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AGUS74 KWCO 131514

HMDNWC



National Hydrologic Discussion - EXPERIMENTAL

NWS National Water Center - Tuscaloosa AL

1015 AM CDT SAT APR 13 2024



.Synopsis...

Flash and urban flooding impacts possible in Hawaii... Ongoing river  

flooding and the potential for new flooding impacts across the Ohio Valley  

into the Northeast... River flooding continues in East Texas, the Lower  

Mississippi Valley, and Southeast... Flooding impacts possible in  

California, Puerto Rico and USVI, and Upper Midwest...



.Discussion...



.Hawaii...

Another round of heavy rainfall with enhanced rainfall rates (up to 2"/hr)  

may elicit new flash and urban flooding impacts across Kauai and Niihau,  

and to a lesser extent Oahu, this evening into early day 2 (Sun). Flood  

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

overflowing streams.



.Ohio Valley into the Northeast...

Minor to isolated moderate river flooding impacts are ongoing and forecast  

across much of IN and OH, becoming less widespread moving into the  

Northeast. Most areas are at or near crest,  but flooding along larger  

mainstem rivers will persist well into next week. Dry weather through day 3  

(Mon) should allow for unimpeded crests and recessions on smaller rivers.



Much of the region is forecast to receive additional rounds of rainfall on  

day 2 (Sun) and again on days 4 - 6 (Tues - Thu) which may bring the  

potential for additional flooding impacts, particularly in southwest PA and  

western WV where conditions are saturated and recovery from recent flooding  

impacts is ongoing. Overall, the progressive nature of this event and the  

modest rainfall totals (1 - 2 mean areal average) will help mitigate any  

widespread responses, but primed soils and elevated streamflows throughout  

the region could lead to some hydrologic sensitivity and result in  

localized flooding impacts, especially in urban and poor drainage areas,  

and in areas of complex terrain.



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

Widespread minor to moderate river flooding, and isolated major river  

flooding (TX/LA) is ongoing and forecast throughout these regions in  

response to heavy rainfall earlier this week. Many of these locations are  

still rising and will crest within the next several days, although flooding  

along larger mainstem rivers will persist well into next week. With no  

significant rainfall expected over the next week, crests and subsequent  

recessions will continue unimpeded, minimizing the risk of any additional  

river flooding impacts.



.California...

Localized flash and urban flooding impacts are possible across coastal  

areas of central and southern CA in response to 1 - 2" of locally heavy  

rainfall through day 2 (Sun). Antecedent conditions are generally dry to  

normal which will help to minimize flooding impacts, however, the  

persistent nature of the rainfall combined with the expansive urban areas  

may quickly lead to urban flooding issues. The National Water Model (NWM)  

Short Range Forecast (SRF) is signaling isolated low-end probabilities for  

rapid-onset flooding over the next 12 hours (less than 50%) from San Jose  

to Santa Barbara. Corresponding annual exceedance probabilities (AEPs)  

remain at or above 50% overall, any small stream rises should stay within  

the channel. This will leave the primary threats as localized flash and  

urban flooding, particularly in areas with poor drainage.



.Puerto Rico and USVI...

Periods of heavy rainfall will increase the potential for urban and small  

stream flooding impacts on days 3 - 5 (Mon - Wed) across the islands.  

Isolated flash flooding may also be possible, especially in areas of steep  

terrain.



.Upper Midwest...

Localized flash and urban flooding impacts may be possible for portions of  

southern MN, northern IA, and southern WI on day 4 (Tue) in response to  

widespread rainfall (isolated totals up to 3") forecast across the region.  

Overall antecedent conditions are dry to normal (less than 55%, 0 - 100 cm  

RSM, NASA SPoRT) with areas of drought in place, particularly across IA,  

suggesting ample soil infiltration capacity is available for excess runoff.  

Streamflows throughout these specific regions are near to above normal when  

compared to historical flows for this time of year (USGS). When combined,  

these conditions suggest a near normal vulnerability to new rainfall and  

potential flooding impacts, and much of the flooding threat will be  

contingent on where the heaviest rainfall totals occur.



//Freeman







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