Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
415 AM EDT Sat Apr 27 2024
Day 1
Valid 12Z Sat Apr 27 2024 - 12Z Sun Apr 28 2024

...A MODERATE RISK OF EXCESSIVE RAINFALL EXISTS ACROSS PORTIONS OF
FAR NORTHERN TEXAS INTO CENTRAL AND EASTERN OKLAHOMA, SOUTHEAST
KANSAS, SOUTHWEST MISSOURI, AND FAR NORTHWEST ARKANSAS...

A significant rainfall event still appears likely Saturday night
across portions of north central TX into central/eastern OK and
portions of southeast KS and southwest MO. Numerous instances of
flash flooding are expected, some of which will likely be
significant in nature.

Overall not much has changed with the expected setup over the past
couple days. The environmental ingredients remain in place for
training/backbuilding convection, especially during the overnight
hours. Persistent and strong mid/upper level forcing, a
significant ramp up in 850mb moisture transport into a stalled
boundary, mean flow parallel to the boundary and weak Corfidi
vectors (due to the strong low level jet aligned parallel to the
mean flow)...all are favorable for training/backbuilding
convection. The overlap of impressive upper level divergence and
strong 850mb moisture convergence , both of which persist upwards
of 6-12 hours, combined with substantial instability and well
above average PWs...all point to a numerous flash flood threat,
ramping up by later in the day into the overnight hours.

Convection will likely get going pretty early in the day and then
persist into the overnight hours. The initial convection should be
more scattered in nature and moving at a decent clip...so would
expect just an isolated flash flood risk initially. However as the
low level jet and moisture transport really ramp up this evening
into the overnight expect we will see upscale growth of convection
into one or more training lines. Of course, the early convection
could play a role in where this boundary and most favorable
training corridor ends up, but overall models remain fairly well
clustered with an axis from north central TX into central/eastern
OK.

Probabilities from the 00z HREF are pretty impressive. EAS
probabilities of exceeding 3" are rather broad and as high as
50-80%. Given EAS probabilities can be considered a smooth point
probability...this indicates an event with a widespread 3"+ QPF
footprint is probable. Embedded within this 3" area will likely be
higher totals...with 5" neighborhood probabilities over 60%, and 8"
probabilities around 30%. This generally is in line with
expectations from previous shifts...that this event has the
potential to drop a swath of 4-8" of rain (isolated 10" max
possible)...with the most likely location from just north of the
Red River into central/eastern OK..including the Norman to Tulsa
corridor. Overall think the 00z HREF QPF and probabilities are
reasonable...although tend to think the southwest flank of
convection could over perform relative to the HREF...with the 00z
GEM Reg and FV3LAM potentially showing plausible outcomes of a QPF
max a bit southwest of the 00z HREFbm max. The northeast extent of
the MDT risk over Southeast KS and southwest MO may see a bit
lower QPF than areas further southwest, however with wetter
antecedent conditions here, flash flood impacts are still likely.

One thing to continue to consider is that convection should become
intense and organized enough to develop a stronger cold pool
resulting in some eastward cell progression with time. While we do
think there will be some eastward progression, the persistent
forcing and strong low level jet both will be opposing a
significant eastward push...and thus tend to think we will see
enough persistence of convection to result in the organized and
significant flash flood threat described above.

Further north, a Marginal risk extends from northeast CO, across
NE and into IA and portions of WI/IL/IN. Gave some consideration to
a Slight risk upgrade over portions of NE and western IA given the
heavy rainfall over these areas on Friday. However the extent of
convective training is a bit more uncertain here, and the higher
probabilities of heavy rain end up a bit south of areas hardest hit
Friday. Thus tend to think flash flooding will be more isolated in
nature today, which fits more into the Marginal risk category.
However will continue to monitor.


Chenard