FOUS30 KWBC 240729
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
329 AM EDT Wed Jun 24 2026

Day 2 Valid 12Z Thu Jun 25 2026 - 12Z Fri Jun 26 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN EFFECT OVER
PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS TO MID-MISSISSIPPI VALLEY...

...Plains to Mid-Mississippi Valley...

Longwave pattern across the western two-thirds of the CONUS will
shift as a strong mid-level trough enters the Pacific Northwest and
begins flattening the ridge axis positioned across the
Southwestern U.S. This will lead to a more zonal regime to setup
from the Central Rockies to the Mid-Mississippi Valley by Thursday,
setting the stage for a potentially significant heavy rainfall
threat across portions of the Central and Southern Plains between
KS/northern OK over into MO and western Ohio Valley. At the
surface, a quasi-stationary front will be progged over southern KS
stretching eastward through MO before hooking back to the northeast
as a cold front on the trailing end of a surface low motioning up
through eastern Ontario. A strong mid-level vort will eject out of
the Central Rockies and migrate eastward within the mean flow,
allowing for lee cyclogenesis to occur over KS as we move into
Thursday afternoon. The forecast is for the surface wave to motion
eastward along the boundary with thunderstorm initiation
transpiring across the Central Plains by late-Thursday afternoon.
As we move into the evening, additional LLJ support will provide
better low-level shear and provide enhanced convergence within the
proximity of the front. This is a relatively classic scenario for a
training axis of heavy convection, especially when you couple with
PWATs likely between 1.7-2.0", a solid +1 to +2 standard
deviations above climatology for the region.

Model signals are still pretty aggressive with the scope of the
event with most of the deterministic outputs showing pockets of 3+
inches for areas of eastern KS through portions of MO. The
deviation comes in the timing of the shortwave ejection and the
latitudinal gain of the heavy rain footprint as guidance disagrees
on the exact placement of the heaviest rainfall. ML guidance is
still generally south of the global NWP suite, a highlight that has
been noted over the past several cycles. ML guidance tends to do
well when it locks into these types of outputs and doesn't waver
too much in specifics, so the trend is to keep the heaviest precip
a bit south of the deterministic and its ensembles. That said, the
orientation of the frontal positioning will be important as that
will likely be the focus for where the heaviest QPF outputs will
occur as the surface wave will ride the thermal gradient posed by
the front in question. Historic bias at this leads tends to favor
guidance being a bit too far north with its QPF footprint in these
scenarios leading to an adjustment further south, correlating with
a better convergent area away from the current depiction.
Considering the magnitudes of the QPF already with little to no
CAMs inclusion, the forecast for locally significant rainfall is
becoming increasingly likely in the D2 period. As of now, the SLGT
risk inherited only went through minor modifications with a high-
end SLGT risk forecast for areas of central to southeast KS through
the southwest and west-central portions of MO, extending towards
the St. Louis metro where the frontal alignment is progged. An
upgrade for portions of this area is not out of the question in the
coming forecast cycles, so this will be something to monitor
closely the next 24-36 hours.

...Southeast U.S...

Remnants of a complex from the previous period will wander into the
Central Gulf coast region and slide eastward into southern GA by
Thursday afternoon. Hi-res at the end of their forecasts are
consistent in the maturation of convection near the remnant
circulation as the disturbance becomes a mechanism for targeted
low-level convergence in a zone of favorable boundary layer
moisture and instability. Signals for locally heavy rainfall of 2+
inches are noted in the deterministic CAMs with the HREF blended
mean QPF between 12z Thursday to 00z Friday showing pockets of
1.5-2" located from the MS coastal areas through the I-10 corridor
towards Tallahassee, back up into southern GA. This is coincident
with the 500mb vorticity trajectory of our mid-level impulse
generated from previous periods thunderstorms which provides a
better target point for heavy rainfall compared to just your
standard pulse convection regime we see in the summer. As a result,
maintained the previous MRGL risk with just some minor adjustments
to account for QPF trends.

...Interior West...

Multiple shortwaves and elevated moisture presence across the
Interior Mountain West will likely lead to another afternoon and
early evening of scattered convection with localized flash flood
concerns on Thursday. The threat remains low-end for the time being
given the current QPF outputs, however this could still provide
some isolated flash flood prospects in those terrain focused zones
across UT/CO, as well as any heavy rain encounters in the favored
slot canyon areas littered over western CO into UT. A MRGL risk was
expanded westward to account for the threat and recent QPF trends
in the guidance.

Kleebauer


Day 3 Valid 12Z Fri Jun 26 2026 - 12Z Sat Jun 27 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN EFFECT OVER
PORTIONS OF THE MID-MISSISSIPPI AND OHIO VALLEY'S...

The period will be defined by the expected forward propagation of
the shortwave trough that will affect the Central Plains, eastward
during the D2, translating into further impacts on the D3.
Ensembles and global deterministic alike continue to signal the
axis of heavy rainfall over the Mid-Mississippi Valley shifting
eastward through the Ohio River Valley with the focus of heaviest
rainfall centered over the Ohio River basin and points north. This
correlates with the mean 500mb vorticity forecast for the shortwave
trough responsible as diffluent flow ahead of the trough axis will
situate over the above area leading to focused ascent and
increasing low to mid-level convergence pattern necessary to bring
about a swath of heavy precipitation.

00z run of the CSU First Guess Fields depict a broad SLGT risk
alignment across the area between southern IN and southern OH down
across neighboring northern KY with the northern periphery
positioned along and south of I-70. Considering the trends in the
CSU First Guess over the last several months, this may be a bit
further north than what may transpire, however the ensemble QPF
alignment of the heaviest precip is generally in that zone, so the
decision was to add the SLGT risk matching the First Guess, but
also hedging a bit further west and south with the expansion in the
end. 01z NBM probs for >2" depict a 30-60% probability output
between St. Louis to just east of Cincinnati with a northern
inflection to the I-70 corridor between Indianapolis to Columbus,
OH. The southern edge did expand south with the 30% probability
from previous forecast to include areas south of the Ohio River, a
testament to the potential to see a slight southern shift in the
QPF focus as we move closer in time. In any case, the probability
for >2" at this lead for the blend was more than suitable enough to
warrant a SLGT risk addition to the now D3 period.

The threat of heavy rainfall, even though more isolated due to the
magnitude of the precipitation expected, is forecast to expand
further east into the eastern Ohio Valley and neighboring areas of
the Central Appalachians and western PA during the period.
Considering the nature of the topographic elements allowing for
those areas to be more prone to heavy rainfall episodes, this will
be an area to monitor for any further adjustments in the risk
which is currently at a MRGL for the time being.

Kleebauer
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