Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Apr 13 2023 17:05:25 AWUS01 KWNH 131705 FFGMPD FLZ000-132300- Mesoscale Precipitation Discussion 0183 NWS Weather Prediction Center College Park MD 104 PM EDT Thu Apr 13 2023 Areas affected...Southeastern Florida Concerning...Heavy rainfall...Flash flooding likely Valid 131700Z - 132300Z Summary...Isolated instances of flash flooding are likely this afternoon with locally heavy rainfall capable of 1-3"/hr rates. This may lead to additional localized rainfall totals of 3-5+ inches, which could possibly aggravate ongoing flooding conditions across the highly sensitive Fort Lauderdale region. Discussion...Convection is beginning to percolate across southeastern portions of the Florida Peninsula, and convective initiation is expected to occur over the next several hours with increasing solar insolation (with much less cloud cover today) and mesoscale convergence/forcing provided from the sea breeze. Concerns for flooding are certainly elevated today, given the locally historic flash flood event that occurred across the Fort Lauderdale area yesterday (with incredible localized 24-hour rainfall totals of 18 to 26 inches observed). Across the broader region of southeast Florida, rainfall totals largely ranged from 3-10 inches over the past 3 days, so antecedent conditions remain sensitive across the Gold Coast (even well outside of the extreme double digit totals from yesterday). While the environment will not be nearly as supportive of very slow moving, organized convection today, there is still an opportunity for locally high rainfall totals of 3-5+ inches (as indicated by 12z HREF 40-km neighborhood probabilities for 3" and 5" exceedance as high as 50% and 10%, respectively). =46rom an ingredients-based perspective, today actually looks just as favorable for locally heavy rainfall as yesterday. The mesoscale environment is characterized by precipitable water values of 1.6-1.8 inches (at or above the 90th percentile, per MFL sounding climatology), ample instability with SB CAPE of 2500-3500 J/kg, and effective bulk shear of 30-40 kts. While these variables should certainly support the organization of deep convection, there are significant differences from yesterday that should limit the prolonged occurrence of very heavy (2-3"+) rainfall rates. These limiting factors include: 1) weaker low-level flow that has veered significantly to the south, providing less coastal convergence and much lower levels of moisture transport, and 2) more unidirectional tropospheric flow that is less supportive of organized supercells in-particular (with straighter hodographs and bunkers right moving vectors that support the easterly progression of discrete convection, should it develop). While these limiting factors should almost certainly prevent any repeats of extreme double digit totals, the 12z HREF (and subsequent HRRR runs) have been in rather good agreement in depicting convective development in the vicinity of the Gold Coast this afternoon (with HREF EAS - ensemble scale agreement - 10-100 km neighborhood probabilities indicating a 10-15% bullseye for 1" exceedance over the region through 00z). Individual HRRR runs since 09z consistently depict the potential for localized 2-4" totals through 23z, while the HREF probability-matched mean depicts similar localized totals as well (most prominently located in the vicinity of Fort Lauderdale). Given the highly vulnerable antecedent conditions and overall favorable environment for convective development and heavy rainfall, localized instances of flash flooding are considered likely (with the aggravation of flooding conditions possible in the Fort Lauderdale region). Churchill ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_dqYW8NcOPlYScahzCcMjhLzPKqy5dTqxc_rbSXtJ8dygXLLTxn4aFW6K8jkYDEkpB-W= H1M3HQsGaGb2qRJ0TliO-J4$ for graphic product... ATTN...WFO...MFL...MLB... ATTN...RFC...SERFC...NWC... LAT...LON 27088016 26837997 26397999 26098004 25678018=20 25498051 25568080 25848082 26128077 26358073=20 26558068 26808061 27018044=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) .