FOUS30 KWBC 061512 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1112 AM 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 RFR 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 TEXAS EASTWARD TO GULF COAST REGION AND SOUTHEAST UNITED STATES... Abundant moisture along a stalled frontal boundary on Thursday will support additional thunderstorm formation along the front. Rapidly weakening forcing at the surface and aloft will greatly diminish convective coverage and restrict the parameters favorable for heavy to excessive rainfall along the Gulf Coast and into central Georgia and South Carolina. Given differences in the way numerical guidance has in terms of how fast the front is progressing...there was some continued adjustments to the placement of the Marginal risk area. South TX Brush Country... An upper low with an associated surface boundary approaching the region should lead to increasing chances for showers and thunderstorms. Expectations are that most of the convection in this time frame will remain west of the international border but there are enough models showing some storms making east of the Rio Grande River with isolated heavier amounts and inferred rainfall rates that could lead to isolated flooding concerns during the late day/evening. Bann Day 3 Valid 12Z Fri May 08 2026 - 12Z Sat May 09 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE LOWER- AND CENTRAL TEXAS COAST ON FRIDAY... Attention shifts to the Lower Texas coast for a risk of excessive rainfall as shortwave energy nears the region from the southern Great Basin and northern Mexico. Low level flow backs in response to the approaching shortwave which results in precipitable water values to exceed 2 inches along the immediate coastline. This occurs at the same time flow aloft is expected to become increasingly diffluent and when the CAPE is approaching 1000 J per kg. This should result in growing coverage of convection that will be capable of producing rainfall rates sufficiently high to result in isolated instances of flash flooding. Bann ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE GULF COAST AND SOUTHEAST UNITED STATES... 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