Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Sep 16 2023 16:03:43 AWUS01 KWNH 161603 FFGMPD VAZ000-NCZ000-GAZ000-TNZ000-KYZ000-ALZ000-162202- Mesoscale Precipitation Discussion 1078 NWS Weather Prediction Center College Park MD 1203 PM EDT Sat Sep 16 2023 Areas affected...TN Valley Concerning...Heavy rainfall...Flash flooding possible Valid 161602Z - 162202Z Summary...Shower and thunderstorms over the last hour are showing increasing rainfall efficiency over the TN Valley. Periods of high rainfall rates exceeding 2.5"/hr at times could yield instances of flash flooding this afternoon. Discussion...MRMS and single radar sources across the TN Valley show some enhanced rainfall rates reaching 2-3"/hr earlier within an area of showers and thunderstorms. A few elevated FLASH CREST responses were noted within the most prolific cells with 2-3"/hr rates just south of the Nashville Metro, and over along the TN/KY border. Recent IR imagery showing warm cloud tops and a lack of lightning with this activity suggests a predominance of efficient warm rain production, which corroborates the prolific estimated rainfall rates. This activity is expanding along and ahead of an elongated surface trough draped across the Southeast, aided by a fetch of southeasterly surface-850 mb moisture transport emanating out of the Gulf Stream. Aloft, the flow was becoming increasingly diffluent over the Southeast as a Midwest upper-trough digs southward. Earlier morning regional soundings around the showers depicted a highly saturated profiles at least through ~500 mb, with PWATs of 1.6-1.9" advecting into the region per recent TPW passes. The persistent moisture transport and steady heating are also leading to uncapped SBCAPE ~ 1000-2000 J/kg over the next few hours, with modest strengthening shear profiles to 25-30 kts. Thus, the expectation is for coverage to increase ahead of the surface trough this afternoon. Individual cell motions should be fairly progressive given 20-25 kts of mean flow. However, the slow forecast movement of the surface trough, strengthening forcing aloft, and moisture transport should support multiple rounds of thunderstorms containing high rainfall rates which could repeat over the same area. Although antecedent conditions across the area are on the dry side, repeat rounds of some high rates exceeding 2.5"/hr at times could lead to bouts of flash flooding going into this afternoon. Asherman ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!4bm8CZGHQe5pQU3d6TJMBS5nnv6B__ndoQRLUyD3KHJ1Ci4Z7AFMYzKhT5uUdk6H3B8i= emSef9KdWz8BP1S5X1eCz7U$ for graphic product... ATTN...WFO...BMX...FFC...GSP...HUN...JKL...LMK...MEG...MRX... OHX...PAH... ATTN...RFC...LMRFC...OHRFC...SERFC...NWC... LAT...LON 37628344 36238247 34338501 33258699 33798788=20 35348799 37208694=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) .