582 FOUS30 KWBC 300806 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 406 AM EDT Thu Apr 30 2026 Day 1 Valid 12Z Thu Apr 30 2026 - 12Z Fri May 01 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN CENTRAL TEXAS... A two part setup for heavy rainfall will materialize over the Lower Mississippi Valley back into Southwest and Central TX during the period. Weak mid-level perturbations will ripple out of the Southern Plains into the Lower Mississippi Valley by late Thursday morning, encountering a generally favorable airmass positioned across central and southern LA into southern MS. Moisture anomalies hovering between 2-3 deviations above normal will reside within that corridor between Baton Rouge to the southeastern corner of LA with a general instability maximum located over the same area. A round of convection will develop across the southern half of the state with the latest CAMs all in agreement on the heaviest rainfall occurring along the I-10 corridor down to around the New Orleans metro, an area more viable for flash flooding due to the urban footprint. Rainfall rates between 2-3"/hr at peak intensity are anticipated in the forecast environment located over southern LA, more than capable for localized flash flood concerns especially when you couple with some of the recent priming from rainfall that occurred the past 24hrs. 00z HREF neighborhood probs for >3" are running hot between 40-60% located directly over the New Orleans metro and neighboring areas around Lake Pontchartrain. The overlap of CAMs signaling heavy rainfall in this vicinity prompted an addition of a MRGL risk for the region which generally extends back along I-10/12, aligning with the position of a quasi-stationary front in the region. Further west into west TX and the Southwestern U.S, a more formidable large scale synoptic evolution will enhance ascent over a broad area of the Southwest US into the southwest portions of TX leading to a rapid development of convective initiation that will lead to scattered flash flood prospects in wake of their development. A strong mid-level shortwave trough will eject out of Chihuahua with sights on the southwest reaches of TX by Friday evening. A moist, unstable airmass will preclude the trough approach with an amplifying mid-level evolution allowing for a strengthening nocturnal LLJ developing across west-central TX down the Rio Grande. At the surface, a weak quasi-stationary front will be positioned across Central TX which will be a key component for maximizing low-level convergence in the areas it resides. Models are consistent in the development of convection across southwest TX by late-afternoon due to the arrival of the mid-level ascent and diurnal instability coupling that will develop during peak heating. As we begin to integrate the LLJ into the pattern, this, combined with the increased forcing and shear provided by the trough approach will enhance a broad convective initiation with the highest coverage likely to ensue over the terrain of southwest TX over into the Edwards Plateau and neighboring Hill Country. 00z HREF neighborhood probs for >2" are pretty robust (50-90%) over the entire area referenced with the highest probs centered over the Lower Trans Pecos into the neighboring Edwards Plateau and Hill Country along and north of I-10. The evolution of the upper pattern inspires a prolonged nocturnal convective regime that will promote hours of heavy rainfall prospects with some places likely to breach 3" where cell training and/or repeated cells occur. This has been very consistent within the means of the QPF distribution the last few days with a solid output promoted via the ML, which has been rock steady on its presentation the last several cycles. The SLGT risk inherited was maintained, but shifted a bit south to account for trends in heavier QPF orientation of the CAMs, trending closer to the ML axis of heaviest precip from the past few days. The overlap of the CAMs and ML provides higher confidence in the setup, thus expectations for scattered flash flood instances are warranted. Kleebauer Day 2 Valid 12Z Fri May 01 2026 - 12Z Sat May 02 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN CENTRAL AND SOUTHEAST TEXAS AND THE CENTRAL GULF COAST... A prolific upper level evolution coupled with a broad axis of formidable moisture anomalies and instability will stand to produce a widespread axis of heavy rainfall across the Southern Plains in TX over through the Lower Mississippi Valley on Friday into Saturday morning. At the surface, a slow-moving quasi-stationary front will orient itself across south-central TX down to around the Gulf coast with a wave of low pressure riding along the boundary during the forecast period. PWAT's will run between the 95-99th percentile (NAEFS climatology) across Hill Country over into Southeast TX and neighboring LA. These PWATs (1.7-2.1") are notable for producing more efficient warm rain processes, noted very well by the warm cloud layer depths presented in various point soundings in the 00z deterministic suite. Thunderstorms will be ongoing the night prior as large scale ascent is maximized with the approach of a strong mid-level shortwave ejecting out of Chihuahua with a well-defined axis of diffluence located downstream of the mean trough. These storms will continue through the morning as the nocturnal LLJ will maintain some of its muster through the evolving synoptic scale process leading to enhanced convergence over Hill Country, eventually migrating eastward into Southeast TX by the late-morning and afternoon. The primary shortwave and attendant surface reflection will quickly advance eastward with the aid of a digging mean trough shoving through the Central US, acting a bit as a "kicker" in the overall upper level synopsis. This will provide a period of enhancement as cells re-ignite across Southeast TX and LA, especially in the confines of the quasi-stationary front positioned over the southeast portion of TX. Where this boundary bisects will be important in the location of convective development and the prospects of training as the mean flow will run relatively parallel to the boundary which typically promotes better training episodes and/or repeated rounds of convection in a given area. Rainfall rates are likely to be between 1-3"/hr in the heavier cells, and multiple rounds of these rates would easily prompt localized totals greater than 3" with a potential for greater than 5" as inferred by the 90th and 95th percentile of the 01z NBM 24hr QPF prob fields. The 00z HREF currently only covers the first half of the period, but it is notable the probs for >3" are very high (50-80%) for a large portion of Central TX, including the I-35 corridor between Austin/San Antonio and along I-10 as you move east between San Antonio and the Houston metro. Heaviest rainfall for these areas will likely materialize for southeast TX after 18z Friday with an ongoing heavy rain threat well into the evening before the large scale pattern shunts east with dry air advection occurring in wake of the shortwave trough passage. This setup is conducive for more widespread flash flood prospects with even some locally significant flood impacts for areas hit the hardest. The current setup likely puts places along I-10 from San Antonio over to Houston, especially the northern suburbs and exurbs in the cross-hairs with the northern extension up towards the Piney Woods area. This is the area with an areal average QPF between 2-3" and local maxima likely to exceed 5" in spots. This axis of heavier rain will expand eastward along I-10 into LA by late-Friday into early Saturday morning putting places from Baton Rouge over into far east TX as the secondary area of interest. A high-end SLGT is currently forecast for this entire corridor referenced above with a potential for a targeted upgrade as we move closer to the period as CAMs come into better focus and we monitor trends in the expected upper evolution. This scenario has a history of a trail of flash flood warnings stretching hundreds of miles, so this is a period to watch very closely. Kleebauer Day 3 Valid 12Z Sat May 02 2026 - 12Z Sun May 03 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHEAST U.S... Progressive upper pattern will lead to a fast-moving convective episode across the Southeast with the primary focus likely occurring over the Florida Panhandle up through southern GA and the Low Country of SC. The setup promotes a relatively favorable environment suitable for heavy rainfall with the stronger cell cores capable of producing rainfall rates between 1-2"/hr. Regional FFG's remain elevated across this portion of the CONUS, however there's enough of a signal for the potential of some urban flooding across the aforementioned areas with the best opportunities in those larger urban footprints in FL and GA. Deterministic outputs range from scattered 1" totals to more bullish 2-3" areal averages, all pending on the propagation speed and magnitude of the anticipated line of convection moving out of AL. Maintained general continuity in the MRGL risk from the previous forecast, but removed the areas near Tampa as rates likely remain insufficient for anything appreciable to trigger flash flooding. Kleebauer 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