Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Nov 28 2023 19:44:13 FOUS30 KWBC 281944 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 243 PM EST Tue Nov 28 2023 Day 1 Valid 16Z Tue Nov 28 2023 - 12Z Wed Nov 29 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Campbell/Kleebauer Day 2 Valid 12Z Wed Nov 29 2023 - 12Z Thu Nov 30 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Campbell/Kleebauer Day 3 Valid 12Z Thu Nov 30 2023 - 12Z Fri Dec 01 2023 ....THERE IS A MARGINAL RISK AREA FROM THE CENTRAL GULF COAST TO THE MID-MISSISSIPPI/OHIO RIVER VALLEY... ....20Z Update... Little changes from the previous D3 MRGL issuance across the Mississippi Valley. A slight expansion on the northern edge of the risk area to align with the ensemble probabilities of 1" of rainfall greater than 20% within the confines of a warm front. Low-level theta-E advection will begin the end of D2 into D3 on the western periphery of a surface ridge centered over the eastern CONUS. Surface low over the plains will evolve with a developing cold front pushing eastward within the time frame. Best ascent will lie within the difluent axis of of the mid-level shortwave exiting the southern plains and along the periphery of both the cold front across east TX into LA/AR, as well as up closer to the warm front where theta-E tongue is forecast to extend into southern and central MO. Instability maximum is fairly tame compared to other more prolific events, but moisture advection from the Gulf will pump PWATs to near 2-2.5 deviations above normal across a large chunk of the Lower and Mid-Mississippi Valley. Considering the antecedent dry conditions in place prior to rainfall and rates likely to max at 1-2"/hr at best, have maintained the previous MRGL risk area, but adjusted slightly on the northern and eastern confines of the threat area to account for recent deterministic and ensemble trends. Kleebauer ....Previous Discussion... Shortwave energy exiting the Rockies into the Southern Plains will help a surface low pressure system to develop, sending a cold front into the Plains and Mississippi Valley. Convection is expected to fire up over eastern Texas and the Gulf Coast then increase coverage and intensity as the front advances, spreading northeast into the Mid-Mississippi/Ohio Valley. Hourly rates of 0.5 inch/hr or greater will be possible along with areal averages of 1 to 3 inches from the Texas Coast to southern Indiana. At this time the heaviest QPF is favoring southwest/southern Louisiana. Recent precipitation has increased soil saturation across portions of the south-central and central U.S. so there may be isolated areas where the expected precipitation may reach or exceed local flash flood guidance. A Marginal Risk is in effect from eastern Texas/Central Gulf Coast north and east to southwest Indiana. Campbell Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!640QYTrxBPI3wWE7STd9NKySx21JF_jqicqlICd9qUGu= r-NTqoJI5aAO9sZ-pd7XQSrWsLoU6BrJt4UrlkDrbMXClnc$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!640QYTrxBPI3wWE7STd9NKySx21JF_jqicqlICd9qUGu= r-NTqoJI5aAO9sZ-pd7XQSrWsLoU6BrJt4UrlkDr0NP4k8c$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!640QYTrxBPI3wWE7STd9NKySx21JF_jqicqlICd9qUGu= r-NTqoJI5aAO9sZ-pd7XQSrWsLoU6BrJt4UrlkDrE6uzV6s$=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) .