Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jan 25 2023 00:28:20 FOUS30 KWBC 250028 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 727 PM EST Tue Jan 24 2023 Day 1 Valid 01Z Wed Jan 25 2023 - 12Z Wed Jan 25 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY... ....16Z Outlook Update... A convective complex has made its way from southeast Texas during the afternoon into Louisiana early this evening...with some training of cells producing heavy rainfall as the complex interacts with a low-level boundary along the Gulf coast. Areas of 2-5 inch totals are expected with this activity, which should result in a few areas of flash flooding today especially within the Slight risk area. WPC Mesoscale Precipitation Discussion 0048 also addresses short-term convective trends through 0110Z. Given the steady progression of the complex, was able to clear southeast Texas and the Upper Texas coast from the outlook area.=20 The Slight Risk area remains focused along and ahead of the most active convection as shown by the core of coldest cloud tops on satellite. The potential still exists for spotty areas of training/merging of cells especially along the effective cold front/outflow. A few spots of enhanced rainfall rates (>1 inch/hr) are expected where this training occurs, potentially causing issues over sensitive/urbanized areas. Overall QPF trends in the 20-22Z suite of models/CAMs suggests that any flash flood threat should become more isolated with time in response to narrowing of convergent low level flow and gradual loss of MUCAPE. This was reflected in the probabilities from the 24/18Z HREF runs...showing low-end probabilities of 2 inch per hour rainfall rates over Louisiana through 03Z before coming to an end. The HREF probabilities showed decreasing coverage and lower probabilities of 1 inch per hour rates later this evening and into the overnight hours as the system moves into parts of Mississippi and Alabama. It was noted that radar trends by 25/00Z were already ahead of the HREF probabilities...while subsequent runs of the HRRR also started showing more progressive eastward motion. Bann Day 2 Valid 12Z Wed Jan 25 2023 - 12Z Thu Jan 26 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHEAST... ....21Z Outlook Update... The ongoing forecast is generally on track. The 12Z suite of model guidance remains consistent in depicting a linear convective complex entering the western extent of the Marginal risk area at around 12Z Wednesday morning. QPF within this band is progged to total 1.5 inch amounts in a 3 hour period in most coarse-grid model guidance, with locally higher amounts expected. FFGs are quite high especially with southward extent (approaching 4 inches/hr across the Florida Panhandle and southern Georgia.=20 Thus, the flash flood threat should remain tied to localized areas of training atop sensitive/urbanized areas and should not become widespread. Marginal (5%) probabililities remain in place to address the threat. A second area of concern is for increasing rain rates from New Jersey through southern New England after 06Z Thursday. Height falls associated with a distinct, yet weakening shortwave trough over the eastern Great Lakes should combine with strong low-level warm advection and convergence to result in 1+ inch totals over a 3 hour period (locally higher). These values are much closer to the 1.5-2.5 inch/3-hr FFG thresholds across the area, and some concern exists that isolated, urbanized areas could experience minor flooding. A Marginal was added for this update to address the threat. Cook ....Previous discussion... The upper level trough responsible for heavy rainfall in the Lower Mississippi Valley today will begin phasing with a northern stream trough and spread precipitation into the eastern third of the country on Wednesday. Guidance appears to highlight one main area of concern. Moisture continues streaming into the central Gulf Coast and Southeast early Tuesday beneath a potent upper jet and phasing upper trough. Rainfall moving through the Florida panhandle will likely be enhanced by a strong cold front succeeding it. Instability will be shallow in northern Florida and Georgia, but a 50-60kt low level jet out of the south will supply modest moisture, on the order of 1-1.75in PWATs, to flow into the region. That being said, soils will be relatively dry and Flash Flood Guidance fairly high so any flash flooding threats should remain marginal. The heavy rainfall threat should subside over the Southeast by early Thursday evening. Precipitation will begin as snowfall in the Northeast before eventually transitioning into rain. The surface low will reintensify as it lifts through the Mid-Atlantic and Northeast. 60-70kt 850mb winds out of the south will supply anomalous PWATs of 1-1.25in, representing 3-4 standard deviations above normal, into the Northeast coast early Thursday morning. Rain rates between 0.1-0.25 won't be too high, but moisture advection running almost parallel to the surface cold front may cause isolated instances of training and flash flooding over the Tri-State metro area. Kebede Day 3 Valid 12Z Thu Jan 26 2023 - 12Z Fri Jan 27 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Kebede/Cook Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6NpHC-LH2XvujvtY9gbTDatPhoxoJ5nYPSbxdXlyhyDG= bc6ugptNzu1rJNCjvV00o5lqW9jI_4tMzqX01z9nBu4nGtQ$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6NpHC-LH2XvujvtY9gbTDatPhoxoJ5nYPSbxdXlyhyDG= bc6ugptNzu1rJNCjvV00o5lqW9jI_4tMzqX01z9nxojtZOg$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6NpHC-LH2XvujvtY9gbTDatPhoxoJ5nYPSbxdXlyhyDG= bc6ugptNzu1rJNCjvV00o5lqW9jI_4tMzqX01z9nY4gF648$=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) .