Subj : HVYRAIN: Excess Rain D1-2 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 1 Valid 12Z Tue Jun 23 2026 - 12Z Wed Jun 24 2026 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN EFFECT OVER PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS TO LOWER MISSISSIPPI VALLEY... ....Central and Southern Plains to Lower Mississippi Valley... Current radar and IR satellite composite depict an ongoing convective scheme within proximity of a quasi-stationary front bisecting the ArkLaTex through the Red River basin and adjacent Lower Mississippi Valley. Locally heavy rainfall has been occurring over the area outlined with cells pulsing up and down between 1-2"/hr, at times leading to totals breaching 1" in spots as we move through the overnight period. Some of these areas have already seen 1-2" of rain prior to this setup meaning some of the top soil layers becoming a bit more compromised than normal. This area in particular will be under the threat of training convection due to the anchoring of thunderstorms along the front and the mean winds running more parallel to the boundary leading to slower storm motions and repeated impacts. The hi-res suite has done a solid job indicating this particular threat lingering through the morning hours which would maintain an elevated flash flood threat over the region prior to the remainder of the D1 potential, which remains active throughout. Additional rainfall totals between I-20 and the Red River over into the heart of the ArkLaTex could easily reach 2-4", locally higher between now and 16z before the setup finally wanes as noted via the recent CAMs. However, this might not be the last rainfall this area receives during the period. As we head into the afternoon and evening hours, the mid and upper pattern across the Western and Central U.S. will setup into a persistent northwesterly flow regime with multiple shortwave ejections out of the Rockies allowing for a maturation of thunderstorms over the High Plains during peak diurnal instability. From there, organization of thunderstorms are likely to occur as they migrate downstream and mature with sufficient mid-level shear presence to maintain any thunderstorm complex generation. This is a relatively classic MCS pattern for this time of the year with heavy rain prospects likely to occur from the Front Range down through KS/OK, eventually migrating into the Lower Mississippi Valley by the end of the forecast period. Totals on D1 are consistent within the means with 1-2" rainfall coverage encompassing a large portion of the Central High Plains down through OK. This puts emphasis on heavy rainfall over the western half of KS into OK for the period with a chance for locally 3+ inches in some of the hardest hit locations. These areas will have already been subject to heavy rainfall in recent periods, so grounds could still be somewhat saturated and more susceptible to flash flooding upfront. 00z HREF EAS probs for >1" are greatest (20-50%) across much of Central and Western OK, extending down towards the Red River between just east of Wichita Falls to the ArkLaTex. Neighborhood probs are elevated between 40-70% for >2" with modest probs at >3" potential and low- end >5" probs still progged over western OK and over the ArkLaTex. The latter is likely a combination of both the overnight and morning convection to start the period, followed by another round possible late in the period as we move into early Wednesday morning. This is something we'll have to monitor closely for any targeted upgrades, pending what occurs initially and what could transpire early Wednesday morning. Given the consistent signal HREF probs forecast, a SLGT risk was maintained across the above area with a high-end SLGT forecast across the ArkLaTex and eastern Red River basin in southeast OK and northeast TX. ....Eastern Virginia to southern portions of the DelMarVa... Current WV satellite and UA analysis indicates a quick-moving shortwave sliding east-northeast through the Tennessee Valley with sights on the southern Mid Atlantic as we move into the morning hours, Tuesday. Current progs are for the shortwave to eject off the VA Capes with a surface low forecast off the southeast VA coast. Prior to the full ejection, sufficiently buoyant environment located across the coastal Mid Atlantic along with increasing mid- level forcing will enhance one last round of convective activity over the southern Mid Atlantic with spells of heavy rainfall forecast over northern NC up through southern and central VA to the Lower Delmarva and VA Tidewater. 00z HREF mean QPF is generally in the 1-2" range with deterministic outputs correlating with 2-4" maxima located over the aforementioned region from I-95 between Richmond to Raleigh and points east. Heaviest footprint is likely to be over the Tidewater region where a prolonged low-level convergence regime between a pre-frontal trough and eventual cold front passage Tuesday afternoon will allow for lingering convection over the region prior to the front finally sweeping everything off the coast. HREF neighborhood probs for >3" are between 40-60% along the I-95 stretch of southern VA to northern NC and 50-80% located over the Lower Delmarva into the Tidewater. Despite the drier antecedent soils leading in, rainfall from the previous period and rates likely to exceed 2"/hr in the strongest cells will be sufficient in causing isolated to widely scattered flash flood prospects in the area. Highest threat will be along I-95 and the immediate Hampton Roads/Virginia Beach area due to the urbanization factors, but the threat is still prevalent just outside those two zones. In coordination with the Wakefield, VA office, have added a small SLGT risk to the Tidewater area encompassing VA Beach and the Hampton Roads area due to heightened concerns given already occurring flash flooding today and the urbanized factors referenced above. The MRGL expands out away from the SLGT to include the Lower Delmarva out into parts of southern VA, mainly south of the Northern Neck. Kleebauer Day 2 Valid 12Z Wed Jun 24 2026 - 12Z Thu Jun 25 2026 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN EFFECT OVER PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS TO LOWER MISSISSIPPI VALLEY... ....High Plains to Lower Mississippi Valley... Persistence in the upper level setup across the CONUS will lead to another day of northwesterly flow over the Front Range to Lower Mississippi leading to convection taking similar trajectories for the period. Consensus is for the initial portion of the forecast to focus over the Southern Plains to Lower Mississippi Valley as the initial complex at the end of D1 will likely traverse southeast through OK into AR/LA, eventually ending as it motions into Mississippi by later Wednesday morning. Heavy rain threat will follow the complex as it maneuvers southeastward with some guidance igniting the complex over LA/MS as it enters a better environment and we see a build-up of instability through the early daytime hours. Progressive nature of any thunderstorm activity will likely preclude more ominous flash flood concerns, however these areas have seen their share of flash flooding the past week, so the areas where any complex moves across will have some susceptibility to hydro concerns. Initial 12hrs in the forecast period (12z Wed - 00z Thu) have a solid signal within the CAMs for heavy rain totals across the aforementioned corridor between eastern OK to south- central MS, backed up by modest neighborhood probs from the correlated HREF signaling >60% chance for at least 2" and 30-50% for at least 3" in the above zone(s). Given the state of the soils and lower FFG's than normal over the region, the prospects for flash flooding a bit higher than normal which led to a maintenance of the SLGT risk inherited over the area. Moving further northwest, a repeat from the previous period will ensue by the late-afternoon time frame as yet another shortwave will eject out of the High Plains of WY and initiate another round of organized convection over the High Plains between WY/NE, pushing south-southeast as it maintains prevalence within the mean northwesterly flow between the stout ridge over the Southwest U.S. and the longwave trough centered over the Northern Plains. Heavy rain footprint will follow a similar line to the D1 period with the core of heaviest rain likely to fall across northeast CO, southwest NE, and western KS during the nocturnal period between 00-12z Thursday. Totals of 1-2" will be common in wake of the thunderstorms, however local totals will once again be pushed closer to 3-5" in the hardest hit locations. Latest ECMWF EFI indices are signaling anomalous QPF distributions within that general zone, as well, which matches up with the heavier QPF depictions we see within the global deterministic and regional model guidance. As a result, the SLGT was kept over the area with little deviation in the previous positioning. ....Southwest U.S... Anomalous mid and upper level moisture will be advected over the Southwestern U.S. as we move into Wednesday 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 Wednesday 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 was added for the low-end threat with emphasis on the terrain in AZ, deserts of southern CA, and slot canyon areas within NV/UT/AZ. Kleebauer $$ --- SBBSecho 3.28-Linux * Origin: Capitol City Online (618:250/10) .