988 FOUS30 KWBC 250021 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 821 PM EDT Fri Apr 24 2026 Day 1 Valid 01Z Sat Apr 25 2026 - 12Z Sat Apr 25 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN PARTS OF THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY.... There is a Marginal Risk of excessive rainfall along and ahead of a cold front this evening into the overnight hours from portions of the Southern Plains into the Lower Mississippi Valley. Thunderstorms initially over the southeastern portion of Oklahoma should continue to build southeastward overnight into an airmass characterized by precipitable water values around 1.6 inches and mixed layer CAPE around 1000 K per kg. This was close to the area where the latest CAMs and the HREF/RRFS ensembles were showing 10 to 25 percent neighborhood probabilities of greater than 3 inch rainfall amounts in less than 6 hours through 25/09Z. Given the recent dry antecedent conditions and the progressive nature of the convection contributed to the decision to hold at a Marginal Risk and not introduce a Slight Risk area. The biggest change was to expand the Marginal Risk area into northern Louisiana and into Mississippi. Bann 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