FOUS30 KWBC 031909
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
309 PM EDT Thu Apr 3 2025

Day 3
Valid 12Z Sat Apr 05 2025 - 12Z Sun Apr 06 2025

...THERE IS A HIGH RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
OZARKS AND LOWER TO MID-MISSISSIPPI VALLEYS WITH MAJOR FLOODING 
EXPECTED...

..LIFE-THREATENING FLASH FLOODING IS EXPECTED ON SATURDAY AFTERNOON
THROUGH SUNDAY MORNING..

...21Z Outlook Update...
Substantial changes were made to the ongoing outlook with the
expectation that deep, slow-moving and intense convection would
still be ongoing across Arkansas at 12Z Saturday. The High Risk
expansion in Arkansas is essentially a continuation of the 
significant flash flood threat from the D2/Fri forecast period.
South-soutwesterly flow aloft at the start of the period is
expected to continue fostering a very slow eastward progression of
convection, while 1.75+ PW values,, 1500+ J/kg MLCAPE, and
convective training/mergers should continue to foster high to
locally extreme rain rates and FFG exceedence on a widespread
basis. At least 3-5 inch rainfall totals are expected, with locally
higher amounts possible.

Eventually, veering flow aloft will result in a faster forward
speed of any convective complex(es) toward the Ohio and Tennessee
River Valleys during the latter half of the forecast period. As 
this occurs, low FFGs are expected to remain from abundant 
antecedent rainfall, and it is very likely that ground conditions
will not have completely recovered from abundant antecedent
rainfall. In this scenario, widespread significant impacts are 
expected with both ongoing and newer instances of flash flooding.

Additional details are available in the previous discussion below.

Cook

...Previous Discussion...

The combination of intense right-entrance region jet dynamics,
highly anomalous atmospheric moisture, and very saturated 
antecedent soil moisture will lead to another high impact flash 
flood forecast for Saturday afternoon through Sunday morning across
the Lower to Mid-Mississippi Valley. This threat will extend 
further east as a cold front helps finally sweep the stagnant
pattern out of the region, but not before another round of heavy
rainfall inundates areas that will be sensitive to any appreciable
rainfall. 

A stout 190-200kt upper jet located over the Great Lakes will lend
to a pronounced upper ascent pattern situated over the Mississippi
Valley during the period. At the surface, our quasi-stationary
front that will linger through the course of several days will
still be confined to similar areas that have been impacted by its
presence in the days prior. Upper low located over the Southwest
U.S. will begin to open up and eject eastward, becoming sheared on
the northern edge due to an amplifying trough digging out of
Canada. To the east, our Western Atlantic ridge that has provided a
stalemate to any frontal progression moving east of the Mississippi
will provide one last period of favorable low to mid-level
convergence as the pattern evolves with the large trough to the
west countering the ridge across the Southeast. In the middle of
the atmospheric squeeze-play, elevated moisture presence and
favorable instability will remain present to be activated with the
addition of diurnal destabilization and increasingly favorable
ascent to match. The combination will allow for a rapid development
of widespread convection across the Missouri Valley with slow
advancement eastward towards the Low to Mid-Mississippi Valley
convergence point. 

This setup has trended prolific in the QPF realm of the forecast
with very little deviation in all major deterministic at this
juncture. An expanse of 3-6" with locally up to 8" of rainfall is
forecast across a large portion of Arkansas extending east-
northeast through far southeastern Missouri, all of western and
central Tennessee and Kentucky, to as far north as the
Ohio/Kentucky border along the Ohio River. Northwest Mississippi
will also lie within the axis of heaviest precipitation leading to
quite a large area of not only heavy precip, but significant
overlap of areas that will have super saturated grounds that will
struggle to maintain the ability to absorb more rainfall. This
setup will yield a very dangerous scenario where widespread flash
flooding with considerable and potentially catastrophic impacts
would be favored. The agreement among all major NWP for substantial
rainfall totals and projected hourly rates >1-2"/hr is a testament
to the overall gravity of what is to come. 

In coordination with the local WFO's across Arkansas, Tennessee,
and Kentucky...a High Risk area for excessive rainfall has been
added over central and eastern AR, all of western TN and KY, far
southeastern MO, and the southern edge of IN. Additional storm
totals will bring multi-day amounts between 8-12" with some areas
potentially reaching as high as 14" over the span of 5 days. A
broad Moderate Risk spans the outer perimeter of the High Risk
leading to several more areas prone to significant flash flood
concerns due to the setup. This is becoming an increasingly
life-threatening situation for areas of the Lower and Mid-
Mississippi Valley region. 

Kleebauer

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