Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jul 12 2023 06:11:03 AWUS01 KWNH 120610 FFGMPD MNZ000-IAZ000-NEZ000-SDZ000-121200- Mesoscale Precipitation Discussion 0703 NWS Weather Prediction Center College Park MD 210 AM EDT Wed Jul 12 2023 Areas affected...Southeast SD...Northwest to Central IA...Ext. Northeast NEB...Ext Southwest MN... Concerning...Heavy rainfall...Flash flooding possible Valid 120610Z - 121200Z SUMMARY...Progressive developing MCS may have a narrow band of training thunderstorms along the warm advective wing of the complex, posing spots of 2-3" and possible localized flash flooding through early morning. DISCUSSION...RADAR mosaic depicts two linear to slightly bowed convective segments rapidly advancing across central SDak. A weakness/inflection between the two appears to be organizing loosely along the 850mb speed convergence trough that extends southeast at the apex of broad but strengthening LLJ across the Central Plains. A surface boundary extends from S SD across central IA (reinforced by northeasterly flow and sharp Td drop to the northeast). Surface to low level moisture is pooled along the boundary but increase into the Corn Belt/Mid-Missouri River Valley increasing into the 70s across E NEB/W IA. The northeasterly flow is sharpening the isentropic ascent angle and with those increasing LLJ flow of 30-35kts, moisture flux convergence significantly increases from SE SD into IA. As such, updrafts will become much more efficient with 2"+/hr rates for thunderstorms along the line. The problem will be duration as deep layer steering is strong combined with strong ESE propagation vectors adding to forward speed. This should limit overall totals along and south of the developing inflection, though sub-hourly 1.5-2" totals are not out of the realm of possibility and could be an issue for urban or easily prone flashy areas to be overwhelmed. Of greater consideration, strong nearly orthogonal ascent over the sharpened frontal boundary should allow for downstream isolated thunderstorms to develop in advance of the main line, pre-conditioning the soils with 1-2" possible. Additionally, with isallobarically accelerated low level flow along/downstream of the squall line/bowing segments, warm advection/moisture convergence should expand the line a few dozen miles downstream of the main line, particularly along and north of the track of the developing MCS inflection/MCV. As such, localized streaks of trained/repeating cells may generate spots of 2-3"+ totals. Given much will fall in 1-2 hours, isolated spots of 1-3hr FFG exceedance are probable for possible spotty incidents of flash flooding by early morning across the MPD area. Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!58QRDcxJuaI9C7oVs0Oqq6nYx3tRorciYEPnlwSvRVtJuOwCt7CKCwDnrBcmd3u6V0dt= _UDfE0Kc31XZlfre7GY4a20$ for graphic product... ATTN...WFO...ABR...ARX...DMX...FSD...LBF...MPX...OAX...UNR... ATTN...RFC...MBRFC...NCRFC...NWC... LAT...LON 44779902 44299645 43169276 41839274 41389421=20 42169707 43009935 43490021 44180020=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) .