Mesoscale Precipitation Discussion 0245
NWS Weather Prediction Center College Park MD
1105 PM EDT Thu May 08 2025

Areas affected...southwestern NC, northwestern SC and northern GA

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

Valid 090300Z - 090700Z

Summary...Continued localized rainfall rates up to 1-2"/hr may
train and repeat over the same areas over the next several hours,
likely resulting in isolated to scattered instances of flash
flooding (with short-term totals of up to 3-5").

Discussion...Ongoing convection over the TN/NC/GA/SC border region
is tending to align in a west-to-east training axis, along an
effective low-level front (most pronounced at 1000-925 mb, per
SPC's SFCOA 02z analysis, but also apparent from 925-700 mb). This
low-level convergence is being driven by inflow/moisture transport
from the S-SW (10-20 kts from 925-850 mb), which is isentropically
ascending over rain-cooled outflow from earlier storms (and is
most apparent in the surface theta E gradient which ranges from
336K to the south to 324K to the north across the MPD).
Significant upper-level divergence is complementing the low-level
convergence, as the region is located near a phased jet structure
in the right-entrance region of a ~90 kt jet streak centered near
the Delmarva and the left-exit region of an increasingly defined,
broader jet streak spanning much of the Deep South (with the
latter becoming more of the primary influence over time).
Otherwise, the mesoscale environment is characterized by MUCAPE of
500-1000 J/kg (plenty sufficient on its own, and possibly
underselling the influence of slantwise instability via isentropic
ascent), precipitable water values of 1.1-1.4 inches (between the
75th and 90th percentile, per GSO sounding climatology), and
effective bulk shear of 30-40 kts.

While convection should have the tendency to propagate towards
towards the southeast over the course of the night (out of the MPD
area and into sandy soils beyond the fall line into the coastal
plain of SC/GA), there may be a several hour period where
convection trains from west-to-east near the aforementioned
effective front (as the upwind propagation vector, subtracting the
850 mb flow from the mean flow of the cloud bearing layer,
supports more due easterly storm motions parallel to the effective
front, as observational trends indicate backbuilding of cells over
the GA/TN/NC border region). Some of the most recent hi-res
guidance (00z ARW/ARW2 and select recent runs of both the HRRR and
experimental RRFS) indicate the potential for localized 3-5"
totals (driven by rainfall rates of up to 1-2"/hr, per both
observational trends and hi-res model data). With FLASH CREST unit
flow data already indicating localized instances of flash flooding
ongoing, expect areal coverage of flash flooding to expand over
the next several hours (with isolated to scattered instances of
flash flooding being likely, given 3-hr FFGs generally ranging
from 2.0-3.0" and the increasing likelihood of training segments).

Churchill

ATTN...WFO...CAE...FFC...GSP...MRX...RAH...

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

LAT...LON   35638217 35548068 35247990 34538040 34098097
            33728220 33988352 34338519 34818538 35098492
            35328380