Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Apr 19 2025 15:52:12 FOUS30 KWBC 191550 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1150 AM EDT Sat Apr 19 2025 Day 1 Valid 16Z Sat Apr 19 2025 - 12Z Sun Apr 20 2025 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FROM NORTH- CENTRAL TEXAS THROUGH MUCH OF SOUTHERN MISSOURI... ....16z Update... Forecast remains largely on track with only minor adjustments necessary based on the new suite of guidance (mainly 12z HREF). Aside from tightening the gradients with increasing confidence in the overall QPF footprint, also expanded the Slight and Marginal risk contours farther to the south (into the Hill Country and south-central portions of TX) given the potential for vigorous convection originating near the dry line. Overall, confidence has increased with regard to the Moderate risk area, and particularly so with localized totals of 5"+ across southeastern OK and adjacent portions of far north TX and northwestern AR (per 12z HREF 40-km=20 neighborhood probabilities for 5" and 8" exceedance of 30-60% and=20 ~10%, respectively). Significant, life threatening flash flooding is possible through this region with 1-3" localized totals having already occurred over the past 24 hours (with associated Flash=20 Flood Guidance over a 6-hr period ranging from 2.0-4.0"). Across=20 southern MO the Moderate risk was maintained, particularly due to=20 much more sensitive/vulnerable antecedent conditions with 2-4"=20 totals much more widespread over the past 24 hours (with associated Flash Flood Guidance of 2.0-2.5") and high confidence in relatively widespread coverage of 2" exceedance (per HREF 10-100km Ensemble=20 Agreement Scale neighborhood probabilities of 50-70%).=20 Churchill ....Previous Discussion... A narrow corridor of 4 to 6+ inches of rainfall likely today across southern Missouri to North-central Texas as thunderstorms train and backbuild along a slow moving/stalled frontal boundary. There has been a consistent and persistent westward trend of the placement of the heaviest rainfall both in the model runs and the deterministic WPC QPF. Once again the risk areas were expanded south and west. The Moderate Risk spans from north-central Texas to the Missouri Ozarks; which had a minor reduction in coverage out of Illinois given the decrease in QPF from the Mid-Mississippi Valley to Ohio. The Slight Risk was also reduced over parts of Illinois and Indiana while extended further into central Texas. The Marginal was trimmed southward across Illinois, Indiana and Ohio while adjusted westward of west-central Texas. On the north side the cold, dry northeasterly flow will be weakening while in the warm sector there will be an ever increasing supply of hot and humid air straight out of the Gulf being advected northward on up to 50 kt winds across Texas and into the frontal interface from north Texas through Oklahoma and Missouri. An upper low ejecting from the mountains into this hot, moist airmass will lead to robust cyclogenesis over Oklahoma by Sunday morning. Campbell Day 2 Valid 12Z Sun Apr 20 2025 - 12Z Mon Apr 21 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE CENTRAL PLAINS AND PORTIONS OF THE MIDDLE AND LOWER MISSISSIPPI VALLEY... The system responsible for the scattered to widespread heavy/excessive rainfall on Saturday will begin to accelerate to the northeast as the upper trough begins to fill. Rainfall amounts should not rival amounts that are expected on Saturday, but additional rainfall on top recently flooded areas remains a potential concern. General model consensus shows a broad footprint of up to 1.25 inches with isolated maximums of 1.5 to 2+ inches anywhere from eastern Nebraska to southern Minnesota and Wisconsin. The exact location of the heaviest amounts has the greatest uncertainty. A Marginal Risk is in place for the Middle and Lower Mississippi Valley and eastern portions of the Central Plains. These areas are north and west of the most sensitive areas of the Mississippi/Ohio River Valleys where streamflows remain high after recent flooding. However, some rain atop recently flooded areas, and runoff from other areas into these rivers, could exacerbate ongoing flooding issues in some areas, so continue to monitor. Campbell/Bann Day 3 Valid 12Z Mon Apr 21 2025 - 12Z Tue Apr 22 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Campbell Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-bcynmWfYhQdXmWqRwHWvxozQk_xSZq_yizmDuf1Ln_V= pyGC3sgL6yVJ7A4LnNgZpDjgPoR3xhVpEW6G98LZu08DuHs$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-bcynmWfYhQdXmWqRwHWvxozQk_xSZq_yizmDuf1Ln_V= pyGC3sgL6yVJ7A4LnNgZpDjgPoR3xhVpEW6G98LZLuIRdYM$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-bcynmWfYhQdXmWqRwHWvxozQk_xSZq_yizmDuf1Ln_V= pyGC3sgL6yVJ7A4LnNgZpDjgPoR3xhVpEW6G98LZsfn09Sg$=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) .