FOUS30 KWBC 151949 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 349 PM EDT Sat Aug 15 2026 Day 1 Valid 16Z Sat Aug 15 2026 - 12Z Sun Aug 16 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PARTS OF THE OHIO VALLEY... 16Z Update... The 12Z HREF and REFS suites did not present any reason to make significant changes, therefore made only minor adjustments to the previous ERO, including the Moderate Risk area centered over the Ohio Valley. While the ongoing convection across the area will likely continue to wane through the remainder of the morning into early afternoon, guidance has been consistent in signaling redevelopment late in the day into the overnight -- with FFG- exceeding rates likely over parts of OH into WV and both ensemble suites indicating amounts over 3 inches likely in some locations. In the High Plains, extended the Slight Risk a little farther north into southeastern Wyoming and the southern Nebraska Panhandle, where soils are relatively moist in spots and both the HREF and RRFS are showing notable probabilities for exceeding 3-hr FFGs this evening. Pereira Previous Discussion... ...Ohio Valley... A Moderate risk has been expanded to stretch from portions of eastern IL through IN and across much of OH. An MCS is forecast to be ongoing at 12z this morning tracking across IL and IN. While this complex should generally exhibit a weakening trend as the morning progresses, it will be traversing a corridor of saturated ground conditions. Consequently, scattered to numerous instances of flash flooding remain expected into the morning hours. Another threat will materialize by this evening into the overnight hours, driven by the remnant MCV from the morning convection. This feature will help focus additional convective development over OH, eventually spreading east southeastward into WV and far southwest PA by late tonight and early Sunday. A very moist airmass characterized by PWs around 2.3" will support intense hourly rainfall rates. A training and backbuilding signature again exists, with deep layer westerly flow and strong low level westerly moisture transport resulting in weak Corfidi vectors. HREF neighborhood FFG exceedance probabilities range from 50-80%, with HREF PMM QPF exceeding FFG thresholds by 200-300% in spots and overall FFG exceedance spatial coverage topping 50%. These impressive metrics support numerous instances of flash flooding tonight over central and southern OH, with the threat spreading into WV and southwest PA by early Sunday. Some of this flash flooding will likely be considerable in nature. ...High Plains... A Slight risk is maintained from eastern CO into central and western KS, reflecting a southward shift relative to continuity. The overall setup remains similar to recent days, with convective forcing along the periphery of the upper ridge interacting with a moist, unstable airmass. A cold front will serve as a primary convective focus, with activity developing north of the boundary where the better moisture/instability will be pooling. Convection initiating over the higher terrain will track eastward and may grow upscale along/north of the front as it moves from CO into KS, aided by upper level jet right entrance dynamics. Isolated to scattered flash flooding is expected, particularly across eastern CO where recent heavy rainfall has lowered FFG thresholds. ...Southeast... A broad Marginal risk continues across the Southeast on the periphery of the strong upper ridge centered over the southern U.S. Anomalous moisture with PWs approaching the the percentile for mid August will be present, and HREF neighborhood probabilities support localized 3" rainfall totals However, overall convective coverage is expected to remain low with a minimal HREF EAS signal. While sea breeze boundaries may provide localized focus, any flash flooding impacts should remain isolated. Chenard Day 2 Valid 12Z Sun Aug 16 2026 - 12Z Mon Aug 17 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF WEST VIRGINIA... 20Z Update... Similar to Day 1, the HREF and REFS ensemble suites did not show reason to make any large changes to the overnight issuance. Minor adjustments included a small expansion of the Moderate Risk farther south along the upslope of the southern WV mountains, where additional QPF has been increasing in this flood-vulnerable area. Farther downstream, extended the Slight Risk into south-central Virginia. While there are difference in the details, there are enough members of the HREF and REFS guidance showing repeating storms dropping southeast of the mountains to raise probabilities for amounts over 3 inches to over 40 percent within the region. Back to the west, the consensus of the guidance showed enough of a decrease in QPF that the western extent of the Slight Risk was trimmed out of parts of the OH Valley. Pereira Previous Discussion... ...OH Valley into the Mid-Atlantic... A Moderate risk upgrade has been issued for portions of WV. Persistent and strong westerly 850mb moisture transport impinging into the complex terrain is concerning, favoring convective training and/or repeat activity. This setup, combined with PW values forecast to exceed 2", supports the potential for numerous instances of flash flooding. An initial round of convection should be ongoing at 12z Sunday with an active training/backbuilding threat. While a relative lull in coverage may occur after this, activity is expected to ramp back up by afternoon into the evening along and ahead of an approaching cold front. While this latter activity may lean more progressive the high PW airmass could easily yield a quick 1-3" of additional rainfall. Given that soil conditions will likely be quite saturated by this time, considerable flash flooding impacts are a distinct possibility in and near the terrain of WV. While some uncertainty with the details exist, the 00z Gem reg, RRFS, REFS hit this area with over 3" of rain. A Slight risk extends eastward across PA, MD, NJ, DE and northern VA. A mid level shortwave/MCV, alongside the synoptic cold front, will provide ample forcing for convection across the region. PWs increasing towards 2.3" and strong low level moisture transport will create an environment conducive to heavy rainfall rates. An MCS approaching from the west at 12z Sunday may tend to weaken as it outruns the primary instability axis, but additional convective initiation is expected in its wake as instability and moisture increase ahead of the front. While the cold front will eventually push the convection along, the environment ahead of the front will be favorable for backbuilding/training with weak Corfidi vectors. Any training will pose a flash flood risk, particularly over sensitive urban corridors. The Slight risk was adjusted southward to align with guidance trends, with the 00z RRFS and REFS matching well with the AIGFS/AIFS axis. The Slight risk was also expanded westward into the OH Valley to account for additional convection over saturated soil conditions. Additional convection is expected along/ahead of the advancing cold front within an airmass characterized by CAPE exceeding 3000 J/kg and PWs near or just over 2". While individual cells should move more quickly compared to previous days, the saturated conditions mean even progressive heavy rates will produce scattered flash flood impacts. ...Southwest... A Slight risk continues from northeast NM into southeast CO, focused along and north of a cold front where low level convergence and easterly upslope flow are maximized beneath upper level right entrance jet dynamics. While PW values are not extremely high, they remain slightly above average, and ample instability will compensate to support isolated to scattered flash flooding from slow moving cells and cell mergers. Guidance from the AIGFS, RRFS, and REFS is in good agreement with this spatial placement. Chenard Day 3 Valid 12Z Mon Aug 17 2026 - 12Z Tue Aug 18 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE OHIO AND TENNESSEE VALLEY AND APPALACHIANS, THE SOUTHWEST AND UPPER MIDWEST ... 20Z Update... No large changes were made to the previous outlook, just minor adjustments based on the 12Z guidance. Pereira Previous Discussion... ...OH/TN valleys into the Appalachians... A southward dropping cold front will serve as a focus for scattered convection on Monday. While overall storm coverage will be reduced compared to previous days, lingering moisture and instability just behind the boundary will maintain a heavy rainfall threat from KY and TN into the central Appalachians, enhanced by local terrain upslope. A Marginal risk is maintained for isolated flash flooding. ...Southwest... A Marginal risk encompasses much of NM and adjacent portions of southeast AZ and southern CO. Beneath an upper level ridge strong instability and slightly above average PWs will interact with embedded shortwave energy trapped in the weak flow. Terrain based initiation is expected during the afternoon, with scattered coverage and cell mergers likely as convection drifts off the higher elevations. ...NE to MN... A Marginal risk continues from central NE into southern MN ahead of an advancing cold front. Frontal forcing will support convective development with localized training or backbuilding potential along the south to southwest flank of convection. While the threat is expected to remain localized...and storms may prove progressive enough to limit impacts...a Marginal risk reflects the low end risk. Chenard Day 4 and Day 5 Valid 12Z Tue Aug 18 2026 - 12Z Thu Aug 20 2026 ...THERE IS A SLIGHT RISKS OF EXCESSIVE RAINFALL ON TUESDAY FOR AREAS OF THE UPPER MIDWEST... 2030Z Update... Changes to the areal extent of the Slight Risk on Tuesday were pretty modest and driven by timing of the mid-level trough coming out of western Canada. Beyond that...the Marginal risk areas on both Tuesday and Wednesday were also pretty modest and done to provide more overlap with QPF spaghetti plots. Bann Previous Discussion... ...Day 4/Tuesday... Main threat for the CONUS on Tuesday will reside across the Upper Midwest/Mississippi Valley thanks to a strong mid-level trough sliding out of western Canada providing a significant increase in large scale forcing across the North-Central U.S. with a target on the Upper Mississippi Valley into the Corn Belt as of the latest ensemble and global deterministic trends. One of the main changes from the previous forecast is a further south focus of the heavier rainfall as the advancement of a cold front and elevated theta_E advection will likely cause a development of widespread convection further south than the previous forecast. The latest National Blend came in farther south as well, actually matching more of the ML algorithms in the EC-AIFS and AI-GEFS ensembles meaning the blend is shifting away from the previous northern output that put the QPF maxima over MN. A deepening surface low materializing within the diffluent mid-level evolution ahead of the trough is slated to propagate southeast out of Canada with an expectation for the low to strengthen quickly as it moves east- southeast over the Upper Midwest. A trailing cold front will extend over the Dakotas. through Iowa/Southern MN, arcing up into the northern Great Lakes by the end of the period. Along and ahead of the front, widespread convective initiation is forecast leading to a swath of heavy rain prospects, including the opportunity for >3" of rain in areas hardest hit. PQPF 90th percentile remains steady in its presentation from previous forecasts depicting between 2.5-3" across Iowa into southwest WI where the consensus is strongest for where the heaviest precip potential may occur. ML guidance is also in agreement on the heavy precip axis located in the same areas across from IA to WI with the max located across Central IA as the 00z ML suite. Considering the latest trends in guidance for a further south impact in the heavy rainfall axis, the SLGT risk inherited was shifted further south to encompass much of IA into WI. The shift into IA is noteworthy due to the antecedent soil moisture that will likely still remain elevated across much of the state due to the previous periods of rainfall that generated widespread flash flooding in the southern and eastern portion of the state. General trends will be monitored closely as any overlap of the some of the more sensitive areas in IA and WI could introduce some targeted upgrades, especially with the signal likely to bear locally higher totals compared to what is being forecast at lead. For now, maintained the SLGT risk, but adjusted based on the latest shift in the QPF mean further south. ...Day 5/Wednesday... Broad ridging across the Southern CONUS and a deep, amplified upper trough across Canada into the Northern U.S. will generate a progressive flow that will entice periods of convection around the western and northern periphery of the ridge with scattered heavy rainfall signatures within those aforementioned domains. The most notable area of precip will likely lie within the Great Lakes down into the Ohio Valley where a cold front advancement will continue to be a focal point for convection along and ahead of the front as it migrates east of the Mississippi Valley towards the east coast. Current signals are not as prolific as the previous periods of excessive rainfall, however the antecedent soils will still likely be in recovery over the areas of interest for the D5 leading to at least isolated instances for flash flooding in the anticipated evolution. Models remain mixed in their magnitude and location of heaviest rainfall, but ensembles maintain some areal QPF maxima in the vicinity of both the Great Lakes down through OH/KY into the western half of WV. These areas are the most susceptible to appreciable impacts given the nature of the soils allowing for at least a MRGL risk to encompass the area to note the potential. Across the Southwest into the Front Range, the western periphery of the ridge will allow for a continued southerly push of warm, moist air poleward with lee troughing likely to be situated from CO down through NM as it materializes within a modest theta_E ridge. Scattered thunderstorms across the terrain will transpire leading to at least the threat for isolated flash flood prospects, especially within any remnant burn scars and complex topography within the Sangre de Cristos down into the Sacramento Mountains, extending southwest towards the terrain of southeastern AZ into the Bootheel of NM. A MRGL risk was added over the area to account for the threat. Kleebauer 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 $$