FOUS30 KWBC 071601 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1101 AM EST Sat Nov 7 2026 Day 1 Valid 16Z Sat Nov 07 2026 - 12Z Sun Nov 08 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF SOUTH, CENTRAL, AND WEST TEXAS... ...16Z Update... GOES water vapor imagery currently shows a closed mid/upper low digging into northwestern Mexico, with large scale forcing for ascent increasing downstream across western Texas. Precipitation will continue to blossom over the next several hours, though weak elevated instability should limit rainfall rates and thus flash flooding potential outside of localized, transient convective cores. The relatively higher threat will begin to take shape farther south and east across southern Texas later this evening into tonight (and espectially into Day 2/Sunday), where an intersection of moist, easterly, upslope flow, a stout low-level jet, and modest surface based instability lead to more sustained convection and higher rainfall rates. Given fairly dry soils and high FFG values, initial rainfall will likely take some time to saturate before any localized flash flooding concerns can materialize (which again becomes relatively more likely going into Day 2). As a result, the current forecast remains on track and only minor cosmetic changes were made to the current Day 1 ERO. Miller ...Previous Discussion... Current radar across the Southwest CONUS into west TX indicates a steady progression of our upper trough as it migrates southeast through AZ with the analyzed height field indicating the trough amplifying and expected to close off over the next 12-24 hrs. As the trough progresses into northern Mexico, anticipating the regional ascent pattern to become favored across southwest TX through the Big Bend leading to minor flash flood prospects within the diffluent pattern materializing downstream of the trough/upper low once it develops. Models remain consistent in their presentations of scattered convective pulses, most of which will be weak and elevated in their organization leading to relatively low chances for flash flooding for areas west of the Pecos River today, but threat is non-zero based on some of the low-end probs, but not enough for a broad risk (MRGL). Across the Stockton Plateau into the Edwards Plateau and neighboring Rio Grande Valley (RGV), the threat will be delayed compared to upstream as the main convective prospects in the afternoon and early evening will be back into Mexico as the primary ascent will be focused within the Mexican State of Coahuila and the in the vicinity of the Serranias del Burro. By the evening into the early morning hours Sunday, expecting a quick development of elevated convection across the RGV into those neighboring areas with the REFS indicating a pretty strong signature for heavy rain across the area between Val Verde down through Maverick counties and counties adjacent. This makes sense synoptically as we begin seeing the influence of increasingly diffluent flow into the RGV with an intersection of a modest 30kt LLJ funneling up the Rio Grande, advecting a richer moisture source within the sfc-700mb layer that can be tapped into for more efficient rainfall prospects. REFS neighborhood and EAS probs indicate a relatively solid chance for locally 1-2" of rainfall along the RGV with perhaps some protrusion into the western edge of Hill Country. This is mainly the beginning of the more active setup that will translate into the eventual D2, but the initial threat will offer a low-end prospect for flash flooding, especially in any urban zones along the RGV up into the Lower Trans Pecos where run off capabilities are higher. A MRGL risk continues to compass those areas of the Stockton Plateau, across into the Concho Valley, and down the Rio Grande with emphasis on the central RGV between Del Rio to Laredo. Kleebauer Day 2 Valid 12Z Sun Nov 08 2026 - 12Z Mon Nov 09 2026 ..THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS SOUTH- CENTRAL AND SOUTH TEXAS... By Sunday morning, the overall synoptic evolution will lend to a classic isentropic pattern situated over the Edwards Plateau through Hill Country, sinking southward into South TX as we move into the back half of Sunday. Prevailing southeast flow between the surface to 850mb will lead to an ushering of low-level moisture that will send PWATs surging between 1.5-2.1" with the highest moisture prevalence located over the Southern RGV over to the Gulf Coast, mainly south of Corpus Christi. Directional shear will entice the potential for mesocyclone development and the ability to sustain convection, mostly elevated, in-of a shallow surface trough bisecting the region, leading to enhanced precipitation rates with longevity due to the persistence in the diffluent flow aloft. This whole setup will materialize and become a fixture for at least 24 hrs with a broad area of moderate to heavy rainfall with embedded convection situated across Southern TX with the core located along and south of I-10. Beginning to see a nice overlap in the placement of the heaviest QPF for the period with a broad 2-3" area situated over the central RGV over into south-central TX with a core located over the Hill Country, down to the southeast near the area of King Ranch. Most of the global and hi-res deterministic are quite bullish on locally heavy totals between 4-6" with the latest 00z ECMWF even coming in with 8+ to the east of Laredo. That seems to be the upper threshold of the potential, especially when assessing the REFS neighborhood probs for >5" hovering between 40-60% in the same location with a modest 20-35% signal to the south and east. ML output is consistent in the heavier QPF placement, as well, with the corridor of the heaviest rain between Hill Country and the central RGV down to the southern tip of TX near Brownsville. With general agreement among ensembles and ML with deterministic overlap, seeing a growing confidence in significant rainfall of >3" in places outlined. The environmental conditions are the only thing that will keep this from being a more prolific setup with the primary convective posture leaning more elevated in nature as we move into Sunday evening as noted via forecast soundings from both the RRFS and GFS/ECMWF deterministic across South TX. This pointed towards maintaining the previous SLGT risk forecast with only smaller adjustments made to align with the latest >2" probabilities within the latest REFS and NBM signaling at least at a 30%. The core of the greatest probs continue to settle between Laredo and Corpus Christi with emphasis on the Webb/Duval/Zapata county areas. Kleebauer Day 3 Valid 12Z Mon Nov 09 2026 - 12Z Tue Nov 10 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTH TEXAS... The pattern will begin to breakdown across the Southern Plains with drier air filtering back in from the north and primary ascent pattern fading with the mid and upper level evolution taking place. Guidance continues to lean into a short time frame in the D3 where some heavy rain chances linger into Monday morning before we finally see the threat scale completely back and the chances end from west to east. Additional totals of 1-2" are possible as noted via some of the global deterministic. The most notable area of interest will likely be over the immediate southern TX coast where the greatest instability and the likely final spot that sees the precip pattern move out. This allowed for confidence in continuing the previous MRGL risk with some adjustment based on the ensemble mean QPF distribution. Not anticipating significant impacts to the southeast TX coastal plain, but will be an area to watch, especially if the threat ends up being a little further west into the population centers of far southern TX. If the heaviest rainfall anchors to the coast, that will likely limit more appreciable impacts due to the sandier soils and lower urban footprint. Kleebauer Day 4 and Day 5 Valid 12Z Tue Nov 10 2026 - 12Z Thu Nov 12 2026 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Hurley 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 $$