Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Nov 10 2024 08:14:28 FOUS30 KWBC 100814 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 314 AM EST Sun Nov 10 2024 Day 1 Valid 12Z Sun Nov 10 2024 - 12Z Mon Nov 11 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS CENTRAL AND SOUTHWEST LOUISIANA... Southwest and Central Louisiana...=20 Moisture and instability from the Gulf gets advected from the=20 vicinity of Raphael northwest to north across portions of the=20 Central Gulf Coast through the Tennessee Valley. A slowly=20 advancing convective complex early this morning across southwest LA is drifting eastward, showing hourly rain totals to 3" and=20 isolated totals to 13" thus far over portions of Allen Parish.=20 There is concern that this complex could hold together past 12z,=20 which is part of the reason for the upgrade to a Slight Risk, after coordinating with the LCH/Lake Charles LA forecast office.=20 Additional activity could form behind it closer to a surface=20 boundary in TX (could be forming at the present time) which is=20 expected to advect eastward during daytime heating. Moderate Risk=20 level impacts cannot be ruled out should such thunderstorm activity persist over recently saturated soils into this afternoon. Southeast Louisiana... The guidance broadly remains unclear as to whether heavy rainfall=20 gets too far ashore southeast LA while mesoscale guidance shows the complex to the west fizzling as it moves into the region.=20 Precipitable water values of 1.5-2" Sunday morning across southeast LA advect offshore with time, which should limit heavy rainfall=20 concerns. Still, hourly rain totals to 2" and local totals to 4"=20 are possible on an isolated basis should storms backbuild or train. Interior Southeast/Mid-South/Tennessee Valley...=20 The forward progress of the front should keep any excessive=20 rainfall concerns minimal in areas a bit north of the Gulf Coast=20 -- some of the risk area from eastern AR to the east-northeast just south of the OH river accounts for recent rains/some soil=20 saturation. In this more northern portion of the Marginal Risk=20 area, hourly totals up to ~1" with local totals to 2" appear to be the maximum potential. A decent amount of the area within the=20 Marginal Risk would find the forecasted rainfall welcome. Changes to continuity were to shave off some of the northeast=20 portion of the Marginal Risk area, using 00z HREF probabilities of=20 0.5"+ as a guide, and include some of far southeast Texas to=20 account for the limited QPF signal there as soils are a bit more=20 sensitive after the past 24-36 hours of heavy rainfall. Central and Southeast LA remain within the Marginal Risk for similar reasons,=20 concerns about locally heavy rains over saturated soils from recent heavy rain. The 00z HREF had low, but existent, probabilities of 3"+ during the day 1/Sunday morning into early Monday time frame. Roth Day 2 Valid 12Z Mon Nov 11 2024 - 12Z Tue Nov 12 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Roth Day 3 Valid 12Z Tue Nov 12 2024 - 12Z Wed Nov 13 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN AND NEAR WESTERN WASHINGTON... Precipitable water values of 0.75-1" advect in as a cold front=20 approaches, perhaps moves ashore, the Washington and northern Oregon coast Wednesday morning. Inflow from the Pacific rises to=20 60 kts at 850 hPa out of the south-southwest with limited=20 instability available near and behind the front. The ingredients=20 appear to be there for hourly rain totals of 0.5"+, which would be most problematic in burn scars. Over the full day, local amounts=20 of 3-4" are advertised for much of the guidance, which would be=20 most problematic along the Skokomish river in the Olympic=20 Peninsula. Enough was there in the guidance for the inherited=20 Marginal Risk area to remain from continuity; simplified its shape. Roth Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8c-A0rdsMNZHVCH_SQet2G_MU0xkzZQqC_u6LIHna_FO= UNqMq6sJ_nc0OXQLdtHhXqhkptLrti1E36fdzEIjQq_mAkw$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8c-A0rdsMNZHVCH_SQet2G_MU0xkzZQqC_u6LIHna_FO= UNqMq6sJ_nc0OXQLdtHhXqhkptLrti1E36fdzEIjByybvPg$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8c-A0rdsMNZHVCH_SQet2G_MU0xkzZQqC_u6LIHna_FO= UNqMq6sJ_nc0OXQLdtHhXqhkptLrti1E36fdzEIjwGJxl7c$=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) .