Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Nov 14 2023 08:05:12 FOUS30 KWBC 140805 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 304 AM EST Tue Nov 14 2023 Day 1 Valid 12Z Tue Nov 14 2023 - 12Z Wed Nov 15 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Kleebauer Day 2 Valid 12Z Wed Nov 15 2023 - 12Z Thu Nov 16 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS SOUTHEAST FLORIDA AND THE NORTHERN KEYS... Continued mid and upper-level trough evolution will preside over the Southeast US with the base of the mean trough into the central Gulf. Surface low present off the central Gulf Coast will continue to slowly propagate eastward with a stationary front situated west to east across the central Gulf into South FL and the adjacent FL Straits. A combination of increased difluent flow downstream of the mean trough and surface convergence within the proxy of the aforementioned stationary boundary will create a favorable environment for a prolonged heavy rain event across South FL, especially for areas south of Melbourne down into the northern Keys. PWAT anomalies approaching 2-2.5 deviations above normal are consistent across all guidance, including the latest NAEFS and ECENS within the above corridor with the primary focus along the urban setting between Fort Lauderdale to Miami. Forecast bufr soundings out of KMIA indicate a rich, moist profile on Wednesday morning and afternoon with saturation deep through the profile with a skinny MLCAPE presence indicative of a textbook heavy rain threat. Area instability isn't overly prolific (~500-1000 J/kg MLCAPE), but the deep moisture flux being advected into the region with ample ascent between 1000-500mb will generate widespread heavy precipitation with rates generally settling between 1-2"/hr and low probabilities of 3"/hr possible given the latest HREF probability around 20-25% between the 18-00z hrs on Wednesday afternoon and early evening. Latest blended guidance has ramped up totals within past succession of runs with now a distinct 2-4" clustering across the southern FL Peninsula, including the Miami Metro. Ensemble bias-corrected mean QPF has jumped over 4" for portions of south FL as well with deterministic output showing local maximum of up to 8" for where the best convergence zone settles and trains overhead. Persistent east-northeast flow due to the formation of a surface low forecast southeast of FL and a sprawling surface high to the north will provide the necessary onshore component and continued low-level moisture advection across the above area. Given the higher chance of flash flood concerns within the urban corridor extending from Miami, north to West Palm Beach, have decided to upgrade the previous MRGL risk to a SLGT with an opportunity for further upgrade to a higher risk category pending the evolution of hi-res guidance and their forecast for where the zone of best convergence and heavy rainfall will occur. Kleebauer Day 3 Valid 12Z Thu Nov 16 2023 - 12Z Fri Nov 17 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS MUCH OF THE EASTERN FLORIDA COAST... Surface low formation off the eastern FL coast will propagate to the north and northeast over the course of Thursday with the best moisture field and low-level ascent being pulled away from the FL Peninsula. Much of the guidance has been keen on degrading the heavy rain potential due to the synoptic evolution of the surface reflection and upper trough across Southeast US. However, there's still some solutions that hang on to the idea of a local heavy rain threat within the confines of the eastern FL coast, especially over the Space Coast region of the state. This is in conjunction with residual moisture present along with a semi-prevalent inverted trough axis that hangs near and just off the coast of FL. ECMWF and multiple ensemble members indicate this potential with the deterministic producing a prolific bullseye of 3-5" somewhere within the confines of the eastern FL coast. This is a low probability type event, but one that could occur given the complexities of a dynamic upper trough propagation and attendant surface low in vicinity of the southeast coast. The NAM is also another model that produces heavy rainfall within the D3 time frame, but its evolution is vastly different than any other guidance at this juncture so will likely discount its solution. This is a lower end MRGL risk for the time being and the period will be monitored closely for any localized impacts within the outlined areas.=20 Kleebauer Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-0wHTNu7INIl9IkoGkEdw9gt3z5AEAIHUU0jC9_qYSgg= nieTdQy2KEogQ6p3h922H35B47jQNQMlkiopDmKQAiubllo$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-0wHTNu7INIl9IkoGkEdw9gt3z5AEAIHUU0jC9_qYSgg= nieTdQy2KEogQ6p3h922H35B47jQNQMlkiopDmKQP9ES2W4$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-0wHTNu7INIl9IkoGkEdw9gt3z5AEAIHUU0jC9_qYSgg= nieTdQy2KEogQ6p3h922H35B47jQNQMlkiopDmKQd4wO2fg$=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. 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