Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Aug 13 2025 08:42:55 AWUS01 KWNH 130842 FFGMPD TNZ000-KYZ000-ALZ000-MSZ000-MOZ000-ARZ000-131330- Mesoscale Precipitation Discussion 0921 NWS Weather Prediction Center College Park MD 442 AM EDT Wed Aug 13 2025 Areas affected...Northeast Arkansas through Central Tennessee Concerning...Heavy rainfall...Flash flooding possible Valid 130841Z - 131330Z Summary...Showers and thunderstorms will drift across the region through morning. Intense rainfall rates of 2-4"/hr will likely cause pockets of 2-3" of rainfall in less than 1 hour. This may cause instances of flash flooding, especially in urban areas. Discussion...Showers and thunderstorms noted on the regional radar mosaic early this morning have rapidly expanded across western and central Tennessee and back into northeast Arkansas. This convection is blossoming within a plume of elevated moisture evident on the GOES-E WV imagery on SW flow emerging from the Gulf Coast downstream of a mid-level trough axis that is still hung back across MO/AR. Cloud top cooling is continuing to occur across the area as well, indicating that convection is going to continue to develop and intensify in response to deep layer ascent provided through modest height falls, weak upper jet diffluence, and low-level convergence along a surface trough. Together these are driving sufficient lift for the rapid uptick in thunderstorm coverage, as this ascent is working upon robust thermodynamics characterized by PWs measured by GPS of more than 2 inches coincident with a ribbon of 1000-2000 J/kg MUCAPE. Storms that have developed already have produced MRMS measured 1-hr rainfall of more than 2 inches in some areas, and the resulting FLASH unit streamflow response has reached 200-400 cfs/smi. This has prompted already at least one FFW SW of Nashville, TN. The concern through the morning will be that these storms will continue to produce excessive rainfall rates of 2-4"/hr, although the HREF and REFS neighborhood probabilities for 2"/1hr are modest at just 10-15%. However, the CAMs are really struggling with the ongoing activity, so the ensemble probabilities are suffering and are likely too low. Additionally, with the primary 850mb inflow from the W/SW, propagation vectors have dropped to 5 kts or less and are aligned with the weak mean 0-6km wind (around 10 kts) to the primary trough axis. This is resulting in cells that at times have net motion near zero, especially near mergers/outflow collisions driven by pulse storms in the weak shear environment, lengthening the duration of this heavy rainfall. Although confidence in the evolution the next few hours is lower than typical due to lack of model support, the recent HRRR has started to capture the ongoing scenario and has exhibited a rapid increase in coverage and amounts of QPF the next few hours. This indicates that the environment will remain favorable for heavy rainfall, and where storms train/stall, 2-3" of rainfall could occur in less than 1 hour, with locally 4" possible by later this morning. Despite elevated FFG from recent dryness, these rainfall rates falling atop any more vulnerable soils or less-permeable urban areas, could result in flash flooding. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!6CTDGpysdS25mf6q1KvIInXWRn_m-k2LUW9IXXpzKQWXqhFp9f5QAxUfPAZIbAGIscEC= Nnoi-oKGS1ChFISn6RX9XMA$ for graphic product... ATTN...WFO...HUN...LMK...LZK...MEG...OHX...PAH... ATTN...RFC...ORN...TIR...NWC... LAT...LON 37008724 36908570 36288544 35738569 35128660=20 34838778 34848882 35069004 35549099 36289126=20 36628992=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) .