WCO issues Area Hydrological Discussion (AHD) at Aug 18, 2:50 PM CDT639
AGUS74 KWCO 181957
AHDNWC
Area Hydrological Discussion #225 - EXPERIMENTAL
NWS National Water Center - Tuscaloosa, AL
250 PM CDT Mon Aug 18 2025
POTENTIAL IMPACTS: Flash, urban, and small stream flooding
WHERE: Eastern Iowa, southern Wisconsin, northern Illinois, and far
northwestern Indiana
WHEN: This evening through tonight
FORECAST RAINFALL AND ANTECEDENT CONDITIONS...
QPF: 1 - 4"+ (HRRR)
QPE: 1 - 3"+ (MRMS, 72hr)
Rain Rates: 1 - 2"/hr (HRRR)
Soil Moisture: 45 - 70% (0 - 10 cm RSM, NASA SPoRT)
Streamflows: Above normal to High (USGS)
DISCUSSION...
Training thunderstorms are forecast overnight which may cause flash,
urban, and small stream flooding across the area of concern, some of
which may be significant. Top soils remain wet and streams are
running high from repeated rounds of rainfall over the past several
days. Additionally, ongoing rainfall this afternoon will act as a
primer for the potential impacts later tonight. Model guidance
suggests potentially high rainfall rates and repeated rounds of heavy
rainfall over flashy basins in southern Wisconsin, which combined
with the factors mentioned above may elicit rapid, out-of-bank rises
and efficient overland flows, particularly in urban areas with poor
drainage.
The NWM Short Range Forecast is signaling increasing rapid-onset
flooding probabilities of 26 - 50% with annual exceedance
probabilities (AEPs) generally near 20%. Of particular concern
however, is low AEPs in basins surrounding the Chicago, IL
metropolitan area that are as low as 2 - 4%. Creeks and streams are
suggested to peak in flow in the next 4 - 8 hours on the tributaries
in Wisconsin and in 8 - 14 hours in portions of northern Illinois as
training continues.
GRAPHICAL REPRESENTATION: weather.gov/owp/operations-ahd
Additional National Water Center products are available at:
weather.gov/owp/operations
//JAC
ATTN...WFO...IWX...ARX...DVN...LOT...MKX
ATTN...RFC...MSR...WPC
Source:
WCO issues Area Hydrological Discussion (AHD) at Aug 18, 2:50 PM CDT---------------
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