Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
415 AM EDT Sat Apr 27 2024
Day 2
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
eastern OK and TX, into western AR/MO. Current expectations are
that convection will have enough of a cold pool by this time to
result in a decent eastward propagation, while also running into a
less unstable airmass with time. While some lingering flash flood
risk into Sunday morning is likely over these areas, the risk
should be on a decreasing trend.

The bigger question becomes what happens by later in the day into
the overnight hours. Ingredients do appear to be in place for
upscale convective growth and some training/backbuilding
potential. There is a slowing front over the area, with strong and
persistent upper level divergence moving over top of this
boundary. Moisture transport is not as strong as what we will see
Saturday night over the Plains, but still note a pretty strong low
level jet and 850mb moisture convergence signature.

Overall this event remains as a higher end Slight risk from
northeast TX into much of AR, and would expect to see scattered
flash flooding across this corridor. A more focused and
concentrated area of more numerous and significant flash flooding
is still a possibility. Based on the ingredients in place, the most
likely location for this appears to be in the vicinity of the
Arklatex. This is also where the 00z GEM reg, UKMET, ECMWF and
FV3LAM have a relative max in QPF. However there remains some
spread with this scenario, and model QPFs are generally lower than
what we are seeing on Saturday night over the Plains. Thus this
event will probably have a bit less flash flood coverage. Still
think a MDT risk upgrade may eventually be needed, with the
Arklatex region the most likely location. However we will have
much more high res guidance to evaluate over the the next 24 hours
than we do now, so would prefer to hold off on any upgrade and
continue to evaluate trends. Either way some flash flooding is
expected, some of which could be locally significant in nature.

A broad Marginal risk extends from MO northward into MN, WI and MI,
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, some of these
areas will have seen heavy rain on previous days...so can not rule
out an eventual need for an embedded Slight risk pending soil and
stream response from this earlier rain.

Chenard