Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Jul 15 2023 09:54:59 AWUS01 KWNH 150954 FFGMPD FLZ000-GAZ000-151500- Mesoscale Precipitation Discussion 0735 NWS Weather Prediction Center College Park MD 553 AM EDT Sat Jul 15 2023 Areas affected...Portions of the FL Panhandle Concerning...Heavy rainfall...Flash flooding possible Valid 151000Z - 151500Z Summary...Increasing convective coverage with slow storm motions may yield localized rainfall rates of 2-3"+/hr, with short-term storm totals of 3-5"+ possible. Isolated instances of flash flooding are possible, and an instance or two of significant flash flooding cannot be ruled out. Discussion...A long-lived mesoscale convective vortex (MCV) continues to exert influence along the FL Panhandle for a second day, after traversing AR/LA/MS/AL on days prior. While the core of the 500 mb vortex itself is now offshore (over the Gulf of Mexico), an elongated axis of vorticity is still impinging northeastward along the coast of the Big Bend of FL (and is most prominent at 700 mb). Low-level (mainly 925 mb) flow and associated moisture transport has increased over the past couple of hours, resulting in increased overrunning and moisture flux convergence, and scattered showers have begun to form in response. Coverage and intensity of convection is expected to increase over the next several hours, but a fair amount of uncertainty still exists with regard to how impactful this convection will become (particularly from an excessive rainfall perspective). The mesoscale environment is otherwise characterized by sufficient instability (ML CAPE 500-1500 J/kg), highly anomalous tropospheric moisture content (precipitable water values of 2.1-2.3 inches, between the 90th percentile and the max moving average, per TLH sounding climatology), and very slow shallow to deep layer mean flow of 5-10 kts. The 06z HREF depicts rather concerning 40-km neighborhood exceedance probabilities for 3" and 5" thresholds through 15z (30-50% and 20-30%, respectively). The accompanying probability matched mean (PMM) QPF depicts isolated to widely scattered 3-5" totals, while more recent runs of the HRRR are more isolated and less intense (depicting any 3"+ totals staying mostly offshore). Given the poor performance of the HRRR with yesterdays event, the HREF PMM looks more realistic, though the overrunning and low-level moisture flux convergence is certainly less impressive than yesterday. And while the coverage and intensity of rainfall was quite impressive yesterday, the sandy soils have largely recovered already with 3-hr FFGs averaging between 3-4". This suggests that flash flood impacts will remain rather localized (at least initially), but given the expected slow storm motions and potential for extreme amounts of 5"+, a significant instance or two of flash flooding cannot be ruled out. Churchill ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!8ORk96SA-grvSm9yH4ZW23KH4YEI4KYAfsAZD3lXZoYi6vJsM02fY-6XQ832WntKs7qh= qv7qpt6ihzCATtFW8Pr-t0g$ for graphic product... ATTN...WFO...JAX...TAE... ATTN...RFC...SERFC...NWC... LAT...LON 30838386 30598328 29928269 29358329 29768369=20 29928412 29578483 29668543 30118558 30358529=20 30678452=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) .