FOUS30 KWBC 050825
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
425 AM EDT Sat Apr 5 2025

Day 1
Valid 12Z Sat Apr 05 2025 - 12Z Sun Apr 06 2025

...THERE IS A HIGH RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
ARKANSAS, THE MID-SOUTH, AND THE LOWER OHIO VALLEY...

...LIFE-THREATENING FLASH FLOODING IS EXPECTED TODAY AND TONIGHT...

Today is expected to be the final day in the multi-day high-
impact flood event that has been unfolding across the Mid-South,
Lower and Mid- Mississippi Valleys, and Lower Ohio Valley. On-going
convection was occurring in a corridor along and north of a quasi
stationary front extending from Arkansas northward into the lower
Mississippi Valley and the nearby portions of the Mid-South into
the Lower Ohio Valley. The expectation is that the overnight
convection will wane...followed by renewed convection upstream that
moves over many of of the same waterlogged areas later this
afternoon and evening. Flow aloft will be highly diffluent to the
east of a mid-level low pushing eastward from the southern Rockies.
This should foster deep convection given favorable shear profile
in the lower part of a moisture-rich atmosphere with upwards of
3000 J per kg of CAPE by the time of maximum afternoon heating.
The combination of slow storm motion and efficient/high rainfall
rates is expected to result in additional widespread coverage of
significant rainfall.

The High Risk of excessive rainfall largely remains in place from
the previously issued outlook...namely areas from Arkansas through
southeastern Missouri to western Tennessee and Kentucky and the
northwest corner of Mississippi. All major deterministic models
depict an expansive footprint of 3-6 inches of rainfall, with
locally up to 7-9 inches. These areas have already received
significant rainfall since Wednesday, and any additional rainfall
could result in a very dangerous flash flooding scenario with
considerable to potentially catastrophic impacts.

There are signals in the computer models that large-scale deep
upper level trough makes its way eastward from the south Rocky mountains...which finally dislodges the front and starts to disrupt
the flow of deep-layer moisture from the Gulf. During the last 6 to
12 hours of the outlook period...shower and thunderstorms begin to
spread south- and eastward. With precipitable water values still
lingering in the 1.8 to 2.0 inch range along the axis of the PW
plume....some locally intense rainfall rates and high rainfall
totals may still result in instances of flash flooding across the
parts of the Tennessee Valley into parts of Alabama in the late
night hours of Sunday morning (an area with considerably drier
antecedent conditions).

Bann


Day 2
Valid 12Z Sun Apr 06 2025 - 12Z Mon Apr 07 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHEAST ON SUNDAY...

On Sunday, upper level southern stream energy that had been
supporting the heavy rainfall event over the past 4 days will begin
to interact with a northern stream trough and accelerate
northeastward. This will push the surface cold front across the
southeast, with an axis of high moisture ahead of and along the
front. There should be enough instability and shear to support
thunderstorms with locally heavy rainfall from the Central Gulf
Coast through Central Alabama and Northern Georgia. Rainfall totals
are expected to reach 2-3+ inches in these areas, and rainfall
rates could challenge FFGs of 2-2.5 inches per hour (although the
3+ inches per 3 hour FFG may be be less likely to be met/exceeded).

Dolan/Bann


Day 3
Valid 12Z Mon Apr 07 2025 - 12Z Tue Apr 08 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHEAST US ON MONDAY.

The focus for any lingering moderate to heavy rainfall will
continue to shift eastward on Monday as the large scale flow
pattern remains progressive. Current model QPF keeps some 1.5 inch
to 2.5 inch totals scattered from far northern Florida northward
into the eastern portions of the Carolinas. The juxtaposition of
the upper jet and the plume of 1.75+ inch precipitable water values
becomes less favorable with time...but the moisture transport of
deeper moisture remains favorable to support a low-end risk of
excessive rainfall (especially in regions of poor drainage),

Bann

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