Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
855 PM EDT Fri Apr 26 2024
Day 1
Valid 01Z Sat Apr 27 2024 - 12Z Sat Apr 27 2024

...A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS ACROSS PORTIONS OF
THE SOUTHERN PLAINS INTO THE LOWER TO MIDDLE MISSISSIPPI VALLEY
OVERNIGHT...

...01Z Excessive Rainfall Discussion...
The focus for additional heavy to potentially excessive rainfall
will continue to be across portions of the Southern Plains into the
Lower and Mid-Mississippi Valley...with a lesser probability of
excessive rainfall farther north. Highest rainfall rates and total
accumulation should continue to fall in the region of deepest
moisture and instability although placement of the cold pool
associated with earlier convection introduces some degree of
uncertainty with any additional convection later this evening and
through the overnight hours. At this point...CAMs are showing cells
becoming more progressive so trimmed some of the western boundary
of the Slight Risk and kept it ahead of QLCS moving into portions
of Arkansas and northeast Texas. Farther north...trimmed the
western boundary near the deep-layer upper cyclone where cooler and
drier air has begun to infiltrate.

Bann


...Summary...
Based on both current observational trends (radar/satellite/
mesoanalysis), along with the latest trends per the 12Z CAM
guidance, the Slight Risk area was expanded a bit farther southwest
to include more of east-central TX, including Fort Hood), while
also trimmed a bit across parts of southeast KS.

...Eastern Portions of the Plains into the Lower Missouri and Mid-
Upper Mississippi Valley...
Ongoing QLCS traversing MO and the MOKSAROK 4-state region is the
main driver for the more enhanced (high-end Slight Risk) across
these areas, though despite airmass destabilization farther west
across central KS, much (though not all) of the latest CAMs show
limited additional rainfall during the remainder of the D1 period
behind the QLCS given the shortwave DNVA.

With time today the better synoptic forcing lifts to the north,
resulting in a downward trend in forcing across the southern half
of the Slight risk, with weakening lower level convergence and also
less pronounced mid/upper level ascent. These larger scale factors
would generally favor weaker and less organized convection with
time today into tonight over these southern areas. Countering this
is a rather favorable thermodynamic environment, with plentiful
instability and moisture. Thus it seems most likely that if
convection this morning over OK and TX can grow upscale enough to
generate an organized outflow/cold pool, which the 12Z HRRR, ARWs,
and NAM CONUS-Nest show, then this mesoscale feature could be
enough to sustain an axis of more robust convection into the
afternoon. Any convection that is able to sustain and grow upscale
may exhibit some training and backbuilding characteristics into
the strong low level jet in place.

Farther north a Marginal risk is in place from northern MO into SD
and MN. Elevated showers and embedded thunderstorms will move
across this region this morning, but will be outrunning the better
instability...which should keep rainfall rates low enough to
prevent any more organized flood threat. As the surface low and
strong mid/upper forcing ejects into the Plains this afternoon
additional convective development is likely from eastern NE/SD into
portions of IA and MN. Some of this activity should be intense,
but generally should be moving at a quick enough pace to limit the
flash flood risk.

Hurley/Chenard