Flash Flood Guidance
Issued by NWS
Issued by NWS
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868 AWUS01 KWNH 181852 FFGMPD VAZ000-NCZ000-WVZ000-SCZ000-190050- Mesoscale Precipitation Discussion 0289 NWS Weather Prediction Center College Park MD 251 PM EDT Sat May 18 2024 Areas affected...Southwest VA...Much of Western and Central NC Concerning...Heavy rainfall...Flash flooding possible Valid 181850Z - 190050Z SUMMARY...Scattered slow-moving areas of showers and thunderstorms are expected to develop this afternoon and continue into the evening hours. Rainfall rates of 1 to 2 inches/hour and slow cell-motions will foster a localized and generally urban concern for flash flooding. DISCUSSION...Early-afternoon visible satellite imagery shows convective initiation underway across the higher terrain of the Blue Ridge from southwest VA down into northwest NC as small-scale terrain induced circulations and differential heating work in tandem with a gradually destabilizing boundary layer for convection to develop. Meanwhile, surface observations shows a quasi-stationary front draped across the region with a wave of low pressure currently noted along the front just west of Greensboro. MLCAPE values across western and central NC have already risen to locally over 1000 J/kg with a rather moist airmass in place characterized by PWs of locally 1.5+ inches from near the NC Triad and points east. The convection initiating near the Blue Ridge should tend to develop off to the southeast with time, with additional convective development expected in close proximity to the aforementioned low center and the greater NC Triad over the next few hours where low-level convergence/forcing will tend to be relatively stronger. Cell-motions are expected to be quite slow given the weak steering currents aloft, and this coupled with rainfall rates that will be capable of reaching 1 to 2 inches/hour will support some spotty storm total amounts that could reach 3 to 4 inches in just a couple of hours. This is supported by the 12Z HREF guidance. Given the rainfall amounts, and moist antecedent conditions and locally high streamflows (as suggested by NASA SPoRT and USGS data respectfully), there should be at least a localized threat for flash flooding. However, the greatest sensitivities will be to the urban corridors and this will include the NC Triad region involving Greensboro and the Raleigh-Durham area. Areas south and east of the NC Triad will also have a regional threat for slow-moving convection going into the evening hours given proximity of the front, and thus some isolated flash flooding will be possible here too. Orrison ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...AKQ...GSP...MHX...RAH...RNK... ATTN...RFC...LMRFC...MARFC...OHRFC...SERFC...NWC... LAT...LON 37538052 37518019 37308005 36837994 36487970 36387850 36157759 35897707 35477669 35137681 34937738 34987804 35057923 35258075 34988206 35088275 35558261 36318150 37228091