FOUS30 KWBC 291541 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1141 AM EDT Thu Oct 29 2026 Day 1 Valid 16Z Thu Oct 29 2026 - 12Z Fri Oct 30 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF WEST AND CENTRAL TEXAS AND SOUTHEASTERN NEW MEXICO... ...Texas & New Mexico... Confidence remains high in a heavy rainfall event this afternoon through tonight across portions of Texas and New Mexico as a mid- level disturbance previously associated with Vance moves into the region this afternoon and evening. Southeasterly low- level flow will prime the atmosphere ahead of the system, increasing PWATs to 1.5-2 inches across much of Texas, which is well above normal for this time of year. This translates to 1.5-1.75" for TX and 1-1.25" for southeast NM. Effective bulk shear is presently near 30 kts, which should organize convection. An upper level southern stream jet will lift across the southern Plains, placing Texas under the favorable right entrance region with enhanced upper level divergence. This will create large scale ascent across the region that should support widespread convection across Texas and southern New Mexico. MU CAPE is forecast to remain near 500-1000 J/kg across in and near portions of the Slight Risk area. The available ingredients support the concept of hourly rain amounts to 2", which could occur with cell mergers, cell training, or where a random mesocyclone occurs. A combination of the 12z REFS/HREF indicates that local totals of 5" are possible very near the TX/MX border. The highest event totals should focus on the southern side of the Slight Risk area where the highest moisture values are expected to pool and will likely produce a high-end Slight Risk scenario. The more widespread risk of flooding will come from the prolonged nature of this event, with moderate to locally heavy rain expected across much of West and Central Texas and into southeastern New Mexico through tonight and into Friday morning. Some of the eastern portion of the risk areas has minimal, if any, top soil, which would aid the flash flooding potential due to increased runoff. The risk areas from this issuance strongly resemble continuity. MO/KS/IA/NE irregular border junction... A warm front at 850 hPa lifts northward, with a pool of instability in its wake. Precipitable water values rise to 1.25" or so. The 12z HREF shows a backbuilding convective scenario unfolding from 04z onward, and shows the probabilities of 3"+ maximize in a point near the NE/MO/KS border junction. The 12z REFS has a milder signal somewhat displaced to the southwest, which is counter its traditional bias. There's enough going for it for add a Marginal Risk. Flash flooding would be most likely in urban areas, where 1.5" in an hour is possible. Roth Day 2 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 develop over the West 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 Friday afternoon. 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 forecast to reach 700-1000 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 Friday afternoon and evening. Deterministic and ensemble model guidance continues to show elevated rainfall totals along and south of the Mogollon Rim where there is a Slight Risk of excessive rainfall. Available hi-res and global models forecast rainfall rates exceeding 3hr FFGs (1-2 inches) across central and southern Arizona on Friday afternoon and evening. Both the HREF and REFS show moderate probabilities (30-60%) of 6hr QPF exceeding 2 inches and precipitation exceeding FFGs. Given the sensitive terrain in the area and relatively moist soils across central and southern Arizona, this setup will likely produce scattered instances of flash flooding. A broader Marginal Risk area surrounds the Slight and includes portions of southern Utah and New Mexico where there will also be scattered convection, but the flash flood risk will be more isolated as rainfall rates are less likely to exceed FFGs. ...Texas and Oklahoma... Widespread moderate to locally heavy rainfall will continue into Friday morning across portions of Texas and Oklahoma as the remnants of TC Vance move northeast across the southern and central Plains. 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 cloud cover will once again limit instability. With favorable dynamics, there should still be enough support for locally heavy rainfall, but it will be tough to get rainfall rates that exceed hourly FFGs. The flood risk will mainly be a function of duration, with rainfall impacts compounding from Thursday into Friday. The highest risk of flash flooding will likely materialize over portions of Texas where the QPF footprints will have a bit of overlap from Thursday to Friday, but the highest rainfall totals on Friday should mainly be displaced to the northeast from the heaviest rainfall on Thursday. The flash flood risk will be relatively low, but enough for isolated instances of flash flooding and a Marginal Risk of excessive rainfall. Dolan Day 3 Valid 12Z Sat Oct 31 2026 - 12Z Sun Nov 01 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF CENTRAL AND SOUTHERN ARIZONA... ...Southwest... A deep upper level trough/low will move over the West Coast on Saturday, sweeping up a potent Pacific shortwave and directing it into the Southwest by Saturday evening. This system will be accompanied by an amplified southern stream jet that will enhance divergence over portions of the Southwest Saturday evening into Saturday night. Ahead of the system, a stream of subtropical moisture will increase PWATs above 1 inch across southern California, southern Nevada, and Arizona, and even above 1.5 inches for portions of central and southern Arizona. These values are highly anomalous (4-6 standard deviations above normal) for this time of year and should support widespread precipitation as the shortwave moves onshore. CAPE will be the limiting factor in this scenario, with cloud cover keeping MUCAPE to only a few hundred J/kg over portions of central and southern Arizona with little to no CAPE elsewhere. Given this setup, locally heavy rainfall will be possible across much of the Southwest, but rainfall rates may be limited outside of favorable locations in Arizona where there is a Slight Risk of excessive rainfall. Portions of Arizona will also see heavy rainfall on Friday, which may increase the sensitivity to flash flooding with additional rainfall through Saturday night. There is still some uncertainty in the timing of this system, the GFS is notably slower than other deterministic (physical and AI) models, but the WPC forecast favors a faster solution that is closer to the general model consensus. This event will continue into Sunday, and conditions are expected to become more conducive for a widespread heavy rainfall event across the Southwest. ...Central Gulf Coast and Lower Mississippi Valley... There is potential for locally heavy rainfall somewhere between the Mid-Mississippi Valley and central Gulf Coast on Saturday, but the risk of flash flooding is questionable at this time. Over the Gulf Coast, an amplified jet will create upper level divergence and southerly flow will increase moisture and instability across the region. The problem will be that the main shortwave triggering convection will be strongest to the north in the Midwest and Ohio Valley. With these ingredients out of sync, it will be hard to get heavy rainfall that exceeds FFGs. Global models have trended lower with QPF, now showing a broad area of 0.5-2 inches over 24 hours, with a high amount of uncertainty in location of the higher totals. Soils from the Mid-Mississippi Valley to the Gulf Coast are anomalously dry, resulting in high FFGs. Most of the area would need over 3 inches of rainfall to cause flash flooding, which is looking unlikely at this time, so the inherited Marginal Risk of excessive rainfall was removed. It's possible a Marginal will be needed for a portion of this area in future forecasts, but there would need to be more agreement on the location of locally heavy rainfall to support it. Dolan Day 4 and Day 5 Valid 12Z Sun Nov 01 2026 - 12Z Tue Nov 03 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHWEST SUNDAY... ...Southwest to Plains/Mississippi Valley... A potentially high impact setup remains possible over the Southwest on Sunday. A deep longwave upper trough will be located over the West Coast early Sunday, while an anomalously far south southern stream shortwave tracks toward/into southern California/northern Mexico while carrying a surface low pressure system, with these features merging later Sunday. The combining features will bring strong forcing to the Southwest, including the right entrance region of the upper jet. Moisture-wise, IVT anomalies start to max out (for this time of year) in southern Arizona and vicinity Sunday per the NAEFS Ensemble Situational Awareness Tables, as strong and deep level Pacific moisture takes aim at the region. Widespread moisture and cloud cover may limit instability a bit, but at least a modest level of instability is forecast to develop, given the strong troughing aloft should steepen lapse rates. Soil moisture remains rather wet in most areas due to heavy rain over the past days and weeks, increasing the flooding threat hydrologically. All this, plus potential terrain enhancements to rainfall, yields what is considered a higher-end Slight Risk across the Southwest on Sunday. Moderate Risk level impacts are possible and this potential will continue to be monitored in future forecasts. A broader Marginal Risk expands west through southern California and east across much of New Mexico. The deep upper trough is forecast to track east across the Intermountain West on Sunday night and Monday, with the southern stream shortwave enhancing flow as it tracks northeast through the eastern side of the broader trough. A strong southerly low level jet will set up across the Plains Sunday night (tail end of Day 4) and Monday ahead of a cold front anchored by a strengthening surface low. Some instability will be pulled all the way north across the Plains/Mississippi Valley toward the Upper Midwest, allowing for some heavy rainfall rates. Will show a broad Marginal Risk for this convective activity as a starting point for the Day 5 outlook. Thunderstorms look to have lower rain rates farther north where there could be slower movement of convection, while higher rates are possible farther south but could be more progressively moving. Additionally, antecedent conditions are drier east of the south-central High Plains for uncertainty in the impacts of heavy rain. Do expect there could be a corridor of heavy rainfall that could overcome drier soil conditions for flooding potential, for a potential embedded Slight Risk in future issuances, but the positioning is uncertain at this point. ...Florida... Shortwave energy spilling into Florida on Sunday and Monday could promote increased convective coverage. PWs should be 1.5-2 standard deviations above average while global models show MUCAPE reaching around 1500 J/kg at times. While much/all of Florida could see scattered thunderstorms with locally heavy rain, will show Marginal Risks for the east coast in particular, because of easterly low level flow for increased convergence, and the urban centers that are more sensitive to heavy rain. Sunday looks to be the primary day for a flash flooding threat, but the AI models in particular maintain some higher rain totals into Monday, so kept the Marginal going through Day 5 as well. Tate 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 $$