578 FOUS30 KWBC 061945 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 345 PM EDT Wed May 6 2026 Day 1 Valid 16Z Wed May 06 2026 - 12Z Thu May 07 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF MISSISSIPPI AND ALABAMA... ...16Z Update... ...Northern Louisiana, Southern Mississippi, and Central/Southern Alabama... In coordination with JAN/Jackson, MS and BMX/Birmingham, AL forecast offices, a Moderate Risk upgrade was introduced with this update over a portion of southern Mississippi and west-central Alabama. CAMs guidance continues to increase the potential rainfall expected over the area late this afternoon through much of the overnight tonight. A slow-moving cold front over the mid-South is colliding with abundant Gulf moisture, notable instability and moisture advection across portions of the South. Corfidi vectors, while a bit fast for truly ideal training, are still aligned parallel to the frontal interface (WSW to ENE) at about 15 kt. PWATs are expected to increase to over 2 inches across the Moderate Risk area and southwest into Louisiana. 850 mb advection at 20-30 kts for much of the day will increase to 30-40 kts across the Moderate Risk area after sunset tonight with the typical nocturnal strengthening of the LLJ. The persistent LLJ advecting deep tropical moisture will have no problem supporting backbuilding convection even into Louisiana, which will then track east along the front, forming a training pattern across southern Mississippi and western Alabama. Finally, in the upper levels, a strong shortwave trough will approach from the north and west late tonight. This will drag the RRQ of a 150 kt jet over this region, which will both enhance broad scale lift, and support convective initiation to the north and west, which will prolong the rainfall event. CAMs guidance is in good agreement that convective initiation across Louisiana and Mississippi will begin around 19Z/2pm CDT this afternoon. By then, with abundant moisture well in place, instability will already be above 3,000 J/kg along and south of the front. Cells will quickly organize into convective clusters aligned along the frontal interface. There is a bit more uncertainty with how far north the training cells get into portions of north-central Alabama. An ensemble of the CAMs suggest that there will be a minimum of rainfall in and around the Birmingham area, suggesting that the northern boundary of the heaviest rain will likely be south of there. The convection across Mississippi will track east into west-central Alabama, where the Moderate Risk continues. By this point the cells should be fairly well congealed and moving away from the strongest instability and moisture advection. However, the storms across Alabama will persist for much longer into the night. Thus, the duration factor of the heavy rain will be more of a factor contributing to flash flooding to the east, while the intensity will be the greater factor to the west. Recent trends in the guidance are following a very common pattern, namely to shift the heaviest rains south and west with time, which follows that the storms track towards where the environment is most favorable...which is towards the moisture source, the Gulf. Thus, concern is increasing for potentially needing extensions of the Moderate towards the south and west later this afternoon through the evening. ...Northeast Alabama, North Georgia, Southeast Tennessee, Far Western North Carolina, and Far western South Carolina... A weakening MCS over this region currently is expected to give way to additional convection from the remnant storms currently over southwest Tennessee and far northern Mississippi, as well as additional convection from day time heating in the space in between along Tennessee's southern border. These storms are also set up in a training pattern. Unlike further south, however, the topography of the southern Appalachians in this area will likely contribute to heightened flash flooding risk concerns through much of the day today, despite significantly less moisture and instability to work with as compared to areas further south and west. An internal higher-end Slight is in place from the northeast corner of Alabama east to cover this higher threat posed by nearly continuous rainfall into the terrain. ...Elsewhere... The Marginal Risk was expanded north and west across portions of Arkansas and Tennessee in response to ongoing convection with a history of training and flash flooding, as well as across portions of central Texas, where training supercells and a bit of backbuilding convection near the Hill Country could pose an isolated flash flooding threat. Wegman Day 2 Valid 12Z Thu May 07 2026 - 12Z Fri May 08 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