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AGUS74 KWCO 151528

HMDNWC



National Hydrologic Discussion - EXPERIMENTAL

NWS National Water Center - Tuscaloosa AL

1015 AM CDT MON APR 15 2024



.Synopsis...

Flash and urban flooding impacts possible in Hawaii... Flooding impacts  

possible in the Upper Midwest and Puerto Rico and USVI... River flooding  

continues in East Texas, the Lower Mississippi Valley, and Southeast and  

the Ohio Valley...



.Discussion...



.Hawaii...

Heavy rainfall and thunderstorms may produce additional flash and urban  

flooding impacts on the central islands through the afternoon. Flood prone  

roads and other low-lying areas may close due to elevated runoff and  

overflowing streams, as this rain falls on saturated soils.



.Upper Midwest...

Localized flooding impacts are possible on day 2 (Tue) from portions of  

northeastern NE and northern IA to southern MN and southwestern WI in  

response to locally heavy rainfall (1 - 3", locally higher) expected. Ahead  

of this event, antecedent soil conditions are relatively dry (less than  

55%, 0 - 100 cm RSM, NASA SPoRT) While this does suggest ample soil  

infiltration capacity at least initially, the lack of available  

evapotranspiration (dormant vegetation), coupled with the potential for  

enhanced rainfall rates, may locally overwhelm infiltration capacity and  

lead to runoff into nearby streams and urban areas.



The GFS-forced NWM is indicating low end rapid onset flooding signals  

throughout the region, with associated AEPs of 10 - 50% suggesting small  

stream responses are possible. The NBM-forced NWM is continuing to signal  

isolated responses, decreasing confidence in impacts. The variability in  

responses from the GFS and NBM-forced NWM increases confidence in the  

potential for isolated impacts, but specifics in terms of placement and  

magnitude still remain uncertain and will be dependent on convective and  

training aspects.



.Puerto Rico and USVI...

Periods of heavy rainfall will continue the threat of flooding on small  

streams and in urban areas through day 3 (Wed). Isolated flash flooding is  

ongoing and imminent. Current soil base saturation conditions are wet to  

saturated (SLIDES-PR) and landslide susceptibility is high to very high  

(USGS), increasing confidence that landslides may also be possible,  

especially in areas of steep terrain.



.Ohio Valley...

Minor to isolated moderate river flooding impacts continue across portions  

of IN and OH. Most points have crested, and should continue to slowly  

recede mostly unimpeded. Additional rainfall on days 2 - 4 (Tue - Thu) may  

elicit renewed rises and/or stalled recessions along portions of the White  

(IN) and Wabash (IN) rivers, however, confidence in the exact location and  

magnitude of impacts remains somewhat uncertain, and will be heavily  

dependent on where convection trains or persists.



.East Texas, Lower Mississippi Valley, and Southeast...

Widespread minor to moderate river flooding, and isolated major river  

flooding (TX/LA), will continue throughout these regions through at least  

mid-week as runoff from recent heavy rainfall routes through the systems.  

With no significant rainfall expected over the next several days, crests  

and subsequent recessions will continue unimpeded for now, minimizing the  

risk of any additional river flooding impacts.



Additional rainfall may return to the region this weekend (days 6 - 7)  

potentially renewing rises and delaying recessions. However, confidence is  

low and the exact location of impacts is unknown due to the extended nature  

of the event.



//Ayala







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