Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Oct 27 2023 15:57:07 FOUS30 KWBC 271557 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1155 AM EDT Fri Oct 27 2023 Day 1 Valid 16Z Fri Oct 27 2023 - 12Z Sat Oct 28 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF NORTHEAST TEXAS INTO THE ARKLATEX... ....16Z Update... General axis of impact within the previous ERO issuance for D1 was well within the means. Did make some expansion of the MRGL and SLGT risk areas to account for the latest hi-res ensemble QPF footprint, as well as taking into account the 10-year and 100-year ARI exceedance probabilities that show the highest threat located south of the DFW metroplex, but also some non-zero potential in the higher ARI intervals across the Concho valley into the TX Hill Country. QPF totals of 2-3" with locally up to 5" will be possible within the highest impacted zones along and south of I-20 from just west of Fort Worth down into central TX where the higher impacts occurred recently with the last event. There is some deviation in the western expanse of the QPF field as some guidance places the mid-level vorticity maxima further out in west-central TX, so wanted to cover for that potential for greater impacts in those zones that include San Angelo into the Edwards Plateau that were also highly impacted recently. The western extent could be fine tuned if ensembles and associated deterministic shift away from that western evolution, so will be something to monitor through the course of the day. Kleebauer=20 =20 ....Northeast Texas into the ArkLaTex...=20=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 progression by Saturday morning becoming nearly stationary from northeast Texas into northwestern Arkansas. The flow should be fairly unidirectional with height near the stalling boundary. Precipitation should become more active along and ahead of this front late Friday afternoon 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+ J/kg should exist, along with increasing effective bulk shear to organize the activity and lead to 2.5" in an hour, with local maxima towards 5" possible as noted by the 00z HREF (40-45% chance of such). A Slight Risk was adjusted southeast based on the most recent guidance. =20=20 Roth=20 Day 2 Valid 12Z Sat Oct 28 2023 - 12Z Sun Oct 29 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE ARKLATEX INTO THE LOWER OHIO VALLEY...=20 =20 ....Northeast TX into the Lower Ohio Valley...=20 Precipitable water values of 1.5-2.2" are expected near a slow-moving front draped across the region ahead of a strengthening positively tilted upper level trough. 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+ J/kg should be sufficient to achieve hourly rain totals to 2.5" at times, which would be a problem across area terrain. Local amounts in the 3-5" range are indicated by the available guidance overall. Despite recent dryness, the Slight Risk area from continuity looked within reason which was shifted minimally based upon the most recent model guidance. Since guidance is converging slowly on the expected axis of heavy rainfall, chances of flash flood exceedance are growing. A Moderate Risk cannot be ruled out at some point, especially if available instability increases within model guidance. =20 Roth Day 3 Valid 12Z Sun Oct 29 2023 - 12Z Mon Oct 30 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM NORTHEAST TEXAS INTO THE LOWER OHIO VALLEY... Southern Plains into the Ohio Valley... Precipitable water values will be in slow decline this period, maximizing above 1.75" early on before falling into the 1.25-1.5" range by Monday morning. A positively tilted upper level trough will be approaching the region from the west and north causing some forward progression to the front across Texas and the Lower Mississippi Valley with time. The degree of low-level inflow and effective bulk shear available should organize convection into training bands during the day Sunday as the flow is fairly uniformly out of the west-southwest with height, but should be fading somewhat Sunday night into Monday morning. MU CAPE of 250-500 J/kg should be sufficient to achieve hourly rain totals of 1-2" at times early on, which would be a problem across area terrain and places that rained heavily the preceding day, but the 00z NAM indicates the instability fades with time on Sunday and Sunday night. Local amounts in the 2-4" range are indicated by the available guidance overall. There was some temptation to raising the threat level to a Moderate Risk, particularly early in the period when the parameters for heavy rainfall look best which would account equally for heavy rainfall continuing into Sunday morning and how much rain fell the preceding day, but the minimal instability forecast was the biggest drawback. Roth Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6fsWU3Um_5_8KveavfYJacdEE1hBskpeiH5HWgfWdRh_= EWHHzyFcNUpgpRKQAHXIWfR4s-b1Bsnn4uY6ZyzDe3m-Jqo$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6fsWU3Um_5_8KveavfYJacdEE1hBskpeiH5HWgfWdRh_= EWHHzyFcNUpgpRKQAHXIWfR4s-b1Bsnn4uY6ZyzDX03oo5A$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6fsWU3Um_5_8KveavfYJacdEE1hBskpeiH5HWgfWdRh_= EWHHzyFcNUpgpRKQAHXIWfR4s-b1Bsnn4uY6ZyzD2q0wwpI$=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) .