Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Sep 02 2024 15:58:54 FOUS30 KWBC 021558 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1158 AM EDT Mon Sep 2 2024 Day 1 Valid 16Z Mon Sep 02 2024 - 12Z Tue Sep 03 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE HILL COUNTRY/CENTRAL TEXAS AND ALONG THE TEXAS GULF COAST... ....16Z Update... ....North Central Texas... No significant changes were made to the inherited ERO risk areas. Heavy rain ongoing across the area will continue through the day. The CAMs guidance has continued to increase across the Hill County and portions of central Texas, generally west of Ft. Worth, southeast of Lubbock, and around and northeast of San Angelo. For that reason, that area of north central Texas is considered in a higher-end Slight risk. Widely scattered to scattered instances of flash flooding are probable with locally significant and considerable flash flooding possible. The rocky soils and some terrain will convert much of the rainfall into runoff...increasing the potential for flash flooding. ....Texas Gulf Coast... The inherited Slight Risk along the Texas Gulf Coast remains largely the same, with minor tweaks this morning. Heavy rainfall associated with westward moving convection with a stationary tropical low may cause localized flash flooding, particularly in any low-lying and urban areas today. Thus far the most organized convection has been stationary over Galveston, extending west to the south of Houston. However, these kinds of localized heavy rains that may train will continue to be a flooding concern for the rest of the day into tonight.=20 ....Carolinas... The biggest change to the ERO this midday is to trim nearly all of SC and GA out of the Marginal Risk. The heaviest rains today are now expected to remain offshore of SC and GA based on the latest CAMs guidance. Heavy showers are impacting the North Carolina beaches and the southern Outer Banks, which remain in a low-end Marginal, but once again the vast majority of the heaviest rains are expected to remain offshore over the Gulf Stream. Wegman ....Previous Discussion... ....Texas... An upper level trough with a mid-level vort will be advancing into western Texas during this period. Meanwhile a surface low hugging the South Texas Coast will maintain easterly flow from the Gulf allowing PW values of 2+ inches to pool over much of the state. The latest guidance continues to depict areal averages of 1 to 5 inches of QPF across the Hill Country into east-central Texas and along much of the Texas coastline. Recent rainfall has increased soil saturation across the state thus lowering FFGs. The hi-res guidance is showing training of slow moving convection capable of 1 to 2.5 inches/hour rain rates which could easily lead to scattered areas of excessive rainfall and localized flash flooding. A Slight Risk areas remains in effect for west-central and central Texas. Additionally, a Slight Risk was added for the coastline today where storms will be producing rates of 1 to 3 inches/hour. ....Carolinas... A cold front sinking through the Mid-Atlantic region will continue to move showers and thunderstorms southward over the Carolinas today. Guidance keeps the bulk of the QPF offshore during this period where there are better dynamics in place however there will still be an isolated threat for localized excessive rainfall and flooding. A Marginal Risk area was maintained for eastern portions of the Carolinas. Campbell Day 2 Valid 12Z Tue Sep 03 2024 - 12Z Wed Sep 04 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF CENTRAL TEXAS... ....Texas... The mid-level vort is expected to exit the region although precipitable water values will remain high (+1 to +2 sigma initially, then decreasing late Tuesday). A large portion of the flooding potential will be contingent on a verified forecast from Day 1/Monday, as Monday will have the heavier rain/stronger storms of the two days. However, even the lesser amounts of rain expected Tuesday should still cause flooding issues in the area with a widespread 1 to 1.5 inches forecast with locally higher amounts. A Slight Risk remains in effect for central portions of the state. The heaviest rains in the state are expected to be along the Gulf Coast from Galveston south and west through Corpus Christi. Locally heavy rains to 2 inches per hour will be possible. For now the greatest flooding threat remains confined to any urban areas, but should Monday's rains overperform here then a Slight may be needed for the hardest hit areas with future updates. ....Idaho/Montana... A potent shortwave trough will interact with up to 2 sigma above normal atmospheric moisture on Tuesday. PW values rising to near 1 inch will support storms capable of heavy rain that may produce isolated flash flooding should the storms impact particularly flood sensitive or more urban areas. Campbell/Wegman Day 3 Valid 12Z Wed Sep 04 2024 - 12Z Thu Sep 05 2024 ....Gulf Coast and Lower Mississippi Valley... The influx of anomalous Gulf Moisture will persist all across the southern tier states while the upper trough and vort exits the plains and into the Mississippi Valley. The surface front will continue to be draped west to east across the South continuing to provide focus for showers and thunderstorms across the region. During the late afternoon and evening hours there will be an intensification of instability and forcing to boost rainfall rates across the Lower Mississippi Valley, particularly over Louisiana, western Mississippi and southeast Arkansas. Most of the guidance are suggesting that 1 to 3 inches will concentrate over this part of the region thus increasing the risk for excessive rainfall and local flooding potential. There is the potential for a few locations for local maximums to exceed 6 inches near northern Louisiana/Arkansas. Onshore flow across southeast Louisiana and southern Mississippi could yield 1 to 4 inches as well. A Slight Risk area was raised for parts of Louisiana, Mississippi and Arkansas. Campbell Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_7CyrNKaYOT9oGTZMe8vlyp70pGGyQ0ZeOvcTXz4luM3= ECci04buLnMQXXnIXtBJEwink9vGOwhJn09ElxGgzFg0pN0$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_7CyrNKaYOT9oGTZMe8vlyp70pGGyQ0ZeOvcTXz4luM3= ECci04buLnMQXXnIXtBJEwink9vGOwhJn09ElxGgR_hn7dM$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_7CyrNKaYOT9oGTZMe8vlyp70pGGyQ0ZeOvcTXz4luM3= ECci04buLnMQXXnIXtBJEwink9vGOwhJn09ElxGgNieyaBw$=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .