Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jun 21 2023 16:24:37 AWUS01 KWNH 211624 FFGMPD NCZ000-SCZ000-GAZ000-TNZ000-212200- Mesoscale Precipitation Discussion 0551 NWS Weather Prediction Center College Park MD 1224 PM EDT Wed Jun 21 2023 Areas affected...Upstate SC, Western NC, Northeast GA Concerning...Heavy rainfall...Flash flooding possible Valid 211622Z - 212200Z Summary...Moderate to heavy showers will continue to spread across the Southern Appalachians through this aftn. Rainfall rates generally around 0.5"/hr could exceed 1"/hr at times in the heaviest rainfall, producing 1-3" of rainfall and isolated flash flooding. Discussion...The regional radar mosaic early this aftn shows widespread moderate rainfall moving across Upstate SC and western NC. This area of rain is being driven by a combination of isentropic ascent atop a stationary front analyzed by WPC along the coastal plain, with additional upslope ascent occurring through easterly 925-850 mb winds at 20-30 kts. A broad closed upper low centered over GA will maintain modest divergence aloft to enhance ascent, and rainfall should remain widespread into the aftn. Although instability is limited by current cloud cover evident on the GOES-E visible imagery, E/SE flow should advect subtly higher instability westward, possibly reaching 250-500 J/kg. This will combine with PWs measured by GPS around 1.7 inches to continue thermodynamics favorable for heavy rain. The high-res guidance is admittedly modest with rainfall amounts noted by 6-hr HREF probabilities for more than 3 inches confined to the Midlands of SC, and probabilities for 1 inch peaking around 50% into the terrain. However, the simulated reflectivity suggests rain will be persistent until a dry slot noted on WV imagery rotates into the area around 22Z. Both the HRRR sub-hourly fields and HREF neighborhood probabilities suggest rain rates will generally be around 0.5"/hr, but could surge at times to above 1"/hr where enhanced ascent occurs through pockets of greater instability or more pronounced upslope flow. This area has been quite saturated recently which will enhance the runoff and flash flood risk today despite the modest rain rates. MRMS 24-hr rainfall has been as much as 2-4" with locally higher amounts, and this is on top of 7-day AHPS rainfall that is as much as 300% of normal. This has compromised FFG, and driven USGS streamflows to well above the 90th percentile. This indicates that soils are generally hydrophobic so any persistent heavy rain could quickly become runoff, which could yield isolated instances of flash flooding, especially across more sensitive terrain. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!85J54FBAj1wTd6V1bn4k6vUoCAHriQEU0hMS3rLNa3Fbg5u2-uneIij7mYJ-I7MlvsTG= B_YEzV2whLD8-W_CdTUC2n4$ for graphic product... ATTN...WFO...CAE...FFC...GSP...MRX...RNK... ATTN...RFC...LMRFC...OHRFC...SERFC...NWC... LAT...LON 36228166 36078116 35708100 35358090 34828072=20 34698069 34458067 34108071 33778093 33638124=20 33628167 33688215 33808270 33998312 34238353=20 34498385 34848419 35328392 35838297 36208215=20 =20=20=20=20=20=20=20=20=20=20=20=20 =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .