608
AWUS01 KWNH 180940
FFGMPD
TNZ000-MSZ000-MOZ000-ARZ000-181500-

Mesoscale Precipitation Discussion 0287
NWS Weather Prediction Center College Park MD
539 AM EDT Sat May 18 2024

Areas affected...Northeast AR...Western TN...Northern MS...

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

Valid 180940Z - 181500Z

SUMMARY...Slow moving thunderstorms capable of 1.5"/hr and
scattered spots of 2-3" totals pose localized flash flooding
through early morning.

DISCUSSION...GOES-E WV suite depicts a fairly concentric vorticity
center across northeastern AR within the broader positive tilt
mid-level trough extending into the Ohio Valley while the base is
filling and shifting east through the Lower Mississippi Valley.
The cyclone is fairly vertically stacked, though winds have
recently picked up particularly along the southeastern quadrant of
the cyclone where greatest instability resides with 1500 J/kg of
uncapped MLCAPE  along the edge of a fairly deep moisture pool
near the upper-low itself.  Recent RAP analysis has denoted an
increase of the low to mid-level moisture convergence in response
to the uptick in winds, resulting in broader vertical ascent and
increased convective coverage. Sfc Tds in the mid to upper 60s and
modest deep layer moisture (with limited negative effects to the
lapse rates) provide 1.5-1.7" of total PWATs for thunderstorms
that are developing.  As such, rates of 1.5-1.75"/hr are most
likely.

Cell motions are very slow near the 500-1000mb thickness trough
that is downshear of the upper-low across NE AR into W TN.  This
should allow for very slow, perhaps slightly chaotic cell motions
with potential for mergers to locally increase rainfall rates in a
very short duration.  As such, spots of 2-3" are possible over the
next few hours scattered within the the eastern hemisphere of the
circulation, with weak but sufficient advection of unstable air
from the south; allowing for some southward propagation as well.
This places the cells closer to naturally lower FFG values across
NE AR/W TN with 1.7-2"/hr and 2-2.5"/3hr but still may also reach
the slightly higher values of N MS and be well within reach of
exceedance.  Therefore scattered incidents of flash flooding may
be possible over the next 4-6hrs as the upper-low very slowly
drifts east-southeast.

Gallina

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...LZK...MEG...

ATTN...RFC...LMRFC...SERFC...NWC...

LAT...LON   36369008 36148888 35558818 34918825 34458889
            34379032 34509098 34829155 35209181 35779182
            36309112