Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Apr 13 2023 08:18:50 FOUS30 KWBC 130818 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 418 AM EDT Thu Apr 13 2023 Day 1 Valid 12Z Thu Apr 13 2023 - 12Z Fri Apr 14 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHEAST... The closed, deep layered low centered over southern Louisiana early this morning will begin to lift north/northeastward today into tonight, taking on a negative tilt later in the period as it becomes absorbed ahead of the approaching longwave trough back over the Plains. A broad area of ascent will be found across the Southeast along and downstream of the advancing low while at the surface, a warm front begins to lift northward through Florida into Georgia. Moist easterly flow ahead of that boundary and then southwesterly flow in its wake overrunning the boundary will bring a surge of higher moisture through the region, characterized by PWs of 1.25-1.5". With roughly 1000 J/kg of CAPE present overlapping with the higher moisture, the ingredients are in place for pockets of locally heavy rainfall and intense rain rates (locally exceeding 1-1.5"/hr) from the central Gulf Coast through portions of the Southeast. While most of the convection is likely to be somewhat progressive with a fast mean flow, the unidirectional mean flow and higher 850 mb inflow suggests some potential for backbuilding. Localized totals of 2-4" appear likely within the Marginal Risk. Generally this is over areas with higher flash flood guidance, thus only expected isolated/localized instances of flash flooding. For this issuance, the Marginal Risk was expanded to cover the urbanized corridor of southeast Florida, where extreme rainfall occurred yesterday/last evening. While the 00Z hi-res guidance and HREF suggests greater risk of intense rainfall will be further north along the FL Peninsula, there is a signal that a trailing convergence area could focus additional afternoon/evening thunderstorms again over S. Florida. Taylor Day 2 Valid 12Z Fri Apr 14 2023 - 12Z Sat Apr 15 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE CAROLINAS... The deep mid/upper level low will begin to open up and weaken as it progresses further to the northeast Friday into Friday night, though with the anomalous moisture in place (upwards of 1.5" PWs) and available instability (1000 J/kg CAPE), locally intense rainfall will be possible across initially the SC Piedmont initially the reaching the NC Piedmont late morning. A secondary round of convection is possible during the afternoon/early evening associated with the main upper level shortwave moving overhead. The combination of steeper lapse rates and peak heating could bring another round of heavier showers and thunderstorms. Rain rates of 1-2"/hr at times both in the morning and afternoon rounds will be possible and the latest deterministic and ensemble guidance shows potential for isolated 2-3" totals. Recent rainfall has primed the soils somewhat and makes the area a little more susceptible to flooding with both soil moisture and streamflows running 75-90 percent above average for mid-April. The combination of the wetter soils over the more urbanized areas of the SC/NC Piedmont may lead to a few instances of flash flooding during the period. Taylor Day 3 Valid 12Z Sat Apr 15 2023 - 12Z Sun Apr 16 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE LOWER MISSISSIPPI VALLEY... Locally heavy rainfall capable of producing flash flooding will be possible Saturday into Saturday night across portions of the Lower Mississippi River Valley. The synoptic setup is expected to feature subtropical jet positioned through the Gulf with an embedded shortwave trough expected to pass through during the first part of the period helping to provide the large scale forcing for ascent. Meanwhile, low level southerly flow ahead of that wave should draw up anomalously high moisture, characterized by PWs exceeding 1.5", possibly as high as 1.75" across the southern portions of Louisiana, Mississippi, and Alabama. With upwards of 30-35 kts of inflow at 850 mb and plenty of instability, locally intense rainfall will be possible. Later in the period, Saturday night, a stronger shortwave trough originating out of the Central Rockies will approach the region. Convection is expected to develop along an advancing cold front between 00Z-12Z Sunday, likely over portions of the ArkLaTex eastward toward central Mississippi. The environment characterized by strong low level moisture transport and sufficient instability will support locally heavy rainfall of 1" to locally 3" over an area that is more sensitive/susceptible to heavy rainfall with recent rainfall departures running 200-300 percent of normal and streamflows above normal as well. Given the expected heavy rainfall over areas with wetter antecedent conditions, the Marginal Risk was expanded northward to include portions of northern Louisiana into west-central Mississippi for the possibility of isolated/scattered instances of flash flooding. Taylor Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4KeVKt4l9JZrJVKv3Pm0EGbj7HaPU8V9U8_P4r-h4vjz= u40Ve3x2XngkkhSvvoT7GyxupG2V2ucAmXZovykNG-FcVcA$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4KeVKt4l9JZrJVKv3Pm0EGbj7HaPU8V9U8_P4r-h4vjz= u40Ve3x2XngkkhSvvoT7GyxupG2V2ucAmXZovykNZfpL_mo$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4KeVKt4l9JZrJVKv3Pm0EGbj7HaPU8V9U8_P4r-h4vjz= u40Ve3x2XngkkhSvvoT7GyxupG2V2ucAmXZovykN85kdzoo$=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) .