Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Sep 26 2024 14:50:31 AWUS01 KWNH 261450 FFGMPD VAZ000-NCZ000-WVZ000-SCZ000-GAZ000-TNZ000-KYZ000-262030- Mesoscale Precipitation Discussion 1066 NWS Weather Prediction Center College Park MD 1049 AM EDT Thu Sep 26 2024 Areas affected...Southern Appalachians Concerning...Heavy rainfall...Flash flooding likely Valid 261449Z - 262030Z Summary...Widespread heavy rain downstream of Hurricane Helene will continue today into the Southern Appalachians. Rainfall rates of 1-2"/hr are likely, which through repeating rounds could produce 2-3" of rain with local maxima of 5". This will enhance flash flooding, with significant impacts becoming likely across the Southern Blue Ridge. Discussion...The regional radar mosaic this morning shows an expansive area of heavy rain across much of the Southeast and into the Southern Appalachians. This is associated with a pronounced moisture plume noted in the GOES-E WV imagery extending downstream from Hurricane Helene in the Gulf of Mexico. PWs within this moisture plume have been measured as high as 1.75 to 2.0 inches on the 12Z U/A observed soundings from KRAX and KFFC. Instability is somewhat limited, only around 100-250 J/kg of MLCAPE, but deep layer ascent is impressive. Mid-level divergence between Helene and a pronounced upper low over IN is combining with a nearly stationary poleward arcing jet streak over TN to leave favorable RRQ over the region, while low-level SE flow continues to upslope into the terrain. In this environment, rainfall rates have already been measured via MRMS as high as 1.25", and these will likely continue through the aftn. During the next several hours, persistent moderate to heavy rain with rates 0.5-1"/hr will lift northward across the area, with embedded convective cells producing locally enhanced rain rates to 2"/hr as reflected by HRRR 15-min rainfall exceeding 0.5". 850mb inflow will remain out of the S/SE through the aftn while gradually intensifying to above 30 kts, resulting in moisture flux that is progged by the SREF to exceed +3 sigma later today. This impressive moisture advection combining with nearly unchanging robust ascent will result in continuous rainfall into areas that have already received 4-8+" of rain the past 24-hours. The HREF neighborhood probabilities indicate a 50-70% (10-20%) chance of more than 3" (5") of rain the next 6 hours, with the highest probabilities across Upstate SC and into far western NC along the Blue Ridge. Elsewhere in northeast GA, eastern TN, and southwest VA, 1-3" of additional rainfall is likely through the aftn. This rainfall occurring atop saturated soils, sensitive terrain, and ongoing flash flooding, will almost certainly enhance impacts across the region. FFG has been extremely compromised to as low as 0.25"/3hrs for which the HREF exceedance probabilities reach above 70%. This lends high confidence to flash flooding and impacts as rain continues across the region. However, across the Blue Ridge, current streamflow anomalies are as much as 400-600% of normal, so any additional rainfall could quickly result in significant and life-threatening flash flood impacts. Additional rainfall this evening will almost certainly necessitate future MPD issuances across this region with widespread significant flash flooding, and possibly locally catastrophic impacts, developing as the rain persists and becomes even more intense into tonight. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!7VIaHIFGs9tb7z-yxhkxhUzgWCRF-29HSujbYUuEdnx4WuiB8dZAQFJz21TUzaVNkwNO= UzZp62A0V08YOLw-JYixReA$ for graphic product... ATTN...WFO...CAE...FFC...GSP...JKL...MRX...RLX...RNK... ATTN...RFC...LMRFC...MARFC...OHRFC...SERFC...NWC... LAT...LON 37668066 37518005 37058039 35718133 35008180=20 33918230 33768241 33478258 33238297 33248347=20 33558382 34008415 34418448 35568425 36848340=20 37388243 37648158=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .