Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat May 10 2025 06:05:12 AWUS01 KWNH 100604 FFGMPD FLZ000-ALZ000-MSZ000-101200- Mesoscale Precipitation Discussion 0248 NWS Weather Prediction Center College Park MD 203 AM EDT Sat May 10 2025 Areas affected...portions of far southern AL/MS into the FL Panhandle Concerning...Heavy rainfall...Flash flooding possible Valid 100600Z - 101200Z Summary...Localized rainfall rates of up to 2-3"/hr may result in short-term totals of 5"+ through 7am CDT. Isolated instances of flash flooding are possible (and could be locally significant over more sensitive low-lying and metro areas). Discussion...A deep layer (surface to 500 mb) vertically tilted cut-off low is becoming more convectively active over the past few hours near the low-level (surface to 850 mb) center (just offshore southeast LA and southern MS). GOES-East infrared imagery depicts cooling cloud tops in association with this recent deep convection, though a rainband farther east (within the core of the warm conveyor belt) has maintained more impressive cold cloud tops with occasional overshooting tops. Both areas of convection are only just beginning to come ashore, though lapse rates remain unimpressive both in the vicinity of the convection and well onshore of both areas (max 2-6 km lapse rates of less than 7deg C/km). That said, a corridor of increasing instability (+300-600 J/kg) is evident over the past several hours in association with the convection near the core of the low-level center (with little change so far in instability farther east into the FL Panhandle). CIRA composite advected layer precipitable water (PWAT) imagery depicts a clear increase in low-level PWAT (sfc-850 mb and 850-700 mb layers), pivoting around the center of the low-level circulation (with both NEXRAD VWP and GOES Derived Motion Wind Vectors (DMW) indicating 15-25 kt flow around a well-defined surface circulation from an ideally placed ~330z ASCAT pass). Total PWATs range from 1.7-1.9 inches (between the 90th percentile and max moving average, per LIX sounding climatology), and low-level moisture transport and convergence (iscentropically ascending) is also being complemented by upper-level diffluence (also evident in NEXRAD VWP and GOES DMW between 400-250 mb) with deep layer (0-6 km) shear of 30-50 kts. The latest hi-res guidance (00z HREF suite, 18z REFS suite, and more recent runs of both the HRRR and RRFS) generally indicates the potential for extreme localized rainfall rates (2-3"/hr) with resulting isolated totals of 3-6"+ through 12z. The spatial disparities in these high QPF totals are relatively wide, but have come into better agreement (with 00z guidance onward) in depicting the greatest potential for localized 5"+ totals in the vicinity of the low-level center (confined to far southern portions of MS/AL, possibly extending into the far western FL Panhandle). This is consistent with the most recent observational trends, and 00z HREF 40-km exceedance probabilities for 5" are indicated to be as high as 10-20% (with corresponding 100-yr ARI exceedance probabilities of 5%). Given the high uncertainty in the manifestation of these localized extreme rainfall rates/totals (which are largely conditionally dependent on localized backbuilding of convection near the low center), isolated instances of flash flooding are considered to be possible. Given the proximity to relatively sensitive low-lying and urbanized metropolitan areas (with 3-6 hour Flash Flood Guidance as low as 1.5-2.0"), locally significant flash flooding is also possible. Churchill ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!4IwHcuJaidVMrh3-h8vB5amiBRsLWyUx5QUfof5c6c67F5wN5s7RgdhJTfIW49aXw5w5= vCEGlp7VOPbfPrbzIZT0-60$ for graphic product... ATTN...WFO...LIX...MOB...TAE... ATTN...RFC...LMRFC...SERFC...NWC... LAT...LON 31188815 31148755 31018700 30838646 30788588=20 30688535 30578502 30398468 30088453 29828468=20 29588498 29708537 30048582 30268632 30278684=20 30238745 30238749 30198859 30228915 30548913=20 30878871=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) .