Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Sep 01 2023 19:47:44 AWUS01 KWNH 011947 FFGMPD FLZ000-GAZ000-ALZ000-MSZ000-020130- Mesoscale Precipitation Discussion 1019 NWS Weather Prediction Center College Park MD 347 PM EDT Fri Sep 01 2023 Areas affected...Southeast from eastern AL through the central FL peninsula Concerning...Heavy rainfall...Flash flooding possible Valid 011945Z - 020130Z Summary...Slow moving thunderstorms with rainfall rates of 2-3"/hr will increase in coverage through the afternoon. Where these storms repeat, or move most slowly, they could produce more than 5 inches of rain in a few locations. Flash flooding is possible. Discussion...The regional radar mosaic this afternoon depicts widespread showers and thunderstorms expanding out of the Gulf of Mexico and lifting north into the Gulf Coast and Florida Peninsula. These storms are developing in response to increased moisture advection east of a retrograding upper low near the ArkLaTex, and PWs as measured by GPS are as high as 2.4 inches, near or above the daily record at several of the Gulf Coast U/A sites. Broad but modest mid-level divergence across the FL Peninsula and into GA is efficiently overlapped with the RRQ/tail of a 70 kt upper jet streak arcing over VA to drive impressive deep layer ascent, with lift additionally aided by SBCAPE of 2000-3000 J/kg. This robust environment is supporting the widespread convection with radar-estimated rainfall rates of 1.5-2.5"/hr according to KVAX. The guidance is in good agreement that convection will continue to increase in coverage and intensity the next several hours as forcing and thermodynamics remain extremely supportive. Although bulk shear will remain weak at less than 20 kts, suggesting generally pulse-type thunderstorms, 0-6km mean winds of just 5-10 kts will allow for slow moving storms, with repeated rounds possible as convection lifts north from the Gulf of Mexico. This could result in areas of 2-3" of rainfall in less than 1 hr due to 15-min rain rates exceeding 1" according to the HRRR sub-hourly. While there is a signal for isolated flash flooding anywhere from eastern AL through the FL peninsula noted by HREF 3-hr FFG of 20-50%, the greatest risk appears to be across the northern and central FL peninsula. Here, a wavy stationary front will advect slowly southward and continue to be a focus for thunderstorm development as easterly flow from the Atlantic merges with southerly flow from the Gulf. The high-res guidance is quite aggressive with rainfall along this axis as the additional lift through the low-level convergence enhances rainfall rates to as much as 1-2"/15 min according to the HRRR. This is also where the most intense HREF signal exists both for 3-hr FFG exceedance and 5"/6 hrs exist, both of which reach 40-50%. As storms repeatedly develop along this front and move very slowly, locally more than 5" of rainfall is possible which could lead to scattered instances of flash flooding. Parts of this area have received 150-200% of normal rainfall in the past 14 days, locally enhancing the flash flood risk in these areas. However, even in places that have been drier the past 2 weeks, these intense rainfall rates could still result in instances of flash flooding. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5olGs55VL0QyFz4ObtbAeuGsPbxRhFSn59N3vI18SPvkNgf_ntAsoJ2Prju58sZXfYiv= gtWv44BAhDNXVP-bZuatReM$ for graphic product... ATTN...WFO...BMX...FFC...JAN...JAX...LIX...MFL...MLB...MOB... TAE...TBW... ATTN...RFC...LMRFC...SERFC...NWC... LAT...LON 33028808 32618624 31928457 31268317 30438217=20 29898184 28638135 27848113 27758111 27028130=20 27108186 27798241 28748275 29488327 30108382=20 30238439 30098496 30128557 30348627 30438727=20 30408802 30488886 30698941 31648950 32528922=20 =20=20=20=20=20=20=20=20=20=20=20=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) .