WCO issues Area Hydrological Discussion (AHD) at Sep 25, 12:38 PM CDT013
AGUS74 KWCO 251742
AHDNWC
Area Hydrological Discussion #273 - EXPERIMENTAL
NWS National Water Center - Tuscaloosa, AL
1238 PM CDT Wed Sep 25 2024
WHAT...Flash and urban flooding
WHERE...Eastern Alabama through far-western NC
WHEN...Through this afternoon
FORECAST RAINFALL AND ANTECEDENT CONDITIONS...
QPF...2 - 4" (HRRR/WPC)
QPE...1 - 3 (6 hr MRMS)
Rates...2 - 2.5"/hr (HRRR/WPC)
Soils...35 - 50%, locally up to 75% (0 - 10 cm, RSM, NASA SPoRT)
Streamflows...Below normal (USGS)
DISCUSSION...
A predecessor rainfall event (PRE) is taking shape over the region
ahead of an approaching frontal boundary and moisture from Hurricane
Helene streaming north into the region, potentially generating
isolated to scattered flash and urban flooding. Despite dry
antecedent conditions region wide, the persistent nature of the
rainfall, coupled with intense rainfall rates will quickly overwhelm
infiltration capacity, generating efficient runoff into nearby
streams and urban areas. Of particular concern for flooding impacts
is the Atlanta metro, given the large urban landscape and the
flash/quick responding nature of tributaries to the Upper
Chattahoochee Basin. Some road closures, as well as areas of standing
water, overflowing of ditches/culverts/storm drains, and flooding of
typical flood prone areas are possible. Rapid stream rises are also
possible in areas of steep terrain, particularly across northeast AL,
northern GA, and far-western SC/NC.
The HRRR-forced NWM is indicating only isolated small stream
responses across the region, likely due to the dry antecedent
conditions in place. However, recent radar trends and model guidance
from the HRRR indicate the potential for training and intense
rainfall rates across this region. A subsequent AHD will likely be
warranted later this evening as heavy rainfall persists across the
region.
GRAPHICAL REPRESENTATION weather.gov/owp/operations-ahd
Additional National Water Center products are available at
weather.gov/owp/operations
//Pritchard
ATTN...WFO...BMX...HUN...OHX...GSP...MRX...MOB...TAE...FFC
ATTN...RFC...ORN...ALR...WPC
Source:
WCO issues Area Hydrological Discussion (AHD) at Sep 25, 12:38 PM CDT---------------
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