Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Nov 28 2022 19:19:00 FOUS30 KWBC 281918 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 218 PM EST Mon Nov 28 2022 Day 1 Valid 16Z Mon Nov 28 2022 - 12Z Tue Nov 29 2022 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman Day 2 Valid 12Z Tue Nov 29 2022 - 12Z Wed Nov 30 2022 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE LOWER MISSISSIPPI AND TENNESSEE VALLEYS AND FOR MUCH OF ALABAMA... ....1930Z Update... Few changes needed with this update. A severe weather outbreak remains likely over most of the northern and western portions of the risk areas. Any repeating supercell thunderstorms will easily have the capability of locally producing 3 inches/hour rainfall rates, albeit for a short time in any one location due to storm movement. According to most of the CAMs, these thunderstorms will persist mainly across Mississippi well into the overnight hours. By around midnight or so, the storms will likely congeal into 1 or 2 squall lines. They will still be strong enough to cause local flash flooding, especially given the moist soils from recent rains over far southern MS & AL but forward speed will be a mitigating factor. That said, there may be some stalling of that squall line over far southern MS & AL, but a bit inland from the coast. If that happens the flash flooding threat locally could be substantially higher. Wegman ....Previous Discussion... A strong shortwave trough ejecting out into the Plains Tuesday will induce deepening cyclogenesis over the Upper Midwest with an associated cold front progressing across portions of the lower Mississippi Valley. The presence of a strong upper-level jet, especially positioned in the favored right entrance region over the Southern Plains, will help bring widespread forcing for ascent across the region. Scattered to widespread thunderstorms is expected to fire up across the Lower Mississippi Valley, the Deep South and into portions of the Tennessee Valley as this is where PW values upwards of 1.5 inches (~2+ std dev) will be streaming northward and encountering an axis of sufficient instability lifting northward with MUCAPE of 1000-2000 J/kg possible. A surge in the low level winds/moisture over portions of eastern Louisiana, Mississippi and Alabama will help support and maintain multiple hours of enhanced rainfall rates of 1 to 2+ inches/hour. For Tennessee and areas north into the Ohio River Valley, dry antecedent conditions, less moisture and weaker storms should keep any training convection to just isolated instances of flash flooding. However, the Lower Mississippi Valley and the Gulf states will be more sensitive to flash flooding and ponding, especially in urban areas. These storms will be capable of producing intense rain rates of 1-2"+/hr and there is some training signal given the southwesterly/southerly mean flow orienting somewhat parallel to expected storm motions. The latest guidance is showing some of the higher QPF spreading further into northwest Georgia and southern/southeast Tennessee. There is the potential for a broad areal average of 1-2" with some signal for isolated 3-4"+ totals during the period. Soil moisture varies from drier than normal across the Tennessee and Ohio Valleys while further south near the Gulf Coast, above normal precipitation over the last few days has brought the top 40 cm soil layer saturation to above 80-90 percent in places. This lead to the eastward expansion of the Slight Risk area that was already in effect. Campbell/Taylor Day 3 The Day 3 outlook will be updated by 2030Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_LvdILXnXDr7kpXuKkjBGWLR4wLIi4iI3w7lnsdZxhQS= 86R2rL98KckV5zzCyC1wcSyLrC9evFyrxbCGq1o-YbuNuro$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_LvdILXnXDr7kpXuKkjBGWLR4wLIi4iI3w7lnsdZxhQS= 86R2rL98KckV5zzCyC1wcSyLrC9evFyrxbCGq1o-b9p_eV4$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_LvdILXnXDr7kpXuKkjBGWLR4wLIi4iI3w7lnsdZxhQS= 86R2rL98KckV5zzCyC1wcSyLrC9evFyrxbCGq1o-R1U7W_g$=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) .