Subj : HVYRAIN: Excess Rain D3-5 To : All From : Mike Powell Date : Tue Jun 23 2026 08:32:26 FOUS30 KWBC 230758 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 358 AM EDT Tue Jun 23 2026 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 $$ --- SBBSecho 3.28-Linux * Origin: Capitol City Online (618:250/10) .