Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Sep 09 2023 16:50:16 AWUS01 KWNH 091650 FFGMPD MDZ000-VAZ000-NCZ000-WVZ000-TNZ000-092230- Mesoscale Precipitation Discussion 1043 NWS Weather Prediction Center College Park MD 1249 PM EDT Sat Sep 09 2023 Areas affected...West Virginia...Western VA...Northwest NC...Far Northeast TN...Far Western MD... Concerning...Heavy rainfall...Flash flooding likely Valid 091650Z - 092230Z SUMMARY...Slow moving thunderstorms with ample moisture to locally produce 1-2"/hr rates and spots of 2-3", falling across steeper slopes possibly inducing scattered but localized incidents of flash flooding this afternoon into evening. DISCUSSION...GOES-E WV suite depicts a broad weak upper-low over the lower Ohio Valley into the central Appalachians with a few subtle shortwave rotating through it. CIRA LPW combined with the WV suite, support a surge of enhanced moisture within the effective warm conveyor belt across SC toward NW NC/SW VA before turning NNE along the spine of the Appalachians. Surface to mid-level enhanced moisture remains within the valleys of the terrain with total PWATs remaining well above normal. Local RADAR and VWP network shows a surge of moisture lifting out of central NC with a bowing segment of thunderstorms delineating the leading edge. This is particularly notable in the 850-500mb range.=20=20 Winds are 10-20kts through that depth but also intersect the terrain favorably for upslope, likely to increase with the approach of the bow. Clear skies through much of the Southern/Central Appalachians have warmed the grounds resulting in increasingly unstable air with CAPES starting to reach 1500-2000 J/kg with reducing capping.=20 GOES-Visible and RADAR has noted a few cells breaking out along the NC/SW VA Blue Ridge ahead of the approaching line. With stronger moisture convergence and further destabilization by 17-18z, coverage of thunderstorms will increase along with rainfall efficiency. Rates of 2"/hr are probable, with totals of 1"-1.25" in 15 minutes becoming more common throughout the afternoon. Cell organization is likely going to be a limiting factor for extreme totals as bulk shear is going to be below 25kts, so cells could collapse upon themselves limiting duration...though outflows are likely to spark new development. Deep layer steering is weak in the mid to upper level flow regime as the main upper low is well southwest and influence of the entrance to the polar jet is well distant across PA/N WV, resulting in a col in flow, this may allow for increased duration or even with redevelopment in close proximity to any initial downdraft for localized repeating. As such, widely scattered spots of 2-3" are probable across the area of concern, with a bit higher chances across central WV, as thunderstorms will be a bit stronger/more mature toward peak heating.=20 Recent heavy rainfall has saturated the shallow soils of the Appalachians as noted by NASA SPoRT 0-40cm soil moisture ratios near 50-60% or generally at 70-90th percentiles based on the random nature of rainfall over the last few days. Low FFG values below 1.5" in an hour are likely to be exceed though the coverage may be much more widely scattered and localized.=20=20 Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-zUXBd0X_oZZpKhv3fMOGwCf2b0yIaFn7er_NNzXjw3wcwdJh-GAO1wNt3th3yRctkx-= vLPZxGcHCGeDlT8TH-L5g94$ for graphic product... ATTN...WFO...LWX...MRX...PBZ...RLX...RNK... ATTN...RFC...LMRFC...MARFC...OHRFC...SERFC...NWC... LAT...LON 39698002 39507850 38287930 37767964 36917999=20 36268083 36238147 36358204 36648285 37068245=20 37578188 38058173 38388143 38928110 39508076=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) .