Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Nov 13 2022 00:08:52 FOUS30 KWBC 130008 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 708 PM EST Sat Nov 12 2022 Day 1 Valid 01Z Sun Nov 13 2022 - 12Z Sun Nov 13 2022 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Bann Day 2 Valid 12Z Sun Nov 13 2022 - 12Z Mon Nov 14 2022 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Orrison Day 3 Valid 12Z Mon Nov 14 2022 - 12Z Tue Nov 15 2022 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS THE UPPER TEXAS COAST AND CENTRAL GULF COAST... 2030Z Update The changes to the ERO for this update include just some trimming of the northern periphery of the Marginal Risk area based on some southward shift in the axis of heaviest QPF and somewhat lesser amounts. The 12Z NAM appears to be a tad too strong with the shortwave trough and corresponding surface wave, with the global model consensus otherwise in rather good agreement with the mass field details. The support remains strong for an axis of rather robust convection to evolve near the Gulf Coast as this energy traverses the region, but the core of the strongest convection (and thus heaviest rainfall totals) may tend to be just offshore over the northern Gulf Coast close in proximity to the frontal placement and ultimate track of the surface low. Orrison Previous Discussion... By the day 3 timeframe, return flow out of the western Gulf of Mexico ahead of an approaching vigorous shortwave over the southern Plains will set the stage for potentially excessive rainfall extending from the Upper Texas Coast to southern Louisiana and eventually southern Mississippi and Alabama by the evening hours. PWATs over 1.5" and dew points into the 60s are forecast to push just inland with the help of a slow-moving warm front and 50 kt low-level jet. This moisture source will be short-lived and struggle to push well inland as a fast moving cold front kicks the convection eastward Monday night. The best intersection of instability, moisture, and shear along the warm front is likely to be near far southwestern Louisiana. So it is likely that is area will be monitored for a potential upgrade. Current QPF depicts widespread 1-3" rainfall amounts are possible within much of the Marginal Risk area and could reach locally higher. However, there remains some notable north-south spread regarding the axis of heaviest rain, with some guidance (00z ECMWF) actually keeping the heaviest rain just offshore. Urban areas are most at risk given the naturally lower threshold for flash floods and ponding water over impervious surfaces. Otherwise, FFG remains relatively high across this part of the country and was an additional factor for not elevating the risk area to a SLGT. Elevated convection is likely farther north into the Lower Mississippi Valley as well, where 1" rainfall totals could be realized, but should remain under FFG. Snell Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_Jb4CpKGfLCBYQgpKn7PiQYAYU2t9-iFMPnRI_PWjQNW= HobJTSUmE9dFveo4ovhFBHI0Hgm1aifAtk69h_6rA2mbz60$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_Jb4CpKGfLCBYQgpKn7PiQYAYU2t9-iFMPnRI_PWjQNW= HobJTSUmE9dFveo4ovhFBHI0Hgm1aifAtk69h_6rrYbMx3I$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_Jb4CpKGfLCBYQgpKn7PiQYAYU2t9-iFMPnRI_PWjQNW= HobJTSUmE9dFveo4ovhFBHI0Hgm1aifAtk69h_6rmb2lg-c$=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 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .