####018005715#### AGUS74 KWCO 091522 HMDNWC National Hydrologic Discussion - EXPERIMENTAL NWS National Water Center - Tuscaloosa AL 1015 AM CDT THU MAY 9 2024 .Synopsis... Major river flooding impacts ongoing in East Texas... Lingering flash flooding impacts in the Tennessee River Valley... Potential for flooding impacts across the Lower Mississippi Valley and Southeast, Puerto Rico, and Hawaii... Ice jam-induced flooding possible in Alaska... Ongoing river flooding in the Upper Midwest and Mid-Mississippi Valley... .Discussion... .East Texas... Prolonged major river flooding impacts along the Lower Trinity and Lower Neches, as well as scattered moderate river flooding impacts, are ongoing throughout the region. The Trinity at Moss Bluff has crested and is forecast to fall below major flood stage by day 3 (Sat) and then continue to fall below moderate flood stage early next week. Both the Trinity at Liberty and the Neches at Saltwater Barrier have also crested, but will remain in major flood stage into next week. While drier conditions have provided some relief to these basins, the wet soils for all column depths have not had an appreciable amount of time to recover and streamflows are still much above climatological normal (USGS). As such, additional rainfall today, and again on days 4 - 5 (Sun - Mon), will likely result in immediate runoff into very sensitive rivers, increasing the potential for additional river flooding impacts, especially in smaller, more responsive basins. Localized flash and urban impacts cannot be ruled out if higher rates were to materialize or if training were to occur. .Tennessee River Valley... Significant heavy rainfall (4 - 8", locally higher) and flash flooding occurred across central TN and northern GA over the last 24 hours leading to numerous flooding impacts. Additionally, the Red River near Port Royal (TN) is forecast to reach major flood stage later this evening. Although rainfall will have ended for the affected regions, associated impacts may linger beyond today. .Lower Mississippi Valley and Southeast... Isolated flash and urban flooding impacts will be possible through this evening in response to widespread moderate to locally heavy rainfall. Latest guidance from WPC indicates the axis of heaviest rainfall (2 - 2.5") is expected across northern LA, central MS, east-central AL, and west-central GA while totals up to 2" are forecast elsewhere. Antecedent conditions are generally near normal to somewhat wet throughout most of the region, with drier conditions in place across southern AL/GA. These conditions should initially allow rainfall to be absorbed into the system. Rainfall should be relatively progressive which will help to diminish the overall flood threat, but isolated flooding impacts cant be ruled out should heavier rainfall/training occur. The National Water Model (NWM) Short Range Forecast is signaling widespread, but low-end, rapid-onset flooding probabilities (less than 25%) throughout most of the region, however, probabilities from Auburn, AL, to Atlanta, GA have started to increase (greater than 50%). Corresponding annual exceedance probabilities (AEPs) are generally at or above 50%, with isolated AEPs below 20% being signaling in the aforementioned area. This suggests most streamflow rises, should they occur, will remain in-channel, but some out-of-channel rises cant be ruled out in smaller, more responsive basins. Nonetheless, any impacts will be dependent on where the heaviest rainfall occurs given the overall progressiveness of the system. Much of the region is forecast to receive additional rounds of rainfall on days 4 - 6 (Sun - Tue) bringing the potential for new flooding impacts. The heaviest rainfall totals are currently forecast on days 5 - 6 (Mon - Tue) along the central and eastern Gulf Coast, and inland across the FL Panhandle/southern GA. Given the extended timeframe and variations in the placement of heaviest QPF, confidence in any potential hydrologic impacts remains low at this time. .Puerto Rico Urban and small stream flooding impacts, along with the chance for isolated flash flooding, will remain possible today. Wet soil conditions and locally elevated streamflows will increase the potential for hydrologic impacts including mudslides in areas of steep terrain. .Hawaii... Flash and urban flooding impacts are possible this afternoon/evening through day 3 (Sat) as locally heavy rainfall sweeps across the islands. .Alaska... Various small ice jams in the Kuskokwim Delta between Akiak and Napakiak are causing high water In Tuluksak. As these jams release, high water and potential flooding impacts will be possible in Akiak, Kwethluk, and Bethel. Looking north to the Yukon River, an ice jam front is also expected to impact the community of Circle. Ice jam breakups and formations are expected to continue along this breakup front as it makes its way down the Yukon River. Ice jams and breakup fronts can evolve rapidly, so refer to the local offices for up-to-date information. .Upper Midwest and Mid-Mississippi Valley... Minor to moderate river flooding is ongoing and forecast across IA, MO, and western IL. Many locations are still rising, with crests expected through the weekend as the elevated flows route downstream. With no significant rainfall expected over the next week, recessions will continue unimpeded. //Freeman $$