Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Feb 19 2025 00:58:28 FOUS30 KWBC 190057 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 757 PM EST Tue Feb 18 2025 Day 1 Valid 01Z Wed Feb 19 2025 - 12Z Wed Feb 19 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG PORTIONS OF THE WESTERN AND CENTRAL GULF COAST... ....01Z Outlook Update... Made minor tweaks to the Day 1 Marginal Risk area, based on the current mesoanalysis and latest trends in the high res guidance. Based on the instability trends from the current mesoanalysis and latest RAP output, along with the 18Z HREF exceedance=20 probabilities (including >1"/hr rainfall rates), have trimmed the=20 western and northwestern areas a bit across portions of eastern TX and western-northern LA. Thermodynamic parameters and more intense rainfall rates this evening and overnight will favor an isolated risk for flash flooding from the Upper TX Coast eastward through southern LA (southern half), southern MS, and southern AL.=20 Hurley ....Discussion... Strengthening southwesterly return flow from the Gulf ahead of an amplifying upper-level shortwave and an associated surface cold front are expected to draw deeper moisture into portions of the central Gulf Coast with PWs climbing to 1.5"+. This moisture, along with increasing lift (via right-entrance region of 120+ kt subtropical jet streak) and marginal instability (MU CAPE rising to near 500 J/kg right along the immediate coast) are likely to be sufficient for a relatively short period of heavy rainfall rates (concentrated between 00-09z, and lasting for around 3 hours total at any one locality). While the potential for training storms looks relatively low (with instability largely lacking prior to the arrival of the progressive storms along the front), chances for any isolated flash flooding appear maximized in the vicinity of Lake Charles (with the best instability resulting in highest odds for 1-2"/hr rainfall rates, and localized totals of 2-4" over a 3-hr period). Elsewhere (and particularly farther north from the immediate coastline) rates will likely struggle to surpass 1"/hr with a lack of instability, though in some places these brief downpours may be enough to cause localized excessive rainfall (particularly into portions of east-central TX and west-central LA where antecedent conditions are wetter, especially compared to relatively dry antecedent conditions in south-central LA). Churchill Day 2 Valid 12Z Wed Feb 19 2025 - 12Z Thu Feb 20 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Orrison Day 3 Valid 12Z Thu Feb 20 2025 - 12Z Fri Feb 21 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Orrison Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9pGfDzNrKltZoDgdsBFMsuER_-8rnkVDr2Mi1zxKffb0= exRi3wEPsMPh5xeJycPglMx4UdzCc75wgq8485N52xivF6Q$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9pGfDzNrKltZoDgdsBFMsuER_-8rnkVDr2Mi1zxKffb0= exRi3wEPsMPh5xeJycPglMx4UdzCc75wgq8485N5vQsSETk$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9pGfDzNrKltZoDgdsBFMsuER_-8rnkVDr2Mi1zxKffb0= exRi3wEPsMPh5xeJycPglMx4UdzCc75wgq8485N5PJcciWM$=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) .