Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Oct 23 2025 00:00:20 FOUS30 KWBC 230000 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 800 PM EDT Wed Oct 22 2025 Day 1 Valid 01Z Thu Oct 23 2025 - 12Z Thu Oct 23 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Pereira Day 2 Valid 12Z Thu Oct 23 2025 - 12Z Fri Oct 24 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHERN PLAINS... ....Southern Plains... Heavy showers and thunderstorms are expected to develop and eject east out across portions of west-central and northwest TX by Thursday evening as the gradual arrival of an upstream upper- trough/closed low over the Southwest begins to interact with deeper layer and increasingly moist/unstable southerly flow across the Rio Grande Valley and toward the Red River Valley. Divergent flow aloft, increasing low to mid-level shear, and MUCAPE values of 1000 to 2000+ J/kg will facilitate broken areas of semi-organized convection that will be capable of producing rainfall rates of up to 1 to 2 inches/hour. The greater concentrations of convection though will likely be Thursday night and Friday morning into portions of the Red River Valley including northwest to north- central TX and southwest OK where stronger low-level convergence in closer proximity to developing surface low pressure and a surface warm front will combine with a strengthening low-level jet for a more sustained convective threat. The models support arrival of an upper-level jet streak with favorable left-exit region jet forcing that will further support an organized convective threat which will include a poleward extension of heavy rainfall through central OK given a nose of elevated instability here north of the aforementioned warm front. Some localized/isolated swaths of 2 to 4+ inch rainfall totals will be possible where some spotty areas of cell-training occur going into the overnight hours. While antecedent conditions are dry, sufficient levels of rainfall may foster an isolated and mainly urban concern for flash flooding. A Marginal Risk of excessive rainfall has been introduced as a result. Orrison Day 3 Valid 12Z Fri Oct 24 2025 - 12Z Sat Oct 25 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHERN PLAINS... 2030Z Update... Changes to the day 3 ERO for the 12Z cycle are rather modest. The larger scale synoptic setup for heavy convective rainfall across the Red River Valley and stretching southward down into the Edwards Plateau is still largely in place as strong dynamic forcing/DPVA associated with the approaching upstream upper-level trough/closed low interacts with a convergent and moist/unstable low-level jet aiming north across the southern Plains. Enhanced frontal convergence and moisture transport aimed into the Red River Valley area may yield a rather organized concern for heavy/excessive rainfall totals which will include potentially the greater DFW metropolitan area. A cold front associated with the height falls will advance rather progressively east across areas of central and southern TX including the Edwards Plateau/Hill Country area and toward the Rio Grange River, but will foster likely favor well-organized areas of strong convection with heavy rainfall rates up to near 2 inches/hour. Some southwestward adjustment to the Slight Risk area was done compared to continuity given the latest models trends for heavier rainfall closer into the warm sector instability near and south of the Red River Valley. Some localized rainfall totals across portions of central and northern TX may approach 3 to 6 inches given proximity of organizing surface low pressure and stronger forcing. Scattered areas of flash flooding including urban flooding impacts will be a concern. Elsewhere, no changes were made with this update to the Marginal Risk across the Pacific Northwest as the latest guidance continues to support the arrival of a moderately strong atmospheric river for this period. Locally a few inches of rain into the coastal ranges are still expected, but given the early-season nature of the event, runoff problems should be highly localized and mainly confined to urban and poor-drainage areas along with the more sensitive burn scar locations. Orrison Previous discussion... ....Southern Plains into the Western Ozarks... Models continue to amplify the mid/upper trough across the southern Rockies-southern High Plains Sat-Sat night as a subtropical jet streak rounds the trough base. Meanwhile, the northern stream jet streak begins to curve across the central Plains-Mid MS Valley, which within a broad right entrance region, would couple with the increasing southern stream forcing and thus lead to a fairly sizable area of robust deep-layer lift and low-level moisture transport. TPWs climb between 1.5 to 2.0" from south to north across the outlook areas, which is around 2 standard deviations above normal for late Oct. Meanwhile, increasing south-southwesterly low level flow (35-40+ kts at 850 mb) will begin to align with while reach the same magnitude of the mean 850-300 mb flow during the period, as the upper trough amplifies and approaching surface front slows down. This will favor a higher likelihood of multiple linear convective segments ahead of the front, with cell training most likely within the Slight Risk area. Guidance shows pockets of 3-6+ inches of rain within the Slight Risk area, particularly across North TX into central-northeast OK. There is still some areal-spread however with respect to the heaviest totals. Given this along with the the dry antecedent conditions (low soil moisture percentiles from NASA SPoRT and high FFG values from the RFCs), for now at least have not considered an upgrade to a Moderate Risk. ....Pacific Northwest into Northwest California... The Marginal Risk area from yesterday's Day 4 ERO was modified only slightly for today's Day 3 ERO. Modest Atmospheric River (AR), level 3 on a 5-level scale per the Center for Western Weather and Water Extremes (CW3E), will push across the coastal and Cascade ranges over WA/OR Friday, then into the northwest CA coastal and Shasta/Siskiyous late Fri and Friday night. IVT values peak around 700-750 Kg/m/s, however only for a brief period of time at any given location as the AR is rather transient (steady southward progression). Guidance is in fairly good agreement with the QPF amounts, averaging 2-4" across the outlook area, with local totals of 5+ inches. Much of this would fall within 12 hours as the AR traverses the area, with peak rates near 0.50"/hr along and near the axis of maximum TPW (1.00-1.25") with some (albeit weak) elevated instability (MUCAPEs ~100-200 J/Kg). This rainfall may induce some localized short-term runoff issues, particularly in more urban/poor drainage areas and over burn scars. Hurley Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6wwKofal635zynqZPaTda8m7d0aMyq5wetD3MR4CEnZ1= uzYTC28UiZAcjB6nYQWy6DComnFVDAKf2EbsPszZElCDePk$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6wwKofal635zynqZPaTda8m7d0aMyq5wetD3MR4CEnZ1= uzYTC28UiZAcjB6nYQWy6DComnFVDAKf2EbsPszZArGXFQo$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6wwKofal635zynqZPaTda8m7d0aMyq5wetD3MR4CEnZ1= uzYTC28UiZAcjB6nYQWy6DComnFVDAKf2EbsPszZpTuu-FY$=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) .