Subj : HVYRAIN: Excess Rain D2-3 To : All From : Mike Powell Date : Wed Jun 24 2026 08:47:13 FOUS30 KWBC 240729 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 329 AM EDT Wed Jun 24 2026 Day 2 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 surface 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. Model signals are still pretty aggressive with the scope of the event with most of the deterministic outputs showing pockets of 3+ inches for areas of eastern KS through portions of MO. The deviation comes in the timing of the shortwave ejection and the latitudinal gain of the heavy rain footprint as guidance disagrees on the exact placement of the heaviest rainfall. ML guidance is still generally south of the global NWP suite, a highlight that has been noted over the past several cycles. ML guidance tends to do well when it locks into these types of outputs and doesn't waver too much in specifics, so the trend is to keep the heaviest precip a bit south of the deterministic and its ensembles. That said, the orientation of the frontal positioning will be important as that will likely be the focus for where the heaviest QPF outputs will occur as the surface wave will ride the thermal gradient posed by the front in question. Historic bias at this leads tends to favor guidance being a bit too far north with its QPF footprint in these scenarios leading to an adjustment further south, correlating with a better convergent area away from the current depiction. Considering the magnitudes of the QPF already with little to no CAMs inclusion, the forecast for locally significant rainfall is becoming increasingly likely in the D2 period. As of now, the SLGT risk inherited only went through minor modifications with a high- end SLGT risk forecast for areas of central to southeast KS through the southwest and west-central portions of MO, extending towards the St. Louis metro where the frontal alignment is progged. An upgrade for portions of this area is not out of the question in the coming forecast cycles, so this will be something to monitor closely the next 24-36 hours. ....Southeast U.S... Remnants of a complex from the previous period will wander into the Central Gulf coast region and slide eastward into southern GA by Thursday afternoon. Hi-res at the end of their forecasts are consistent in the maturation of convection near the remnant circulation as the disturbance becomes a mechanism for targeted low-level convergence in a zone of favorable boundary layer moisture and instability. Signals for locally heavy rainfall of 2+ inches are noted in the deterministic CAMs with the HREF blended mean QPF between 12z Thursday to 00z Friday showing pockets of 1.5-2" located from the MS coastal areas through the I-10 corridor towards Tallahassee, back up into southern GA. This is coincident with the 500mb vorticity trajectory of our mid-level impulse generated from previous periods thunderstorms which provides a better target point for heavy rainfall compared to just your standard pulse convection regime we see in the summer. As a result, maintained the previous MRGL risk with just some minor adjustments to account for QPF trends. ....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 3 Valid 12Z Fri Jun 26 2026 - 12Z Sat Jun 27 2026 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN EFFECT OVER PORTIONS OF THE MID-MISSISSIPPI AND OHIO VALLEY'S... The period will be defined by the expected forward propagation of the shortwave trough that will affect the Central Plains, eastward during the D2, translating into further impacts on the D3. Ensembles and global deterministic alike continue to signal the axis of heavy rainfall over the Mid-Mississippi Valley shifting eastward through the Ohio River Valley with the focus of heaviest rainfall centered over the Ohio River basin and points north. This correlates with the mean 500mb vorticity forecast for the shortwave trough responsible as diffluent flow ahead of the trough axis will situate over the above area leading to focused ascent and increasing low to mid-level convergence pattern necessary to bring about a swath of heavy precipitation. 00z run of the CSU First Guess Fields depict a broad SLGT risk alignment across the area between southern IN and southern OH down across neighboring northern KY with the northern periphery positioned along and south of I-70. Considering the trends in the CSU First Guess over the last several months, this may be a bit further north than what may transpire, however the ensemble QPF alignment of the heaviest precip is generally in that zone, so the decision was to add the SLGT risk matching the First Guess, but also hedging a bit further west and south with the expansion in the end. 01z NBM probs for >2" depict a 30-60% probability output between St. Louis to just east of Cincinnati with a northern inflection to the I-70 corridor between Indianapolis to Columbus, OH. The southern edge did expand south with the 30% probability from previous forecast to include areas south of the Ohio River, a testament to the potential to see a slight southern shift in the QPF focus as we move closer in time. In any case, the probability for >2" at this lead for the blend was more than suitable enough to warrant a SLGT risk addition to the now D3 period. The threat of heavy rainfall, even though more isolated due to the magnitude of the precipitation expected, is forecast to expand further east into the eastern Ohio Valley and neighboring areas of the Central Appalachians and western PA during the period. Considering the nature of the topographic elements allowing for those areas to be more prone to heavy rainfall episodes, this will be an area to monitor for any further adjustments in the risk which is currently at a MRGL for the time being. Kleebauer $$ --- SBBSecho 3.28-Linux * Origin: Capitol City Online (618:250/10) .