800
AGUS74 KWCO 301523
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1015 AM CDT WED JUL 30 2025

.Synopsis...
Locally considerable flash and urban flooding in the Central Plains into
the Upper Great Lakes...Isolated flash and urban flooding may occur in
portions of the Northern Plains and the Mid-Atlantic into the
Northeast...Isolated flash and arroyo flooding continues for Colorado and
New Mexico...

.Central Plains into the Upper Great Lakes...
A complex of thunderstorms will continue to push eastward this morning,
bringing the threat for locally considerable flash and urban flooding to
the area of concern, including that of IA, MO, and IL. Top-soils are
generally wet (40-75%, 0-10 cm RSM, NASA SPoRT), especially in IA and
portions of NE, with other areas rather dry to normal. However, high
rainfall rates may locally overwhelm remaining infiltration capacity,
leading to excess runoff. Streamflows vary across the region, with
streamflows highest in IA, where river flooding is already ongoing or
forecast (minor to isolated major riverine flooding). Additional
out-of-bank rises will also be possible, with some locally significant
rises also possible. Urban areas will be particularly susceptible to flash
flooding.

The National Water Model (NWM) Short-Range Forecast (SRF) continues to
highlight rapid-onset flooding (ROF) across the area, with the greatest
consistency in IA, generally 25-50% with isolated probabilities greater
than 75%. Lowest annual-exceedance probabilities (AEPs) are also located
across IA, with some additional lower AEPs in northwest IL. Peak flow
arrival times are ongoing or forecast from 4 to 9 hours on smaller reaches,
with the larger streams and rivers forecast 14 to 18 hours and beyond.
Given these signals and the higher rainfall rates, locally significant
flooding will be possible, particularly in eastern IA.

.Northern Plains...
Heavy rainfall will bring the threat of isolated flash flooding today in
portions of southeast MT and northern WY. Areas of high rainfall rates may
result in flooding impacts, especially in areas around burn scars,
low-lying areas, and small streams.

.Colorado and New Mexico...
Isolated flash and arroyo flooding is possible in portions of CO and NM as
monsoonal moisture continues today. High rainfall rates and training
thunderstorms over recent burn scars, urban, and poorly drained areas may
pose a significant risk of flooding impacts.

.Mid-Atlantic into the Northeast...
Heavy rainfall on day 2 (Thu) will bring the possibility of flooding
impacts to areas along the Mid-Atlantic and Northeast regions, primarily
from the Carolinas northeastward to MA. Antecedent conditions range from
dry to normal in most areas (55-75%, 0-10 cm RSM NASA SPoRT). There is low
confidence on the exact location of heaviest rainfall given inconsistencies
with QPF models however, any training of rainfall may result in flooding
impacts.

//TMK





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