FOUS30 KWBC 271550
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1150 AM EDT Wed May 27 2026

Day 1
Valid 16Z Wed May 27 2026 - 12Z Thu May 28 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
SOUTHEAST TEXAS, CENTRAL GULF COAST, AND AREAS OF THE OHIO VALLEY
TO CENTRAL APPALACHIANS...

16Z update... A modest eastward adjustment of the Marginal Risk was
made across eastern Maryland and into the Virginia Outer banks and
western Delaware for ongoing convection. Refer to MPD #258 for
further details for the near-term heavy rain/flash flooding threat.
Multiple cells are expected to focus/repeat over portions of
northern West Virginia with rainfall rates upwards of 1.5-2 in/hr
this afternoon and evening which would place this part of the
region in the higher end of the flash flooding threat within the
Slight Risk area.

Campbell

12Z Special...
Minor adjustment was made to the southern extent of the Marginal
Risk across South Texas to reflect ongoing convection. Refer to MPD
#256 for further details regarding the near-term heavy rain/flash
flooding threat across this region.

Pereira

...Texas to Central Gulf Coast...

Radar this evening is pretty telling with the current evolution
over TX revealing quite the complex of thunderstorms migrating
eastward out Hill Country into the I-35 corridor. These storms will
continue to shove eastward with assistance from both a relatively
solid mean steering flow and outflow propagation stemming from the
organized convection. Aloft, two notable features are depicted via
WV satellite and UA analysis across the Southern Plains. The first
is a well-defined negatively tilted trough oriented over NM into
the TX Panhandle that will be slow to deviate from its current
positioning over the course of the D1, even some prospects of the
upper pattern closing off across the Panhandle area of TX/OK which
would allow for some general enhancement of organized convective
clusters under the primary circulation stemming from any upper
low (ULL). In any case, this general upper pattern across the
region will entice broad cyclonic flow across the south-central
portion of the CONUS leading to convective development around the
periphery of the trough/ULL with an extension of activity likely to
be situated from southeastern CO, across KS and OK, and eventually
swinging back into the Lower Mississippi Valley. Instability maxima
will still be located further to the south and east within closer
proxy to the Gulf, however the upper levels and generally above
normal PWAT anomalies over the entire scope of the Southern Plains
should still act as a favorable environment for locally heavy
rainfall leading to some flash flood prospects over the arcing area
referenced above.

That said, one of the wild cards at play in this setup is the
maturation/development of any MCV structures that would locally
enhance convective episodes and likely trigger a more beneficial
low-level convergence pattern capable of better flash flood
prospects. This has been an output via some of the CAMs this
evening, most notably the HRRR where MCV development across OK
would trigger some locally enhanced precip maxima located within
the broad cyclonic presence. These features are tough to forecast
in the short term with more of a nowcasting component likely to be
instituted before committing to anything more concrete in the
forecast, so this will bear watching over the course of the D1.

The more notable feature of interest for this evening and carrying
through the D1 will likely be the evolution of a trailing vorticity
maxima ejecting out of Coahuila this evening with the current
radar/sat composite indicating a cluster of thunderstorms currently
migrating east out of the Mexican state. The current MCS over Texas
has a defined southern edge arcing back into south TX with a strong
cell currently situated above 50 miles to the east of Laredo.
Recent 00z CAMs indicate the Mexican disturbance following the tail
end of the complex over TX and focusing on a heavy rain core
trailing across south TX with a due east push of the mid-level
disturbance. Consensus on heavy rainfall for the period will begin
across southeast TX with the highlight likely to start around
Corpus Christi and surrounds with moderate to heavy rain lingering
across the Upper TX coast. As the outflow from the current complex
shoves east, the environment will become stabilized behind the
complex leading to a weakening convective regime as the disturbance
to the south begins to enter into the region. There's some
discrepancy on the specifics of the convective placement as we step
through the morning, but the trends are for the immediate TX Gulf
coast into southern LA as being the most notable areas of interest
with the evolution of expected heavy rainfall during the D1. This
is reflected well within the neighborhood prob fields off the
latest HREF signaling >3" running between 40-70% across the entire
stretch from Port O'Connor all the way towards New Orleans.
Downstream prospects are more in due part to the continued
southerly flow continuing to advect deep moisture into the region
allowing for an environment capable of producing heavy convection
during peak afternoon heating. The migration of the outflow on the
northern edge of the current complex will likely skirt the southern
portion of LA with some models maintaining its presence as far east
as southeastern LA before it finally dwindles. In any case, the
environmental favorability in the period lies within that coastal
plain where elevated theta_E's lend to a heightened threat for
heavy rainfall in anything that crops up with hourly rates likely
to reach 2-3"/hr in the heavier cell cores.

Considering the complex evolutions referenced above for both areas
of interest, the highest probabilities aligning with the Upper TX
and Central Gulf coast allows for a continued SLGT risk positioning
in these locations with a broad MRGL encompassing the overall
cyclonic pattern oriented over the Southern Plains to Lower
Mississippi Valley. Will still need to monitor the evolution
closely as deviations in the outflow positioning, or the
introduction of either closed ULL reflections or MVC's over the
Southern Plains could very well aid in additional upgrades in any
areas encompassed by these features.

...Ohio Valley to Central Appalachians...

Latest surface analysis over the Ohio Valley to Mid Atlantic
indicates a defined quasi-stationary front bisecting northern KY
through southern WV into central VA with pockets of showers
currently migrating northeast within the mean flow around a broad
ridge extension off the Atlantic seaboard. This frontal alignment
and lingering mid-level vorticity analyzed over the Ohio Valley
will lead to scattered to widespread convective regime over the
course of today with a heightened threat for locally heavy rainfall
occurring by late-morning and afternoon as environmental
destabilization takes shape. The frontal placement will be
important with regards to eventual convective initiation as this
will become a focal point for any future development over the
course of the afternoon. Model consensus is the boundary wavering
slowly to the north during the morning as a weak disturbance begins
to ride along the boundary leading to some minor regional
amplification and a slow push north of the front to about the
latitude of I-70. A sweeping trough exiting out of Ontario will
also help tighten an axis of confluence across the Midwest and
Ohio Valley by later in the afternoon, enticing a squeeze of the
thermal gradient and regional instability axis that aligns with the
frontal placement.

Instability markers by the afternoon hours will run between
2000-3000 J/kg for MUCAPE with weak shear presence leading to
scattered to widespread thunderstorm initiation along and south of
the front with generally modest cell motions to the southeast after
development. PWAT anomalies will sit firmly within +2 standard
deviations above climo within the proposed area of impact, a factor
that will correlate to strong cell cores capable of heavier
downpours with hourly rates between 1-2"/hr. Previous periods of
rainfall in the last three to four days have really brought down
the areal FFG markers for all 1/3/6 hour thresholds with a vast
majority of places along the Ohio River basin and points north
running <1"/hr in the hourly exceedance indicator. This points to
any heavier convective impacts could cause issues with the remnant
soil moisture and hydrologic concerns that are lingering after the
last event. This is especially true for eastern OH, southwest PA,
and western WV where complex topography only exacerbate the
potential in these zones. The latest 00z HREF continues to paint a
favorable concept of heavier rain prospects along and south of I-70
with a corridor of heavier rainfall likely to occur over southeast
IN through southern OH into northwest WV. EAS probs for >1" are
actually pretty elevated (50-80%) in the zone along I-79 over
towards the Appalachian front in WV with modest probs of 25-40%
located along the aforementioned line extending through IN/OH. A
lot of the flash flood focus will likely correlate with the hourly
rates and overlap of heavy rain over areas still saturated from
previous periods. Considering the antecedent conditions and
expected widespread convective regime along the front, the SLGT
risk was maintained for an increasing threat for flash flooding
during the period.

...Northern Rockies...

Relatively buoyant environment within a deep, anomalous moisture
presence across the Northern Rockies along with regional ascent
provided by sheared vorticity maxima maneuvering through the area
will allow for another round of widely scattered convection to
materialize across the Lewis Range in northwest MT. Instability and
regional forcing will be a bit less than the previous period,
however sensitivities  remain from remnant burn scars present
within the mountainous terrain in the aforementioned area which is
a cause for concern for any cells that happen to occur over the
burn scars themselves. Hourly rates between 0.5-1"/hr in the
stronger cell cores would be capable of providing localized flash
flood impacts over those more sensitive grounds and this setup will
maintain the prospects given the anomalous moisture presence as
PWATs remain above the 90th percentile over the entire stretch of
the Northern Rockies. The previous MRGL risk inherited was
maintained given the relative continuity.

Kleebauer


Day 2
Valid 12Z Thu May 28 2026 - 12Z Fri May 29 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE CENTRAL AND SOUTHERN PLAINS, NORTHERN ROCKIES, LOWER
MISSISSIPPI VALLEY, AND SOUTHEAST FLORIDA...

...Plains to Lower Mississippi Valley...

A bit of an omega block pattern is shaping up across the CONUS with
a broad upper trough axis fixated over the Central and Southern
Plains with with ridging in place over the top. This will cause a
rather chaotic flow under the mean trough with deep moisture and
several smaller mid-level perturbations basically "stuck" under the
the overall trough axis. Ample instability with deep moisture
presence will certain be a cause for continuing at least a
scattered heavy rain footprint across areas under the influence of
the trough. Scattered elevated probabilities between 30-60% exists
for localized amounts >2" from KS all the way into the Southeast
U.S. with the maxima split between KS and the Central Gulf coast.
The two areas are different in the reasoning as the primary center
of the trough will be fixed over KS leading to the best upper
forcing pattern and stagnant flow remaining parked over the area as
we move through D2. Pending the amount of rain that falls over the
course of D1, a targeted upgrade is possible, but maintained the
MRGL and will reassess as we move forward in future updates to see
if an upgrade is warranted. The Central Gulf coast will remain in a
favorable instability maxima with weak flow likely a component that
could lead to isolated heavy totals stemming from slow-moving
convection. The area from the Upper TX coast over through southern
GA has been leaning wet over the past week, so antecedent
conditions are a little more unforgiving for these types of setups.
In any case, the threat remains modest, at best, so the MRGL risk
was sufficient for the pattern with any upgrades likely to stem
from more near term sampling of the radar trends.

...Florida...

Active sea breeze pattern with weakening steering flow will lead
to a period of heavy rainfall across the southeast FL coast on
Thursday afternoon. Consensus within guidance is for an active
period between 18-00z Thu/Fri that would allow for heavy convection
with slow forward propagations to impact the South Florida metro
corridor from West Palm Beach down to Miami. Latest 00z HREF is
modestly robust with the signature for at least 3" off the
neighborhood probabilities with a steady 60-90% output along the
southeastern coast of FL with the maxima generally confined to the
Miami Metro up to West Palm Beach. This correlates strongly with
what has been advertised via regional and global guidance the past
few days with the deterministic CAMs even indicating some 4-6"
bullseye's within the main QPF footprint. This is a relatively
classic pattern capable of locally significant rainfall within a
deep moisture presence as PWAT anomalies sit between +1 to +2
standard deviations within the various ensemble packages. A MRGL
risk remains in effect for the period across the South Florida
metro corridor.

...Northern Rockies...

Maturing ULL over the west coast will allow for a broad axis of
diffluent flow across the interior northwest with the highlight of
scattered convection likely to pivot further west into eastern WA,
northern ID, and the western slopes of the Northern Rockies.
Signals are not as prevalent compared to previous periods, however
the environmental conditions are still favorable, especially when
it comes to PWAT anomalies still generally running between the
90-95th percentile across northeast WA into northern ID. Burn scar
remnants will likely be the most susceptible to seeing impacts, so
the threat remains low-end and generally localized. Maintained
continuity from the previous forecast with a MRGL risk in place
across the aforementioned areas.

Kleebauer


Day 3
Valid 12Z Fri May 29 2026 - 12Z Sat May 30 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHEAST U.S...

Strong Canadian high pressure pressing in from the north will lead
to a persistent quasi-stationary turned cold front to press south
over the course of Thursday into Friday with convection likely to
spawn along and ahead of the front with dry air advecting behind
the front leading to a cutoff of activity. Jury is still out on
specifics with the placement of the front generally over the
Carolina's by Friday morning with slow push south as the day wears
on. Frontal alignment is more of a arcing back into the Tennessee
Valley as the persistent troughing in the South-Central Plains will
likely maintain some southerly flow for areas along and west of the
Mississippi. Anywhere within proximity to this front will be
subject to various convective outputs with some heavier cells
likely intertwined in over the pattern. No discernible areas of
interest are present at this juncture, however the environmental
favorability likely points to the best chances occurring across
the Southeast into the lower Tennessee Valley. A broad MRGL is
forecast for the above areas through the Lower Mississippi Valley.

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