AWUS01 KWNH 090311 FFGMPD NCZ000-SCZ000-GAZ000-TNZ000-090700- Mesoscale Precipitation Discussion 0245 NWS Weather Prediction Center College Park MD 1110 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 seagmants). Churchill ...Please see www.wpc.ncep.noaa.gov for graphic product... 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