Hydrometeorological Discussion
Issued by NWS Tuscaloosa, AL
Issued by NWS Tuscaloosa, AL
026 AGUS74 KWCO 251516 HMDNWC National Hydrologic Discussion - EXPERIMENTAL NWS National Water Center - Tuscaloosa AL 1015 AM CDT TUE JUN 25 2024 .Synopsis... Additional rounds of rainfall in the Northern Plains and the Upper and Middle Mississippi Valley... Flash flooding possible in the Four Corners region, Great Lakes and Northeast...Snowmelt induced flooding continues in Alaska... .Discussion... .Northern Plains and the Upper and Middle Mississippi Valley... Widespread moderate to major river flooding is ongoing and/or forecast across southeast SD, southern MN, northern IA and record flooding is ongoing along the Vermillion, West Fork of the Des Moines, Little Sioux, and the Minnesota rivers. Many of these rivers are already in recession, but will remain in flood status well into next week. Additional rainfall is expected over the next week (1 - 3", NBM), which could exacerbate the ongoing flooding and delay recessions however, the heaviest totals are currently forecast to mostly stay in south-central IA, away from the worst of the ongoing flooding. Topsoils have recovered slightly from last weeks rain, but are still near saturation (0 - 10 cm RSM, NASA SPoRT), and rainfall will quickly convert to runoff into streams, rivers, and low-lying areas. In MN, the Rapidan Dam along the Blue Earth River has breached and is in danger of a total failure as of Tuesday morning. Multiple levee failures in IA have also led to additional flooding impacts. In southern IA, northern MO, and western IL, 2 - 3" of rainfall is expected, and antecedent conditions are less favorable for runoff compared to areas further north. That being said, southern IA is somewhat hydrologically sensitive with topsoils in the 50 - 60% range (0 - 10 cm RSM, NASA SPoRT) and above average flows (USGS). Within-bank rises to area streams are likely, and some localized flooding impacts are possible. Northern MO and western IL are both on the drier side and should be able to absorb the rainfall without significant flooding impacts. Flash and urban flooding is possible anywhere heavy rainfall persists or storm training sets up. .Four Corners... Moisture will persist over the region throughout the week, particularly in parts of NM and AZ, leading to locally heavy rainfall and the potential for flash flooding. Areas that have recently received rainfall may continue to face a risk of flash flooding and excessive runoff. The highest flood threat is in areas with recent burn scars, slot canyons, dry washes, and regions where training and more persistent storms occur. .Great Lakes... Flooding impacts are possible for states along the Great Lakes today as convective rainfall sweeps across the area. Antecedent conditions are relatively dry with topsoils generally between 40 - 55% RSM (0 - 10 cm, NASA SPoRT) and streams running at or below annual mean flows. These conditions will likely preclude any significant small stream or riverine response to this rainfall, but high rainfall rates could lead to localized instances of flash and urban flooding. .Northeast... Isolated incidences of flash and urban flooding on day 2 (Wed) and again on Sat (day 5) remain possible across the region as multiple frontal boundaries generate scattered showers and storms. Outside of urban areas, the Adirondacks and northern New England (VT/NH/ME) are most vulnerable to hydrologic responses given wet soils (60 - 75% RSM, 0 - 10 cm NASA SPoRT) from recent rainfall. Impacts will be dependent on storm motion and the intensity of rainfall rates. .Alaska... Warming temperatures continue to cause snow and ice melt at high elevations, leading to rivers running high in areas across Southcentral AK. Minor flooding on the Chilkat River near Klukwan continues into early this week. Also, there continues to be high water on the Nuyakuk River near Dillingham. The Skwentna and Yentna Rivers will also likely have high water with out-of-bank conditions today. //Bliss/Pritchard $$