775
AGUS74 KWCO 221458
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1015 AM CDT SUN SEP 22 2024

.Synopsis...
Rainfall and isolated flash flooding possible across the Southern Plains
into the Ohio Valley... Coastal flooding along the Eastern Seaboard...
Heavy rain and possible river rises across Southeast Alaska... Rainfall by
the end of this week for portions of the Gulf Coast...

.Discussion...

.Southern Plains into the Ohio Valley...
Moderate to heavy rainfall is ongoing across parts of TX, OK, and the
Middle Mississippi Valley and is expected to traverse across the Ohio
Valley on days 2 - 3 (Mon - Tue), bringing rainfall totals up to 3" (WPC).
Antecedent conditions are dry across most of the region, which should
mitigate the flood threat outside of urban areas, but the potential for
localized flooding impacts is still possible anywhere that sees persistent
heavy rainfall. One area to watch is the eastern Ozarks, as the complex
terrain and near normal antecedent conditions increases confidence in the
potential for localized flooding. The Ohio Valley on the other hand is
especially dry, with topsoils in the 5 - 30% RSM range (0 - 10 cm, NASA
SPoRT) and streamflows running below to much below normal annual mean flows
(USGS). Almost all of the lower/middle portion of the valley is in drought
status ranging from D1 (moderate) to D4 (Exceptional) (USDM), so any
rainfall will be beneficial.

.Eastern Seaboard...
Widespread minor-to-moderate and isolated major coastal flooding associated
with high astronomical tides and onshore flow continues to be possible from
Savannah, GA to Portland, ME through early this week. The Carolinas are
also seeing compounding effects due to lingering runoff from recent heavy
rains. Check with your local NWS office for more information related to
coastal flooding impacts.

.Southeast Alaska...
An atmospheric river that has brought 2 - 5" (MRMS) to the southern Alaska
Panhandle is expected to depart the area today before another is forecast
to move over the panhandle day 2 - 3 (Mon - Tue), bringing an additional 2
- 3" of rainfall (GFS). Confidence remains low for any potential small
stream or river flooding associated with the second AR, but the potential
cannot be entirely ruled out.

.Gulf Coast...
Heavy rainfall in association with a potential tropical system is possible
across the central and/or eastern Gulf Coast by the end of this week. The
FL Peninsula and the eastern half of the Panhandle are currently the most
hydrologically vulnerable regions along the Gulf Coast, with soils near or
above 50% RSM (10 - 40 cm, NASA SPoRT) and streamflows above to much above
normal. Should the system track over FL, minor to moderate river flooding
is possible (MMEFS). Uncertainty remains high as to the timing, placement,
and magnitude of potential flooding impacts, but confidence is increasing
in the occurrence of flooding somewhere along the central and/or eastern
Gulf Coast, and this system will continue to be monitored closely.

//Bliss



$$