaction/cold pool
generation is likely to be the main driver of ideal training axis
which is very difficult to lock down this far out.  Still the risk
for  However, this is across more complex orography in the upslope
of the Cumberland Plateau, and an axis of considerable flash
flooding is likely to evolve.  Eventually, leading edge convection
should be fast moving but will move through higher terrain of the
southern Appalachians and so portions of W NC, N GA are included
in this MPD.




LAT...LON   37788917 37738772 36828547 36108396 35418316
            34638334 34058404 34058525 34598660 35618820

Download in GIS format:    Shapefile
 | KML

Last Updated: 928 PM EDT Wed May 08 2024

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