####018005372#### AGUS74 KWCO 281507 HMDNWC National Hydrologic Discussion - EXPERIMENTAL NWS National Water Center - Tuscaloosa AL 1015 AM CDT SUN APR 28 2024 .Synopsis... Considerable impacts remain possible across portions of the Central and Southern Plains into the Midwest...flooding impacts possible across East Texas and the Lower Mississippi Valley...Flooding impacts to continue in Puerto Rico...Flooding from recent/rainfall and snowmelt across the Great Basin and Intermountain West... .Discussion... .Central and Southern Plains into the Midwest... Considerable flooding impacts remain possible through this morning across portions of eastern OK, southeast KS, northwest AR, and southwest MO as heavy rainfall continues across the region. Outside of this particular area, flooding impacts remain possible through this afternoon across portions of IA and IL. Scattered minor and moderate to isolated major river flooding is ongoing and forecast across southeast KS, far-northeast OK, and much of western/central MO in the wake of 3 - 5"+ that fell overnight. These rivers are expected to crest and recede over the next couple of days. Ongoing rainfall across these regions is expected to diminish later this morning, although resultant runoff will continue to generate areas of flooding. The latest guidance of the HRRR-forced National Water Model (NWM) is indicating widespread stream responses from northeast OK through southern WI, with peak flows expected to begin later this morning. The High Flow Magnitude Forecast indicate annual exceedance probabilities (AEPs) as low as 2% portions of across the Osage (KS/MO), Blackwater (MO), Neosho (KS/MO/OK), Verdigris (KS/OK), Grand (MO), and Chariton (MO) river basins, which is in decent agreement with forecasted moderate to major RFC forecast. Minor to moderate river flooding is also forecast along the North and South Fabius Rivers, as well as the Fox River in extreme northeastern MO. After a brief reprieve on day 2 (Mon), additional periods of rainfall are possible across this same region on days 3 - 5 (Tue - Fri), potentially generating new and renewed flooding impacts. The latest guidance from both the GFS and NBM-forced NWM are indicating scattered small stream responses on days 4 - 5 (Wed - Thu) across these regions. While there is uncertainty in the exact placement and magnitude of the impacts, this area will have to be closely monitored for new and renewed flooding impacts due to ongoing saturated antecedent conditions. .East Texas and the Lower Mississippi River Valley... Flash, urban, and small stream flooding impacts are likely through day 2 (Mon) as slow-moving thunderstorms (with enhanced rainfall rates) impact the region. Soils remain saturated across northeast TX, northern LA, AR, and western MS (60 - 80% RSM, NASA SPoRT) and the intense nature of the rainfall will likely diminish any remaining infiltration capacity, resulting in immediate runoff and leading to subsequent flooding. Additionally, ongoing river flooding in these regions will likely worsen, as new and renewed flooding impacts are likely, especially across northeastern TX where renewed rises to moderate flood are now forecast. For today, the HRRR-forced NWM is indicating scattered small stream responses across much of east TX and into central AR, with peak flows expected later this afternoon. Corresponding AEPs, per the High Flow Magnitude Forecast, are as low as 2% in portions of the Upper Trinity (TX) and Sabine (TX) basins, suggesting that significant small stream rises and resultant flooding is possible. Impacts will be driven by intense rainfall rates and slow storm motions. The threat of heavy rainfall and resultant flooding will shift to much of LA and southern MS on day 2 (Mon), and both the GFS and NBM-forced NWM continue to indicate scattered small stream responses across these regions. Soils are somewhat drier across southern MS and southern LA, but given the intensity of the rainfall, these conditions may be quickly overwhelmed and localized flooding impacts are possible. Corresponding AEPs are generally at or near the high water threshold (1.3 - 1.6 ARI), which suggests that most rises here will remain in channel. Similar to areas to the north and west, heavy rainfall rates will be the primary driver for flooding impacts. .Puerto Rico... Showers and thunderstorms this afternoon across portions of interior and southwestern PR may generate urban and small stream flooding impacts. Given already saturated soils, river rises and mudslides are possible, especially in areas of steep terrain.After a brief reprieve on days 2 and 3 (Mon - Tue), a wet pattern will return mid-next week. .Great Basin and Intermountain West... Elevated flows will continue along area rivers, creeks, and streams across portions of southern ID/UT and northern NV in response to runoff from mid-to-high elevation snowmelt and recent rainfall. The Portneuf River at Pocatello, ID, is expected to crest in moderate flood stage early this week, and slowly recede thereafter. //JDP $$