FOUS30 KWBC 231553 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1153 AM EDT Sat May 23 2026 Day 1 Valid 16Z Sat May 23 2026 - 12Z Sun May 24 2026 ...THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL FOR SOUTHEASTERN TEXAS, SOUTHERN LOUISIANA, AND THE UPPER OHIO VALLEY... 16Z Update... ...Southern Plains to Lower Mississippi Valley... GOES East satellite paints a chaotic picture with numerous clusters of thunderstorms that stretch from just east of the Rio Grande to as far east as southern Louisiana. A convective complex emerging off of the Sierra Madre is tracking east into South TX where RAP mesoanalysis depicts 3-hr MLCAPE changes of >600 J/kg. There is also a narrow theta-e gradient just north of Corpus Christi with SE 850mb intersecting the boundary. This environment, along with the approaching 500mb vort max providing support aloft, will sustain and likely ignite additional storms in South TX today with rainfall rates of 2-2.5"/hr, perhaps even 2" of rainfall in 30 minutes, in the most intense cells. That said, these storms are embedded within a 20-30kt 850-300mb mean wind flow, which should keep storms moving along. The biggest threat for flash flooding likely lies along and just south of the 850mb theta-e axis where intersecting low-level winds could trigger storms in advance of the MCS tracking over the Rio Grande. Latest 12Z HREF shows a narrow area from just southwest of Houston with moderate-to-high chances (50-70%) for 3hr QPF > 3hr FFG between 18-21Z. Storms may linger between Houston and Galveston on east to Beaumont through this afternoon before dissipating this evening. WPC's Metwatch Desk has issued a couple of MPDs (215 and 216) highlighting the ongoing flash flood threat for southern LA (215) and southern TX (216). Please refer to WPC Metwatch MPDs for the latest information as the day progresses. Given the progressive nature of the storms, opted to maintain what is a "high-end Slight" from the Upper TX Coast to southern LA. The Slight also extends south to just north of the Rio Grande. Scattered areas of flash flooding are possible today with more urbanized setting most vulnerable. Localized cases of significant flash flooding can occur, particularly if back-building and training cells along the Upper TX Coast on east to southern LA transpire. Residents in these areas should ensure they have a reliable method to receive any flash flood warnings issued today and this evening. Farther east, a 300mb disturbance will eject east over the ArkLaTex at the same time a southerly IVT out of the western Gulf advects anomalous moisture into the southern MS Valley this afternoon and into tonight. Sufficient shear coupled with MUCAPE >2,000 J/kg will trigger numerous thunderstorms from northern LA and the ArkLaTex on east through the Lower MS Valley and even as far north as the Ozarks. Storms may flare up over AL as well, where NASA SPoRT-LIS 0-40cm anomalies are >90%. For these reasons, the Marginal Risk was extended to cover all of MS/AL and into the TN Valley. ...Ohio Valley... 12Z surface analysis shows a classing CAD signature in the East with a N-S oriented stalled front from the Cumberland Plateau on north to the OH River. The front oriented SW-NE from from the Lower MS Valley to the Lower OH Valley will slowly advance east, but will not advance east much towards the Upper OH Valley today. As the primary low in northwest OH moves northeast towards Lake Erie, the warm sector will advance north into eastern OH and western PA with a narrow tongue of 500-1,000 J/kg of MLCAPE encompassing eastern KY, southern and eastern OH, and western WV. Latest HRRR and RAP soundings show highly saturated soundings (>85%) in the 1000-500mb layer, warm cloud layers up to 12,000ft deep, and upshear Corfidi vectors <10 kts in some cases. Cloud layer winds are uniformly out of the SW, intersecting the lifting warm front in eastern OH and western PA and parallel to the quasi-stationary front to the west. This setup is ripe for not only thunderstorms containing efficient warm-rain processes, but also for training and back-building cells. FFGs remain quite low with 1-hr FFGs <1" in some areas, and 3-hr FFGs <1.5" along and just west of the OH River. NASA SPoRT-LIS also shows >95% soil saturation percentiles for much of the region. With these factors, opted to upgrade to a Slight Risk from northeast KY on north and east into the Upper OH Valley. Scattered instances of flash flooding are possible, with locally significant flash flooding not out ot the realm of possibility. This is backed by the latest 12Z HREF guidance that show ...Southeast... From Florida on north to the Carolinas, the region lies on the western periphery of a Bermuda high while embedded 500mb disturbances track over the region due to broad longwave troughing to the west. A stalled front in the Carolinas, marking the southern fringe of the CAD signal in the East, will act as a trigger for additional storms today thanks to southerly 850mb flow intersecting the front. The Carolinas and into central GA will sport an IVT >400 kg/m/s today that will provide no shortage of atmospheric moisture aloft. PWATs >1.75" are likely (above the 97.5 climatological percentile) in the Carolinas and MUCAPE up to 1,000 J/kg provides a favorable environment for rainfall rates up to 1.5"/hr. Farther south into GA, where instability is greater, rainfall rates eclipsing 2"/hr are possible this afternoon and evening. Some CAMs do show the potential for strong thunderstorms with torrential rainfall rates potentially sneaking into the Atlanta metro area this afternoon. The "Peach State" is consumed in severe drought conditions, so much of this rainfall will be welcomed. That said, excessive rainfall rates referenced above in urbanized locations or areas that drain poorly could still see cases of flash flooding occur. The Marginal Risk was expanded for to encompass most of the state (GA coast line the lone exception). Farther south, strong surface based heating is ongoing from Tampa Bay on north and east towards Orlando and the northern FL Atlantic coast. 12Z CAMs show good agreement on a cluster of potent thunderstorms flaring up with rainfall rates between 2-3"/hr possible. PWs in FL are anomalous as well for late May with >2.0" PWs likely and plenty of instability (>1,000 J/kg MLCAPE). While much of FL can certainly use the rain, many CAMs show these storms flaring up over some of the Sunshine State's main thoroughfares (I-10, I-75, I-4 most notably). Storms should subside later tonight, but torrential downpours in urbanized areas could pose a flash flood threat this afternoon and evening. Due to these factors, the Marginal Risk was expanded into northern and central FL today. Mullinax Day 2 Valid 12Z Sun May 24 2026 - 12Z Mon May 25 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE UPPER TEXAS COAST INTO SOUTHWESTERN LOUISIANA... A slow moving upper trof expected to amplify somewhat day 2 as it pushes from eastern Texas into the Lower MS Valley. This will likely help fire another round of convection in the vicinity of the Upper TX coast, eastward into southern LA. At the moment, it appears the best instability ahead of this next closed low will be suppressed southward into the northern Gulf in the wake of the active day 1 convection. This may support the heaviest rains being shunted southward and off the coast day 2, as suggested by the RRFS mean and the FV3LAM. There is still a lot of model spread, but WPC qpf has trended south, with the heaviest offshore. Subsequently, the previous slight risk area has been trimmed on the north end, confined to the far Upper TX coast into southwest LA. There may be overlap of the day 1 and day 2 heavy rain areas over the Upper TX coast into southwest LA. However, at the moment, the risk level was maintained as slight as there is still model spread with the day 2 heaviest qpf axis. No significant changes made to the previous broad marginal risk area extending northeastward from the Central Gulf Coast, across the South and into the Southern to Central Appalachians. Similar to the day 1 period, there will continue to be an axis of much above average PW values stretching across these areas, with embedded shortwaves in the broad southwesterly mid to upper level flow, supporting widespread scattered convection, locally heavy rains and isolated runoff issues. Oravec Day 3 Valid 12Z Mon May 25 2026 - 12Z Tue May 26 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE SOUTHERN APPALACHIANS... A small slight risk area was introduced in the vicinity of the Southern Appalachians from north Georgia into the Upstate of SC and far southwestern NC. A very broad region of much above average PW values, 2 to 2.5+ standard deviations above the mean, will stretch from the Central gulf coast, northeastward across the South, Tennessee Valley, Southern Appalachians and into the Southern Mid- Atlantic during day 3. Similar to the day 2 period, broad south southwesterly mid to upper level flow with embedded shortwaves will support additional widespread scattered convection across these areas. While locally heavy rains are likely across a large region in this anomalous PW axis, there is model signal for concentration of heavy precip into the upslope regions of the Southern Appalachians, with a small slight risk area depicted here. Included the Atlanta metro in the slight risk area given the sensitivity to potential urban issues. There may be additional slight risk areas in this anomalous PW axis depicted in future updates, but low confidence with placement at this time. Oravec 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