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AGUS74 KWCO 071526

HMDNWC



National Hydrologic Discussion - EXPERIMENTAL

NWS National Water Center - Tuscaloosa AL

915 AM CST THU MAR 7 2024



.Synopsis...

Locally considerable flash, urban, small stream, and river flooding  

possible this weekend across the Southeast...Moderate to heavy rainfall  

today in North Texas...Urban and small stream flooding impacts through  

tonight in Puerto Rico...Ongoing river flooding in the Mid-Atlantic and  

Northeast...



.Discussion...



.Southeast...

A second system will sweep across the Southeast beginning day 2 - 3 (Fri -  

Sat), bringing heavy rainfall and additional flooding impacts to the areas  

already saturated from recent rainfall. Locally considerable flash, urban,  

and small stream flooding impacts will be possible especially across  

central AL and northern GA. Widespread QPF totals of 1 - 3+" are expected,  

with the highest totals expected across central GA. Past 48-hour rainfall  

dropped widespread totals of 1 - 2", and notably the Atlanta metropolitan  

area received a bullseye of up to 4" (MRMS). This rainfall has primed the  

region for efficient runoff processes with soils in the 55 - 75% RSM (0 -  

10 cm, NASA SPoRT) and streams running above normal to much above normal  

compared to climatological normals (USGS). With this second round of  

rainfall, flash, urban, and small stream flooding impacts are expected some  

of which may be considerable, and there is potential for additional  

riverine flooding. MMEFS is signaling widespread minor riverine flooding  

across the region, mainly in areas across AL, GA and SC, with some isolated  

moderate flooding possible, mostly across central GA. The National Water  

Model (NWM) NBM/GFS-forced Medium Range Forecasts (MRFs) are generally in  

good agreement as far as timing and placement of flooding impacts, but the  

GFS continues to show stronger signals with respect to magnitude that may  

be overdone. Signals from the NBM-forced NWM Maximum High Flow Magnitude  

forecast have widespread Annual Exceedance Probabilities (AEPs) in the 50%  

range, with isolated AEPs, generally in areas surrounding central GA, from  

20 - 10%. These signals support the occurrence of impactful flash, urban,  

and small stream flooding.



North Texas...

Isolated moderate to heavy rainfall will bring the potential for urban  

flooding impacts today for areas surrounding Dallas. Top soil conditions (0  

- 10 cm) are rather dry (30 - 40%, NASA SPoRT) and streamflows are running  

normal in areas surrounding Dallas (USGS) implying that there is some  

storage capacity available for the forecast rainfall. However, higher  

rainfall rates and the possibility of training may lead to runoff and rises  

along streams, particularly in urban areas. Areas that receive heavier  

rainfall rates will be more vulnerable to flooding, especially in low-lying  

and poorly drained areas.



Puerto Rico...

Locally heavy rainfall will bring the potential for urban and small stream  

flooding impacts through tonight from the interior to the northwest portion  

of the island and areas surrounding El Yunque.



.Mid-Atlantic and Northeast...

Minor to isolated moderate river flooding is ongoing and forecast due to  

recent rainfall and snowmelt across portions of the Mid-Atlantic and  

Northeast. Most rivers will crest today and tomorrow. Rainfall returns to  

the region late this weekend which could bring a few new and renewed river  

rises.



//Kirkpatrick







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