FOUS30 KWBC 290027 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 827 PM EDT Wed Oct 28 2026 Day 1 Valid 01Z Thu Oct 29 2026 - 12Z Thu Oct 29 2026 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Kleebauer Day 2 Valid 12Z Thu Oct 29 2026 - 12Z Fri Oct 30 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF WEST AND CENTRAL TEXAS... ...Texas and New Mexico... Conditions will be favorable for widespread convection across portions of Texas and New Mexico on Thursday as mid-level energy associated with the remnants of TC Vance move into the region. As the wave approaches, southeasterly low-level flow will bring anomalous Gulf moisture into the south-central U.S., increasing PWATs across Texas to 1.5-2 inches, which is well above normal for this time of year. In addition to mid-level destabilization from the wave, enhanced upper level divergence in the right entrance region of a southern stream jet will support a broad region of ascent across Texas. These ingredients combined with at least modest CAPE (slightly limited due to widespread cloud cover) are expected to support an organized heavy rainfall event. Model guidance continues to trend north and west with the QPF footprint of this event, which has resulted in a northward expansion of the preexisting Slight Risk area across portions of West and Central Texas. There is good agreement from model guidance showing the heaviest precipitation totals (2-4 inches, locally higher) focusing between the Stockton and Edwards Plateaus and the Midland area. This cycle's HREF guidance pointed to at least moderate probabilities for 3 inches in this area but dropped off to less than 15 percent for 5 inches. Rainfall rates of 1 to 2 inches per hour (locally higher) will be possible within the Slight Risk area. There was not enough of a signal to introduce a Moderate Risk this cycle, moreso due to the general lower confidence in more extreme rainfall totals or rates. Surrounding the Slight Risk area, there is a broader Marginal Risk area that covers much of the western half of Texas to account for locally heavy rainfall potential extending further north and west. The Marginal Risk also includes southern New Mexico where the combination of Gulf and Pacific moisture will allow for scattered to widespread convection, and there should be sufficient CAPE to allow for locally heavy rainfall rates. Locally heavy rainfall over sensitive terrain and burn scars could cause flash flooding, especially considering how saturated soils are after recent heavy rains in this region. Dolan/Taylor Day 3 Valid 12Z Fri Oct 30 2026 - 12Z Sat Oct 31 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF CENTRAL AND SOUTHERN ARIZONA... ...Southwest... Broad troughing will move into the western U.S. with embedded shortwave energy moving across portions of the Southwest on Friday. Meanwhile, a strong southern stream jet will approach Baja California, placing Arizona under the favorable left exit region with enhanced upper level divergence. Southerly low-level flow will direct Pacific moisture into the area as well, bringing PWATs up to 1-1.4 inches across the southern half of Arizona (2-3 standard deviations above normal). This warm, moist air mass will also increase instability, with MUCAPE values potentially exceeding 1000 J/kg across much of southern Arizona. With favorable conditions throughout the atmospheric column, scattered to widespread convection is expected to develop with the passing of the upper shortwave. Model guidance has been consistently showing elevated precipitation totals along and south of the Mogollon Rim, and there is a Slight Risk of excessive rainfall in place that includes most of central and southern Arizona. The Slight Risk also includes some of the terrain in southwestern New Mexico that should also see scattered convection. Persistent showers/storms with moderate to locally heavy rainfall rates could result in scattered instances of flash flooding, especially near steep terrain and burn scars. The risk of flash flooding is also slightly heightened across portions of Arizona and New Mexico where an anomalously wet pattern has resulted in increased soil moisture. Much of the southwestern U.S. is included in a broader Marginal Risk area due to increased moisture and support for at least isolated to scattered convection, but the flash flood risk is a bit lower since the best moisture and instability will be limited to southern Arizona. ...Texas and Oklahoma... The mid-level circulation associated with the remnants of TC Vance will continue to move north across the southern and central Plains on Friday while becoming more organized, which could support a continued heavy rainfall threat for portions of Texas and Oklahoma. The southern stream jet should shift north, maintaining favorable conditions for convection over the area through Friday afternoon. Anomalous moisture will remain in place across the southern Plains, but instability may become the limiting factor for heavy rainfall. The best instability looks to be displaced to the north across the central Plains and into the Midwest while cloud cover limits instability to the south. If convection can tap into enough instability, there will still be at least an isolated risk of flash flooding across Texas and Oklahoma and even into southern Kansas, and there is a Marginal Risk in place for isolated to widely scattered instances of flash flooding. Dolan/Taylor Day 4 and Day 5 Valid 12Z Sat Oct 31 2026 - 12Z Mon Nov 02 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHWEST THIS WEEKEND... ...Southwest... 20Z Update: The general synoptic pattern for the Southwest into Southern California remains consistent in its presentation with the latest 12z NWP suite and ML outputs. A high-end scenario for flash flooding in the D5 time frame (12z Sun - 12z Mon) is increasingly likely given the progged upper level evolution and anomalous moisture advection regime slated to impact the region during the middle to late part of the weekend, extending a bit into early next week. Recent QPF trends label much of AZ through southern UT and the Four Corners area as the primary impact points for this coming event with the greatest PWAT anomalies and positive vorticityadvection moving directly into the region allowing for widespread heavy rainfall, especially into the terrain with prevailing upslope flow likely. Ensemble mean QPF is currently robust at such leads with area wide 1-2" markers showing up in Mogollon Rim, northern AZ mountains, and the Canyon areas of both northwest AZ into southern UT. The area out by the Four Corners towards the San Juans will see another bout of heavy rainfall with the expansion likely into areas further south towards Navajo Nation. These areas have already seen multiple moderate to high impact events the past 2-3 months with one recently causing significant flash flooding across the above areas. This setup will likely spur another threat for such a scenario leading to a heightened risk for upgrades in the coming forecast updates. So long as the signal remains consistent, the threat will likely trend towards a more impactful scenario with plenty of guidance leaning in that direction as of the 12z global deterministic and ensemble suite. Kleebauer ..Previous Discussion.. An anomalous and potentially high impact setup is taking shape for the Southwest as a longwave trough moves into the West Coast this weekend. The depth of the trough over the eastern Pacific may drop below the climatological 1st percentile for the time of year. Deep, broad southwesterly flow downstream of the trough will tap into subtropical and tropical moisture, driving PW values to near or even above record values for the time of year. The combination of strong dynamic forcing and wind fields, and near record caliber moisture will support a broad swath of moderate to heavy precipitation, maximized across orographically favored slopes. Given lingering hydrologic sensitivity from preceding rainfall across the region, runoff issues and some flooding appears likely even without significant convective enhancement. Widespread cloud cover should generally limit destabilization, but if and where pockets of CAPE are able to develop, a more pronounced flash flood threat could evolve. Forecast guidance exhibits some convergence, with the 00z ECMWF and AIGFS tending towards the consistent AIFS solution. Our preference is in this direction, with less weight given to the GFS. This model preference paints an overall wetter and more impactful scenario for the Southwest. While Saturday (day 4) sits ahead of the strongest synoptic scale forcing, the anomalous moisture axis will be established. A Slight risk has been introduced centered across central AZ into southern NV. Many of these areas will have seen heavy rain and convection on Friday (day 3), leaving hydrologic conditions more primed. Although large scale forcing and instability may dip compared to Friday, persistent 850mb moisture transport and modest instability should be sufficient to sustain some convection and a continued isolated to scattered flash flood risk. Stronger large scale forcing overspreads the region on Sunday (day 5) as the main trough axis approaches, resulting in more widespread precipitation. While cloud cover will hinder destabilization, cooling aloft and some cloud breaks should support some destabilization as the trough axis approaches. The greatest overlap of forcing, moisture and instability is forecast across portions of AZ into southern NV and southern UT, where a day 5 Slight risk has been issued. An expansive Marginal risk surrounds this corridor to account for the broad stratiform rain and lower rain rates falling over a saturated region. Given the magnitude of moisture, dynamics and terrain enhancement, the setup has the potential to produce Moderate risk level impacts if adequate instability materializes. Trends will be closely monitored over the coming days. Confidence is a bit lower over southern CA. Model guidance indicates that an area of low pressure could enhance the convective threat and rain rates late Saturday night into Sunday morning. Because this straddles the day 4 and 5 forecast periods and mesoscale details remain fluid, southern CA will remain within a Marginal risk for now. However, an upgrade to a Slight risk on day 4 and/or day 5 remains a distinct possibility on subsequent forecast updates. Chenard ...Central Gulf Coast into the Lower MS Valley... 20Z Update: The only change to the previous forecast was to expand the MRGL risk further east, mainly for areas south of I-20 through MS/AL as ensembles continue to depict heavier rain chances downstream despite spread within the deterministic. ML guidance is more correlated to the heaviest rainfall in-of the Lower Mississippi Valley which matches the previous forecast. Considering the spread in both the D4 and D5 time frames, refrained from much change and any upgrade opportunities. Believe the setup is conducive for localized 3+ inch totals in spots, but not as keen on the widespread nature of the heavier totals as indicated via the ensemble bias corrected guidance. FFG's remain elevated in this area of the country to begin with, so that will also thwart more appreciable impacts with most of the flash flooding potentially relegated to those urbanized zones where the run off potential is more common given the impervious surfaces present. Maintained the MRGL risk as a result. Kleebauer ..Previous Discussion.. The system responsible for the Southern Plains heavy rainfall on day 2 and 3 will shift into the lower and mid MS Valley on day 4 (Sat). The mid level shortwave and left exit of an impressive jet will provide synoptic ascent for convection. Limiting factors for flooding will be a fairly quick progression of the system, questionable instability, and very dry antecedent conditions. Overall, the model signal for flash flooding is not as robust as it was yesterday and considerable model spread remains. We continue to not prefer the quicker GFS solution, instead favoring something closer to a consensus of the ECMWF/AIFS/AIGFS. Given the dry antecedent conditions, any flash flood threat will likely be high rain rate driven over urban areas or other sensitive basins. Based on our model preferences mentioned above, the best chance of this occurring is pretty far south, from the central Gulf Coast into portions of the lower MS Valley. Thus the Marginal risk was confined to just these areas with this update. Too much model spread to introduce a risk on day 5. The GFS is an outlier and not preferred. If there is a flash flood risk this day it is probably centered over FL, where the EC/AIFS/AIGFS show an axis of more concentrated convective potential. Chenard 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 $$