FOUS30 KWBC 260747
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
347 AM EDT Tue May 26 2026

Day 1
Valid 12Z Tue May 26 2026 - 12Z Wed May 27 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE CENTRAL GULF COAST, AND CENTRAL TO WEST TEXAS...

...Texas...

Current WV satellite and upper air analysis indicates a broad,
negatively- tilted trough axis migrating eastward out of the
Southwestern CONUS into the Southern High Plains this evening. A
broad diffluent pattern exists downstream of the mean trough with
several small mid-level perturbations causing a panoply of
convectively driven cells to materialize across the terrain of
eastern NM, spreading eastward into the adjacent High Plains as
surface troughing exists over southwest TX up through the eastern
NM plains. Increased large scale ascent will become fixated over
much of west TX, spreading further through the High Plains as
widespread shower and thunderstorm activity continues through the
morning and afternoon hours today. A plethora of convective
activity with relatively slow to modest propagation speeds will
translate into bouts of heavier rainfall across the southern half
of the TX Panhandle down through the Permian Basin and western
Rolling Plains the first half of the period leading to rainfall
totals between 1-3" over the aforementioned areas. Greatest
opportunity for flash flooding will exist across urbanized settings
and areas where copious low water crossings are present, creating
drainage concerns on a localized scale.

As we step into the late-morning and early afternoon time frame,
the focus will shift south into the Pecos River Valley and adjacent
Stockton Plateau where convection will initiate off the dryline
situated over the area with assistance from an approaching
shortwave sliding eastward out of Chihuahua. Ample shear and
favorable instability fields reflect the initiation of
supercellular storm modes with additional multi-cell development
along and ahead of the dryline leading to strong cell cores capable
of heavy rainfall as the environmental moisture anomalies sit
firmly between +1 to +2 deviations above climo. Storm motion
vectors maintain a relatively steady forward propagation to the
east and southeast from the initiation point allowing for a trail
of significant rain totals between 1-3", locally higher to
materialize from the southern Permian Basin down through the
Stockton Plateau, Lower Trans Pecos, and eventually into the mid
and lower Concho Valley by the evening. This setup is classic for
scattered flash flood instances, especially in those more urban
zones and areas of high low water crossing concentrations that are
littered over the above zones, albeit this potential is greater
than what will occur a bit further north. This reflected well
within the 00z HREF neighborhood and EAS prob fields pertaining to
the >2" threshold where both probabilities remain elevated area
wide, but a notable maxima is positioned over the Lower Trans Pecos
and those areas surrounding within the Permian Basin and Concho
Valley. The maxima extends into the northern Edwards Plateau, a
likely conjecture that correlates to the proposed motion of the
expected complex of thunderstorms motioning out from areas to the west-northwest. This zone is part of a larger areal extent of heavy
rainfall anticipated for the period with a second axis likely to
materialize after sunset.

Rainfall will likely be winding down in areas west TX that are
located along and west of the Pecos River after 00z Wednesday, but
the setup will shift focus into more of a nocturnal issue as we
pivot our attention south over the central RGV as a strong mid-
level vorticity maxima ejects out of Coahuila later this evening
and slides east into the Edwards Plateau and neighboring Hill
Country. There's a general consensus on this setup across guidance
with some degree of broad heavy convection migrating into the
above areas enticing a dousing of rainfall as the pattern evolves
overnight. We'll see the introduction of a LLJ only add to the low-
level convergence regime spurred on by the expected evolution
likely allowing quite the rainfall signature in wake of the
disturbance's trajectory. US57 to I-10 is the prospectus area of
interest, which includes much of southern and central Hill Country
with the very end of the period likely to see some of the activity
make it beyond the I-35 corridor near San Antonio and even make
headway towards Corpus Christi. The highest confidence area
according to the neighborhood probability fields for >3" remains
over the Hill Country to the I-35 corridor between Austin to San
Antonio with the maximum (40-60%) located in those areas just west
of the metro corridor along and near I-10. Probabilities for >5" do
drop off significantly to <20% everywhere with a majority of the
probs closer to 10%, so the magnitude within guidance is relatively
consistent with a signature of 2-4" with locally up to 5" in the
hardest hit areas. This is still plentiful to cause problems when
it occurs, so the threat is well within the bounds of a SLGT, even
leaning towards the higher end of the threshold for flash flooding.
This area up through the southern Permian Basin and Stockton
Plateau will be monitored closely for any potential targeted
upgrades in future updates.

The SLGT risk encompasses a broad area of TX spanning much of west
TX all the way to about 75 miles east of I-35 with the northern
periphery right up against the Red River and the southern points
running from Corpus Christi to near Laredo.

...Southeast to Mid Atlantic...

Confluent area on the western edge of a broad Western Atlantic
ridge and a trough centered over the Southern Plains will continue
for at least one more period with another round of convergence and
heavy convection focused over the Central Gulf Coast to areas
inland between southeast MS into the southern half of AL. This area
will have seen multiple days of impact from heavier convection to
begin with, so current priming of the soils could enact a greater
flash flood potential in general with an emphasis on areas that
received 3+ inches over the last 24 hours. Highest probabilities
for >3" reside across the corridor extending from New Orleans over
through Mobile into the western FL Panhandle and points just north
of I-10. This area has received considerable rainfall the past 24
hours with some places in the FL Panhandle receiving over 6 inches
of rainfall the past few days. Despite what was a drier environment
heading into the weekend, this area is sufficiently saturated in
the top soil layer leading to greater run off capabilities as we
step through today. The greatest axis of convergence within the
hi-res suite has been pin-pointed over the western FL Panhandle
where >5" neighborhood probs are running as high as 40-50% for a
small area between Pensacola to west of Tallahassee, including
Panama City beach along the coast. Radar analysis this evening is a
pretty good indication of the persistent southerly flow off the
Gulf in this narrow corridor, so this area in particular is one to
watch for the period. This area over to New Orleans is well defined
into the SLGT risk with a higher-end of the risk threshold forecast
for this zone.

Further north, the confluent pattern on the western edge of the
ridge up to the frontal alignment in the Mid Atlantic stands to be
a focal point for another day of scattered to widespread convection
with general rates between 1-2"/hr across the Appalachian front and
1-3"/hr in the adjacent lower elevations located over GA/SC/NC/VA.
These areas have been hit multiple times the past few days with
several flash flood warnings issued due to the convective impacts
the past 24 hours. This only stands to continue for another period
given pattern persistence, so wanted to make sure this was
reflected in the new D1 issuance. In coordination with several
offices across the Southeast to Mid Atlantic, a SLGT risk expansion
was noted up through the aforementioned areas of the Southern
Appalachians into the neighboring Piedmont of the Carolina's,
southern VA, and most of the northern half of GA.

...Northern Rockies...

Energetic disturbance ejecting out of the Pacific Northwest and
British Columbia will make headway into the Northern Rockies by
later this afternoon leading to a period of convective activity to
spawn along the Lewis Range down into the high valleys of western
MT. PWATs running over 1" across the Northern Rockies is well above
climo norms, closer to the 99th percentile as noted by the latest
NAEFS outputs, more than sufficient to be a problem for any more
sensitive topographic features present given the complex
topography. Multiple burn scars in the area will also be under
threat for seeing rainfall rates between 0.5-1"/hr at times, a
threshold that could cause rapid run off and debris flows if cells
linger over the sensitive areas. This is not a widespread flash
flood prospect, but isolated to widely scattered instances cannot
be ruled out considering the above environment. A MRGL risk remains
in place to account for the lower end threat.

Kleebauer
$$
--- MultiMail/DOS
* Origin: Project Scorpio TEST (618:250/6)

FOUS30 KWBC 271225
QPFERD

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

Day 1 Valid 1223Z 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...

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
$$
--- MultiMail/DOS
* Origin: Project Scorpio TEST (618:250/6)