FOUS30 KWBC 082000 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 300 PM EST Sun Nov 8 2026 Day 1 Valid 16Z Sun Nov 08 2026 - 12Z Mon Nov 09 2026 ..THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS SOUTH- CENTRAL AND SOUTH TEXAS... ...16Z Update... The latest runs of the HRRR seem to have the best handle on the ongoing mesoscale setup across South Texas, depicting a persistent, convergent line of convection from near Brownsville northward to near Corpus Christi and points westward towards Duval county. Subsidence west of this line has allowed precipitation to mostly diminish, and models indicate any rainfall that returns should be much less problematic. In coordination with WFO BRO, decided to trim most of the SW portion of their CWA out of the existing SLGT risk and keep it confined closer to the coast. North of BRO's CWA, the concern is for another round of convective development later this evening and overnight to bring more heavy rain to an area that has already received more than 2" (with some locations from east of Laredo eastward to near Kingsville having received over 5"). Given those concerns, the SLGT (which is considered to be an "enhanced" SLGT) remains in place with only minor adjustments to account for the latest observational trends and model guidance. Miller ...Previous Discussion... Current UA analysis and WV satellite presentation depict a deep, closed upper reflection positioned over northern MX with a prevailing southwest flow aloft encompassing the Southern Plains of TX. A modest diffluent signature within the associated height fields indicate a persistent ascent pattern between the Big Bend down into the lower Rio Grande Valley (RGV) leading to copious waves of showers and thunderstorms positioned along the RGV, extending northeast into the northeastern part of the state. Recent radar trends indicate a larger areal extent of convection positioned along the immediate RGV as the coupling of large scale ascent from our trough/ULL over MX interacts with a budding 30-40kt LLJ centered basically on top of the RGV itself. This setup is going according to plan with guidance and the current analysis in- line with the general synoptic evolution and the precipitation distribution across the state. Expectation is for heavy rainfall to continue with a conglomeration of convection centered over south- central TX in the vicinity of a strengthening surface trough positioned over the interior portions of South Texas, mainly bisecting the areas between Bexar county down to Cameron at the southern tip of the state. Assessment of the hi-res CAMs indicate a multi-wave scenario with one round of heavy rainfall in the early portion of the forecast transitioning to a complex of convection centered over the eastern sections of Webb county over towards Corpus Christi by the afternoon. Latest hi-res ensemble outputs note a solid 2-4", locally higher occurring during the afternoon and early evening hours before we see some re-firing of the convection over Deep South TX with the re- development of the nocturnal LLJ tonight into early Monday. REFS blended mean QPF is fairly robust with a widespread 3-6" with as much as 8" occurring during the full period with rates generally capped between 1-2"/hr at peak intensity as MUCAPE will remain relatively low despite the modest theta_E presence. REFS neighborhood probabilities for >3" remain elevated with a large area of 60-90% probs centered over much of South TX, mainly south of I-10 with the highest threat over the area encompassed by Webb county over towards Corpus Christi. This area, despite fairly high FFG thresholds, will still have a better than normal opportunity for flash flooding due to extended priming and longevity of the convective pattern overhead. Rainfall rates coupled with the longstanding expectation of moderate to heavy rain will boost the threat as we move forward in the D1 leading to the best chances occurring in the late-afternoon and evening time frame today, carrying into early Monday morning. The previous SLGT and enhanced SLGT forecast was relatively unchanged from the last update as guidance remains in solid agreement on the convective details and heavy precipitation positioning. A targeted upgrade is possible pending the evolution and observed trends in the rainfall accumulations and relevant flood obs that could occur. This would likely be proposed in future updates, but current indications signal a continuation of the SLGT risk with enhanced wording for those above locations. Kleebauer Day 2 Valid 12Z Mon Nov 09 2026 - 12Z Tue Nov 10 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTH TEXAS... ...20Z Update... Forecast thinking generally remains the same for the Day 2/Monday ERO, featuring a gradual decline in convection after 18Z as instability wanes. Prior to 18Z, showers and storms are still likely to contain heavy rainfall rates, which could lead to flash flooding concerns lingering from Day 1 into Day 2. The 12Z HRRR and 12Z RRFS/REFS in particular are highlighting the potential for another focused/convergent line of convection to set up along and just inland of the Gulf Coast from Brownsville to Corpus Christi Monday morning, with 2-4"+ of additional rainfall on top of what has already fallen (and will fall through the remainder of Day 1). Given the recent positive performance of the HRRR, this scenario is plausible and would certainly justify a small targeted upgrade to a SLGT risk. However, in coordination with WFO BRO, opted to hold off on an upgrade pending additional observational and guidance trends heading into this evening and overnight. Otherwise, the existing MRGL risk was largely left unchanged aside from minor adjustments to fit the latest guidance. Miller ...Previous Discussion... Expectation is for the setup to begin slowly breaking down on Monday with the mid and upper level pattern transitioning from less of a closed reflection to a more positively tilted upper trough positioned over the Southern Plains. The low-level flow will remain more east to northeast across all of South Texas leading to a small area of convergence within proximity to a decaying surface trough positioned over the region. Models are consistent in their interpretation of lingering rainfall for areas south and southeast of I-10 with the best threat likely over the interior areas to the west and northwest of Corpus Christi, down through the far South Texas coastal plain. Models are typically within the range of an additional 0.5-1" on average with locally higher totals possible in a narrow corridor along the decaying surface trough. That said, there's a few ensemble members from the REFS suite, as well as the HRRR that are more bullish with local totals pushing 2-4" additional, on top of what will already be a very saturated ground after what transpires on D1. It's something we'll monitor closely as this would prompt a short term upgrade until the threat fully wanes after 18z Monday, an agreement from all models with a sharp decline in FFG exceedance probabilities for all 1/3/6 hour thresholds. The previous MRGL risk was maintained as a result, but will assess in the coming forecast updates to see if a targeted upgrade is necessary for that area just inland of the South TX coast. Kleebauer Day 3 Valid 12Z Tue Nov 10 2026 - 12Z Wed Nov 11 2026 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Miller Day 4 and Day 5 Valid 12Z Wed Nov 11 2026 - 12Z Fri Nov 13 2026 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Bann 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 $$