Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Sep 27 2023 20:45:46 AWUS01 KWNH 272045 FFGMPD FLZ000-280230- Mesoscale Precipitation Discussion 1107 NWS Weather Prediction Center College Park MD 445 PM EDT Wed Sep 27 2023 Areas affected...Northern and Central Florida Peninsula Concerning...Heavy rainfall...Flash flooding possible Valid 272044Z - 280230Z Summary...Slow moving thunderstorms will expand across the Florida Peninsula through this evening. Rainfall rates within the more intense convection could exceed 3"/hr at times. These storms will move slowly, producing locally more than 5 inches of rainfall, which could lead to isolated instances of flash flooding. Discussion...The regional radar mosaic this afternoon depicts widespread showers and thunderstorms aligned from WSW to ENE across the northern Florida Peninsula. These storms are developing within impressive convergence along a slowly sinking stationary front analyzed by WPC, and within the diffluent tail of a weak upper level jet streak. This ascent is working across favorable thermodynamics characterized by PWs of 2.2-2.4 inches as analyzed by GPS and measured by the 15Z KXMR sounding, which is above the daily record for the site. Additionally, a ribbon of SBCAPE exceeding 2500 J/kg is analyzed by the SPC RAP, with regional forecast soundings measuring deep warm cloud depths above 14,000 ft, indicative of efficient warm rain processes. These warm rain processes are being observed via radar-estimated rain rates reaching 2.5+"/hr on KMLB, resulting in modest FLASH response already. The high-res guidance is in very good agreement, at least on a broad scale, with the evolution through this evening. While there is some north-south placement uncertainty in the axis of heaviest rainfall, there is a clear signal among the guidance and associated ensemble systems that heavy rainfall will envelop much of the northern and central peninsula. As the boundary sinks slowly southward and the jet streak remains over the Mid-Atlantic, plentiful ascent into the robust thermodynamics will result in continued convective development. Effective bulk shear will remain minimal, so pulse-type storms are expected to be dominant, but resultant outflows and storm mergers could additionally lead to more widespread development. These storms will all have the potential to produce 3"/hr rain rates as progged by HREF rain-rate probabilities reaching 20-25%, and supported by the HRRR 15-min product suggesting 0.75-1" of rainfall. Despite the pulse nature of these storms which should limit their overall lifespans, very slow motions on 0-6km mean winds of just 5 kts, will allow for multiple rounds of storms in some areas. This has a high likelihood of producing more than 3" of rain south of the front, with local totals above 5" possible as reflected by both HREF and RRFS TL probabilities. FFG remains quite high across the Peninsula at 3"/1hr and 3-4"/3 hrs, so FFG exceedance probabilities are modest. However, recent rainfall measured by the NSSL 24-hr QPE has been as much as 2-4" in some areas, which has helped more impressively saturate the top 10cm soils according to NASA SPoRT. The consistent signal for heavy rain among the various high-res suggests that where these higher totals can occur, especially over urban areas or soils primed from yesterday's rain, isolated instances of flash flooding could occur. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_L6BIQ0d8a4et9ffLBhmq9LmLVWnm9LAcL9NGPeXA1jvx2-Lfqk9XbIL9qOxJB6TOUr5= A3bwGwpOLuhyyZW9a_JULlw$ for graphic product... ATTN...WFO...JAX...MLB...TBW... ATTN...RFC...SERFC...NWC... LAT...LON 30538135 29988112 28988075 28448053 27918056=20 27688100 27448156 27338219 27348257 27788276=20 28348267 28768273 29388288 29978239 30378174=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) .