Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jan 23 2023 20:23:36 FOUS30 KWBC 232023 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 323 PM EST Mon Jan 23 2023 Day 1 Valid 16Z Mon Jan 23 2023 - 12Z Tue Jan 24 2023 ....16Z Update... The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman Day 2 Valid 12Z Tue Jan 24 2023 - 12Z Wed Jan 25 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY... ....2030Z Update... For the most part, the guidance remains in excellent agreement regarding the evolution of the event expected on Tuesday. The only change of significance was to trim the Marginal back in Alabama. Many of the CAMs now cover the entire event through Tuesday night, and most of them agree that northern AL is really getting the "leftover" convection that is much stronger further south and west in the Slight Risk area. All of the convection is also expected into northern AL after sunset, so daytime heating (such as it is this time of year) will not be a contributing factor to the meager instability. Otherwise, QPF amounts across much of the Slight Risk area has come down, particularly in northern areas of northeast TX and northern LA, however there still may be enough instability and enough of the CAMs suggest convection will still be robust in these areas, so opted to leave these the same despite the lower total QPF. Ultimately strong storms exceeding 1 hr FFGs appear most likely than any longer term FFGs being exceeded. The overall convective line, which will be the when the strongest storms and heaviest rainfall occur, will be moving quickly. It's the combination of that heavy rain following behind the prefrontal convection that is expected to cause any widely scattered flash flooding. Wegman ....Previous Discussion... The latest guidance has come into much better agreement regarding the evolution of an upper-level low over the Southern Plains on Tuesday. A potent upper trough and favorable jet dynamics should support a fast moving surface low pressure system moving from southern Texas through the central Gulf Coast Tuesday morning through early Wednesday. The upper trough will tap into a reservoir of Gulf moisture (PWATs between 1-2in) and send it streaming into southeastern Texas and the central Gulf Coast on Tuesday. A line of heavy rainfall and thunderstorms are expected to initiate somewhere in southeastern Texas and spread eastward along the Gulf coast where it will encounter some decent instability with MUCAPE hovering between 500-1000J/Kg along the immediate coastlines of Texas and Louisiana. A southerly low level jet at around 60kts will provide ample shearing for these fast moving storms. Rainfall rates between 0.75-1.5in/hr over saturated soils and the presence of low FFG will amplify flash flooding concerns for the area encompassed by the Slight Risk. The 00z Canadian regional and ECMWF hourly QPF were favored since they appeared to capture the magnitude and timing of the rainfall reasonably well. First Guess ERO fields and a number of local offices supported the risk areas drawn for this day 2 period. Kebede Day 3 The Day 3 outlook will be updated by 2030Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4JdBtVux680eZ3ZVVFqI1hU-iK2kdnzA8sxluC4N9luR= CcrTy4LHHZ6yqlMucFuVue-tAf-hxsU1L-DpELNKrnO_78o$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4JdBtVux680eZ3ZVVFqI1hU-iK2kdnzA8sxluC4N9luR= CcrTy4LHHZ6yqlMucFuVue-tAf-hxsU1L-DpELNK_hIi6lo$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4JdBtVux680eZ3ZVVFqI1hU-iK2kdnzA8sxluC4N9luR= CcrTy4LHHZ6yqlMucFuVue-tAf-hxsU1L-DpELNKfJhJcNQ$=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) .