@ FOUS30 KWBC 200800 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 400 AM EDT Wed May 20 2026 Day 1 Valid 12Z Wed May 20 2026 - 12Z Thu May 21 2026 ...THERE ARE SLIGHT RISKS FOR EXCESSIVE RAINFALL OVER PORTIONS OF SOUTHWEST TEXAS, AS WELL AS FOR EASTERN LOUISIANA INTO SOUTHERN MISSISSIPPI... ...Southwest Texas... Numerous showers and thunderstorms are expected to develop over much of southwest Texas, generally along the Rio Grande from south Texas through the Edwards Plateau this afternoon into tonight. Convection is likely to initiate over the mountains of Mexico and along the dry line north and northeast of the Big Bend Region this afternoon. Meanwhile a surge of deep Gulf moisture, characterized by PWATs nearing 2 inches, will advect up the Rio Grande Valley on a 15-25 kt southeast wind from the Gulf. Where the dry line and this surge of moisture meet is where the heaviest and most persistent showers and storms capable of producing heavy rain will occur. This appears most likely in the portion of the Edwards Plateau near Del Rio. A higher-end Slight remains in effect for this area where the greatest potential of seeing 3 inches or more of rain areally, with locally higher amounts exists. HREF neighborhood probabilities peak over 30% of seeing 5 inches of rain in this area. Given the steep topography, rocky soils, and climatologically dry nature of the area, flash flooding appears likely, especially where the storms are most persistent. During the evening, the storms are likely to separate both from the mountains of Mexico as well as the dry line. They will follow generally parallel to the Rio Grande towards the southeast, following the influx of deep Gulf moisture and instability. Due to recent heavy rainfall from Laredo east through Corpus Christi, the soils here are more saturated, and therefore should be more likely to convert more rainfall to runoff, despite the storms by that point likely being quite progressive. Thus, the Slight extends south to around Laredo. ...Eastern Louisiana into Southern Mississippi... In coordination with LIX/Slidell, LA and JAN/Jackson, MS forecast offices, a small Slight Risk upgrade was introduced with this update for eastern Louisiana into southern Mississippi. A stalling out cold front over central Louisiana will provide the greatest forcing for storms as it tries to progress eastward. Deep Gulf moisture and instability will ramp up ahead of the front with peak heating. However, thunderstorms may still be in progress along the coast from the current storms over Texas. New convective initiation will occur along the front, likely just east of the Mississippi River in Mississippi, and those storms will link up with other clusters of storms further south and west over southwestern Louisiana. Since the front will be slow-moving, and there will be a steady southerly flow of Gulf moisture out ahead of it, the storms will likely have some training elements to them. During peak heating in the mid to late afternoon, the storms will progress into Baton Rouge and New Orleans, adding an urban element to the flash flooding threat. Given the proclivities for those urban areas to flash flood during heavy rain events, the Slight Risk upgrade was introduced. The storms will then progress north into southern Mississippi, which while far less urban, still has somewhat wetter- than-normal soils, which could also promote flash flooding in some areas. Wegman Day 2 Valid 12Z Thu May 21 2026 - 12Z Fri May 22 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHERN PLAINS AND PINEY WOODS REGIONS... ...Southern Plains into the Piney Woods... The dry line across western Texas and Oklahoma will make a big push to the east through the Day 2/Thursday period. The former cold front over eastern Texas will retreat as a warm front towards the north and as renewed push of deep Gulf moisture advects northward with the low level jet. Further, a deep positively tilted longwave trough will eject into the Plains from the Rockies during this period. The combination off all of these factors will result in a large and widespread area of convection stretching from the Gulf Coast of Texas north across eastern Oklahoma and Kansas, as far north as Kansas City. Starting from the south, the convection along the Texas Gulf coast will be associated with the dry line pushing quickly east and running into plentiful Gulf moisture ahead of it. Expect most of the storms from Houston south and west to be fast movers with the dry line. Most of these storms will impact coastal communities Thursday morning. Further north, there will likely be convection ongoing at the start of the period across north Texas (near the Wichita Falls area) and into southwestern Oklahoma. These storms will increase in coverage through the morning as they progress over central Oklahoma. Meanwhile by afternoon, the storms will blossom over northeast Texas and down into northern Louisiana. With moisture continuing to advect north, expect numerous clusters of storms over much of eastern Oklahoma, eventually moving into western Arkansas in the early evening. These areas got pockets of 1-3 inches of rain yesterday, so the newly saturated soils across western Arkansas should support widely scattered instances of flash flooding as multiple rounds of storms move through, and they backbuild south and west. Due to the southerly flow of Gulf moisture, some convection should also progress northward into eastern Kansas and western Missouri through the evening. By this far north instability will be lacking, so not expecting particularly heavy rain, but all of the stronger storms to the south will have merged into a larger area of moderate rain into Kansas and Missouri, which have also seen heavy rains lately, supporting Slight Risk levels of flash flooding. The steady rain there could continue well into Thursday night. ...Southern Appalachians... The clash of a cool air mass behind a back door cold front over Virginia and tropical Atlantic moisture across the Southeast characterized by PWATs over 1.5 inches will support areas of showers and storms across portions of southwest Virginia, western North Carolina, and perhaps into far eastern Tennessee Thursday afternoon into Thursday night. Training convection along the front will be likely, especially along the Virginia/North Carolina border area, where the topography of the southern Appalachians could locally further enhance rainfall rates. Instability will be marginal however due to extensive cloud cover over this area. While the meteorology may support a bit more widespread flooding, the hydrology will be strongly working against that. A long-term drought over the area and extremely dry soils compared to climatology will make much of the rain expected in this area beneficial. However, due to training, plentiful moisture that will support areas of heavy rainfall, and the topography, isolated instances of flash flooding are probable. For now the area remains in a Marginal Risk, but a Slight may need to be considered if forecast rainfall amounts in this area increase appreciably over the next day or so. Wegman Day 3 Valid 12Z Fri May 22 2026 - 12Z Sat May 23 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER THE LOWER TO MID MISSISSIPPI VALLEY, OHIO VALLEY, AND PORTIONS OF THE SOUTHERN PLAINS... As a longwave trough over the northern Plains pivots northeastward through the period, a surface cold front tracking along with it will likely slow its eastward progress along the Mississippi and Ohio Valleys. Plentiful Gulf moisture ahead of the front will support numerous areas of convection all throughout the Marginal Risk area. With the greatest upper level forcing moving away from the front, it will become an increasing struggle to organize the convection in a way such that flooding becomes more likely. From the Ohio Valley to the Mid-Atlantic, plentiful cloud cover and much cooler temperatures will keep the instability near zero, precluding any meaningful heavy rainfall in favor of a long-duration light to moderate rainfall. The heaviest rains appear most likely into the far southern Appalachians (northern AL/GA, western Carolinas, and Tennessee). This is the area that appears most likely to have a Slight Risk upgrade with future updates. Elsewhere, other MCSs may impact the lower Missouri Valley, and along the Texas coast. Dry line convection into Friday evening may impact a good amount of Oklahoma, but once again the storms do not appear to be able to organize to increase the flooding threat beyond the isolated/Marginal category. Wegman 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