Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Oct 25 2025 00:11:24 FOUS30 KWBC 250011 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 811 PM EDT Fri Oct 24 2025 Day 1 Valid 01Z Sat Oct 25 2025 - 12Z Sat Oct 25 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHERN PLAINS... ....Southern Plains... An upper level low near the NM/CO border is leading to a broad area of upper divergence across the Southern Plains. SPC mesoanalyses show 40-50 kts of effective bulk shear across central and eastern TX. Both the 12z REFS and 18z HREF guidance indicate that a few=20 possible convective maxima are expected overnight where 3"+ is=20 possible through 12z...near to northwest of the Dallas/Fort Worth=20 metro area (which has already partially evolved), north of Eagle=20 Pass TX (which would evolve over the next several hours), and=20 across Southeast TX (whose timing would be early Saturday morning), all downwind of MU CAPE pools of 2000+ J/kg. The biggest initial=20 impact is near and northwest of Dallas/Fort Worth where a=20 broadening area of convection's forward propagation is being held up northeast of a couple convective arcs/bows/mesoscale cyclones.=20 There should be some attempt for the convective pattern to solidify and form a LEWP/QLCS with time. Wherever convective progression=20 can be held up for a couple of hours, 2.5" amounts in an hour and=20 local amounts of 5" are possible. Maintained the Slight Risk area=20 but made adjustments per radar reflectivity trends, as well as the most recent HREF and REFS guidance, which appear a little slow.=20 Scattered areas of flash flooding, especially for more urbanized=20 locations, will be a concern. ....Pacific Northwest into Northwest California... As the heavy rain threat across the Pacific Northwest is winding down, the Marginal Risk area was removed. Roth Day 2 Valid 12Z Sat Oct 25 2025 - 12Z Sun Oct 26 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHEAST TEXAS INTO CENTRAL ARKANSAS AND WESTERN MISSISSIPPI... ....2030z Update... The slight risk area over the South was expanded eastward into portions of southeastern Louisiana and western Mississippi, where a notable neighborhood probability signal of exceeding 3" exists. The high qpf signal shifted south and east since the previous issuance as a result. A round of convection in the morning could prime soils for another round in the evening, which would carry higher rain rates due to a recharged instability and moisture plume. ERO first guess fields indicate a 15-40% probability of ARI exceedance or UFVS-verified flash flooding across much of the highlighted areas. The marginal risk over the Northwest remains in place without any changes due to a lack of significant changes in the qpf guidance. The heaviest rain associated with an atmospheric river event will occur late Saturday morning into the afternoon. Kebede ....Previous Discussion... Multiple rounds of heavy showers and thunderstorms are expected to impact the broader northwest Gulf Coast region this period, with one initial axis of convection likely ongoing Saturday morning across areas of southeast to east-central TX and advancing across western Louisiana and southern Arkansas. This will be the carryover of organized convection from the day 1 period which should be interacting at least initially with a 40+ kt southerly low-level jet off the western Gulf. Precipitable water values at or above 1.75 inches and MUCAPE values locally of 2000+ J/kg will support high rainfall rates potentially exceeding 2 inches/hour with the stronger storms. The arrival of an upper- level jet streak in the subtropical stream combined with the interaction with the southern stream closed low/trough axis crossing the southern Plains will favor a renewed convective outbreak across areas of eastern Texas through portions of western and southern Louisiana Saturday afternoon through early Sunday. Even though antecedent conditions are quite dry, the concern for multiple rounds of convection which combined may yield some 3 to 5+ inch totals, will probably be enough to support a threat for scattered areas of flash flooding. The more sensitive urbanized locations will be at greatest risk for impacts. For this update, the Slight Risk area was expanded given the footprint of 2+ inch rainfall amounts within a broadened region of instability shown by the models. This is also consistent with the latest deterministic QPF from WPC. ....Pacific Northwest and Northwest California... Multiple rounds of moisture transport into the coastal ranges will continue for the period as atmospheric river activity continues. Locally a few additional inches of rain will be possible for the windward slopes of the terrain, but given the early-season and relatively modest nature of this atmospheric river activity, any flooding concerns are expected to be isolated at best. Therefore, the Marginal Risk area is maintained with no changes for this update cycle. Bann Day 3 Valid 12Z Sun Oct 26 2025 - 12Z Mon Oct 27 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE MID-AND LOWER-MISSISSIPPI VALLEY, TENNESSEE VALLEY, SOUTHERN APPALACHIANS AND SOUTHEAST... ....2030z Update... Separate axes of precipitation will impact different parts of the marginal risk area on Sunday. Convection associated with the mid- level low will spread across the Tennessee Valley generating quarter to half inch rain rates within a weakly destabilized environment (200-400J/Kg MUCAPE). Another line of storms will spread across the Central Gulf Coast beneath ripples of shortwave energy breaking away from the parent mid-level low to its north. PWATs of 1-2" may support any isolated instances of excessive rainfall/flash flooding within the marginal risk area. Models are trending toward a higher qpf solution along the Central Gulf Coast, but there's still enough uncertainty on the exact placement (read: Euro outlier) to mitigate any upgrades at this time. Kebede ....Previous Discussion... Maintained a Marginal Risk area across portions of the southern and middle Mississippi Valley. The risk across the southern should diminish once a cold front passes through the area early in the period and the deeper moisture/instability get shunted eastward. Farther north where the moisture is not as deep...concern is more from mid-level frontogenesis and upper level divergence leading to locally enhanced rainfall rates where antecedent conditions have been somewhat wetter than other locations. There is plenty uncertainty as to whether there will be a second round of storms capable of producing locally heavy rainfall...so overall confidence is below average which precludes anything higher than a Marginal risk. Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8cMPhbgY4smnoGHjjeDmhrTWFhGdd5Grr4KCRmsQgRJX= LAIwDFUoS6y5ilnXRYe5rLJxHcJnJvEVkGhvKkv9cL9cUtI$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8cMPhbgY4smnoGHjjeDmhrTWFhGdd5Grr4KCRmsQgRJX= LAIwDFUoS6y5ilnXRYe5rLJxHcJnJvEVkGhvKkv9Odo6lss$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8cMPhbgY4smnoGHjjeDmhrTWFhGdd5Grr4KCRmsQgRJX= LAIwDFUoS6y5ilnXRYe5rLJxHcJnJvEVkGhvKkv9f9c8P84$=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 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .