Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Dec 03 2024 18:46:48 FOUS30 KWBC 031846 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 146 PM EST Tue Dec 3 2024 Day 1 Valid 16Z Tue Dec 03 2024 - 12Z Wed Dec 04 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTH TEXAS... ....16z Update... No changes needed to the inherited Marginal Risk, as an isolated instance or two of flash flooding remains possible over portions of South TX. The 12z HREF continues to support the idea of isolated 3-5" totals near the coast (though some members keep nearly all of the deep convection just offshore). Churchill ....Previous Discussion... A moist airmass (characterized by 1.4+ inch PW values) will=20 migrate slowly northwestward through the day along a surface trough located near the south Texas coast. Convergence along that trough=20 axis will support areas of deep convection through the day, with=20 kinematic profiles supporting slow storm motions even as mid-level=20 flow weakens during the forecast period. Isolated spots of 2-4 inch rainfall amounts appear possible per latest CAMS in the Marginal=20 Risk area. Isolated flash flood potential will exist in this=20 regime. Cook Day 2 Valid 12Z Wed Dec 04 2024 - 12Z Thu Dec 05 2024 Western Gulf Coast... Convection is expected to move through portions of eastern TX and=20 LA near a weak area of baroclinic low pressure. While some=20 instability exists near the Upper TX Coast (500+ J/kg of CAPE), the 850 hPa inflow is veering which along with the cyclone's=20 progression argues for convective progression. Precipitable water=20 values are expected to lie mainly in the 1.5-1.75" range. Effective bulk shear and low- level inflow appear sufficient for some level=20 of convective organization, but the progression should keep heavy=20 rainfall modest. The 12z Canadian Regional has local maxima in the=20 4"+ range within LA, the 12z ECMWF has backed off the amounts it=20 advertises across southwest LA. The 12z mesoscale guidance wasn't=20 emphatic on the heavy rain prospects, showing pockets of 20-30%=20 chance of 3"+ amounts. As flash flood guidance values are high due=20 to minuscule rainfall over the past week, the rainfall expected is=20 expected to be mostly welcome and not a significant flash flood=20 concern. While the threat of flash flooding is non-zero should=20 convection train or backbuild, which could lead to 2" an hour=20 totals should it happen, any occurrences would be isolated at best, and the probability of rainfall exceeding flash flood guidance is=20 still considered to be less than 5 percent. Roth Day 3 Valid 12Z Thu Dec 05 2024 - 12Z Fri Dec 06 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Roth/Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-JNPMi0I351-aVI304flnfpOPNh6KFSxGVuZec4s7BCh= mi8SgdjFAbpE3LcLYJUc7l5L8oK1kkDVkj78nZG1NTLjQp0$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-JNPMi0I351-aVI304flnfpOPNh6KFSxGVuZec4s7BCh= mi8SgdjFAbpE3LcLYJUc7l5L8oK1kkDVkj78nZG1PueUiZk$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-JNPMi0I351-aVI304flnfpOPNh6KFSxGVuZec4s7BCh= mi8SgdjFAbpE3LcLYJUc7l5L8oK1kkDVkj78nZG13aWxpnE$=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) .