Subj : HVYRAIN: Excess Rain D3-5 To : All From : Mike Powell Date : Thu Jun 18 2026 07:39:13 FOUS30 KWBC 180826 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 426 AM EDT Thu Jun 18 2026 Day 3 Valid 12Z Sat Jun 20 2026 - 12Z Sun Jun 21 2026 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE CENTRAL PLAINS AS WELL AS FOR PORTIONS OF THE SOUTHEAST... ....Central Plains... A large area of heavy rain associated with a developing MCS starting Saturday afternoon and continuing into Saturday night will bring multiple inches of rain to a large area of southeastern Nebraska through northwestern Missouri. Storms are expected to initiate Saturday afternoon with peak heating. An LLJ of southeasterly flow will pump deep Gulf moisture up the Plains through the day. A developing surface low and upper level shortwave strengthening the low over Colorado will eject into the Plains. 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 in the form of an MCS. The MCS will track southeast into southeastern Nebraska, far northern Kansas, and eventually to the Missouri River. Additional storms capable of multiple inch per hour rain rates will develop on the southern end of the MCS, where the greatest rainfall totals will be. Urban areas in the path including Lincoln and maybe Omaha, Nebraska, Topeka, Kansas, and eventually St. Joseph and Kansas City, Missouri after midnight will likely be impacted. Widely scattered instances of flash flooding are likely. Given the amount of moisture present for these storms to feed on and the urban areas likely to be impacted, additional increases in forecast rainfall may require an upgrade to a Moderate Risk with future updates. Since CAMs do poorly and the models frequently shift where the heaviest rains will be leading up to an event, the Moderate Risk was not considered at this time. ....Southeast... An MCS tracking from the Ozarks following the same front that entered interior portions of the Southeast as a cold front on Friday will help that same front now retreat as a warm front on Saturday. Heavy rains are expected Saturday morning over the Slight Risk area from northern Mississippi to southern Alabama as storms track southeastward along the retreating front. Daytime heating will likely support additional clusters of storms into the afternoon in these areas. The heaviest rains over the most widespread area will be Saturday morning in northern Mississippi. They will be less organized as they move into southern Alabama Saturday afternoon, but given the prior day's expected rains in these same areas, the Slight Risk includes southern Alabama as well. Wegman Day 4 and Day 5 Valid 12Z Sun Jun 21 2026 - 12Z Tue Jun 23 2026 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF THE OZARKS THROUGH THE MIDWEST AND INTO THE UPPER OHIO VALLEY... Day 4... By the start of the day 4 forecast period a potent shortwave and related surface low are expected to eject eastward out of the central Plains into the Midwest. There will also be a trailing frontal boundary extending into the southern Plains to add a focus for additional thunderstorms. There remains some uncertainty regarding the speed and latitude of these features, but PWs above the 90th climatological percentile (per the 00z GEFS) overlapping with soils likely still recovering from recent heavy rain in the Midwest will lead to at least scattered flash flooding concerns. NBM probabilities for at least 2" are between 30-55% and cover much of the SLGT risk area. Locally higher totals are likely given the convective environment. The progressive nature of these storms may end up limiting the severity of flash flood impacts, but a MDT risk upgrade is possible should training/back-building elements become more obvious in the short range updates. This is especially the case given the sensitivity of the affected regions to additional rainfall. Day 5... The shortwave and low pressure on day 4 is forecast to continue east towards the Mid-Atlantic and Northeast, with additional uncertainties in latitude and speed. Additionally, thunderstorms should reform along the attached frontal boundary extending westward across the Tennessee Valley and into the southern Plains. At the moment most convection appears scattered in nature and low confidence in placement of heavier QPF. Therefore, a MRGL risk is highlighted and will be refined in future updates. Additional thunderstorm activity is likely into the High Plains, with uncertainty surrounding the impact of a nearby southern Canada upper low on thunderstorm activity in the northern High Plains. Snell $$ --- SBBSecho 3.28-Linux * Origin: ILink: CCO - capitolcityonline.net (454:3/107) .