382 FOUS30 KWBC 242025 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 425 PM EDT Fri Apr 24 2026 Day 1 Valid 16Z Fri Apr 24 2026 - 12Z Sat Apr 25 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN THE MID SOUTH... 16Z update... A MCS will support reinvigoration of convection across Oklahoma and Arkansas during the afternoon and evening hours, most likely on the upshear flank of the cold pool with west-southwesterly low level inflow and an upstream reservoir of strong instability. The latest CAMs maintain a several hours of NW to SE tracking cells that pulsate up to 2 inches/hour while tracking central and southern Arkansas. Local terrain may lead to additional enhancement. Soil saturation across this part of Arkansas has been drier of late which does limit the scale of flash flooding risk. At this time a Slight Risk was not raised and the inherited Marginal Risk was maintained with no adjustments. Campbell A convective line that had stalled over northern Oklahoma between 02Z and 06Z has recently shown signs of slow forward progress. This increases confidence in the general evolution depicted in the 00Z hi-res model guidance suite, which shows the line reaching northern Arkansas and east-central Oklahoma by the start of the forecast period at 12Z Friday, and continuing southeast through much of central and eastern Arkansas through the daytime hours. The end result should be an increasingly stable air mass and widespread cloud cover over those same portions of Arkansas, and adjacent southern Missouri and western Tennessee, associated with gradually decaying convection, a cold pool and surface meso-high. For these reasons, and trends to the southwest with the heaviest precipitation in both hi-res and AI guidance, the Marginal Risk has been shifted likewise. A reinvigoration of convection in the afternoon and evening is most likely on the upshear flank of the cold pool with west-southwesterly low level inflow and an upstream reservoir of strong instability. The potential exists for periods of training convection along and near the existing outflow boundary (likely on the order of 1-3 hours), which may provide opportunities for localized corridors of heavy rainfall with 1-2 inch per hour rain rates, and resulting flash flooding. The precise placement remains somewhat uncertain, so the Marginal Risk remains relatively broad to account for a variety of scenarios. In particular, the risk area was fanned out a bit more to the north and west than deterministic WPC QPF would imply, because of the relatively slow pace of the ongoing convection and the very common northeast placement bias in this sort of mesoscale setup respectively. Lamers Day 2 Valid 12Z Sat Apr 25 2026 - 12Z Sun Apr 26 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE ARKLATEX REGION INTO EASTERN OKLAHOMA AND SOUTHEAST KANSAS... 21Z update... Consensus maintains a QPF footprint with a general axis of orientation of NW to SE spanning from southeast Kansas to northern Louisiana. Latest trends and WPC QPF did increase amounts modestly for portions of southern Arkansas and northern Louisiana which helped support the need for a minor expansion of the Marginal Risk area over this part of the region. Neighborhood probabilities show up to 10% for exceeding 3 inches in the vicinity of the borders of Oklahoma, Texas, and Arkansas. Campbell It seems likely that scattered thunderstorms will develop on Saturday afternoon in a corridor of strong instability across the Southern Plains. However, there remains considerable uncertainty as to the position of surface boundaries and the northward extent of the strongest instability. Despite model guidance depicting a variety of mesoscale scenarios, most models do show organized convective clusters pushing southeast along the 1000-500mb thickness gradient into the evening and overnight hours. This motion could allow for some training and areas of locally heavy rainfall; the strong instability and PWs of 1.2 to 1.5 inches would support 1-2 inch per hour rain rates. If those rain rates can be sustained for a couple hours, localized flash flooding would be possible. For now the Marginal Risk was maintained as model guidance does not really show any extended duration of training at this point, and there is not enough model agreement to identify a preferred corridor for heavy rainfall. Lamers Day 3 Valid 12Z Sun Apr 26 2026 - 12Z Mon Apr 27 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN THE CENTRAL PLAINS AND OZARKS... 21Z update... Very minor westward expansion of the Marginal was made across central North Dakota and Nebraska to reflect the modest western shift of the QPF footprint in the Plains. Still expecting a more broad area of rainfall from South Dakota/Minnesota to the Lower Mississippi Valley in NW to SE axis. Campbell Strong cyclogenesis in the central Plains on Sunday will facilitate significant northward moisture transport and a more expansive area of thunderstorm activity stretching from the Dakotas south toward Arkansas. The stronger signal for heavy rain exists further north where stronger synoptic forcing and mid-upper level height falls will be focused. However, instability is expected to be more limited in those areas. Nevertheless, the combination of moderate instability with PWs exceeding 1 inch and potential for more persistence of rain and thunderstorms could yield localized flash flooding. Further south, stronger instability could support higher rain rates, but weaker forcing overall may keep convection scattered and reduce opportunities for training and focused corridors of heavy rainfall. Some portions of Kansas, Missouri, Oklahoma, and Arkansas will likely have experienced substantial rainfall in the preceding several days, and so may be more prone to runoff issues if organized thunderstorms are more persistent. The expected tradeoffs between convective coverage and available instability, with respect to the overall flash flood threat, only merit a broad Marginal Risk at this time. Lamers Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt