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Hydrometeorological Discussion
Issued by NWS Tuscaloosa, AL
Issued by NWS Tuscaloosa, AL
945 AGUS74 KWCO 291517 HMDNWC National Hydrologic Discussion - EXPERIMENTAL NWS National Water Center - Tuscaloosa AL 1017 AM CDT SAT JUN 29 2024 .Synopsis... Renewed flooding possible next week for the Upper and Middle Mississippi Valley.... Isolated flooding potential across portions of the Northeast today... Daily convection across the Four Corners Region... Heavy rainfall potential early-to-mid next week across Puerto Rico/USVI as TS Beryl tracks south of the region... Increased snowmelt and glacier runoff in Alaska... .Discussion... .Upper and Middle Mississippi Valley... Widespread moderate to major river flooding is ongoing across far southeast SD, southern MN, and northern IA and is forecast through next week along the Missouri (moderate) and Mississippi (moderate to major) River mainstems. Rain returns to the region beginning day 3 (Mon) and lingers through day 5 (Wed). Ample deep layer soil moisture remains in place (60 - 80% relative soil moisture (RSM) 0 - 100 cm NASA SPoRT), suggesting that the already elevated/flooded rivers across the region will likely respond fairly efficiently to the expected rainfall/runoff. Generally 1 - 2" inches of rain is expected for the entire event, which is likely not enough to cause widespread new and renewed river flooding, however some basins could see some new and renewed river rises/flooding (National Water Model (NWM) Medium Range forecast (MRF) High Water Probability) if heavier totals (2 - 3"+) materialize with any convection. At the very minimum, delayed recessions of ongoing flooding and isolated flash flooding can be expected. New river flooding impacts will be possible, with some new and renewed rises into minor and moderate flood being possible (HEFS, CR Ensemble QPF hydrographs) if the heavier aforementioned rainfall totals come to fruition. The NWM MRF (NBM and GFS forced) continue to indicate potential for widespread new and renewed river rises early next week in response to this rainfall with peak flows mostly on days 4 - 7 (Tue - Fri) across southern MN, western WI, and IA. The magnitude of response is still uncertain, but the NWM MRF is indicating potential for 4 - 20% AEP flows on many smaller tributary rivers across the aforementioned region, so trends will need to be closely monitored heading into next week. .Northeast... Moderate to heavy rainfall today (Sat) will bring the potential for isolated flash and urban flooding to portions of eastern OH, western/northern PA, and western NY. Soils are generally moist, with room for infiltration (50 - 65% RSM, 0 - 10 cm NASA SPoRT). Though there is available infiltration capacity, prolonged periods of moderate-to-heavy rain could overwhelm soils, increasing the chance of rapid runoff and flooding impacts, especially in any areas of complex terrain. The HRRR-forced NWM Short Range Forecast (SRF) has consistently been signaling potential for small stream flooding across northeast OH, through northwest PA, and into western NY. This is where rapid onset flooding (ROF) probabilities are highest (25%), albeit still relatively low. This is the area that received 1 - 3" of rain over the past 2 days as well, and will see some additional priming rainfall today ahead of the more intense rainfall later this afternoon/evening, so isolated flooding impacts can be expected. .Four Corners Region... Daily scattered thunderstorms will bring the potential of isolated flash and urban flooding to the Four Corners region through next week. Locations that have received multiple rounds of rainfall over the past week are most susceptible to flooding impacts as soil moisture increases. The highest flood threat is in areas with recent burn scars, slot canyons, dry washes, and regions where training and more persistent storms occur. .Puerto Rico/USVI... Moderate to heavy rainfall early-to-mid next week will bring the potential for isolated flooding impacts across the islands. Streamflows across the region are generally normal to above normal in comparison to both the daily and annual climatological normals, suggesting soil capacity is nearing saturation in response to recent rainfall. This increases the potential for rapid runoff and flooding concerns, and trends in forecast rainfall amounts will need to closely be monitored heading through the weekend as Tropical Storm Beryl progresses west. .Alaska... Recently warm temperatures continue to lead to increased snowmelt and glacier runoff, leading to rivers running high in areas across southern AK. Minor flooding on the Chilkat River near Klukwan continues through at least the weekend. Also, elevated flows and localized flooding is possible along the Skwentna, Yentna, and Nuyakuk Rivers. //JEC $$