FOUS30 KWBC 110815
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
415 AM EDT Sun Aug 11 2024

Day 1
Valid 12Z Sun Aug 11 2024 - 12Z Mon Aug 12 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR CENTRAL UTAH
THROUGH NORTHWESTERN ARIZONA, PORTIONS OF THE OZARKS AND CENTRAL
PLAINS, AND FOR THE COASTAL CAROLINAS...

...Central Utah through Northwestern Arizona...

Monsoonal moisture will continue to draw northward across the Four
Corners region today. The jet stream and an upper level jet streak
will be set up across northern Utah today. PWATs increasing above
0.75 inches will boost portions of southern Utah to 2.5 sigma above
normal. With moisture and forcing in place, expect a renewed round
of afternoon convection across this area. With previous days' 
storms having soaked the soils in some areas, the flash flooding
threat will be higher today as compared to previous days across
Utah and portions of northwestern Arizona. The Slight risk area was
expanded southward with this update to include much of the Grand
Canyon and points north, including Glen Canyon. 

...Portions of the Ozarks and Central Plains...

Convection currently ongoing across central Oklahoma will continue
southeastward into southeast Oklahoma and Missouri this morning.
This MCS will likely dissipate as often happens late this morning
with daytime heating, but the primary event is expected tonight, 
and perhaps in the form of 2 separate areas. Gulf moisture racing
north with the LLJ will interact both with an upper level
shortwave, a stalled front over the area, and countering flow from
an area of high pressure over the Midwest helping hold the surface
front in place despite the deep moisture moving in from the
southwest on the other side of the front. Training convection is
likely to develop, especially over Oklahoma where the Slight risk
area remains in place with few changes. 00Z HREF neighborhood probabilities
remain over 50% for 3 inches of rain in the 24 hrs ending at 12Z,
but much of that rain is likely during the overnight hours. 

...Coastal Carolinas...

Guidance has been gradually shifting south and east/closer to the
coast with the axis of the heaviest rain with the afternoon
convection expected tonight. Thus, the Slight and surrounding
Marginal risk areas have been shrunk to the southeast accordingly.
Nonetheless antecedent conditions along the coast remain very
favorable in the recovery post-Debby. Expect similar coverage of
flash flood warnings as today's storms, but are likely to occur
further east. Given the uncertainty as to where the storms will
form, the Marginal risk still extends into central NC and western
SC for the potential for more widely scattered storms, as well as
across eastern Georgia.

Wegman


Day 2
Valid 12Z Mon Aug 12 2024 - 12Z Tue Aug 13 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE FOUR
CORNERS REGION EAST TO THE MID-MISSISSIPPI VALLEY AS WELL AS FOR
PORTIONS OF THE COASTAL CAROLINAS...

...Four Corners Region to the Mid-Mississippi Valley...

Concern continues to increase with potential heavy rain and
subsequent flash flooding in various areas. For the Four Corners,
no major changes are expected, but with the greatest moisture
having shifted east, convective coverage should be lesser on Monday
as compared to today. Meanwhile, the signal for heavy rain remains
strong from eastern Colorado into western Kansas. Easterly flow
north of an ejecting low will draw plentiful Gulf moisture into the
High Plains of Colorado. Meanwhile, a stalled front to the north
will supply lower level forcing. The result will be an area of
heavy rain caused by training storms moving east along the front,
as moisture flowing northwestward on the warm side of the front
supports backbuilding. There remains some uncertainty both with the
placement of the heaviest rains, and for Kansas, the development of
drought conditions potentially resulting in less flooding. However,
it appears likely a Slight will be needed as plentiful moisture
will support storms capable of rates to 2 inches per hour, which in
areas of training storms should overcome otherwise high FFGs.

Further east into Missouri, lingering storms from tonight will
continue into Monday morning. Then, the stalled out front over the
area will begin to reorient, but pivoting over Missouri. This
should reduce the overall coverage of rainfall over Missouri for 
the day, but will keep the area in the crosshairs for heavy
rainfall going forward. 

...Coastal Carolinas...

Some lingering storms are possible along the coast Monday afternoon as
the front over the area dissipates. With much reduced storm 
coverage, the Marginal remains over the area for the potential for 
isolated instances of flash flooding. This would likely be the 
result of sea breeze interactions.

Wegman


Day 3
Valid 12Z Tue Aug 13 2024 - 12Z Wed Aug 14 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE FOUR
CORNERS REGION TO THE MID-MISSISSIPPI VALLEY, AS WELL AS FOR
EASTERN NORTH CAROLINA...

...Missouri...

A renewed push of Gulf moisture with the LLJ will impact a
persistent front across Missouri today. This will likely result in
an area of training thunderstorms capable of localized flash
flooding. The area is likely to be upgraded to a Slight with future
updates and higher confidence, but given the counter flow out of
the northeast on the dry side of the front over the Midwest, it's
likely that training storms are likely to impact a narrow corridor
over Missouri along the front. There is potential that the St.
Louis metro may be part of the heavy rain corridor.

...Eastern North Carolina...

A bit stronger moisture push off the Atlantic may result in more
widespread showers and storms a bit further inland into North
Carolina. With little to organize the convection however, the flash
flooding threat remains isolated.

Wegman
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