Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Dec 15 2022 01:12:31 AWUS01 KWNH 150112 FFGMPD NCZ000-SCZ000-FLZ000-GAZ000-TNZ000-ALZ000-MSZ000-150710- Mesoscale Precipitation Discussion 1164 NWS Weather Prediction Center College Park MD 811 PM EST Wed Dec 14 2022 Areas affected...Much of AL...Northern and Western GA...FL Panhandle...Adjacent Portions of MS/TN/NC/SC Concerning...Heavy rainfall...Flash flooding possible Valid 150110Z - 150710Z Summary...Isolated to scattered instances of flash flooding will remain possible across much of Southeast through the early overnight hours. Localized rainfall rates as high as 1-2"/hr with additional totals up to 2-3 inches. Discussion...A squall line continues to march eastward across portions of the Deep South this evening, encompassing the bulk of the warm sector of an associated low pressure system currently located over northern AL. This will bring the worst of the rainfall rates (1-2"/hr) to southern AL and the FL Panhandle over the next 6 hours. The mesoscale environment within the warm sector is characterized by wide-ranging MU CAPE of 250-2000 J/kg (maximized across far southern AL and the FL Panhandle), precipitable water values of 1.4-1.8 inches (well above the 90th percentile and near the max moving average per LIX and BMX sounding climatology), and very impressive effective deep layer shear of 50-70 kts. These parameters are likely to continue to sustain deep organized convective well into the night, maintaining the flash flood threat for much of the Deep South.=20 3-hourly totals have been as high as 2-4 inches across southeast LA and southern MS this afternoon, where the best instability and deep layer moisture parameters have overlapped (and resulted in training elements of convection). Localized rainfall rates in this region have generally maxed out at 1-2"/hr, whereas rates have been much more limited (peaking at 0.5-1.0"/hr) north of the warm sector (northern MS/AL) from mainly straiform rainfall. While this alone would suggest that the greatest flash flood risk will exist across the Deep South in association with the best rainfall rates, the antecedent conditions (and associated flash flood guidance) make the situation a bit more complex. This is because the wettest antecedent conditions exist across northern AL/GA and into the Southern Appalachians (southern Middle and East TN into far western NC/SC), per NASA SPoRT LIS relative soil moisture (RSM) as high as 60-75% within the 0-1m layer (as high as the 70-90th percentile). Conversely, much of the Deep South has relatively dry antecedent conditions, with corresponding RSM as low as 20-40% (as low as the 20th percentile or lower). This complex mixture of relatively high rain rates/low soil moisture and relatively low rain rates/high soil moisture (along with an increasingly progressive and gradually weakening squall line) suggest that flash flooding will be possible across a broad area of the Southeast overnight (with isolated to scattered coverage of events anticipated). Localized rates of 1-2"/hr will continue into southern AL and the FL Panhandle through midnight before gradually tapering off, with some additional totals as high as 2-3 inches. Poor drainage areas (including metropolitan areas) will have the greatest risk of realizing flash flooding across the highlighted area, and extra caution should be exercised by motorists during the overnight hours. Churchill ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!6JZaVDsnwvT7yONrUvpnFOEkeJFDdLtEWwKnqahDiOkcCgJuDKP7-yEqYfajyWSZi8Ff= MU3pyzcF7oWPFOP68dBvHfA$ for graphic product... ATTN...WFO...BMX...CAE...FFC...GSP...HUN...LIX...MOB...MRX... OHX...TAE... ATTN...RFC...LMRFC...OHRFC...SERFC...NWC... LAT...LON 35528331 35348261 35148221 34508204 33678275=20 33248348 32488396 31598435 30478455 29788503=20 29738571 30068664 29938787 30228883 31038856=20 31968803 32918772 33738772 34518758 34998693=20 35358605 35518476=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) .