Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jul 22 2025 19:29:53 AWUS01 KWNH 221929 FFGMPD FLZ000-230130- Mesoscale Precipitation Discussion 0779 NWS Weather Prediction Center College Park MD 329 PM EDT Tue Jul 22 2025 Areas affected...Southern Florida Peninsula Concerning...Heavy rainfall...Flash flooding possible Valid 221930Z - 230130Z Summary...Showers and thunderstorms expanding along an outflow boundary will spread across the southern half of the Florida peninsula through this evening. Rainfall rates of 2-4"/hr at times are expected, leading to 2-3" of rain with local amounts up to 5" possible. This may produce instances of flash flooding. Discussion...The regional radar mosaic this afternoon shows convection expanding along an outflow boundary (OFB) that is gradually shifting SE across the Florida Peninsula. Thunderstorms along this boundary have had radar-estimated rain rates above 2"/hr, and MRMS 1-hr measured rainfall as much as 2.5". While convection is deepening primarily in response to low-level convergence along this OFB, a jet streak positioned over the Bahamas is leaving modest diffluence atop the peninsula as well to help drive ascent, which is acting upon robust thermodynamics characterized by PWs of 2-2.3 inches as measured by recent U/A soundings and GPS, overlapping SBCAPE that has climbed to as high as 4000 J/kg according to the SPC mesoanalysis. The guidance has come into better agreement with the evolution during the next few hours, and there is increasing confidence that thunderstorms will expand across most of the southern peninsula, especially between 20Z-00Z. This is supported as well by extrapolation of activity building along the OFB, which as it sinks southeast will impinge into the extremely anomalous environment. This will support not only greater coverage of convection, but also intensification of storms, and HREF neighborhood rain rate probabilities surge to above 60% for 2"/hr coincident with 15-min HRRR rainfall exceeding 1" (brief 4"/hr rates). At the same time, this OFB may collide with the westward moving sea breeze from the east coast which is currently noted via the GOES-E day-cloud microphysics RGB just west of I-95, with additional convection developing along that boundary and during collisions. It is uncertain as to exactly how things will evolve when these boundaries meet. 850mb inflow behind the OFB is 10-15 kts from the Gulf, which exceeds the mean wind, and may be enough to push the combined axis back to the east. Whether that happens or not will impact the flash flood risk back towards the urban Gold Coast (if this does not happen the I-95 corridor would escape the heaviest rain) but some of the guidance does indicate this potential. Either way, with rain rates likely reaching 4"/hr and backbuilding or chaotic cell movement leading to slow storm motions, total rainfall of 2-4" is likely, with local amounts above 5" possible (HREF 30-40% chance). While the greatest risk for flash flooding will be across any of the impacted urban corridors, the slow motion of these intense rainfall rates could cause impacts anywhere across the southern peninsula through this evening. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!7JHoM-LifgdMXa-5Tp3J1u2ix9htvCLEk9OX42HJVA4eXBczSfyzfHbYAx1TqQ42R01j= JP94FIA8d_hVVoIx37gIVR0$ for graphic product... ATTN...WFO...MFL...MLB...TBW... ATTN...RFC...ALR...NWC... LAT...LON 28008091 27958037 27578006 27308002 26427995=20 25688020 25478045 25398102 25518146 25848192=20 26628227 27318208 27688173 27918132=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 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .