FOUS30 KWBC 241558 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1158 AM EDT Wed Jun 24 2026 Day 1 Valid 16Z Wed Jun 24 2026 - 12Z Thu Jun 25 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN EFFECT FROM THE CENTRAL HIGH PLAINS THROUGH THE MID-SOUTH TO THE CENTRAL GULF COAST... 16Z Update... Risk outline areas were largely left as-is, with continued location uncertainty in expected overnight convection tonight through the central High Plains. 12Z HREF/REFS probs were still rather scattered within the broad Slight Risk area, but did note the HREF EAS probs increase over eastern OK into western AR, due in part to ongoing convection late this morning. With more saturated soils this area may be more susceptible to flash flooding today. Fracasso ...Central High Plains... The period will maintain a relatively stagnant upper pattern with a broad northern trough and stout mid and upper ridge axis centered over northern Mexico into the Southwest U.S. The setup is conducive for yet another active evening as pronounced shortwave will eject out of the Rockies and migrate southeastward into the Central Plains after 00z Thursday. Initiation of thunderstorms over the WY/CO Front Range will occur after sunset with more convective activity firing downstream into western NE and northwest KS as we head through the evening. Ample shear and mid-level ascent plus a well-defined theta_E ridge positioned within a quasi-stationary front bisecting the High Plains will act as both a focal point for convection, as well as the driver for aiding in intensification of any mesocyclone development after initiation. All models from hi- res CAMs suites to globals have some type of convective mode forming over the Central High Plains Wednesday evening allowing for high confidence in areas of not only severe weather, but accompanying heavy rainfall thanks to elevated PWAT's centered over the Central and Southern High Plains. HREF neighborhood probs for >2" are high (50-80%) across the corridor centered over northeastern CO, southwestern NE, and northwest KS, the inflection point of both cell initiation and expected forward propagation area of any convection as cell mergers occur and grow upscale. Some of these areas will have been hit pretty hard the prior evening leading to lower FFG's as recovery time for soils will be limited (<24hrs). In this case, the SLGT risk inherited is sufficient with a high-end SLGT risk forecast over that tri-state zone between CO/NE/KS as models continue to forecast heavy convection over that area with run-to-run consistency. The SLGT will extend through the rest of western KS and much of the CO Front Range with the expectation of cell motions moving through the area the back-end of the D1 period. ...Southern Plains to Central Gulf Coast... The pattern across the Southern Plains to Central Gulf Coast will remain a complicated scenario that will come down to the positioning of a quasi-stationary front oriented over the OK to the Lower Mississippi Valley, as well as the handling of multiple MCV's and their general locations that will dictate where heavy rain prospects would unfold for the D1. Models have struggled with the overall handling of the MCV currently migrating through AR/LA with the 02z HRRR offering the best handle on the timing and magnitude of precipitation accompanying the complex. You can see the northern inflection in the MCV over western AR will act as a region of localized convergence with cells maintaining very slow motions with the current storms orienting northwest to southeast to the west of Little Rock. Further south, the line is more progressive within the complex with a bit of a bowing segment ejecting eastward across the AR/LA state line with the heaviest precip focused over northern LA. Indications for the trajectory of the complex point to a continued eastward progression, followed by a turn to the east-southeast as it moves into MS, eventually making headway towards southern AL. This is in part to the general mid-level steering flow, as well as the defined theta_E gradient oriented in the same northwest to southeast alignment. Typical forward propagation centers over these distinct gradient alignments and this should be no different with a majority of guidance signaling the complex's motion into that area of the Southeast. In this case, this would open the door to enhanced low-level convergence within proximity of the disturbance and well within an environment conducive for scattered to widespread thunderstorm activity boasting potential for 2-3"/hr rates given the depth of moisture within the column, especially over southern MS. Upwind back over northern LA, secondary formation of convection along the persistent quasi-stationary front is anticipated over the early portion of D1 thanks to regional focus of low-level convergence left behind by our complex vacating to the east- southeast. Cell motion vectors within the latest CAMs for the period between 10-15z Wednesday are incredibly light leading to very slow cell propagations for hours prior to the dissipation of the threat. This area has already been hit several times in the past week with local FFG's running very low with widespread ground saturation noted by the latest discussions from the local WFO's. This will prolong the threat for flash flooding through the morning before we finally see the threat dwindle in part to the ridge further west finally building back overhead and shifting the front further north before dying off by early Thursday morning. In this case, the SLGT risk forecast will be maintained with the highest threat for flash flooding likely over the AR/LA border into southern MS. ...Western U.S... Anomalous mid and upper level moisture will be advected over the Southwestern U.S. through today 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 later this 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 remains the forecast for the low- end threat with emphasis on the terrain in AZ, deserts of southern CA, and slot canyon areas within NV/UT/AZ. ...Midwest... Despite the addition of a risk in the area, a non-zero potential for flash flooding exists over portions of southern WI into northern IL with the best threat likely within the urban corridor surrounding both Milwaukee and Chicago and its adjacent suburbs. Localized totals between 1-2" are plausible, especially in proximity to the warm front that exists ahead of a surface low migrating southeast through the Upper Midwest over the period. The frontal positioning will be the focus for the heavier rainfall threat as added low-level convergence will act as a focus for any convection in the area, offering a short term training concern as we move through the late-morning and afternoon. The threat is very isolated in nature with a few CAMs signaling more robust outputs, but not enough consensus to draw a definitive location for the threat. In coordination with the local offices in the area, decided to maintain a nil ERO posture, but make note of a low-end, <5% threat for flash flooding at some point in the front half of the D1. Kleebauer 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 Day 4 and Day 5 Valid 12Z Sat Jun 27 2026 - 12Z Mon Jun 29 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN EFFECT ACROSS PARTS OF THE OHIO VALLEY INTO THE CENTRAL APPALACHIANS ON SATURDAY... Day 4...By Saturday, the trough over the Pacific Northwest deepens significantly (below the 0.5 climatological percentile per the 00Z ECMWF) and further increases the upper ridging downstream over the Midwest/Great Lakes. Meanwhile, subtle troughing over the Northeast will allow for an inflection point in the lingering stationary front over the Ohio Valley, with this front lifting northward over the central U.S. and sliding southward along the East Coast. Heavy rainfall will remain possible along this frontal boundary as it lingers over the region and potential MCVs progress eastward, with typical uncertainty at this forecast range. Deterministic forecast guidance highlights rainfall amounts of 1-3" possible and given the convective/training storm environment, locally higher amounts can be expected. Heavy rain may also extend eastward into the Mid- Atlantic, but storms may be progressive enough to limit flash flood risk as well as potentially a limited amount of instability available. Additionally, heavy rainfall potential 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". Some thunderstorms may extend south-southeast into the Middle Missouri Valley, but greater uncertainty exists this far south. 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. Day 5...Large spread in outcomes across the northern tier reduced confidence enough to omit a MRGL risk with the latest outlook centered on Sunday. The frontal boundary sinking southward across the Mid- Atlantic and stretching west-northwest across the Ohio Valley by Sunday also appears to lose enough gradient to focus numerous showers or thunderstorms. These areas will be monitored in future updates. 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 $$