FOUS30 KWBC 060823
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
323 AM EST Wed Nov 6 2024

Day 1
Valid 12Z Wed Nov 06 2024 - 12Z Thu Nov 07 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF 
THE SOUTHEAST...

In coordination with CAE/Columbia, SC and FFC/Peachtree City, GA
forecast offices, a Moderate Risk upgrade was introduced with this
update.

A plume of deep tropical moisture, indirectly associated with
Hurricane Rafael will continue overspreading portions of the
Southeast today. The moisture plume will run into a developing
front over Georgia and South Carolina. An upper level jet streak
will add lift to the atmosphere. Late today into this evening, the
nocturnal low level jet's strengthening will kick the moisture 
advection into high gear. Frontogenesis occurring over Georgia and
South Carolina will act to focus the heavy rain over the narrow
Moderate Risk corridor. Expect training convection to develop
during the evening which will persist through the overnight and
while slowly weakening in the pre-dawn hours, is likely to continue
into western South Carolina into Day 2/Thursday. 

HREF probabilities show a 20 to 25 percent chance of a 100 year
rainfall event in the Moderate Risk area. FFGs are very high in the
area due to recent dry conditions with only very light rain. This
has likely made some of the clay soils quite hydrophobic. The
hydrophobic soils will likely increase the runoff from the heavy
rain, which will likely quickly exceed FFGs as the heavy rain
likely persists for multiple hours. 

Wegman


Day 2
Valid 12Z Thu Nov 07 2024 - 12Z Fri Nov 08 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHEAST AS WELL AS FOR MUCH OF THE TEXAS PANHANDLE AND WESTERN OKLAHOMA...

...Southeast...

Heavy rain will be ongoing across Georgia and especially South
Carolina at the start of the period Thursday morning. While the
rainfall will be diminishing in intensity, it's expected after the
much heavier rains of Wednesday night, that the lighter totals
forecast for Thursday will still be influential since antecedent
conditions will be radically different by then as compared to where
they are now. The Slight Risk threat largely is for the Thursday
morning period with lingering rainfall from Wednesday night. Expect
the rain to continue diminishing through the day as the moisture 
plume shifts westward with Hurricane Rafael. 

...Texas Panhandle and Western Oklahoma...

A positively tilted longwave trough and associated upper level 
energy in the form of jet streaks and shortwave energy will support
the development of a strong low over the southern Plains. To the
west, a significant amount of the low's moisture will fall in the 
form of snow. Where the precipitation will remain as rain, expect
steady heavy rain across the Texas Panhandle and western Oklahoma.
While rates are not generally expected to be notably heavy, the
flood threat will be primarily focused on the long duration of
steady rain, as well as the fact that much of this area was hit
very hard with heavy rain a few days ago, so soils and rivers
remain elevated in this region. Thus, low FFGs support the Slight
Risk upgrade. 

Wegman


Day 3
Valid 12Z Fri Nov 08 2024 - 12Z Sat Nov 09 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
CENTRAL AND SOUTHERN PLAINS...

The upper level low over the Southwest will eject into the Plains
on Friday. There will be significant upper level energy associated
with the low, which combined with strong frontogenesis, plentiful
Gulf moisture advecting up the Plains on the low level jet, and a
strengthening surface low...expect heavier rainfall amounts across
Oklahoma and Kansas on Friday as compared with Wednesday. While
north Kansas didn't see as much rain a few days back compared with
areas further south...much of the rest of the Slight risk area does
overlap with both the heavy rain from a few days ago but continued
rainfall from Day 2/Thursday. Thus, added an internal higher-end
Slight for western Oklahoma into south Kansas. Depending on how
much rain the area gets on Day 2, there is some potential for a
Moderate Risk upgrade in this area with future updates.

Wegman


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