Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Oct 26 2023 07:19:27 FOUS30 KWBC 260719 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 318 AM EDT Thu Oct 26 2023 Day 1 Valid 12Z Thu Oct 26 2023 - 12Z Fri Oct 27 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF WISCONSIN TO MICHIGAN & CENTRAL TO EASTERN TEXAS...=20 =20 Our potent shortwave over TX will eject northeast into the Central Plains, eventually crossing into the Midwest Thursday night into Early Friday. Convective development is expected along and south of a front where the theta-E gradient will be present. Scattered showers and thunderstorms over IA/MN will advance northeastward through the period, but an enhancement in the afternoon and evening hours is anticipated due to the increasing ascent provided by the shortwave presence. Heavy rainfall is expected downwind of the pool of 500+ J/kg MU CAPE. The Marginal Risk concern in eastern IA and northwest IL would be if 1.5"+ totals seen on some of the guidance near the IA/IL border materialized within an hour, which could become an urban problem. HREF probabilities for 3"/12-hrs are modest, running between 20-30% within an area that has seen a fair amount of rainfall very recently. The combination of long duration locally heavy rainfall will provide an opportunity for flash flooding concerns, especially within the zone extending from central WI eastward into northwest MI where the lower FFGs exist from the previous convective event. Risk areas saw some rearrangement, but not major changes from continuity. =20 Across central and eastern TX, very anomalous moisture presence will persist due to prevailing southerly flow ahead of the mean trough to the west and the western flank of our mid-level ridge east of the Mississippi. MU CAPE of 1000+ J/kg should exist in this area. PWAT indices between 2-2.3" will be common along and east of I-35 and south of I-20. Weak mid-level forcing advecting up from MX and the adjacent Gulf will meet a convergence point created from the area convection that will be decaying to the west. This environment should support hourly rain totals to 2.5", which would be more overwhelming in urban environments, given recent dryness. The guidance shows some variance, but enough agreement that the Slight Risk area was nudged south. =20 Roth Day 2 Valid 12Z Fri Oct 27 2023 - 12Z Sat Oct 28 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF NORTHERN TEXAS...=20 =20 ....Northeast Texas, southeast Oklahoma into northwest Arkansas...=20 The anomalous PW axis across eastern Texas will begin to lift northeastward into the ArkLaTex ahead of the strong cold front sinking southeastward through the Central to Southern Plains.=20 This front is expected to slow its southeastward push towards Saturday morning becoming nearly stationary from northeast Texas into northwestern Arkansas. Precipitation should become more active along and ahead of this front late Friday afternoon=20 into the early hours of Saturday when well-defined frontal convergence and favorable right entrance region jet dynamics enhance upward vertical motions in the anomalous PW axis. The model consensus is for a narrow axis of potentially moderate to heavy totals along this front from north Texas into southeast Oklahoma and northwest Arkansas which should occur late Friday into early Saturday, aided by the nocturnal low-level jet. MU CAPE of 1000-2000 J/kg should exist, along with increasing effective bulk shear to organize the activity and lead to 2.5" in an hour, roughly the maximum forecast for the guidance during the period. A Slight Risk was added where the forecast heavy rainfall best overlaps with the heavy rainfall occurred over the past 24 hours.=20 =20 Roth Day 3 Valid 12Z Sat Oct 28 2023 - 12Z Sun Oct 29 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN AND NEAR THE OZARKS & THE OUACHITA MOUNTAINS... Northeast TX into the Lower Ohio Valley... Precipitable water values of 1.5-2.2" are expected near a slow-moving front draped across the region. The degree of low-level inflow and effective bulk shear available should organize convection into training bands as the flow is fairly uniformly out of the west-southwest with height. MU CAPE of 500-1000 J/kg should be sufficient to achieve hourly rain totals to 2.5" at times, which would be a problem across area terrain.=20 Local amounts in the 3-5" range are indicated by the available guidance overall. Despite recent dryness, the existing Slight Risk area appeared best which was shifted minimally based upon the most recent model guidance. Roth Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6gni4GiSv9by6zll4uhhCw42_mC5NSehtXM2nXBS5iuJ= 2cWkAi0wP_qTnQKlFe26MNHdbrKg43-62F0eunk_S1dvq_A$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6gni4GiSv9by6zll4uhhCw42_mC5NSehtXM2nXBS5iuJ= 2cWkAi0wP_qTnQKlFe26MNHdbrKg43-62F0eunk_ASBzUZo$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6gni4GiSv9by6zll4uhhCw42_mC5NSehtXM2nXBS5iuJ= 2cWkAi0wP_qTnQKlFe26MNHdbrKg43-62F0eunk_vRkpoZ0$=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) .