684
AGUS74 KWCO 261523
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1015 AM CDT SAT JUL 26 2025

.Synopsis...
Flash and urban flooding, along with riverine flooding, is ongoing and
forecast across portions of the Middle Mississippi Valley into the Ohio
Valley...Flash flooding remains possible due to Tropical Storm Krosa in
Guam and the Mariana Islands...Isolated flash and urban flooding may occur
in the Upper Midwest...Isolated flash and arroyo flooding is possible late
in the period for the Desert Southwest...

.Middle Mississippi Valley into the Ohio Valley...
The threat for flash and urban flooding continues across the region through
tomorrow as showers and thunderstorms continue to push eastward. Overnight
showers of 1 - 3" (MRMS) in portions of MO, IA, and IL have left soils wet
(NASA SPoRT) and streams much above normal (USGS), maintaining a risk of
enhanced flows and rapid rises on streams. Additionally, minor to isolated
moderate river flooding is ongoing and forecast to continue into next week,
however, the highest flows are likely to crest by day 2 (Sun).

As this system progresses into the Ohio River Valley, antecedent conditions
become much more dry and the threat for flooding diminishes. Popup
thunderstorms with embedded heavy rates that train over flashy basins can
still threaten to overwhelm the hydrologic systems and produce some local
impacts. This is true in particular in WV and western PA, as steep and
complex terrain compounds the factors above. Regardless, widespread
flooding responses are unlikely to develop.

The National Water Model Short Range Forecast continues to signal the
possibility of rapid onset flooding responses (26 - 50%) across northern
MO, IA, and IL through this morning as ongoing rainfall continues but
appears to be winding down. As previously mentioned, ground conditions
become more dry as the system pushes east and that is reflected in the NWM
Medium Range Forecast services with a noticeable lack of signals.

.Guam and Mariana Islands...
Heavy rainfall from Tropical Storm Krosa may cause flash, urban, and small
stream flooding through late tonight. An additional 1 - 3", locally higher
possible, of heavy rainfall will continue across the islands. Small stream
flooding may linger through the weekend as high flows are routed downstream.

.Upper Midwest...
Isolated flash and urban flooding is possible through day 2 (Sun) and
showers and thunderstorms produce 1 - 2" of rainfall. Streams are running
above normal (USGS) and top soils are generally near to slightly above
normal (NASA SPoRT). Training rainfall and high rainfall rates will be the
primary driver for flooding impacts across the region. Basins that
experience these conditions may also experience rapid rises on streams that
are already vulnerable to additional input.

.Desert Southwest...
Isolated flash and arroyo flooding is possible as multiple rounds of
monsoonal moisture moves into the area by day 3 (Mon) and continues through
the week. Daily totals of 0.5 - 1" of rainfall are forecast with some
higher totals potentially embedded in these storms. While widespread
hydrologic responses are unlikely, terrain and training pose a threat
nonetheless, particularly in and near recently burned areas. Confidence in
the exact placement and magnitude of responses remains low due to the
extended range of the forecast so this area should be closely monitored for
further development.

//JAC

$$