FOUS30 KWBC 070137 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 937 PM EDT Wed May 6 2026 Day 1 Valid 01Z Thu May 07 2026 - 12Z Thu May 07 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF MISSISSIPPI AND ALABAMA... 01Z Update... ...Gulf Coast States into the Southern Appalachians and Interior Southeast... Evening adjustments to the ERO include trimming the entire northwest flanks of the MRGL and SLGT risk areas where the heavier convective rainfall has largely ended across the Mid-South and portions of the TN Valley. Also, given the latest trends from the CAMs, most of Texas has been taken out of the MRGL risk as a cold front continues to advance south and allows for a more stable airmass to increasingly overspread the Hill Country and adjacent areas of south-central Texas. The SLGT and MDT risk areas have been adjusted somewhat across the Deep South with some southwest to northeast oriented refinement across MS/AL/GA that takes into account the ongoing supercell outbreak and expectations for general cell-merger and MCS consolidation going into the overnight hours. This integrates the 18Z HREF, 12Z EC-AIFS and recent HRRR solutions which maintain significant convective organization and gradually introduce concerns for cell-training as the convection becomes well-aligned with the deeper layer and strongly sheared steering flow across the region. It should be noted that guidance continues to support somewhat heavier rainfall totals across portions of northern Georgia and also update South Carolina with some convection becoming locally concentrated near and just ahead of the approaching cold front from the north. As such, the SLGT risk area has been expanded off to the east a bit. For MS/AL in particular, high PWs locally reaching 2 inches, coupled with moderate to strong instability (1500 to 2500+ J/kg of MLCAPE) will be key players along with the shear to foster rainfall rates capable of reaching 2+ inches/hour. The cell-training and cell- merger concerns will support some 2 to 4 inch rainfall totals with isolated heavier amounts, and there is some hires CAM guidance that supports 5+ inch totals overnight. The threat for flash flooding will be increasing over the next several hours, which will include urban flooding impacts. Please consult the latest WPC MPDs for additional information. Orrison Day 2 Valid 12Z Fri May 08 2026 - 12Z Sat May 09 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE CENTRAL GULF COAST THROUGH SOUTHERN GEORGIA AS WELL AS FOR PORTIONS OF THE RIO GRANDE VALLEY OF SOUTH TEXAS... ...2030Z Update... ...Central Gulf Coast through Southern Georgia... By the start of the period 12Z Thursday, the clash of air masses between a cooler, dry air mass over much of the interior Southeast and a very warm, unstable, tropical air mass off the Gulf to the south will be waning, with the former air mass winning out. The front will be on the move towards the south and east Thursday morning. This will be combined with a fast moving shortwave at the base of a deep longwave trough to support the progressive movement of the storms south and east across southern Alabama, south Georgia, and eventually the northern Panhandle of Florida. As the front moves over southern Alabama and central Georgia early Thursday morning, some backbuilding due to southwesterly moisture advection could still result in localized areas of training between storms as the entire system moves southeastward. Combined with a few burn scars across far south Georgia due to recent wildfires, the Marginal Risk inherited was largely left unchanged, other than trimming it back from the South Carolina coast due to natural flood resistance and less expected rainfall there. The flood threat will rapidly diminish Thursday afternoon as the front dissipates across north Florida. ...Rio Grande Valley... A weak area of surface low pressure is expected to develop Thursday at the end of the same front moving across the Southeast. This low will have abundant atmospheric moisture to work with, some upper level support in the right entrance region of a jet, and an approaching shortwave trough over west Texas. Thermal heating will allow for convective development over the mountains of Mexico. Westerly flow may allow a few of those storms to survive tracking east off the mountains and across the Rio Grande. While many areas of south Texas have very dry soils, the abundance of moisture (PWATs over 2 inches) will support storms that will be capable of multi-inch-per-hour rates. This intensity of rain may overcome the dry soils to result in isolated instances of flash flooding. The Marginal was left largely unchanged with this update. Wegman Day 3 Valid 12Z Fri May 08 2026 - 12Z Sat May 09 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE UPPER TEXAS GULF COAST THROUGH THE LOWER MISSISSIPPI VALLEY... ...2030Z Update... Return flow off the Gulf on Friday will run into the same stalled front that will be lifting north as a warm front during the day. Ample moisture with PWATs of 1.75 inches and up will support numerous thunderstorm development as early as midday, then continuing through the afternoon, with additional storms impacting the area late Friday night. This will support a renewed flash flooding risk, especially since several urban areas, including Houston, San Antonio, and New Orleans could be involved. Due to the abundance of moisture and continuing southerly flow off the western Gulf resupplying moisture lost to rainfall, expect backbuilding and training thunderstorms to impact the Slight Risk area, which will support widely scattered instances of flash flooding. While some areas are starting out drier than normal for soil moisture, most are right around average for this time of year. This could allow for the storms to overwhelm local soils, especially in urban areas, a bit sooner, contributing to the widely scattered flash flooding threat. Wegman ...Previous Discussion... The risk of excessive rainfall will be focused along the low-level boundary that builds into the region on Day 2 and stalls along a west to east axis. Precipitable water values in excessive of 1.5 inches should be pooling along the boundary on Friday...with higher precipitable water values returning northward later in the day on Friday and through Friday night/early Saturday morning. Southern stream shortwave energy become southerly during the day and increases. The Marginal risk area is conditional in the sense that a Slight could be needed depending on observed rainfall on Day 2, the degree of overlap with Day 3 QPF and the amount of urbanization. Bann 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