Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jan 22 2023 00:54:07 FOUS30 KWBC 220054 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 753 PM EST Sat Jan 21 2023 Day 1 Valid 01Z Sun Jan 22 2023 - 12Z Sun Jan 22 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE GULF COAST... A localized flash flood risk may develop later tonight across portions of coastal AL into the FL Panhandle, where a Marginal risk will be maintained. A warm front lifting north across the Gulf of Mexico should approach the coastline later tonight, bringing with it an increase in surface based instability. Meanwhile 850mb south southwesterly winds will increase into the 30-50 kt range, approximately equal to and aligned with the deeper layer mean winds. So in addition to the moisture transport associated with these winds, the flow is also supportive of some backbuilding/training potential near the coast. Sill not completely clear how things will evolve, but the 18z HREF and other guidance does indicate a decent chance of localized 3"+ rainfall totals by 12z within the Marginal risk area. FFG is quite high across the region, so even rainfall of this magnitude may not be enough to cause much of a flash flood concern, but with some training potential and indications in most guidance of deep convection getting onshore, can not rule out some localized flash flood concerns by 12z Sunday. We opted to remove the northern extent of the Marginal risk with this update. Stronger deep layer ascent here will support an axis of 1-2" of rain through 12z in spots...however a lack of instability should keep rainfall rates generally 0.5" in an hour and less. Thus not thinking these rates or the overall rainfall totals will be enough to cause anything more than some areas of ponding water. Thus we opted to focus the Marginal risk closer to where the better instability and warm front has a greater chance of producing higher rainfall rates and totals later tonight. Chenard Day 2 Valid 12Z Sun Jan 22 2023 - 12Z Mon Jan 23 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHEAST... ....2030Z Update... Some notable changes were made to the ERO for the Sunday time period. The axis of heaviest rainfall associated with this event has been shifting south, and note that there is an ongoing moderate drought across nearly all of the coastal Carolinas into the Virginia Beach area. Due primarily to these factors, the inherited Marginal Risk was trimmed significantly towards the south, in coordination with the AKQ/Wakefield, VA and RAH/Raleigh, NC forecast offices. The current Marginal Risk area follows the heaviest QPF in the latest WPC forecast as well. Another primary limiting factor across NC and VA is a lack of instability, which will struggle even to get to 500 J/kg of MUCAPE. There was even some pause given to the severe drought ongoing across portions of the eastern FL Panhandle, but more abundant moisture and some preconditioning of the soils from tonight's convection may mitigate that. Overall, the threat appears to be even on the low side of the Marginal Risk (closer to 5%), and continued lowering of QPF in this area in the guidance should result in the consideration of removal of the Marginal Risk altogether. PWATs in this area have come down a bit closer to the 1.5", and local and brief rainfall rates around 1/2 inch/hour remain possible, but these rates are unlikely to overcome high FFGs, dry soils, and aforementioned drought conditions in any except the most vulnerable risk areas. Wegman ....Previous Discussion... A southern stream system will phase with a northern stream trough over the Ohio/Tennessee Valley on Sunday. Mid-level flow out of the South will continue to supply moisture advection into the Southeast and eventually up the East Coast later into Monday morning. There's a decent signal for a line of convection to develop along a strengthening cold front and deepening low pressure system moving from the central Gulf Coast to Southeast coast late Sunday afternoon into the evening. PWATs between 1.5-2" and rainfall rates between 0.25-0.5in/hr may form along the axis of enhanced frontogenesis linked to convection/instability Sunday evening. The latest deterministic guidance is in reasonable agreement with the orientation and magnitude of the maximum qpf stripe extending from the Florida Panhandle to the Carolina coast. The GFS and EC have had great run-to-run consistency with respect to their 24 hour totals along the East Coast. The 00z NAM and 00z UKMET appear to be on the northern and southern extent, respectively, of the 00z suite of guidance with respect to their axis of greatest qpf. Kebede Day 3 Valid 12Z Mon Jan 23 2023 - 12Z Tue Jan 24 2023 ....2030Z Update... The probability of rainfall exceeding flash flood guidance is less than 5 percent. The inherited Marginal Risk across a swath of Texas was removed with this update. There has been a notable decrease in nearly all of the guidance of rainfall expected to occur in this area during this period. As such, the chance of excessive rains has diminished below criteria. Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_Jh2JRyeFbw0TWQkyARKn8TBzZURTMXD9iI7kqkt5ZXP= hE8ebTqHeoBX94FemfnBCljboMDOQVYwbN0ClBF6imEj7f0$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_Jh2JRyeFbw0TWQkyARKn8TBzZURTMXD9iI7kqkt5ZXP= hE8ebTqHeoBX94FemfnBCljboMDOQVYwbN0ClBF6qn5xJKw$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_Jh2JRyeFbw0TWQkyARKn8TBzZURTMXD9iI7kqkt5ZXP= hE8ebTqHeoBX94FemfnBCljboMDOQVYwbN0ClBF62Mgc_JI$=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) .