613
AGUS74 KWCO 071527
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
930 AM CST THU NOV 7 2024

.Synopsis...
Continued rainfall and river rises across portions of the Southeast and the
Gulf Coast... Additional rainfall and potential flooding for the Southern
Plains and Lower Missouri and Lower Mississippi River Basins... Prolonged
rainfall for the Northwest... Daily flood potential continues for Puerto
Rico and the USVI...

.Discussion...

.Southeast and the Gulf Coast...
Across southeast GA into central SC, wIdespread heavy rainfall (3 - 6"+)
has been observed over the past 12 hours (MRMS), with pockets of 6 - 10"
across Valdosta, GA, the Statesboro - Waynesboro, GA area, and much of
south-central SC. This rainfall is making its way into the river systems
across the region, as evidenced by river observations, with flows on many
smaller tributaries expected to continue to rise through this morning. This
is supported by the National Water Model (NWM), which suggests peak flows
across the region on smaller rivers beginning this morning and continuing
through this evening. Additionally, the NWM short range forecast (SRF)
suggests potential for fairly widespread flows with AEPs of 4 - 10%,
suggesting locally significant small stream flooding impacts will be
possible from I-16 in southeast GA northeastward through the Congaree
National Park Region southeast of Columbia, SC. Additional rainfall of 1 -
3" will be possible into early this afternoon, potentially resulting in
additional flash flooding and exacerbated small stream responses,
especially considering that soils are near saturation (50 - 95% 0 - 10 cm
RSM, NASA SPoRT) and streamflows are already on the rise. Recent
deterministic runs of the NWM short range forecast show potential for these
additional flooding impacts with Rapid Onset Flooding (ROF) signals across
the same region mentioned above.

Minor to moderate river flooding will continue for the foreseeable future
along the Withlacoochee and St. Johns rivers across central Florida.

Hurricane Rafael is forecast to meander over the south-central Gulf of
Mexico this weekend and early next week. Interests in the southern and
southwestern Gulf of Mexico should monitor the progress of this system.

.Southern Plains...
Flash and urban flooding, with localized small stream flooding, is expected
across portions of west/north-central TX into western OK and possibly into
far south-central KS tonight through day 2 (Fri) due to heavy rainfall (2 -
5"). Most of this region has seen 2 - 5" of rain over the past week (RFC
QPE), with portions of western OK seeing 5 - 8", maintaining top layer soil
moisture (40 - 60% 0 - 10 cm RSM, NASA SPoRT) and elevated streamflows
running much above normal (USGS). The greatest area of concern is likely
west TX/northwest TX into southwest OK, where the highest QPF over the next
two days is expected to overlap some of the vulnerable antecedent
conditions. The NWM SRF is starting to show potential for isolated ROF
across these regions, however most of the QPF is expected late tonight into
day 2 (Fri), beyond the 18-hr forecast period of the NWM SRF. We expect NWM
SRF signals to increase in areal coverage as we head into tonight. The NWM
MRF is showing scattered river rises with peak flows on most headwaters by
the end of day 3 (Sat), however, there is not a widespread signal for
significant river flooding at this time. Probabilities for high water flows
(1.6 and 3.2 ARI flows) are highest in the corridor from just northwest of
Abilene, TX through western OK into the Wichita, KS region, increasing
confidence in potential for small stream flooding in this region. Generally
speaking this is the region HEFS is showing the best potential for river
flooding as well, where isolated river flooding is possible with this
event. Precipitation in NM and CO is expected to be mostly frozen rather
than liquid, which will mitigate the flooding concerns in those areas.

.Lower Missouri and Lower Mississippi River Basins...
In the wake of heavy rainfall that impacted the region, widespread minor
and isolated moderate-to-major river flooding is forecast or ongoing for
numerous rivers across MO and AR, particularly in the Meramec basin in
eastern MO. This is slated to continue through the weekend. Additional
rainfall (1 - 2"+) is expected on day 3 (Sat), which could prolong and
exacerbate river flooding, and produce new flash and small stream flooding
impacts given the wet soils (NASA SPoRT) and above normal streamflows
(USGS) in place. The NWM Medium Range Forecast (MRF) suggests isolated new
river rises across the region, but widespread/high magnitude river rises
are not anticipated at this time. Isolated flash flooding will be possible
for all of the Lower Mississippi River Basin on day 3 (Sat).

.Northwest...
Several rounds of moderate to locally heavy rainfall will start to impact
the region over the weekend, continuing into next week, for western OR and
WA, bringing an isolated risk of flash and urban flooding to the region,
including near burn scars. With relative soil moisture of 50 - 65% (0 - 10
cm RSM, NASA SPoRT), streamflows running near normal, and possible lower
snow levels, all this will help mitigate any widespread flooding impacts,
especially on rivers. Nonetheless, isolated river flooding will be possible
(HEFS) by early-to-mid next week, particularly on rivers draining the
Olympics and Cascades in western WA.

.Puerto Rico and the USVI...
Daily rainfall will continue to bring the risk of flash, urban, and small
stream flooding to the islands through this weekend, especially across
eastern portions of the island that have seen 5- 15" of rain over the past
week (RFC QPE), and have saturated soils and above normal stream flows
(USGS).

//JEC

$$