282 FOUS30 KWBC 010054 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 854 PM EDT Thu Apr 30 2026 Day 1 Valid 01Z Fri May 01 2026 - 12Z Fri May 01 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF CENTRAL TEXAS... 0130Z Update...Trimmed the northern peripheries of both the Slight and Marginal Risk areas, based largely on observational and guidance trends. Airmass continues to stabilize behind the front per the latest SPC mesoanalysis (negative deep-layer MUCAPE trends over the last 3 hours). Several consecutive HRRRs have supported this southward shift in the elevated ERO threat, which at this point based on the 18Z HREF/RRFS exceedance probabilities, would support the Marginal Risk and embedded low-end Slight Risk area across pars of Central TX. Hurley 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... 21Z update...Very minor reshaping of the Marginal and Slight Risk areas made to reflect small adjustments made in the QPF forecast. The axis of the heaviest rainfall still forecast to span from eastern Texas to eastern Louisiana and southern Mississippi where the best moisture convergence and instability will be present. Recent rains across the western an central Gulf states will have increased soil saturation, lessening the effects of major drought and lowering the amount of additional rainfall required for scattered areas of flash flooding. Hourly rates of 1 to 3 inches/hr to streak from eastern Texas to eastern Louisiana. Campbell 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... 21Z update... Minor broadening of the northern and southern boundary of the Marginal across southern Georgia and northern Florida. The environment described below is still expected along with the potential for isolated flash flooding concerns. Campbell 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