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Hydrometeorological Discussion
Issued by NWS Tuscaloosa, AL
Issued by NWS Tuscaloosa, AL
910 AGUS74 KWCO 211521 HMDNWC National Hydrologic Discussion - EXPERIMENTAL NWS National Water Center - Tuscaloosa AL 1015 AM CDT FRI JUN 21 2024 .Synopsis... Considerable flooding is possible in the Northern Plains and Upper Midwest... Flash flooding possible in the Four Corners region... Localized urban flooding possible in the Northeast... Snow-melt induced flooding in Alaska... .Discussion... .Northern Plains and Upper Midwest... Flash, urban, and river flooding, with considerable impacts, are expected today through the weekend from a multi-day storm system bringing repeat rounds of heavy rainfall across the region. Widespread moderate to major river flooding is expected across southeast SD, southern MN, and northern IA this weekend into next week. Many locations along the Mississippi River will approach flood stage towards next weekend. A brief lull is then expected on day 3 (Sun) before additional rounds on days 4 - 5 (Mon - Tue), although this rainfall should be less significant. The heaviest rainfall (7-day totals) continues to be placed across southeastern SD, southern MN, and central WI (3 - 5", locally higher possible). Soil conditions are wet to saturated in areas of eastern SD and southern MN (0 - 10 cm, 80 - 90% RSM, NASA SPoRT) and streamflows are running much above normal for all days of the year, suggesting limited infiltration capacity. Given these conditions, it will not take much rainfall to generate immediate runoff and subsequent flooding of small streams and creeks, as well as low-lying and poorly drained locations in urban areas. Each additional round of rainfall will serve to further compound the flood potential. The National Water Model (NWM) Short Range Forecast (SRF) is responding accordingly with widespread responses and the potential for rapid-onset flooding near 25 - 50% with more local responses near 75%. Corresponding annual-exceedance probabilities (AEPs) below 20% are seen across basins within the aforementioned region of SD/IA/MN, where high flows are ongoing and significant river flooding is expected. The Medium Range Forecast (MRF) is much the same as far as responses, however, AEPs tend to be more aggressive in the medium-range indicating more out-of-bank rises in the long run.. .Four Corners... Locally heavy rainfall, bringing the potential for flash flooding in states surrounding the Four Corners region, will be of concern today, especially in areas of eastern UT, southwest CO and northern to central NM. The flood threat is highest in areas on recent burn scars, slot canyons, dry washes and where training is likely to occur. .Northeast... The potential exists for localized flooding impacts in primarily urban areas today through day 4 (Mon) as showers and thunderstorms develop across the region. Outside of sensitive urban areas, near normal relative soil moisture values (50 - 70%, 0 - 10 cm, NASA SPoRT) and near to below mean annual streamflows (USGS) suggest sufficient infiltration capacity overall to capture runoff. These factors, combined with modest rainfall amounts (less than 2", WPC), will help to mitigate any widespread hydrologic responses and limit the threat to urban, low-lying, and poor drainage areas. .Alaska... Warming temperatures continue to cause snow and ice melt at high elevations, leading to rivers running high in areas across Southcentral Alaska. Minor flooding on the Chilkat River near Klukwan continues as well as high water on the Nuyakuk River near Dillingham. //Kirkpatrick $$