WCO issues Area Hydrological Discussion (AHD) at Jul 21, 4:01 PM CDT683
AGUS74 KWCO 212107
AHDNWC
Area Hydrological Discussion #192 - EXPERIMENTAL
NWS National Water Center - Tuscaloosa, AL
401 PM CDT Sun Jul 21 2024
WHAT: Isolated flash, urban, and small stream flooding
WHERE: Southwest LA, southern MS, central AL, central GA
WHEN: Through this late this evening
FORECAST RAINFALL AND ANTECEDENT CONDITIONS...
QPF: 2 - 5 locally (HRRR/WPC)
Rates: 1 - 2+/hr
Soil Moisture: Recently increased to 55 - 75% (0 - 10 cm RSM NASA
SPoRT)
Streamflows: Recently increased to normal (USGS)
DISCUSSION...
Localized areas of prolonged heavy rainfall and isolated flooding
impacts are expected through this evening across the area of concern.
Over the past few days, conditions have moistened up in response to
daily convection across the region. Soil moisture conditions have
increased from dry to 55 - 75% RSM in the top layer, and streamflows
have increased to more near normal values rather than below normal.
With additional heavy rainfall being a certainty at this point this
afternoon and evening, the overall threat and potential for flooding
impacts has drastically increased, primarily on smaller tributaries
and in urban areas. Larger streams and rivers will likely not respond
in an impactful manner given the dry deep layer soils that remain in
place.
The National Water Model (NWM) Short Range Forecast (SRF) is showing
an increased potential for small stream response across the region,
with the most consistent forecast responses for rapid onset flooding
(ROF) being across southeast MS (north of Hattiesburg) through
west-central AL (near Demopolis), and from the Montgomery, AL area
through central GA. This is where NWM SRF probabilities for ROF are
rapidly increasing to over 25%, and while that is still a low
probability, it is expected that this upward trend in threat will
continue given recent radar trends. There has been some signal for
streams rising to flows with AEPs 10% on some of the smaller
tributaries across the previously mentioned regions as well,
increasing confidence in the potential for flooding impacts in those
regions.
GRAPHICAL REPRESENTATION weather.gov/owp/operations-ahd
Additional National Water Center products are available at
weather.gov/owp/operations
//JEC
ATTN...WFO...LIX...JAN...BMX...MOB...FFC
ATTN...RFC...ORN...ALR...WPC
Source:
WCO issues Area Hydrological Discussion (AHD) at Jul 21, 4:01 PM CDT---------------
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