####018003366#### AGUS74 KWCO 241518 HMDNWC National Hydrologic Discussion - EXPERIMENTAL NWS National Water Center - Tuscaloosa AL 1018 AM CDT WED APR 24 2024 .Synopsis... Isolated flooding impacts will be possible through this weekend in Puerto Rico... Low confidence flooding potential across the Ozarks/Southern Plains through the Lower and Mid Mississippi Valley late this week through the weekend... Snow melt induced river rises across 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 (Sat). As this rainfall continues on saturated soils and elevated streamflows, rapid river rises and landslides in areas of steep terrain are also possible. .Ozarks/Southern Plains through the Lower and Mid Mississippi Valley... There is potential for at least isolated flooding impacts from northeastern OK through southern WI beginning on day 2 (Thu) and continuing through day 6 (Mon) as multiple waves of showers and thunderstorms impact the region. Confidence is still very low with respect to which areas will see the best potential for new flooding impacts given relatively high QPF placement uncertainty. Antecedent conditions are variable, with drier conditions across eastern OK/KS and western MO/IA to somewhat wet across northeast TX, AR, eastern MO, and IL where soil moisture and streamflows remain elevated (NASA SPoRT, USGS) from recent rainfall, and is the most susceptible to flooding impacts. If much of the rainfall over the next six days ends up falling across the drier aforementioned region, flooding impacts may end up being quite minimal, whereas if the heavier rainfall ends up across the more vulnerable region further east and south (east TX through the lower MS Valley), a more widespread hydrologic response would be possible. Both the GFS and NBM-forced National Water Model continue to indicate widespread small stream responses across these regions, beginning on days 3 - 5 (Fri - Sun), with peak flow arrival times on days 5 - 7 (Sun - Tue). Corresponding annual exceedance probabilities (AEPs), per the High Flow Magnitude Forecast, generally show in-bank responses (AEPs at 50%) across the region. However, there have been somewhat consistent signals for flows with lower AEPs across northern MO, eastern IA, and into IL, suggesting that isolated river flooding impacts 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. .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 stage this weekend and minor flooding along the Owyhee River (NV) will persist through next week. Cooler weather this weekend should slow the rate of snowmelt. //JEC $$