Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Sep 30 2024 20:17:27 FOUS30 KWBC 302017 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 417 PM EDT Mon Sep 30 2024 Day 1 Valid 16Z Mon Sep 30 2024 - 12Z Tue Oct 01 2024 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF EASTERN WEST VIRGINIA AND VIRGINIA... ....16Z Update... No major changes were needed to the ERO Risk areas in the Virginias and North Carolina. A rapidly weakening upper level shortwave will retreat northeastward up the spine of the Appalachians today. This will force additional shower activity with perhaps some convective or thunderstorm development into southern Virginia and North Carolina. Instability will be a major limiting factor as to convective coverage and intensity today. Without it, much of the rain will be mostly shower activity. Low FFGs into central Virginia's Shenandoah Valley are a big contributing factor towards maintaining the Slight, as the northern end of the risk areas has seen forecasted rainfall come down. Meanwhile, for southern VA and NC, any instability that can be generated will support stronger convection in those areas. Much of that will be offset from where FFGs are lowest, keeping the flood threat largely in check. Thus, the best chances of flooding will be in urbanized and low-lying/flood prone areas. Due to rainfall yesterday largely underperforming forecasts, at least in the lowest FFG areas, the internal higher- end Slight area was removed with this update, bringing the entire Slight in the lower end of the category. Wegman ....Previous Discussion... The latest guidance continues to show the south/southeast trend of where the heaviest rain is expected to occur Monday across the Virginias. During this time the slow moving upper low will be transferring its energy to a coastal low feature located offshore Virginia and North Carolina. This will likely lead to a prolonged local enhancement in hourly rainfall rates near the Blue Ridge of 1 to 1.5 inches/hour during this period. Soils near saturation from recent rains will keep the threat for flash flooding elevated for much of this region. A Slight Risk for excessive rainfall remains in effect for extreme eastern West Virginia, northern/central Virginia, and north-central North Carolina. The Marginal Risk was extended to cover much of coastal North Carolina in association with the developing coastal low potentially locally increasing rainfall totals due to slow- moving convection especially on the western side of Pamlico Sound. Campbell Day 2 Valid 12Z Tue Oct 01 2024 - 12Z Wed Oct 02 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR SOUTHEAST VIRGINIA INTO NORTHEAST NORTH CAROLINA AS WELL AS FOR CENTRAL FLORIDA... ....Virginia/North Carolina... A departing mesolow will move off the coast of VA/NC on Tuesday. Periods of heavy rain may continue from Richmond south and east through Hampton Roads and portions of far northeastern North Carolina and the northern Outer Banks. When added to expected rainfall in this region tonight, isolated flash flooding is possible. Much of the rain is expected through about mid-afternoon or so before the low is far enough out into the Atlantic to no longer pose a flooding risk. Thus, a Marginal Risk was introduced=20 with this update. ....Central Florida... A disturbance moving along the stationary front over central Florida may support more widespread shower and thunderstorm activity from Tampa through Orlando to the Space Coast Tuesday afternoon. Training of the convection and impacts with the urban centers may result in isolated flash flooding. Here too a small Marginal Risk was introduced with this update. Wegman Day 3 Valid 12Z Wed Oct 02 2024 - 12Z Thu Oct 03 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6DFxXlusxpX7g3ut4Y4TrUr8-Lbob8CcUiCrzE1xncf4= oxkV1w81xPxskAs_x3Vu7t7z7stxp7iLP0pXUbEBZP9xZQ0$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6DFxXlusxpX7g3ut4Y4TrUr8-Lbob8CcUiCrzE1xncf4= oxkV1w81xPxskAs_x3Vu7t7z7stxp7iLP0pXUbEBSKHyM3Q$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6DFxXlusxpX7g3ut4Y4TrUr8-Lbob8CcUiCrzE1xncf4= oxkV1w81xPxskAs_x3Vu7t7z7stxp7iLP0pXUbEBeuqotNs$=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) .