Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu May 18 2023 11:27:43 AWUS01 KWNH 181127 FFGMPD SCZ000-GAZ000-181730- Mesoscale Precipitation Discussion 0309 NWS Weather Prediction Center College Park MD 726 AM EDT Thu May 18 2023 Areas affected...South Carolina...Adjacent Eastern Georgia... Concerning...Heavy rainfall...Flash flooding possible Valid 181130Z - 181730Z SUMMARY...Widely scattered highly efficient but slow moving tropical showers may pose localized 2-5" totals and possible flash flooding conditions. DISCUSSION...A southern stream shortwave is located across central GA lifting east-northeast with subtle diffluent region of 3H jet streak arching across Upstate SC into NC, providing weak but sufficient broad scale ascent across the region. A surface low appears to be developing near Savannah with a warm front parallel to the southeast coast before angling eastward across the central Gulf Stream. Backed low level flow is advecting increased higher theta-E air westward across much of SC with mid-60s to low 70s Tds at the surface and total PWats over 1.75". Instability is currently limited to the coastal Low country and Gulf stream, but strengthening easterly flow in response to the surface/low level pressure falls and solar heating will should increase near/along the frontal zone.=20 Upstream, the northern stream trough is digging across the Delta Region of Western TN into MS, sharpening the overall trof and broadening the upper-level pattern for increased divergence aloft and further surface/coastal cyclogenesis, while weakening mid to upper level flow to support very slow potentially retrograding mean steering flow. With favorable proximity to MUCAPE/isentropic ascent, low level shear along the warm front. Shallow, potentially rotating updrafts should be slow moving but allow for consistent, less restricted updrafts for locally increased moisture flux convergence and efficient rainfall production. Rain rates of 2"/hr with shorter duration increase to 3"/hr and slow motions may allow for highly localized but 2-5" rainfall totals in less than 3hrs. An example this morning was noted over S Orangeburg county where near 3+" fell in 1-2hrs. Environmental trends supported by Hi-Res CAMs, including the most recent hourly HRRR runs suggest increase in convective coverage is expected after 15z, with increasing instability in low cap environment. Rapid inundation/flash flooding is going to be highly contingent on locality/urban proximity given most of the cells should be close to the warm front and therefore coast/Low country. Very sandy/swampy soils are probable to even absorb/retain these rates and totals, though urban locations dotted through the area will be susceptible throughout the morning into early afternoon hours, All considered, flooding is considered possible in urban/road areas, though with a low possibility across rural areas near the pocket of lower FFG across Elbert/McDuffie, GA into McCormick, SC counties...even though that area is further away from best instability axis/isentropic ascent near the frontal zone.=20=20=20 Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-VeCeqZRHwcc9EjoqvtV2l2JOmcpo-wOJTKDBjhQsJNgHt33mTWRdYEx21uIevKjTXoX= wKTGXK7I-z03KT7ZXQno9Co$ for graphic product... ATTN...WFO...CAE...CHS...FFC...GSP...ILM... ATTN...RFC...SERFC...NWC... LAT...LON 34368233 34228141 34048049 34097967 33837892=20 33447888 32977922 32408025 32118121 32558214=20 33278274 34138296=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) .