####018003381#### AGUS74 KWCO 011509 HMDNWC National Hydrologic Discussion - EXPERIMENTAL NWS National Water Center - Tuscaloosa AL 1015 AM CDT MON APR 1 2024 .Synopsis... Isolated flash and urban flooding along with minor river flooding across the Mid-Mississippi and Ohio Valleys into the Mid-Atlantic... .Discussion... .Mid-Mississippi and Ohio Valleys into the Mid-Atlantic... Isolated flash and urban flooding, widespread river rises, including minor flooding is expected across the region as moderate to heavy rainfall (1 - 3" with locally higher amounts WPC) expands eastward late this afternoon and through the overnight. Light rainfall continues to push out of the region leaving soils on the wetter side along with elevated streamflows, particularly across northern IL. Soil moisture is generally greater (65 - 75% 0 - 10 cm Relative Soil Moisture (RSM) (NASA SPoRT)) across northern IL/IN/OH and southwestern PA and 50 - 60% across southern portions of the Ohio Valley. Streamflows have increased across northern IL with more isolated rises further east across the Upper Ohio River Valley (NWM Streamflow Anomaly Analysis). The heaviest forecast rainfall is expected slightly further south; however, overlap in the new rainfall and recent rainfall is present along with some variability among the different hi-res model guidance. These factors suggest that depending on where the heaviest rainfall materializes, northern IL/IN, OH, and western PA will be more susceptible to flash and urban flooding. River flooding is also forecast across the Illinois and Wabash River basins with some smaller streams and rivers already in minor flood in southern portions of the Chicago metropolitan area. Smaller rivers are forecast to crest through the week with larger rivers such as the Illinois and Wabash Rivers will remain in flood into next week. The ongoing minor flooding combined with additional rainfall tonight suggests greater confidence in potential flooding impacts across that area. The HRRR-Forced National Water Model (NWM) Short Range Forecast (SRF) is starting to capture the earliest QPF for the event; however, by this afternoon, it will fully ingest all the forecast QPF for the event. Signals will likely start to expand across the region later this morning. Both the GFS- and NBM-Forced NWM Medium Range Forecasts (MRF) have been signaling the potential for rapid-onset flooding during recent runs with some of the more robust signals across OH, WV, and southwestern PA; however, the highwater thresholds for the Ohio Valley have been considered very low relative to the rest of the US suggesting signals may be overdone. This is more evident in both MRF versions of the Maximum High Flow Magnitude Forecast which show widespread highwater responses and more isolated significant responses (lower Annual Exceedance Probabilities (AEPs) for streamflow). Isolated flash flooding also remains a concern especially with potential heavy rainfall and training. Additionally, MMEFS is signaling potential for widespread minor to isolated moderate river flooding. Dry conditions will settle in for the remainder of the week allowing unimpeded recessions to begin. //Smith $$