Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jul 22 2024 00:14:03 AWUS01 KWNH 220013 FFGMPD GAZ000-TNZ000-ALZ000-MSZ000-220515- Mesoscale Precipitation Discussion 0684 NWS Weather Prediction Center College Park MD 813 PM EDT Sun Jul 21 2024 Areas affected...Southern TN...Northern AL...Far Northwest GA... Concerning...Heavy rainfall...Flash flooding likely Valid 220015Z - 220515Z SUMMARY...Continued back-building relative stationary cell motions on the upwind side of outflow; as well as training profile on the southeast side continue to pose flash flooding risk into early overnight period. Scattered spots of 3-4" are likely to continue localized flash flooding conditions. DISCUSSION...Earlier convection in proximity to the stationary front draped across Middle Tennessee has kicked out an outflow boundary toward the west and south reinforcing the FGEN across south-central TN. Weak southwesterly 850mb isentropic ascent will help to maintain/back-build storms along the western side of the outflow boundary. Cell motions appear to be nearing equal and opposite to the propagation to allow for localized stationary cells. Given surface Tds to 70F and deep layer moisture in the 1.75" range, rates of 1.5-2"/hr are probable and so spots of 3-4" will be possible before cold pool dominates and propagation to the southwest occurs or stabilizing local environment stops the next cycle given winds provide weak convergence/isentropic ascent over cold pool to overcome increasing capping. There is mixed signals in guidance, providing low confidence, but any cells that do maintain will pose that higher risk potential for flash flooding given the slow motions. Further southeast across SE TN/NW GA/N AL, stronger updrafts continue to break through the cirrus with cooling tops below -60C across Limestone/Madison county,AL, as well as, the more persistent cells near Meigs/Hamilton county, TN. Weak low to mid-level flow and back-building forcing, has brough effective cell motions to be less than 5kts, but also remain oriented favorably to the deep layer flow. Outflow/reinforced stationary front FGEN forcing is weak as it is parallel to the mean flow, but any cold pools generated by the ongoing convection will support similar back-building/over-running conditions expected across Western TN/into NW AL. Spots of focused 3-4" totals are likely to continue to produce flash flooding conditions through the next few hours in to the early overnight period, when low light visibility increases the potential for deadly consequences of crossing flooded roads.=20 Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!4lsn-5sP9waNju_dlK2-iZgZAN_020-tvzu39qJ1hya_n2g7o_cuDhvKr4_xqD2SSS5C= whtK_jMg-WWJo_0pqeDWyVI$ for graphic product... ATTN...WFO...FFC...HUN...MEG...MRX...OHX... ATTN...RFC...LMRFC...OHRFC...SERFC...NWC... LAT...LON 36328468 35868404 35308417 34708519 34378637=20 34358768 34498839 34708879 35208900 35858882=20 35938849 35598816 35408774 35428656 36208545=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .