Subj : HVYRAIN: Excessive Rainfa To : All From : Mike Powell Date : Wed Apr 23 2025 07:55:00 FOUS30 KWBC 230759 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 359 AM EDT Wed Apr 23 2025 Day 1 Valid 12Z Wed Apr 23 2025 - 12Z Thu Apr 24 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE PLAINS AND THE SOUTHEAST... Persistent Gulf moisture advecting northward through the Gulf states over a stalled frontal boundary draped across the Southeast will continue to produce scattered to widespread convection capable of producing heavy rainfall. Rounds of showers and thunderstorms will fire up along the the boundary from Texas to the Carolinas with some training and backbuilding expected. Given there will be very little movement of the front the storms are likely to track over many of the same areas being impacted by ongoing showers and storms of late, which locally increases the flash flooding risk. A convective complex tracking east across the Hill Country during the very early hours of Wednesday is spreading 0.5 to 1 inch/hour rain rates along its path which may lead to isolated urban flash flooding. Refer to WPC mesoscale precipitation discussion #160 for more details. The latest guidance has better confidence that the wettest areas will likely focus over southern Nebraska and northern Kansas. This too will be the result of an MCS or clusters of thunderstorms developing and training multiple times over the same areas. The Marginal remains in place as the consensus of heaviest rains on the order of 1-2 inches (locally higher, of course) is in a portion of Kansas and Nebraska that has largely missed out on recent heavy rainfall, and the antecedent dry conditions should help to offset and delay the greatest impacts from any heavy rain. The area of the Marginal of least concern appears to be over Oklahoma, which while seeing some scattered shower and thunderstorm activity, should be between the MCSs/areas of more organized and persistent convection. However, due to heavy rainfall, lower FFGs over much of the state lower the threshold needed to achieve flash flooding, so the Marginal is largely unchanged there. Campbell/Wegman Day 2 Valid 12Z Thu Apr 24 2025 - 12Z Fri Apr 25 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF KANSAS, OKLAHOMA, ARKANSAS AND MISSOURI... Multiple clusters of thunderstorms will likely be ongoing in different portions of the ERO risk areas at the start of the Day 3/Thursday time period. These MCS's will likely weaken and dissipate through the late morning, as MCS's typically do. However, with peak heating and the increased instability there will be renewed rounds of showers and thunderstorms. Since this is likely to occur over many of the same areas hit with recent heavy rain this will once again renew the potential for localized flash flooding over portions of the Southeast. Much of the guidance has areal averages of 1 to 2 inches with higher maximums possible falling over much of the same footprint in the day(s) prior. The potential for a new MCS to form Thursday night will keep the threat for flash flooding elevated. The inherited Slight Risk remained largely untouched as it continued to reflect the areas with the greater threat for flash flooding. In similar fashion as Day 1, the low level jet will keep a steady influx of Gulf moisture over the stalled boundary which will maintain support for heavier rainfall with the strongest storms, and greater coverage of showers and storms in general. A Marginal Risk covers the northern Gulf states and Southeast. Campbell Day 3 Valid 12Z Fri Apr 25 2025 - 12Z Sat Apr 26 2025 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL MID-MISSISSIPPI VALLEY/Tennessee VALLEY TO PORTIONS OF THE NORTHEAST... Recent and ongoing rainfall over some portions of this broad region will make some areas susceptible to additional rains. During this period a surface low pressure system and its attendant front will likely track from the Mississippi Valley toward the Great Lakes region and interior Northeast. This system will usher in showers and thunderstorms to areas with increased soil saturation and lower FFGs. The broad Marginal Risk was maintained from the Tennessee Valley to the New Hampshire/Maine border given the increasing signal for heavier and more widespread QPF. Campbell $$ --- SBBSecho 3.20-Linux * Origin: ILink: CCO - capitolcityonline.net (454:3/105) .