FOUS30 KWBC 201650 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1250 PM EDT Sat Jun 20 2026 Day 1 Valid 16Z Sat Jun 20 2026 - 12Z Sun Jun 21 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL IN EFFECT FOR PARTS OF THE CENTRAL PLAINS AND LOWER MISSOURI VALLEY... ...Central Plains and Missouri Valley... A large area of heavy rain associated with a developing MCS starting this evening and continuing into early Sunday is expected to bring widespread heavy rainfall and flash flooding across portions of the central Plains into the Missouri Valley. The greatest threat for numerous instances of flash flooding currently is expected across southeastern Nebraska, northeastern Kansas, and far northwestern Missouri/southwestern Iowa. Storms are expected to initiate Saturday afternoon with peak heating over the central High Plains and ahead of a racing shortwave crossing the Rockies. Meanwhile, a LLJ of southeasterly flow will increase WAA and pump deep Gulf moisture up the Plains through the day. This will force the dryline to race eastward in response. The warm front associated with the low and the dry line will uplift the deep moisture, resulting in widespread shower and thunderstorm development across Nebraska as early as this afternoon. These storms are expected to grow upscale into an expansive, organized convective system into the evening and overnight hours that will then track southeasterly across the risk area. The latest deterministic guidance shows areal average rainfall totals along the expected path of the MCS in the 2-4" range with locally higher amounts of 4-6", more than sufficient to lead to potentially widespread flash flooding, which has prompted the level 3/4 Moderate Risk. As is usually the case with convective systems the exact path and duration will be determined by more mesoscale details than the guidance can typically pin down. Some CAMs (like the NAM3k) favor the northern axis of heavy rain across southeast Nebraska closer to the developing surface low/MCV, whereas the 00z RRFS favors a southern solution and heaviest rainfall across central Kansas. Regardless, PWs surging to 2" by tonight and increased forcing will support rainfall rates within thunderstorms to be intense and around 2-3"/hr. These rates could be exacerbated by cell mergers and brief training to quickly lead to flash flooding concerns. The 00Z REFS and HREF both highlight neighborhood probabilities of 3" per 6-hrs (above local FFG) around 40-50%+ within the MDT through 12Z Sun and then extending into the Day 2 period. Should these heavier rates intersect with urban area, significant impacts from flash flooding cannot be ruled out. ...Eastern Texas through the Southeast... 1600Z Update... Per collaboration with the affected WFOs, have expanded the Slight Risk down the Middle and Lower TX Coast (and adjacent inland counties), based on the current observational/mesoanalysis trends along with the recent (12Z) high-res CAM trends and HREF probabilistic suite. Airmass remains primed for highly efficient rainfall rates, with PWs over 2.25" and mixed-layer CAPEs quite robust between 2000-3000 J/Kg. All ahead of a slow-moving upper level vort lobe along/inland of the Gulf Coast (MCV over S. TX), where Gulf breezes will enhance the low-level moisture convergence farther inland. Hurley Previous discussion... One more day of scattered slow-moving storms is expected today across the Deep South between eastern TX and southeast GA/northeast FL. The lingering frontal boundary draped north of the Gulf Coast will begin to lift north during the day and leave convection widely scattered, but with one area of more focused activity between central MS and coastal southeast GA/northeast FL. This is likely during the morning and midday hours and supported by most CAMs as high pressure over the Tennessee Valley keeps the thermal/moisture gradient rather sharp and focuses ongoing thunderstorm activity within PWs above 2". Both the 00Z REFS and 00Z HREF highlight elevated chances (40-50%) for at least 3" in 6-hrs near Birmingham, AL. This could be an area within the SLGT risk that sees more severe flash flood impacts should a higher-end scenario develop. Lingering MCV(s) across eastern TX and the Lower Mississippi Valley could also add a focus for more organized thunderstorm activity, while also adding to the short term uncertainty. The soils in this region remain extremely saturated and sensitive to additional intense rainfall rates, leading to the potential for scattered instances of flash flooding and the SLGT risk of excessive rainfall, even for locations that can typically take 2-3" of rain. Snell Day 2 Valid 12Z Sun Jun 21 2026 - 12Z Mon Jun 22 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL IN EFFECT FOR PARTS OF THE CENTRAL PLAINS, MIDDLE MISSISSIPPI VALLEY, AND OHIO VALLEY... ...Northern Missouri through central Illinois and Indiana... By the start of the day 2 forecast period a potent shortwave and related surface low/MCV are expected to eject eastward out of the central Plains into the Midwest. There still remains at least some uncertainty regarding the speed and latitude of these features (NAM3k a northern outlier for example), but PWs and IVT above the 90th climatological percentile (per the 00z GEFS) overlapping with soils likely still recovering from recent heavy rain in the Midwest will likely lead to a swath of scattered flash flooding. A MDT risk was introduced with the latest outlook, spanning from MO to central IN. Heavy rain near a strengthening surface low and increased lift along an eastward stretching warm front across the Ohio Valley will overlap with saturated soils and swollen rivers across much of IL and IN. This will be one axis for potentially widespread flash flooding, with another axis lingering across southwest MO into eastern KS and possibly a relative minimum in between (right now most likely centered around central to southeast MO). This MO/KS potential is associated with the southwestern tail of an expected MCS, where flow may become parallel to the outflow boundary/front and promote both training thunderstorms and redevelopment of storms by Sunday evening. NBM probabilities for at least 2" remain very high (between 70-90%) and cover much of northern MO, central IL, and central IN. Locally higher totals (CAMs depict potential for 4-7" totals) are likely given the convective environment. 00Z HREF and 18Z REFS probabilities for exceeding 3-hr FFG are around 30-60% across IL and IN, where antecedent ground conditions are wettest. The progressive nature of these storms may end up limiting the severity of flash flood impacts, but coverage of flash flooding impacts is expected to be widespread enough in the Midwest/Ohio Valley to warrant the level 3/4 MDT risk upgrade. ...Eastern Kansas to Southwest Missouri... More information regarding the southern end of the Saturday night thunderstorm complex/MCS likely to sink southeastward near a trailing cold front and impact areas near the Ozarks Sunday. 850 mb flow is expected to become quite convergent extending from central KS to southern MO, which will likely be the focus for training convection potential early on and then reforming activity later in Sunday associated with additional shortwave activity moving eastward across the Plains. However, there is some uncertainty surrounding if this boundary can sink further south during the day and keep storms somewhat progressive. This all combines for guidance to currently depict current QPF amounts of 3-4" and an average localized max of 6". This area also includes soils saturated due to a recent wet weather pattern, with NASA SPoRT-LIS depicting pockets above the 80th percentile in the 0-40cm soil moisture layer. Lastly, 00Z REFS and HREF probabilities are agreeable with 40-70% values for exceeding 3" per 6-hrs. Snell Day 3 Valid 12Z Mon Jun 22 2026 - 12Z Tue Jun 23 2026 ...THERE IS A SLIGHT RISK IN EFFECT FROM THE OHIO VALLEY TO SOUTHERN PLAINS... Day 3 continues to be an active pattern through a good portion of the CONUS, east of the Mississippi with a progressive trough axis pushing through the Great Lakes and Northeast leading to periods of moderate to heavy rainfall from the Ohio Valley into the Mid Atlantic and Northeast. Areas of the Northeast are subject to thunderstorm prospects with the best chance for flash flooding likely to occur in the urban footprint from Philadelphia up to Boston with an expansion inland to the Hudson Valley down through eastern PA. Current probs off the latest ensembles and National Blend indicate a large zone of 30-50% probs for >2" across the aforementioned area above with deterministic outputs closer to 2-3.5" into parts of Southern New England. MRGL risk inherited remains in effect, but there's potential here for an upgrade as we move closer to the D2 window, but want to see more of the CAMs to make that decision. Limiting factor here remains low instability and while there is a window for heavier rates to linger for 3 to 6 hours, the system overall is progressive. Some uncertainty also exists south of central NJ along the eastern Mid-Atlantic regarding overall coverage of thunderstorms. Across the Southern U.S., heavy precipitation will preclude another round of convection forming along a quasi-stationary front draped from the Southern High Plains to the Southeastern CONUS. Probs for >1" are highest in-of the areas of Eastern OK into the Lower Mississippi and southwestern Tennessee Valleys. Elevated theta_E's and PWAT anomalies +2 dev. or greater indicate a formidable environment capable of continued heavy rain potential that will likely produce rainfall of 2-4", at least in some of the thunderstorm activity that develops. The focal point along the front will likely be where the heaviest rain will occur, or at least be a low-level convergence mechanism that can enhance regional convection. There's high enough confidence in the location of convection for the D3 period to overlap with areas that will have seen several inches the periods prior which led to a level 2/4 SLGT risk positioned over portions of the Southern Plains through parts of the Lower Mississippi and neighboring Tennessee. The risk extends through the Smokey Mountains up into parts of the Central Appalachians in eastern KY up into WV as the convergence regime follows the frontal positioning over these areas. Greatest chances for multiple rounds of slow-moving thunderstorms capable of 2"+ hourly rainfall rates currently appears to be over southeast OK into central AR and will be monitored closely once CAMs are within range of the forecast time period. Snell Day 4 and Day 5 Valid 12Z Tue Jun 23 2026 - 12Z Thu Jun 25 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS, LOWER MISSISSIPPI VALLEY, AND SOUTHEASTERN U.S ON BOTH DAY 4 AND DAY 5... Day 4 is a transition period into a more typical summertime regime for the CONUS with a longwave trough over the Northern U.S. and a dome of mid and upper ridging orienting itself across the southwestern CONUS. Positioning of the trough/ridge pattern will cause a persistent northwesterly flow within the mid and upper levels across the Central and Southern High Plains over into the Lower Mississippi Valley as progressive shortwave pulses eject out of the Rockies and ride the prevailing northwesterlies in place between the ridge and trough. This highlights potential for MCS development and flash flooding scenarios from the Front Range and points southeast as the steering flow orients between the base of the trough and the northeastern flank of the ridge. This is historically projecting a case of thunderstorm maturation and upscale growth over the area between CO/KS down through OK/TX with potentially the Red River Basin as a focus for thunderstorm activity. Eventually, this ends up migrating into the ArkLaTex and/or Lower Mississippi area which is showing up in the QPF footprint on ensembles. There has been little variance in the recent global ensemble suite with the deterministic output also showing very similar outcomes, at varying magnitudes with the synoptic evolution generally stable with run-to-run continuity. The entire setup continues through Day 5, as well, with repetition in the mid and upper pattern as multiple vorticity maxima slide out of the Central Rockies and migrate east-southeast through the mean flow between the trough and ridge setup. QPF distribution for both days is relatively even, however the D4 period is currently the most aggressive in terms of precipitation magnitudes depicted as the time frame notes a stronger mid-level disturbance ejecting out of the Front Range with heavy rain prospects spanning from southwestern NE down through KS/OK, eventually into the Lower Mississippi Valley as you work through the end of D4 into D5. PQPF signatures for >1" of precipitation are already pushing above 40% at lead for much of the aforementioned area, a testament to a stable signal for widespread moderate to heavy rain prospects as both the thermodynamic and kinematic evolutions remain favorable for the D4 and D5 periods. Expectation is for eventual upgrades across portions of the outlined area as we move closer, especially if the signal remains stable and the hi-res deterministic begin outlining the higher rate characteristics for the precipitation. Greatest risk for an upgrade is likely to occur where there will be multiple days of convective overlap allowing for falling FFG's and more susceptible hydrologic impacts as regional streams and rivers become more prone to flooding. This is a scenario where we'll be monitoring the evolution closely as more appreciable impacts are plausible in this synoptic scale persistence. 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 $$