FOUS30 KWBC 191535 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1135 AM EDT Tue May 19 2026 Day 1 Valid 16Z Tue May 19 2026 - 12Z Wed May 20 2026 ...THERE ARE SLIGHT RISKS FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHERN PLAINS AS WELL AS FOR SOUTHERN ILLINOIS AND INDIANA... ..16Z Update.. A line of convection is ongoing and continuing to push southward in eastern OK and northern AR. The inherited SLGT area in TX was expanded northward into parts of southern OK and southwestern AR, to account for an expected round of convection along an outflow boundary, along with convection along the progressing cold front thereafter. While the system is expected to be fairly progressive, rainfall rates will remain quite high. Latest HREF neighborhood probabilities suggest there is a greater-than 70% liklihood of rainfall exceeding an inch per hour, and a greater-than 40% liklihood of rainfall exceeding 2 inches per hour in the early afternoon hours. The SLGT area was also expanded into the Texas Gulf Coast to account for an expected development of a low- level convergence axis along the coast ahead of the cold front this evening and overnight. Latest deterministic guidance suggests a solid low-level jet developing overnight, bringing in rich Gulf moisture, with PWATs potentially exceeding 2 inches. Meanwhile, the SLGT risk area over southern IN and IL was largely unchanged. While some CAM QPF disagreement remains over the amount of rainfall expected, and where the main QPF core is expected to occur, antecendant rainfall over prior days and very low FFGs justify the SLGT being maintained. Blanco-Alcala ..Previous Discussion.. ...Texas... A line of intense showers and thunderstorms currently expanding south across northern and western Oklahoma will continue south and east through the early morning into northeast Texas. With peak solar heating around midday, the line of storms will encounter an increasingly unstable, and increasingly moist air mass situated across much of Texas. Guidance suggests that several lines of storms will develop in north Texas through the early afternoon. Cold pools and lift ahead of the lines should allow individual cells to develop out ahead of the lines, which will locally increase the duration of heavy rains in those areas hit by first the cells, and then the line shortly thereafter. This could cause local flash flooding, especially should that occur over the Metroplex or other urban areas in north Texas. By mid to late afternoon, upper level energy may support areas of convection across central and south Texas that will be separate from any lines to the north. Mergers with the lines as they press south across the state and any individual cell mergers within the clusters of storms may also pose a localized flash flooding threat. By evening, the storms will continue pushing into south Texas, potentially impacting the San Antonio and Houston metros before they push into the Gulf and deep south Texas through the predawn hours. Overall the above-described scenario should keep flash flooding instances mostly to localized, widely scattered occasions. However, since the storms will cover much of the state, it's probable that in flood prone areas, the flash flooding threat could be greater. Unsurprisingly with so many clusters of storms expected, the CAMs are not having a great handle on them, so the Slight was expanded to cover the Texas Triangle. Despite the antecedent dry soil conditions over most of the state, PWATs will likely exceed 2 inches along the Gulf Coast for when the storms reach there tonight. Thus, any and all storms will be capable of heavy rainfall rates that could cause flash flooding. ...Southern Illinois and Indiana... After rounds of showers and storms caused flash flooding in portions of Illinois and Indiana yesterday, the soils in the area are generally saturated due to widespread multiple-inch totals from yesterday/Monday. Much of the day today will be dry. Towards evening however, renewed rounds of showers and thunderstorms will develop with the approach of a strong cold front, significant moisture and instability advection ahead of the front, and upper level disturbances helping add to the overall environmental forcing. Thus, overnight, expect multiple rounds of training showers and thunderstorms tracking up the Ohio River Valley. With a robust LLJ supporting the storms, they should have no trouble maintaining their organization despite the lack of solar heating. Since the soils are fully saturated, most, if not all the rainfall will convert to runoff. Thus, the inherited Slight Risk was expanded southwest to include much of southern Illinois with this update. Wegman Day 2 Valid 12Z Wed May 20 2026 - 12Z Thu May 21 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE EDWARDS PLATEAU REGION OF SOUTHWEST TEXAS... A developing low level jet of deep Gulf moisture will advect northwestward up the Rio Grande in south and southwest Texas in response to height falls and an approaching shortwave moving towards that area from Mexico. Numerous showers and thunderstorms will develop late afternoon across the Edwards Plateau as a dry line pushes east from the Big Bend area. The storms feeding off PWATs of 1-1.5 inches, which is 2-2.5 sigma above normal for this time of year in that part of the country are expected to become plenty capable of producing heavy rain in an otherwise dry part of the country. More susceptibility and plenty of topography in the area will reduce the amount of rainfall needed to develop flash flooding concerns. A general 1.5 to 2 inches of rain are expected in the Edwards Plateau along the Rio Grande, likely falling in a 1-3 hour period as the storms track eastward down the plateau. Thus, a higher-end Slight is in effect from Eagle Pass north and west. As the storms move off the Rio Grande into central Texas, generally towards San Antonio, they should weaken with time as they separate from the dry line and the upper level shortwave rapidly races away by the predawn hours Thursday. This should diminish the flash flooding threat further east for this period. Another area of more concentrated shower and thunderstorm activity will impact the lower Mississippi Valley along the Louisiana/Mississippi border Wednesday afternoon and evening. Due to high FFGs and a lack of agreement in the guidance as to the convective evolution, the area remains in a Marginal for now, but should heavy rain producing storms move over an urban area such as Baton Rouge, then flash flooding could occur. This area will need to be monitored for a Slight Risk upgrade with future updates. Wegman Day 3 Valid 12Z Thu May 21 2026 - 12Z Fri May 22 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE SOUTHERN PLAINS THROUGH THE OZARKS... Numerous areas of showers and thunderstorms will impact the Slight Risk area on Thursday through Thursday night. An ensemble of guidance that covers the Day 3/Thursday period generally agree that Thursday morning, the strongest storms will be across coastal Texas through central Texas. These storms will track northeastward and grow upscale as the impact areas from northern Louisiana, northeast Texas, and Oklahoma. Thursday evening, a new round of storms impacts south Texas as the rest of the storms push northeast into Arkansas, northeast Oklahoma, and into Kansas, which then continue northeast up the mid-Mississippi River Valley and a separate area of storms impacts the Kansas City area. Despite this broad evolution, there is very little confidence on how the storms will behave/merge or track. Thus, the Slight covers likely more saturated soils after rainfall expected in many of these areas on Days 1 and 2. There will be no shortage of moisture and instability across the Slight Risk area, especially the southern half, so it's likely any limiting factor will be a generally progressive forward speed to the storms, and cold pool interactions. It's likely that with future updates, CAMs guidance should help narrow down where the greatest threats for storms will be on Thursday. This should allow the Slight to shrink a bit with better confidence, though much of the region should see at least some rainfall. 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