Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Feb 18 2025 15:40:54 FOUS30 KWBC 181539 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1039 AM EST Tue Feb 18 2025 Day 1 Valid 12Z Tue Feb 18 2025 - 12Z Wed Feb 19 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG PORTIONS OF THE CENTRAL GULF COAST... ....16Z Outlook Update... The ongoing forecast is generally on track and no changes are needed to the Marginal Risk area. Model consensus is that widespread areas of 1 inch rainfall totals are expected across east-central Texas into western Louisiana, and higher amounts (in the 2-3.5 inch range) are expected from far southeast Texas through southeastern Louisiana especially in the 00Z-12Z period. The greatest buoyancy will be confined to coastal areas, and training/repeating cells could result in local 1-2 inch/hr rain=20 rates at times and pose a risk of excessive runoff -- especially if that rainfall can materialize in/near urbanized areas. Nearer-term convective trends will be monitored for any potential focus of=20 intense rainfall rates that may require a small Slight Risk upgrade -- especially across south-central and southeastern Louisiana overnight. See the previous outlook below for more information. Cook ....Previous Outlook... Strengthening southwesterly return flow from the Gulf ahead of an=20 amplifying upper-level shortwave and an associated surface cold=20 front are expected to draw deeper moisture into portions of the central Gulf Coast with PWs climbing to 1.5"+. This moisture,=20 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).=20 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.=20 Churchill 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.=20 Churchill Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_HaQ4YSrJu_-K0rwCchUp9rudT3xlErpEgMRKbcDLKi3= lO1g0MsDOJMFANIJ4zwiU0sT-u-20pgpaV-SR1N8wY-kg10$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_HaQ4YSrJu_-K0rwCchUp9rudT3xlErpEgMRKbcDLKi3= lO1g0MsDOJMFANIJ4zwiU0sT-u-20pgpaV-SR1N8SEvfz7E$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_HaQ4YSrJu_-K0rwCchUp9rudT3xlErpEgMRKbcDLKi3= lO1g0MsDOJMFANIJ4zwiU0sT-u-20pgpaV-SR1N8kouQtEI$=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) .