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AGUS74 KWCO 181517

HMDNWC



National Hydrologic Discussion - EXPERIMENTAL

NWS National Water Center - Tuscaloosa AL

1015 AM CDT THU APR 18 2024



.Synopsis...

Potential for renewed rises and isolated flooding impacts in Southern  

Plains and Lower Mississippi Valley... Continued threat of flooding in  

Puerto Rico and USVI... Ongoing flooding in the Ohio Valley...



.Discussion...



.Southern Plains and Lower Mississippi Valley...

Rounds of rainfall returning to the region this weekend may result in  

renewed rises on rivers as well as isolated flash and urban flooding  

impacts where training occurs. Top soils (0 - 10cm RSM, NASA SPoRT) along  

with streamflows (USGS) in eastern TX, western LA, and southern AR have had  

some time to recover from previous events which may help to mitigate  

initial flooding responses. However, forecast heavy rainfall (1 - 3",  

locally higher amounts possible) will likely overwhelm ground conditions,  

making the region more vulnerable to runoff. If rainfall of this magnitude  

were to materialize, flooding in ditches, low water crossings, and poorly  

drained areas would be expected. Looking further west into central TX, dry  

soils (15 - 40% RSM) and below normal streamflows should mitigate any  

widespread flooding responses.



Across the region, minor to moderate river flooding continues, particularly  

in the Neches (TX) and Sabine (TX/LA) river basins due to slow draining  

basin characteristics and routed flows. Rivers across the region are  

currently forecast to remain above flood stage well into next week, and  

ensemble river models indicate that renewed rises, and/or delays in  

recessions are possible through the weekend across those basins.



The GFS-forced National Water Model (NWM) Medium Range Forecast (MRF)  

continues to suggest highwater responses in eastern TX with arrival times  

estimated by day 4 (Sun). However, the NBM-forced NWM MRF lacks signals and  

is much more muted in eastern TX because the day 3 (Sat) NBM accumulated  

precipitation forecast is further north in northern TX and southern OK with  

lower rainfall totals. Considering the spread of model solutions,  

confidence remains low in the exact magnitude and location of the highest  

QPF amounts. Nonetheless, potential hydrologic impacts cannot be ruled out  

if more robust totals occur.



.Puerto Rico and USVI...

Flooding in urban areas, on roads, along small streams, and along washes  

will remain possible into this afternoon as periods of heavy rainfall  

continue. Isolated flash flooding and landslides remain possible in  

saturated areas of steep terrain. Afternoon convection will pick back up  

this weekend, and reintroduce these flood threats particularly in the  

interior and western portions of the island.



.Ohio Valley...

Scattered minor river flooding will continue across the White (IN) and  

Wabash (IN/IL) river basins and along the lower Ohio River through this  

weekend. Light to locally moderate rainfall (1 - 2" WPC QPF) on day 1 (Thu)  

is forecast in the eastern portions of the Ohio Valley, roughly  

corresponding with the location of the broad crest of the flood wave. The  

additional precipitation may impede some recessions on the elevated streams  

and rivers. However, dry conditions are expected through the weekend,  

mitigating further enhancement of flooding impacts.



//JAC











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