####018002876#### AGUS74 KWCO 231520 HMDNWC National Hydrologic Discussion - EXPERIMENTAL NWS National Water Center - Tuscaloosa AL 1015 AM CDT TUE APR 23 2024 .Synopsis... Flooding impacts expected to continue in Puerto Rico... Flooding possible late week from the Ozarks through the Mid-Mississippi Valley... Snowmelt induced flooding in the Great Basin and Intermountain West... .Discussion... .Puerto Rico... Daily showers and thunderstorms will continue to generate urban and small stream flooding impacts through day 4 (Fri), particularly across interior and eastern PR. As this rainfall continues on saturated soils and elevated streamflows, rapid river rises and landslides in areas of steep terrain are also possible. .Ozarks through the Mid-Mississippi Valley... There is increasing confidence in the potential for at least localized flooding impacts from northeastern OK through southern WI beginning on day 3 (Thu) and continuing through day 6 (Sun) as multiple waves of showers and thunderstorms impact the region. Antecedent conditions are variable, with drier conditions across the Ozarks (OK/AR/MO) to somewhat wet across northern IL and southern WI, where soil moisture and streamflows remain elevated (NASA SPoRT, USGS) from recent rainfall, and is the most susceptible to flooding impacts. Both the GFS and NBM-forced National Water Model continue to indicate widespread small stream responses across these regions, primarily on days 5 - 6 (Sat - Sun), with peak flow arrival times on days 6 - 7 (Sun - Mon). Corresponding annual exceedance probabilities (AEPs), per the High Flow Magnitude Forecast, generally show in-bank responses (AEPs at 50%) across the region. However, isolated AEPs down to 2% are noted across portions of eastern IA, northern IL, and southern WI, suggesting that localized significant stream responses are possible. River ensemble guidance (HEFS) also suggests some isolated rises to at least minor flood stage (30% chance of exceedance) across portions of the Mid-Mississippi Valley. Enhanced rainfall rates and potentially training convection will be the primary driver of flooding impacts. .Great Basin and Intermountain West... Mid-to-high elevation snowmelt (SNODAS) will continue to generate elevated flows on area rivers, streams and creeks over the next several days. Rainfall this weekend is not expected to cause widespread impacts, although sharp stream rises are possible in areas of heavier rainfall. The Portneuf River at Pocatello, ID is expected to crest in moderate flood state on day 5 (Sat) and minor flooding along the Owyhee River (NV) will persist through next week. Cooler weather this weekend should slow the degree of snowmelt. //Pritchard $$