Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Mar 26 2023 23:15:15 AWUS01 KWNH 262315 FFGMPD GAZ000-ALZ000-270500- Mesoscale Precipitation Discussion 0134 NWS Weather Prediction Center College Park MD 714 PM EDT Sun Mar 26 2023 Areas affected...Central AL...West Central GA Concerning...Heavy rainfall...Flash flooding likely Valid 262310Z - 270500Z SUMMARY...An approaching complex of storms, followed by potential back building and training convection will likely result in areas of flash flooding. Areas most prone to flash flooding are in central AL and west-central GA where recent rounds of thunderstorms have made soils more sensitive to heavy rainfall rates. DISCUSSION...A 500mb disturbance tracking into the Lower MS Valley and the right-entrance region of a strengthening 250mb jet streak are providing favorable vertical ascent aloft over much of the South this afternoon. Convection has blossomed along two boundaries; a front stretching from northern LA to the southern Appalachians, and a surface trough located over southern AL and southern GA. Southwesterly 850mb winds are steadily increasing this afternoon and will become as strong as 45-50 knots between 02-05Z. This 850mb LLJ is responsible for the supply of rich 850mb moisture flux oriented quasi-parallel to front and nearby surface trough. In addition, 850-300mb mean flow and effective bulk shear vectors are oriented parallel to the front. These are key ingredients in establishing the potential for not only training thunderstorms, but back-building thunderstorms so long as the 850mb flow continues to provide rich 850mb moisture and theta-e advection into the front. As the LLJ increases, so will PWs across the highlighted region to as high as 1.75" this evening. In addition, MUCAPE heading into the evening hours will approach or slightly surpass 2,000 J/kg, giving ample instability to cells within the warm sector as well as for elevated convection along the front. Effective bulk wind shear is exceptional throughout the highlighted region with values of 60-70 kts, along with effective SRH values forecast to reach 200-300 m2/s2 this evening. These values are critical to maintain organized thunderstorms. Lastly, RH values in the 1000-500mb layer will reach as high as 90% saturation and warm cloud layers as deep as 10,000'. These storms will become more efficient rainfall producers as the LLJ intensifies this evening and warm rain processes become more favored. The textbook synoptic and mesoscale drivers mentioned above are a recipe for flash flooding. It is exacerbated by two other factors; one of which is the swath of land from central AL to west-central GA that received between 2-5" worth of rainfall within the past 12 hours. These locations, on average, contain <1.5" 1-hr FFGs with some areas that received the highest amounts of rainfall featuring <1" 1-hr FFGs. There is also the more urbanized corridor along I-20 that includes the metro areas of Atlanta, Birmingham, and Tuscaloosa, although the bulk of the most intense thunderstorm activity may reside just to the south of I-20. Hourly rainfall rates of up to 2"/hr are possible within the most intense areas of convection. Rapid rises in nearby creeks and poor drainage areas could occur, as well as flooded roadways that will be increasingly more difficult to identify as the sun sets. Mullinax ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!6rZjpuLn-VJDYl_7FYaYwiWaxrlZFwaM38uHlNKM9SqVPqhKBBYAIQNS-Pz7mX5KJFKg= YS9V8oW0KIYo8NRpdkw-G-c$ for graphic product... ATTN...WFO...BMX...FFC... ATTN...RFC...SERFC...NWC... LAT...LON 33908516 33878447 33708416 33128425 32508622=20 32178722 32678756 33118801 33368762 33678672=20 33858575=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) .