Hydrometeorological Discussion
Issued by NWS Tuscaloosa, AL
Issued by NWS Tuscaloosa, AL
575 AGUS74 KWCO 291518 HMDNWC National Hydrologic Discussion - EXPERIMENTAL NWS National Water Center - Tuscaloosa AL 1015 AM CDT SUN SEP 29 2024 .Synopsis... Widespread river flooding and lingering flooding impacts across the Southeast into the Southern Appalachians... Isolated urban and small stream flooding possible in the Central Appalachians... .Discussion... .Southeast into the Southern Appalachians... Residual considerable flooding impacts are expected to persist for the foreseeable future as the Southern Appalachians recover from Helene. Rivers draining the Blue Ridge Escarpment such as the Broad, French Broad, and Catawba have crested, and should continue to slowly recede. A much needed dry spell over the next week should allow for adequate recessions. Further south into the coastal plains, widespread minor and moderate river flooding, as well as isolated major river flooding, will persist well into next week, as runoff from Helene continues to route downstream. Crests are expected along these rivers by mid-week, and dry weather through day 7 (Sat) should allow for unimpeded recessions. Looking ahead, both the GFS and NBM-forced National Water Model (NWM) are indicating scattered stream responses across the northern Gulf Coast as potentially heavy rainfall impacts the region, although there is high uncertainty in the exact location and magnitude due to the extended nature of the forecast. However, given how saturated this region is from Helene, this region will need to be closely monitored by potential new flooding impacts. .Central Appalachians... Periods of convective rainfall through day 2 (Mon) may generate isolated urban and small stream flooding. Antecedent conditions across MD and southern PA are generally on the dry side, which may preclude most if any hydrologic responses. However, further south into VA and WV, recent rainfall has wetted soils, thus elevating soil moisture and streamflow conditions. This factor, combined with the complex terrain of the region, will enhance the runoff potential, especially in areas where more robust rainfall rates are to materialize. The HRRR-forced NWM is indicating isolated small stream responses across the region for later today. Isolated significant stream rises are possible, as corresponding annual exceedance probabilities from the High Flow Magnitude are as low as 10%. //Pritchard $$