844
FOUS30 KWBC 300811
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
411 AM EDT Thu May 30 2024

Day 1
Valid 12Z Thu May 30 2024 - 12Z Fri May 31 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS MUCH OF THE
CENTRAL AND SOUTHERN PLAINS...

Two primary areas of convection remain across the Central and
Southern Plains with the latter currently progressing southeast
through the central Panhandle with eyes for north TX later this
morning. The premise for the D1 period will be widespread
convective development across TX up through the Front Range due to
a plethora of mid-level perturbations ejecting eastward out of the
Rockies and initiating a north-south wall of thunderstorms within a
defined theta-E ridge axis. Current QPF forecast based off the
latest HREF and associated CAMs has two main areas of focus for
the period. The first being a conglomeration of convective
development over west TX that will surge eastward with favorable
mid-level ascent thanks to a stronger shortwave pivoting through
the southern plains by this afternoon and beyond. A broad footprint
of 2+" of precip is forecast off pretty much all deterministic
within the confines of the northern Concho Valley up through north
TX, spreading east over the northern Hill Country out to the I-35
corridor from DFW down through Killeen. This has been the focal
point for an area of enhanced flash flood potential given the broad
swath of QPF with embedded totals breaching 3-4+" within the
deterministic and bias corrected ensemble. The area from the Red
River, south will be the best area for heightened flash flood
impacts with the forecasted QPF, as well as the signal for rainfall
rates to exceed 2"/hr at times as depicted within the probabilistic
fields indicating upwards of 60% neighborhood probability for that
to occur. This entire setup is breeding grounds for a matured MCS
that will likely slide eastward with extension that can cover
impacts from the metroplex down through central TX in the overnight
hours. As a result, this area is well within the standards for a
SLGT risk maintenance, as well as wording for a "higher end" SLGT
risk potential with an outside opportunity for a targeted MDT in
later updates, pending convective evolution.

Further north, several shortwaves will traverse the central plains,
interacting with the favorable environment ahead of the primary
ascent pattern thanks to a poleward expanse of unstable air brought
about by the backside of a sprawling surface ridge located east of
the Mississippi. Guidance is pin-pointing an area in-of central and
eastern NE down through KS as the target for a secondary QPF maxima
brought on by a potential MCS developing and moving over the above
areas. HREF probabilities are also fairly high for the area around
eastern NE with the EAS signals for at least 2" as high as the
signals across the southern plains. A few CAMs and global output
indicate as much as 4-5" of rainfall possible somewhere within the
confines of the MCS initiation point which would lead to some
flooding concerns, even in areas with higher FFG`s compared to
those over north TX. A SLGT risk remains steady over the central
plains, mainly east of the 100W parallel.

A few other areas note for local impacts include; west TX Lower
Trans-Pecos up through the eastern Permian Basin for another round
of thunderstorms that would impact an area that has seen multiple
rounds of heavy rain and flooding making this an isolated target of
opportunity. Isolated to scattered thunderstorms across OK will
have plenty of instability and elevated moisture to contribute to
local impacts, especially in any organized clusters, or if the
Central Plains MCS pushes south as some CAMs indicate. That would
lead to more widespread flood potential, thus why the area remains
solidly in the SLGT risk. The last area is well to the north within
the northern Midwest as a strong upper trough continues to provide
large scale ascent within the northern plains. Recent ML output
has been targeting the area over southern and east-central MN over
into western WI for a few days and synoptically, it makes sense
given the area situated in the RER of a prominent upper jet
bisecting the northern plains in Manitoba. Precip amounts are
generally between 0.75-1.5", but for the urban corridors within the
Twin City metro, that could be enough to spur some localized flash
flood concerns in stronger echoes.

Kleebauer


Day 2
Valid 12Z Fri May 31 2024 - 12Z Sat Jun 01 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE CENTRAL AND SOUTHERN PLAINS THROUGH THE ARKLATEX AND LOWER
MISSISSIPPI VALLEY...

Active convective pattern from the previous period will shift to
the east with a strengthening shortwave trough maneuvering to the
east through the Mississippi Valley during the forecast period.
Recent trends within guidance have signaled the area from east TX
over through the Lower Mississippi Valley as the focal point for
heaviest precip, correlating well with the favorable upper pattern,
as well as the best deep layer moisture and instability being
shifted eastward thanks to a surface low forecast to progress
northeastward out of the Southern Plains with a cold front trailing
the primary low. Environment will stabilize in wake of the surface
reflection passing to the east, finally putting an end to the
onslaught of convective activity that has plagued the state of TX
for the past several days. Organized convection in the beginning of
the period will be the area(s) to monitor as guidance is not
completely in-line for where the convective clusters in the
Southern Plains will head. Recent ensemble bias corrected data, as
well as the NBM and ML output have situated the QPF maxima
generally over the Ozarks down through AR/LA with totals breaching
3" even within the means. The probability matched mean, which
incorporates some highlighted maxima embedded within the means has
precip totals getting closer to 4-5" within portions of the Lower
Mississippi Valley, relevant to the expected synoptic evolution and
accompanying instability axis residing in a targeted warm-sector
downstream of the approaching cold front to the west and a
stationary boundary bisecting portions of the Deep South into the
Southeastern US. This would certainly benefit the area in question
with the best thermodynamic potential, and it correlates well with
the focused mid-level ascent provided by the strengthening
shortwave trough pivoting into the region. As a result, the SLGT
risk from previous forecast was maintained for continuity and
sufficient agreement among the ensemble suite.

There is an opportunity for greater impacts across southeast TX as
some CAMs deliver the central TX MCS from the previous period over
into the Gulf Coast as the complex progression moves into the area
that has been hit with multiple heavy rain events in previous
weeks, including yesterday. ML output does show a signal for that
area, so the SLGT risk was extended a bit to the south and
southwest to cover for the potential.

Kleebauer


Day 3
Valid 12Z Sat Jun 01 2024 - 12Z Sun Jun 02 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS MUCH OF
THE SOUTHEAST U.S, OHIO VALLEY, MISSISSIPPI VALLEY, AND THE CENTRAL
AND SOUTHERN PLAINS...

The period beyond D2 is contingent on the anticipated convective
evolution downstream and the positioning of the strong mid-level
shortwave ejecting through the Tennessee Valley by the second half
of the period. Latest trends favor a widespread axis of convective
potential with the best instability fields located over the
Southeast U.S, and best upper forcing targeting the Ohio Valley and
central Midwest. There will likely be a focal point in heaviest
precip as we move closer to the period of interest, but for now
maintained continuity from previous forecast with some expansion on
the northern end of the MRGL risk area, as well as some areas to
the west in the plains due to some thunderstorm concerns with
locally heavy rainfall potential. QPF maxima is currently in-of AL
and portions of the Ohio Valley with totals generally 1-2" with as
high as 3" depicted within the means. Look for the max to shift
upwards in time as the environment and pattern evolution become
more stable and hi-res deterministic can lead to a consensus on
where the threat will be most prominent. The broad MRGL will
suffice until those details become clearer.

Kleebauer


Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt