650 FOUS30 KWBC 231559 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1159 AM EDT Tue Jun 23 2026 Day 1 Valid 16Z Tue Jun 23 2026 - 12Z Wed Jun 24 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN EFFECT OVER PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS TO LOWER RED RIVER VALLEY AS WELL AS SOUTHEAST VIRGINIA... ...Central and Southern Plains through Lower Mississippi Valley... As of 16Z...Organized heavy rain over OK from strong southerly flow over a frontal zone. Prior extreme rainfall near Texarkana has shifted to the northeast into OK, but may get impacted again this overnight from organized activity originating from storms currently along the western Neb/KS border. That may be progressive, so a Moderate does not seem needed at this time. Southern/central OK is under imminent heavy rain concern through early afternoon given thunderstorm clusters along the TX Panhandle/OK border shifting south-southeast while the activity from Texarkana over southeast OK propagates north-northeast. This area is considered to be an enhanced area in the Slight Risk, but also not a Moderate at this time. Will note that 12Z CAMs are struggling with the western OK/TX Panhandle activity, so for now the Slight Risk was expanded west a bit. Northwest flow around the high centered over far west Texas will drive the aforementioned MCS activity tonight across KS, OK through the lower Red River Valley. This should be progressive, but could further complicate excessive rainfall concerns over areas hit by heavy rain through this afternoon. Further activity from the Front Range/northern Sangre de Cristos will shift onto the high plains overnight as well. The Slight Risk was expanded west and north a bit. Meanwhile the Marginal was removed from northeast Nebraska based on 12Z CAMs and radar trends. ...Central North Carolina through Eastern Virginia and the DelMarVa... Scattered heavy thunderstorms in central NC shift northeast through the afternoon and perhaps hang on around Hampton Roads this evening, this activity is ahead of a mid level trough axis over the VA/NC Piedmont. Expanded the Marginal Risk to cover the current activity into NC and expanded north into southern NJ based on 12Z and later CAMs. A forthcoming MPD (#507) will have further details. Given the urban areas and PW at least two sigma above normal, the Slight Risk was maintained. Jackson Day 2 Valid 12Z Wed Jun 24 2026 - 12Z Thu Jun 25 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN EFFECT OVER PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS TO LOWER MISSISSIPPI VALLEY... ...High Plains to Lower Mississippi Valley... Persistence in the upper level setup across the CONUS will lead to another day of northwesterly flow over the Front Range to Lower Mississippi leading to convection taking similar trajectories for the period. Consensus is for the initial portion of the forecast to focus over the Southern Plains to Lower Mississippi Valley as the initial complex at the end of D1 will likely traverse southeast through OK into AR/LA, eventually ending as it motions into Mississippi by later Wednesday morning. Heavy rain threat will follow the complex as it maneuvers southeastward with some guidance igniting the complex over LA/MS as it enters a better environment and we see a build-up of instability through the early daytime hours. Progressive nature of any thunderstorm activity will likely preclude more ominous flash flood concerns, however these areas have seen their share of flash flooding the past week, so the areas where any complex moves across will have some susceptibility to hydro concerns. Initial 12hrs in the forecast period (12z Wed - 00z Thu) have a solid signal within the CAMs for heavy rain totals across the aforementioned corridor between eastern OK to south- central MS, backed up by modest neighborhood probs from the correlated HREF signaling >60% chance for at least 2" and 30-50% for at least 3" in the above zone(s). Given the state of the soils and lower FFG's than normal over the region, the prospects for flash flooding a bit higher than normal which led to a maintenance of the SLGT risk inherited over the area. Moving further northwest, a repeat from the previous period will ensue by the late-afternoon time frame as yet another shortwave will eject out of the High Plains of WY and initiate another round of organized convection over the High Plains between WY/NE, pushing south-southeast as it maintains prevalence within the mean northwesterly flow between the stout ridge over the Southwest U.S. and the longwave trough centered over the Northern Plains. Heavy rain footprint will follow a similar line to the D1 period with the core of heaviest rain likely to fall across northeast CO, southwest NE, and western KS during the nocturnal period between 00-12z Thursday. Totals of 1-2" will be common in wake of the thunderstorms, however local totals will once again be pushed closer to 3-5" in the hardest hit locations. Latest ECMWF EFI indices are signaling anomalous QPF distributions within that general zone, as well, which matches up with the heavier QPF depictions we see within the global deterministic and regional model guidance. As a result, the SLGT was kept over the area with little deviation in the previous positioning. ...Southwest U.S... Anomalous mid and upper level moisture will be advected over the Southwestern U.S. as we move into Wednesday as prevailing southwesterly flow around the western flank of the ridge over northern Mexico will help usher in warm, moist Pacific airmass centered off Baja. The addition of elevated moisture into the region coupled with intense heating across the Desert Southwest will lead to increased boundary layer instability and the ability to generate afternoon convection for the first time in a while over the deserts of southern CA into the Great Basin by Wednesday afternoon. Models are not too enthused by sense of magnitude, however with PWAT anomalies pushing +2 to +3 standard deviations across the area by the afternoon period, it stands to reason that some of the convection could be sufficient in causing localized flash flood prospects over those more prone areas like slot canyons in the interior and flashier portions of southern CA. A MRGL risk was added for the low-end threat with emphasis on the terrain in AZ, deserts of southern CA, and slot canyon areas within NV/UT/AZ. Kleebauer Day 3 Valid 12Z Thu Jun 25 2026 - 12Z Fri Jun 26 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN EFFECT OVER PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS TO MID-MISSISSIPPI VALLEY... ...Plains to Mid-Mississippi Valley... Longwave pattern across the western two-thirds of the CONUS will shift as a strong mid-level trough enters the Pacific Northwest and begins flattening the ridge axis positioned across the Southwestern U.S. This will lead to a more zonal regime to setup from the Central Rockies to the Mid-Mississippi Valley by Thursday, setting the stage for a potentially significant heavy rainfall threat across portions of the Central and Southern Plains between KS/northern OK over into MO and western Ohio Valley. At the surface, a quasi-stationary front will be progged over southern KS stretching eastward through MO before hooking back to the northeast as a cold front on the trailing end of a low motioning up through eastern Ontario. A strong mid-level vort will eject out of the Central Rockies and migrate eastward within the mean flow, allowing for lee cyclogenesis to occur over KS as we move into Thursday afternoon. The forecast is for the surface wave to motion eastward along the boundary with thunderstorm initiation transpiring across the Central Plains by late-Thursday afternoon. As we move into the evening, additional LLJ support will provide better low-level shear and provide enhanced convergence within the proximity of the front. This is a relatively classic scenario for a training axis of heavy convection, especially when you couple with PWATs likely between 1.7-2.0", a solid +1 to +2 standard deviations above climatology for the region. Models are persistent in their interpretation for an axis of heavy precipitation likely causing several inches of rain to fall in the time of late-Thursday afternoon through the overnight period into Friday. Deterministic outputs are a bit offset from each other on exact placement of the heaviest rainfall, however ensembles are closer in their alignment when assessing the recent QPF outputs. The ML outputs, especially the EC-AIFS and its ensemble are consistently further south with eyes on southeastern KS through southern MO into the confluence of the rivers near the Mississippi/Ohio. This has been a steady state over the past several runs which usually indicates the ML guidance might be on to the next trend of the deterministic. This is also the trend recently in guidance is a southern shift in the short term as frontal progression usually digs further south than forecast at the medium range and instability maximum in conjunction with organized convection follows suit. The current forecast SLGT risk was relatively maintained as it followed the prospectus trend anticipated, however did expand a bit on the northern and eastern periphery to account for the latest QPF distribution and mean error of fronts at 3+ day leads. ...Interior West... Multiple shortwaves and elevated moisture presence across the Interior Mountain West will likely lead to another afternoon and early evening of scattered convection with localized flash flood concerns on Thursday. The threat remains low-end for the time being given the current QPF outputs, however this could still provide some isolated flash flood prospects in those terrain focused zones across UT/CO, as well as any heavy rain encounters in the favored slot canyon areas littered over western CO into UT. A MRGL risk was expanded westward to account for the threat and recent QPF trends in the guidance. Kleebauer Day 4 and Day 5 Valid 12Z Fri Jun 26 2026 - 12Z Sun Jun 28 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE MID-MISSISSIPPI VALLEY AND OHIO VALLEY ON FRIDAY AS WELL AS PARTS OF THE NORTHERN PLAINS ON SATURDAY... Day 4...Deepening upper trough over the Pacific Northwest on Friday increases downstream ridging within a mostly zonal flow regime east of the Rockies to the start the forecast period and shifts the heavy rainfall threat along the a quasi-stationary frontal boundary east- northeast from the Ozarks to the Upper Ohio Valley. PWs are expected to be modest around 2" and between the 75th-90th percentile. Ensemble clusters 75th percentile QPF are generally 1-3", but with some spread in location between a focus over the Midwest or over the upper Ohio Valley and central Appalachians. NBM and ECENS probabilities for at least 1" of rain are between 30-60% between MO and southwest PA. Additionally, westerly mid-level flow parallel to the aforementioned boundary does bring the potential for training thunderstorms and increases the risk for at least scattered flash flooding. A MRGL risk was maintained for now given some lingering location uncertainty at this range, but an upgrade to a SLGT risk is possible with future updates. Day 5...By Saturday the trough over the Pacific Northwest deepens significantly (below the 1st climatological percentile per the 00Z ECMWF) and further increases the upper ridging downstream over the Midwest/Great Lakes. Heavy rainfall remains possible along the frontal boundary draped over the Ohio Valley, but even more uncertainty exists at this range given the western edge of the front will be lifting northward. However, more certainty with respect to potentially heavy rain exists over the northern Plains as a leading shortwave ejects north-northeast over the region and within the left-exit region of a strengthening upper jet streaking above the northern Rockies. A warm front is also expected to remain nearby and extend from the northern High Plains to the Midwest. This will allow for thunderstorms to potentially focus along or become elevated to the north-northeast of the boundary and tap into PWs above 1.5". Global deterministic guidance depicts 2-4" of rainfall is possible, with NBM and ECENS probabilities for at least 1" in 24-hrs around 30-70% (highest in ND). This prompts a MRGL risk and allows for potential upgrades should confidence increase in amounts above 3" and greater location certainty. Snell 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 $$