Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jul 30 2025 15:11:39 AWUS01 KWNH 301511 FFGMPD VAZ000-NCZ000-WVZ000-SCZ000-GAZ000-TNZ000-KYZ000-302100- Mesoscale Precipitation Discussion 0830 NWS Weather Prediction Center College Park MD 1110 AM EDT Wed Jul 30 2025 Areas affected...Southern Appalachians...Cumberland Plateau... Concerning...Heavy rainfall...Flash flooding possible Valid 301510Z - 302100Z SUMMARY...Core of deep layer moisture, slow steering with favorable outflow may support very efficient, but slow moving thunderstorms capable of 2"+/hr rates and localized 3-4" totals possible. Given complex terrain, incidents of flash flooding are possible. DISCUSSION...GOES-E WV suite and RAP analysis shows a weakness in the sub-tropical ridge generally centered from a weak shortwave center in far north-central GA extending northeastward along the spine of the Southern Appalachians. Strong curvature of the upper-level jet across TN becomes much more favorable for right entrance ascent pattern into the 30+kt jet streak in WV across the eastern Cumberland Plateau into the Appalachians. While in the lower levels, the flow is very weak at 5-10kts but still has a generally south to southeast confluence along the eastern slopes of terrain supporting some deep layer moisture convergence though 500mb with enhanced 850-700mb Tds centered across the area of concern. So though the vertical shear is weak; the outflow aloft may allow for a few updraft cycles to support some very weak organization than pure pulse convection. Total PWat values are naturally reduced due to the higher elevation/resolution of the RAP analysis; though values of 2-2.25" are analyzed in the lower terrain surrounding and values of 1.75-2" in E Carolina are 2-2.5 standard anomalies above normal.=20 Instability values of 1500-2500 J/kg exist through depth over the Cumberland Plateau and GOES-E Vis shows ample clear skies mainly north of GA/SC across the Smokies into W VA; to further support increasing values through strong insolation. As such, a few Tcu are seen along the spine of the Smokies with broadening Cu fields along the Cumberland spine and east across W NC into W VA.=20 Scattered over-turning is expected and with very slow motions and ample moisture flux, potential for 1.5 to 2"/hr may occur even with first stronger cells. Slow outflow generation is likely to trigger newer development along convergence with the terrain/other outflow boundaries increasing the updraft width with each cycle; eventually potential for 2+"/hr rates are possible from 18-21z.=20=20 Weak steering will allow for scattered to numerous localized 2" totals though a widely scattered incident or two of localized 3-4" remain possible (through to the evening hours) as noted in recent 12z guidance suite providing some confidence. Given nature of the updrafts/activity, incidents of flash flooding are considered possible. This increase in potential/coverage and confidence will result in an upgrade to a Slight Risk of Excessive Rainfall with the upcoming 16z ERO update.=20 Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!92rFSCqBJH4fepn2zV98365vvVLO4FDx11xqQYrz9abeDpdMTjRb7ihHgKKYYBmQSA3E= sMrrs8us4VSYU4DPSLlAQZA$ for graphic product... ATTN...WFO...FFC...GSP...JKL...MRX...OHX...RLX...RNK... ATTN...RFC...ALR...ORN...RHA...TIR...NWC... LAT...LON 37828024 37287975 35928153 35488213 34888325=20 34818411 35058522 35548557 36238493 37048313=20 37408195=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 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .