Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Mar 17 2024 07:36:44 FOUS30 KWBC 170736 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 336 AM EDT Sun Mar 17 2024 Day 1 Valid 12Z Sun Mar 17 2024 - 12Z Mon Mar 18 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR SOUTHERN LOUISIANA & THE UPPER TEXAS COAST... Organized convection in the vicinity of a front and a surface low, which should lie between southeast TX and southwest LA Sunday=20 morning, is expected to lead to heavy rainfall for portions of the=20 northern Gulf coast, though confidence in how far inland is not=20 overly high at this time due to a generally southerly trend in the=20 guidance QPF when compared to 24 hours ago. Sufficient 850 hPa=20 inflow off of the Gulf of Mexico, up to 40 kts, will lure=20 precipitable water values of 1.5-1.75" into the region and MU CAPE=20 up to 2000 J/kg. However, ML and surface-based CAPE gradients=20 should be coastal and/or just offshore, which is usually a better=20 tool with precipitable water values close to 1.75". Difluence aloft should be fostered by increasing troughing across the Great Lakes, Midwest, and Mississippi Valley. There remains a signal in the=20 guidance for cooling temperatures at 700 hPa, which is of concern=20 as the 1000-500 hPa thickness diffluence appears to be along the LA coast. A mid-level capping inversion won't be present which could=20 allow convection to be outflow-driven more equatorward. This means=20 that there is some chance that organized convection could shift=20 slightly offshore the Gulf Coast at some point in its evolution,=20 leading to decreasing confidence in the heavy rainfall threat the=20 farther east you go along the Gulf Coast. The guidance shows a bit=20 of progression to the convective pattern, as an upper trough=20 sharpens across the Ohio and Mississippi Valleys and helps act to=20 shift the moisture plume/best 850 hPa inflow east with time. Hourly rain totals to 2.5" with local amounts to 5" are possible where=20 limited cell training occurs and/or mesocyclones happen to develop. Because of the heavy rainfall that has occurred recently, the=20 Slight Risk accounts for both the previous couple days of rainfall=20 and the expected rainfall from early Sunday morning onward. The=20 northern portion has been shifted a little south of continuity=20 across portions of southeast LA and southern MS, which was=20 coordinated with the LIX/Slidell LA forecast office. Roth Day 2 Valid 12Z Mon Mar 18 2024 - 12Z Tue Mar 19 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Roth Day 3 Valid 12Z Tue Mar 19 2024 - 12Z Wed Mar 20 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Roth Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9Ni4pyWQfino80fkX7Jgtr3yJUsfWwcnWpNE90nysXek= Kf-_-h13VI3v2yOw26-6Dgd_60Bj9QPz7Uzx2Jwe3JaEutA$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9Ni4pyWQfino80fkX7Jgtr3yJUsfWwcnWpNE90nysXek= Kf-_-h13VI3v2yOw26-6Dgd_60Bj9QPz7Uzx2JweUcZM3PY$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9Ni4pyWQfino80fkX7Jgtr3yJUsfWwcnWpNE90nysXek= Kf-_-h13VI3v2yOw26-6Dgd_60Bj9QPz7Uzx2JwenPu9J00$=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) .