AWUS01 KWNH 151644
FFGMPD
TNZ000-KYZ000-ALZ000-MSZ000-LAZ000-152230-

Mesoscale Precipitation Discussion 0063
NWS Weather Prediction Center College Park MD
1244 PM EDT Sat Mar 15 2025

Areas affected...Northern MS...Northwest AL...Western to Middle TN...South-Central KY...

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

Valid 151645Z - 152230Z

SUMMARY...Strong, highly efficient rotating thunderstorms capable
of 1.5-2"/hr rates likely to train for a hour or so as the line
slowly advances eastward. Subtle buckles in the QLCS may result
in further enhanced duration with a spot or two of 4-5" possible.=20
Rates and totals are likely to result in scattered to numerous
incidents of flash flooding to accompany severe weather risk.

DISCUSSION...GOES-E WV suite depicts secondary upper-level low
deepening across OK/N TX with lower scale shortwave resulting in
some negative tilting. This results in broadening of dual jet
structure with very impressive downstream baroclinic shield across
the Mid-MS Valley into Lower Ohio Valley denoting the very strong
divergence aloft, especially in proximity to 130kt 250H jet streak
exiting over N IL into LP of MI. The wedge of diffluence across
the area of concern will provide strong large scale ascent to
maintain the well above average low level wind flow; 850mb 50-65kt
southerly with backed sfc to boundary layer 20+ kt flow pumping
higher theta-E air across E MS/AL into southern Middle TN with Tds
increasing from low 60s to upper-60s/low 70s. Mid-level EML has
been mixing out, but has allowed for increasing unstable air mass
(2000-2500 MLCAPE) along the sharp pre-frontal pressure trough
from W TN back to a developing surface wave in NE LA. Overall the
strength of the low level flow and solid low level moisture (up to
1.5" TPW) resulting in highly anomalous flux values near 3-3.5 Std
Dev from normal and generally about 1000+ kg/m/s of IVT.

As such, very strong, broad and likely rotating updrafts will
further enhancing localized moisture flux due to isallobaric flow
but also strong convergence to add about .5"/hr to general
updrafts. WoFS solutions continue to have many of the runs
supporting .3-.5"/5 minute rates with this broader cores allowing
for increased duration and hourly totals of up to 2"/hr. So any
given storm may overwhelm urban/prone flooding locations even if
isolated or along/ahead of the main line. The greater concern,
particularly further north where deeper mean flow will allow for
more of pivot point to develop for the longer line of cells,
should increase potential for SW to NE training convection,
especially near/downstream of the surface wave as it lifts from NE
LA across central MS to Middle TN.

Current surface observations and RADAR mosaic suggest a weak
WAA/isentropic boundary across south-central Middle TN eastward
toward the southern Cumberland Plateau due to earlier convection.
WoFS, HRRR and RAP rapidly refreshing guidance all suggest, this
boundary will maintain with a buckle noted in the SB/MLCAPE fields
though MUCAPE will support elevated convection downstream across
northern Middle TN into south-central KY. As such, this
inflection near the MS/TN/NW AL border continues to be highest
potential for those longer duration/training events with 4-5"
totals possible through 22z...slowly lifting northeastward across
Middle TN into the later evening hours. This also overlaps with
rainfall reduced FFG values and will likely result in scattered to
numerous incidents of flash flooding this afternoon into early
evening. Scattered incidents are likely further north into KY
where FFG and instability are lower; as well as south into central
MS where cells will be stronger, but duration is likely to be
lower and FFGs a bit higher.

Gallina

ATTN...WFO...BMX...HUN...JAN...LMK...MEG...OHX...PAH...

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

LAT...LON 37528646 37418538 36678505 35748543 34328659=20
32888788 32158867 31798983 32109095 33489055=20
34948934 36448791

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