Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jul 17 2023 16:59:06 AWUS01 KWNH 171659 FFGMPD FLZ000-172300- Mesoscale Precipitation Discussion 0752 NWS Weather Prediction Center College Park MD 1258 PM EDT Mon Jul 17 2023 Areas affected...Southeast Florida Peninsula Concerning...Heavy rainfall...Flash flooding possible Valid 171700Z - 172300Z Summary...Thunderstorms expanding across the Florida Peninsula this afternoon will drift eastward and merge with the east coast sea breeze. This could result in nearly stationary thunderstorms with rainfall rates of 3"/hr. Flash flooding is possible. Discussion...The GOES-E visible imagery this morning shows scattered Cu and TCu already developing within an extremely favorable thermodynamic environment, with additional convection blossoming along storm outflow boundaries. The 12Z U/A soundings at KTBW and KMFL indicated deep column saturation with PWs of 2-2.3 inches, above the 90th percentile for the date. This was in an environment with weak lapse rates and near-record melting levels suggesting efficient warm rain processes will dominate today. Additionally, 0-6km mean winds were just 5-10 kts, indicating slow moving storms will be the norm as convection blossoms within MUCAPE exceeding 3000 J/kg according to the SPC RAP analysis. An upper level trough noted both in RAP 300mb wind progs and also through varying directions in the cirrus-level outflow appearing in the visible satellite will help drive ascent, while low-level inflow generally onshore from the Gulf of Mexico at 10-15 kts will resupply the impressive moisture and instability onto the peninsula through the evening. The high-res guidance is initializing with convective coverage that is a but underdone compared to current reflectivity, but even so is depicting significant convective coverage this aftn/eve. Although synoptic forcing is generally weak, the extreme overlap of moisture and instability should result in widespread thunderstorms developing along the eastward advancing gulf breeze, with additional thunderstorms likely occurring on outflow boundaries as minimal bulk shear produces pulse-type thunderstorms. In general, these storms should have limited temporal duration, but will still likely produce 2-3"/hr rates as progged by the HREF neighborhood probabilities, with 15-min rainfall exceeding 1" at times (4"/hr rates) as shown by the HRRR. These rates will produce a least an isolated flash flood risk. However, as the gulf breeze convection interacts with the pinned east coast sea breeze, Corfidi vectors will veer to the SW at just 0-5 kts, indicating the likelihood of stalling or backbuilding storms along the urban corridor from the Space Coast southward through the Gold Coast. Here, some subtly enhanced bulk shear could result in stalled multi-cell clusters, and the HREF probabilities suggest a 15-25% chance for locally more than 5" of rain. Recent rainfall noted by AHPS 7 and 14 day departures has been slightly above normal along the east coast, leading to slightly above normal streamflow anomalies and modest reductions in FFG. However, much of the area can still likely handle these heavy rain rates as noted by low FFG exceedance probabilities. This indicates that the most likely area for flash flood impacts today will be where any storms can organize/stall across urban areas as the more impermeable surfaces lead to rapid runoff. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!44F7YMNpue1uEp5NAE-FBFZyIPKnEZIQ9-WogyJIIByHy2cD454Q6Lj5r1sFOADNfdsI= fZSzXusDS8CEuvvDDoiMBxA$ for graphic product... ATTN...WFO...MFL...MLB... ATTN...RFC...SERFC...NWC... LAT...LON 28658101 28628060 28218039 27898024 27438008=20 26897993 26507997 26258003 25948009 25628024=20 25308045 25258065 25638069 26408063 26928059=20 27348082 27978107=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) .