Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon May 12 2025 07:36:03 AWUS01 KWNH 120734 FFGMPD ALZ000-121100- Mesoscale Precipitation Discussion 0258 NWS Weather Prediction Center College Park MD 333 AM EDT Mon May 12 2025 Areas affected...portions of eastern AL Concerning...Heavy rainfall...Flash flooding possible Valid 120730Z - 121100Z Summary...Continued hourly rainfall totals of up to 1-2" are likely to result in localized 2-3" accumulations over the next several hours. Isolated to scattered instances of flash flooding are possible.=20 Discussion...Persistent boundary layer moisture flux convergence just to the north of the triple point of a vertically stacked, deep layer (sfc-200 mb) cut-off low/cyclone is maintaining a cluster of thunderstorms across east-central AL (with MRMS estimating localized hourly totals as high as 1-2" at times). The convection has become increasingly linearly organized from south-to-north within the deep layer mean flow, backbuilding towards the triple point where 20-30 kts of low-level (primarily near the 925 mb isobaric surface/295K isentropic surface) is providing locally enhanced convergence/lift. In the mid- to upper-levels (400-250 mb), broad diffluence (within the left-exit region of a ~100 kt jet streak) and a distinct potential vorticity max upstream should continue to promote large scale lift and convective longevity. The mesoscale environment is characterized by ML CAPE of 250-1000 J/kg (and increasing by ~200 J/kg over the past several hours), precipitable water values of 1.3-1.5 inches (between the 75th and 90th percentile, per BMX sounding climatology), and effective bulk shear of 20-40 kts. Given the favorable environment and recent observational trends, the expectation is that isolated to scattered 1-2" hourly totals will continue over the next several hours, and the potential exists for localized training/repeating of these heavy rainfall rates. Hi-res CAMs (recent hourly runs of the HRRR and RRFS) insist that this activity will shift abruptly towards the northeast over the next 2-3 hours (as the low-level flow is expected to veer over the next couple of hours, largely cutting off the locally enhanced moisture transport/convergence). Even so, this will likely result in 2-3" of isolated to scattered rainfall totals through 10-11z (falling to the north and east of the Montgomery and Birmingham metro areas where MRMS estimates 1-2" of rainfall has occurred over the past several hours). Antecedent soil conditions are quite wet, with accompanying 3-hr Flash Flood Guidance (FFGs) generally range from 1.5-2.5" (as NASA SPoRT-LIS 0-1m soil moisture remains well above the 90th percentile across the region). Isolated to scattered instances of flash flooding are possible. Churchill ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_J_SPlRrOXtcghp3L4_NDB5gp-OB0sKIYbLllyz9vOPrylqtZzfDLiBT4AysRcBSK3X-= 4bO7GdHADcPyymcyRHtOpMI$ for graphic product... ATTN...WFO...BMX...HUN... ATTN...RFC...LMRFC...SERFC...NWC... LAT...LON 34278653 34188564 33388533 32158541 32018580=20 32278604 32718625 33268647 33758657=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) .