433
AGUS74 KWCO 051531
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1015 AM CDT SAT JUL 5 2025

.Synopsis...
Considerable flooding continues in Texas today...Rainfall associated with
Tropical Storm Chantal may generate flooding across the Carolinas through
early next week...Isolated flash and urban flooding possible across
portions of the Northern/Central Plains to portions of the Mid-to-Upper
Mississippi Valley...

.Texas...
Considerable flooding is ongoing over portions of the Texas Hill Country
into Central Texas this morning as additional heavy rainfall (4 - 8",
locally higher amounts of 12+") has resulted in numerous instances of
significant flash and urban flooding and moderate to major flooding along
portions of the San Saba, San Gabriel, and Colorado rivers. Similar to
yesterday, the system generating this extreme rainfall remains nearly
stationary and ample moisture and daytime heating this afternoon will once
again cause redevelopment of heavy rainfall. Ongoing precipitation
northwest of the Austin metro may result in significant and
life-threatening impacts, given the dense urban infrastructure and steep
terrain of the Hill Country. Impacts of large areas of standing water, road
closures, and water rescues have already occurred and more instances of
these impacts are expected through the morning hours. The HRRR, which
forces the National Water Model (NWM) Short Range Forecast, has been
struggling to resolve the details of the ongoing convection,
underestimating the amount of QPF expected. As such, the HRRR-forced NWM is
grossly underestimated and not in line with current radar trends.
Additional convection this afternoon is expected outside of the already
impacted areas however, significant flooding is possible given the intense
nature of the rainfall and if there is some overlap with the areas
currently inundated, new and renewed flooding impacts, some of which may be
significant, are possible this evening. Minor to moderate river flooding
along the Rio Grande will continue into early next week.

.Carolinas...
Periods of heavy rainfall associated with Tropical Storm Chantal may
generate isolated flash and urban flooding across the Coastal Plain of the
Carolinas through day 3 (Mon). Antecedent conditions for most of the region
are generally dry (50% RSM, 0 - 10 cm NASA SPoRT) however, soils are
nearing saturation along the immediate coast from the NC/SC border through
the Outer Banks (60 - 70% RSM, 0 - 10 cm NASA SPoRT), thus making this
region somewhat vulnerable to flooding impacts. Training bands of rainfall
and locally enhanced rainfall rates will be the primary drivers for
flooding.

.Northern/Central Plains to portions of the Mid-to-Upper Mississippi
Valley...
Periods of moderate to locally heavy rainfall today will continue the risk
of isolated flash and urban flooding impacts to portions of IA, MN, and WI.
While rainfall totals are generally modest (2"), antecedent conditions
remain wet following repeated rounds of rainfall over the past week,
indicating some vulnerability to new and renewed flooding. The HRRR-forced
NWM are indicating the potential for rapid-onset flooding across portions
of southern MN, northern IA, and western and central WI this afternoon,
with peak flows expected later this evening. Corresponding AEPs, per the
High Flow Magnitude Forecast, suggest that most rises should remain within
bank (50% or greater AEPs) however, some higher magnitude AEPs (10%)  are
noted across the region, indicating an isolated potential for significant
stream rises. Localized training convection will be the primary driver for
flooding impacts, although the overall progressive nature of the rainfall
will mitigate more widespread flooding across the region. Additional
rainfall is expected across the region early to midweek next week however,
there remains some uncertainty in the exact placement of heaviest rainfall.

//JDP





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