Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Aug 03 2023 00:38:52 AWUS01 KWNH 030038 FFGMPD ILZ000-MOZ000-030630- Mesoscale Precipitation Discussion 0842 NWS Weather Prediction Center College Park MD 838 PM EDT Wed Aug 02 2023 Areas affected...Central & Eastern MO...Southern IL Concerning...Heavy rainfall...Flash flooding likely Valid 030040Z - 030630Z SUMMARY...Widespread thunderstorms developing this evening will train and back-build over parts of the Middle MS Valley overnight. Flash flooding is expected tonight with some areas seeing likely to see significant impacts that include flooded roadways. DISCUSSION...00Z surface analysis showed a frontal boundary that was positioned over central KS and extended east towards the MS-OH River Confluence. The air-mass is particularly hot and steamy to the south and west of the front with dew points in the upper 70s in parts of south-central MO. Farther north, a remnant MCV spiraling over southern IA is responsible for an ongoing cluster of showers and storms over central IL and southeast IA. As the sun sets, 850mb winds over the south-central Plains and Ozarks will accelerate, leading to increased 850mb theta-e advection directly into the frontal boundary. 23Z RAP forecast shows the fetch of southwesterly 850mb moisture transport will only strengthen heading into the overnight hours. There is no shortage of moisture and instability available for developing thunderstorms to generate prolific rainfall rates tonight. As much as 2,000-3,000 J/kg of MLCAPE will be present within the warm sector to the SW of the front. In terms of moisture, PWs will be between 2.0-2.5" over central MO and into southern IL. PWs of this magnitude are uncommon in the Middle MS Valley, as evidence by 12Z NAEFS depicting the PWs present are above the 99th climatological percentile at 00Z and 06Z tonight. Warm cloud layers will also be in excess of 12,000' deep in most cases. Vertical wind shear will only compound the threat for excessive rainfall. 12Z HREF showed a large increase in 0-1km SRH >200 m2/s2 in south-central MO after 00Z, which combined with 0-6km wind shear between 35-50 knots allows storms to develop mesocyclones and sustain them for long periods of time. Hourly rainfall rates above 3" is likely in the most intense cells, with 2" totals falling in as little as 30 minutes also possible. This setup gives rise to organized clusters of rotating thunderstorms following along the frontal boundary and/or the surface trough located near the St. Louis metro area. The 18Z HREF shows a bullseye of 50-80% probabilities for 3-hr QPF to surpass 3-hr FFGs between 00-03Z this evening. The 18Z HREF continues to highlight areas just west of St. Louis for the best odds of flash flooding 03-06Z. This swath of excessive rainfall will stretch as far south and east as the MS-OH Confluence. Areas just west of St. Louis already dealt with flash flooding earlier this morning. Due to the recent CAMs beginning to show the core of heaviest rainfall shifting more into central MO where 3-hr FFGs are as low as 1.5" in some cases, this supported, in collaboration with PAH/LSX/EAX, the upgrade in the ERO to a High Risk this evening. In conclusion, this is likely to be the first in a series of MPDs highlighting the flash flood threat in the mid-MS Valley tonight. Note that the bulk of the flash flooding is likely to occur well after sunset, making flooded roads considerably more difficult to identify. Mullinax ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-z56eukL7A_wEaMIvhUyWXK7_w0nvy-GZIAiOp6Pk9HtRaMOr0AHUuQoB6L8emCiOvqJ= EQDLatmteph6fKpprZ2Mjt8$ for graphic product... ATTN...WFO...EAX...LSX...PAH...SGF... ATTN...RFC...LMRFC...MBRFC...NCRFC...OHRFC...NWC... LAT...LON 39419265 39169071 38788981 37588871 36808950=20 37259084 37779222 38039377 39019404=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) .