FOUS30 KWBC 261913 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 313 PM EDT Tue May 26 2026 Day 1 Valid 16Z Tue May 26 2026 - 12Z Wed May 27 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE CENTRAL GULF COAST, CENTRAL TO WEST TEXAS AND THE OHIO VALLEY... ...Texas... Current WV satellite and upper air analysis indicates a broad, negatively- tilted trough axis migrating eastward out of the Southwestern CONUS into the Southern High Plains this evening. A broad diffluent pattern exists downstream of the mean trough with several small mid-level perturbations causing a panoply of convectively driven cells to materialize across the terrain of eastern NM, spreading eastward into the adjacent High Plains as surface troughing exists over southwest TX up through the eastern NM plains. Increased large scale ascent will become fixated over much of west TX, spreading further through the High Plains as widespread shower and thunderstorm activity continues through the morning and afternoon hours today. A plethora of convective activity with relatively slow to modest propagation speeds will translate into bouts of heavier rainfall across the southern half of the TX Panhandle down through the Permian Basin and western Rolling Plains the first half of the period leading to rainfall totals between 1-3" over the aforementioned areas. Greatest opportunity for flash flooding will exist across urbanized settings and areas where copious low water crossings are present, creating drainage concerns on a localized scale. As we step into the late-morning and early afternoon time frame, the focus will shift south into the Pecos River Valley and adjacent Stockton Plateau where convection will initiate off the dryline situated over the area with assistance from an approaching shortwave sliding eastward out of Chihuahua. Ample shear and favorable instability fields reflect the initiation of supercellular storm modes with additional multi-cell development along and ahead of the dryline leading to strong cell cores capable of heavy rainfall as the environmental moisture anomalies sit firmly between +1 to +2 deviations above climo. Storm motion vectors maintain a relatively steady forward propagation to the east and southeast from the initiation point allowing for a trail of significant rain totals between 1-3", locally higher to materialize from the southern Permian Basin down through the Stockton Plateau, Lower Trans Pecos, and eventually into the mid and lower Concho Valley by the evening. This setup is classic for scattered flash flood instances, especially in those more urban zones and areas of high low water crossing concentrations that are littered over the above zones, albeit this potential is greater than what will occur a bit further north. This reflected well within the 00z HREF neighborhood and EAS prob fields pertaining to the >2" threshold where both probabilities remain elevated area wide, but a notable maxima is positioned over the Lower Trans Pecos and those areas surrounding within the Permian Basin and Concho Valley. The maxima extends into the northern Edwards Plateau, a likely conjecture that correlates to the proposed motion of the expected complex of thunderstorms motioning out from areas to the west-northwest. This zone is part of a larger areal extent of heavy rainfall anticipated for the period with a second axis likely to materialize after sunset. Rainfall will likely be winding down in areas west TX that are located along and west of the Pecos River after 00z Wednesday, but the setup will shift focus into more of a nocturnal issue as we pivot our attention south over the central RGV as a strong mid- level vorticity maxima ejects out of Coahuila later this evening and slides east into the Edwards Plateau and neighboring Hill Country. There's a general consensus on this setup across guidance with some degree of broad heavy convection migrating into the above areas enticing a dousing of rainfall as the pattern evolves overnight. We'll see the introduction of a LLJ only add to the low- level convergence regime spurred on by the expected evolution likely allowing quite the rainfall signature in wake of the disturbance's trajectory. US57 to I-10 is the prospectus area of interest, which includes much of southern and central Hill Country with the very end of the period likely to see some of the activity make it beyond the I-35 corridor near San Antonio and even make headway towards Corpus Christi. The highest confidence area according to the neighborhood probability fields for >3" remains over the Hill Country to the I-35 corridor between Austin to San Antonio with the maximum (40-60%) located in those areas just west of the metro corridor along and near I-10. Probabilities for >5" do drop off significantly to <20% everywhere with a majority of the probs closer to 10%, so the magnitude within guidance is relatively consistent with a signature of 2-4" with locally up to 5" in the hardest hit areas. This is still plentiful to cause problems when it occurs, so the threat is well within the bounds of a SLGT, even leaning towards the higher end of the threshold for flash flooding. This area up through the southern Permian Basin and Stockton Plateau will be monitored closely for any potential targeted upgrades in future updates. The SLGT risk encompasses a broad area of TX spanning much of west TX all the way to about 75 miles east of I-35 with the northern periphery right up against the Red River and the southern points running from Corpus Christi to near Laredo. ...Southeast to Mid Atlantic to Ohio Valley... 16Z update... A Slight Risk was hoisted for portions of the Ohio Valley along the stalled west-east frontal boundary, from southeast Missouri to eastern Kentucky. Scattered to widespread convection have been lifting through the region this morning over sensitive soils. Local 1hr/3hr FFGs are as low as 1/1.5 inches and with hourly rates pulsating up to 1.5-2+ inches/hr over this part of the country could quickly reach or exceed the FFGs. Minor westward adjustment to the Slight Risk over eastern Louisiana was made to reflect the latest QPF guidance and trends. The Gulf Coast and into western Georgia is where much of the CAMs are focusing narrow streaks of heavy to intense rainfall for this period with accumulations of 2-3+ inches. Campbell Confluent area on the western edge of a broad Western Atlantic ridge and a trough centered over the Southern Plains will continue for at least one more period with another round of convergence and heavy convection focused over the Central Gulf Coast to areas inland between southeast MS into the southern half of AL. This area will have seen multiple days of impact from heavier convection to begin with, so current priming of the soils could enact a greater flash flood potential in general with an emphasis on areas that received 3+ inches over the last 24 hours. Highest probabilities for >3" reside across the corridor extending from New Orleans over through Mobile into the western FL Panhandle and points just north of I-10. This area has received considerable rainfall the past 24 hours with some places in the FL Panhandle receiving over 6 inches of rainfall the past few days. Despite what was a drier environment heading into the weekend, this area is sufficiently saturated in the top soil layer leading to greater run off capabilities as we step through today. The greatest axis of convergence within the hi- res suite has been pin-pointed over the western FL Panhandle where >5" neighborhood probs are running as high as 40-50% for a small area between Pensacola to west of Tallahassee, including Panama City beach along the coast. Radar analysis this evening is a pretty good indication of the persistent southerly flow off the Gulf in this narrow corridor, so this area in particular is one to watch for the period. This area over to New Orleans is well defined into the SLGT risk with a higher-end of the risk threshold forecast for this zone. Further north, the confluent pattern on the western edge of the ridge up to the frontal alignment in the Mid Atlantic stands to be a focal point for another day of scattered to widespread convection with general rates between 1-2"/hr across the Appalachian front and 1-3"/hr in the adjacent lower elevations located over GA/SC/NC/VA. These areas have been hit multiple times the past few days with several flash flood warnings issued due to the convective impacts the past 24 hours. This only stands to continue for another period given pattern persistence, so wanted to make sure this was reflected in the new D1 issuance. In coordination with several offices across the Southeast to Mid Atlantic, a SLGT risk expansion was noted up through the aforementioned areas of the Southern Appalachians into the neighboring Piedmont of the Carolina's, southern VA, and most of the northern half of GA. ...Northern Rockies... 16Z update... Convection this morning has been firing up across eastern Washington and northern Idaho, areas very similar in topography with sensitive locations as described below. The western boundary of the Marginal Risk was expanded into eastern Washington to cover this convection and more expected later in the day. Campbell Energetic disturbance ejecting out of the Pacific Northwest and British Columbia will make headway into the Northern Rockies by later this afternoon leading to a period of convective activity to spawn along the Lewis Range down into the high valleys of western MT. PWATs running over 1" across the Northern Rockies is well above climo norms, closer to the 99th percentile as noted by the latest NAEFS outputs, more than sufficient to be a problem for any more sensitive topographic features present given the complex topography. Multiple burn scars in the area will also be under threat for seeing rainfall rates between 0.5-1"/hr at times, a threshold that could cause rapid run off and debris flows if cells linger over the sensitive areas. This is not a widespread flash flood prospect, but isolated to widely scattered instances cannot be ruled out considering the above environment. A MRGL risk remains in place to account for the lower end threat. Kleebauer Day 2 Valid 12Z Wed May 27 2026 - 12Z Thu May 28 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE EASTERN HALF OF TEXAS, PORTIONS OF THE LOWER MISSISSIPPI VALLEY, AND AREAS OF THE OHIO VALLEY TO CENTRAL APPALACHIANS... 21Z update... A new Marginal Risk area was raised for eastern Washington, northern Idaho and western Montana. Deep moisture over the region maintaining above climo PW values for late May. A wave making its way through the region along with differential heating will help trigger convection capable of rain rates upwards of 0.50 to 1+ inches/hr in isolated areas. These rates, if falling over recent burn scars and other sensitive locations have the potential to cause isolated flash flooding and/or debris flows in steep terrain. However a limiting factor will be that the areal coverage of thunder will be less than that of the Day 1 period. Campbell ...Texas to Lower Mississippi Valley... The broad upper level evolution occurring upstream over the Southern Plains will continue to shift east with the large scale forcing driving into the eastern half of TX leading to heavy rain prospects over the eastern portions of Hill Country, the I-35 corridor and much of east TX, including the middle and upper TX coastal areas on Wednesday. Environmental conditions for heavy rainfall are most favorable along the TX and LA Gulf coast areas with a corridor of elevated theta_E's aligned from Corpus Christi up through the Lower Sabine to about 100 miles inland. The setup is contingent on the behavior of the convective pattern upstream into the central portion of the state and the migration of the thunderstorm complex exiting out of I-35. The general consensus is the maxima for precip will likely occur in proximity to the same areas that were hit within the past week; the area along the upper TX coast from Houston up to Lake Charles. This is very well defined within the probability fields in both the HREF and the AIFS-ENS where >3" is likely (60-90%) within the confines of that zone with the HREF even signaling modest >5" potential (40-60%) in that same zone. There's still some uncertainty in the behavior of any mesoscale complexes that end up materializing from all the convective development the previous evening and if they cause any significant shifts in the potential. In this case, this leads to a broad SLGT risk with a MRGL risk encompassing over the Southern Plains to Lower Mississippi Valley as broad upper forcing will likely spur scattered convection all across areas from western KS down through OK in the setup. Areas away from east TX and the Lower Mississippi will have more isolated heavy rain prospects, comparatively, so the threat remains elevated in the SLGT risk within these particular locations. ...Ohio Valley... 21Z update... A minor westward nudge was made across Indiana along with a south and east expansion across West Virginia to account for the latest model trends and WPC QPF. Campbell Conditions will become increasingly favorable for heavy rainfall across the Ohio Valley going into Wednesday from a multitude of features that will ultimately couple into something more formidable during peak diurnal instability. Sheared vorticity stemming from previous period convection will likely settle over the central Ohio Valley with a west to east bisecting quasi-stationary front positioned just north of the Ohio River basin. A sweeping trough exiting out of Ontario will help tighten an axis of confluence across the Midwest and Ohio Valley by Wednesday afternoon, enticing a squeeze of the thermal gradient and regional instability axis that aligns with the frontal placement. Destabilization by the afternoon hours will lead to scattered to widespread thunderstorm initiation along the boundary with convective episodes likely to spawn heavier cells capable of hourly rates between 1-2"/hr as PWAT anomalies sit firmly within +2 standard deviations above climo. Previous periods of rainfall in the last three to four days have really brought down the areal FFG markers for all 1/3/6 hour thresholds with a vast majority of places along the Ohio River basin and points north running <1"/hr in the hourly exceedance indicator. This points to any heavier convective impacts could cause issues with the remnant soil moisture and hydrologic concerns that are lingering after the last event. This is especially true for eastern OH, southwest PA, and western WV where complex topography only exacerbate the potential in these zones. 3-hour FFG exceedance probabilities from the 00z HREF are between 20-40% for a large portion of eastern IN through the southern half of OH into southwest PA with a maxima of 40-60% located across northwest WV between US50 and WV7. Considering the antecedent conditions and expected widespread convective regime along the front, a SLGT risk was added for an increasing threat for flash flooding Wednesday. Kleebauer Day 3 Valid 12Z Thu May 28 2026 - 12Z Fri May 29 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS, NORTHERN ROCKIES, LOWER MISSISSIPPI VALLEY, AND SOUTHEAST FLORIDA... 21Z update... A new Marginal Risk area was raised for eastern Washington, northern Idaho and western Montana to carry on the elevated threat potential described in the Day 1 and Day 2 periods. A minor westward expansion of the Marginal Risk was made for Palm Beach County to account for trends and the new WPC QPF, elsewhere remains in good order. Campbell ...Plains to Lower Mississippi Valley... Breakdown of the persistent pattern for areas east of the Continental Divide will lead to weaker steering flow, but still enough moisture, lingering boundaries, and remnant mid-level vorticity to spur up bouts of scattered convection all across parts of the Central and Southern Plains into the Mississippi Valley. This setup is a far cry from what we've experienced the past several days, so the prospects of widespread flash flooding are much lower comparatively. However, environmental conditions and deep moisture presence still remain favorable along the northern periphery of the trough lingering across east TX which places the best opportunity for convective episodes to be located over the aforementioned areas. Ensemble QPF footprint is most notable across the Central Gulf coast and upper TX coastal plain, likely in part to the positioning of the trough and the fact the most prevalent theta_E is situated along the immediate Gulf. It's a period to monitor for any small scale features that could enhance convective potential further, but for now, a broad MRGL exists to cover for the threat. ...Florida... Active sea breeze pattern with weakening steering flow will lead to a period of heavy rainfall across the southeast FL coast on Thursday afternoon. Consensus within guidance is for an active period between 18-00z Thu/Fri that would allow for heavy convection with slow forward propagations to impact the South Florida metro corridor from West Palm Beach down to Miami. Globals and regional guidance even have some 2+" totals already in the output, and that's before the CAM's even have a depiction. Typically, this is a sign for heavy rainfall prospects capable of flash flooding, especially when you consider the PWATs running +1 to +2 deviations across that area of the Peninsula. A MRGL risk remains for that urban corridor of southeastern FL. 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