Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jan 24 2023 19:25:47 FOUS30 KWBC 241925 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 224 PM EST Tue Jan 24 2023 Day 1 Valid 16Z Tue Jan 24 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... With time, an organizing convective complex will increase in size across southeast Texas while interacting with a warm front near the Gulf Coast to produce repeating/training convection and heavy rainfall. Areas of 2-4 inch totals are expected with this activity, which should result in a few areas of flash flooding today especially within the Slight risk area. Recently issued MPD #37 also addresses short-term convective trends through 21Z. The biggest change to the ongoing outlook is to expand the Marginal risk area across portions of central Mississippi, central/southwestern Alabama, and southeastern Louisiana. As the convective complex progresses eastward, spotty areas of training/merging of cells are expected especially along the effective cold front/outflow. As this occurs, a few spots of enhanced rainfall rates (>1 inch/hr) are expected, potentially causing issues over sensitive/urbanized areas. Overall QPF trends in the 12Z suite of models/CAMs suggests that any flash flood threat should become more isolated with time and eastward extent east of the Mississippi River. Cook ....Previous Discussion... A potent and fast moving upper-level low will swing through the Southern Plains and Mississippi Valley today. Strong jet dynamics should support a strong and progressive surface low pressure system propagating from southern Texas through the central Gulf Coast through early Wednesday morning. The upper trough will tap into a reservoir of Gulf moisture (PWATs between 1-2in) and send it streaming into southeastern Texas and the central Gulf Coast. A line of heavy rainfall and thunderstorms are expected to initiate somewhere in southeastern Texas and spread eastward along the Gulf coast where they will encounter some decent instability, with MUCAPE hovering between 500-1000J/Kg, along the immediate coastlines of Texas and Louisiana. A southerly low level jet at around 60kts will provide ample shearing for these fast moving storms. Rainfall rates between 0.75-1.5in/hr over saturated soils and the presence of low FFG will amplify flash flooding concerns for the area encompassed by the Slight Risk. There's potential for parts of the central Texas coast and points inland to over perform their QPF, particularly within thunderstorms, due to favorable dynamics and instability this afternoon. First Guess ERO fields and a number of local offices supported the risk areas drawn for this day 1 outlook. Kebede 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!5jbO4NUVXNqJnjIGJlpPbyPR5Ur_Gy7uz6bfIOdaPniB= n80fz3cRKVump17z0qRfV61lmSiQ-qDUjiVgv1fwK_m5Ahg$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5jbO4NUVXNqJnjIGJlpPbyPR5Ur_Gy7uz6bfIOdaPniB= n80fz3cRKVump17z0qRfV61lmSiQ-qDUjiVgv1fwBkEAnLs$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5jbO4NUVXNqJnjIGJlpPbyPR5Ur_Gy7uz6bfIOdaPniB= n80fz3cRKVump17z0qRfV61lmSiQ-qDUjiVgv1fwJ91tDnc$=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) .