Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Sep 30 2023 08:48:34 FOUS30 KWBC 300848 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 447 AM EDT Sat Sep 30 2023 Day 1 Valid 12Z Sat Sep 30 2023 - 12Z Sun Oct 01 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE GREAT BASIN, NEW MEXICO AND FAR WEST TEXAS, UPPER MIDWEST, AND FLORIDA... ....Great Basin/Nevada... A deep upper-trough will transport a plume of moisture (1-2 PWAT stndv) into the West today. A cold front associated with a deepening low pressure system will act as a focus for convection over the Great Basin, in particular. There's been some consolidation and better agreement between the hi-res and global guidance with respect to the location of the axis of heaviest precipitation. Some parts of central Nevada, southeastern Oregon and southwestern Idaho could see rainfall rates around 0.25"/hr with isolated higher amounts. Ample forcing over elevated terrain could lead to more efficient/enhanced rain rates. Between 1-3" of rainfall is expected through tonight. ....New Mexico/west Texas... Convection supported by a deep upper trough to the West and leading shortwave energy will support another localized flash flood threat over parts of eastern New Mexico and into west Texas. Decent instability (1000J/kg+), modest moisture flux and a favorable low level jet may produce bursts of heavy rainfall over our marginal risk area. Urban areas and dry washes are most vulnerable of flash flooding. ....Upper Midwest... An embedded shortwave within an omega ridge will continue driving convection through this afternoon. The heaviest rainfall may already be occurring over parts of eastern Minnesota and northwestern Wisconsin. That being said, impressive forcing, instability (1000J/Kg+) and moisture (2-3 PWAT stndv) could still generate excessive rainfall leading to isolated instances of flash flooding. ....Florida... A slow moving shortwave trough will allow for the continuation of scattered to isolated thunderstorms across the central/southern peninsula today. Some cells may produce localized heavy rainfall within the marginal risk area. Antecedent conditions will also contribute to the sensitivity to any isolated heavy rainfall threats. Kebede Day 2 Valid 12Z Sun Oct 01 2023 - 12Z Mon Oct 02 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF FLORIDA AND THE SOUTHERN HIGH PLAINS OF NEW MEXICO AND TEXAS... ....Southern High Plains of New Mexico/Texas... The deep diffluent pattern over the Great Plains will continue to generate convection in the Southern Plains on Sunday. Instability around 1000J/Kg and PWATs of over 1" could support some instances o flash flooding Sunday afternoon and evening. The global models appear to be well clustered over the Southern High Plains as well, however the past couple of GFS runs appear to suggest that the heaviest rainfall will occur on the southern edge of the marginal risk area so an upgrade is not necessary at this time. Ensemble mean exceedence probabilities of 1" in 24 hours including the 00z GEFS are well clustered over the northeastern New Mexico and the Texas panhandle. ....Florida... Shortwave energy present across the state of Florida will support isolated flash flooding concerns on Sunday. Scattered to isolated thunderstorms will continue to develop along a quasi-stationary front draped across the southern peninsula. There will be plenty of instability in place so there's always the risk of some cells over performing current forecasts with efficient rainfall rates that exceed flash flood guidance. Kebede Day 3 Valid 12Z Mon Oct 02 2023 - 12Z Tue Oct 03 2023 ,...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE SOUTHERN HIGH PLAINS OF NEW MEXICO AND TEXAS... ....Southern High Plains... The Southern High Plains will be under the influence of deep diffluent flow from a potent upper trough propagating through the West on Monday. This will be coupled with the arrival of a strong upper jet aloft and favorable low level jet dynamics. Cape values in the 1000-1500J/Kg range and moisture anomalies well over 2 standard deviations (1-1.5in") should support thunderstorm activity with excessive rainfall potential. The latest guidance has certainly trended wetter and is well clustered over the Southern High Plains region for the location of heaviest rainfall potential. The ensemble mean excellence probabilities are in good agreement for 1 and 2" within the drawn marginal risk area. Mitigating factors for an upgrade at this time include relatively dry soils and high flash flood guidance. Potential severe thunderstorms could overcome the mitigating factors by producing higher rain rates, but there is still some uncertainty around the severe weather threat at this time. Kebede Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!5J6uq5ln7ZhxhBPG5cMIBAuE0Y18RjUadKK_PdmuZSkr= 4ttdJJeIh_mQoEx3KGPZyDdj3Zp9EcnzUyaL78yjD_SvpO0$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5J6uq5ln7ZhxhBPG5cMIBAuE0Y18RjUadKK_PdmuZSkr= 4ttdJJeIh_mQoEx3KGPZyDdj3Zp9EcnzUyaL78yjdG-yQ1Y$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5J6uq5ln7ZhxhBPG5cMIBAuE0Y18RjUadKK_PdmuZSkr= 4ttdJJeIh_mQoEx3KGPZyDdj3Zp9EcnzUyaL78yjeZaqGVU$=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) .