####018006362#### AGUS74 KWCO 261517 HMDNWC National Hydrologic Discussion - EXPERIMENTAL NWS National Water Center - Tuscaloosa AL 1015 AM CDT FRI APR 26 2024 .Synopsis... Flooding impacts excepted this week across the Central and Southern Plains into the Midwest and across East Texas and the Lower MIssissippi River Valley... Daily rainfall continues in Puerto Rico... Snowmelt continues in the Great Basin and Intermountain West... .Discussion... .Central and Southern Plains into the Midwest... Considerable flooding impacts are possible on days 2 and 3 (Sat - Sun) across portions of eastern OK, northwest AR, southeast KS, and southwest MO as multiple waves of showers and thunderstorms bring torrential rainfall to the region. Outside of this particular area, flooding impacts are possible through the weekend across much of these regions. For today, the primary focus will be from southern OK through the Ozarks and into the Lower Missouri Valley. Convection ongoing across OK will expand in coverage across portions of northwestern AR and southern MO through the morning, bringing a potential for at least localized flooding impacts. The most vulnerable area for flooding is centered across southwestern MO, as rainfall yesterday (widespread 2 - 4", locally up to 7", past 24 hour MRMS QPE) has drastically reduced infiltration capacity in soils and has generated isolated minor river flooding across the region. Additional rainfall today will likely worsen ongoing flooding and generate new flooding impacts, such as large areas of standing water in fields, along roadways and at low water crossings, overflowing of ditches and culverts, and flooding in areas of poor drainage. Further south into portions of northern TX/southern OK, antecedent conditions are less favorable for flooding impacts (at least initially) and will be mainly driven by intense rainfall rates and potential training convection over the region. There remains some uncertainty in the exact placement and magnitude of potential impacts as the HRRR, which forces the National Water Model (NWM) Short Range Forecast, has been inconsistent in the placement of the heaviest QPF and may be underestimating the amount of rainfall forecast. The latest guidance is indicating scattered small stream responses from eastern OK through southern MO, with the most robust responses across southwest MO. Corresponding annual exceedance probabilities (AEPs) are as low as 2% near Springfield, MO, which suggests at least locally significant stream rises are possible, especially where convection trains or persists. The threat for flooding increases on day 2 into day 3 (Sat - Sun), as additional rounds of showers and storms track over the same regions. These repeated rounds of storms will play a key role in setting the antecedent conditions for day 2, as it is likely that rainfall today will diminish infiltration capacity and rainfall tomorrow (2 - 4", locally higher) will immediately runoff into area creeks and streams, generating flooding impacts, some of which may be considerable. River flooding is possible as well, as river ensemble guidance (HEFS, PQPF) continues to suggest the potential for minor to isolated moderate river flooding across these regions and these rivers are generally quick responding. Further north into portions of the Mid-Mississippi Valley, flooding impacts are expected to be more localized and areas of river flooding may occur where more robust rainfall rates materialize. The NWM Medium Range Forecast (MRF) continues to indicate widespread small stream responses across these regions on days 2 - 5 (Sat - Tue). The most consistent signals from the NWM MRF have been across eastern KS through northern MO into southeast IA/northwest IL, where probabilities for rapid onset flooding (ROF) are between 25 - 50%. Corresponding AEPs are mostly near 50% with probabilities as low as 2% on smaller streams across eastern OK, northwestern AR, southeastern KS, and portions of southern/central MO increasing confidence in the potential for considerable flooding impacts. .East Texas and the Lower Mississippi River Valley... Rain will progress across the region today, however any flooding impacts will be isolated and most likely across northeast TX into AR. The primary concern for flooding impacts will be on days 3 - 4 (Sun - Mon) across the ArkLaTex through the ArkLaMiss where some places could see 2 - 4" of rainfall (WPC). Soils are wet (NASA SPoRT) and streamflows are above normal (USGS) as basins continue to recover from previous rainfall events. Rivers are still in recession and in flood stage across this region as well, so new and renewed river flooding will be a concern. Flash flooding, widespread small stream responses (NWM MRF), and isolated minor-to-moderate river flooding is possible (HEFS/PQPF Ensembles). Of note, the NWM MRF continues to signal potential for more significant flows on smaller tributaries south of Little Rock, where conditions are hydrologically vulnerable. .Puerto Rico... Daily showers and thunderstorms will continue to generate flash, urban and small stream flooding impacts through day 2 (Sat). As this rainfall continues on saturated soils and elevated streamflows, rapid river rises and landslides in areas of steep terrain are also possible. .Great Basin and Intermountain West... Elevated flows will continue along area rivers, creeks, and streams across portions of southern ID, northern NV, and northern UT in response to mid-to-high elevation snowmelt. Periods of rainfall through day 2 (Sat), generally in areas below 6000, may cause sharp rises in quick responding streams and creeks, especially in areas where prolonged rainfall materializes. Cooler temperatures over the next several days will likely slow high elevation snowmelt. The Portneuf River at Pocatello, ID, is expected to crest in moderate flood stage this weekend with minor flooding along the Owyhee River (NV/OR) will persist for the foreseeable future. //Kirkpatrick/Pritchard $$