Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
423 AM EDT Fri Apr 26 2024
Day 3
Valid 12Z Sun Apr 28 2024 - 12Z Mon Apr 29 2024

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

Convection will likely be ongoing at 12z Sunday across portions of
OK and TX, a continuation of the Moderate risk day described above
for Saturday night. Current expectations are that convection will
have enough of a cold pool by this time to result in a decent
eastward propagation. Thus the flash flood risk should be
decreasing into Sunday morning, although some continued flash
flood risk is probable.

The bigger question becomes what happens on Sunday night. There is
some model disagreement on this, although the majority of solutions
would suggest an additional round of upscale convective development
is likely. This is also generally supported when looking at things
from an ingredients based perspective. With the main low lifting
off to the northeast over the Upper MS Valley, the portion of the
front over TX and AR should become nearly stationary. Meanwhile we
see a strong and persistent upper level divergence signature
centered near the TX/AR border, and a trailing mid level shortwave
ejecting into the southern Plains should only help to enhance lift
near the stalled low level convergence axis. Overall, ingredients
are similar to what we will see Saturday night over OK, thus
training and backbuilding convection appears probable.

Still think this event may very well eventually need a Moderate
risk given the setup and ingredients in place. However there
remains a bit of uncertainty with regards to where the best
convective training will be...with anywhere from northeast TX into
AR within the range of possibilities. Given this uncertainty, and
the fact that the overall synoptic setup, while similar to
Saturday night, is probably not quite as favorable (also noting
slightly lower model QPFs compared to day 2)...think sticking with
a higher end Slight risk is the best course of action for now.
Plus, rainfall Friday will likely play a role in if/where soil and
stream conditions will be more sensitive for flash flooding come
Sunday...so knowing how convection plays out Friday may help with
any eventual MDT risk placement Sunday. Thus the Slight risk
remains for now, and will continue to evaluate on future shifts.

A broad Marginal risk extends from MO northward into MN and WI,
generally along and east of the strong low and mid/upper forcing.
Convection here, while locally intense, should be quick moving,
limiting the extent of any flash flood risk. However this will be
the second strong low pressure and convective threat within a 3
day period...so can not rule out an eventual need for an embedded
Slight risk pending soil and stream response from round 1.

Chenard