AGUS74 KWCO 042018
AHDNWC

Area Hydrological Discussion #098 - EXPERIMENTAL
NWS National Water Center - Tuscaloosa, AL
313 PM CDT Sat May 04 2024

WHAT: Flash, urban, and small stream flooding
WHERE: Central Texas
WHEN: Through early tomorrow morning

FORECAST RAINFALL AND ANTECEDENT CONDITIONS...
QPF 1 - 4, locally higher (HRRR)
QPE 2 - 5 (24 hr MRMS)
Rates 1 - 3/hr (HRRR)
Relative Soil Moisture 40 - 75% (0 - 10cm, NASA SPoRT)

DISCUSSION...
Heavy convective rainfall forecast through tonight may lead to flash
and urban flooding impacts, along with rapid rises on small streams
and arroyos. Antecedent soil conditions remain variable as scattered
heavy rainfall over the past 24 hours have moistened some surface
soils but left others near normal. Soils in this region are generally
finely grained (USA SSURGO - Soil Hydrologic Group) resulting in
impeded downward movement and a slow rate of infiltration.
Streamflows have responded in kind with more elevated streamflows
corresponding to the locations where higher rainfall totals were
observed. As such, the primary concern will be flooding impacts in
elevated streams and areas with low infiltration. However, heavy
rainfall rates can still overwhelm dry, hydrophobic soils leading to
rapid runoff and associated rapid rises in arroyos. Urban areas and
low-lying crossings remain vulnerable where heavy, training rainfall
occurs.

The NWM SRF continues to highlight rapid-onset flooding (ROF)
probabilities up to 50% and annual-exceedance probabilities (AEPs)
around 50%, with some smaller streams signaling 10 - 4%. High Water
Arrival Time Forecast suggests that small streams will reach their
high water thresholds within the next 10-14 hours and their
associated peaks a few hours after. Current trends suggest that while
these small stream impacts may be short lived, some of them may be
significant.

GRAPHICAL REPRESENTATION weather.gov/owp/operations-ahd

Additional National Water Center products are available at
weather.gov/owp/operations

//Capp

ATTN...WFO...LUB...MAF...SJT...FWD...EWX...HGX...OUN
ATTN...RFC...TUA...FWR...WPC