FOUS30 KWBC 292013 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 413 PM 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 THE SOUTHWEST... ...Southwest... Broad troughing will develop over the West with embedded shortwaves moving across portions of the area 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), more typical of values during their summer monsoon. This warm, moist air mass will also increase instability, with MUCAPE values forecast to reach 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. The available ingredients support 2" an hour amounts. Given the sensitive terrain in the area, urban areas, dry washes/arroyos, burn scars, slot/box canyons, and relatively moist soils, this setup will likely produce scattered instances of flash flooding. A broader Marginal Risk area surrounds the Slight and includes portions of the Great Basin 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. ...Southern/Central Plains & Midwest... Widespread moderate to locally heavy rainfall will continue into Friday morning across portions of Texas and Oklahoma as a shortwave moves northeast across the southern and central Plains and interacts with a returning front. Any lingering convective activity from Thursday night/early Friday morning could be ongoing in and near IA at the start of the period. The southern stream jet should shift north, maintaining favorable conditions for convection through Friday afternoon. Anomalous moisture will remain in place across the southern Plains and precipitable water values of 1.25"+ broaden in scale across portions of the Midwest/Corn Belt. Cloud cover could limit instability. With favorable dynamics, there should still be enough support for locally heavy rainfall, up to 1.5" in an hour, which would be most problematic in urban areas. The flood risk will mainly be a function of duration, with rainfall impacts compounding from Thursday into Friday. The highest risk of flash flooding is more likely materialize over portions of Texas/Oklahoma and in/near IA which have the highest potential for heavy rains. The flash flood risk will be relatively low, but enough for isolated to widely scattered instances of flash flooding and a Marginal Risk of excessive rainfall. Roth Day 3 Valid 12Z Sat Oct 31 2026 - 12Z Sun Nov 01 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN AND NEAR PORTIONS OF ARIZONA... ...Southwest... A deep layer 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 are more representative of moderately active monsoon days. This 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 less CAPE elsewhere. Given this setup, locally heavy rainfall will be possible across much of the Southwest, but high 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. 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-South and central Gulf Coast on Saturday. Over the Gulf Coast, an amplified jet will create upper level divergence. Low- level confluence is seen in the guidance and the precipitable water values are plentiful, with values of 1.75-2" forecast. Over 1000 J/kg of MU/ML CAPE is expected/forecast. The problem will be that the main shortwave triggering convection will be strongest to the north in the Midwest and Ohio Valley, which is leading to lower values of effective bulk shear, roughly 20 kts near the Gulf Coast, implying a pulse character to convection that forms. 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 approached in the 12z GFS/UKMET and 00z ECMWF guidance. The ingredients support hourly rain amounts to 2.5", likely from cell mergers or wherever random training manages to occur, which would be more than sufficient for issues in urban areas. While there remains some spread on location, enough ingredients appear to be there for isolated to widely scattered flash flooding. A Marginal Risk has been introduced on this cycle. ...Florida Gold Coast... An approaching shortwave aloft interacts with a moist, easterly low- level flow off of the Gulf Stream. Precipitable water values rise to 1.75-2". ML CAPE rises to 2000 J/kg or so. With the flow being antiparallel with height, effective bulk shear should be sufficient for thunderstorm organization, which could organize into short, efficient training bands for 1-2 hours at a time. Hourly rain amounts to 3" are possible, given the ingredients. Isolated flash flooding is possible within the South Florida urban landscape, so raised a Marginal Risk for this region. Roth 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... 21Z Update... A set up which has the potential to result in a high impact rainfall set up remains in the realm of possibilities on Sunday based on the latest deterministic and ensemble runs. The threat is tied to a combination enhanced moisture transport into a region that has been rather wet still...with some enhancement of the amounts in region where the moisture interacts with the terrain. The placement varied a bit but the overall picture is similar and covered by the previously-issued outlook. Bann Previous Excessive Rainfall Discussion... 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... 21Z Update... Few changes needed. Bann Previous Excessive Rainfall Discussion... 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 $$