FOUS30 KWBC 210052
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
852 PM EDT Sat Jun 20 2026

Day 1
Valid 01Z Sun Jun 21 2026 - 12Z Sun Jun 21 2026

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL IN EFFECT FOR
PARTS OF THE CENTRAL PLAINS AND LOWER MISSOURI VALLEY...

01Z Update...
Only minor adjustments to the outlook area in the Plains/Lower
Missouri Valley. Numerical guidance continuity was good and radar
showed storms beginning upscale growth in roughly the right place
across the western outlook area. Not overly concerned about
excessive amounts from the warm advection rainfall about ready to
move out of the eastern portion of the outlook. More significant
changes were made along from South Texas along the gulf coast into
portions of Georgia and northern Florida. Additional convection in
the guidance later tonight precluded removing the Slight risk
along the Texas coast into Louisiana...while on-going convection
with locally heavy rainfall rates precluded removal of the Slight
Risk there even though the expectation was for weakening and
dissipation during the late-evening.

Bann

...Central Plains and Missouri Valley...

A large area of heavy rain associated with a developing MCS
starting this evening and continuing into early Sunday is expected
to bring widespread heavy rainfall and flash flooding across
portions of the central Plains into the Missouri Valley. The
greatest threat for numerous instances of flash flooding currently
is expected across southeastern Nebraska, northeastern Kansas, and
far northwestern Missouri/southwestern Iowa. Storms are expected
to initiate Saturday afternoon with peak heating over the central
High Plains and ahead of a racing shortwave crossing the Rockies.
Meanwhile, a LLJ of southeasterly flow will increase WAA and pump
deep Gulf moisture up the Plains through the day. This will force
the dryline to race eastward in response. The warm front associated
with the low and the dry line will uplift the deep moisture,
resulting in widespread shower and thunderstorm development across
Nebraska as early as this afternoon. These storms are expected to
grow upscale into an expansive, organized convective system into
the evening and overnight hours that will then track southeasterly
across the risk area.

The latest deterministic guidance shows areal average rainfall
totals along the expected path of the MCS in the 2-4" range with
locally higher amounts of 4-6", more than sufficient to lead to
potentially widespread flash flooding, which has prompted the
level 3/4 Moderate Risk. As is usually the case with convective
systems the exact path and duration will be determined by more
mesoscale details than the guidance can typically pin down. Some
CAMs (like the NAM3k) favor the northern axis of heavy rain across
southeast Nebraska closer to the developing surface low/MCV,
whereas the 00z RRFS favors a southern solution and heaviest
rainfall across central Kansas. Regardless, PWs surging to 2" by
tonight and increased forcing will support rainfall rates within
thunderstorms to be intense and around 2-3"/hr. These rates could
be exacerbated by cell mergers and brief training to quickly lead
to flash flooding concerns. The 00Z REFS and HREF both highlight
neighborhood probabilities of 3" per 6-hrs (above local FFG) around
40-50%+ within the MDT through 12Z Sun and then extending into the


Day 2
Valid 12Z Sun Jun 21 2026 - 12Z Mon Jun 22 2026

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL IN EFFECT FOR
PARTS OF THE CENTRAL PLAINS, MIDDLE MISSISSIPPI VALLEY, AND OHIO
VALLEY...

...2000 UTC update...

For the most part, the outlook areas on Day 2 are largely intact.
Based on the latest (12Z) suite of deterministic and probabilistic
guidance, including CAMs, have nudged the southern periphery of the
Moderate Risk a tad farther south across eastern MO and southern
IL-IN. A bit of a messy setup ahead of the front, with multiple
meso-convective enhanced shortwaves embedded within the broader
upper trough. Because of this, expect a multi-modal heavy rainfall
footprint north-south when all is said and done. That said,
forecast confidence in deciphering such deterministic details at
this stage given the convective component is low, and as a result
for now it's probably best to defer to later shifts with tightening
up the Moderate Risk area.

Otherwise, the trends support a small southeast shift in the Slight
Risk over the Northern Plains (SD-northeast NE). Lastly, based on
the antecedent soils and likelihood of additional activity
associated along a lingering vort lobe (enhanced by Gulf breezes),
have also expanded the Marginal Risk area to the Middle-Upper TX
Coast to portions of the central Gulf Coast.

Hurley
Original discussion below..
...Northern Missouri through central Illinois and Indiana...
By the start of the day 2 forecast period a potent shortwave and
related surface low/MCV are expected to eject eastward out of the
central Plains into the Midwest. There still remains at least some
uncertainty regarding the speed and latitude of these features
(NAM3k a northern outlier for example), but PWs and IVT above the
90th climatological percentile (per the 00z GEFS) overlapping with
soils likely still recovering from recent heavy rain in the Midwest
will likely lead to a swath of scattered flash flooding. A MDT
risk was introduced with the latest outlook, spanning from MO to
central IN. Heavy rain near a strengthening surface low and
increased lift along an eastward stretching warm front across the
Ohio Valley will overlap with saturated soils and swollen rivers
across much of IL and IN. This will be one axis for potentially
widespread flash flooding, with another axis lingering across
southwest MO into eastern KS and possibly a relative minimum in
between (right now most likely centered around central to
southeast MO). This MO/KS potential is associated with the
southwestern tail of an expected MCS, where flow may become
parallel to the outflow boundary/front and promote both training
thunderstorms and redevelopment of storms by Sunday evening.
NBM probabilities for at least 2" remain very high (between
70-90%) and cover much of northern MO, central IL, and central IN.
Locally higher totals (CAMs depict potential for 4-7" totals) are
likely given the convective environment. 00Z HREF and 18Z REFS
probabilities for exceeding 3-hr FFG are around 30-60% across IL
and IN, where antecedent ground conditions are wettest. The
progressive nature of these storms may end up limiting the severity
of flash flood impacts, but coverage of flash flooding impacts is
expected to be widespread enough in the Midwest/Ohio Valley to
warrant the level 3/4 MDT risk upgrade.
...Eastern Kansas to Southwest Missouri...
More information regarding the southern end of the Saturday night
thunderstorm complex/MCS likely to sink southeastward near a
trailing cold front and impact areas near the Ozarks Sunday. 850 mb
flow is expected to become quite convergent extending from central
KS to southern MO, which will likely be the focus for training
convection potential early on and then reforming activity later in
Sunday associated with additional shortwave activity moving
eastward across the Plains. However, there is some uncertainty
surrounding if this boundary can sink further south during the day
and keep storms somewhat progressive. This all combines for
guidance to currently depict current QPF amounts of 3-4" and an
average localized max of 6". This area also includes soils
saturated due to a recent wet weather pattern, with NASA SPoRT-LIS
depicting pockets above the 80th percentile in the 0-40cm soil
moisture layer. Lastly, 00Z REFS and HREF probabilities are
agreeable with 40-70% values for exceeding 3" per 6-hrs.
Snell


Day 3
Valid 12Z Mon Jun 22 2026 - 12Z Tue Jun 23 2026

...THERE IS A SLIGHT RISK IN EFFECT FROM THE OHIO VALLEY TO
SOUTHERN PLAINS...

...2000 UTC Update....

The notable change made to the Day 3 ERO was to expand the Slight
Risk. The main driver was the favorable deep-layer moisture
profiles per the latest guidance, effectively shifting the axis of
2-2.25" PWATs into the Mid Atlantic and southern New England.
Instability at this point appears lacking, however in similar
patterns (per the ERO first guess fields) highly-efficient rainfall
rates in late June will more likely lead to more issues (perhaps
more than just isolated) across the urban corridors and other areas
susceptible to flash flooding. At this point, the EFI per last
night's 00Z ECMWF is around 0.8, which along with PWATs near 2
standard deviations above normal, would certainly support an
upgrade to at least a low-end Slight Risk over these areas (at
least 15% 40km neighborhood probability).

Hurley
Original discussion below..
Day 3 continues to be an active pattern through a good portion of
the CONUS, east of the Mississippi with a progressive trough axis
pushing through the Great Lakes and Northeast leading to periods of
moderate to heavy rainfall from the Ohio Valley into the Mid
Atlantic and Northeast. Areas of the Northeast are subject to
thunderstorm prospects with the best chance for flash flooding
likely to occur in the urban footprint from Philadelphia up to
Boston with an expansion inland to the Hudson Valley down through
eastern PA. Current probs off the latest ensembles and National
Blend indicate a large zone of 30-50% probs for >2" across the
aforementioned area above with deterministic outputs closer to
2-3.5" into parts of Southern New England. MRGL risk inherited
remains in effect, but there's potential here for an upgrade as we
move closer to the D2 window, but want to see more of the CAMs to
make that decision. Limiting factor here remains low instability
and while there is a window for heavier rates to linger for 3 to 6
hours, the system overall is progressive. Some uncertainty also
exists south of central NJ along the eastern Mid-Atlantic regarding
overall coverage of thunderstorms.
Across the Southern U.S., heavy precipitation will preclude another
round of convection forming along a quasi-stationary front draped
from the Southern High Plains to the Southeastern CONUS. Probs for
>1" are highest in-of the areas of Eastern OK into the Lower
Mississippi and southwestern Tennessee Valleys. Elevated theta_E's
and PWAT anomalies +2 dev. or greater indicate a formidable
environment capable of continued heavy rain potential that will
likely produce rainfall of 2-4", at least in some of the
thunderstorm activity that develops. The focal point along the
front will likely be where the heaviest rain will occur, or at
least be a low-level convergence mechanism that can enhance
regional convection. There's high enough confidence in the location
of convection for the D3 period to overlap with areas that will
have seen several inches the periods prior which led to a level 2/4
SLGT risk positioned over portions of the Southern Plains through
parts of the Lower Mississippi and neighboring Tennessee. The risk
extends through the Smokey Mountains up into parts of the Central
Appalachians in eastern KY up into WV as the convergence regime
follows the frontal positioning over these areas. Greatest chances
for multiple rounds of slow-moving thunderstorms capable of 2"+
hourly rainfall rates currently appears to be over southeast OK
into central AR and will be monitored closely once CAMs are within
range of the forecast time period.
Snell


Day 4 and Day 5
Valid 12Z Tue Jun 23 2026 - 12Z Thu Jun 25 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF
THE CENTRAL AND SOUTHERN PLAINS, LOWER MISSISSIPPI VALLEY, AND
SOUTHEASTERN U.S ON BOTH TUESDAY AND WEDNESDAY...

2030Z Excessive Rainfall Discussion Update...
Overall...changes were pretty minimal and were done mainly to
expand the coverage of the outlook area given placement/spread  of
QPF in spaghetti plots. Synoptically, the pattern evolution is
comparable to the previous discussion.

Bann


Previous Excessive Rainfall Outlook...
Day 4 is a transition period into a more typical summertime regime
for the CONUS with a longwave trough over the Northern U.S. and a
dome of mid and upper ridging orienting itself across the
southwestern CONUS. Positioning of the trough/ridge pattern will
cause a persistent northwesterly flow within the mid and upper
levels across the Central and Southern High Plains over into the
Lower Mississippi Valley as progressive shortwave pulses eject out
of the Rockies and ride the prevailing northwesterlies in place
between the ridge and trough. This highlights potential for MCS
development and flash flooding scenarios from the Front Range and
points southeast as the steering flow orients between the base of
the trough and the northeastern flank of the ridge. This is
historically projecting a case of thunderstorm maturation and
upscale growth over the area between CO/KS down through OK/TX with
potentially the Red River Basin as a focus for thunderstorm
activity. Eventually, this ends up migrating into the ArkLaTex
and/or Lower Mississippi area which is showing up in the QPF
footprint on ensembles. There has been little variance in the
recent global ensemble suite with the deterministic output also
showing very similar outcomes, at varying magnitudes with the
synoptic evolution generally stable with run-to-run continuity. The
entire setup continues through Day 5, as well, with repetition in
the mid and upper pattern as multiple vorticity maxima slide out of
the Central Rockies and migrate east-southeast through the mean
flow between the trough and ridge setup.
QPF distribution for both days is relatively even, however the D4
period is currently the most aggressive in terms of precipitation
magnitudes depicted as the time frame notes a stronger mid-level
disturbance ejecting out of the Front Range with heavy rain
prospects spanning from southwestern NE down through KS/OK,
eventually into the Lower Mississippi Valley as you work through
the end of D4 into D5. PQPF signatures for >1" of precipitation are
already pushing above 40% at lead for much of the aforementioned
area, a testament to a stable signal for widespread moderate to
heavy rain prospects as both the thermodynamic and kinematic
evolutions remain favorable for the D4 and D5 periods. Expectation
is for eventual upgrades across portions of the outlined area as we
move closer, especially if the signal remains stable and the hi-res
deterministic begin outlining the higher rate characteristics for
the precipitation. Greatest risk for an upgrade is likely to occur
where there will be multiple days of convective overlap allowing
for falling FFG's and more susceptible hydrologic impacts as
regional streams and rivers become more prone to flooding. This is
a scenario where we'll be monitoring the evolution closely as more
appreciable impacts are plausible in this synoptic scale
persistence.
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



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