Mesoscale Precipitation Discussion 0038 NWS Weather Prediction Center College Park MD 1156 AM EST Sat Jan 27 2024 Areas affected...Northern GA...Upstate SC...Western NC... Concerning...Heavy rainfall...Flash flooding possible Valid 271700Z - 272300Z SUMMARY...Enhanced Moisture flux into upslope portion of Southern Appalachians with strong WAA. Embedded thunderstorms to develop & potentially repeat with 1-1.5"/hr rates and spots of 2-3" totals across saturated/dormant soils. Localized flash flooding is possible through evening. DISCUSSION...GOES-E depicts a mature deep layer cyclone across the Lower Mississippi Valley with warm conveyor belt/pre-frontal trough crossing the central Gulf Coast into the Cumberland Plateau, providing deep moisture flux along increasing low level flow with 20-25kts of southerly flow across GA increasing to near 40kts back along/west of the warm conveyor belt. At the surface, a stationary front remains well defined across northern AL/GA angling between I-85 and I-20 across SC; solid east-northeasterly and northeasterly flow continue to dam in slightly cooler but still moist air across much of the area of concern. However, surface and VWP across central GA, denote that strengthening WAA and in steepening the isentropic gradient across N GA/SC, convergence has sparked a few shallow convective cells scattered within the region. Upper-level diffluence as the 3H jet turns north into the Ohio River Valley, will support further evacuation through the afternoon into evening hours broadening light to moderate showers in the upslope regions of NE GA, SC and W NC, with those continued embedded cells capable of quick .25-.5" totals, setting the stage for saturating the upper few centimeters of an already saturated 0-40cm layer. NASA SPoRT LIS ratios are well above normal into the 90-98th percentiles and values of 80-90%, particularly across the highest slopes of NC but also along a swath from near Columbus to Athens, GA which may be fully saturated. As such, FFG values which are 1-2"/hr and 1.5-2.5"/3hr may be a bit high and and may have increased runoff potential for any showers. Of greatest concerns, a bit of filtered insolation within the warm advective regime along/ahead of the pre-frontal trough may allow for some steepened lapse rates and MUCAPE values of 500-750 J/kg by late afternoon, especially further east into E GA/SC. Total PWAT values start reaching 1.5" on that 30-40kt LL flow supporting strong flux into any cells that develop. As such, a stronger convective signal is noted in the 12z Hi-Res CAMs and recent HRRR runs across the area of concern, even off the upslope regions closer toward the fall-line in GA/SC, but HREF signals suggest 1"/hr from 30-50% and 2"/3hrs up to 20% about 21-00z across NE GA into SC, providing some confidence in efficient rainfall production. Combined with prolonged moderate rainfall in NC/Upstate SC, totals of 1-3" may be scattered across the area of concern through 00z with localized flash flooding considered possible. Gallina ATTN...WFO...CAE...FFC...GSP...MRX... ATTN...RFC...LMRFC...SERFC...NWC... LAT...LON 35858205 35748094 34788062 33798181 33158318 33288431 33678460 34308473 35018427 35678331Download in GIS format: Shapefile | KML
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